#!nobacktrace
;;; porting srfi-19 reference implementation to ypsilon
;;; -- y.fujita.lwp

(library (srfi srfi-19)
  (export time-duration
          time-monotonic
          time-tai
          time-utc
          current-date
          current-julian-day
          current-modified-julian-day
          current-time
          time-resolution
          make-time
          time?
          time-type
          time-nanosecond
          time-second
          set-time-type!
          set-time-nanosecond!
          set-time-second!
          copy-time
          time<=?
          time<?
          time=?
          time>=?
          time>?
          time-difference
          time-difference!
          add-duration
          add-duration!
          subtract-duration
          subtract-duration!
          make-date
          date?
          date-nanosecond
          date-second
          date-minute
          date-hour
          date-day
          date-month
          date-year
          date-zone-offset
          date-year-day
          date-week-day
          date-week-number
          date->julian-day
          date->modified-julian-day
          date->time-monotonic
          date->time-tai
          date->time-utc
          julian-day->date
          julian-day->time-monotonic
          julian-day->time-tai
          julian-day->time-utc
          modified-julian-day->date
          modified-julian-day->time-monotonic
          modified-julian-day->time-tai
          modified-julian-day->time-utc
          time-monotonic->date
          time-monotonic->julian-day
          time-monotonic->modified-julian-day
          time-monotonic->time-tai
          time-monotonic->time-tai!
          time-monotonic->time-utc
          time-monotonic->time-utc!
          time-tai->date
          time-tai->julian-day
          time-tai->modified-julian-day
          time-tai->time-monotonic
          time-tai->time-monotonic!
          time-tai->time-utc
          time-tai->time-utc!
          time-utc->date
          time-utc->julian-day
          time-utc->modified-julian-day
          time-utc->time-monotonic
          time-utc->time-monotonic!
          time-utc->time-tai
          time-utc->time-tai!
          date->string
          string->date)
  (import (core) (srfi srfi-6))

  (define-record-type time
    (fields
     (mutable type time-type set-time-type!)
     (mutable nanosecond time-nanosecond set-time-nanosecond!)
     (mutable second time-second set-time-second!)))

  (define-record-type date
    (fields
     (mutable nanosecond date-nanosecond tm:set-date-nanosecond!)
     (mutable second date-second tm:set-date-second!)
     (mutable minute date-minute tm:set-date-minute!)
     (mutable hour date-hour tm:set-date-hour!)
     (mutable day date-day tm:set-date-day!)
     (mutable month date-month tm:set-date-month!)
     (mutable year date-year tm:set-date-year!)
     (mutable zone-offset date-zone-offset tm:set-date-zone-offset!)))

  (define current-seconds
    (lambda ()
      (div (microsecond) 1000000)))

  (define current-milliseconds
    (lambda ()
      (div (microsecond) 1000)))

  (define tm:local-tz-offset
    (lambda ()
      (div (- (microsecond->utc 0)) 1000000)))

  (define (tm:time-error caller type value)
    (if (member type tm:time-error-types)
        (if value
            (error caller (format "TIME-ERROR type ~s: ~s" type value))
            (error caller (format "TIME-ERROR type ~s" type)))
        (error caller (format "TIME-ERROR unsupported error type ~s" type))))

  (define current-process-milliseconds (lambda () 0))
  (define current-gc-milliseconds (lambda () 0))
  (define read-line get-line)
  (define eof (eof-object))

;; SRFI-19: Time Data Types and Procedures.
;;
;; Copyright (C) I/NET, Inc. (2000, 2002, 2003). All Rights Reserved.
;;
;; This document and translations of it may be copied and furnished to others,
;; and derivative works that comment on or otherwise explain it or assist in its
;; implementation may be prepared, copied, published and distributed, in whole or
;; in part, without restriction of any kind, provided that the above copyright
;; notice and this paragraph are included on all such copies and derivative works.
;; However, this document itself may not be modified in any way, such as by
;; removing the copyright notice or references to the Scheme Request For
;; Implementation process or editors, except as needed for the purpose of
;; developing SRFIs in which case the procedures for copyrights defined in the SRFI
;; process must be followed, or as required to translate it into languages other
;; than English.
;;
;; The limited permissions granted above are perpetual and will not be revoked
;; by the authors or their successors or assigns.
;;
;; This document and the information contained herein is provided on an "AS IS"
;; basis and THE AUTHOR AND THE SRFI EDITORS DISCLAIM ALL WARRANTIES, EXPRESS OR
;; IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
;; INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
;; MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


;; -- Bug fixes.
;;
;; MAKE-TIME had parameters seconds and nanoseconds reversed; change all
;;           references in file to match.  Will F: 2002-10-15
;;
;; DATE-YEAR-DAY returned the wrong day; tm:year-day fixed to do the right
;;               thing. Will F: 2002-10-15
;;               It also called an undefined error procedure.
;;
;; DISPLAYING procedure removed. Will F: 2002-10-15.
;;
;; TM:NANO constant corrected. 2002-11-04.
;;
;; The following fixes by Will Fitzgerald, February, 2003.
;;  -- Thanks to Steven Ma and others.
;;
;; (CURRENT-TIME 'TIME-THREAD) added.
;;
;; TIME-RESOLUTION for TIME-PROCESS added.
;;
;; TIME comparison procedures (time=?, etc. fixed.
;;
;; Corrected errors in converting between TAI and UTC time.
;;
;; TAI and UTC date converters no longer look at leap seconds,
;; which was an error.
;;
;; corrections to calls to tm:time-error
;;
;; timezone offset not used in date->time-utc and date->julian-day
;;
;; typos in tm:integer-reader-exact, tm:string->date,
;; time-monotonic->time-utc!, tm:char->int fixed
;;
;; corrected "~k", "~f" formatting for date->string (includes fix for
;; "~4"
;;
;; 'split-real' fixed.
;;
;; fixed julian-day->time-utc and variants.
;;
;; changes 2003-02-26, based on comments by Martin Gasbichler.
;;
;; moronic, overly complicated COPY-TIME procedure changed
;; to simple version suggested by Martin Gasbichler.
;;
;; To provide more portability, changed #\Space to #\space
;; and #\tab to #\Tab to (integer->char 9)
;;
;; changed arity-3 calls to / and - to arity 2 calls (again,
;; for more general portability).
;;
;; split-real fixed again -- by removing it, and using
;; 'fractional part'. Will Fitzgerald 5/16/2003.
;; --------------------------------------------------------------

;; ypsilon -- y.fujita.lwp

  (define-syntax receive
    (syntax-rules ()
      ((receive formals expression body ...)
       (call-with-values (lambda () expression)
         (lambda formals body ...)))))

;;; -- we want receive later on for a couple of small things
;;

;; :OPTIONAL is nice, too

  (define-syntax :optional
    (syntax-rules ()
      ((_ val default-value)
       (if (null? val) default-value (car val)))))

  (define time-tai 'time-tai)
  (define time-utc 'time-utc)
  (define time-monotonic 'time-monotonic)
#;(define time-thread 'time-thread)
#;(define time-process 'time-process)
  (define time-duration 'time-duration)

;; example of extension (MZScheme specific)
#;(define time-gc 'time-gc)

;;-- LOCALE dependent constants

  (define tm:locale-number-separator ".")

  (define tm:locale-abbr-weekday-vector (vector "Sun" "Mon" "Tue" "Wed"
                                                "Thu" "Fri" "Sat"))
  (define tm:locale-long-weekday-vector (vector "Sunday" "Monday"
                                                "Tuesday" "Wednesday"
                                                "Thursday" "Friday"
                                                "Saturday"))
;; note empty string in 0th place.
  (define tm:locale-abbr-month-vector   (vector "" "Jan" "Feb" "Mar"
                                                "Apr" "May" "Jun" "Jul"
                                                "Aug" "Sep" "Oct" "Nov"
                                                "Dec"))
  (define tm:locale-long-month-vector   (vector "" "January" "February"
                                                "March" "April" "May"
                                                "June" "July" "August"
                                                "September" "October"
                                                "November" "December"))

  (define tm:locale-pm "PM")
  (define tm:locale-am "AM")

;; See date->string
  (define tm:locale-date-time-format "~a ~b ~d ~H:~M:~S~z ~Y")
  (define tm:locale-short-date-format "~m/~d/~y")
  (define tm:locale-time-format "~H:~M:~S")
  (define tm:iso-8601-date-time-format "~Y-~m-~dT~H:~M:~S~z")
;;-- Miscellaneous Constants.
;;-- only the tm:tai-epoch-in-jd might need changing if
;;   a different epoch is used.

  (define tm:nano (expt 10 9))
  (define tm:sid  86400)    ; seconds in a day
  (define tm:sihd 43200)    ; seconds in a half day
  (define tm:tai-epoch-in-jd 4881175/2) ; julian day number for 'the epoch'


;;; A Very simple Error system for the time procedures
;;;
  (define tm:time-error-types
    '(invalid-clock-type
      unsupported-clock-type
      incompatible-time-types
      not-duration
      dates-are-immutable
      bad-date-format-string
      bad-date-template-string
      invalid-month-specification
      ))

;; ypsilon -- y.fujita.lwp
#|
  (define (tm:time-error caller type value)
    (if (member type tm:time-error-types)
        (if value
            (error caller "TIME-ERROR type ~S: ~S" type value)
            (error caller "TIME-ERROR type ~S" type))
        (error caller "TIME-ERROR unsupported error type ~S" type)))
|#

;; A table of leap seconds
;; See ftp://maia.usno.navy.mil/ser7/tai-utc.dat
;; and update as necessary.
;; this procedures reads the file in the abover
;; format and creates the leap second table
;; it also calls the almost standard, but not R5 procedures read-line
;; & open-input-string
;; ie (set! tm:leap-second-table (tm:read-tai-utc-date "tai-utc.dat"))

  (define (tm:read-tai-utc-data filename)
    (define (convert-jd jd)
      (* (- (inexact->exact jd) tm:tai-epoch-in-jd) tm:sid))
    (define (convert-sec sec)
      (inexact->exact sec))
    (let ( (port (open-input-file filename))
           (table '()) )
      (let loop ((line (read-line port)))
        (if (not (eq? line eof))
            (begin
              (let* ( (data (read (open-input-string (string-append "(" line ")"))))
                      (year (car data))
                      (jd   (cadddr (cdr data)))
                      (secs (cadddr (cdddr data))) )
                (if (>= year 1972)
                    (set! table (cons (cons (convert-jd jd) (convert-sec secs)) table)))
                (loop (read-line port))))))
      table))

;; each entry is ( utc seconds since epoch . # seconds to add for tai )
;; note they go higher to lower, and end in 1972.
  (define tm:leap-second-table
    '((1136073600 . 33)
      (915148800 . 32)
      (867715200 . 31)
      (820454400 . 30)
      (773020800 . 29)
      (741484800 . 28)
      (709948800 . 27)
      (662688000 . 26)
      (631152000 . 25)
      (567993600 . 24)
      (489024000 . 23)
      (425865600 . 22)
      (394329600 . 21)
      (362793600 . 20)
      (315532800 . 19)
      (283996800 . 18)
      (252460800 . 17)
      (220924800 . 16)
      (189302400 . 15)
      (157766400 . 14)
      (126230400 . 13)
      (94694400 . 12)
      (78796800 . 11)
      (63072000 . 10)))

  (define (read-leap-second-table filename)
    (set! tm:leap-second-table (tm:read-tai-utc-data filename))
    (values))

  (define (tm:leap-second-delta utc-seconds)
    (letrec ( (lsd (lambda (table)
                     (cond
                      ((>= utc-seconds (caar table))
                       (cdar table))
                      (else (lsd (cdr table)))))) )
      (if (< utc-seconds  (* (- 1972 1970) 365 tm:sid)) 0
          (lsd  tm:leap-second-table))))

;; going from tai seconds to utc seconds ...
  (define (tm:leap-second-neg-delta tai-seconds)
    (letrec ( (lsd (lambda (table)
                     (cond ((null? table) 0)
                           ((<= (cdar table) (- tai-seconds (caar table)))
                            (cdar table))
                           (else (lsd (cdr table)))))) )
      (if (< tai-seconds  (* (- 1972 1970) 365 tm:sid)) 0
          (lsd  tm:leap-second-table))))

;;; the time structure; creates the accessors, too.
;;; wf: changed to match srfi documentation. uses mzscheme structures & inspectors

;; ypsilon -- y.fujita.lwp
#|
  (define-struct time (type nanosecond second) (make-inspector))
|#

;; thanks, Martin Gasbichler ...

  (define (copy-time time)
    (make-time (time-type time)
               (time-second time)
               (time-nanosecond time)))

;;; current-time

;;; specific time getters.
;;; these should be rewritten to be os specific.
;;
;; -- using gnu gettimeofday() would be useful here -- gets
;;    second + millisecond
;;    let's pretend we do, using mzscheme's current-seconds & current-milliseconds
;;    this is supposed to return utc.
;;

  (define (tm:get-time-of-day)
    (values (current-seconds)
            (abs (remainder (current-milliseconds) 1000))))

  (define (tm:current-time-utc)
    (receive (seconds ms) (tm:get-time-of-day)
      (make-time  time-utc (* ms 10000) seconds )))

  (define (tm:current-time-tai)
    (receive (seconds ms) (tm:get-time-of-day)
      (make-time time-tai
                 (* ms 10000)
                 (+ seconds (tm:leap-second-delta seconds))
                 )))

  (define (tm:current-time-ms-time time-type proc)
    (let ((current-ms (proc)))
      (make-time time-type
                 (* (remainder current-ms 1000) 10000)
                 (quotient current-ms 10000)
                 )))

;; -- we define it to be the same as tai.
;;    a different implemation of current-time-montonic
;;    will require rewriting all of the time-monotonic converters,
;;    of course.

  (define (tm:current-time-monotonic)
    (receive (seconds ms) (tm:get-time-of-day)
      (make-time time-monotonic
                 (* ms 10000)
                 (+ seconds (tm:leap-second-delta seconds))
                 )))

#;(define (tm:current-time-thread)
    (tm:current-time-ms-time time-process current-process-milliseconds))

#;(define (tm:current-time-process)
    (tm:current-time-ms-time time-process current-process-milliseconds))

#;(define (tm:current-time-gc)
    (tm:current-time-ms-time time-gc current-gc-milliseconds))

  (define (current-time . clock-type)
    (let ( (clock-type (:optional clock-type time-utc)) )
      (cond
       ((eq? clock-type time-tai) (tm:current-time-tai))
       ((eq? clock-type time-utc) (tm:current-time-utc))
       ((eq? clock-type time-monotonic) (tm:current-time-monotonic))
     #;((eq? clock-type time-thread) (tm:current-time-thread))
     #;((eq? clock-type time-process) (tm:current-time-process))
     #;((eq? clock-type time-gc) (tm:current-time-gc))
       (else (tm:time-error 'current-time 'invalid-clock-type clock-type)))))

;; -- time resolution
;; this is the resolution of the clock in nanoseconds.
;; this will be implementation specific.

  (define (time-resolution . clock-type)
    (let ((clock-type (:optional clock-type time-utc)))
      (cond
       ((eq? clock-type time-tai) 10000)
       ((eq? clock-type time-utc) 10000)
       ((eq? clock-type time-monotonic) 10000)
     #;((eq? clock-type time-thread) 10000)
     #;((eq? clock-type time-process) 10000)
     #;((eq? clock-type time-gc) 10000)
       (else (tm:time-error 'time-resolution 'invalid-clock-type clock-type)))))

;; -- time comparisons

  (define (tm:time-compare-check time1 time2 caller)
    (if (or (not (and (time? time1) (time? time2)))
            (not (eq? (time-type time1) (time-type time2))))
        (tm:time-error caller 'incompatible-time-types #f)
        #t))

  (define (time=? time1 time2)
    (tm:time-compare-check time1 time2 'time=?)
    (and (= (time-second time1) (time-second time2))
         (= (time-nanosecond time1) (time-nanosecond time2))))

  (define (time>? time1 time2)
    (tm:time-compare-check time1 time2 'time>?)
    (or (> (time-second time1) (time-second time2))
        (and (= (time-second time1) (time-second time2))
             (> (time-nanosecond time1) (time-nanosecond time2)))))

  (define (time<? time1 time2)
    (tm:time-compare-check time1 time2 'time<?)
    (or (< (time-second time1) (time-second time2))
        (and (= (time-second time1) (time-second time2))
             (< (time-nanosecond time1) (time-nanosecond time2)))))

  (define (time>=? time1 time2)
    (tm:time-compare-check time1 time2 'time>=?)
    (or (>= (time-second time1) (time-second time2))
        (and (= (time-second time1) (time-second time2))
             (>= (time-nanosecond time1) (time-nanosecond time2)))))

  (define (time<=? time1 time2)
    (tm:time-compare-check time1 time2 'time<=?)
    (or (<= (time-second time1) (time-second time2))
        (and (= (time-second time1) (time-second time2))
             (<= (time-nanosecond time1) (time-nanosecond time2)))))

;; -- time arithmetic

  (define (tm:time->nanoseconds time)
    (define (sign1 n)
      (if (negative? n) -1 1))
    (+ (* (time-second time) tm:nano)
       (time-nanosecond time)))

  (define (tm:nanoseconds->time time-type nanoseconds)
    (make-time time-type
               (remainder nanoseconds tm:nano)
               (quotient nanoseconds tm:nano)))

  (define (tm:nanoseconds->values nanoseconds)
    (values (abs (remainder nanoseconds tm:nano))
            (quotient nanoseconds tm:nano)))

  (define (tm:time-difference time1 time2 time3)
    (if (or (not (and (time? time1) (time? time2)))
            (not (eq? (time-type time1) (time-type time2))))
        (tm:time-error 'time-difference 'incompatible-time-types #f))
    (set-time-type! time3 time-duration)
    (if (time=? time1 time2)
        (begin
          (set-time-second! time3 0)
          (set-time-nanosecond! time3 0))
        (receive
            (nanos secs)
            (tm:nanoseconds->values (- (tm:time->nanoseconds time1)
                                       (tm:time->nanoseconds time2)))
          (set-time-second! time3 secs)
          (set-time-nanosecond! time3 nanos)))
    time3)

  (define (time-difference time1 time2)
    (tm:time-difference time1 time2 (make-time #f #f #f)))

  (define (time-difference! time1 time2)
    (tm:time-difference time1 time2 time1))

  (define (tm:add-duration time1 duration time3)
    (if (not (and (time? time1) (time? duration)))
        (tm:time-error 'add-duration 'incompatible-time-types #f))
    (if (not (eq? (time-type duration) time-duration))
        (tm:time-error 'add-duration 'not-duration duration)
        (let ( (sec-plus (+ (time-second time1) (time-second duration)))
               (nsec-plus (+ (time-nanosecond time1) (time-nanosecond duration))) )
          (let ((r (remainder nsec-plus tm:nano))
                (q (quotient nsec-plus tm:nano)))
            ; (set-time-type! time3 (time-type time1))
            (if (negative? r)
                (begin
                  (set-time-second! time3 (+ sec-plus q -1))
                  (set-time-nanosecond! time3 (+ tm:nano r)))
                (begin
                  (set-time-second! time3 (+ sec-plus q))
                  (set-time-nanosecond! time3 r)))
            time3))))

  (define (add-duration time1 duration)
    (tm:add-duration time1 duration (make-time (time-type time1) #f #f)))

  (define (add-duration! time1 duration)
    (tm:add-duration time1 duration time1))

  (define (tm:subtract-duration time1 duration time3)
    (if (not (and (time? time1) (time? duration)))
        (tm:time-error 'add-duration 'incompatible-time-types #f))
    (if (not (eq? (time-type duration) time-duration))
        (tm:time-error 'tm:subtract-duration 'not-duration duration)
        (let ( (sec-minus  (- (time-second time1) (time-second duration)))
               (nsec-minus (- (time-nanosecond time1) (time-nanosecond duration))) )
          (let ((r (remainder nsec-minus tm:nano))
                (q (quotient nsec-minus tm:nano)))
            (if (negative? r)
                (begin
                  (set-time-second! time3 (- sec-minus q 1))
                  (set-time-nanosecond! time3 (+ tm:nano r)))
                (begin
                  (set-time-second! time3 (- sec-minus q))
                  (set-time-nanosecond! time3 r)))
            time3))))

  (define (subtract-duration time1 duration)
    (tm:subtract-duration time1 duration (make-time (time-type time1) #f #f)))

  (define (subtract-duration! time1 duration)
    (tm:subtract-duration time1 duration time1))

;; -- converters between types.

  (define (tm:time-tai->time-utc! time-in time-out caller)
    (if (not (eq? (time-type time-in) time-tai))
        (tm:time-error caller 'incompatible-time-types time-in))
    (set-time-type! time-out time-utc)
    (set-time-nanosecond! time-out (time-nanosecond time-in))
    (set-time-second!     time-out (- (time-second time-in)
                                      (tm:leap-second-neg-delta
                                       (time-second time-in))))
    time-out)

  (define (time-tai->time-utc time-in)
    (tm:time-tai->time-utc! time-in (make-time #f #f #f) 'time-tai->time-utc))

  (define (time-tai->time-utc! time-in)
    (tm:time-tai->time-utc! time-in time-in 'time-tai->time-utc!))

  (define (tm:time-utc->time-tai! time-in time-out caller)
    (if (not (eq? (time-type time-in) time-utc))
        (tm:time-error caller 'incompatible-time-types time-in))
    (set-time-type! time-out time-tai)
    (set-time-nanosecond! time-out (time-nanosecond time-in))
    (set-time-second!     time-out (+ (time-second time-in)
                                      (tm:leap-second-delta
                                       (time-second time-in))))
    time-out)

  (define (time-utc->time-tai time-in)
    (tm:time-utc->time-tai! time-in (make-time #f #f #f) 'time-utc->time-tai))

  (define (time-utc->time-tai! time-in)
    (tm:time-utc->time-tai! time-in time-in 'time-utc->time-tai!))

;; -- these depend on time-monotonic having the same definition as time-tai!
  (define (time-monotonic->time-utc time-in)
    (if (not (eq? (time-type time-in) time-monotonic))
        (tm:time-error 'time-monotoinc->time-utc 'incompatible-time-types time-in))
    (let ((ntime (copy-time time-in)))
      (set-time-type! ntime time-tai)
      (tm:time-tai->time-utc! ntime ntime 'time-monotonic->time-utc)))

  (define (time-monotonic->time-utc! time-in)
    (if (not (eq? (time-type time-in) time-monotonic))
        (tm:time-error 'time-monotonic->time-utc! 'incompatible-time-types time-in))
    (set-time-type! time-in time-tai)
    (tm:time-tai->time-utc! time-in time-in 'time-monotonic->time-utc))

  (define (time-monotonic->time-tai time-in)
    (if (not (eq? (time-type time-in) time-monotonic))
        (tm:time-error 'time-monotonic->time-tai 'incompatible-time-types time-in))
    (let ((ntime (copy-time time-in)))
      (set-time-type! ntime time-tai)
      ntime))

  (define (time-monotonic->time-tai! time-in)
    (if (not (eq? (time-type time-in) time-monotonic))
        (tm:time-error 'time-monotonic->time-tai! 'incompatible-time-types time-in))
    (set-time-type! time-in time-tai)
    time-in)

  (define (time-utc->time-monotonic time-in)
    (if (not (eq? (time-type time-in) time-utc))
        (tm:time-error 'time-utc->time-monotonic 'incompatible-time-types time-in))
    (let ((ntime (tm:time-utc->time-tai! time-in (make-time #f #f #f)
                                         'time-utc->time-monotonic)))
      (set-time-type! ntime time-monotonic)
      ntime))

  (define (time-utc->time-monotonic! time-in)
    (if (not (eq? (time-type time-in) time-utc))
        (tm:time-error 'time-utc->time-montonic! 'incompatible-time-types time-in))
    (let ((ntime (tm:time-utc->time-tai! time-in time-in
                                         'time-utc->time-monotonic!)))
      (set-time-type! ntime time-monotonic)
      ntime))

  (define (time-tai->time-monotonic time-in)
    (if (not (eq? (time-type time-in) time-tai))
        (tm:time-error 'time-tai->time-monotonic 'incompatible-time-types time-in))
    (let ((ntime (copy-time time-in)))
      (set-time-type! ntime time-monotonic)
      ntime))

  (define (time-tai->time-monotonic! time-in)
    (if (not (eq? (time-type time-in) time-tai))
        (tm:time-error 'time-tai->time-monotonic!  'incompatible-time-types time-in))
    (set-time-type! time-in time-monotonic)
    time-in)

;; ypsilon -- y.fujita.lwp
#|
;; -- date structures

  (define-struct date (nanosecond second minute hour day month year zone-offset) (make-inspector))

;; redefine setters

  (define tm:set-date-nanosecond! set-date-nanosecond!)
  (define tm:set-date-second! set-date-second!)
  (define tm:set-date-minute! set-date-minute!)
  (define tm:set-date-hour! set-date-hour!)
  (define tm:set-date-day! set-date-day!)
  (define tm:set-date-month! set-date-month!)
  (define tm:set-date-year! set-date-year!)
  (define tm:set-date-zone-offset! set-date-zone-offset!)
|#

  (define (set-date-second! date val)
    (tm:time-error 'set-date-second! 'dates-are-immutable date))

  (define (set-date-minute! date val)
    (tm:time-error 'set-date-minute! 'dates-are-immutable date))

  (define (set-date-day! date val)
    (tm:time-error 'set-date-day! 'dates-are-immutable date))

  (define (set-date-month! date val)
    (tm:time-error 'set-date-month! 'dates-are-immutable date))

  (define (set-date-year! date val)
    (tm:time-error 'set-date-year! 'dates-are-immutable date))

  (define (set-date-zone-offset! date val)
    (tm:time-error 'set-date-zone-offset! 'dates-are-immutable date))

;; gives the julian day which starts at noon.
  (define (tm:encode-julian-day-number day month year)
    (let* ((a (quotient (- 14 month) 12))
           (y (- (- (+ year 4800) a) (if (negative? year) -1 0)))
           (m (- (+ month (* 12 a)) 3)))
      (+ day
         (quotient (+ (* 153 m) 2) 5)
         (* 365 y)
         (quotient y 4)
         (- (quotient y 100))
         (quotient y 400)
         -32045)))

  (define (tm:char-pos char str index len)
    (cond
     ((>= index len) #f)
     ((char=? (string-ref str index) char)
      index)
     (else
      (tm:char-pos char str (+ index 1) len))))

  (define (tm:fractional-part r)
    (if (integer? r) "0"
        (let ((str (number->string (exact->inexact r))))
          (let ((ppos (tm:char-pos #\. str 0 (string-length str))))
            (substring str  (+ ppos 1) (string-length str))))))

;; gives the seconds/date/month/year
  (define (tm:decode-julian-day-number jdn)
    (let* ((days (truncate jdn))
           (a (+ days 32044))
           (b (quotient (+ (* 4 a) 3) 146097))
           (c (- a (quotient (* 146097 b) 4)))
           (d (quotient (+ (* 4 c) 3) 1461))
           (e (- c (quotient (* 1461 d) 4)))
           (m (quotient (+ (* 5 e) 2) 153))
           (y (+ (* 100 b) d -4800 (quotient m 10))))
      (values ; seconds date month year
       (* (- jdn days) tm:sid)
       (+ e (- (quotient (+ (* 153 m) 2) 5)) 1)
       (+ m 3 (* -12 (quotient m 10)))
       (if (>= 0 y) (- y 1) y))
      ))

;; relies on the fact that we named our time zone accessor
;; differently from MzScheme's....
;; This should be written to be OS specific.

;; ypsilon -- y.fujita.lwp
#|
  (define (tm:local-tz-offset)
    (date-time-zone-offset (seconds->date (current-seconds))))
|#

;; special thing -- ignores nanos
  (define (tm:time->julian-day-number seconds tz-offset)
    (+ (/ (+ seconds
             tz-offset
             tm:sihd)
          tm:sid)
       tm:tai-epoch-in-jd))

  (define (tm:find proc l)
    (if (null? l)
        #f
        (if (proc (car l))
            #t
            (tm:find proc (cdr l)))))

  (define (tm:tai-before-leap-second? second)
    (tm:find (lambda (x)
               (= second (- (+ (car x) (cdr x)) 1)))
             tm:leap-second-table))

  (define (tm:time->date time tz-offset ttype)
    (if (not (eq? (time-type time) ttype))
        (tm:time-error 'time->date 'incompatible-time-types  time))
    (let* ( (offset (:optional tz-offset (tm:local-tz-offset))) )
      (receive (secs date month year)
          (tm:decode-julian-day-number
           (tm:time->julian-day-number (time-second time) offset))
        (let* ( (hours    (quotient secs (* 60 60)))
                (rem      (remainder secs (* 60 60)))
                (minutes  (quotient rem 60))
                (seconds  (remainder rem 60)) )
          (make-date (time-nanosecond time)
                     seconds
                     minutes
                     hours
                     date
                     month
                     year
                     offset)))))

  (define (time-tai->date time . tz-offset)
    (if (tm:tai-before-leap-second? (time-second time))
        ;; if it's *right* before the leap, we need to pretend to subtract a second ...
        (let ((d (tm:time->date (subtract-duration! (time-tai->time-utc time) (make-time time-duration 0 1)) tz-offset time-utc)))
          (tm:set-date-second! d 60)
          d)
        (tm:time->date (time-tai->time-utc time) tz-offset time-utc)))

  (define (time-utc->date time . tz-offset)
    (tm:time->date time tz-offset time-utc))

;; again, time-monotonic is the same as time tai
  (define (time-monotonic->date time . tz-offset)
    (tm:time->date time tz-offset time-monotonic))

  (define (date->time-utc date)
    (let ( (nanosecond (date-nanosecond date))
           (second (date-second date))
           (minute (date-minute date))
           (hour (date-hour date))
           (day (date-day date))
           (month (date-month date))
           (year (date-year date))
           (offset (date-zone-offset date)) )
      (let ( (jdays (- (tm:encode-julian-day-number day month year)
                       tm:tai-epoch-in-jd)) )
        (make-time
         time-utc
         nanosecond
         (+ (* (- jdays 1/2) 24 60 60)
            (* hour 60 60)
            (* minute 60)
            second
            (- offset))
         ))))

  (define (date->time-tai d)
    (if (= (date-second d) 60)
        (subtract-duration! (time-utc->time-tai! (date->time-utc d)) (make-time time-duration 0 1))
        (time-utc->time-tai! (date->time-utc d))))

  (define (date->time-monotonic date)
    (time-utc->time-monotonic! (date->time-utc date)))

  (define (tm:leap-year? year)
    (or (= (modulo year 400) 0)
        (and (= (modulo year 4) 0) (not (= (modulo year 100) 0)))))

  (define (leap-year? date)
    (tm:leap-year? (date-year date)))

;; tm:year-day fixed: adding wrong number of days.
  (define  tm:month-assoc '((0 . 0) (1 . 31)  (2 . 59)   (3 . 90)   (4 . 120)
                            (5 . 151) (6 . 181)  (7 . 212)  (8 . 243)
                            (9 . 273) (10 . 304) (11 . 334)))

  (define (tm:year-day day month year)
    (let ((days-pr (assoc (- month 1) tm:month-assoc)))
      (if (not days-pr)
          (tm:time-error 'date-year-day 'invalid-month-specification month))
      (if (and (tm:leap-year? year) (> month 2))
          (+ day (cdr days-pr) 1)
          (+ day (cdr days-pr)))))

  (define (date-year-day date)
    (tm:year-day (date-day date) (date-month date) (date-year date)))

;; from calendar faq
  (define (tm:week-day day month year)
    (let* ((a (quotient (- 14 month) 12))
           (y (- year a))
           (m (+ month (* 12 a) -2)))
      (modulo (+ day y (quotient y 4) (- (quotient y 100))
                 (quotient y 400) (quotient (* 31 m) 12))
              7)))

  (define (date-week-day date)
    (tm:week-day (date-day date) (date-month date) (date-year date)))

  (define (tm:days-before-first-week date day-of-week-starting-week)
    (let* ( (first-day (make-date 0 0 0 0
                                  1
                                  1
                                  (date-year date)
                                  #f))
            (fdweek-day (date-week-day first-day))  )
      (modulo (- day-of-week-starting-week fdweek-day)
              7)))

  (define (date-week-number date day-of-week-starting-week)
    (quotient (- (date-year-day date)
                 (tm:days-before-first-week  date day-of-week-starting-week))
              7))

  (define (current-date . tz-offset)
    (time-utc->date (current-time time-utc)
                    (:optional tz-offset (tm:local-tz-offset))))

;; given a 'two digit' number, find the year within 50 years +/-
  (define (tm:natural-year n)
    (let* ( (current-year (date-year (current-date)))
            (current-century (* (quotient current-year 100) 100)) )
      (cond
       ((>= n 100) n)
       ((<  n 0) n)
       ((<=  (- (+ current-century n) current-year) 50)
        (+ current-century n))
       (else
        (+ (- current-century 100) n)))))

;; ypsilon -- y.fujita.lwp
#|
  (define (date->julian-day date)
    (let ( (nanosecond (date-nanosecond date))
           (second (date-second date))
           (minute (date-minute date))
           (hour (date-hour date))
           (day (date-day date))
           (month (date-month date))
           (year (date-year date))
           (offset (date-zone-offset date)) )
      (+ (tm:encode-julian-day-number day month year)
         (- 1/2)
         (+ (/ (/ (+ (* hour 60 60)
                     (* minute 60) second (/ nanosecond tm:nano)) tm:sid)
               (- offset))))))
|#

;; ypsilon -- y.fujita.lwp
  (define (date->julian-day date)
    (let ( (nanosecond (date-nanosecond date))
           (second (date-second date))
           (minute (date-minute date))
           (hour (date-hour date))
           (day (date-day date))
           (month (date-month date))
           (year (date-year date))
           (offset (date-zone-offset date)) )
      (+ (tm:encode-julian-day-number day month year)
         (- 1/2)
         (+ (/ (+ (* hour 60 60)
                  (* minute 60)
                  second
                  (/ nanosecond tm:nano)
                  (- offset))
               tm:sid)))))
;; ypsilon -- y.fujita.lwp

  (define (date->modified-julian-day date)
    (- (date->julian-day date)
       4800001/2))

  (define (time-utc->julian-day time)
    (if (not (eq? (time-type time) time-utc))
        (tm:time-error 'time-utc->julian-day 'incompatible-time-types  time))
    (+ (/ (+ (time-second time) (/ (time-nanosecond time) tm:nano))
          tm:sid)
       tm:tai-epoch-in-jd))

  (define (time-utc->modified-julian-day time)
    (- (time-utc->julian-day time)
       4800001/2))

  (define (time-tai->julian-day time)
    (if (not (eq? (time-type time) time-tai))
        (tm:time-error 'time-tai->julian-day 'incompatible-time-types  time))
    (+ (/ (+ (- (time-second time)
                (tm:leap-second-delta (time-second time)))
             (/ (time-nanosecond time) tm:nano))
          tm:sid)
       tm:tai-epoch-in-jd))

  (define (time-tai->modified-julian-day time)
    (- (time-tai->julian-day time)
       4800001/2))

;; this is the same as time-tai->julian-day
  (define (time-monotonic->julian-day time)
    (if (not (eq? (time-type time) time-monotonic))
        (tm:time-error 'time-monotonic->julian-day 'incompatible-time-types  time))
    (+ (/ (+ (- (time-second time)
                (tm:leap-second-delta (time-second time)))
             (/ (time-nanosecond time) tm:nano))
          tm:sid)
       tm:tai-epoch-in-jd))

  (define (time-monotonic->modified-julian-day time)
    (- (time-monotonic->julian-day time)
       4800001/2))

  (define (julian-day->time-utc jdn)
    (let ( (nanosecs (* tm:nano tm:sid (- jdn tm:tai-epoch-in-jd))) )
      (make-time time-utc
                 (remainder nanosecs tm:nano)
                 (floor (/ nanosecs tm:nano)))))

  (define (julian-day->time-tai jdn)
    (time-utc->time-tai! (julian-day->time-utc jdn)))

  (define (julian-day->time-monotonic jdn)
    (time-utc->time-monotonic! (julian-day->time-utc jdn)))

  (define (julian-day->date jdn . tz-offset)
    (let ((offset (:optional tz-offset (tm:local-tz-offset))))
      (time-utc->date (julian-day->time-utc jdn) offset)))

  (define (modified-julian-day->date jdn . tz-offset)
    (let ((offset (:optional tz-offset (tm:local-tz-offset))))
      (julian-day->date (+ jdn 4800001/2) offset)))

  (define (modified-julian-day->time-utc jdn)
    (julian-day->time-utc (+ jdn 4800001/2)))

  (define (modified-julian-day->time-tai jdn)
    (julian-day->time-tai (+ jdn 4800001/2)))

  (define (modified-julian-day->time-monotonic jdn)
    (julian-day->time-monotonic (+ jdn 4800001/2)))

  (define (current-julian-day)
    (time-utc->julian-day (current-time time-utc)))

  (define (current-modified-julian-day)
    (time-utc->modified-julian-day (current-time time-utc)))

;; returns a string rep. of number N, of minimum LENGTH,
;; padded with character PAD-WITH. If PAD-WITH if #f,
;; no padding is done, and it's as if number->string was used.
;; if string is longer than LENGTH, it's as if number->string was used.

  (define (tm:padding n pad-with length)
    (let* ( (str (number->string n))
            (str-len (string-length str)) )
      (if (or (> str-len length)
              (not pad-with))
          str
          (let* ( (new-str (make-string length pad-with))
                  (new-str-offset (- (string-length new-str)
                                     str-len)) )
            (do ((i 0 (+ i 1)))
              ((>= i (string-length str)))
              (string-set! new-str (+ new-str-offset i)
                           (string-ref str i)))
            new-str))))

  (define (tm:last-n-digits i n)
    (abs (remainder i (expt 10 n))))

  (define (tm:locale-abbr-weekday n)
    (vector-ref tm:locale-abbr-weekday-vector n))

  (define (tm:locale-long-weekday n)
    (vector-ref tm:locale-long-weekday-vector n))

  (define (tm:locale-abbr-month n)
    (vector-ref tm:locale-abbr-month-vector n))

  (define (tm:locale-long-month n)
    (vector-ref tm:locale-long-month-vector n))

  (define (tm:vector-find needle haystack comparator)
    (let ((len (vector-length haystack)))
      (define (tm:vector-find-int index)
        (cond
         ((>= index len) #f)
         ((comparator needle (vector-ref haystack index)) index)
         (else (tm:vector-find-int (+ index 1)))))
      (tm:vector-find-int 0)))

  (define (tm:locale-abbr-weekday->index string)
    (tm:vector-find string tm:locale-abbr-weekday-vector string=?))

  (define (tm:locale-long-weekday->index string)
    (tm:vector-find string tm:locale-long-weekday-vector string=?))

  (define (tm:locale-abbr-month->index string)
    (tm:vector-find string tm:locale-abbr-month-vector string=?))

  (define (tm:locale-long-month->index string)
    (tm:vector-find string tm:locale-long-month-vector string=?))

;; do nothing.
;; Your implementation might want to do something...
;;
  (define (tm:locale-print-time-zone date port)
    (values))

;; Again, locale specific.
  (define (tm:locale-am/pm hr)
    (if (> hr 11) tm:locale-pm tm:locale-am))

  (define (tm:tz-printer offset port)
    (cond
     ((= offset 0) (display "Z" port))
     ((negative? offset) (display "-" port))
     (else (display "+" port)))
    (if (not (= offset 0))
        (let ( (hours   (abs (quotient offset (* 60 60))))
               (minutes (abs (quotient (remainder offset (* 60 60)) 60))) )
          (display (tm:padding hours #\0 2) port)
          (display (tm:padding minutes #\0 2) port))))

;; A table of output formatting directives.
;; the first time is the format char.
;; the second is a procedure that takes the date, a padding character
;; (which might be #f), and the output port.
;;
  (define tm:directives
    (list
     (cons #\~ (lambda (date pad-with port) (display #\~ port)))

     (cons #\a (lambda (date pad-with port)
                 (display (tm:locale-abbr-weekday (date-week-day date))
                          port)))
     (cons #\A (lambda (date pad-with port)
                 (display (tm:locale-long-weekday (date-week-day date))
                          port)))
     (cons #\b (lambda (date pad-with port)
                 (display (tm:locale-abbr-month (date-month date))
                          port)))
     (cons #\B (lambda (date pad-with port)
                 (display (tm:locale-long-month (date-month date))
                          port)))
     (cons #\c (lambda (date pad-with port)
                 (display (date->string date tm:locale-date-time-format) port)))
     (cons #\d (lambda (date pad-with port)
                 (display (tm:padding (date-day date)
                                      #\0 2)
                          port)))
     (cons #\D (lambda (date pad-with port)
                 (display (date->string date "~m/~d/~y") port)))
     (cons #\e (lambda (date pad-with port)
                 (display (tm:padding (date-day date)
                                      #\space 2)
                          port)))
     (cons #\f (lambda (date pad-with port)
                 (if (> (date-nanosecond date)
                        tm:nano)
                     (display (tm:padding (+ (date-second date) 1)
                                          pad-with 2)
                              port)
                     (display (tm:padding (date-second date)
                                          pad-with 2)
                              port))
                 (let* ((ns (tm:fractional-part (/
                                                 (date-nanosecond date)
                                                 tm:nano 1.0)))
                        (le (string-length ns)))
                   (if (> le 2)
                       (begin
                         (display tm:locale-number-separator port)
                         (display (substring ns 2 le) port))))))
     (cons #\h (lambda (date pad-with port)
                 (display (date->string date "~b") port)))
     (cons #\H (lambda (date pad-with port)
                 (display (tm:padding (date-hour date)
                                      pad-with 2)
                          port)))
     (cons #\I (lambda (date pad-with port)
                 (let ((hr (date-hour date)))
                   (if (> hr 12)
                       (display (tm:padding (- hr 12)
                                            pad-with 2)
                                port)
                       (display (tm:padding hr
                                            pad-with 2)
                                port)))))
     (cons #\j (lambda (date pad-with port)
                 (display (tm:padding (date-year-day date)
                                      pad-with 3)
                          port)))
     (cons #\k (lambda (date pad-with port)
                 (display (tm:padding (date-hour date)
                                      #\0 2)
                          port)))
     (cons #\l (lambda (date pad-with port)
                 (let ((hr (if (> (date-hour date) 12)
                               (- (date-hour date) 12) (date-hour date))))
                   (display (tm:padding hr  #\space 2)
                            port))))
     (cons #\m (lambda (date pad-with port)
                 (display (tm:padding (date-month date)
                                      pad-with 2)
                          port)))
     (cons #\M (lambda (date pad-with port)
                 (display (tm:padding (date-minute date)
                                      pad-with 2)
                          port)))
     (cons #\n (lambda (date pad-with port)
                 (newline port)))
     (cons #\N (lambda (date pad-with port)
                 (display (tm:padding (date-nanosecond date)
                                      pad-with 9)
                          port)))
     (cons #\p (lambda (date pad-with port)
                 (display (tm:locale-am/pm (date-hour date)) port)))
     (cons #\r (lambda (date pad-with port)
                 (display (date->string date "~I:~M:~S ~p") port)))
     (cons #\s (lambda (date pad-with port)
                 (display (time-second (date->time-utc date)) port)))
     (cons #\S (lambda (date pad-with port)
                 (if (> (date-nanosecond date)
                        tm:nano)
                     (display (tm:padding (+ (date-second date) 1)
                                          pad-with 2)
                              port)
                     (display (tm:padding (date-second date)
                                          pad-with 2)
                              port))))
     (cons #\t (lambda (date pad-with port)
                 (display (integer->char 9) port)))
     (cons #\T (lambda (date pad-with port)
                 (display (date->string date "~H:~M:~S") port)))
     (cons #\U (lambda (date pad-with port)
                 (if (> (tm:days-before-first-week date 0) 0)
                     (display (tm:padding (+ (date-week-number date 0) 1)
                                          #\0 2) port)
                     (display (tm:padding (date-week-number date 0)
                                          #\0 2) port))))
     (cons #\V (lambda (date pad-with port)
                 (display (tm:padding (date-week-number date 1)
                                      #\0 2) port)))
     (cons #\w (lambda (date pad-with port)
                 (display (date-week-day date) port)))
     (cons #\x (lambda (date pad-with port)
                 (display (date->string date tm:locale-short-date-format) port)))
     (cons #\X (lambda (date pad-with port)
                 (display (date->string date tm:locale-time-format) port)))
     (cons #\W (lambda (date pad-with port)
                 (if (> (tm:days-before-first-week date 1) 0)
                     (display (tm:padding (+ (date-week-number date 1) 1)
                                          #\0 2) port)
                     (display (tm:padding (date-week-number date 1)
                                          #\0 2) port))))
     (cons #\y (lambda (date pad-with port)
                 (display (tm:padding (tm:last-n-digits
                                       (date-year date) 2)
                                      pad-with
                                      2)
                          port)))
     (cons #\Y (lambda (date pad-with port)
                 (display (date-year date) port)))
     (cons #\z (lambda (date pad-with port)
                 (tm:tz-printer (date-zone-offset date) port)))
     (cons #\Z (lambda (date pad-with port)
                 (tm:locale-print-time-zone date port)))
     (cons #\1 (lambda (date pad-with port)
                 (display (date->string date "~Y-~m-~d") port)))
     (cons #\2 (lambda (date pad-with port)
                 (display (date->string date "~k:~M:~S~z") port)))
     (cons #\3 (lambda (date pad-with port)
                 (display (date->string date "~k:~M:~S") port)))
     (cons #\4 (lambda (date pad-with port)
                 (display (date->string date "~Y-~m-~dT~k:~M:~S~z") port)))
     (cons #\5 (lambda (date pad-with port)
                 (display (date->string date "~Y-~m-~dT~k:~M:~S") port)))
     ))

  (define (tm:get-formatter char)
    (let ( (associated (assoc char tm:directives)) )
      (if associated (cdr associated) #f)))

  (define (tm:date-printer date index format-string str-len port)
    (if (>= index str-len)
        (values)
        (let ( (current-char (string-ref format-string index)) )
          (if (not (char=? current-char #\~))
              (begin
                (display current-char port)
                (tm:date-printer date (+ index 1) format-string str-len port))

              (if (= (+ index 1) str-len) ; bad format string.
                  (tm:time-error 'tm:date-printer 'bad-date-format-string
                                 format-string)
                  (let ( (pad-char? (string-ref format-string (+ index 1))) )
                    (cond
                     ((char=? pad-char? #\-)
                      (if (= (+ index 2) str-len) ; bad format string.
                          (tm:time-error 'tm:date-printer 'bad-date-format-string
                                         format-string)
                          (let ( (formatter (tm:get-formatter
                                             (string-ref format-string
                                                         (+ index 2)))) )
                            (if (not formatter)
                                (tm:time-error 'tm:date-printer 'bad-date-format-string
                                               format-string)
                                (begin
                                  (formatter date #f port)
                                  (tm:date-printer date (+ index 3)
                                                   format-string str-len port))))))

                     ((char=? pad-char? #\_)
                      (if (= (+ index 2) str-len) ; bad format string.
                          (tm:time-error 'tm:date-printer 'bad-date-format-string
                                         format-string)
                          (let ( (formatter (tm:get-formatter
                                             (string-ref format-string
                                                         (+ index 2)))) )
                            (if (not formatter)
                                (tm:time-error 'tm:date-printer 'bad-date-format-string
                                               format-string)
                                (begin
                                  (formatter date #\space port)
                                  (tm:date-printer date (+ index 3)
                                                   format-string str-len port))))))
                     (else
                      (let ( (formatter (tm:get-formatter
                                         (string-ref format-string
                                                     (+ index 1)))) )
                        (if (not formatter)
                            (tm:time-error 'tm:date-printer 'bad-date-format-string
                                           format-string)
                            (begin
                              (formatter date #\0 port)
                              (tm:date-printer date (+ index 2)
                                               format-string str-len port))))))))))))

  (define (date->string date .  format-string)
    (let ( (str-port (open-output-string))
           (fmt-str (:optional format-string "~c")) )
      (tm:date-printer date 0 fmt-str (string-length fmt-str) str-port)
      (get-output-string str-port)))

  (define (tm:char->int ch)
    (cond
     ((char=? ch #\0) 0)
     ((char=? ch #\1) 1)
     ((char=? ch #\2) 2)
     ((char=? ch #\3) 3)
     ((char=? ch #\4) 4)
     ((char=? ch #\5) 5)
     ((char=? ch #\6) 6)
     ((char=? ch #\7) 7)
     ((char=? ch #\8) 8)
     ((char=? ch #\9) 9)
     (else (tm:time-error 'string->date 'bad-date-template-string
                          (list "Non-integer character" ch )))))

;; read an integer upto n characters long on port; upto -> #f if any length
  (define (tm:integer-reader upto port)
    (define (accum-int port accum nchars)
      (let ((ch (peek-char port)))
        (if (or (eof-object? ch)
                (not (char-numeric? ch))
                (and upto (>= nchars  upto )))
            accum
            (accum-int port (+ (* accum 10) (tm:char->int (read-char
                                                           port))) (+
                                                                    nchars 1)))))
    (accum-int port 0 0))

  (define (tm:make-integer-reader upto)
    (lambda (port)
      (tm:integer-reader upto port)))

;; read an fractional integer upto n characters long on port; upto -> #f if any length
;;
;; The return value is normalized to upto decimal places. For example, if upto is 9 and
;; the string read is "123", the return value is 123000000.
  (define (tm:fractional-integer-reader upto port)
    (define (accum-int port accum nchars)
      (let ((ch (peek-char port)))
        (if (or (eof-object? ch)
                (not (char-numeric? ch))
                (and upto (>= nchars  upto )))
            (* accum (expt 10 (- upto nchars)))
            (accum-int port (+ (* accum 10) (tm:char->int (read-char port))) (+ nchars 1)))))
    (accum-int port 0 0))

  (define (tm:make-fractional-integer-reader upto)
    (lambda (port)
      (tm:fractional-integer-reader upto port)))

;; read *exactly* n characters and convert to integer; could be padded
  (define (tm:integer-reader-exact n port)
    (let ( (padding-ok #t) )
      (define (accum-int port accum nchars)
        (let ((ch (peek-char port)))
          (cond
           ((>= nchars n) accum)
           ((eof-object? ch)
            (tm:time-error 'string->date 'bad-date-template-string
                           "Premature ending to integer read."))
           ((char-numeric? ch)
            (set! padding-ok #f)
            (accum-int port (+ (* accum 10) (tm:char->int (read-char
                                                           port)))
                       (+ nchars 1)))
           (padding-ok
            (read-char port) ; consume padding
            (accum-int port accum (+ nchars 1)))
           (else ; padding where it shouldn't be
            (tm:time-error 'string->date 'bad-date-template-string
                           "Non-numeric characters in integer read.")))))
      (accum-int port 0 0)))

  (define (tm:make-integer-exact-reader n)
    (lambda (port)
      (tm:integer-reader-exact n port)))

  (define (tm:zone-reader port)
    (let ( (offset 0)
           (positive? #f) )
      (let ( (ch (read-char port)) )
        (if (eof-object? ch)
            (tm:time-error 'string->date 'bad-date-template-string
                           (list "Invalid time zone +/-" ch)))
        (if (or (char=? ch #\Z) (char=? ch #\z))
            0
            (begin
              (cond
               ((char=? ch #\+) (set! positive? #t))
               ((char=? ch #\-) (set! positive? #f))
               (else
                (tm:time-error 'string->date 'bad-date-template-string
                               (list "Invalid time zone +/-" ch))))
              (let ((ch (read-char port)))
                (if (eof-object? ch)
                    (tm:time-error 'string->date 'bad-date-template-string
                                   (list "Invalid time zone number" ch)))
                (set! offset (* (tm:char->int ch)
                                10 60 60)))
              (let ((ch (read-char port)))
                (if (eof-object? ch)
                    (tm:time-error 'string->date 'bad-date-template-string
                                   (list "Invalid time zone number" ch)))
                (set! offset (+ offset (* (tm:char->int ch)
                                          60 60))))
              (let ((ch (read-char port)))
                (if (eof-object? ch)
                    (tm:time-error 'string->date 'bad-date-template-string
                                   (list "Invalid time zone number" ch)))
                (set! offset (+ offset (* (tm:char->int ch)
                                          10 60))))
              (let ((ch (read-char port)))
                (if (eof-object? ch)
                    (tm:time-error 'string->date 'bad-date-template-string
                                   (list "Invalid time zone number" ch)))
                (set! offset (+ offset (* (tm:char->int ch)
                                          60))))
              (if positive? offset (- offset)))))))

;; looking at a char, read the char string, run thru indexer, return index
  (define (tm:locale-reader port indexer)
    (let ( (string-port (open-output-string)) )
      (define (read-char-string)
        (let ((ch (peek-char port)))
          (if (char-alphabetic? ch)
              (begin (write-char (read-char port) string-port)
                (read-char-string))
              (get-output-string string-port))))
      (let* ( (str (read-char-string))
              (index (indexer str)) )
        (if index index (tm:time-error 'string->date
                                       'bad-date-template-string
                                       (list "Invalid string for " indexer))))))

  (define (tm:make-locale-reader indexer)
    (lambda (port)
      (tm:locale-reader port indexer)))

  (define (tm:make-char-id-reader char)
    (lambda (port)
      (if (char=? char (read-char port))
          char
          (tm:time-error 'string->date
                         'bad-date-template-string
                         "Invalid character match."))))

;; A List of formatted read directives.
;; Each entry is a list.
;; 1. the character directive;
;; a procedure, which takes a character as input & returns
;; 2. #t as soon as a character on the input port is acceptable
;; for input,
;; 3. a port reader procedure that knows how to read the current port
;; for a value. Its one parameter is the port.
;; 4. a action procedure, that takes the value (from 3.) and some
;; object (here, always the date) and (probably) side-effects it.
;; In some cases (e.g., ~A) the action is to do nothing

  (define tm:read-directives
    (let ( (ireader4 (tm:make-integer-reader 4))
           (ireader2 (tm:make-integer-reader 2))
           (fireader9 (tm:make-fractional-integer-reader 9))
           (ireaderf (tm:make-integer-reader #f))
           (eireader2 (tm:make-integer-exact-reader 2))
           (eireader4 (tm:make-integer-exact-reader 4))
           (locale-reader-abbr-weekday (tm:make-locale-reader
                                        tm:locale-abbr-weekday->index))
           (locale-reader-long-weekday (tm:make-locale-reader
                                        tm:locale-long-weekday->index))
           (locale-reader-abbr-month   (tm:make-locale-reader
                                        tm:locale-abbr-month->index))
           (locale-reader-long-month   (tm:make-locale-reader
                                        tm:locale-long-month->index))
           (char-fail (lambda (ch) #t))
           (do-nothing (lambda (val object) (values)))
           )

      (list
       (list #\~ char-fail (tm:make-char-id-reader #\~) do-nothing)
       (list #\a char-alphabetic? locale-reader-abbr-weekday do-nothing)
       (list #\A char-alphabetic? locale-reader-long-weekday do-nothing)
       (list #\b char-alphabetic? locale-reader-abbr-month
             (lambda (val object)
               (tm:set-date-month! object val)))
       (list #\B char-alphabetic? locale-reader-long-month
             (lambda (val object)
               (tm:set-date-month! object val)))
       (list #\d char-numeric? ireader2 (lambda (val object)
                                          (tm:set-date-day!
                                           object val)))
       (list #\e char-fail eireader2 (lambda (val object)
                                       (tm:set-date-day! object val)))
       (list #\h char-alphabetic? locale-reader-abbr-month
             (lambda (val object)
               (tm:set-date-month! object val)))
       (list #\H char-numeric? ireader2 (lambda (val object)
                                          (tm:set-date-hour! object val)))
       (list #\k char-fail eireader2 (lambda (val object)
                                       (tm:set-date-hour! object val)))
       (list #\m char-numeric? ireader2 (lambda (val object)
                                          (tm:set-date-month! object val)))
       (list #\M char-numeric? ireader2 (lambda (val object)
                                          (tm:set-date-minute!
                                           object val)))
       (list #\N char-numeric? fireader9 (lambda (val object)
                                           (tm:set-date-nanosecond! object val)))
       (list #\S char-numeric? ireader2 (lambda (val object)
                                          (tm:set-date-second! object val)))
       (list #\y char-fail eireader2
             (lambda (val object)
               (tm:set-date-year! object (tm:natural-year val))))
       (list #\Y char-numeric? ireader4 (lambda (val object)
                                          (tm:set-date-year! object val)))
       (list #\z (lambda (c)
                   (or (char=? c #\Z)
                       (char=? c #\z)
                       (char=? c #\+)
                       (char=? c #\-)))
             tm:zone-reader (lambda (val object)
                              (tm:set-date-zone-offset! object val)))
       )))

  (define (tm:string->date date index format-string str-len port template-string)
    (define (skip-until port skipper)
      (let ((ch (peek-char port)))
        (if (eof-object? ch)
            (tm:time-error 'string->date 'bad-date-format-string template-string)
            (if (not (skipper ch))
                (begin (read-char port) (skip-until port skipper))))))
    (if (>= index str-len)
        (begin
          (values))
        (let ( (current-char (string-ref format-string index)) )
          (if (not (char=? current-char #\~))
              (let ((port-char (read-char port)))
                (if (or (eof-object? port-char)
                        (not (char=? current-char port-char)))
                    (tm:time-error 'string->date 'bad-date-format-string template-string))
                (tm:string->date date (+ index 1) format-string str-len port template-string))
              ;; otherwise, it's an escape, we hope
              (if (> (+ index 1) str-len)
                  (tm:time-error 'string->date 'bad-date-format-string template-string)
                  (let* ( (format-char (string-ref format-string (+ index 1)))
                          (format-info (assoc format-char tm:read-directives)) )
                    (if (not format-info)
                        (tm:time-error 'string->date 'bad-date-format-string template-string)
                        (begin
                          (let ((skipper (cadr format-info))
                                (reader  (caddr format-info))
                                (actor   (cadddr format-info)))
                            (skip-until port skipper)
                            (let ((val (reader port)))
                              (if (eof-object? val)
                                  (tm:time-error 'string->date 'bad-date-format-string template-string)
                                  (actor val date)))
                            (tm:string->date date (+ index 2) format-string  str-len port template-string))))))))))

  (define (string->date input-string template-string)
    (define (tm:date-ok? date)
      (and (date-nanosecond date)
           (date-second date)
           (date-minute date)
           (date-hour date)
           (date-day date)
           (date-month date)
           (date-year date)
           (date-zone-offset date)))
    (let ( (newdate (make-date 0 0 0 0 #f #f #f (tm:local-tz-offset))) )
      (tm:string->date newdate
                       0
                       template-string
                       (string-length template-string)
                       (open-input-string input-string)
                       template-string)
      (if (tm:date-ok? newdate)
          newdate
          (tm:time-error 'string->date 'bad-date-format-string (list "Incomplete date read. " newdate template-string)))))

  ) ;[end]
