emacs/lisp/calendar/parse-time.el

;;; parse-time.el --- parsing time strings -*- lexical-binding: t -*-

;; Copyright (C) 1996, 2000-2025 Free Software Foundation, Inc.

;; Author: Erik Naggum <erik@naggum.no>
;; Keywords: util

;; This file is part of GNU Emacs.

;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;; With the introduction of the `encode-time', `decode-time', and
;; `format-time-string' functions, dealing with time became simpler in
;; Emacs.  However, parsing time strings is still largely a matter of
;; heuristics and no common interface has been designed.

;; `parse-time-string' parses a time in a string and returns a list of
;; values, just like `decode-time', where unspecified elements in the
;; string are returned as nil (except unspecified DST is returned as -1).
;; `encode-time' may be applied on these values to obtain an internal
;; time value.

;;; Code:

(require 'cl-lib)
(require 'iso8601)
(eval-when-compile (require 'subr-x))

;; Byte-compiler warnings
(defvar parse-time-elt)
(defvar parse-time-val)

(defsubst parse-time-string-chars (char)
  (cond ((<= ?a char ?z) ?a)
        ((<= ?0 char ?9) ?0)
        ((eq char ?+) 1)
        ((eq char ?-) -1)
        ((eq char ?:) ?d)))

(defun parse-time-tokenize (string)
  "Tokenize STRING into substrings.
Each substring is a run of \"valid\" characters, i.e., lowercase
letters, digits, plus or minus signs or colons."
  (let ((start nil)
	(end (length string))
	(all-digits nil)
	(list ())
	(index 0)
	(c nil))
    (while (< index end)
      (while (and (< index end)		;Skip invalid characters.
		  (not (setq c (parse-time-string-chars (aref string index)))))
        (incf index))
      (setq start index
            all-digits (eq c ?0))
      (while (and (< (incf index) end)	;Scan valid characters.
		  (setq c (parse-time-string-chars (aref string index))))
	(setq all-digits (and all-digits (eq c ?0))))
      (if (<= index end)
	  (push (if all-digits (cl-parse-integer string :start start :end index)
		  (substring string start index))
		list)))
    (nreverse list)))

(defvar parse-time-months '(("jan" . 1) ("feb" . 2) ("mar" . 3)
			    ("apr" . 4) ("may" . 5) ("jun" . 6)
			    ("jul" . 7) ("aug" . 8) ("sep" . 9)
			    ("oct" . 10) ("nov" . 11) ("dec" . 12)
			    ("january" . 1) ("february" . 2)
			    ("march" . 3) ("april" . 4) ("june" . 6)
			    ("july" . 7) ("august" . 8)
			    ("september" . 9) ("october" . 10)
			    ("november" . 11) ("december" . 12)))
(defvar parse-time-weekdays '(("sun" . 0) ("mon" . 1) ("tue" . 2)
			      ("wed" . 3) ("thu" . 4) ("fri" . 5)
			      ("sat" . 6) ("sunday" . 0) ("monday" . 1)
			      ("tuesday" . 2) ("wednesday" . 3)
			      ("thursday" . 4) ("friday" . 5)
			      ("saturday" . 6)))
(defvar parse-time-zoneinfo `(("z" 0) ("ut" 0) ("gmt" 0)
			      ("pst" ,(* -8 3600)) ("pdt" ,(* -7 3600) t)
			      ("mst" ,(* -7 3600)) ("mdt" ,(* -6 3600) t)
			      ("cst" ,(* -6 3600)) ("cdt" ,(* -5 3600) t)
			      ("est" ,(* -5 3600)) ("edt" ,(* -4 3600) t))
  "(zoneinfo seconds-off daylight-savings-time-p)")

(defvar parse-time-rules
  `(((6) parse-time-weekdays)
    ((3) (1 31))
    ((4) parse-time-months)
    ((5) (100))
    ((2 1 0)
     ,(lambda () (and (stringp parse-time-elt)
                      (= (length parse-time-elt) 8)
                      (= (aref parse-time-elt 2) ?:)
                      (= (aref parse-time-elt 5) ?:)))
     [0 2] [3 5] [6 8])
    ((8 7) parse-time-zoneinfo
     ,(lambda () (car parse-time-val))
     ,(lambda () (cadr parse-time-val)))
    ((8)
     ,(lambda ()
        (and (stringp parse-time-elt)
             (= 5 (length parse-time-elt))
             (or (= (aref parse-time-elt 0) ?+)
                 (= (aref parse-time-elt 0) ?-))))
     ,(lambda () (* 60 (+ (cl-parse-integer parse-time-elt :start 3 :end 5)
                          (* 60 (cl-parse-integer parse-time-elt :start 1 :end 3)))
                    (if (= (aref parse-time-elt 0) ?-) -1 1))))
    ((5 4 3)
     ,(lambda () (and (stringp parse-time-elt)
                      (= (length parse-time-elt) 10)
                      (= (aref parse-time-elt 4) ?-)
                      (= (aref parse-time-elt 7) ?-)))
     [0 4] [5 7] [8 10])
    ((2 1 0)
     ,(lambda () (and (stringp parse-time-elt)
                      (= (length parse-time-elt) 5)
                      (= (aref parse-time-elt 2) ?:)))
     [0 2] [3 5] ,(lambda () 0))
    ((2 1 0)
     ,(lambda () (and (stringp parse-time-elt)
                      (= (length parse-time-elt) 4)
                      (= (aref parse-time-elt 1) ?:)))
     [0 1] [2 4] ,(lambda () 0))
    ((2 1 0)
     ,(lambda () (and (stringp parse-time-elt)
                      (= (length parse-time-elt) 7)
                      (= (aref parse-time-elt 1) ?:)))
     [0 1] [2 4] [5 7])
    ((5) (50 110) ,(lambda () (+ 1900 parse-time-elt)))
    ((5) (0 49) ,(lambda () (+ 2000 parse-time-elt))))
  "(slots predicate extractor...)")
;;;###autoload(put 'parse-time-rules 'risky-local-variable t)

;;;###autoload
(defun parse-time-string (string &optional form)
  "Parse the time in STRING into (SEC MIN HOUR DAY MON YEAR DOW DST TZ).
STRING should be an ISO 8601 time string, e.g., \"2020-01-15T16:12:21-08:00\",
or something resembling an RFC 822 (or later) date-time, e.g.,
\"Wed, 15 Jan 2020 16:12:21 -0800\".  This function is
somewhat liberal in what format it accepts, and will attempt to
return a \"likely\" value even for somewhat malformed strings.
The values returned are identical to those of `decode-time', but
any unknown values other than DST are returned as nil, and an
unknown DST value is returned as -1.
Note that, unlike `decode-time', this function does not interpret
the time string, and in particular the values of DST and TZ do not
affect the returned value of date and time, they only affect the
last two members of the returned value.  This function simply
parses the textual representation of date and time into separate
numerical values, and doesn't care whether the time is local or UTC.

See `decode-time' for the meaning of FORM."
  (condition-case ()
      (iso8601-parse string form)
    (wrong-type-argument
     (let ((time (list nil nil nil nil nil nil nil -1 nil))
	   (temp (parse-time-tokenize (downcase string))))
       (while temp
	 (let ((parse-time-elt (pop temp))
	       (rules parse-time-rules)
	       (exit nil))
	   (while (and rules (not exit))
	     (let* ((rule (pop rules))
		    (slots (pop rule))
		    (predicate (pop rule))
		    (parse-time-val))
	       (when (and (not (nth (car slots) time)) ;not already set
			  (setq parse-time-val
				(cond ((and (consp predicate)
					    (not (functionp predicate)))
				       (and (numberp parse-time-elt)
					    (<= (car predicate) parse-time-elt)
					    (or (not (cdr predicate))
						(<= parse-time-elt
						    (cadr predicate)))
					    parse-time-elt))
				      ((symbolp predicate)
				       (cdr (assoc parse-time-elt
						   (symbol-value predicate))))
				      ((funcall predicate)))))
		 (setq exit t)
		 (while slots
		   (let ((new-val (if rule
				      (let ((this (pop rule)))
					(if (vectorp this)
					    (cl-parse-integer
					     parse-time-elt
					     :start (aref this 0)
					     :end (aref this 1))
					  (funcall this)))
				    parse-time-val)))
		     (setf (nth (pop slots) time) new-val))))))))
       time))))

(defun parse-iso8601-time-string (date-string &optional form)
  "Parse an ISO 8601 time string, such as \"2020-01-15T16:12:21-08:00\".
Fall back on parsing something resembling an RFC 822 (or later) date-time.
This function is like `parse-time-string' except that it returns
a Lisp timestamp when successful.

See `decode-time' for the meaning of FORM."
  (when-let* ((time (parse-time-string date-string form)))
    (encode-time time)))

(provide 'parse-time)

;;; parse-time.el ends here