;;; my-exif.el --- Private fix to exif.el           -*- lexical-binding: t; -*-

;; Copyright (C) 2019-2021 Free Software Foundation, Inc.
;; Copyright (C) 2021 AKIYAMA Kouhei

;; Original Author: Lars Magne Ingebrigtsen <larsi@gnus.org>
;; Author: AKIYAMA Kouhei <misohena@gmail.com>
;; Keywords: images

;; This program 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.

;; This program 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 this program.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;; I can't write a fix request in English, so I am making fix privately.

;; Changes:

;; - [Bug] Skip APP1 segments that are not Exif (Such as XMP Meta Info)
;; - [Bug] Fix reading big-endian offset
;;         => already fixed https://git.savannah.gnu.org/cgit/emacs.git/commit/lisp/image/exif.el?id=72bcc6f988350329f3c0eb2f86af17f3ed97cf40
;; - [Bug] Fix reading small tag value (< 4-bytes) in big-endian
;; - [Add] Add support for reading sub Exif info and GPS info
;; - [Add] Add support for reading multiple components in a tag (Such as latitude, longitude)
;; - [Add] Add tag names I often see

;;; Code:

(require 'exif)

(defun my-exif-prop-find (exif tag)
  (seq-find (lambda (e) (equal (plist-get e :tag) tag)) exif))

(defun my-exif-prop-value (exif tag &optional key)
  (plist-get (my-exif-prop-find exif tag) (or key :value)))

(defun my-exif-3rationals-to-float (v neg)
  (let ((value (+
                (/ (caar v) (* 1.0 (cdar v)))
                (/ (caadr v) (* 60.0 (cdadr v)))
                (/ (caaddr v) (* 3600.0 (cdaddr v))))))
    (if neg (- value) value)))

;;

(defun my-exif-parse-file (file)
  (cl-letf (((symbol-function 'exif--parse-jpeg)
             #'my-exif--find-app1-exif-in-jpeg) ;; [BugFix] Support APP1 segments that are not Exif (Such as XMP)
            ((symbol-function 'exif--parse-exif-chunk)
             #'my-exif--parse-exif-chunk))
    (exif-parse-file file)))

(defun my-exif--find-app1-exif-in-jpeg ()
  (unless (= (exif--read-number-be 2) #xffd8) ; SOI (start of image)
    (signal 'exif-error "Not a valid JPEG file"))
  (cl-loop for segment = (exif--read-number-be 2)
           for size = (exif--read-number-be 2)
           ;; Stop parsing when we get to SOS (start of stream);
           ;; this is when the image itself starts, and there will
           ;; be no more chunks of interest after that.
           while (not (= segment #xffda)) ;;FFDA=SOS
           do (if (and (= segment #xffe1) ;;FFE1=APP1
                       (equal (save-excursion (exif--read-chunk 6))
                              (string ?E ?x ?i ?f ?\0 ?\0)))
                  ;; Return APP1 Exif
                  ;; (Matched to return value of exif--parse-jpeg)
                  (cl-return (list
                              (cons segment (exif--read-chunk (- size 2)))))
                ;; Skip segment
                (forward-char (- size 2)))))

(defun my-exif--parse-exif-chunk (data)
  (with-temp-buffer
    (set-buffer-multibyte nil)
    (insert data)
    (goto-char (point-min))
    ;; The Exif data is in the APP1 JPEG chunk and starts with
    ;; "Exif\0\0".
    (unless (equal (exif--read-chunk 6) (string ?E ?x ?i ?f ?\0 ?\0))
      (signal 'exif-error "Not a valid Exif chunk"))
    (delete-region (point-min) (point))
    (let* ((endian-marker (exif--read-chunk 2))
           (le (cond
                ;; "Motorola" is big-endian.
                ((equal endian-marker "MM")
                 nil)
                ;; "Intel" is little-endian.
                ((equal endian-marker "II")
                 t)
                (t
                 (signal 'exif-error
                         (format "Invalid endian-ness %s" endian-marker))))))
      ;; Another magical number.
      (unless (= (exif--read-number 2 le) #x002a)
        (signal 'exif-error "Invalid TIFF header length"))
      (let ((offset (exif--read-number 4 le))) ;; <==== [BugFix] 2 => 4 ====
        ;; Jump to where the IFD (directory) starts and parse it.
        (when (> (1+ offset) (point-max))
          (signal 'exif-error "Invalid IFD (directory) offset"))
        (goto-char (1+ offset))
        (my-exif--parse-directory le)))))

(defun my-exif--parse-directory (le)
  (let ((dir
         (cl-loop repeat (exif--read-number 2 le)
                  collect (my-exif--read-value le))))
    (let ((next (exif--read-number 4 le)))
      (if (> next 0)
          ;; There's more than one directory; if so, jump to it and
          ;; keep parsing.
          (progn
            (when (> (1+ next) (point-max))
              (signal 'exif-error "Invalid IFD (directory) next-offset"))
            (goto-char (1+ next))
            (nconc dir (my-exif--parse-directory le)))
        ;; We've reached the end of the directories.
        dir))))

(defvar my-exif-pointer-tags '(34665 ;;Exif IFD Pointer
                               34853)) ;;GPS Info IFD Pointer

(defun my-exif--read-value (le)
  ;; [Add] Support multiple components
  ;; [BugFix] Reading small value length < 4 and big-endian
  (let* ((tag (exif--read-number 2 le))
         (format (exif--read-number 2 le))
         (field-format (my-exif--field-format format))
         (type (car field-format))
         (bytes/component (cdr field-format))
         (num-components (exif--read-number 4 le))
         (num-bytes (* num-components bytes/component))
         (components
          (save-excursion
            (when (> num-bytes 4)
              ;; If the length of the data is
              ;; more than 4 bytes, then it's
              ;; actually stored after this
              ;; directory, and the value
              ;; here is just the offset to
              ;; use to find the data.
              (let ((offset (exif--read-number 4 le)))
                (when (> (+ (1+ offset) num-bytes)
                         (point-max))
                  (signal 'exif-error
                          "Premature end of file"))
                (goto-char (1+ offset))))

            (pcase type
              ;;@todo support signed
              ;;@todo support float and double
              ((or 'byte 'short 'long
                   's-byte 's-short 's-long)
               (cl-loop repeat num-components
                        collect (exif--read-number bytes/component le)))
              ((or 'rational 's-rational)
               (cl-loop repeat num-components
                        collect (cons
                                 (exif--read-number 4 le)
                                 (exif--read-number 4 le))))
              ('ascii
               (buffer-substring (point) (+ (point) num-bytes -1)));;Chop off trailing zero byte.
              ('undefined
               (buffer-substring (point) (+ (point) num-bytes)))
              (_
               nil))))
         (value (cond
                 ((eq type 'ascii)
                  components)
                 ((eq type 'undefined)
                  components)
                 ((= num-components 1)
                  (car components))
                 (t
                  components)))
         (pointee (when (and (memq tag my-exif-pointer-tags)
                             (integerp value))
                    (save-excursion
                      (goto-char (1+ value))
                      (my-exif--parse-directory le)))))
    ;; Skip Value (4 bytes)
    (goto-char (+ (point) 4))

    (nconc
     (list
      :tag tag
      :tag-name (cadr (assq tag my-exif-tag-alist))
      :format format
      :format-type (car field-format)
      :value value)
     (when pointee
       (list :pointee pointee)))))

(defun my-exif--field-format (number)
  (cl-case number
    (1 (cons 'byte 1))
    (2 (cons 'ascii 1))
    (3 (cons 'short 2))
    (4 (cons 'long 4))
    (5 (cons 'rational 8))
    (6 (cons 's-byte 1))
    (7 (cons 'undefined 1))
    (8 (cons 's-short 2))
    (9 (cons 's-long 4))
    (10 (cons 's-rational 8))
    (11 (cons 'float 4))
    (12 (cons 'double 8))
    (otherwise (cons 'unknown 1))))

(defvar my-exif-tag-alist
  '((11 processing-software)
    (256 image-width)
    (257 image-length)
    (258 bits-per-sample)
    (259 compression)
    (262 photometric-interpretation)
    (270 image-description)
    (271 make)
    (272 model)
    (273 strip-offsets)
    (274 orientation)
    (277 samples-per-pixel)
    (282 x-resolution)
    (283 y-resolution)
    (296 resolution-unit)
    (305 software)
    (306 date-time)
    (315 artist)
    (513 jpeg-interchange-format)
    (514 jpeg-interchange-format-length)
    (531 ycbcr-positioning)
    (33434 exposure-time)
    (33437 f-number)
    (34665 exif-ifd-pointer)
    (34850 exposure-program)
    (34853 gps-info-ifd-pointer)
    (34855 iso-speed-ratings)
    (36864 exif-version)
    (36867 date-time-original)
    (36868 date-time-digitized)
    (37121 components-configuration)
    (37377 shutter-speed-value)
    (37378 aperture-value)
    (37379 brightness-value)
    (37380 exposure-bias-value)
    (37381 max-aperture-value)
    (37382 subject-distance)
    (37383 metering-mode)
    (37384 light-source)
    (37385 flash)
    (37386 focal-length)
    (37520 sub-sec-time)
    (37521 sub-sec-time-original)
    (37522 sub-sec-time-digitized)
    (40960 flashpix-version)
    (40961 color-space)
    (40962 pixel-x-dimension)
    (40963 pixel-y-dimension)
    (40964 related-sound-file)
    (40965 interoperability-tag)
    (41495 sensing-method)
    (41729 scene-type)
    (41985 custom-rendered)
    (41986 exposure-mode)
    (41987 white-balance)
    (41988 digital-zoom-ratio)
    (41989 focal-length-in-35mm-film)
    (41990 scene-capture-type)
    (41991 gain-control)
    (41992 contrast)
    (41993 saturation)
    (41994 sharpness)
    (41995 device-setting-description)
    (41996 subject-distance-range))
  "Alist of tag values and their names.")

;;

(defun my-exif-encode-date-time (exif-date-time-str)
  (when exif-date-time-str
    (encode-time
     (nconc
      (nreverse
       (mapcar #'string-to-number
               (split-string exif-date-time-str "[ :]")))
      (list nil nil nil)))))

(defun my-exif-date-time-original (exif)
  (when-let ((exif-ifd (my-exif-prop-value exif 34665 :pointee))
             (date-time-original (my-exif-prop-value exif-ifd 36867)))
    (my-exif-encode-date-time date-time-original)))

(defun my-exif-latlng (exif)
  (when-let ((gps (my-exif-prop-value exif 34853 :pointee))
             (lat-ref (my-exif-prop-value gps 1))
             (lat (my-exif-prop-value gps 2))
             (lng-ref (my-exif-prop-value gps 3))
             (lng (my-exif-prop-value gps 4)))
    (cons
     (my-exif-3rationals-to-float lat
                                  (string= lat-ref "S"))
     (my-exif-3rationals-to-float lng
                                  (string= lng-ref "W")))))

(provide 'my-exif)