#! /usr/bin/env ruby
#
# exif-touch - a tool to change time stamp of jpeg files using EXIF info.
#
# Usage: 
#
#   % exif-touch *.jpg
#
# Copyright (C) 2003 Satoru Takabayashi <satoru@namazu.org> 
#     All rights reserved.
#     This is free software with ABSOLUTELY NO WARRANTY.
#
# You can redistribute it and/or modify it under the terms
# of Ruby's licence.
#

module Exif
  HEADER_OFFSET1 = 12
  HEADER_OFFSET2 = 8

  module_function
  def exif_file? (filename)
    exif_header = "\xff\xd8\xff\xe1"
    magic = File.open(filename) {|f| f.read(4) }
    magic == exif_header
  end

  def read_directory (f, read_ushort, read_ulong)
    n = read_ushort.call(f)
    n.times {
      tag   = read_ushort.call(f)
      type  = read_ushort.call(f)
      size  = read_ulong.call(f)
      value = read_ulong.call(f)
      yield(f, tag, type, size, value)
    }
  end

  def get_endian (f)
    f.seek(HEADER_OFFSET1)
    data = f.read(2)
    if data == "\x49\x49"
      :little_endian
    elsif data == "\x4d\x4d"
      :big_endian
    else
      raise 'unknown format'
    end
  end

  def get_time (filename)
    time = File.mtime(filename)
    begin
      raise 'not an exif file' unless exif_file?(filename)
      File.open(filename) {|f|
        read_ushort = lambda {|f| f.read(2).unpack('v').first }
        read_ulong  = lambda {|f| f.read(4).unpack('V').first }
        if get_endian(f) == :big_endian
          read_ushort = lambda {|f| f.read(2).unpack('n').first }
          read_ulong  = lambda {|f| f.read(4).unpack('N').first }
        end

        f.seek(HEADER_OFFSET1 + HEADER_OFFSET2)
        special_offset = nil
        read_directory(f, read_ushort, read_ulong) {|f, tag, type, size, value|
          special_offset = value if tag == 0x8769
        }
        raise if special_offset.nil?

        f.seek(HEADER_OFFSET1 + special_offset)
        read_directory(f, read_ushort, read_ulong) {|f, tag, type, size, value|
          if tag == 0x9003
            curpos = f.pos
            f.seek(HEADER_OFFSET1 + value)
            s = f.read(size) # 2003:01:26 16:37:04
            if /(\d\d\d\d):(\d\d):(\d\d) (\d\d):(\d\d):(\d\d)/.match(s)
              year = $1.to_i;  mon  = $2.to_i
              day  = $3.to_i;  hour = $4.to_i
              min  = $5.to_i;  sec  = $6.to_i
              time = Time.mktime(year, mon, day, hour, min, sec)
            end
            f.seek(curpos)
          end
        }
      }
    rescue => e
      STDERR.puts "exif-touch: #{filename}: #{e.message}"
      exit 1
    end
    return time
  end
end

if __FILE__ == $0
  def fmt (t)
    t.strftime("%Y-%m-%d %H:%M:%S")
  end

  ARGV.each {|filename|
    if Exif.exif_file?(filename)
      old = File.mtime(filename)
      new = Exif.get_time(filename)
      File.utime(new, new, filename)
      puts "#{filename}: #{fmt(old)} -> #{fmt(new)}"
    else
      puts "#{filename}: not an exif file"
    end
  }
end