Fixes my photos date / time by applying the difference between the registered and the correct date. Requires `mini_exiftool` Gem and "ExifTool by Phil Harvey"

fix_photo_datetime.rb

require 'mini_exiftool'

def correct_date_time(wrong_date_time, offset)
  c = wrong_date_time + offset

  # Removes timezone
  Time.new(c.year, c.month, c.day, c.hour, c.min, c.sec)
end

def apply_offset_to_photo(path, offset)
  photo = MiniExiftool.new(path)

  date_time = correct_date_time(photo.date_time_original, offset)

  update_date_time(photo, date_time)
  photo.save!
end

# Manually selected every field in MiniExiftool.new(photo_path).to_hash that
# looked like a relevant date_time field.
# Those fields may be different depending on the camera used.
def update_date_time(photo, date_time)
  photo.file_modify_date = date_time
  photo.modify_date = date_time
  photo.date_time_original = date_time
  photo.create_date = date_time
  # sony specific
  photo.sony_date_time = date_time
end

def time_offset(photo_path, correct_date_time)
  photo = MiniExiftool.new(photo_path)
  correct_date_time - photo.date_time_original
end


# Here I pick a photo for witch I know the correct date / time.
# Any photo where a clock is visible is useful.
# Based on that I calculate the difference between the correct date / time and 
# the registered date / time.
# Using that difference I can fix every photo's timestamp.
#
# TODO: mini_exiftool initializes Time objects using the machine's local 
# timezone. Since EXIF tags don't store timezone, it's necessary to consider
# how timezones affect the calculations.
offset = time_offset('DSC05366.JPG', Time.new(2016, 12, 24, 12, 29, 0))

Dir['./*.JPG'].each do |photo_path|
  apply_offset_to_photo(photo_path, offset)
end