from __future__ import division
#!/usr/bin/env python
# FormatTIFFHelpers.py
#   Copyright (C) 2011 Diamond Light Source, Graeme Winter
#
#   This code is distributed under the BSD license, a copy of which is
#   included in the root directory of this package.
#
# Helper code to assist with reading TIFF file headers, which are by their
# nature binary so we need to mess with things like byte swapping.

import struct

LITTLE_ENDIAN = 1234
BIG_ENDIAN = 4321

from dxtbx.format.Format import Format

def tiff_byte_order(filename):
  '''Determine the byte order for the file from the magic numbers at the
  very start of the file.'''

  four_bytes = Format.open_file(filename, 'rb').read(4)

  if 'II' in four_bytes[:2]:
    assert(struct.unpack('<H', four_bytes[2:])[0] == 42)
    return LITTLE_ENDIAN
  elif 'MM' in four_bytes[:2]:
    assert(struct.unpack('>H', four_bytes[2:])[0] == 42)
    return BIG_ENDIAN

  raise RuntimeError, '%s not recognised as TIFF' % filename

def read_basic_tiff_header(filename):
  '''Read the TIFF header (assuming for the moment a 4k header...) and
  return ... something.'''

  # things we hope to learn from the vanilla TIFF header

  image_width = None
  image_height = None
  image_depth = None
  header_size = None
  byte_order = None

  # OK then let's get started - and let's assume that the size is > 1 kb

  byte_order = tiff_byte_order(filename)
  tiff_header = Format.open_file(filename, 'rb').read(1024)

  if byte_order == LITTLE_ENDIAN:
    _I = '<I'
    _H = '<H'
  else:
    _I = '>I'
    _H = '>H'

  offset = struct.unpack(_I, tiff_header[4:8])[0]

  ntags = struct.unpack(_H, tiff_header[offset:offset + 2])[0]
  start = offset + 2

  for j in range(ntags):
    type_desc = struct.unpack(_H, tiff_header[start:start + 2])[0]
    start += 2
    type_type = struct.unpack(_H, tiff_header[start:start + 2])[0]
    start += 2
    type_size = struct.unpack(_I, tiff_header[start:start + 4])[0]
    start += 4
    if type_type == 4:
      type_offset_or_value = struct.unpack(
          _I, tiff_header[start:start + 4])[0]
      start += 4
    elif type_type == 3:
      type_offset_or_value = struct.unpack(
          _H, tiff_header[start:start + 2])[0]
      start += 4

    if type_desc == 256:
      image_width = type_offset_or_value
    elif type_desc == 257:
      image_height = type_offset_or_value
    elif type_desc == 258:
      image_depth = type_offset_or_value
    elif type_desc == 273:
      header_size = type_offset_or_value

  return image_width, image_height, image_depth, header_size, byte_order

def read_tiff_image_description(tiff_header, byte_order):
  '''Search the TIFF header for an image description.'''

  # OK then let's get started - and let's assume that the size is > 1 kb

  if byte_order == LITTLE_ENDIAN:
    _I = '<I'
    _H = '<H'
  else:
    _I = '>I'
    _H = '>H'

  offset = struct.unpack(_I, tiff_header[4:8])[0]
  ntags = struct.unpack(_H, tiff_header[offset:offset + 2])[0]
  start = offset + 2

  header_text = None

  for j in range(ntags):
    type_desc = struct.unpack(_H, tiff_header[start:start + 2])[0]
    start += 2
    type_type = struct.unpack(_H, tiff_header[start:start + 2])[0]
    start += 2
    type_size = struct.unpack(_I, tiff_header[start:start + 4])[0]
    start += 4
    if type_type == 4:
      type_offset_or_value = struct.unpack(
          _I, tiff_header[start:start + 4])[0]
      start += 4
    elif type_type == 3:
      type_offset_or_value = struct.unpack(
          _H, tiff_header[start:start + 2])[0]
      start += 4
    elif type_type == 2:
      type_offset_or_value = struct.unpack(
          _I, tiff_header[start:start + 4])[0]
      start += 4

    if type_desc == 270:
      start = type_offset_or_value
      end = type_offset_or_value + type_size
      header_text = tiff_header[start:end].strip()

  return header_text

if __name__ == '__main__':

  import sys

  for arg in sys.argv[1:]:

    width, height, depth, header, order = read_basic_tiff_header(arg)

    print '(%d x %d) @ %d + %d' % (width, height, depth, header)

    tiff_header = Format.open_file(arg, 'rb').read(header)

    text = read_tiff_image_description(tiff_header, order)

    if text:
      print text
    else:
      print 'No text found'