#!/usr/bin/env python
#
# prw2ppm - convert Artlantis Preview files to PPM
#
# Copyright (C) 2012  Antonio Ospite <ospite@studenti.unina.it>
#
# 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 <http://www.gnu.org/licenses/>.

import os
import sys
import struct


def get_be32(f):
    fmt = '>I'

    length = struct.calcsize(fmt)
    data = f.read(length)
    value = struct.unpack_from(fmt, data)

    return  value[0]


def to_rgb(data):
    r = (data & 0x00FF0000) >> 16
    g = (data & 0x0000FF00) >> 8
    b = (data & 0x000000FF)

    return (r, g, b)


def usage(name):
    sys.stdout.write("usage: %s <prw file>\n" % name)


def prw2ppm(prw_filename, ppm_filename):
    f = open(prw_filename, "rb")

    # file type or frame number,
    # or maybe the type of the first packet? (run-length or raw)
    file_type = get_be32(f)
    if file_type != 1:
        sys.stdderr.write("Unknown preview file type.\n")
        sys.exit(1)

    width = get_be32(f)
    height = get_be32(f)

    outfile = open(ppm_filename, "w")

    outfile.write("P3\n")
    outfile.write("%d %d\n" % (width, height))
    outfile.write("%d\n" % 255)

    n = 0
    n_pixels = width * height

    # Read the first packet here,
    # AFAIK it is always a run-length packet
    count = get_be32(f)
    data = get_be32(f)
    old_data = data

    while True:
        if data == old_data:
            # run-length packet
            for i in range(0, count):
                outfile.write("%d %d %d\n" % to_rgb(data))
        else:
            # raw packet
            outfile.write("%d %d %d\n" % to_rgb(data))
            for i in range(0, count - 1):
                data = get_be32(f)
                outfile.write("%d %d %d\n" % to_rgb(data))

        n += count
        if n == n_pixels:
            break

        old_data = data

        # read next packet
        count = get_be32(f)
        data = get_be32(f)

    outfile.close()


if __name__ == "__main__":

    if len(sys.argv) < 2:
        usage(sys.argv[0])
        sys.exit(1)

    prw_filename = sys.argv[1]

    basename_no_ext = os.path.splitext(prw_filename)[0]
    ppm_filename = basename_no_ext + ".ppm"

    prw2ppm(prw_filename, ppm_filename)

    sys.exit(0)