#!/usr/bin/python
# Recalculate the length fields in the header of a WAV file.
# Adam Sampson <ats@offog.org>
#
# I managed to persuade ecasound to produce a WAV file with the length set to
# zero (probably by killing it in a funny way before it had a chance to write
# them properly), and writing this was quicker than doing the recording again.

import sys, os, struct

def print_header(header):
	print "  Chunk size:", struct.unpack("<i", header[4:8])[0]
	print "  Data size:", struct.unpack("<i", header[40:44])[0]

def main(args):
	if len(args) != 1:
		print "Usage: fix-wav-length WAV-FILE"
		return 1

	fd = os.open(args[0], os.O_RDWR)

	os.lseek(fd, 0, 0)
	header = os.read(fd, 44)
	if (len(header) != 44 or header[:4] != "RIFF"
	    or header[12:16] != "fmt " or header[36:40] != "data"):
		print "Sorry, this doesn't look like a WAV file."
		return 1
	if struct.unpack("<h", header[20:22])[0] != 1:
		print "Sorry, this isn't a linear PCM file."
		return 1
	print "Existing header:"
	print_header(header)

	length = os.fstat(fd).st_size
	if length >= 1L << 32:
		print "File is longer than 2GB -- setting length to less than that."
		print "This will ignore the remaining data in the file."
		length = (1L << 32) - 36 - 4 - 4

	chunk_size = length - 4
	data_size = chunk_size - 36
	header = (header[:4]
	          + struct.pack("<i", chunk_size)
	          + header[8:40]
	          + struct.pack("<i", data_size))
	print "New header:"
	print_header(header)

	os.lseek(fd, 0, 0)
	os.write(fd, header)
	print "Written."

	os.close(fd)

	return 0

if __name__ == "__main__":
	sys.exit(main(sys.argv[1:]))