#!/usr/bin/python2.6

"""
Chops alignments in a MAF file to piece of a specified length. A random set of
non overlapping chunks of exactly the specified chop length will be produced

usage: %prog [options] < maf > maf
  -l, --length: Chop to exactly this length in columns (default 100)
"""

import sys

import sys, random
import bx.align.maf
from optparse import OptionParser

def main():

    # Parse command line arguments

    parser = OptionParser()
    parser.add_option( "-l", "--length", action="store", type="int", default=100, help="" )

    ( options, args ) = parser.parse_args()

    length = options.length
    maf_reader = bx.align.maf.Reader( sys.stdin )
    maf_writer = bx.align.maf.Writer( sys.stdout )

    for m in maf_reader:
        for chopped in chop( m, length ):
            maf_writer.write( chopped )

def chop( m, length ):
    maf_length = m.text_size
    chunk_count = maf_length // length
    lost_bases = maf_length % length
    skip_amounts = [0] * ( chunk_count + 1 )
    for i in range( 0, lost_bases ): skip_amounts[ random.randrange( 0, chunk_count + 1 ) ] += 1
    start = 0
    rval = []
    for i in range( 0, chunk_count ):
        start += skip_amounts[ i ]
        n = m.slice( start, start + length )
        if check_len( n ): rval.append( m.slice( start, start + length ) )
        start += length
    return rval

def check_len( a ):
    for c in a.components:
        if c.size == 0: return False
    return True 
    

if __name__ == "__main__": main()
