#!/opt/chipster/tools/Python-2.7.12/bin/python

"""
Read BED file and extend each record to the specified minimum length. If chromosome 
size information is provided trim extended intervals.

usage: %prog amount [ chrom_file ] < bed_file
"""

import sys
from bx.intervals.io import GenomicIntervalReader

length = int( sys.argv[1] )
chrom_len = None
if len( sys.argv ) > 2:
    chrom_len = dict( ( fields[0], int( fields[1] ) ) for fields in map( str.split, open( sys.argv[2] ) ) )

for interval in GenomicIntervalReader( sys.stdin ):
    if interval.end - interval.start < length:
        start = interval.start
        end = interval.end
        # Extend in positive direction on strand
        if interval.strand == "+":
            end = start + length
        else:
            start = end - length
        # Trim 
        if start < 0:
            start = 0
        if chrom_len and end > chrom_len[interval.chrom]:
            end = chrom_len[interval.chrom]
        # Set new start and end
        interval.start = start
        interval.end = end
    # Output possibly adjusted interval
    print interval