def expand(args):
    """
    %prog expand bes.fasta reads.fastq

    Expand sequences using short reads. Useful, for example for getting BAC-end
    sequences. The template to use, in `bes.fasta` may just contain the junction
    sequences, then align the reads to get the 'flanks' for such sequences.
    """
    import math

    from jcvi.formats.fasta import Fasta, SeqIO
    from jcvi.formats.fastq import readlen, first, fasta
    from jcvi.formats.blast import Blast
    from jcvi.formats.base import FileShredder
    from jcvi.apps.bowtie import align, get_samfile
    from jcvi.apps.align import blast

    p = OptionParser(expand.__doc__)
    p.set_depth(depth=200)
    p.set_firstN()
    opts, args = p.parse_args(args)

    if len(args) != 2:
        sys.exit(not p.print_help())

    bes, reads = args
    size = Fasta(bes).totalsize
    rl = readlen([reads])
    expected_size = size + 2 * rl
    nreads = expected_size * opts.depth / rl
    nreads = int(math.ceil(nreads / 1000.)) * 1000

    # Attract reads
    samfile, logfile = align([bes, reads, "--reorder", "--mapped",
           "--firstN={0}".format(opts.firstN)])

    samfile, mapped, _ = get_samfile(reads, bes, bowtie=True, mapped=True)
    logging.debug("Extract first {0} reads from `{1}`.".format(nreads, mapped))

    pf = mapped.split(".")[0]
    pf = pf.split("-")[0]
    bespf = bes.split(".")[0]
    reads = pf + ".expand.fastq"
    first([str(nreads), mapped, "-o", reads])

    # Perform mini-assembly
    fastafile = reads.rsplit(".", 1)[0] + ".fasta"
    qualfile = ""
    if need_update(reads, fastafile):
        fastafile, qualfile = fasta([reads])

    contigs = op.join(pf, "454LargeContigs.fna")
    if need_update(fastafile, contigs):
        cmd = "runAssembly -o {0} -cpu 8 {1}".format(pf, fastafile)
        sh(cmd)
    assert op.exists(contigs)

    # Annotate contigs
    blastfile = blast([bes, contigs])
    mapping = {}
    for query, b in Blast(blastfile).iter_best_hit():
        mapping[query] = b

    f = Fasta(contigs, lazy=True)
    annotatedfasta = ".".join((pf, bespf, "fasta"))
    fw = open(annotatedfasta, "w")
    keys = list(Fasta(bes).iterkeys_ordered())  # keep an ordered list
    recs = []
    for key, v in f.iteritems_ordered():
        vid = v.id
        if vid not in mapping:
            continue
        b = mapping[vid]
        subject = b.subject
        rec = v.reverse_complement() if b.orientation == '-' else v
        rec.id = rid = "_".join((pf, vid, subject))
        rec.description = ""
        recs.append((keys.index(subject), rid, rec))

    recs = [x[-1] for x in sorted(recs)]
    SeqIO.write(recs, fw, "fasta")
    fw.close()

    FileShredder([samfile, logfile, mapped, reads, fastafile, qualfile, blastfile, pf])
    logging.debug("Annotated seqs (n={0}) written to `{1}`.".\
                    format(len(recs), annotatedfasta))

    return annotatedfasta