def main(argv=None):
    """script main.

    parses command line options in sys.argv, unless *argv* is given.
    """

    if argv is None:
        argv = sys.argv

    # setup command line parser
    parser = U.OptionParser(version="%prog version: $Id$",
                            usage=usage,
                            description=globals()["__doc__"])
    group = U.OptionGroup(parser, "dedup-specific options")

    group.add_option("--output-stats", dest="stats", type="string",
                     default=False,
                     help="Specify location to output stats")

    parser.add_option_group(group)

    # add common options (-h/--help, ...) and parse command line
    (options, args) = U.Start(parser, argv=argv)

    U.validateSamOptions(options, group=False)

    if options.random_seed:
        np.random.seed(options.random_seed)

    if options.stdin != sys.stdin:
        in_name = options.stdin.name
        options.stdin.close()
    else:
        raise ValueError("Input on standard in not currently supported")

    if options.stdout != sys.stdout:
        if options.no_sort_output:
            out_name = options.stdout.name
        else:
            out_name = U.getTempFilename(dir=options.tmpdir)
            sorted_out_name = options.stdout.name
        options.stdout.close()
    else:
        if options.no_sort_output:
            out_name = "-"
        else:
            out_name = U.getTempFilename(dir=options.tmpdir)
            sorted_out_name = "-"

    if not options.no_sort_output:  # need to determine the output format for sort
        if options.out_sam:
            sort_format = "sam"
        else:
            sort_format = "bam"

    if options.in_sam:
        in_mode = "r"
    else:
        in_mode = "rb"

    if options.out_sam:
        out_mode = "wh"
    else:
        out_mode = "wb"

    if options.stats and options.ignore_umi:
        raise ValueError("'--output-stats' and '--ignore-umi' options"
                         " cannot be used together")

    infile = pysam.Samfile(in_name, in_mode)
    outfile = pysam.Samfile(out_name, out_mode, template=infile)

    if options.paired:
        outfile = sam_methods.TwoPassPairWriter(infile, outfile)

    nInput, nOutput, input_reads, output_reads = 0, 0, 0, 0

    if options.detection_method:
        bam_features = detect_bam_features(infile.filename)

        if not bam_features[options.detection_method]:
            if sum(bam_features.values()) == 0:
                raise ValueError(
                    "There are no bam tags available to detect multimapping. "
                    "Do not set --multimapping-detection-method")
            else:
                raise ValueError(
                    "The chosen method of detection for multimapping (%s) "
                    "will not work with this bam. Multimapping can be detected"
                    " for this bam using any of the following: %s" % (
                        options.detection_method, ",".join(
                            [x for x in bam_features if bam_features[x]])))

    gene_tag = options.gene_tag
    metacontig2contig = None

    if options.chrom:
        inreads = infile.fetch(reference=options.chrom)

    else:
        if options.per_contig and options.gene_transcript_map:
            metacontig2contig = sam_methods.getMetaContig2contig(
                infile, options.gene_transcript_map)
            metatag = "MC"
            inreads = sam_methods.metafetcher(infile, metacontig2contig, metatag)
            gene_tag = metatag

        else:
            inreads = infile.fetch()

    # set up ReadCluster functor with methods specific to
    # specified options.method
    processor = network.ReadDeduplicator(options.method)

    bundle_iterator = sam_methods.get_bundles(
        options,
        metacontig_contig=metacontig2contig)

    if options.stats:
        # set up arrays to hold stats data
        stats_pre_df_dict = {"UMI": [], "counts": []}
        stats_post_df_dict = {"UMI": [], "counts": []}
        pre_cluster_stats = []
        post_cluster_stats = []
        pre_cluster_stats_null = []
        post_cluster_stats_null = []
        topology_counts = collections.Counter()
        node_counts = collections.Counter()
        read_gn = umi_methods.random_read_generator(
            infile.filename, chrom=options.chrom,
            barcode_getter=bundle_iterator.barcode_getter)

    for bundle, key, status in bundle_iterator(inreads):

        nInput += sum([bundle[umi]["count"] for umi in bundle])

        while nOutput >= output_reads + 100000:
            output_reads += 100000
            U.info("Written out %i reads" % output_reads)

        while nInput >= input_reads + 1000000:
            input_reads += 1000000
            U.info("Parsed %i input reads" % input_reads)

        if options.stats:
            # generate pre-dudep stats
            average_distance = umi_methods.get_average_umi_distance(bundle.keys())
            pre_cluster_stats.append(average_distance)
            cluster_size = len(bundle)
            random_umis = read_gn.getUmis(cluster_size)
            average_distance_null = umi_methods.get_average_umi_distance(random_umis)
            pre_cluster_stats_null.append(average_distance_null)

        if options.ignore_umi:
            for umi in bundle:
                nOutput += 1
                outfile.write(bundle[umi]["read"])

        else:

            # dedup using umis and write out deduped bam
            reads, umis, umi_counts = processor(
                bundle=bundle,
                threshold=options.threshold)

            for read in reads:
                outfile.write(read)
                nOutput += 1

            if options.stats:

                # collect pre-dudupe stats
                stats_pre_df_dict['UMI'].extend(bundle)
                stats_pre_df_dict['counts'].extend(
                    [bundle[UMI]['count'] for UMI in bundle])

                # collect post-dudupe stats
                post_cluster_umis = [bundle_iterator.barcode_getter(x)[0] for x in reads]
                stats_post_df_dict['UMI'].extend(umis)
                stats_post_df_dict['counts'].extend(umi_counts)

                average_distance = umi_methods.get_average_umi_distance(post_cluster_umis)
                post_cluster_stats.append(average_distance)

                cluster_size = len(post_cluster_umis)
                random_umis = read_gn.getUmis(cluster_size)
                average_distance_null = umi_methods.get_average_umi_distance(random_umis)
                post_cluster_stats_null.append(average_distance_null)

    outfile.close()

    if not options.no_sort_output:
        # sort the output
        pysam.sort("-o", sorted_out_name, "-O", sort_format, out_name)
        os.unlink(out_name)  # delete the tempfile

    if options.stats:

        # generate the stats dataframe
        stats_pre_df = pd.DataFrame(stats_pre_df_dict)
        stats_post_df = pd.DataFrame(stats_post_df_dict)

        # tally the counts per umi per position
        pre_counts = collections.Counter(stats_pre_df["counts"])
        post_counts = collections.Counter(stats_post_df["counts"])
        counts_index = list(set(pre_counts.keys()).union(set(post_counts.keys())))
        counts_index.sort()
        with U.openFile(options.stats + "_per_umi_per_position.tsv", "w") as outf:
            outf.write("counts\tinstances_pre\tinstances_post\n")
            for count in counts_index:
                values = (count, pre_counts[count], post_counts[count])
                outf.write("\t".join(map(str, values)) + "\n")

        # aggregate stats pre/post per UMI
        agg_pre_df = aggregateStatsDF(stats_pre_df)
        agg_post_df = aggregateStatsDF(stats_post_df)

        agg_df = pd.merge(agg_pre_df, agg_post_df, how='left',
                          left_index=True, right_index=True,
                          sort=True, suffixes=["_pre", "_post"])

        # TS - if count value not observed either pre/post-dedup,
        # merge will leave an empty cell and the column will be cast as a float
        # see http://pandas.pydata.org/pandas-docs/dev/missing_data.html
        # --> Missing data casting rules and indexing
        # so, back fill with zeros and convert back to int
        agg_df = agg_df.fillna(0).astype(int)

        agg_df.index = [x.decode() for x in agg_df.index]
        agg_df.index.name = 'UMI'
        agg_df.to_csv(options.stats + "_per_umi.tsv", sep="\t")

        # bin distances into integer bins
        max_ed = int(max(map(max, [pre_cluster_stats,
                                   post_cluster_stats,
                                   pre_cluster_stats_null,
                                   post_cluster_stats_null])))

        cluster_bins = range(-1, int(max_ed) + 2)

        def bin_clusters(cluster_list, bins=cluster_bins):
            ''' take list of floats and return bins'''
            return np.digitize(cluster_list, bins, right=True)

        def tallyCounts(binned_cluster, max_edit_distance):
            ''' tally counts per bin '''
            return np.bincount(binned_cluster,
                               minlength=max_edit_distance + 3)

        pre_cluster_binned = bin_clusters(pre_cluster_stats)
        post_cluster_binned = bin_clusters(post_cluster_stats)
        pre_cluster_null_binned = bin_clusters(pre_cluster_stats_null)
        post_cluster_null_binned = bin_clusters(post_cluster_stats_null)

        edit_distance_df = pd.DataFrame(
            {"unique": tallyCounts(pre_cluster_binned, max_ed),
             "unique_null": tallyCounts(pre_cluster_null_binned, max_ed),
             options.method: tallyCounts(post_cluster_binned, max_ed),
             "%s_null" % options.method: tallyCounts(post_cluster_null_binned, max_ed),
             "edit_distance": cluster_bins},
            columns=["unique", "unique_null", options.method,
                     "%s_null" % options.method, "edit_distance"])

        # TS - set lowest bin (-1) to "Single_UMI"
        edit_distance_df['edit_distance'][0] = "Single_UMI"

        edit_distance_df.to_csv(options.stats + "_edit_distance.tsv",
                                index=False, sep="\t")

    # write footer and output benchmark information.
    U.info(
        "Reads: %s" % ", ".join(["%s: %s" % (x[0], x[1]) for x in
                                 bundle_iterator.read_events.most_common()]))

    U.info("Number of reads out: %i" % nOutput)

    if not options.ignore_umi:  # otherwise processor has not been used
        U.info("Total number of positions deduplicated: %i" %
               processor.UMIClusterer.positions)
        if processor.UMIClusterer.positions > 0:
            U.info("Mean number of unique UMIs per position: %.2f" %
                   (float(processor.UMIClusterer.total_umis_per_position) /
                    processor.UMIClusterer.positions))
            U.info("Max. number of unique UMIs per position: %i" %
                   processor.UMIClusterer.max_umis_per_position)
        else:
            U.warn("The BAM did not contain any valid "
                   "reads/read pairs for deduplication")

    U.Stop()
script main.

    parses command line options in sys.argv, unless *argv* is given.