"""Adds xref targets to the top of files."""

import sys
import os

testing = False

DONT_TOUCH = (
    './index.txt',
)


def target_name(fn):
    if fn.endswith('.txt'):
        fn = fn[:-4]
    return '_' + fn.lstrip('./').replace('/', '-')


def process_file(fn, lines):
    lines.insert(0, '\n')
    lines.insert(0, '.. %s:\n' % target_name(fn))
    try:
        f = open(fn, 'w')
    except IOError:
        print("Can't open %s for writing. Not touching it." % fn)
        return
    try:
        f.writelines(lines)
    except IOError:
        print("Can't write to %s. Not touching it." % fn)
    finally:
        f.close()


def has_target(fn):
    try:
        f = open(fn, 'r')
    except IOError:
        print("Can't open %s. Not touching it." % fn)
        return (True, None)
    readok = True
    try:
        lines = f.readlines()
    except IOError:
        print("Can't read %s. Not touching it." % fn)
        readok = False
    finally:
        f.close()
        if not readok:
            return (True, None)

    if len(lines) < 1:
        print("Not touching empty file %s." % fn)
        return (True, None)
    if lines[0].startswith('.. _'):
        return (True, None)
    return (False, lines)


def main(argv=None):
    if argv is None:
        argv = sys.argv

    if len(argv) == 1:
        argv.extend('.')

    files = []
    for root in argv[1:]:
        for (dirpath, dirnames, filenames) in os.walk(root):
            files.extend([(dirpath, f) for f in filenames])
    files.sort()
    files = [os.path.join(p, fn) for p, fn in files if fn.endswith('.txt')]

    for fn in files:
        if fn in DONT_TOUCH:
            print("Skipping blacklisted file %s." % fn)
            continue

        target_found, lines = has_target(fn)
        if not target_found:
            if testing:
                print '%s: %s' % (fn, lines[0]),
            else:
                print "Adding xref to %s" % fn
                process_file(fn, lines)
        else:
            print "Skipping %s: already has a xref" % fn

if __name__ == '__main__':
    sys.exit(main())