"""Cache lines from files.

This is intended to read lines from modules imported -- hence if a filename

is not found, it will look down the module search path for a file by

that name.

"""

import sys

import os

__all__ = ["getline", "clearcache", "checkcache"]

def getline(filename, lineno, module_globals=None):

    lines = getlines(filename, module_globals)

    if 1 <= lineno <= len(lines):

        return lines[lineno-1]

    else:

        return ''

# The cache

cache = {} # The cache

def clearcache():

    """Clear the cache entirely."""

    global cache

    cache = {}

def getlines(filename, module_globals=None):

    """Get the lines for a file from the cache.

    Update the cache if it doesn't contain an entry for this file already."""

    if filename in cache:

        return cache[filename][2]

    else:

        return updatecache(filename, module_globals)

def checkcache(filename=None):

    """Discard cache entries that are out of date.

    (This is not checked upon each call!)"""

    if filename is None:

        filenames = cache.keys()

    else:

        if filename in cache:

            filenames = [filename]

        else:

            return

    for filename in filenames:

        size, mtime, lines, fullname = cache[filename]

        if mtime is None:

            continue   # no-op for files loaded via a __loader__

        try:

            stat = os.stat(fullname)

        except os.error:

            del cache[filename]

            continue

        if size != stat.st_size or mtime != stat.st_mtime:

            del cache[filename]

def updatecache(filename, module_globals=None):

    """Update a cache entry and return its list of lines.

    If something's wrong, print a message, discard the cache entry,

    and return an empty list."""

    if filename in cache:

        del cache[filename]

    if not filename or filename[0] + filename[-1] == '<>':

        return []

    fullname = filename

    try:

        stat = os.stat(fullname)

    except os.error, msg:

        basename = os.path.split(filename)[1]

        # Try for a __loader__, if available

        if module_globals and '__loader__' in module_globals:

            name = module_globals.get('__name__')

            loader = module_globals['__loader__']

            get_source = getattr(loader, 'get_source', None)

            if name and get_source:

                if basename.startswith(name.split('.')[-1]+'.'):

                    try:

                        data = get_source(name)

                    except (ImportError, IOError):

                        pass

                    else:

                        if data is None:

                            # No luck, the PEP302 loader cannot find the source

                            # for this module.

                            return []

                        cache[filename] = (

                            len(data), None,

                            [line+'\n' for line in data.splitlines()], fullname

                        )

                        return cache[filename][2]

        # Try looking through the module search path.

        for dirname in sys.path:

            # When using imputil, sys.path may contain things other than

            # strings; ignore them when it happens.

            try:

                fullname = os.path.join(dirname, basename)

            except (TypeError, AttributeError):

                # Not sufficiently string-like to do anything useful with.

                pass

            else:

                try:

                    stat = os.stat(fullname)

                    break

                except os.error:

                    pass

        else:

            # No luck

##          print '*** Cannot stat', filename, ':', msg

            return []

    try:

        fp = open(fullname, 'rU')

        lines = fp.readlines()

        fp.close()

    except IOError, msg:

##      print '*** Cannot open', fullname, ':', msg

        return []

    size, mtime = stat.st_size, stat.st_mtime

    cache[filename] = size, mtime, lines, fullname

    return lines