"""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"""Discard cache entries that are out of date.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.startswith('<') and filename.endswith('>')):
return []

fullname = filename
try:
stat = os.stat(fullname)
except OSError:
basename = filename

# 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:
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, which is only useful
# when handling a relative filename.
if os.path.isabs(filename):
return []

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.
continue
try:
stat = os.stat(fullname)
break
except os.error:
pass
else:
return []
try:
with open(fullname, 'rU') as fp:
lines = fp.readlines()
except IOError:
return []
if lines and not lines[-1].endswith('\n'):
lines[-1] += '\n'
size, mtime = stat.st_size, stat.st_mtime
cache[filename] = size, mtime, lines, fullname
return lines