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__revision__ = "__FILE__ __REVISION__ __DATE__ __DEVELOPER__"

__doc__ = """
CacheDir support
"""

import json
import os
import stat
import sys

import SCons.Action
import SCons.Warnings

cache_enabled = True
cache_debug = False
cache_force = False
cache_show = False
cache_readonly = False

def CacheRetrieveFunc(target, source, env):
    t = target[0]
    fs = t.fs
    cd = env.get_CacheDir()
    cachedir, cachefile = cd.cachepath(t)
    if not fs.exists(cachefile):
        cd.CacheDebug('CacheRetrieve(%s):  %s not in cache\n', t, cachefile)
        return 1
    cd.CacheDebug('CacheRetrieve(%s):  retrieving from %s\n', t, cachefile)
    if SCons.Action.execute_actions:
        if fs.islink(cachefile):
            fs.symlink(fs.readlink(cachefile), t.get_internal_path())
        else:
            env.copy_from_cache(cachefile, t.get_internal_path())
        st = fs.stat(cachefile)
        fs.chmod(t.get_internal_path(), stat.S_IMODE(st[stat.ST_MODE]) | stat.S_IWRITE)
    return 0

def CacheRetrieveString(target, source, env):
    t = target[0]
    fs = t.fs
    cd = env.get_CacheDir()
    cachedir, cachefile = cd.cachepath(t)
    if t.fs.exists(cachefile):
        return "Retrieved `%s' from cache" % t.get_internal_path()
    return None

CacheRetrieve = SCons.Action.Action(CacheRetrieveFunc, CacheRetrieveString)

CacheRetrieveSilent = SCons.Action.Action(CacheRetrieveFunc, None)

def CachePushFunc(target, source, env):
    if cache_readonly:
        return

    t = target[0]
    if t.nocache:
        return
    fs = t.fs
    cd = env.get_CacheDir()
    cachedir, cachefile = cd.cachepath(t)
    if fs.exists(cachefile):
        # Don't bother copying it if it's already there.  Note that
        # usually this "shouldn't happen" because if the file already
        # existed in cache, we'd have retrieved the file from there,
        # not built it.  This can happen, though, in a race, if some
        # other person running the same build pushes their copy to
        # the cache after we decide we need to build it but before our
        # build completes.
        cd.CacheDebug('CachePush(%s):  %s already exists in cache\n', t, cachefile)
        return

    cd.CacheDebug('CachePush(%s):  pushing to %s\n', t, cachefile)

    tempfile = cachefile+'.tmp'+str(os.getpid())
    errfmt = "Unable to copy %s to cache. Cache file is %s"

    if not fs.isdir(cachedir):
        try:
            fs.makedirs(cachedir)
        except EnvironmentError:
            # We may have received an exception because another process
            # has beaten us creating the directory.
            if not fs.isdir(cachedir):
                msg = errfmt % (str(target), cachefile)
                raise SCons.Errors.EnvironmentError(msg)

    try:
        if fs.islink(t.get_internal_path()):
            fs.symlink(fs.readlink(t.get_internal_path()), tempfile)
        else:
            fs.copy2(t.get_internal_path(), tempfile)
        fs.rename(tempfile, cachefile)
        st = fs.stat(t.get_internal_path())
        fs.chmod(cachefile, stat.S_IMODE(st[stat.ST_MODE]) | stat.S_IWRITE)
    except EnvironmentError:
        # It's possible someone else tried writing the file at the
        # same time we did, or else that there was some problem like
        # the CacheDir being on a separate file system that's full.
        # In any case, inability to push a file to cache doesn't affect
        # the correctness of the build, so just print a warning.
        msg = errfmt % (str(target), cachefile)
        SCons.Warnings.warn(SCons.Warnings.CacheWriteErrorWarning, msg)

CachePush = SCons.Action.Action(CachePushFunc, None)

# Nasty hack to cut down to one warning for each cachedir path that needs
# upgrading.
warned = dict()

class CacheDir(object):

    def __init__(self, path):
        try:
            import hashlib
        except ImportError:
            msg = "No hashlib or MD5 module available, CacheDir() not supported"
            SCons.Warnings.warn(SCons.Warnings.NoMD5ModuleWarning, msg)
            path = None
        self.path = path
        self.current_cache_debug = None
        self.debugFP = None
        self.config = dict()
        if path is None:
            return
        # See if there's a config file in the cache directory. If there is,
        # use it. If there isn't, and the directory exists and isn't empty,
        # produce a warning. If the directory doesn't exist or is empty,
        # write a config file.
        config_file = os.path.join(path, 'config')
        if not os.path.exists(config_file):
            # A note: There is a race hazard here, if two processes start and
            # attempt to create the cache directory at the same time. However,
            # python doesn't really give you the option to do exclusive file
            # creation (it doesn't even give you the option to error on opening
            # an existing file for writing...). The ordering of events here
            # as an attempt to alleviate this, on the basis that it's a pretty
            # unlikely occurence (it'd require two builds with a brand new cache
            # directory)
            if os.path.isdir(path) and len(os.listdir(path)) != 0:
                self.config['prefix_len'] = 1
                # When building the project I was testing this on, the warning
                # was output over 20 times. That seems excessive
                global warned
                if self.path not in warned:
                    msg = "Please upgrade your cache by running " +\
                          " scons-configure-cache.py " +  self.path
                    SCons.Warnings.warn(SCons.Warnings.CacheVersionWarning, msg)
                    warned[self.path] = True
            else:
                if not os.path.isdir(path):
                    try:
                        os.makedirs(path)
                    except OSError:
                        # If someone else is trying to create the directory at
                        # the same time as me, bad things will happen
                        msg = "Failed to create cache directory " + path
                        raise SCons.Errors.EnvironmentError(msg)
                        
                self.config['prefix_len'] = 2
                if not os.path.exists(config_file):
                    try:
                        with open(config_file, 'w') as config:
                            json.dump(self.config, config)
                    except:
                        msg = "Failed to write cache configuration for " + path
                        raise SCons.Errors.EnvironmentError(msg)
        else:
            try:
                with open(config_file) as config:
                    self.config = json.load(config)
            except ValueError:
                msg = "Failed to read cache configuration for " + path
                raise SCons.Errors.EnvironmentError(msg)
            

    def CacheDebug(self, fmt, target, cachefile):
        if cache_debug != self.current_cache_debug:
            if cache_debug == '-':
                self.debugFP = sys.stdout
            elif cache_debug:
                self.debugFP = open(cache_debug, 'w')
            else:
                self.debugFP = None
            self.current_cache_debug = cache_debug
        if self.debugFP:
            self.debugFP.write(fmt % (target, os.path.split(cachefile)[1]))

    def is_enabled(self):
        return cache_enabled and not self.path is None

    def is_readonly(self):
        return cache_readonly

    def cachepath(self, node):
        """
        """
        if not self.is_enabled():
            return None, None

        sig = node.get_cachedir_bsig()
        subdir = sig[:self.config['prefix_len']].upper()
        dir = os.path.join(self.path, subdir)
        return dir, os.path.join(dir, sig)

    def retrieve(self, node):
        """
        This method is called from multiple threads in a parallel build,
        so only do thread safe stuff here. Do thread unsafe stuff in
        built().

        Note that there's a special trick here with the execute flag
        (one that's not normally done for other actions).  Basically
        if the user requested a no_exec (-n) build, then
        SCons.Action.execute_actions is set to 0 and when any action
        is called, it does its showing but then just returns zero
        instead of actually calling the action execution operation.
        The problem for caching is that if the file does NOT exist in
        cache then the CacheRetrieveString won't return anything to
        show for the task, but the Action.__call__ won't call
        CacheRetrieveFunc; instead it just returns zero, which makes
        the code below think that the file *was* successfully
        retrieved from the cache, therefore it doesn't do any
        subsequent building.  However, the CacheRetrieveString didn't
        print anything because it didn't actually exist in the cache,
        and no more build actions will be performed, so the user just
        sees nothing.  The fix is to tell Action.__call__ to always
        execute the CacheRetrieveFunc and then have the latter
        explicitly check SCons.Action.execute_actions itself.
        """
        if not self.is_enabled():
            return False

        env = node.get_build_env()
        if cache_show:
            if CacheRetrieveSilent(node, [], env, execute=1) == 0:
                node.build(presub=0, execute=0)
                return True
        else:
            if CacheRetrieve(node, [], env, execute=1) == 0:
                return True

        return False

    def push(self, node):
        if self.is_readonly() or not self.is_enabled():
            return
        return CachePush(node, [], node.get_build_env())

    def push_if_forced(self, node):
        if cache_force:
            return self.push(node)

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