#
#  Copyright (C) 2017-2018 Codethink Limited
#
#  This program is free software; you can redistribute it and/or
#  modify it under the terms of the GNU Lesser General Public
#  License as published by the Free Software Foundation; either
#  version 2 of the License, or (at your option) any later version.
#
#  This library is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU
#  Lesser General Public License for more details.
#
#  You should have received a copy of the GNU Lesser General Public
#  License along with this library. If not, see <http://www.gnu.org/licenses/>.
#
#  Authors:
#        Tristan Maat <tristan.maat@codethink.co.uk>

import os
import string
from collections import Mapping, namedtuple

from ..element import _KeyStrength
from .._exceptions import ArtifactError, ImplError, LoadError, LoadErrorReason
from .._message import Message, MessageType
from .. import utils
from .. import _yaml


# An ArtifactCacheSpec holds the user configuration for a single remote
# artifact cache.
#
# Args:
#     url (str): Location of the remote artifact cache
#     push (bool): Whether we should attempt to push artifacts to this cache,
#                  in addition to pulling from it.
#
class ArtifactCacheSpec(namedtuple('ArtifactCacheSpec', 'url push')):

    # _new_from_config_node
    #
    # Creates an ArtifactCacheSpec() from a YAML loaded node
    #
    @staticmethod
    def _new_from_config_node(spec_node):
        _yaml.node_validate(spec_node, ['url', 'push'])
        url = _yaml.node_get(spec_node, str, 'url')
        push = _yaml.node_get(spec_node, bool, 'push', default_value=False)
        if not url:
            provenance = _yaml.node_get_provenance(spec_node)
            raise LoadError(LoadErrorReason.INVALID_DATA,
                            "{}: empty artifact cache URL".format(provenance))
        return ArtifactCacheSpec(url, push)


# An ArtifactCache manages artifacts.
#
# Args:
#     context (Context): The BuildStream context
#
class ArtifactCache():
    def __init__(self, context):
        self.context = context
        self.required_artifacts = set()
        self.extractdir = os.path.join(context.artifactdir, 'extract')
        self.max_size = context.cache_quota
        self.estimated_size = None

        self.global_remote_specs = []
        self.project_remote_specs = {}

        self._local = False

        os.makedirs(context.artifactdir, exist_ok=True)

    ################################################
    #  Methods implemented on the abstract class   #
    ################################################

    # get_artifact_fullname()
    #
    # Generate a full name for an artifact, including the
    # project namespace, element name and cache key.
    #
    # This can also be used as a relative path safely, and
    # will normalize parts of the element name such that only
    # digits, letters and some select characters are allowed.
    #
    # Args:
    #    element (Element): The Element object
    #    key (str): The element's cache key
    #
    # Returns:
    #    (str): The relative path for the artifact
    #
    def get_artifact_fullname(self, element, key):
        project = element._get_project()

        # Normalize ostree ref unsupported chars
        valid_chars = string.digits + string.ascii_letters + '-._'
        element_name = ''.join([
            x if x in valid_chars else '_'
            for x in element.normal_name
        ])

        assert key is not None

        # assume project and element names are not allowed to contain slashes
        return '{0}/{1}/{2}'.format(project.name, element_name, key)

    # setup_remotes():
    #
    # Sets up which remotes to use
    #
    # Args:
    #    use_config (bool): Whether to use project configuration
    #    remote_url (str): Remote artifact cache URL
    #
    # This requires that all of the projects which are to be processed in the session
    # have already been loaded and are observable in the Context.
    #
    def setup_remotes(self, *, use_config=False, remote_url=None):

        # Initialize remote artifact caches. We allow the commandline to override
        # the user config in some cases (for example `bst push --remote=...`).
        has_remote_caches = False
        if remote_url:
            self._set_remotes([ArtifactCacheSpec(remote_url, push=True)])
            has_remote_caches = True
        if use_config:
            for project in self.context.get_projects():
                artifact_caches = _configured_remote_artifact_cache_specs(self.context, project)
                if artifact_caches:  # artifact_caches is a list of ArtifactCacheSpec instances
                    self._set_remotes(artifact_caches, project=project)
                    has_remote_caches = True
        if has_remote_caches:
            self._initialize_remotes()

    # specs_from_config_node()
    #
    # Parses the configuration of remote artifact caches from a config block.
    #
    # Args:
    #   config_node (dict): The config block, which may contain the 'artifacts' key
    #
    # Returns:
    #   A list of ArtifactCacheSpec instances.
    #
    # Raises:
    #   LoadError, if the config block contains invalid keys.
    #
    @staticmethod
    def specs_from_config_node(config_node):
        cache_specs = []

        artifacts = config_node.get('artifacts', [])
        if isinstance(artifacts, Mapping):
            cache_specs.append(ArtifactCacheSpec._new_from_config_node(artifacts))
        elif isinstance(artifacts, list):
            for spec_node in artifacts:
                cache_specs.append(ArtifactCacheSpec._new_from_config_node(spec_node))
        else:
            provenance = _yaml.node_get_provenance(config_node, key='artifacts')
            raise _yaml.LoadError(_yaml.LoadErrorReason.INVALID_DATA,
                                  "%s: 'artifacts' must be a single 'url:' mapping, or a list of mappings" %
                                  (str(provenance)))
        return cache_specs

    # append_required_artifacts():
    #
    # Append to the list of elements whose artifacts are required for
    # the current run. Artifacts whose elements are in this list will
    # be locked by the artifact cache and not touched for the duration
    # of the current pipeline.
    #
    # Args:
    #     elements (iterable): A set of elements to mark as required
    #
    def append_required_artifacts(self, elements):
        # We lock both strong and weak keys - deleting one but not the
        # other won't save space in most cases anyway, but would be a
        # user inconvenience.

        for element in elements:
            strong_key = element._get_cache_key(strength=_KeyStrength.STRONG)
            weak_key = element._get_cache_key(strength=_KeyStrength.WEAK)

            for key in (strong_key, weak_key):
                if key and key not in self.required_artifacts:
                    self.required_artifacts.add(key)

                    # We also update the usage times of any artifacts
                    # we will be using, which helps preventing a
                    # buildstream process that runs in parallel with
                    # this one from removing artifacts in-use.
                    try:
                        self.update_atime(element, key)
                    except FileNotFoundError:
                        pass

    # clean():
    #
    # Clean the artifact cache as much as possible.
    #
    def clean(self):
        artifacts = self.list_artifacts()

        while self.calculate_cache_size() >= self.context.cache_quota - self.context.cache_lower_threshold:
            try:
                to_remove = artifacts.pop(0)
            except IndexError:
                # If too many artifacts are required, and we therefore
                # can't remove them, we have to abort the build.
                #
                # FIXME: Asking the user what to do may be neater
                default_conf = os.path.join(os.environ['XDG_CONFIG_HOME'],
                                            'buildstream.conf')
                detail = ("There is not enough space to build the given element.\n"
                          "Please increase the cache-quota in {}."
                          .format(self.context.config_origin or default_conf))

                if self.calculate_cache_size() > self.context.cache_quota:
                    raise ArtifactError("Cache too full. Aborting.",
                                        detail=detail,
                                        reason="cache-too-full")
                else:
                    break

            key = to_remove.rpartition('/')[2]
            if key not in self.required_artifacts:
                self.remove(to_remove)

        # This should be O(1) if implemented correctly
        return self.calculate_cache_size()

    # get_approximate_cache_size()
    #
    # A cheap method that aims to serve as an upper limit on the
    # artifact cache size.
    #
    # The cache size reported by this function will normally be larger
    # than the real cache size, since it is calculated using the
    # pre-commit artifact size, but for very small artifacts in
    # certain caches additional overhead could cause this to be
    # smaller than, but close to, the actual size.
    #
    # Nonetheless, in practice this should be safe to use as an upper
    # limit on the cache size.
    #
    # If the cache has built-in constant-time size reporting, please
    # feel free to override this method with a more accurate
    # implementation.
    #
    # Returns:
    #     (int) An approximation of the artifact cache size.
    #
    def get_approximate_cache_size(self):
        # If we don't currently have an estimate, figure out the real
        # cache size.
        if self.estimated_size is None:
            self.estimated_size = self.calculate_cache_size()

        return self.estimated_size

    ################################################
    # Abstract methods for subclasses to implement #
    ################################################

    # initialize_remotes():
    #
    # This will contact each remote cache.
    #
    # Args:
    #     on_failure (callable): Called if we fail to contact one of the caches.
    #
    def initialize_remotes(self, *, on_failure=None):
        pass

    # contains():
    #
    # Check whether the artifact for the specified Element is already available
    # in the local artifact cache.
    #
    # Args:
    #     element (Element): The Element to check
    #     key (str): The cache key to use
    #
    # Returns: True if the artifact is in the cache, False otherwise
    #
    def contains(self, element, key):
        raise ImplError("Cache '{kind}' does not implement contains()"
                        .format(kind=type(self).__name__))

    # list_artifacts():
    #
    # List artifacts in this cache in LRU order.
    #
    # Returns:
    #     ([str]) - A list of artifact names as generated by
    #               `ArtifactCache.get_artifact_fullname` in LRU order
    #
    def list_artifacts(self):
        raise ImplError("Cache '{kind}' does not implement list_artifacts()"
                        .format(kind=type(self).__name__))

    # remove():
    #
    # Removes the artifact for the specified ref from the local
    # artifact cache.
    #
    # Args:
    #     ref (artifact_name): The name of the artifact to remove (as
    #                          generated by
    #                          `ArtifactCache.get_artifact_fullname`)
    #
    def remove(self, artifact_name):
        raise ImplError("Cache '{kind}' does not implement remove()"
                        .format(kind=type(self).__name__))

    # update_atime():
    #
    # Update the access time of an element.
    #
    # Args:
    #     element (Element): The Element to mark
    #     key (str): The cache key to use
    #
    def update_atime(self, element, key):
        raise ImplError("Cache '{kind}' does not implement update_atime()"
                        .format(kind=type(self).__name__))

    # extract():
    #
    # Extract cached artifact for the specified Element if it hasn't
    # already been extracted.
    #
    # Assumes artifact has previously been fetched or committed.
    #
    # Args:
    #     element (Element): The Element to extract
    #     key (str): The cache key to use
    #
    # Raises:
    #     ArtifactError: In cases there was an OSError, or if the artifact
    #                    did not exist.
    #
    # Returns: path to extracted artifact
    #
    def extract(self, element, key):
        raise ImplError("Cache '{kind}' does not implement extract()"
                        .format(kind=type(self).__name__))

    # commit():
    #
    # Commit built artifact to cache.
    #
    # Args:
    #     element (Element): The Element commit an artifact for
    #     content (str): The element's content directory
    #     keys (list): The cache keys to use
    #
    def commit(self, element, content, keys):
        raise ImplError("Cache '{kind}' does not implement commit()"
                        .format(kind=type(self).__name__))

    # can_diff():
    #
    # Whether this cache implementation can diff (unfortunately
    # there's no way to tell if an implementation is going to throw
    # ImplError without abc).
    #
    def can_diff(self):
        return False

    # diff():
    #
    # Return a list of files that have been added or modified between
    # the artifacts described by key_a and key_b.
    #
    # Args:
    #     element (Element): The element whose artifacts to compare
    #     key_a (str): The first artifact key
    #     key_b (str): The second artifact key
    #     subdir (str): A subdirectory to limit the comparison to
    #
    def diff(self, element, key_a, key_b, *, subdir=None):
        raise ImplError("Cache '{kind}' does not implement diff()"
                        .format(kind=type(self).__name__))

    # has_fetch_remotes():
    #
    # Check whether any remote repositories are available for fetching.
    #
    # Args:
    #     element (Element): The Element to check
    #
    # Returns: True if any remote repositories are configured, False otherwise
    #
    def has_fetch_remotes(self, *, element=None):
        return False

    # has_push_remotes():
    #
    # Check whether any remote repositories are available for pushing.
    #
    # Args:
    #     element (Element): The Element to check
    #
    # Returns: True if any remote repository is configured, False otherwise
    #
    def has_push_remotes(self, *, element=None):
        return False

    # push():
    #
    # Push committed artifact to remote repository.
    #
    # Args:
    #     element (Element): The Element whose artifact is to be pushed
    #     keys (list): The cache keys to use
    #
    # Returns:
    #   (bool): True if any remote was updated, False if no pushes were required
    #
    # Raises:
    #   (ArtifactError): if there was an error
    #
    def push(self, element, keys):
        raise ImplError("Cache '{kind}' does not implement push()"
                        .format(kind=type(self).__name__))

    # pull():
    #
    # Pull artifact from one of the configured remote repositories.
    #
    # Args:
    #     element (Element): The Element whose artifact is to be fetched
    #     key (str): The cache key to use
    #     progress (callable): The progress callback, if any
    #
    # Returns:
    #   (bool): True if pull was successful, False if artifact was not available
    #
    def pull(self, element, key, *, progress=None):
        raise ImplError("Cache '{kind}' does not implement pull()"
                        .format(kind=type(self).__name__))

    # link_key():
    #
    # Add a key for an existing artifact.
    #
    # Args:
    #     element (Element): The Element whose artifact is to be linked
    #     oldkey (str): An existing cache key for the artifact
    #     newkey (str): A new cache key for the artifact
    #
    def link_key(self, element, oldkey, newkey):
        raise ImplError("Cache '{kind}' does not implement link_key()"
                        .format(kind=type(self).__name__))

    # calculate_cache_size()
    #
    # Return the real artifact cache size.
    #
    # Implementations should also use this to update estimated_size.
    #
    # Returns:
    #
    # (int) The size of the artifact cache.
    #
    def calculate_cache_size(self):
        raise ImplError("Cache '{kind}' does not implement calculate_cache_size()"
                        .format(kind=type(self).__name__))

    ################################################
    #               Local Private Methods          #
    ################################################

    # _message()
    #
    # Local message propagator
    #
    def _message(self, message_type, message, **kwargs):
        args = dict(kwargs)
        self.context.message(
            Message(None, message_type, message, **args))

    # _set_remotes():
    #
    # Set the list of remote caches. If project is None, the global list of
    # remote caches will be set, which is used by all projects. If a project is
    # specified, the per-project list of remote caches will be set.
    #
    # Args:
    #     remote_specs (list): List of ArtifactCacheSpec instances, in priority order.
    #     project (Project): The Project instance for project-specific remotes
    def _set_remotes(self, remote_specs, *, project=None):
        if project is None:
            # global remotes
            self.global_remote_specs = remote_specs
        else:
            self.project_remote_specs[project] = remote_specs

    # _initialize_remotes()
    #
    # An internal wrapper which calls the abstract method and
    # reports takes care of messaging
    #
    def _initialize_remotes(self):
        def remote_failed(url, error):
            self._message(MessageType.WARN, "Failed to fetch remote refs from {}: {}".format(url, error))

        with self.context.timed_activity("Initializing remote caches", silent_nested=True):
            self.initialize_remotes(on_failure=remote_failed)

    # _add_artifact_size()
    #
    # Since we cannot keep track of the cache size between threads,
    # this method will be called by the main process every time a
    # process that added something to the cache finishes.
    #
    # This will then add the reported size to
    # ArtifactCache.estimated_size.
    #
    def _add_artifact_size(self, artifact_size):
        if not self.estimated_size:
            self.estimated_size = self.calculate_cache_size()

        self.estimated_size += artifact_size

    # _set_cache_size()
    #
    # Similarly to the above method, when we calculate the actual size
    # in a child thread, we can't update it. We instead pass the value
    # back to the main thread and update it there.
    #
    def _set_cache_size(self, cache_size):
        self.estimated_size = cache_size


# _configured_remote_artifact_cache_specs():
#
# Return the list of configured artifact remotes for a given project, in priority
# order. This takes into account the user and project configuration.
#
# Args:
#     context (Context): The BuildStream context
#     project (Project): The BuildStream project
#
# Returns:
#   A list of ArtifactCacheSpec instances describing the remote artifact caches.
#
def _configured_remote_artifact_cache_specs(context, project):
    project_overrides = context.get_overrides(project.name)
    project_extra_specs = ArtifactCache.specs_from_config_node(project_overrides)

    return list(utils._deduplicate(
        project_extra_specs + project.artifact_cache_specs + context.artifact_cache_specs))