# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, You can obtain one at http://mozilla.org/MPL/2.0/.

from __future__ import absolute_import, print_function, unicode_literals
import logging
import re

from .graph import Graph
from .taskgraph import TaskGraph
from slugid import nice as slugid

logger = logging.getLogger(__name__)
TASK_REFERENCE_PATTERN = re.compile('<([^>]+)>')


def optimize_task_graph(target_task_graph, params, do_not_optimize, existing_tasks=None):
    """
    Perform task optimization, without optimizing tasks named in
    do_not_optimize.
    """
    named_links_dict = target_task_graph.graph.named_links_dict()
    label_to_taskid = {}

    # This proceeds in two phases.  First, mark all optimized tasks (those
    # which will be removed from the graph) as such, including a replacement
    # taskId where applicable.  Second, generate a new task graph containing
    # only the non-optimized tasks, with all task labels resolved to taskIds
    # and with task['dependencies'] populated.
    annotate_task_graph(target_task_graph=target_task_graph,
                        params=params,
                        do_not_optimize=do_not_optimize,
                        named_links_dict=named_links_dict,
                        label_to_taskid=label_to_taskid,
                        existing_tasks=existing_tasks)
    return get_subgraph(target_task_graph, named_links_dict, label_to_taskid), label_to_taskid


def resolve_task_references(label, task_def, taskid_for_edge_name):
    def repl(match):
        key = match.group(1)
        try:
            return taskid_for_edge_name[key]
        except KeyError:
            # handle escaping '<'
            if key == '<':
                return key
            raise KeyError("task '{}' has no dependency named '{}'".format(label, key))

    def recurse(val):
        if isinstance(val, list):
            return [recurse(v) for v in val]
        elif isinstance(val, dict):
            if val.keys() == ['task-reference']:
                return TASK_REFERENCE_PATTERN.sub(repl, val['task-reference'])
            else:
                return {k: recurse(v) for k, v in val.iteritems()}
        else:
            return val
    return recurse(task_def)


def annotate_task_graph(target_task_graph, params, do_not_optimize,
                        named_links_dict, label_to_taskid, existing_tasks):
    """
    Annotate each task in the graph with .optimized (boolean) and .task_id
    (possibly None), following the rules for optimization and calling the task
    kinds' `optimize_task` method.

    As a side effect, label_to_taskid is updated with labels for all optimized
    tasks that are replaced with existing tasks.
    """

    # set .optimized for all tasks, and .task_id for optimized tasks
    # with replacements
    for label in target_task_graph.graph.visit_postorder():
        task = target_task_graph.tasks[label]
        named_task_dependencies = named_links_dict.get(label, {})

        # check whether any dependencies have been optimized away
        dependencies = [target_task_graph.tasks[l] for l in named_task_dependencies.itervalues()]
        for t in dependencies:
            if t.optimized and not t.task_id:
                raise Exception(
                    "task {} was optimized away, but {} depends on it".format(
                        t.label, label))

        # if this task is blacklisted, don't even consider optimizing
        replacement_task_id = None
        if label in do_not_optimize:
            optimized = False
        # Let's check whether this task has been created before
        elif existing_tasks is not None and label in existing_tasks:
            optimized = True
            replacement_task_id = existing_tasks[label]
        # otherwise, examine the task itself (which may be an expensive operation)
        else:
            optimized, replacement_task_id = task.optimize(params)

        task.optimized = optimized
        task.task_id = replacement_task_id
        if replacement_task_id:
            label_to_taskid[label] = replacement_task_id

        if optimized:
            if replacement_task_id:
                logger.debug("optimizing `{}`, replacing with task `{}`"
                             .format(label, replacement_task_id))
            else:
                logger.debug("optimizing `{}` away".format(label))
                # note: any dependent tasks will fail when they see this
        else:
            if replacement_task_id:
                raise Exception("{}: optimize_task returned False with a taskId".format(label))


def get_subgraph(annotated_task_graph, named_links_dict, label_to_taskid):
    """
    Return the subgraph of annotated_task_graph consisting only of
    non-optimized tasks and edges between them.

    To avoid losing track of taskIds for tasks optimized away, this method
    simultaneously substitutes real taskIds for task labels in the graph, and
    populates each task definition's `dependencies` key with the appropriate
    taskIds.  Task references are resolved in the process.
    """

    # resolve labels to taskIds and populate task['dependencies']
    tasks_by_taskid = {}
    for label in annotated_task_graph.graph.visit_postorder():
        task = annotated_task_graph.tasks[label]
        if task.optimized:
            continue
        task.task_id = label_to_taskid[label] = slugid()
        named_task_dependencies = {
                name: label_to_taskid[label]
                for name, label in named_links_dict.get(label, {}).iteritems()}
        task.task = resolve_task_references(task.label, task.task, named_task_dependencies)
        task.task.setdefault('dependencies', []).extend(named_task_dependencies.itervalues())
        tasks_by_taskid[task.task_id] = task

    # resolve edges to taskIds
    edges_by_taskid = (
        (label_to_taskid.get(left), label_to_taskid.get(right), name)
        for (left, right, name) in annotated_task_graph.graph.edges
        )
    # ..and drop edges that are no longer in the task graph
    edges_by_taskid = set(
        (left, right, name)
        for (left, right, name) in edges_by_taskid
        if left in tasks_by_taskid and right in tasks_by_taskid
        )

    return TaskGraph(
        tasks_by_taskid,
        Graph(set(tasks_by_taskid), edges_by_taskid))