# This file is part of the MapProxy project.
# Copyright (C) 2010, 2011 Omniscale <http://omniscale.de>
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

from __future__ import print_function, division

import sys
from collections import deque
from contextlib import contextmanager
from itertools import zip_longest
from http.client import HTTPException

import queue

from mapproxy.config import base_config
from mapproxy.grid.meta_grid import MetaGrid
from mapproxy.source import SourceError
from mapproxy.config import local_base_config
from mapproxy.util.lock import LockTimeout
from mapproxy.seed.util import format_seed_task
from mapproxy.seed.cachelock import DummyCacheLocker, CacheLockedError

from mapproxy.seed.util import (exp_backoff, limit_sub_bbox,
                                status_symbol, BackoffError)

import logging
log = logging.getLogger(__name__)

NONE = 0
CONTAINS = -1
INTERSECTS = 1

# Decide whether to use multiprocessing or threading. multiprocessing should be faster but
# it is not well supported on all platforms. Especially regarding lambdas and anonymous
# function/classes which are used in proj.py for example.
#
# Since Python 3.8, MacOS uses a non-forking start method for multiprocessing which
# inhibits similar restrictions to Windows.
if sys.platform == 'win32' or sys.platform == 'darwin':
    import threading
    proc_class = threading.Thread
    queue_class = queue.Queue
else:
    import multiprocessing
    proc_class = multiprocessing.Process
    queue_class = multiprocessing.Queue


class TileWorkerPool(object):
    """
    Manages multiple TileWorker.
    """

    def __init__(self, task, worker_class, size=2, dry_run=False, progress_logger=None):
        self.tiles_queue = queue_class(size)
        self.task = task
        self.dry_run = dry_run
        self.procs = []
        self.progress_logger = progress_logger
        conf = base_config()
        for _ in range(size):
            worker = worker_class(self.task, self.tiles_queue, conf)
            worker.start()
            self.procs.append(worker)

    def process(self, tiles, progress):
        if not self.dry_run:
            while True:
                try:
                    self.tiles_queue.put(tiles, timeout=5)
                except queue.Full:
                    alive = False
                    for proc in self.procs:
                        if proc.is_alive():
                            alive = True
                            break
                    if not alive:
                        log.warning('no workers left, stopping')
                        raise SeedInterrupted
                    continue
                else:
                    break

            if self.progress_logger:
                self.progress_logger.log_step(progress)

    def stop(self, force=False):
        """
        Stop seed workers by sending None-sentinel and joining the workers.

        :param force: Skip sending None-sentinel and join with a timeout.
                      For use when workers might be shutdown already by KeyboardInterrupt.
        """
        if not force:
            alives = 0
            for proc in self.procs:
                if proc.is_alive():
                    alives += 1

            while alives:
                # put None-sentinels to queue as long as we have workers alive
                try:
                    self.tiles_queue.put(None, timeout=1)
                    alives -= 1
                except queue.Full:
                    alives = 0
                    for proc in self.procs:
                        if proc.is_alive():
                            alives += 1

        if force:
            timeout = 1.0
        else:
            timeout = None
        for proc in self.procs:
            proc.join(timeout)


class TileWorker(proc_class):
    def __init__(self, task, tiles_queue, conf):
        super().__init__()
        proc_class.daemon = True
        self.task = task
        self.tile_mgr = task.tile_manager
        self.tiles_queue = tiles_queue
        self.conf = conf

    def run(self):
        with local_base_config(self.conf):
            try:
                self.work_loop()
            except KeyboardInterrupt:
                return
            except BackoffError:
                return


class TileSeedWorker(TileWorker):
    def work_loop(self):
        while True:
            tiles = self.tiles_queue.get()
            if tiles is None:
                return
            with self.tile_mgr.session():
                exp_backoff(self.tile_mgr.load_tile_coords, args=(tiles,),
                            max_repeat=100, max_backoff=600,
                            exceptions=(SourceError, IOError, HTTPException), ignore_exceptions=(LockTimeout, ))


class TileCleanupWorker(TileWorker):
    def work_loop(self):
        while True:
            tiles = self.tiles_queue.get()
            if tiles is None:
                return
            with self.tile_mgr.session():
                self.tile_mgr.remove_tile_coords(tiles)


class SeedProgress(object):
    def __init__(self, old_progress_identifier=None):
        self.progress = 0.0
        self.level_progress_percentages = [1.0]
        self.level_progresses = None
        self.level_progresses_level = 0
        self.progress_str_parts = []
        self.old_level_progresses = old_progress_identifier

    def step_forward(self, subtiles=1):
        self.progress += self.level_progress_percentages[-1] / subtiles

    @property
    def progress_str(self):
        return ''.join(self.progress_str_parts)

    @contextmanager
    def step_down(self, i, subtiles):
        if self.level_progresses is None:
            self.level_progresses = []
        self.level_progresses = self.level_progresses[:self.level_progresses_level]
        self.level_progresses.append((i, subtiles))
        self.level_progresses_level += 1
        self.progress_str_parts.append(status_symbol(i, subtiles))
        self.level_progress_percentages.append(self.level_progress_percentages[-1] / subtiles)

        yield

        self.level_progress_percentages.pop()
        self.progress_str_parts.pop()

        self.level_progresses_level -= 1
        if self.level_progresses_level == 0:
            self.level_progresses = []

    def already_processed(self):
        return self.can_skip(self.old_level_progresses, self.level_progresses)

    def current_progress_identifier(self):
        if self.already_processed() or self.level_progresses is None:
            return self.old_level_progresses
        return self.level_progresses[:]

    @staticmethod
    def can_skip(old_progress, current_progress):
        """
        Return True if the `current_progress` is behind the `old_progress` -
        when it isn't as far as the old progress.

        >>> SeedProgress.can_skip(None, [(0, 4)])
        False
        >>> SeedProgress.can_skip([], [(0, 4)])
        True
        >>> SeedProgress.can_skip([(0, 4)], None)
        False
        >>> SeedProgress.can_skip([(0, 4)], [(0, 4)])
        False
        >>> SeedProgress.can_skip([(1, 4)], [(0, 4)])
        True
        >>> SeedProgress.can_skip([(0, 4)], [(0, 4), (0, 4)])
        False

        >>> SeedProgress.can_skip([(0, 4), (0, 4), (2, 4)], [(0, 4), (0, 4)])
        False
        >>> SeedProgress.can_skip([(0, 4), (0, 4), (2, 4)], [(0, 4), (0, 4), (1, 4)])
        True
        >>> SeedProgress.can_skip([(0, 4), (0, 4), (2, 4)], [(0, 4), (0, 4), (2, 4)])
        False
        >>> SeedProgress.can_skip([(0, 4), (0, 4), (2, 4)], [(0, 4), (0, 4), (3, 4)])
        False
        >>> SeedProgress.can_skip([(0, 4), (0, 4), (2, 4)], [(0, 4), (1, 4)])
        False
        >>> SeedProgress.can_skip([(0, 4), (0, 4), (2, 4)], [(0, 4), (1, 4), (0, 4)])
        False
        """
        if current_progress is None:
            return False
        if old_progress is None:
            return False
        if old_progress == []:
            return True
        for old, current in zip_longest(old_progress, current_progress, fillvalue=None):
            if old is None:
                return False
            if current is None:
                return False
            if old < current:
                return False
            if old > current:
                return True
        return False

    def running(self):
        return True


class StopProcess(Exception):
    pass


class SeedInterrupted(Exception):
    pass


class TileWalker(object):
    """
    TileWalker traverses through all tiles in a tile grid and calls worker_pool.process
    for each (meta) tile. It traverses the tile grid (pyramid) depth-first.
    Intersection with coverages are checked before handling subtiles in the next level,
    allowing to determine if all subtiles should be seeded or skipped.
    """

    def __init__(self, task, worker_pool, handle_stale=False, handle_uncached=False, handle_all=False,
                 work_on_metatiles=True, skip_geoms_for_last_levels=0, progress_logger=None,
                 seed_progress=None):
        self.tile_mgr = task.tile_manager
        self.task = task
        self.worker_pool = worker_pool
        self.handle_all = handle_all
        self.handle_stale = handle_stale
        self.handle_uncached = handle_uncached
        self.work_on_metatiles = work_on_metatiles
        self.skip_geoms_for_last_levels = skip_geoms_for_last_levels
        self.progress_logger = progress_logger

        num_seed_levels = len(task.levels)
        if num_seed_levels >= 4:
            self.report_till_level = task.levels[num_seed_levels-2]
        else:
            self.report_till_level = task.levels[num_seed_levels-1]
        meta_size = self.tile_mgr.meta_grid.meta_size if self.tile_mgr.meta_grid else (1, 1)
        self.tiles_per_metatile = meta_size[0] * meta_size[1]
        self.grid = MetaGrid(self.tile_mgr.grid, meta_size=meta_size, meta_buffer=0)
        self.count = 0
        self.seed_progress = seed_progress or SeedProgress()

        # It is possible that we 'walk' through the same tile multiple times
        # when seeding irregular tile grids[0]. limit_sub_bbox prevents that we
        # recurse into the same area multiple times, but it is still possible
        # that a tile is processed multiple times. Locking prevents that a tile
        # is seeded multiple times, but it is possible that we count the same tile
        # multiple times (in dry-mode, or while the tile is in the process queue).

        # Tile counts can be off by 280% with sqrt2 grids.
        # We keep a small cache of already processed tiles to skip most duplicates.
        # A simple cache of 64 tile coordinates for each level already brings the
        # difference down to ~8%, which is good enough and faster than a more
        # sophisticated FIFO cache with O(1) lookup, or even caching all tiles.

        # [0] irregular tile grids: where one tile does not have exactly 4 subtiles
        # Typically when you use res_factor, or a custom res list.
        self.seeded_tiles = {x: deque(maxlen=64) for x in task.levels}

    def walk(self):
        assert self.handle_stale or self.handle_uncached
        bbox = self.task.coverage.extent.bbox_for(self.tile_mgr.grid.srs)
        if self.seed_progress.already_processed():
            # nothing to seed
            self.seed_progress.step_forward()
        else:
            try:
                self._walk(bbox, self.task.levels)
            except StopProcess:
                pass
        self.report_progress(self.task.levels[0], self.task.coverage.bbox)

    def _walk(self, cur_bbox, levels, current_level=0, all_subtiles=False):
        """
        :param cur_bbox: the bbox to seed in this call
        :param levels: list of levels to seed
        :param all_subtiles: seed all subtiles and do not check for
                             intersections with bbox/geom
        """
        bbox_, tiles, subtiles = self.grid.get_affected_level_tiles(cur_bbox, current_level)
        total_subtiles = tiles[0] * tiles[1]
        if len(levels) < self.skip_geoms_for_last_levels:
            # do not filter in last levels
            all_subtiles = True
        subtiles = self._filter_subtiles(subtiles, all_subtiles)

        if current_level in levels and current_level <= self.report_till_level:
            self.report_progress(current_level, cur_bbox)

        if not self.seed_progress.running():
            if current_level in levels:
                self.report_progress(current_level, cur_bbox)
            self.tile_mgr.cleanup()
            raise StopProcess()

        process = False
        if current_level in levels:
            levels = levels[1:]
            process = True

        for i, (subtile, sub_bbox, intersection) in enumerate(subtiles):
            if subtile is None:  # no intersection
                self.seed_progress.step_forward(total_subtiles)
                continue
            if levels:  # recurse to next level
                sub_bbox = limit_sub_bbox(cur_bbox, sub_bbox)
                if intersection == CONTAINS:
                    all_subtiles = True
                else:
                    all_subtiles = False

                with self.seed_progress.step_down(i, total_subtiles):
                    if self.seed_progress.already_processed():
                        self.seed_progress.step_forward()
                    else:
                        self._walk(sub_bbox, levels, current_level=current_level+1,
                                   all_subtiles=all_subtiles)

            if not process:
                continue

            # check if subtile was already processed. see comment in __init__
            if subtile in self.seeded_tiles[current_level]:
                if not levels:
                    self.seed_progress.step_forward(total_subtiles)
                continue
            self.seeded_tiles[current_level].appendleft(subtile)

            if not self.work_on_metatiles:
                # collect actual tiles
                handle_tiles = self.grid.tile_list(subtile)
            else:
                handle_tiles = [subtile]

            if self.handle_all:
                handle_tiles = [t for t in handle_tiles if
                                t is not None]
            elif self.handle_uncached:
                handle_tiles = [t for t in handle_tiles if
                                t is not None and
                                not self.tile_mgr.is_cached(t)]
            elif self.handle_stale:
                handle_tiles = [t for t in handle_tiles if
                                t is not None and
                                self.tile_mgr.is_stale(t)]
            if handle_tiles:
                self.count += 1
                self.worker_pool.process(handle_tiles, self.seed_progress)

            if not levels:
                self.seed_progress.step_forward(total_subtiles)

        if len(levels) >= 4:
            # call cleanup to close open caches
            # for connection based caches
            self.tile_mgr.cleanup()

    def report_progress(self, level, bbox):
        if self.progress_logger:
            self.progress_logger.log_progress(self.seed_progress, level, bbox,
                                              self.count * self.tiles_per_metatile)

    def _filter_subtiles(self, subtiles, all_subtiles):
        """
        Return an iterator with all sub tiles.
        Yields (None, None, None) for non-intersecting tiles,
        otherwise (subtile, subtile_bbox, intersection).
        """
        for subtile in subtiles:
            if subtile is None:
                yield None, None, None
            else:
                sub_bbox = self.grid.meta_tile(subtile).bbox
                if all_subtiles:
                    intersection = CONTAINS
                else:
                    intersection = self.task.intersects(sub_bbox)
                if intersection:
                    yield subtile, sub_bbox, intersection
                else:
                    yield None, None, None


class SeedTask(object):
    def __init__(self, md, tile_manager, levels, refresh_timestamp, refresh_all, coverage):
        self.md = md
        self.tile_manager = tile_manager
        self.grid = tile_manager.grid
        self.levels = levels
        self.refresh_timestamp = refresh_timestamp
        self.refresh_all = refresh_all
        self.coverage = coverage

    @property
    def id(self):
        return self.md['name'], self.md['cache_name'], self.md['grid_name'], tuple(self.levels)

    def intersects(self, bbox):
        if self.coverage.contains(bbox, self.grid.srs):
            return CONTAINS
        if self.coverage.intersects(bbox, self.grid.srs):
            return INTERSECTS
        return NONE


class CleanupTask(object):
    """
    :param coverage: area for the cleanup
    :param complete_extent: ``True`` if `coverage` equals the extent of the grid
    """

    def __init__(self, md, tile_manager, levels, remove_timestamp, remove_all, coverage, complete_extent=False):
        self.md = md
        self.tile_manager = tile_manager
        self.grid = tile_manager.grid
        self.levels = levels
        self.remove_timestamp = remove_timestamp
        self.remove_all = remove_all
        self.coverage = coverage
        self.complete_extent = complete_extent

    @property
    def id(self):
        return 'cleanup', self.md['name'], self.md['cache_name'], self.md['grid_name']

    def intersects(self, bbox):
        if self.coverage.contains(bbox, self.grid.srs):
            return CONTAINS
        if self.coverage.intersects(bbox, self.grid.srs):
            return INTERSECTS
        return NONE


def seed(tasks, concurrency=2, dry_run=False, skip_geoms_for_last_levels=0,
         progress_logger=None, cache_locker=None, skip_uncached=False):
    if cache_locker is None:
        cache_locker = DummyCacheLocker()

    active_tasks = tasks[::-1]
    while active_tasks:
        task = active_tasks[-1]
        print(format_seed_task(task))

        wait = len(active_tasks) == 1
        try:
            with cache_locker.lock(task.md['cache_name'], no_block=not wait):
                if progress_logger and progress_logger.progress_store:
                    progress_logger.current_task_id = task.id
                    start_progress = progress_logger.progress_store.get(task.id)
                else:
                    start_progress = None
                seed_progress = SeedProgress(old_progress_identifier=start_progress)
                seed_task(task, concurrency, dry_run, skip_geoms_for_last_levels, progress_logger,
                          seed_progress=seed_progress, skip_uncached=skip_uncached)
        except CacheLockedError:
            print('    ...cache is locked, skipping')
            active_tasks = [task] + active_tasks[:-1]
        else:
            active_tasks.pop()


def seed_task(task, concurrency=2, dry_run=False, skip_geoms_for_last_levels=0,
              progress_logger=None, seed_progress=None, skip_uncached=False):
    if task.coverage is False:
        return
    if task.refresh_timestamp is not None:
        task.tile_manager._expire_timestamp = task.refresh_timestamp
    task.tile_manager.minimize_meta_requests = False

    work_on_metatiles = True
    if task.tile_manager.rescale_tiles:
        work_on_metatiles = False

    tile_worker_pool = TileWorkerPool(task, TileSeedWorker, dry_run=dry_run,
                                      size=concurrency, progress_logger=progress_logger)
    # If the configuration requests to only refresh tiles which are already in cache,
    # tile walker parameters shall be adapted
    handle_stale = skip_uncached
    handle_uncached = not skip_uncached
    handle_all = task.refresh_all
    tile_walker = TileWalker(task, tile_worker_pool, handle_uncached=handle_uncached, handle_stale=handle_stale,
                             handle_all=handle_all, skip_geoms_for_last_levels=skip_geoms_for_last_levels,
                             progress_logger=progress_logger, seed_progress=seed_progress,
                             work_on_metatiles=work_on_metatiles,
                             )
    try:
        tile_walker.walk()
    except KeyboardInterrupt:
        tile_worker_pool.stop(force=True)
        raise
    finally:
        tile_worker_pool.stop()
