#!/usr/bin/env python3
# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved


import copy
import itertools
import logging
from typing import List

import torch
import torch.nn as nn
from d2go.modeling.modeldef.fbnet_modeldef_registry import FBNetV2ModelArch
from detectron2.layers import ShapeSpec
from detectron2.modeling import (
    BACKBONE_REGISTRY,
    RPN_HEAD_REGISTRY,
    Backbone,
    build_anchor_generator,
)
from detectron2.modeling.backbone.fpn import FPN, LastLevelMaxPool, LastLevelP6P7
from detectron2.modeling.roi_heads import box_head, keypoint_head, mask_head
from detectron2.utils.logger import log_first_n
from mobile_cv.arch.fbnet_v2 import fbnet_builder as mbuilder
from mobile_cv.arch.utils.helper import format_dict_expanding_list_values

from .modules import (
    KeypointRCNNPredictor,
    KeypointRCNNPredictorNoUpscale,
    KeypointRCNNIRFPredictorNoUpscale,
    KeypointRCNNConvUpsamplePredictorNoUpscale,
    MaskRCNNConv1x1Predictor,
    RPNHeadConvRegressor,
)


logger = logging.getLogger(__name__)

FBNET_BUILDER_IDENTIFIER = "fbnetv2"


def _get_builder_norm_args(cfg):
    norm_name = cfg.MODEL.FBNET_V2.NORM
    norm_args = {"name": norm_name}
    assert all(isinstance(x, dict) for x in cfg.MODEL.FBNET_V2.NORM_ARGS)
    for dic in cfg.MODEL.FBNET_V2.NORM_ARGS:
        norm_args.update(dic)
    return norm_args


def _merge_fbnetv2_arch_def(cfg):
    arch_def = {}
    assert all(
        isinstance(x, dict) for x in cfg.MODEL.FBNET_V2.ARCH_DEF
    ), cfg.MODEL.FBNET_V2.ARCH_DEF
    for dic in cfg.MODEL.FBNET_V2.ARCH_DEF:
        arch_def.update(dic)
    return arch_def


def _parse_arch_def(cfg):
    arch = cfg.MODEL.FBNET_V2.ARCH
    arch_def = cfg.MODEL.FBNET_V2.ARCH_DEF
    assert (arch != "" and not arch_def) ^ (
        not arch and arch_def != []
    ), "Only allow one unset node between MODEL.FBNET_V2.ARCH ({}) and MODEL.FBNET_V2.ARCH_DEF ({})".format(
        arch, arch_def
    )
    arch_def = FBNetV2ModelArch.get(arch) if arch else _merge_fbnetv2_arch_def(cfg)
    # NOTE: arch_def is a dictionary describing the CNN architecture for creating
    # the detection model. It can describe a wide range of models including the
    # original FBNet. Each key-value pair expresses either a sub part of the model
    # like trunk or head, or stores other meta information.
    message = 'Using un-unified arch_def for ARCH "{}" (without scaling):\n{}'.format(
        arch, format_dict_expanding_list_values(arch_def)
    )
    log_first_n(logging.INFO, message, n=1, key="message")
    return arch_def


def _get_fbnet_builder_and_arch_def(cfg):
    arch_def = _parse_arch_def(cfg)

    # NOTE: one can store extra information in arch_def to configurate FBNetBuilder,
    # after this point, builder and arch_def will become independent.
    basic_args = arch_def.pop("basic_args", {})

    builder = mbuilder.FBNetBuilder(
        width_ratio=cfg.MODEL.FBNET_V2.SCALE_FACTOR,
        width_divisor=cfg.MODEL.FBNET_V2.WIDTH_DIVISOR,
        bn_args=_get_builder_norm_args(cfg),
    )
    builder.add_basic_args(**basic_args)

    return builder, arch_def


def _get_stride_per_stage(blocks):
    """
    Count the accummulated stride per stage given a list of blocks. The mbuilder
    provides API for counting per-block accumulated stride, this function leverages
    it to count per-stage accumulated stride.

    Input: a list of blocks from the unified arch_def. Note that the stage_idx
        must be contiguous (not necessarily starting from 0), and can be
        non-ascending (not tested).
    Output: a list of accumulated stride per stage, starting from lowest stage_idx.
    """
    stride_per_block = mbuilder.count_stride_each_block(blocks)

    assert len(stride_per_block) == len(blocks)
    stage_idx_set = {s["stage_idx"] for s in blocks}
    # assume stage idx are contiguous, eg. 1, 2, 3, ...
    assert max(stage_idx_set) - min(stage_idx_set) + 1 == len(stage_idx_set)
    start_stage_id = min(stage_idx_set)
    ids_per_stage = [
        [i for i, s in enumerate(blocks) if s["stage_idx"] == stage_idx]
        for stage_idx in range(start_stage_id, start_stage_id + len(stage_idx_set))
    ]  # eg. [[0], [1, 2], [3, 4, 5, 6], ...]
    block_stride_per_stage = [
        [stride_per_block[i] for i in ids] for ids in ids_per_stage
    ]  # eg. [[1], [2, 1], [2, 1, 1, 1], ...]
    stride_per_stage = [
        list(itertools.accumulate(s, lambda x, y: x * y))[-1]
        for s in block_stride_per_stage
    ]  # eg. [1, 2, 2, ...]
    accum_stride_per_stage = list(
        itertools.accumulate(stride_per_stage, lambda x, y: x * y)
    )  # eg. [first*1, first*2, first*4, ...]

    assert accum_stride_per_stage[-1] == mbuilder.count_strides(blocks)
    return accum_stride_per_stage


def fbnet_identifier_checker(func):
    """Can be used to decorate _load_from_state_dict"""

    def wrapper(self, state_dict, prefix, *args, **kwargs):
        possible_keys = [k for k in state_dict.keys() if k.startswith(prefix)]
        if not all(FBNET_BUILDER_IDENTIFIER in k for k in possible_keys):
            logger.warning(
                "Couldn't match FBNetV2 pattern given prefix {}, possible keys: \n{}".format(
                    prefix, "\n".join(possible_keys)
                )
            )
            if any("xif" in k for k in possible_keys):
                raise RuntimeError(
                    "Seems a FBNetV1 trained checkpoint is loaded by FBNetV2 model,"
                    " which is not supported. Please consider re-train your model"
                    " using the same setup as before (it will be FBNetV2). If you"
                    " need to run the old FBNetV1 models, those configs can be"
                    " still found, see D19477651 as example."
                )
        return func(self, state_dict, prefix, *args, **kwargs)

    return wrapper


# pyre-fixme[11]: Annotation `Sequential` is not defined as a type.
class FBNetModule(nn.Sequential):
    @fbnet_identifier_checker
    def _load_from_state_dict(self, *args, **kwargs):
        return super()._load_from_state_dict(*args, **kwargs)


def build_fbnet(cfg, name, in_channels):
    """
    Create a FBNet module using FBNet V2 builder.
    Args:
        cfg (CfgNode): the config that contains MODEL.FBNET_V2.
        name (str): the key in arch_def that represents a subpart of network
        in_channels (int): input channel size
    Returns:
        nn.Sequential: the first return is a nn.Sequential, each element
            corresponds a stage in arch_def.
        List[ShapeSpec]: the second return is a list of ShapeSpec containing the
            output channels and accumulated strides for that stage.
    """
    builder, raw_arch_def = _get_fbnet_builder_and_arch_def(cfg)
    # Reset the last_depth for this builder (might have been cached), this is
    # the only mutable member variable.
    builder.last_depth = in_channels

    # NOTE: Each sub part of the model consists of several stages and each stage
    # has several blocks. "Raw" arch_def (Dict[str, List[List[Tuple]]]) uses a
    # list of stages to describe the architecture, which is more compact and
    # thus written as builtin metadata (inside FBNetV2ModelArch) or config
    # (MODEL.FBNET_V2.ARCH_DEF). "Unified" arch_def (Dict[str, List[Dict]])
    # uses a list blocks from all stages instead, which is recognized by builder.
    arch_def = mbuilder.unify_arch_def(raw_arch_def, [name])
    arch_def = {name: arch_def[name]}
    logger.info(
        "Build FBNet using unified arch_def:\n{}".format(
            format_dict_expanding_list_values(arch_def)
        )
    )
    arch_def_blocks = arch_def[name]

    stages = []
    trunk_stride_per_stage = _get_stride_per_stage(arch_def_blocks)
    shape_spec_per_stage = []
    for i, stride_i in enumerate(trunk_stride_per_stage):
        stages.append(
            builder.build_blocks(
                arch_def_blocks,
                stage_indices=[i],
                prefix_name=FBNET_BUILDER_IDENTIFIER + "_",
            )
        )
        shape_spec_per_stage.append(
            ShapeSpec(
                channels=builder.last_depth,
                stride=stride_i,
            )
        )
    return FBNetModule(*stages), shape_spec_per_stage


class FBNetV2Backbone(Backbone):
    """
    Backbone (bottom-up) for FBNet.

    Hierarchy:
        trunk0:
            xif0_0
            xif0_1
            ...
        trunk1:
            xif1_0
            xif1_1
            ...
        ...

    Output features:
        The outputs from each "stage", i.e. trunkX.
    """

    def __init__(self, cfg):
        super(FBNetV2Backbone, self).__init__()
        stages, shape_specs = build_fbnet(
            cfg, name="trunk", in_channels=cfg.MODEL.FBNET_V2.STEM_IN_CHANNELS
        )

        self._trunk_stage_names = []
        self._trunk_stages = []

        self._out_feature_channels = {}
        self._out_feature_strides = {}
        for i, (stage, shape_spec) in enumerate(zip(stages, shape_specs)):
            name = "trunk{}".format(i)
            self.add_module(name, stage)
            self._trunk_stage_names.append(name)
            self._trunk_stages.append(stage)
            self._out_feature_channels[name] = shape_spec.channels
            self._out_feature_strides[name] = shape_spec.stride

        # returned features are the final output of each stage
        self._out_features = self._trunk_stage_names
        self._trunk_stage_names = tuple(self._trunk_stage_names)

    def __prepare_scriptable__(self):
        ret = copy.deepcopy(self)
        ret._trunk_stages = nn.ModuleList(ret._trunk_stages)
        for k in self._trunk_stage_names:
            delattr(ret, k)
        return ret

    @fbnet_identifier_checker
    def _load_from_state_dict(self, *args, **kwargs):
        return super()._load_from_state_dict(*args, **kwargs)

    # return features for each stage
    def forward(self, x):
        features = {}
        for name, stage in zip(self._trunk_stage_names, self._trunk_stages):
            x = stage(x)
            features[name] = x
        return features


class FBNetV2FPN(FPN):
    """
    FPN module for FBNet.
    """

    pass


def build_fbnet_backbone(cfg):
    return FBNetV2Backbone(cfg)


@BACKBONE_REGISTRY.register()
class FBNetV2C4Backbone(Backbone):
    def __init__(self, cfg, _):
        super(FBNetV2C4Backbone, self).__init__()
        self.body = build_fbnet_backbone(cfg)
        self._out_features = self.body._out_features
        self._out_feature_strides = self.body._out_feature_strides
        self._out_feature_channels = self.body._out_feature_channels

    def forward(self, x):
        return self.body(x)


@BACKBONE_REGISTRY.register()
def FBNetV2FpnBackbone(cfg, _):
    backbone = FBNetV2FPN(
        bottom_up=build_fbnet_backbone(cfg),
        in_features=cfg.MODEL.FPN.IN_FEATURES,
        out_channels=cfg.MODEL.FPN.OUT_CHANNELS,
        norm=cfg.MODEL.FPN.NORM,
        top_block=LastLevelMaxPool(),
    )

    return backbone


@BACKBONE_REGISTRY.register()
def FBNetV2RetinaNetBackbone(cfg, _):
    bottom_up = build_fbnet_backbone(cfg)
    in_channels_p6p7 = bottom_up.output_shape()[cfg.MODEL.FPN.IN_FEATURES[-1]].channels
    top_block = LastLevelP6P7(in_channels_p6p7, cfg.MODEL.FPN.OUT_CHANNELS)
    top_block.in_feature = cfg.MODEL.FPN.IN_FEATURES[-1]
    backbone = FBNetV2FPN(
        bottom_up=bottom_up,
        in_features=cfg.MODEL.FPN.IN_FEATURES,
        out_channels=cfg.MODEL.FPN.OUT_CHANNELS,
        norm=cfg.MODEL.FPN.NORM,
        top_block=top_block,
    )

    return backbone


@RPN_HEAD_REGISTRY.register()
class FBNetV2RpnHead(nn.Module):
    def __init__(self, cfg, input_shape: List[ShapeSpec]):
        super(FBNetV2RpnHead, self).__init__()

        in_channels = [x.channels for x in input_shape]
        assert len(set(in_channels)) == 1
        in_channels = in_channels[0]
        anchor_generator = build_anchor_generator(cfg, input_shape)
        num_cell_anchors = anchor_generator.num_cell_anchors
        box_dim = anchor_generator.box_dim
        assert len(set(num_cell_anchors)) == 1
        num_cell_anchors = num_cell_anchors[0]

        self.rpn_feature, shape_specs = build_fbnet(
            cfg, name="rpn", in_channels=in_channels
        )
        self.rpn_regressor = RPNHeadConvRegressor(
            in_channels=shape_specs[-1].channels,
            num_anchors=num_cell_anchors,
            box_dim=box_dim,
        )

    def forward(self, x: List[torch.Tensor]):
        x = [self.rpn_feature(y) for y in x]
        return self.rpn_regressor(x)


@box_head.ROI_BOX_HEAD_REGISTRY.register()
class FBNetV2RoIBoxHead(nn.Module):
    def __init__(self, cfg, input_shape: ShapeSpec):
        super(FBNetV2RoIBoxHead, self).__init__()

        self.roi_box_conv, shape_specs = build_fbnet(
            cfg, name="bbox", in_channels=input_shape.channels
        )
        self._out_channels = shape_specs[-1].channels

        self.avgpool = nn.AdaptiveAvgPool2d(1)

    def forward(self, x):
        x = self.roi_box_conv(x)
        if len(x.shape) == 4 and (x.shape[2] > 1 or x.shape[3] > 1):
            x = self.avgpool(x)
        return x

    @property
    @torch.jit.unused
    def output_shape(self):
        return ShapeSpec(channels=self._out_channels)


@keypoint_head.ROI_KEYPOINT_HEAD_REGISTRY.register()
class FBNetV2RoIKeypointHead(keypoint_head.BaseKeypointRCNNHead):
    def __init__(self, cfg, input_shape: ShapeSpec):
        super(FBNetV2RoIKeypointHead, self).__init__(
            cfg=cfg,
            input_shape=input_shape,
        )

        self.feature_extractor, shape_specs = build_fbnet(
            cfg, name="kpts", in_channels=input_shape.channels
        )

        self.predictor = KeypointRCNNPredictor(
            in_channels=shape_specs[-1].channels,
            num_keypoints=cfg.MODEL.ROI_KEYPOINT_HEAD.NUM_KEYPOINTS,
        )

    def layers(self, x):
        x = self.feature_extractor(x)
        x = self.predictor(x)
        return x


@keypoint_head.ROI_KEYPOINT_HEAD_REGISTRY.register()
class FBNetV2RoIKeypointHeadKRCNNPredictorNoUpscale(keypoint_head.BaseKeypointRCNNHead):
    def __init__(self, cfg, input_shape: ShapeSpec):
        super(FBNetV2RoIKeypointHeadKRCNNPredictorNoUpscale, self).__init__(
            cfg=cfg,
            input_shape=input_shape,
        )

        self.feature_extractor, shape_specs = build_fbnet(
            cfg,
            name="kpts",
            in_channels=input_shape.channels,
        )

        self.predictor = KeypointRCNNPredictorNoUpscale(
            in_channels=shape_specs[-1].channels,
            num_keypoints=cfg.MODEL.ROI_KEYPOINT_HEAD.NUM_KEYPOINTS,
        )

    def layers(self, x):
        x = self.feature_extractor(x)
        x = self.predictor(x)
        return x


@keypoint_head.ROI_KEYPOINT_HEAD_REGISTRY.register()
class FBNetV2RoIKeypointHeadKPRCNNIRFPredictorNoUpscale(
    keypoint_head.BaseKeypointRCNNHead,
):
    def __init__(self, cfg, input_shape: ShapeSpec):
        super(FBNetV2RoIKeypointHeadKPRCNNIRFPredictorNoUpscale, self).__init__(
            cfg=cfg,
            input_shape=input_shape,
        )

        self.feature_extractor, shape_specs = build_fbnet(
            cfg,
            name="kpts",
            in_channels=input_shape.channels,
        )

        self.predictor = KeypointRCNNIRFPredictorNoUpscale(
            cfg,
            in_channels=shape_specs[-1].channels,
            num_keypoints=cfg.MODEL.ROI_KEYPOINT_HEAD.NUM_KEYPOINTS,
        )

    def layers(self, x):
        x = self.feature_extractor(x)
        x = self.predictor(x)
        return x


@keypoint_head.ROI_KEYPOINT_HEAD_REGISTRY.register()
class FBNetV2RoIKeypointHeadKPRCNNConvUpsamplePredictorNoUpscale(
    keypoint_head.BaseKeypointRCNNHead,
):
    def __init__(self, cfg, input_shape: ShapeSpec):
        super(
            FBNetV2RoIKeypointHeadKPRCNNConvUpsamplePredictorNoUpscale, self
        ).__init__(
            cfg=cfg,
            input_shape=input_shape,
        )

        self.feature_extractor, shape_specs = build_fbnet(
            cfg,
            name="kpts",
            in_channels=input_shape.channels,
        )

        self.predictor = KeypointRCNNConvUpsamplePredictorNoUpscale(
            cfg,
            in_channels=shape_specs[-1].channels,
            num_keypoints=cfg.MODEL.ROI_KEYPOINT_HEAD.NUM_KEYPOINTS,
        )

    def layers(self, x):
        x = self.feature_extractor(x)
        x = self.predictor(x)
        return x


@mask_head.ROI_MASK_HEAD_REGISTRY.register()
class FBNetV2RoIMaskHead(mask_head.BaseMaskRCNNHead):
    def __init__(self, cfg, input_shape: ShapeSpec):
        super(FBNetV2RoIMaskHead, self).__init__(
            cfg=cfg,
            input_shape=input_shape,
        )

        self.feature_extractor, shape_specs = build_fbnet(
            cfg,
            name="mask",
            in_channels=input_shape.channels,
        )

        num_classes = cfg.MODEL.ROI_HEADS.NUM_CLASSES
        self.predictor = MaskRCNNConv1x1Predictor(shape_specs[-1].channels, num_classes)

    def layers(self, x):
        x = self.feature_extractor(x)
        x = self.predictor(x)
        return x
