# Copyright (c) Facebook, Inc. and its affiliates.

import importlib.util
import os
import sys
import tempfile
from contextlib import ExitStack, contextmanager
from copy import deepcopy
from unittest import mock
import torch
from torch import nn

# need some explicit imports due to https://github.com/pytorch/pytorch/issues/38964
import detectron2  # noqa F401
from detectron2.structures import Instances

_counter = 0


def _clear_jit_cache():
    from torch.jit._recursive import concrete_type_store
    from torch.jit._state import _jit_caching_layer

    concrete_type_store.type_store.clear()  # for modules
    _jit_caching_layer.clear()  # for free functions


def _add_instances_conversion_methods(newInstances):
    """
    Add to_instances/from_instances methods to the scripted Instances class.
    """
    cls_name = newInstances.__name__

    @torch.jit.unused
    def to_instances(self):
        """
        Convert scripted Instances to original Instances
        """
        ret = Instances(self.image_size)
        for name in self._field_names:
            val = getattr(self, "_" + name, None)
            if val is not None:
                ret.set(name, val)
        return ret

    @torch.jit.unused
    def from_instances(instances: Instances):
        """
        Create scripted Instances from original Instances
        """
        fields = instances.get_fields()
        image_size = instances.image_size
        ret = newInstances(image_size)
        for name, val in fields.items():
            assert hasattr(ret, f"_{name}"), f"No attribute named {name} in {cls_name}"
            setattr(ret, name, deepcopy(val))
        return ret

    newInstances.to_instances = to_instances
    newInstances.from_instances = from_instances


@contextmanager
def patch_instances(fields):
    """
    A contextmanager, under which the Instances class in detectron2 is replaced
    by a statically-typed scriptable class, defined by `fields`.
    See more in `export_torchscript_with_instances`.
    """

    with tempfile.TemporaryDirectory(prefix="detectron2") as dir, tempfile.NamedTemporaryFile(
        mode="w", encoding="utf-8", suffix=".py", dir=dir, delete=False
    ) as f:
        try:
            # Objects that use Instances should not reuse previously-compiled
            # results in cache, because `Instances` could be a new class each time.
            _clear_jit_cache()

            cls_name, s = _gen_instance_module(fields)
            f.write(s)
            f.flush()
            f.close()

            module = _import(f.name)
            new_instances = getattr(module, cls_name)
            _ = torch.jit.script(new_instances)
            # let torchscript think Instances was scripted already
            Instances.__torch_script_class__ = True
            # let torchscript find new_instances when looking for the jit type of Instances
            Instances._jit_override_qualname = torch._jit_internal._qualified_name(new_instances)

            _add_instances_conversion_methods(new_instances)
            yield new_instances
        finally:
            try:
                del Instances.__torch_script_class__
                del Instances._jit_override_qualname
            except AttributeError:
                pass
            sys.modules.pop(module.__name__)


def _gen_instance_class(fields):
    """
    Args:
        fields (dict[name: type])
    """

    class _FieldType:
        def __init__(self, name, type_):
            assert isinstance(name, str), f"Field name must be str, got {name}"
            self.name = name
            self.type_ = type_
            self.annotation = f"{type_.__module__}.{type_.__name__}"

    fields = [_FieldType(k, v) for k, v in fields.items()]

    def indent(level, s):
        return " " * 4 * level + s

    lines = []

    global _counter
    _counter += 1

    cls_name = "ScriptedInstances{}".format(_counter)

    field_names = tuple(x.name for x in fields)
    lines.append(
        f"""
class {cls_name}:
    def __init__(self, image_size: Tuple[int, int]):
        self.image_size = image_size
        self._field_names = {field_names}
"""
    )

    for f in fields:
        lines.append(
            indent(2, f"self._{f.name} = torch.jit.annotate(Optional[{f.annotation}], None)")
        )

    for f in fields:
        lines.append(
            f"""
    @property
    def {f.name}(self) -> {f.annotation}:
        # has to use a local for type refinement
        # https://pytorch.org/docs/stable/jit_language_reference.html#optional-type-refinement
        t = self._{f.name}
        assert t is not None
        return t

    @{f.name}.setter
    def {f.name}(self, value: {f.annotation}) -> None:
        self._{f.name} = value
"""
        )

    # support method `__len__`
    lines.append(
        """
    def __len__(self) -> int:
"""
    )
    for f in fields:
        lines.append(
            f"""
        t = self._{f.name}
        if t is not None:
            return len(t)
"""
        )
    lines.append(
        """
        raise NotImplementedError("Empty Instances does not support __len__!")
"""
    )

    # support method `has`
    lines.append(
        """
    def has(self, name: str) -> bool:
"""
    )
    for f in fields:
        lines.append(
            f"""
        if name == "{f.name}":
            return self._{f.name} is not None
"""
        )
    lines.append(
        """
        return False
"""
    )

    # support method `to`
    lines.append(
        f"""
    def to(self, device: torch.device) -> "{cls_name}":
        ret = {cls_name}(self.image_size)
"""
    )
    for f in fields:
        if hasattr(f.type_, "to"):
            lines.append(
                f"""
        t = self._{f.name}
        if t is not None:
            ret._{f.name} = t.to(device)
"""
            )
        else:
            # For now, ignore fields that cannot be moved to devices.
            # Maybe can support other tensor-like classes (e.g. __torch_function__)
            pass
    lines.append(
        """
        return ret
"""
    )

    # support method `getitem`
    lines.append(
        f"""
    def __getitem__(self, item) -> "{cls_name}":
        ret = {cls_name}(self.image_size)
"""
    )
    for f in fields:
        lines.append(
            f"""
        t = self._{f.name}
        if t is not None:
            ret._{f.name} = t[item]
"""
        )
    lines.append(
        """
        return ret
"""
    )
    return cls_name, os.linesep.join(lines)


def _gen_instance_module(fields):
    # TODO: find a more automatic way to enable import of other classes
    s = """
from copy import deepcopy
import torch
from torch import Tensor
import typing
from typing import *

import detectron2
from detectron2.structures import Boxes, Instances

"""

    cls_name, cls_def = _gen_instance_class(fields)
    s += cls_def
    return cls_name, s


def _import(path):
    # https://docs.python.org/3/library/importlib.html#importing-a-source-file-directly
    spec = importlib.util.spec_from_file_location(
        "{}{}".format(sys.modules[__name__].__name__, _counter), path
    )
    module = importlib.util.module_from_spec(spec)
    sys.modules[module.__name__] = module
    spec.loader.exec_module(module)
    return module


# TODO: this is a private utility. Should be made more useful through a model export api.
@contextmanager
def patch_builtin_len(modules=()):
    """
    Patch the builtin len() function of a few detectron2 modules
    to use __len__ instead, because __len__ does not convert values to
    integers and therefore is friendly to tracing.

    Args:
        modules (list[stsr]): names of extra modules to patch len(), in
            addition to those in detectron2.
    """

    def _new_len(obj):
        return obj.__len__()

    with ExitStack() as stack:
        MODULES = [
            "detectron2.modeling.roi_heads.fast_rcnn",
            "detectron2.modeling.roi_heads.mask_head",
        ] + list(modules)
        ctxs = [stack.enter_context(mock.patch(mod + ".len")) for mod in MODULES]
        for m in ctxs:
            m.side_effect = _new_len
        yield


def patch_nonscriptable_classes():
    """
    Apply patches on a few nonscriptable detectron2 classes.
    Should not have side-effects on eager usage.
    """
    # __prepare_scriptable__ can also be added to models for easier maintenance.
    # But it complicates the clean model code.

    from detectron2.modeling.backbone import ResNet, FPN

    # Due to https://github.com/pytorch/pytorch/issues/36061,
    # we change backbone to use ModuleList for scripting.
    # (note: this changes param names in state_dict)

    def prepare_resnet(self):
        ret = deepcopy(self)
        ret.stages = nn.ModuleList(ret.stages)
        for k in self.stage_names:
            delattr(ret, k)
        return ret

    ResNet.__prepare_scriptable__ = prepare_resnet

    def prepare_fpn(self):
        ret = deepcopy(self)
        ret.lateral_convs = nn.ModuleList(ret.lateral_convs)
        ret.output_convs = nn.ModuleList(ret.output_convs)
        for name, _ in self.named_children():
            if name.startswith("fpn_"):
                delattr(ret, name)
        return ret

    FPN.__prepare_scriptable__ = prepare_fpn
