import json
import os
from typing import Any, Dict, Optional

import torch
from stream3r.models.stream3r import STream3R


class StreamSession:
    """
    A causal streaming inference session with KV cache management for STream3R.
    """
    def __init__(self, model: STream3R, mode: str, *, window_size: Optional[int] = None, config_path: Optional[str] = None):
        self.model = model
        self.mode = mode
        self.aggregator_kv_cache_depth = model.aggregator.depth
        self.camera_head_kv_cache_depth = model.camera_head.trunk_depth
        self.camera_head_iterations = 4
        self.window_size = self._resolve_window_size(window_size, config_path)

        if self.mode not in ["causal", "window"]:
            raise ValueError(f"Unsupported attention mode when using kv_cache: {self.mode}")

        self.clear()

    def _clear_predictions(self):
        self.predictions = dict()
    
    def _update_predictions(self, predictions):
        for k in ["pose_enc", "world_points", "world_points_conf", "depth", "depth_conf", "images"]:
            if k in predictions:
                self.predictions[k] = torch.cat(
                    [self.predictions.get(k, torch.empty(0, device=predictions[k].device)), predictions[k]],
                    dim=1
                )

    def _clear_cache(self):
        self.aggregator_kv_cache_list = [[None, None] for _ in range(self.aggregator_kv_cache_depth)]
        self.camera_head_kv_cache_list = [[[None, None] for _ in range(self.camera_head_kv_cache_depth)] for _ in range(self.camera_head_iterations)]
    
    def _update_cache(self, aggregator_kv_cache_list, camera_head_kv_cache_list):
        if self.mode == "causal":
            self.aggregator_kv_cache_list = aggregator_kv_cache_list
            self.camera_head_kv_cache_list = camera_head_kv_cache_list
        elif self.mode == "window":
            for k in range(2):
                for i in range(self.aggregator_kv_cache_depth):
                    h, w = self.predictions["depth"].shape[2], self.predictions["depth"].shape[3]
                    P = h * w // self.model.aggregator.patch_size // self.model.aggregator.patch_size + self.model.aggregator.patch_start_idx
                    anchor_token = aggregator_kv_cache_list[i][k][:, :, :P]
                    window_tokens = aggregator_kv_cache_list[i][k][:, :, max(P, aggregator_kv_cache_list[i][k].size(2)-self.window_size*P):]
                    self.aggregator_kv_cache_list[i][k] = torch.cat(
                        [
                            anchor_token,
                            window_tokens
                        ],
                        dim=2
                    )
                for i in range(self.camera_head_iterations):
                    for j in range(self.camera_head_kv_cache_depth):
                        anchor_token = camera_head_kv_cache_list[i][j][k][:, :, :1]
                        window_tokens = camera_head_kv_cache_list[i][j][k][:, :, max(1, camera_head_kv_cache_list[i][j][k].size(2)-self.window_size):]
                        self.camera_head_kv_cache_list[i][j][k] = torch.cat(
                            [
                                anchor_token,
                                window_tokens
                            ],
                            dim=2
                        )
        else:
            raise ValueError(f"Unsupported attention mode when using kv_cache: {self.mode}")

    def _get_cache(self):
        return self.aggregator_kv_cache_list, self.camera_head_kv_cache_list

    def get_all_predictions(self):
        return self.predictions
    
    def get_last_prediction(self):
        last_predictions = dict()
        for k in ["pose_enc", "world_points", "world_points_conf", "depth", "depth_conf", "images"]:
            if k in self.predictions:
                last_predictions[k] = self.predictions[k][:, -1:]
        return last_predictions

    def clear(self):
        self._clear_predictions()
        self._clear_cache()

    @staticmethod
    def _detach_to_cpu(cache_like):
        if isinstance(cache_like, torch.Tensor):
            return cache_like.detach().cpu()
        if isinstance(cache_like, list):
            return [StreamSession._detach_to_cpu(elem) for elem in cache_like]
        if isinstance(cache_like, tuple):
            return tuple(StreamSession._detach_to_cpu(elem) for elem in cache_like)
        return cache_like

    @staticmethod
    def _to_device(cache_like, device: torch.device):
        if isinstance(cache_like, torch.Tensor):
            return cache_like.to(device)
        if isinstance(cache_like, list):
            return [StreamSession._to_device(elem, device) for elem in cache_like]
        if isinstance(cache_like, tuple):
            return tuple(StreamSession._to_device(elem, device) for elem in cache_like)
        return cache_like

    def _default_device(self) -> torch.device:
        try:
            return next(self.model.parameters()).device
        except StopIteration:
            return torch.device("cpu")

    def _resolve_window_size(self, override: Optional[int], config_path: Optional[str]) -> int:
        if override is not None:
            return override

        config_path = config_path or os.path.abspath(
            os.path.join(os.path.dirname(__file__), "..", "configs", "stream_session.json")
        )

        default_window_size = 25

        if not os.path.exists(config_path):
            return default_window_size

        try:
            with open(config_path, "r", encoding="utf-8") as handle:
                data = json.load(handle)
        except (json.JSONDecodeError, OSError):
            return default_window_size

        window_size = data.get("window_size")

        if isinstance(window_size, int) and window_size > 0:
            return window_size

        return default_window_size

    def save_cache(self, file_path: str) -> None:
        aggregator_cache, camera_cache = self._get_cache()

        payload: Dict[str, Any] = {
            "metadata": {
                "mode": self.mode,
                "aggregator_depth": self.aggregator_kv_cache_depth,
                "camera_head_depth": self.camera_head_kv_cache_depth,
                "camera_head_iterations": self.camera_head_iterations,
                "window_size": self.window_size,
                "patch_size": getattr(self.model.aggregator, "patch_size", None),
                "patch_start_idx": getattr(self.model.aggregator, "patch_start_idx", None),
            },
            "aggregator_cache": self._detach_to_cpu(aggregator_cache),
            "camera_cache": self._detach_to_cpu(camera_cache),
            "predictions": {k: v.detach().cpu() for k, v in self.predictions.items()},
        }

        dir_name = os.path.dirname(file_path)
        if dir_name:
            os.makedirs(dir_name, exist_ok=True)

        torch.save(payload, file_path)

    def load_cache(self, file_path: str, *, device: Optional[torch.device] = None, strict: bool = True) -> None:
        if device is None:
            device = self._default_device()

        payload = torch.load(file_path, map_location="cpu")

        metadata: Dict[str, Any] = payload.get("metadata", {})

        expected_metadata = {
            "mode": self.mode,
            "aggregator_depth": self.aggregator_kv_cache_depth,
            "camera_head_depth": self.camera_head_kv_cache_depth,
            "camera_head_iterations": self.camera_head_iterations,
            "window_size": self.window_size,
        }

        for key, expected_value in expected_metadata.items():
            actual_value = metadata.get(key)
            if strict and actual_value != expected_value:
                raise ValueError(
                    f"Loaded cache metadata mismatch for '{key}': expected {expected_value}, got {actual_value}"
                )

        if strict:
            patch_size = getattr(self.model.aggregator, "patch_size", None)
            patch_start_idx = getattr(self.model.aggregator, "patch_start_idx", None)
            if metadata.get("patch_size") not in (None, patch_size):
                raise ValueError(
                    f"Loaded cache metadata mismatch for 'patch_size': expected {patch_size}, got {metadata.get('patch_size')}"
                )
            if metadata.get("patch_start_idx") not in (None, patch_start_idx):
                raise ValueError(
                    f"Loaded cache metadata mismatch for 'patch_start_idx': expected {patch_start_idx}, got {metadata.get('patch_start_idx')}"
                )

        self.aggregator_kv_cache_list = self._to_device(payload.get("aggregator_cache", []), device)
        self.camera_head_kv_cache_list = self._to_device(payload.get("camera_cache", []), device)
        self.predictions = {
            k: v.to(device) if isinstance(v, torch.Tensor) else v
            for k, v in payload.get("predictions", {}).items()
        }

    def forward_stream(self, images):
        aggregator_kv_cache_list, camera_head_kv_cache_list = self._get_cache()

        outputs = self.model(
            images=images, 
            mode=self.mode, 
            aggregator_kv_cache_list=aggregator_kv_cache_list, 
            camera_head_kv_cache_list=camera_head_kv_cache_list, 
        )

        self._update_predictions(outputs)
        self._update_cache(outputs["aggregator_kv_cache_list"], outputs["camera_head_kv_cache_list"])

        return self.get_all_predictions()