import os
import torch
import torch.nn as nn
import numpy as np
import json
import logging

logger = logging.getLogger(__name__)

class BMTEngine:
    """
    Inference Engine for Bi-modal Transformer (BMT) Dense Video Captioning.
    Handles Proposal Generation and Captioning.
    """
    def __init__(self, model_dir, device="cpu"):
        self.model_dir = model_dir
        self.device = device
        self.tokenizer = None
        self.caption_model = None
        self.proposal_model = None
        
        self.paths = {
            "caption": os.path.join(model_dir, "best_cap_model.pt"),
            "proposal": os.path.join(model_dir, "best_prop_model.pt"),
            "i3d": os.path.join(model_dir, "rgb_imagenet.pt"),
            "vggish": os.path.join(model_dir, "vggish_model.ckpt"),
            "vocab": os.path.join(model_dir, "vocabulary.json")
        }

    def load_models(self):
        try:
            # Check for vocab first
            if os.path.exists(self.paths["vocab"]):
                with open(self.paths["vocab"], "r") as f:
                    self.vocab = json.load(f)
                logger.info("BMT Vocabulary loaded.")
            else:
                logger.warning(f"Vocabulary not found at {self.paths['vocab']}. Defaulting to dummy vocab for now.")
                self.vocab = {"word_to_idx": {}, "idx_to_word": {}}

            # Load Captioning Model
            if os.path.exists(self.paths["caption"]):
                # Note: BMT typically uses a custom architecture. We'll need the model class definition.
                # For now, we load the state dict and assume the architecture is handled.
                self.caption_model = torch.load(self.paths["caption"], map_location=self.device)
                logger.info("BMT Captioning module loaded.")
            else:
                logger.error(f"Captioning model not found at {self.paths['caption']}")

            # Load Proposal Model
            if os.path.exists(self.paths["proposal"]):
                self.proposal_model = torch.load(self.paths["proposal"], map_location=self.device)
                logger.info("BMT Proposal module loaded.")
            else:
                logger.error(f"Proposal model not found at {self.paths['proposal']}")

            return True
        except Exception as e:
            logger.error(f"Error loading BMT models: {e}")
            return False

    def generate_proposals(self, video_features, audio_features=None):
        """
        Runs the Proposal Generation module on extracted features.
        Returns a list of (start, end) timestamps.
        """
        # Placeholder implementation for proposal generation
        # Real BMT uses a Transformer encoder/decoder for this
        if self.proposal_model is None:
            return [(0.0, 5.0)] # Fallback to single segment if model missing
            
        # Mocking BMT proposal logic for now
        # In a real implementation, we'd pass features through self.proposal_model
        return [(0.0, 5.0), (5.0, 10.0)] 

    def generate_captions(self, video_features, audio_features=None, proposals=None):
        """
        Generates captions for given video/audio features and proposed segments.
        """
        if not proposals:
            proposals = [(0.0, 10.0)]
            
        results = []
        for start, end in proposals:
            # Logic to generate caption for the specific segment [start, end]
            # 1. Slice features for the segment
            # 2. Run through captioning model
            # 3. Decode tokens
            caption = f"Event detected between {start:.1f}s and {end:.1f}s" # Placeholder
            results.append({
                "start": start,
                "end": end,
                "caption": caption
            })
            
        return results

    def run_inference(self, video_path, mode="video"):
        """
        Complete pipeline: Features -> Proposals -> Captions
        """
        # 1. Feature Extraction (To be implemented in bmt_utils.py)
        # 2. Load features
        # 3. Predict
        logger.info(f"Running BMT inference on {video_path} in {mode} mode.")
        
        # Placeholder for real inference
        dummy_proposals = [(0.0, 2.5), (3.0, 7.5)]
        return self.generate_captions(None, None, dummy_proposals)