#!/usr/bin/env python3
"""
utils.compositing
─────────────────────────────────────────────────────────────────────────────
Handles frame-level compositing (foreground frame + mask + background).
Public API
----------
replace_background_hq(frame_bgr, mask, background_bgr, fallback_enabled=True) → np.ndarray
"""
from __future__ import annotations
import logging
from typing import Tuple
import cv2
import numpy as np

log = logging.getLogger(__name__)

# Exception class that cv_processing.py expects
class BackgroundReplacementError(Exception):
    """Exception raised for background replacement errors"""
    pass

__all__ = ["replace_background_hq", "BackgroundReplacementError"]

# ────────────────────────────────────────────────────────────────────────────
# Main entry
# ────────────────────────────────────────────────────────────────────────────
def replace_background_hq(
    frame_bgr: np.ndarray,
    mask: np.ndarray,
    background_bgr: np.ndarray,
    fallback_enabled: bool = True,
) -> np.ndarray:
    """
    • Ensures background is resized to frame
    • Accepts mask in {0,1} or {0,255} or float32
    • Tries edge-feathered advanced blend, else simple overlay
    """
    if frame_bgr is None or mask is None or background_bgr is None:
        raise ValueError("Invalid input to replace_background_hq")
    
    h, w = frame_bgr.shape[:2]
    background = cv2.resize(background_bgr, (w, h), interpolation=cv2.INTER_LANCZOS4)
    m = _process_mask(mask)
    
    try:
        return _advanced_composite(frame_bgr, background, m)
    except Exception as e:
        log.warning(f"Advanced compositing failed: {e}")
        if not fallback_enabled:
            raise
        return _simple_composite(frame_bgr, background, m)

# ────────────────────────────────────────────────────────────────────────────
# Advanced compositor (feather + subtle colour-match)
# ────────────────────────────────────────────────────────────────────────────
def _advanced_composite(fg, bg, mask_u8):
    # 1) Smooth / feather
    mask = cv2.GaussianBlur(mask_u8.astype(np.float32), (5, 5), 1.0) / 255.0
    mask = np.power(mask, 0.8)  # shrink bleed
    mask3 = mask[..., None]
    
    # 2) Edge colour-match to reduce halo
    fg_adj = _colour_match_edges(fg, bg, mask)
    
    # 3) Blend
    comp = fg_adj.astype(np.float32) * mask3 + bg.astype(np.float32) * (1 - mask3)
    return np.clip(comp, 0, 255).astype(np.uint8)

def _colour_match_edges(fg, bg, alpha):
    edge = cv2.Sobel(alpha, cv2.CV_32F, 1, 1, ksize=3)
    edge = (np.abs(edge) > 0.05).astype(np.float32)
    
    if not np.any(edge):
        return fg
    
    adj = fg.astype(np.float32).copy()
    mix = 0.1
    adj[edge > 0] = adj[edge > 0] * (1 - mix) + bg[edge > 0] * mix
    return adj.astype(np.uint8)

# ────────────────────────────────────────────────────────────────────────────
# Simple fallback compositor
# ────────────────────────────────────────────────────────────────────────────
def _simple_composite(fg, bg, mask_u8):
    m = mask_u8.astype(np.float32) / 255.0
    m3 = m[..., None]
    return (fg.astype(np.float32) * m3 + bg.astype(np.float32) * (1 - m3)).astype(np.uint8)

# ────────────────────────────────────────────────────────────────────────────
# Utilities
# ────────────────────────────────────────────────────────────────────────────
def _process_mask(mask):
    """Ensure uint8 0/255 single-channel"""
    if mask.ndim == 3:
        mask = cv2.cvtColor(mask, cv2.COLOR_BGR2GRAY)
    
    if mask.dtype != np.uint8:
        mask = (mask * 255).astype(np.uint8) if mask.max() <= 1 else mask.astype(np.uint8)
    
    _, mask = cv2.threshold(mask, 127, 255, cv2.THRESH_BINARY)
    return mask