import os
from pathlib import Path
from typing import List, Dict, Union

import cv2
import numpy as np
from deepface import DeepFace

# Avoid RetinaFace/tf-keras mismatch: use OpenCV face detector backend
DETECTOR = os.getenv("FACE_DETECTOR", "opencv")
MODEL_NAME = os.getenv("FACE_MODEL", "VGG-Face")  # or "Facenet512", "ArcFace", ...
DIST_THRESHOLD = float(os.getenv("FACE_DIST_THRESHOLD", "0.35"))  # lower => stricter

def _list_images(folder: Path) -> list[Path]:
    exts = {".jpg", ".jpeg", ".png", ".bmp"}
    return [p for p in folder.glob("*") if p.suffix.lower() in exts]

def _ensure_faces_dir(dir_path: str) -> Path:
    p = Path(dir_path)
    if not p.exists() or not any(p.iterdir()):
        # Return as-is; caller will print friendly message
        return p
    return p

def _embed(img_bgr: np.ndarray):
    # DeepFace.represent expects RGB
    rgb = cv2.cvtColor(img_bgr, cv2.COLOR_BGR2RGB)
    reps = DeepFace.represent(
        rgb, model_name=MODEL_NAME, detector_backend=DETECTOR, enforce_detection=False
    )
    # represent returns list of dicts. If none detected, empty list.
    if not reps:
        return None
    # take first face (for counting/verification, that’s fine)
    return np.array(reps[0]["embedding"], dtype=np.float32)

def _cosine(a, b):
    a = a / (np.linalg.norm(a) + 1e-9)
    b = b / (np.linalg.norm(b) + 1e-9)
    return float(np.dot(a, b))

def recognize_faces(frame_bgr: np.ndarray, faces_dir: str, topk: int = 3) -> Union[str, List[Dict]]:
    """
    Returns:
      - str message if faces dir missing/empty or no faces detected.
      - List[{"name": str, "score": float}] otherwise (score = 1 - cosine distance).
    """
    gallery_root = _ensure_faces_dir(faces_dir)
    if not gallery_root.exists():
        return f"Warning: faces folder '{faces_dir}' not found."
    gallery_imgs = _list_images(gallery_root)
    if not gallery_imgs:
        return f"Warning: faces folder '{faces_dir}' is empty."

    # embed incoming frame (first face)
    probe = _embed(frame_bgr)
    if probe is None:
        return "No face in frame"

    # compare to gallery
    scores = []
    for p in gallery_imgs:
        img = cv2.imread(str(p))
        if img is None:
            continue
        emb = _embed(img)
        if emb is None:
            continue
        cos = _cosine(probe, emb)
        # convert to distance-like: higher is better (similarity)
        scores.append({"name": p.stem, "score": cos})

    scores.sort(key=lambda x: x["score"], reverse=True)
    # Filter with threshold if provided (using cosine similarity ~ 1.0 is perfect)
    filtered = [s for s in scores if (1.0 - s["score"]) <= DIST_THRESHOLD]
    return filtered[:topk]