from __future__ import annotations

import os
import time
from pathlib import Path

from flask import Flask, jsonify, request, send_from_directory

from generate_question import (
    APP_TITLE,
    QUESTION_LIMIT,
    QuestionGenerator,
    format_questions,
    normalize_text,
    parse_question_count,
    resolve_model_dir,
)

IGNORED_MODEL_DIR_NAMES = {
    ".git",
    ".vscode",
    "__pycache__",
    "backend",
    "frontend",
    "venv",
}


def project_root() -> Path:
    return Path(__file__).resolve().parents[1]


def build_generator(
    model_dir: str | Path | None = None,
    prefer_nested_model: bool = True,
) -> QuestionGenerator:
    root = project_root()
    selected_model_dir = (
        Path(model_dir).expanduser()
        if model_dir is not None
        else Path(os.getenv("HVU_MODEL_DIR", str(root / "t5-viet-qg-finetuned"))).expanduser()
    )
    if not selected_model_dir.is_absolute():
        selected_model_dir = root / selected_model_dir

    return QuestionGenerator(
        model_dir=str(selected_model_dir),
        task_prefix=os.getenv("HVU_TASK_PREFIX", "sinh câu hỏi"),
        max_source_length=int(os.getenv("HVU_MAX_SOURCE_LENGTH", "512")),
        max_new_tokens=int(os.getenv("HVU_MAX_NEW_TOKENS", "64")),
        device=os.getenv("HVU_DEVICE", "auto"),
        cpu_threads=_read_optional_int(os.getenv("HVU_CPU_THREADS")),
        gpu_dtype=os.getenv("HVU_GPU_DTYPE", "auto"),
        prefer_nested_model=prefer_nested_model,
    )


def _read_optional_int(value: str | None) -> int | None:
    if value in (None, ""):
        return None
    return int(value)


def _humanize_model_segment(value: str) -> str:
    normalized = value.replace("_", "-")
    parts: list[str] = []
    for part in normalized.split("-"):
        lowered = part.lower()
        if not lowered:
            continue
        if lowered in {"t5", "qg", "qa", "hvu"}:
            parts.append(lowered.upper())
        elif lowered == "seq2seq":
            parts.append("Seq2Seq")
        elif lowered == "checkpoint":
            parts.append("Checkpoint")
        elif part.isdigit():
            parts.append(part)
        else:
            parts.append(part.capitalize())
    return "-".join(parts) or "Model"


def _display_model_name(meta: dict[str, object]) -> str:
    raw_name = Path(str(meta.get("model_root") or meta.get("model_dir") or "model")).name
    return _humanize_model_segment(raw_name)


def _model_label(relative_path: str | Path) -> str:
    path = Path(relative_path)
    return path.name or "model"


def _iter_model_candidates(root: Path):
    for child in sorted(root.iterdir(), key=lambda path: path.name.lower()):
        if not child.is_dir() or child.name.startswith(".") or child.name in IGNORED_MODEL_DIR_NAMES:
            continue

        if (child / "config.json").exists():
            yield {"path": child, "prefer_nested_model": False}

        for nested_name in ("best-model", "final-model"):
            nested = child / nested_name
            if nested.is_dir() and (nested / "config.json").exists():
                yield {"path": nested, "prefer_nested_model": False}


def _discover_available_models(
    root: Path,
    active_generator: QuestionGenerator | None = None,
) -> list[dict[str, str]]:
    models: list[dict[str, str]] = []
    seen_model_roots: set[str] = set()
    root = root.resolve()

    for candidate_info in _iter_model_candidates(root):
        candidate = candidate_info["path"]
        prefer_nested_model = bool(candidate_info["prefer_nested_model"])
        model_key = str(candidate.resolve())
        if model_key in seen_model_roots:
            continue

        try:
            relative_candidate = candidate.resolve().relative_to(root)
        except ValueError:
            continue

        seen_model_roots.add(model_key)
        models.append(
            {
                "id": relative_candidate.as_posix(),
                "label": _model_label(relative_candidate),
                "model_root": str(candidate.resolve()),
                "model_dir": str(resolve_model_dir(candidate, prefer_nested_model=False).resolve()),
                "prefer_nested_model": prefer_nested_model,
            }
        )

    if active_generator is not None:
        current_root = active_generator.model_root.resolve()
        current_dir = active_generator.model_dir.resolve()
        exists = any(
            Path(item["model_root"]).resolve() == current_root
            or Path(item["model_dir"]).resolve() == current_dir
            for item in models
        )
        if not exists:
            models.append(
                {
                    "id": current_root.as_posix(),
                    "label": _display_model_name(active_generator.metadata()),
                    "model_root": str(current_root),
                    "model_dir": str(current_dir),
                    "prefer_nested_model": False,
                }
            )

    return models


def _selected_model_id(
    app: Flask,
    models: list[dict[str, str]],
    active_generator: QuestionGenerator | None = None,
) -> str:
    explicit_selection = str(app.config.get("SELECTED_MODEL_ID") or "").strip()
    if explicit_selection and any(item["id"] == explicit_selection for item in models):
        return explicit_selection

    active_generator = active_generator or _generator(app)
    current_root = active_generator.model_root.resolve()
    current_dir = active_generator.model_dir.resolve()

    for item in models:
        if Path(item["model_dir"]).resolve() == current_dir:
            return item["id"]

    for item in models:
        if Path(item["model_root"]).resolve() == current_root:
            return item["id"]

    return models[0]["id"] if models else ""


def _switch_generator(app: Flask, model_id: str) -> QuestionGenerator:
    available_models = _discover_available_models(app.config["PROJECT_ROOT"], _generator(app))
    selected_model = next((item for item in available_models if item["id"] == model_id), None)
    if selected_model is None:
        raise ValueError("Model được chọn không hợp lệ hoặc chưa tồn tại trong thư mục dự án.")

    current_model_id = _selected_model_id(app, available_models)
    if current_model_id != model_id:
        app.config["GENERATOR"] = build_generator(
            selected_model["model_root"],
            prefer_nested_model=bool(selected_model.get("prefer_nested_model")),
        )

    app.config["SELECTED_MODEL_ID"] = model_id
    return _generator(app)


def _info_payload(app: Flask, active_generator: QuestionGenerator | None = None) -> dict[str, object]:
    active_generator = active_generator or _generator(app)
    meta = active_generator.metadata()
    available_models = _discover_available_models(app.config["PROJECT_ROOT"], active_generator)
    selected_model_id = _selected_model_id(app, available_models, active_generator)
    model_name = next(
        (item["label"] for item in available_models if item["id"] == selected_model_id),
        _display_model_name(meta),
    )

    return {
        "ok": True,
        "title": APP_TITLE,
        "model_name": model_name,
        "selected_model_id": selected_model_id,
        "available_models": [{"id": item["id"], "label": item["label"]} for item in available_models],
        "meta": meta,
    }


def create_app(generator: QuestionGenerator | None = None) -> Flask:
    root = project_root()
    frontend_root = root / "frontend"

    app = Flask(__name__, static_folder=None)
    app.json.ensure_ascii = False
    app.config["GENERATOR"] = generator or build_generator()
    app.config["PROJECT_ROOT"] = root
    app.config["FRONTEND_ROOT"] = frontend_root
    app.config["SELECTED_MODEL_ID"] = ""

    @app.get("/")
    def index():
        return send_from_directory(app.config["FRONTEND_ROOT"], "index.html")

    @app.get("/frontend/<path:filename>")
    def frontend_file(filename: str):
        return send_from_directory(app.config["FRONTEND_ROOT"], filename)

    @app.get("/assets/<path:filename>")
    def asset_file(filename: str):
        return send_from_directory(app.config["PROJECT_ROOT"], filename)

    @app.get("/api/info")
    def info():
        return jsonify(_info_payload(app))

    @app.post("/api/model")
    def set_model():
        payload = request.get_json(silent=True) or {}
        model_id = str(payload.get("model_id") or "").strip()
        if not model_id:
            return jsonify({"ok": False, "error": "Vui lòng chọn model trước khi chuyển."}), 400

        try:
            active_generator = _switch_generator(app, model_id)
        except ValueError as exc:
            return jsonify({"ok": False, "error": str(exc)}), 404

        return jsonify(_info_payload(app, active_generator))

    @app.post("/api/generate")
    def generate():
        payload = request.get_json(silent=True) or {}
        requested_model_id = str(payload.get("model_id") or "").strip()

        if requested_model_id:
            try:
                active_generator = _switch_generator(app, requested_model_id)
            except ValueError as exc:
                return jsonify({"ok": False, "error": str(exc)}), 400
        else:
            active_generator = _generator(app)

        text = normalize_text(payload.get("text"))
        if not text:
            return jsonify({"ok": False, "error": "Vui lòng nhập đoạn văn bản trước khi sinh câu hỏi."}), 400

        raw_count = payload.get("num_questions")
        if raw_count in (None, ""):
            count = 100
        else:
            try:
                count = int(raw_count)
            except (TypeError, ValueError):
                return jsonify({"ok": False, "error": "Số câu hỏi phải là số nguyên trong khoảng 1 đến 100."}), 400

            if count < 1 or count > QUESTION_LIMIT:
                return jsonify({"ok": False, "error": f"Số câu hỏi phải nằm trong khoảng 1 đến {QUESTION_LIMIT}."}), 400

        started = time.perf_counter()
        try:
            questions = active_generator.generate(text, parse_question_count(count))
        except Exception as exc:  # noqa: BLE001
            return jsonify({"ok": False, "error": str(exc)}), 500

        elapsed_ms = round((time.perf_counter() - started) * 1000, 2)
        info_payload = _info_payload(app, active_generator)
        return jsonify(
            {
                "ok": True,
                "text": text,
                "num_questions": count,
                "questions": questions,
                "formatted": format_questions(questions),
                "elapsed_ms": elapsed_ms,
                "model_name": info_payload["model_name"],
                "selected_model_id": info_payload["selected_model_id"],
                "meta": active_generator.metadata(),
            }
        )

    return app


def _generator(app: Flask) -> QuestionGenerator:
    generator: QuestionGenerator = app.config["GENERATOR"]
    return generator