"""Question pool validation."""

from __future__ import annotations

import json
from pathlib import Path
from typing import Any

from app.scoring import SCORE_FNS

OPTION_KEYS = {"A", "B", "C", "D"}


class PoolValidationError(ValueError):
    pass


def parse_pool_json(pool_json: str | dict[str, Any]) -> dict[str, Any]:
    if isinstance(pool_json, str):
        try:
            data = json.loads(pool_json)
        except json.JSONDecodeError as exc:
            raise PoolValidationError(f"Invalid JSON: {exc.msg}") from exc
    else:
        data = pool_json
    return validate_pool(data)


def load_pool_from_file(path: str | Path) -> dict[str, Any]:
    p = Path(path)
    if not p.exists():
        raise PoolValidationError(f"Pool file not found: {p}")
    try:
        raw = p.read_text(encoding="utf-8")
    except OSError as exc:
        raise PoolValidationError(f"Could not read pool file {p}: {exc}") from exc
    return parse_pool_json(raw)


def validate_pool(data: dict[str, Any]) -> dict[str, Any]:
    if not isinstance(data, dict):
        raise PoolValidationError("Pool must be a JSON object")
    title = data.get("title")
    if not isinstance(title, str) or not title.strip():
        raise PoolValidationError("Pool title is required")
    score_fn = data.get("score_fn", "linear_decay")
    if score_fn not in SCORE_FNS:
        raise PoolValidationError(f"Unknown score function: {score_fn}")
    time_limit_default = _positive_int(data.get("time_limit_default", 60), "time_limit_default")
    questions = data.get("questions")
    if not isinstance(questions, list) or not questions:
        raise PoolValidationError("Pool must include at least one question")

    normalized_questions: list[dict[str, Any]] = []
    for index, question in enumerate(questions):
        if not isinstance(question, dict):
            raise PoolValidationError(f"Question {index} must be an object")
        normalized_questions.append(_validate_question(question, index, time_limit_default))

    out: dict[str, Any] = {
        "title": title.strip(),
        "score_fn": score_fn,
        "time_limit_default": time_limit_default,
        "questions": normalized_questions,
    }
    session_id = data.get("session_id")
    if session_id is not None:
        if not isinstance(session_id, str) or not session_id.strip():
            raise PoolValidationError("session_id, if present, must be a non-empty string")
        out["session_id"] = session_id.strip()
    return out


def question_count(pool: dict[str, Any]) -> int:
    return len(pool["questions"])


def get_question(pool: dict[str, Any], question_idx: int) -> dict[str, Any]:
    try:
        return pool["questions"][question_idx]
    except IndexError as exc:
        raise PoolValidationError("Question index out of range") from exc


def question_time_limit(pool: dict[str, Any], question_idx: int) -> int:
    question = get_question(pool, question_idx)
    return int(question.get("time_limit") or pool["time_limit_default"])


def public_question_payload(pool: dict[str, Any], question_idx: int) -> dict[str, Any]:
    question = get_question(pool, question_idx)
    return {
        "question_idx": question_idx,
        "text": question["text"],
        "options": question["options"],
        "time_limit": question_time_limit(pool, question_idx),
    }


def _validate_question(question: dict[str, Any], index: int, default_limit: int) -> dict[str, Any]:
    qid = question.get("id")
    if not isinstance(qid, str) or not qid.strip():
        raise PoolValidationError(f"Question {index} id is required")
    text = question.get("text")
    if not isinstance(text, str) or not text.strip():
        raise PoolValidationError(f"Question {index} text is required")
    options = question.get("options")
    if not isinstance(options, dict) or set(options) != OPTION_KEYS:
        raise PoolValidationError(f"Question {index} options must be exactly A, B, C, D")
    for key, value in options.items():
        if not isinstance(value, str) or not value.strip():
            raise PoolValidationError(f"Question {index} option {key} is required")
    correct = question.get("correct")
    if correct not in OPTION_KEYS:
        raise PoolValidationError(f"Question {index} correct must be one of A, B, C, D")

    normalized = {
        "id": qid.strip(),
        "text": text.strip(),
        "options": {key: options[key].strip() for key in sorted(OPTION_KEYS)},
        "correct": correct,
    }
    if "time_limit" in question and question["time_limit"] is not None:
        normalized["time_limit"] = _positive_int(question["time_limit"], f"Question {index} time_limit")
    else:
        normalized["time_limit"] = default_limit
    explanation = question.get("explanation")
    if explanation is not None:
        if not isinstance(explanation, str):
            raise PoolValidationError(f"Question {index} explanation must be text")
        normalized["explanation"] = explanation.strip()
    return normalized


def _positive_int(value: Any, label: str) -> int:
    if isinstance(value, bool) or not isinstance(value, int) or value <= 0:
        raise PoolValidationError(f"{label} must be a positive integer")
    return value