"""학습 진행 상태 (progress) API — review-complete + review-queue (Phase 1).

review-complete: 사용자가 오답/모르겠음 문제를 검토했음을 표시. due_at 최초 부여.
review-queue: 5 탭 (due_today / pending_review / chronic / regressed / mastered) 으로 progress 조회.
"""

from __future__ import annotations

from datetime import datetime, timedelta, timezone
from typing import Annotated

from fastapi import APIRouter, Depends, HTTPException, Query
from pydantic import BaseModel
from sqlalchemy import and_, func, or_, select
from sqlalchemy.ext.asyncio import AsyncSession

from core.auth import get_current_user
from core.database import get_session
from models.study_question import StudyQuestion
from models.study_question_progress import StudyQuestionProgress
from models.study_topic import StudyTopic
from models.user import User

router = APIRouter(prefix="/study-topics", tags=["study-progress"])

# 1차 due_at 부여 시 디폴트 1일 뒤
DEFAULT_FIRST_DUE_DAYS = 1


def _verify_topic_owner(topic: StudyTopic | None, user: User) -> None:
    if topic is None or topic.deleted_at is not None or topic.user_id != user.id:
        raise HTTPException(status_code=404, detail="주제를 찾을 수 없습니다")


@router.post("/{topic_id}/questions/{question_id}/review-complete", status_code=204)
async def review_complete(
    topic_id: int,
    question_id: int,
    user: Annotated[User, Depends(get_current_user)],
    session: Annotated[AsyncSession, Depends(get_session)],
):
    """확인완료 처리 — last_reviewed_at + (wrong/unsure 인 경우) due_at 최초 부여.

    이미 due_at 박힌 문제면 due_at 그대로 유지 (큐 위치 보존).
    정답 맞춘 문제면 due_at 박지 않음 (큐 폭발 방지).
    """
    topic = await session.get(StudyTopic, topic_id)
    _verify_topic_owner(topic, user)

    q = await session.get(StudyQuestion, question_id)
    if q is None or q.deleted_at is not None or q.user_id != user.id or q.study_topic_id != topic_id:
        raise HTTPException(status_code=404, detail="문제를 찾을 수 없습니다")

    progress = (
        await session.execute(
            select(StudyQuestionProgress).where(
                StudyQuestionProgress.user_id == user.id,
                StudyQuestionProgress.study_topic_id == topic_id,
                StudyQuestionProgress.study_question_id == question_id,
            )
        )
    ).scalar_one_or_none()
    if progress is None:
        # attempt 없는데 review-complete 시도. 진척 상태가 없어 의미 없음.
        raise HTTPException(status_code=409, detail="아직 시도한 적이 없는 문제입니다")

    now = datetime.now(timezone.utc)
    progress.last_reviewed_at = now

    # due_at 최초 부여는 wrong/unsure 일 때만. 이미 박혀있으면 유지.
    if progress.last_outcome in ("wrong", "unsure") and progress.due_at is None:
        progress.review_stage = 0
        progress.due_at = now + timedelta(days=DEFAULT_FIRST_DUE_DAYS)

    await session.commit()


# ─── review-queue ───


class ReviewQueueItem(BaseModel):
    question_id: int
    question_text: str
    subject: str | None
    scope: str | None
    exam_round: str | None
    exam_question_number: int | None
    last_outcome: str | None
    last_attempted_at: datetime | None
    last_reviewed_at: datetime | None
    due_at: datetime | None
    review_stage: int | None
    pattern_state: str | None


class ReviewQueueResponse(BaseModel):
    tab: str
    total: int
    items: list[ReviewQueueItem]
    page: int
    page_size: int


def _truncate(text: str, n: int = 80) -> str:
    if not text:
        return ""
    s = text.strip()
    return s if len(s) <= n else s[:n].rstrip() + "…"


@router.get("/{topic_id}/review-queue", response_model=ReviewQueueResponse)
async def review_queue(
    topic_id: int,
    user: Annotated[User, Depends(get_current_user)],
    session: Annotated[AsyncSession, Depends(get_session)],
    tab: str = Query(..., pattern="^(due_today|pending_review|chronic|regressed|mastered)$"),
    page: int = Query(1, ge=1),
    page_size: int = Query(50, ge=1, le=200),
):
    """5 탭 진행 상태 조회.

    - due_today:       progress.due_at <= now() AND review_stage < 4
    - pending_review:  last_outcome IN (wrong, unsure)
                       AND (last_reviewed_at IS NULL OR last_reviewed_at < last_attempted_at)
    - chronic:         pattern_state = 'chronic_wrong'
    - regressed:       pattern_state = 'regressed'
    - mastered:        review_stage >= 4
    """
    topic = await session.get(StudyTopic, topic_id)
    _verify_topic_owner(topic, user)

    base = (
        select(StudyQuestionProgress, StudyQuestion)
        .join(StudyQuestion, StudyQuestion.id == StudyQuestionProgress.study_question_id)
        .where(
            StudyQuestionProgress.user_id == user.id,
            StudyQuestionProgress.study_topic_id == topic_id,
            StudyQuestion.deleted_at.is_(None),
        )
    )

    now = datetime.now(timezone.utc)
    if tab == "due_today":
        base = base.where(
            StudyQuestionProgress.due_at.is_not(None),
            StudyQuestionProgress.due_at <= now,
            or_(
                StudyQuestionProgress.review_stage.is_(None),
                StudyQuestionProgress.review_stage < 4,
            ),
        ).order_by(StudyQuestionProgress.due_at.asc())
    elif tab == "pending_review":
        base = base.where(
            StudyQuestionProgress.last_outcome.in_(("wrong", "unsure")),
            or_(
                StudyQuestionProgress.last_reviewed_at.is_(None),
                and_(
                    StudyQuestionProgress.last_reviewed_at.is_not(None),
                    StudyQuestionProgress.last_attempted_at.is_not(None),
                    StudyQuestionProgress.last_reviewed_at
                    < StudyQuestionProgress.last_attempted_at,
                ),
            ),
        ).order_by(StudyQuestionProgress.last_attempted_at.desc().nulls_last())
    elif tab == "chronic":
        base = base.where(
            StudyQuestionProgress.pattern_state == "chronic_wrong",
        ).order_by(StudyQuestionProgress.last_attempted_at.desc().nulls_last())
    elif tab == "regressed":
        base = base.where(
            StudyQuestionProgress.pattern_state == "regressed",
        ).order_by(StudyQuestionProgress.last_attempted_at.desc().nulls_last())
    elif tab == "mastered":
        base = base.where(
            StudyQuestionProgress.review_stage.is_not(None),
            StudyQuestionProgress.review_stage >= 4,
        ).order_by(StudyQuestionProgress.last_attempted_at.desc().nulls_last())

    # total
    total_row = await session.execute(
        select(func.count()).select_from(base.subquery())
    )
    total = int(total_row.scalar() or 0)

    # paged
    rows = (
        await session.execute(
            base.offset((page - 1) * page_size).limit(page_size)
        )
    ).all()

    items = [
        ReviewQueueItem(
            question_id=q.id,
            question_text=_truncate(q.question_text, 80),
            subject=q.subject,
            scope=q.scope,
            exam_round=q.exam_round,
            exam_question_number=q.exam_question_number,
            last_outcome=p.last_outcome,
            last_attempted_at=p.last_attempted_at,
            last_reviewed_at=p.last_reviewed_at,
            due_at=p.due_at,
            review_stage=p.review_stage,
            pattern_state=p.pattern_state,
        )
        for (p, q) in rows
    ]

    return ReviewQueueResponse(
        tab=tab, total=total, items=items, page=page, page_size=page_size,
    )