"""SR / Task CRUD + status transition endpoints."""
from datetime import datetime
from typing import List, Optional
from uuid import uuid4

from fastapi import APIRouter, Depends, HTTPException, Query
from sqlalchemy import select, func
from sqlalchemy.ext.asyncio import AsyncSession

from database import get_db
from models import (
    AuditLog, Institution, SRCreate, SROut, SRRequest, SRStatus,
    SRStatusUpdate, SRType, compute_log_hash
)

router = APIRouter(prefix="/api/tasks", tags=["tasks"])

# Valid state transitions
_TRANSITIONS: dict[str, list[str]] = {
    SRStatus.RECEIVED:             [SRStatus.PARSED, SRStatus.REJECTED],
    SRStatus.PARSED:               [SRStatus.PENDING_APPROVAL, SRStatus.REJECTED],
    SRStatus.PENDING_APPROVAL:     [SRStatus.APPROVED, SRStatus.REJECTED],
    SRStatus.APPROVED:             [SRStatus.IN_PROGRESS, SRStatus.REJECTED],
    SRStatus.IN_PROGRESS:          [SRStatus.PENDING_PM_VALIDATION, SRStatus.FAILED_ROLLBACK],
    SRStatus.PENDING_PM_VALIDATION:[SRStatus.COMPLETED, SRStatus.FAILED_ROLLBACK],
    SRStatus.COMPLETED:            [],
    SRStatus.FAILED_ROLLBACK:      [],
    SRStatus.REJECTED:             [],
}


def _new_sr_id() -> str:
    return f"SR-{datetime.now().strftime('%Y%m%d')}-{str(uuid4())[:6].upper()}"


async def _write_audit(db: AsyncSession, sr_id: str, actor: str,
                        action: str, detail: str) -> None:
    from sqlalchemy import select as sel
    result = await db.execute(
        sel(AuditLog).where(AuditLog.sr_id == sr_id)
                      .order_by(AuditLog.id.desc()).limit(1)
    )
    last = result.scalars().first()
    prev_hash = last.log_hash if last else None
    ts = datetime.now().isoformat()
    log_hash = compute_log_hash(prev_hash, actor, action, detail, ts)
    db.add(AuditLog(
        sr_id=sr_id, actor=actor, action=action, detail=detail,
        prev_hash=prev_hash, log_hash=log_hash
    ))


@router.get("", response_model=List[SROut])
async def list_tasks(
    status: Optional[str]  = Query(None),
    sr_type: Optional[str] = Query(None),
    priority: Optional[str]= Query(None),
    keyword: Optional[str] = Query(None),
    skip: int = 0,
    limit: int = 50,
    db: AsyncSession = Depends(get_db),
):
    q = select(SRRequest).order_by(SRRequest.created_at.desc())
    if status:
        q = q.where(SRRequest.status == status)
    if sr_type:
        q = q.where(SRRequest.sr_type == sr_type)
    if priority:
        q = q.where(SRRequest.priority == priority)
    if keyword:
        q = q.where(SRRequest.title.contains(keyword))
    q = q.offset(skip).limit(limit)
    result = await db.execute(q)
    return result.scalars().all()


@router.get("/stats")
async def get_stats(db: AsyncSession = Depends(get_db)):
    total = (await db.execute(select(func.count(SRRequest.id)))).scalar()
    by_status: dict[str, int] = {}
    for s in SRStatus:
        cnt = (await db.execute(
            select(func.count(SRRequest.id)).where(SRRequest.status == s)
        )).scalar()
        if cnt:
            by_status[s.value] = cnt
    by_type: dict[str, int] = {}
    for t in SRType:
        cnt = (await db.execute(
            select(func.count(SRRequest.id)).where(SRRequest.sr_type == t)
        )).scalar()
        if cnt:
            by_type[t.value] = cnt
    return {"total": total, "by_status": by_status, "by_type": by_type}


@router.get("/{sr_id}", response_model=SROut)
async def get_task(sr_id: str, db: AsyncSession = Depends(get_db)):
    result = await db.execute(select(SRRequest).where(SRRequest.sr_id == sr_id))
    sr = result.scalars().first()
    if not sr:
        raise HTTPException(404, detail="SR을 찾을 수 없습니다.")
    return sr


@router.post("", response_model=SROut, status_code=201)
async def create_task(payload: SRCreate, db: AsyncSession = Depends(get_db)):
    inst_id = None
    if payload.inst_code:
        r = await db.execute(
            select(Institution).where(Institution.inst_code == payload.inst_code)
        )
        inst = r.scalars().first()
        if inst:
            inst_id = inst.id

    sr = SRRequest(
        sr_id=_new_sr_id(),
        inst_id=inst_id,
        sr_type=payload.sr_type,
        title=payload.title,
        description=payload.description,
        status=SRStatus.RECEIVED,
        priority=payload.priority,
        requested_by=payload.requested_by,
        assigned_to=payload.assigned_to,
        target_server=payload.target_server,
    )
    db.add(sr)
    await db.flush()
    await _write_audit(db, sr.sr_id, payload.requested_by, "SR_CREATED", f"SR 생성: {payload.title}")
    await db.commit()
    await db.refresh(sr)
    return sr


@router.patch("/{sr_id}/status", response_model=SROut)
async def update_status(sr_id: str, payload: SRStatusUpdate,
                         db: AsyncSession = Depends(get_db)):
    result = await db.execute(select(SRRequest).where(SRRequest.sr_id == sr_id))
    sr = result.scalars().first()
    if not sr:
        raise HTTPException(404, detail="SR을 찾을 수 없습니다.")

    allowed = _TRANSITIONS.get(SRStatus(sr.status), [])
    if payload.status not in allowed:
        raise HTTPException(400, detail=f"'{sr.status}' → '{payload.status}' 전이는 허용되지 않습니다.")

    old_status = sr.status
    sr.status = payload.status
    sr.updated_at = datetime.now()
    detail = payload.comment or f"상태 변경: {old_status} → {payload.status}"
    await _write_audit(db, sr_id, payload.actor, "STATUS_CHANGED", detail)
    await db.commit()
    await db.refresh(sr)
    return sr