import uuid

from fastapi import APIRouter, Depends, HTTPException, status
from sqlalchemy.ext.asyncio import AsyncSession

from app.core.deps import get_current_user, get_db_session, require_study_member, require_study_roles
from app.crud import audit as audit_crud
from app.crud import milestone as milestone_crud
from app.crud import study as study_crud
from app.crud import task as task_crud
from app.crud import user as user_crud
from app.schemas.task import TaskCreate, TaskRead, TaskUpdate
from app.schemas.user import UserDisplay

router = APIRouter()

ALLOW_ASSIGNEE_UPDATE_STATUS = False


async def _ensure_study_exists(db: AsyncSession, study_id: uuid.UUID):
    study = await study_crud.get(db, study_id)
    if not study:
        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Study not found")
    return study


async def _validate_milestone(db: AsyncSession, study_id: uuid.UUID, milestone_id: uuid.UUID | None):
    if milestone_id is None:
        return
    milestone = await milestone_crud.get(db, milestone_id)
    if not milestone:
        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Milestone not found")
    if milestone.study_id != study_id:
        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail="Milestone does not belong to study")


@router.post(
    "/",
    response_model=TaskRead,
    status_code=status.HTTP_201_CREATED,
    dependencies=[Depends(require_study_roles(["PM"]))],
)
async def create_task(
    study_id: uuid.UUID,
    task_in: TaskCreate,
    db: AsyncSession = Depends(get_db_session),
    current_user=Depends(get_current_user),
) -> TaskRead:
    await _ensure_study_exists(db, study_id)
    await _validate_milestone(db, study_id, task_in.milestone_id)
    task = await task_crud.create(db, study_id, task_in, created_by=current_user.id)
    assignee = None
    if task.assignee_id:
        assignee = await user_crud.get_by_id(db, task.assignee_id)
    await audit_crud.log_action(
        db,
        study_id=study_id,
        entity_type="task",
        entity_id=task.id,
        action="CREATE_TASK",
        detail=f"Task {task.id} created",
        operator_id=current_user.id,
        operator_role=current_user.role,
    )
    return _to_task_read(task, assignee)


@router.get(
    "/",
    response_model=list[TaskRead],
    dependencies=[Depends(require_study_member())],
)
async def list_tasks(
    study_id: uuid.UUID,
    milestone_id: uuid.UUID | None = None,
    assignee_id: uuid.UUID | None = None,
    status: str | None = None,
    db: AsyncSession = Depends(get_db_session),
) -> list[TaskRead]:
    await _ensure_study_exists(db, study_id)
    tasks = await task_crud.list_tasks(db, study_id, milestone_id=milestone_id, assignee_id=assignee_id, status=status)
    assignee_ids = {t.assignee_id for t in tasks if t.assignee_id}
    users_map = await user_crud.get_users_by_ids(db, assignee_ids)
    result: list[TaskRead] = []
    for t in tasks:
        user = users_map.get(t.assignee_id)
        result.append(_to_task_read(t, user))
    return result


@router.patch(
    "/{task_id}",
    response_model=TaskRead,
    dependencies=[Depends(require_study_roles(["PM"]))],
)
async def update_task(
    study_id: uuid.UUID,
    task_id: uuid.UUID,
    task_in: TaskUpdate,
    db: AsyncSession = Depends(get_db_session),
    current_user=Depends(get_current_user),
) -> TaskRead:
    await _ensure_study_exists(db, study_id)
    task = await task_crud.get(db, task_id)
    if not task or task.study_id != study_id:
        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Task not found")
    if task_in.milestone_id:
        await _validate_milestone(db, study_id, task_in.milestone_id)

    old_status = task.status
    updated = await task_crud.update(db, task, task_in)
    assignee = None
    if updated.assignee_id:
        assignee = await user_crud.get_by_id(db, updated.assignee_id)
    detail = None
    if task_in.status and task_in.status != old_status:
        detail = f"task {task_id} status {old_status} -> {task_in.status}"
    await audit_crud.log_action(
        db,
        study_id=study_id,
        entity_type="task",
        entity_id=task_id,
        action="UPDATE_TASK" if not detail else "TASK_STATUS_CHANGE",
        detail=detail or "Task updated",
        operator_id=current_user.id,
        operator_role=current_user.role,
    )
    return _to_task_read(updated, assignee)


def _to_task_read(task, assignee) -> TaskRead:
    return TaskRead(
        id=task.id,
        study_id=task.study_id,
        milestone_id=task.milestone_id,
        title=task.title,
        description=task.description,
        assignee_id=task.assignee_id,
        assignee=UserDisplay.model_validate(assignee) if assignee else None,
        priority=task.priority,
        due_date=task.due_date,
        status=task.status,
        completed_at=task.completed_at,
        created_by=task.created_by,
        created_at=task.created_at,
        updated_at=task.updated_at,
    )