"""Task service — kleinste Einheit unter Action (AP1.5)."""

from __future__ import annotations

from datetime import datetime
from typing import Any, Literal, Optional

from psycopg2.extras import RealDictCursor

from db import get_connection
from services.actions import get_action
from services.audit import log_audit

TaskStatus = Literal["open", "in_progress", "done", "discarded"]
TASK_STATUSES = frozenset({"open", "in_progress", "done", "discarded"})

_TASK_COLUMNS = """
    id, tenant_id, action_id, title, description, status,
    roadmap_item_id, sort_order, due_at, created_at, updated_at
"""


def _serialize_row(row: dict[str, Any]) -> dict[str, Any]:
    result = dict(row)
    for key in ("id", "tenant_id", "action_id", "roadmap_item_id"):
        if result.get(key):
            result[key] = str(result[key])
    if result.get("due_at"):
        result["due_at"] = result["due_at"].isoformat()
    for ts in ("created_at", "updated_at"):
        if result.get(ts):
            result[ts] = result[ts].isoformat()
    return result


def _validate_status(status: str) -> None:
    if status not in TASK_STATUSES:
        raise ValueError(f"Ungültiger Task-Status: {status}")


def _get_action_or_raise(*, tenant_id: str, action_id: str) -> dict[str, Any]:
    action = get_action(tenant_id=tenant_id, action_id=action_id)
    if not action:
        raise ValueError("Arbeitspaket nicht gefunden")
    return action


def _validate_roadmap_item_for_action(
    cur, *, tenant_id: str, initiative_id: str, roadmap_item_id: Optional[str]
) -> None:
    if not roadmap_item_id:
        return
    cur.execute(
        """
        SELECT 1 FROM roadmap_items ri
        JOIN roadmaps r ON r.id = ri.roadmap_id AND r.tenant_id = ri.tenant_id
        WHERE ri.id = %s AND ri.tenant_id = %s AND r.initiative_id = %s
        """,
        (roadmap_item_id, tenant_id, initiative_id),
    )
    if not cur.fetchone():
        raise ValueError("Gate gehört nicht zum Vorhaben des Arbeitspakets")


def create_task(
    *,
    tenant_id: str,
    action_id: str,
    title: str,
    description: str = "",
    status: TaskStatus = "open",
    roadmap_item_id: Optional[str] = None,
    sort_order: int = 0,
    due_at: Optional[datetime] = None,
    user_id: Optional[str] = None,
) -> dict[str, Any]:
    title = title.strip()
    if not title:
        raise ValueError("Titel ist erforderlich")
    _validate_status(status)
    action = _get_action_or_raise(tenant_id=tenant_id, action_id=action_id)

    conn = get_connection()
    try:
        with conn.cursor(cursor_factory=RealDictCursor) as cur:
            _validate_roadmap_item_for_action(
                cur,
                tenant_id=tenant_id,
                initiative_id=action["initiative_id"],
                roadmap_item_id=roadmap_item_id,
            )
            cur.execute(
                f"""
                INSERT INTO tasks (
                    tenant_id, action_id, title, description, status,
                    roadmap_item_id, sort_order, due_at
                )
                VALUES (%s, %s, %s, %s, %s, %s, %s, %s)
                RETURNING {_TASK_COLUMNS}
                """,
                (
                    tenant_id,
                    action_id,
                    title,
                    description,
                    status,
                    roadmap_item_id,
                    sort_order,
                    due_at,
                ),
            )
            row = _serialize_row(dict(cur.fetchone()))
        conn.commit()
    finally:
        conn.close()

    log_audit(
        "task.created",
        user_id=user_id,
        tenant_id=tenant_id,
        details={"task_id": row["id"], "action_id": action_id, "title": title},
    )
    return row


def list_tasks_for_action(*, tenant_id: str, action_id: str) -> list[dict[str, Any]]:
    _get_action_or_raise(tenant_id=tenant_id, action_id=action_id)
    conn = get_connection()
    try:
        with conn.cursor(cursor_factory=RealDictCursor) as cur:
            cur.execute(
                f"""
                SELECT {_TASK_COLUMNS}
                FROM tasks
                WHERE tenant_id = %s AND action_id = %s
                ORDER BY sort_order ASC, created_at ASC
                """,
                (tenant_id, action_id),
            )
            return [_serialize_row(dict(r)) for r in cur.fetchall()]
    finally:
        conn.close()


def get_task(*, tenant_id: str, task_id: str) -> Optional[dict[str, Any]]:
    conn = get_connection()
    try:
        with conn.cursor(cursor_factory=RealDictCursor) as cur:
            cur.execute(
                f"SELECT {_TASK_COLUMNS} FROM tasks WHERE id = %s AND tenant_id = %s",
                (task_id, tenant_id),
            )
            row = cur.fetchone()
            return _serialize_row(dict(row)) if row else None
    finally:
        conn.close()


def update_task(
    *,
    tenant_id: str,
    task_id: str,
    user_id: Optional[str] = None,
    title: Optional[str] = None,
    description: Optional[str] = None,
    status: Optional[TaskStatus] = None,
    roadmap_item_id: Optional[str] = None,
    clear_roadmap_item: bool = False,
    sort_order: Optional[int] = None,
    due_at: Optional[datetime] = None,
    clear_due_at: bool = False,
) -> Optional[dict[str, Any]]:
    existing = get_task(tenant_id=tenant_id, task_id=task_id)
    if not existing:
        return None

    action = _get_action_or_raise(tenant_id=tenant_id, action_id=existing["action_id"])
    updates: list[str] = []
    params: list[Any] = []

    if title is not None:
        title = title.strip()
        if not title:
            raise ValueError("Titel ist erforderlich")
        updates.append("title = %s")
        params.append(title)
    if description is not None:
        updates.append("description = %s")
        params.append(description)
    if status is not None:
        _validate_status(status)
        updates.append("status = %s")
        params.append(status)
    if clear_roadmap_item:
        updates.append("roadmap_item_id = NULL")
    elif roadmap_item_id is not None:
        conn = get_connection()
        try:
            with conn.cursor() as cur:
                _validate_roadmap_item_for_action(
                    cur,
                    tenant_id=tenant_id,
                    initiative_id=action["initiative_id"],
                    roadmap_item_id=roadmap_item_id,
                )
        finally:
            conn.close()
        updates.append("roadmap_item_id = %s")
        params.append(roadmap_item_id)
    if sort_order is not None:
        updates.append("sort_order = %s")
        params.append(sort_order)
    if clear_due_at:
        updates.append("due_at = NULL")
    elif due_at is not None:
        updates.append("due_at = %s")
        params.append(due_at)

    if not updates:
        return existing

    updates.append("updated_at = NOW()")
    params.extend([task_id, tenant_id])

    conn = get_connection()
    try:
        with conn.cursor(cursor_factory=RealDictCursor) as cur:
            cur.execute(
                f"""
                UPDATE tasks SET {", ".join(updates)}
                WHERE id = %s AND tenant_id = %s
                RETURNING {_TASK_COLUMNS}
                """,
                params,
            )
            row = cur.fetchone()
            if not row:
                return None
            result = _serialize_row(dict(row))
        conn.commit()
    finally:
        conn.close()

    log_audit(
        "task.updated",
        user_id=user_id,
        tenant_id=tenant_id,
        details={"task_id": task_id},
    )
    return result


def delete_task(*, tenant_id: str, task_id: str, user_id: Optional[str] = None) -> bool:
    conn = get_connection()
    try:
        with conn.cursor() as cur:
            cur.execute(
                "DELETE FROM tasks WHERE id = %s AND tenant_id = %s RETURNING id",
                (task_id, tenant_id),
            )
            deleted = cur.fetchone() is not None
        conn.commit()
    finally:
        conn.close()

    if deleted:
        log_audit(
            "task.deleted",
            user_id=user_id,
            tenant_id=tenant_id,
            details={"task_id": task_id},
        )
    return deleted