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

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"})
TERMINAL_TASK_STATUSES = frozenset({"done", "discarded"})
MAX_TASK_DEPTH = 10

_TASK_COLUMNS = """
    id, tenant_id, action_id, parent_task_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", "parent_task_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 _load_action_task_maps(
    cur, *, tenant_id: str, action_id: str
) -> tuple[dict[str, dict[str, Any]], dict[str, list[str]]]:
    cur.execute(
        f"""
        SELECT {_TASK_COLUMNS}
        FROM tasks
        WHERE tenant_id = %s AND action_id = %s
        """,
        (tenant_id, action_id),
    )
    rows = [dict(r) for r in cur.fetchall()]
    by_id = {str(r["id"]): r for r in rows}
    by_parent: dict[str, list[str]] = {}
    for row in rows:
        parent_id = row.get("parent_task_id")
        if parent_id:
            by_parent.setdefault(str(parent_id), []).append(str(row["id"]))
    return by_id, by_parent


def _collect_descendant_ids(task_id: str, by_parent: dict[str, list[str]]) -> set[str]:
    result: set[str] = set()
    stack = list(by_parent.get(task_id, []))
    while stack:
        child_id = stack.pop()
        if child_id in result:
            continue
        result.add(child_id)
        stack.extend(by_parent.get(child_id, []))
    return result


def _task_depth_from_map(
    task_id: str,
    by_id: dict[str, dict[str, Any]],
    memo: dict[str, int],
) -> int:
    if task_id in memo:
        return memo[task_id]
    row = by_id.get(task_id)
    if not row or not row.get("parent_task_id"):
        memo[task_id] = 1
        return 1
    parent_id = str(row["parent_task_id"])
    depth = 1 + _task_depth_from_map(parent_id, by_id, memo)
    memo[task_id] = depth
    return depth


def _subtree_height(task_id: str, by_parent: dict[str, list[str]]) -> int:
    children = by_parent.get(task_id, [])
    if not children:
        return 1
    return 1 + max(_subtree_height(child_id, by_parent) for child_id in children)


def _validate_parent_task(
    cur,
    *,
    tenant_id: str,
    action_id: str,
    task_id: Optional[str],
    parent_task_id: Optional[str],
) -> None:
    if not parent_task_id:
        return
    if task_id and parent_task_id == task_id:
        raise ValueError("Task kann nicht sein eigener Parent sein")

    cur.execute(
        f"""
        SELECT {_TASK_COLUMNS}
        FROM tasks
        WHERE id = %s AND tenant_id = %s AND action_id = %s
        """,
        (parent_task_id, tenant_id, action_id),
    )
    parent = cur.fetchone()
    if not parent:
        raise ValueError("Parent-Task gehört nicht zu diesem Arbeitspaket")

    by_id, by_parent = _load_action_task_maps(cur, tenant_id=tenant_id, action_id=action_id)
    if task_id:
        descendants = _collect_descendant_ids(task_id, by_parent)
        if parent_task_id in descendants:
            raise ValueError("Zyklus: Parent darf kein Nachfahr sein")

    memo: dict[str, int] = {}
    parent_depth = _task_depth_from_map(parent_task_id, by_id, memo)
    subtree_height = _subtree_height(task_id, by_parent) if task_id else 1
    if parent_depth + subtree_height > MAX_TASK_DEPTH:
        raise ValueError(f"Maximale Task-Tiefe ({MAX_TASK_DEPTH}) würde überschritten")


def _has_open_children(cur, *, tenant_id: str, task_id: str) -> bool:
    cur.execute(
        """
        SELECT 1 FROM tasks
        WHERE tenant_id = %s AND parent_task_id = %s
          AND status NOT IN ('done', 'discarded')
        LIMIT 1
        """,
        (tenant_id, task_id),
    )
    return cur.fetchone() is not None


def _rollup_parent_status(cur, *, tenant_id: str, parent_task_id: str) -> None:
    cur.execute(
        """
        SELECT status FROM tasks
        WHERE tenant_id = %s AND parent_task_id = %s
        """,
        (tenant_id, parent_task_id),
    )
    child_statuses = [row[0] for row in cur.fetchall()]
    if not child_statuses:
        return
    if any(status not in TERMINAL_TASK_STATUSES for status in child_statuses):
        return

    cur.execute(
        """
        UPDATE tasks
        SET status = 'done', updated_at = NOW()
        WHERE id = %s AND tenant_id = %s AND status NOT IN ('done', 'discarded')
        RETURNING parent_task_id
        """,
        (parent_task_id, tenant_id),
    )
    row = cur.fetchone()
    if row and row[0]:
        _rollup_parent_status(cur, tenant_id=tenant_id, parent_task_id=str(row[0]))


def create_task(
    *,
    tenant_id: str,
    action_id: str,
    title: str,
    description: str = "",
    status: TaskStatus = "open",
    parent_task_id: Optional[str] = None,
    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_parent_task(
                cur,
                tenant_id=tenant_id,
                action_id=action_id,
                task_id=None,
                parent_task_id=parent_task_id,
            )
            _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, parent_task_id, title, description, status,
                    roadmap_item_id, sort_order, due_at
                )
                VALUES (%s, %s, %s, %s, %s, %s, %s, %s, %s)
                RETURNING {_TASK_COLUMNS}
                """,
                (
                    tenant_id,
                    action_id,
                    parent_task_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,
            "parent_task_id": parent_task_id,
        },
    )
    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,
    parent_task_id: Optional[str] = None,
    clear_parent_task: bool = False,
    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)
    if clear_parent_task:
        updates.append("parent_task_id = NULL")
    elif parent_task_id is not None:
        updates.append("parent_task_id = %s")
        params.append(parent_task_id)
    if clear_roadmap_item:
        updates.append("roadmap_item_id = NULL")
    elif roadmap_item_id is not None:
        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)

    conn = get_connection()
    try:
        with conn.cursor(cursor_factory=RealDictCursor) as cur:
            if parent_task_id is not None and not clear_parent_task:
                _validate_parent_task(
                    cur,
                    tenant_id=tenant_id,
                    action_id=existing["action_id"],
                    task_id=task_id,
                    parent_task_id=parent_task_id,
                )
            if roadmap_item_id is not None and not clear_roadmap_item:
                _validate_roadmap_item_for_action(
                    cur,
                    tenant_id=tenant_id,
                    initiative_id=action["initiative_id"],
                    roadmap_item_id=roadmap_item_id,
                )
            if status is not None:
                if status == "done" and _has_open_children(
                    cur, tenant_id=tenant_id, task_id=task_id
                ):
                    raise ValueError(
                        "Task kann nicht abgeschlossen werden — offene Unteraufgaben vorhanden"
                    )
                updates.append("status = %s")
                params.append(status)

            if not updates:
                return existing

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

            if status == "done" and result.get("parent_task_id"):
                _rollup_parent_status(
                    cur,
                    tenant_id=tenant_id,
                    parent_task_id=str(result["parent_task_id"]),
                )
        conn.commit()
    finally:
        conn.close()

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


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(
                """
                SELECT 1 FROM tasks
                WHERE parent_task_id = %s AND tenant_id = %s
                LIMIT 1
                """,
                (task_id, tenant_id),
            )
            if cur.fetchone():
                raise ValueError(
                    "Task hat Unteraufgaben — zuerst löschen oder verschieben"
                )
            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