"""
任务系统核心 — 原子认领 + 依赖图 + Agent 状态管理

参考 Claude Code src/utils/tasks.ts 的设计模式：
- claimTask 使用 DB 行锁（SELECT FOR UPDATE）实现原子认领
- block/blockedBy 双向依赖管理
- Agent busy/idle 状态跟踪
"""
from sqlalchemy.orm import Session
from sqlalchemy import and_
from typing import List, Optional, Dict, Any
from datetime import datetime
from dataclasses import dataclass, field
from enum import Enum
import logging

from app.models.task import Task
from app.core.exceptions import NotFoundError, ValidationError

logger = logging.getLogger(__name__)


# ──────────────────────────── 状态定义 ────────────────────────────

class TaskStatus(str, Enum):
    PENDING = "pending"
    IN_PROGRESS = "in_progress"
    AWAITING_APPROVAL = "awaiting_approval"
    COMPLETED = "completed"
    FAILED = "failed"
    CANCELLED = "cancelled"


class AgentStatus(str, Enum):
    IDLE = "idle"
    BUSY = "busy"


@dataclass
class ClaimResult:
    success: bool
    reason: Optional[str] = None  # task_not_found / already_claimed / already_resolved / blocked / agent_busy
    task: Optional[Task] = None
    busy_with_tasks: List[str] = field(default_factory=list)   # agent_busy 时
    blocked_by_tasks: List[str] = field(default_factory=list)  # blocked 时


@dataclass
class AgentState:
    agent_id: str
    name: str = ""
    agent_type: str = ""
    status: AgentStatus = AgentStatus.IDLE
    current_tasks: List[str] = field(default_factory=list)


# ──────────────────────────── 任务系统 ────────────────────────────

class TaskSystem:
    """任务认领与依赖管理系统"""

    def __init__(self, db: Session):
        self.db = db

    # ── 原子认领 ──

    def claim_task(
        self,
        task_id: str,
        agent_id: str,
        check_busy: bool = True,
    ) -> ClaimResult:
        """
        使用 SELECT FOR UPDATE 原子认领任务。

        检查顺序:
        1. 任务存在性
        2. 未被其他 Agent 认领
        3. 任务未完成
        4. 所有 blockedBy 依赖已满足
        5. (可选) Agent 不忙碌
        """
        # SELECT FOR UPDATE — 锁定行直到事务提交
        task = (
            self.db.query(Task)
            .filter(Task.id == task_id)
            .with_for_update()
            .first()
        )

        if not task:
            return ClaimResult(success=False, reason="task_not_found")

        # 检查是否已被其他 Agent 认领
        if task.owner and task.owner != agent_id:
            return ClaimResult(success=False, reason="already_claimed", task=task)

        # 检查是否已完成
        if task.status == TaskStatus.COMPLETED.value:
            return ClaimResult(success=False, reason="already_resolved", task=task)

        # 检查依赖: blockedBy 中的任务必须全部完成
        blocked_by = task.depends_on or []
        if blocked_by:
            unresolved = (
                self.db.query(Task)
                .filter(
                    and_(
                        Task.id.in_(blocked_by),
                        Task.status != TaskStatus.COMPLETED.value,
                    )
                )
                .all()
            )
            if unresolved:
                return ClaimResult(
                    success=False,
                    reason="blocked",
                    task=task,
                    blocked_by_tasks=[t.id for t in unresolved],
                )

        # 检查 Agent 是否忙碌
        if check_busy:
            agent_open_tasks = (
                self.db.query(Task)
                .filter(
                    and_(
                        Task.owner == agent_id,
                        Task.status.in_([
                            TaskStatus.PENDING.value,
                            TaskStatus.IN_PROGRESS.value,
                            TaskStatus.AWAITING_APPROVAL.value,
                        ]),
                        Task.id != task_id,
                    )
                )
                .all()
            )
            if agent_open_tasks:
                return ClaimResult(
                    success=False,
                    reason="agent_busy",
                    task=task,
                    busy_with_tasks=[t.id for t in agent_open_tasks],
                )

        # 认领
        task.owner = agent_id
        task.status = TaskStatus.IN_PROGRESS.value
        if task.started_at is None:
            task.started_at = datetime.now()

        self.db.commit()
        self.db.refresh(task)
        logger.info(f"Task {task_id} claimed by agent {agent_id}")
        return ClaimResult(success=True, task=task)

    # ── 依赖管理 ──

    def block_task(self, from_task_id: str, to_task_id: str) -> bool:
        """
        设置任务依赖: from_task 阻塞 to_task。
        即: to_task 依赖 from_task 完成后才能执行。

        等价于:
        - from_task.blocks += to_task_id
        - to_task.depends_on += from_task_id
        """
        from_task = self.db.query(Task).filter(Task.id == from_task_id).first()
        to_task = self.db.query(Task).filter(Task.id == to_task_id).first()

        if not from_task or not to_task:
            return False

        # 检测循环依赖: 如果 to_task 已经（直接或间接）被 from_task 依赖，则形成环
        if self._would_create_cycle(from_task_id, to_task_id):
            raise ValidationError(
                f"无法设置依赖 {from_task_id} → {to_task_id}: 会产生循环依赖"
            )

        # from_task 阻塞 to_task
        blocks = list(from_task.blocks or [])
        if to_task_id not in blocks:
            blocks.append(to_task_id)
            from_task.blocks = blocks

        # to_task 被 from_task 阻塞
        depends = list(to_task.depends_on or [])
        if from_task_id not in depends:
            depends.append(from_task_id)
            to_task.depends_on = depends

        self.db.commit()
        logger.info(f"Task dependency set: {from_task_id} blocks {to_task_id}")
        return True

    def unblock_task(self, from_task_id: str, to_task_id: str) -> bool:
        """移除任务依赖"""
        from_task = self.db.query(Task).filter(Task.id == from_task_id).first()
        to_task = self.db.query(Task).filter(Task.id == to_task_id).first()

        if not from_task or not to_task:
            return False

        blocks = list(from_task.blocks or [])
        if to_task_id in blocks:
            blocks.remove(to_task_id)
            from_task.blocks = blocks

        depends = list(to_task.depends_on or [])
        if from_task_id in depends:
            depends.remove(from_task_id)
            to_task.depends_on = depends

        self.db.commit()
        return True

    def _would_create_cycle(self, from_id: str, to_id: str) -> bool:
        """检查 from → to 是否会产生循环依赖"""
        # 收集 to_task 直接和间接阻塞的所有任务
        visited = set()
        stack = [to_id]
        while stack:
            current = stack.pop()
            if current == from_id:
                return True
            if current in visited:
                continue
            visited.add(current)
            task = self.db.query(Task).filter(Task.id == current).first()
            if task and task.blocks:
                for blocked_id in task.blocks:
                    if blocked_id not in visited:
                        stack.append(blocked_id)
        return False

    # ── Agent 状态 ──

    def get_agent_status(self, agent_id: str) -> AgentState:
        """获取 Agent 忙闲状态及当前持有的任务"""
        open_tasks = (
            self.db.query(Task)
            .filter(
                and_(
                    Task.owner == agent_id,
                    Task.status.in_([
                        TaskStatus.PENDING.value,
                        TaskStatus.IN_PROGRESS.value,
                        TaskStatus.AWAITING_APPROVAL.value,
                    ]),
                )
            )
            .all()
        )

        task_ids = [t.id for t in open_tasks]
        status = AgentStatus.BUSY if task_ids else AgentStatus.IDLE

        return AgentState(
            agent_id=agent_id,
            status=status,
            current_tasks=task_ids,
        )

    def get_all_agent_statuses(self, task_list_owner_ids: List[str]) -> List[AgentState]:
        """批量获取多个 Agent 的状态"""
        result = []
        for agent_id in task_list_owner_ids:
            result.append(self.get_agent_status(agent_id))
        return result

    # ── 任务释放 ──

    def unassign_agent_tasks(
        self,
        agent_id: str,
    ) -> List[Task]:
        """释放 Agent 持有的所有未完成任务（Agent 下线/终止时调用）"""
        open_tasks = (
            self.db.query(Task)
            .filter(
                and_(
                    Task.owner == agent_id,
                    Task.status.in_([
                        TaskStatus.PENDING.value,
                        TaskStatus.IN_PROGRESS.value,
                        TaskStatus.AWAITING_APPROVAL.value,
                    ]),
                )
            )
            .with_for_update()
            .all()
        )

        unassigned = []
        for task in open_tasks:
            task.owner = None
            task.status = TaskStatus.PENDING.value
            unassigned.append(task)
            logger.info(f"Task {task.id} unassigned from agent {agent_id}")

        if unassigned:
            self.db.commit()

        return unassigned

    def release_task(self, task_id: str, agent_id: str) -> bool:
        """释放单个任务（Agent 主动放弃）"""
        task = (
            self.db.query(Task)
            .filter(Task.id == task_id)
            .with_for_update()
            .first()
        )

        if not task or task.owner != agent_id:
            return False

        task.owner = None
        task.status = TaskStatus.PENDING.value
        self.db.commit()
        logger.info(f"Task {task_id} released by agent {agent_id}")
        return True

    # ── 任务完成/失败 ──

    def complete_task(self, task_id: str, result: Optional[Dict[str, Any]] = None) -> Optional[Task]:
        """标记任务完成"""
        task = self.db.query(Task).filter(Task.id == task_id).first()
        if not task:
            return None

        task.status = TaskStatus.COMPLETED.value
        task.result = result or {}
        task.completed_at = datetime.now()
        self.db.commit()
        self.db.refresh(task)

        # 检查被此任务阻塞的任务是否现在可以执行
        self._check_unblocked_tasks(task)
        return task

    def fail_task(self, task_id: str, error_message: str = "") -> Optional[Task]:
        """标记任务失败"""
        task = self.db.query(Task).filter(Task.id == task_id).first()
        if not task:
            return None

        task.status = TaskStatus.FAILED.value
        task.error_message = error_message
        task.completed_at = datetime.now()
        self.db.commit()
        self.db.refresh(task)
        return task

    def _check_unblocked_tasks(self, completed_task: Task) -> None:
        """检查被已完成任务阻塞的任务是否已解除阻塞"""
        blocks = completed_task.blocks or []
        for blocked_id in blocks:
            blocked_task = self.db.query(Task).filter(Task.id == blocked_id).first()
            if not blocked_task:
                continue
            # 检查 blocked_task 的所有依赖是否都已满足
            deps = blocked_task.depends_on or []
            all_deps_met = True
            for dep_id in deps:
                dep = self.db.query(Task).filter(Task.id == dep_id).first()
                if dep and dep.status != TaskStatus.COMPLETED.value:
                    all_deps_met = False
                    break
            if all_deps_met and blocked_task.status == TaskStatus.PENDING.value:
                logger.info(
                    f"Task {blocked_id} is now unblocked (all dependencies met)"
                )

    # ── 查询辅助 ──

    def get_unresolved_blockers(self, task_id: str) -> List[Task]:
        """获取某个任务尚未完成的阻塞任务"""
        task = self.db.query(Task).filter(Task.id == task_id).first()
        if not task or not task.depends_on:
            return []

        return (
            self.db.query(Task)
            .filter(
                and_(
                    Task.id.in_(task.depends_on),
                    Task.status != TaskStatus.COMPLETED.value,
                )
            )
            .all()
        )

    def get_next_available_tasks(self, goal_id: str, limit: int = 10) -> List[Task]:
        """获取下一个可执行的任务（依赖已满足、未被认领）"""
        # 获取 goal 下所有任务
        all_tasks = (
            self.db.query(Task)
            .filter(Task.goal_id == goal_id)
            .all()
        )

        available = []
        for task in all_tasks:
            if task.status != TaskStatus.PENDING.value:
                continue
            if task.owner is not None:
                continue
            # 检查依赖
            deps = task.depends_on or []
            blocked = False
            for dep_id in deps:
                dep = next((t for t in all_tasks if t.id == dep_id), None)
                if dep and dep.status != TaskStatus.COMPLETED.value:
                    blocked = True
                    break
            if not blocked:
                available.append(task)
                if len(available) >= limit:
                    break

        return available