"""工单状态机与权限判定（纯函数，不碰 ORM 以外的世界）。

状态机：

    open ──accept──▶ accepted ──start──▶ in_progress ──submit──▶ pending_verify
                                          ▲                          │
                                          └────────reject────────────┘
                                                                     │approve
                                                                     ▼
                                                                   done

`canceled` 可以从任何未终结状态进入；`done` 与 `canceled` 是终态。

两条刻意的规则：

1. **驳回不是打回 open，而是回 in_progress**。办理人已经在做了，让他重新"认领"一次纯属折腾；
   驳回次数单独计数（`reject_count`），用来提示"这事返工过"。
2. **谁也不能替别人验收**，除了管理员/所有者。提需求的人验收是这套流程的核心信任点，
   如果办理人能自己点"通过"，工单就退化成"打个勾"。
"""

from __future__ import annotations

import uuid

from ..errors import AppError, ErrorCode

TICKET_TRANSITIONS: dict[str, tuple[str, ...]] = {
    "open": ("accepted", "canceled"),
    "accepted": ("in_progress", "canceled"),
    "in_progress": ("pending_verify", "canceled"),
    "pending_verify": ("done", "in_progress", "canceled"),
    "done": (),
    "canceled": (),
}

# 动作 → (允许的前置状态, 目标状态)；cancel 特殊处理
ACTION_RULES: dict[str, tuple[tuple[str, ...], str]] = {
    "accept": (("open",), "accepted"),
    "start": (("accepted",), "in_progress"),
    "submit": (("in_progress",), "pending_verify"),
    "approve": (("pending_verify",), "done"),
    "reject": (("pending_verify",), "in_progress"),
}

CANCELABLE = ("open", "accepted", "in_progress", "pending_verify")

NOW_FIELD: dict[str, str] = {
    "accepted": "accepted_at",
    "pending_verify": "submitted_at",
    "done": "verified_at",
}


def ensure_transition(current: str, target: str) -> None:
    allowed = TICKET_TRANSITIONS.get(current, ())
    if target not in allowed:
        raise AppError(
            ErrorCode.TICKET_STATUS_INVALID,
            f"工单当前是「{current}」，不能直接变成「{target}」",
            details={"from": current, "to": target, "allowed": list(allowed)},
        )


def target_status(action: str, current: str) -> str:
    """动作 → 目标状态，顺带校验前置状态。"""
    if action == "cancel":
        if current not in CANCELABLE:
            raise AppError(
                ErrorCode.TICKET_STATUS_INVALID,
                f"「{current}」的工单不能取消",
                details={"from": current, "allowed": list(CANCELABLE)},
            )
        return "canceled"

    if action not in ACTION_RULES:
        raise AppError(ErrorCode.BAD_REQUEST, f"未知动作：{action}")

    allowed_from, target = ACTION_RULES[action]
    if current not in allowed_from:
        raise AppError(
            ErrorCode.TICKET_STATUS_INVALID,
            f"工单当前是「{current}」，不能执行「{action}」",
            # allowed 回答"现在还能去哪儿"，allowed_from 回答"这个动作要什么前置状态"：
            # 客户端两种都要用得上，别让它自己拼。
            details={
                "from": current,
                "action": action,
                "allowed": list(TICKET_TRANSITIONS.get(current, ())),
                "allowed_from": list(allowed_from),
            },
        )
    return target


def ensure_can_act(
    *,
    action: str,
    actor_id: uuid.UUID,
    role: str,
    assignee_id: uuid.UUID | None,
    requester_id: uuid.UUID | None,
) -> None:
    """谁能做这个动作。

    管理员/所有者可以代任何人操作（人休假、离职时的兜底），
    普通成员只能动自己的位置上的事。
    """
    is_admin = role in ("owner", "admin")
    is_assignee = assignee_id is not None and actor_id == assignee_id
    is_requester = requester_id is not None and actor_id == requester_id

    if action in ("accept", "start", "submit"):
        allowed = is_assignee or is_admin
        hint = "只有被指派的人才能操作这条工单"
    elif action in ("approve", "reject"):
        allowed = is_requester or is_admin
        hint = "只有提出这条工单的人（或管理员）才能验收"
    elif action == "cancel":
        allowed = is_requester or is_assignee or is_admin
        hint = "只有提出人、办理人或管理员能取消"
    else:
        allowed = is_admin or is_requester
        hint = "权限不足"

    if not allowed:
        raise AppError(ErrorCode.TICKET_FORBIDDEN, hint, details={"action": action})


def returned_task_status(ticket_status: str) -> str | None:
    """工单状态变化后，原任务该回到什么状态；None 表示不动。

    闭环回流只发生在验收通过那一刻——这是"事情真的办完了"的唯一信号。
    取消不回填：取消意味着不办了，原任务继续躺在 blocked 里等人处理才对。
    """
    if ticket_status == "done":
        return "todo"
    return None