namespace LivingVillage.Desktop

open LivingVillage.Kernel

/// P54 职业切片三：把 Kernel 的当日任务状态机接到 Desktop 运行时（玩家可见 / 可完成）。
///
/// 全部为纯函数：接受任务、按**真实世界事件/信号**推进、给出短中文反馈。
/// 完成判定只复用 Kernel 既有 `Occupation.advanceTask` / `applySignal`
/// （其内部是 `satisfiesCompletion`），绝不按日历索引硬编码计数。
module TaskRuntime =

    /// 完成短中文反馈：有设计口径物品奖励时带「+物品×数量」。
    let completionText (task: Occupation.DailyTask) (reward: (Sim.ItemKind * int) option) : string =
        let headline = sprintf "任务完成：%s" (Occupation.taskNameOf task.TemplateId)
        match reward with
        | Some(item, quantity) -> sprintf "%s +%s×%d" headline (Occupation.itemNameOf item) quantity
        | None -> headline

    let private completionMessage
        (before: Occupation.DailyTask option)
        (after: Occupation.DailyTask option)
        (reward: (Sim.ItemKind * int) option)
        : string option =
        match before, after with
        | Some previous, Some current when previous.State = Occupation.Active && current.State = Occupation.Done ->
            Some(completionText current reward)
        | _ -> None

    /// 接受当日任务（Offered → Active）；无任务 / 已在进行 / 终态时无变化、无反馈。
    let accept (state: Occupation.State) : Occupation.State * string option =
        match state.Today with
        | Some task when task.State = Occupation.Offered ->
            { state with Today = Some { task with State = Occupation.Active } },
            Some(sprintf "已接受任务：%s" (Occupation.taskNameOf task.TemplateId))
        | _ -> state, None

    /// 用一条既有世界事件推进当日任务；Active → Done 时返回（含奖励的）短中文反馈。
    let advanceWithEvent (event: Sim.InteractionEvent) (state: Occupation.State) : Occupation.State * string option =
        let before = state.Today
        let next, reward = Occupation.advanceTaskWithReward event state
        next, completionMessage before next.Today reward

    /// 用一条已折叠的任务信号（到达瓦片 / 观察 / 夜在水边）推进当日任务。
    let advanceWithSignal (signal: Occupation.TaskSignal) (state: Occupation.State) : Occupation.State * string option =
        let before = state.Today
        let next, reward = Occupation.applySignalToState signal state
        next, completionMessage before next.Today reward

    /// 折叠多条信号（后面的不覆盖已得到的完成反馈）。
    let foldSignals (signals: Occupation.TaskSignal list) (state: Occupation.State) : Occupation.State * string option =
        signals
        |> List.fold
            (fun (current, found) signal ->
                let next, message = advanceWithSignal signal current
                next, (match found with Some _ -> found | None -> message))
            (state, None)

    /// 由真实世界环境折叠出的任务信号：跨瓦片 → 到达；夜 + 水边 → 夜在水边。
    /// `previousTile = None`（尚未建立基线）时不产生到达信号，避免开局即误判完成。
    let environmentSignals
        (isNight: bool)
        (nearWater: bool)
        (previousTile: (int * int) option)
        (tile: int * int)
        : Occupation.TaskSignal list =
        [ if previousTile.IsSome && previousTile.Value <> tile then yield Occupation.ArrivedAt tile
          if isNight && nearWater then yield Occupation.NightAtWater ]

    /// 比较两份职业状态，返回本次推进是否让当日任务完成（供交易等路径复用）。
    let completedMessageWithReward
        (before: Occupation.State option)
        (after: Occupation.State option)
        (reward: (Sim.ItemKind * int) option)
        : string option =
        completionMessage
            (before |> Option.bind (fun state -> state.Today))
            (after |> Option.bind (fun state -> state.Today))
            reward