namespace LivingVillage.Desktop

open LivingVillage.Kernel

type MenuPage =
    | MainMenu
    | OccupationSelect
    | Settings
    | Controls
    | Playing
    | LoadError

type MenuItem =
    | ContinueItem
    | NewGameItem
    | LoadItem
    | SettingsItem
    | ControlsItem
    | ExitItem

type MenuSetting =
    | OneXSetting
    | TwoXSetting
    | FiveXSetting
    | PauseSetting

type MenuInput =
    | Up
    | Down
    | Confirm
    | Back

type MenuCommand =
    | NoCommand
    | ContinueGame
    | StartNewGame
    | StartNewGameWith of Occupation.Kind option
    | LoadGame
    | ApplySettings of SimulationControl
    | ExitGame

type ControlRow =
    { Keys: string
      Action: string }

type MenuState =
    { Page: MenuPage
      Selected: int
      HasCurrentWorld: bool
      ReturnPage: MenuPage
      Settings: SimulationControl
      Error: string option }

module MenuState =

    let settings : MenuSetting list =
        [ OneXSetting; TwoXSetting; FiveXSetting; PauseSetting ]

    let controlRows : ControlRow list =
        [ { Keys = "WASD"; Action = "移动" }
          { Keys = "E"; Action = "互动" }
          { Keys = "1-6"; Action = "对话" }
          { Keys = "Q"; Action = "观察" }
          { Keys = "TAB"; Action = "需求" }
          { Keys = "C"; Action = "年鉴" }
          { Keys = "L"; Action = "关系" }
          { Keys = "P"; Action = "暂停" }
          { Keys = "F1/F2/F3"; Action = "速度" }
          { Keys = "F6"; Action = "保存" }
          { Keys = "F7"; Action = "读取" }
          { Keys = "ESC"; Action = "菜单或关闭" }
          { Keys = "UP/DOWN"; Action = "选择" }
          { Keys = "ENTER"; Action = "确认" } ]

    let create (simulationControl: SimulationControl) (hasCurrentWorld: bool) : MenuState =
        { Page = MainMenu
          Selected = 0
          HasCurrentWorld = hasCurrentWorld
          ReturnPage = MainMenu
          Settings = simulationControl
          Error = None }

    /// P16 开始界面收敛为三项：开始（无存档）或继续（回到进行中的世界）/ 读档 / 退出。
    /// 设置与操作说明不再占用开始界面，仍可在游戏内通过 F1/F2/F3 与 P 打开。
    let items (state: MenuState) : MenuItem list =
        if state.HasCurrentWorld then
            [ ContinueItem; LoadItem; ExitItem ]
        else
            [ NewGameItem; LoadItem; ExitItem ]

    let settingsLabel setting : string =
        match setting with
        | OneXSetting -> "1倍速"
        | TwoXSetting -> "2倍速"
        | FiveXSetting -> "5倍速"
        | PauseSetting -> "暂停"

    let itemLabel item : string =
        match item with
        | ContinueItem -> "继续"
        | NewGameItem -> "开始"
        | LoadItem -> "读档"
        | SettingsItem -> "设置"
        | ControlsItem -> "操作说明"
        | ExitItem -> "退出"

    /// 开局四选一 + 「暂不选择」（None = 旧行为，无职业）。
    let occupationOptions : Occupation.Kind option list =
        [ Some Occupation.Farmer
          Some Occupation.Fisher
          Some Occupation.Peddler
          Some Occupation.Scholar
          None ]

    let occupationLabel (occupation: Occupation.Kind option) : string =
        match occupation with
        | Some kind -> Occupation.nameOf kind
        | None -> "暂不选择"

    let selectedOccupation (state: MenuState) : Occupation.Kind option =
        occupationOptions |> List.item state.Selected

    let private optionsFor (state: MenuState) : int =
        match state.Page with
        | MainMenu -> items state |> List.length
        | OccupationSelect -> occupationOptions.Length
        | Settings -> settings.Length
        | _ -> 0

    let private moveBy (delta: int) (state: MenuState) : MenuState =
        let count = optionsFor state
        if count = 0 then
            state
        else
            let next = (state.Selected + delta) % count
            let wrapped = if next < 0 then next + count else next
            { state with Selected = wrapped }

    let move direction state =
        match direction with
        | Up -> moveBy -1 state
        | Down -> moveBy 1 state
        | Confirm
        | Back -> state

    let selectedItem (state: MenuState) : MenuItem =
        items state |> List.item state.Selected

    let selectedSetting (state: MenuState) : MenuSetting =
        settings |> List.item state.Selected

    let private selectedControl (state: MenuState) : SimulationControl =
        match selectedSetting state with
        | OneXSetting -> { state.Settings with Paused = false; Speed = OneX }
        | TwoXSetting -> { state.Settings with Paused = false; Speed = TwoX }
        | FiveXSetting -> { state.Settings with Paused = false; Speed = FiveX }
        | PauseSetting -> { state.Settings with Paused = true }

    let enterGame (state: MenuState) : MenuState =
        { state with Page = Playing; Selected = 0; ReturnPage = MainMenu; Error = None }

    let setCurrentWorld (hasCurrentWorld: bool) (state: MenuState) : MenuState =
        { state with HasCurrentWorld = hasCurrentWorld }

    let setSettings (simulationControl: SimulationControl) (state: MenuState) : MenuState =
        { state with Settings = simulationControl }

    let openMain (state: MenuState) : MenuState =
        { state with Page = MainMenu; Selected = 0; ReturnPage = MainMenu; Error = None }

    let openSettings (state: MenuState) : MenuState =
        { state with Page = Settings; Selected = 0; ReturnPage = state.Page; Error = None }

    /// 新档确认后进入职业选择页；默认选中「暂不选择」= 不写职业的旧行为。
    let openOccupationSelect (state: MenuState) : MenuState =
        { state with
            Page = OccupationSelect
            Selected = occupationOptions.Length - 1
            ReturnPage = state.Page
            Error = None }

    let openControls (state: MenuState) : MenuState =
        { state with Page = Controls; Selected = 0; ReturnPage = state.Page; Error = None }

    /// P key: open the full key list as a pause-help page. The simulation is paused while
    /// the page is open; the caller keeps the previous control and restores it on exit.
    let enterPauseHelp (control: SimulationControl) (state: MenuState) : MenuState * SimulationControl =
        openControls state, { control with Paused = true }

    let showLoadError (message: string) (state: MenuState) : MenuState =
        { state with Page = LoadError; Selected = 0; ReturnPage = MainMenu; Error = Some message }

    let private returnFromSubpage (state: MenuState) : MenuState =
        match state.ReturnPage with
        | Playing -> { state with Page = Playing; Selected = 0; Error = None }
        | _ -> openMain state

    /// Leaving the pause-help page returns to the page it was opened from and restores
    /// the exact simulation control the player had before.
    let exitPauseHelp (original: SimulationControl) (state: MenuState) : MenuState * SimulationControl =
        returnFromSubpage state, original

    let private confirmMain (state: MenuState) : MenuState * MenuCommand =
        match selectedItem state with
        | ContinueItem -> enterGame state, ContinueGame
        | NewGameItem -> state, StartNewGame
        | LoadItem -> state, LoadGame
        | SettingsItem -> openSettings state, NoCommand
        | ControlsItem -> openControls state, NoCommand
        | ExitItem -> state, ExitGame

    let update (input: MenuInput) (state: MenuState) : MenuState * MenuCommand =
        match input with
        | Up -> move Up state, NoCommand
        | Down -> move Down state, NoCommand
        | Back ->
            match state.Page with
            | MainMenu -> state, ExitGame
            | OccupationSelect -> openMain state, NoCommand
            | Settings
            | Controls -> returnFromSubpage state, NoCommand
            | LoadError -> openMain state, NoCommand
            | Playing -> openMain state, NoCommand
        | Confirm ->
            match state.Page with
            | MainMenu -> confirmMain state
            | OccupationSelect -> state, StartNewGameWith (selectedOccupation state)
            | Settings ->
                let nextSettings = selectedControl state
                { state with Settings = nextSettings }, ApplySettings nextSettings
            | Controls -> state, NoCommand
            | LoadError -> openMain state, NoCommand
            | Playing -> state, NoCommand