namespace LivingVillage.Desktop

open Microsoft.Xna.Framework
open LivingVillage.Kernel
open LivingVillage.Kernel.Sim

type M6DayNight =
    | Day
    | Night

type M6RenderProfile =
    { Mode: M6DayNight
      Background: Color
      WorldTint: Color
      Blend: float32
      LanternGlow: float32
      SkyWarmth: float32 }

module M6Presentation =

    let dayNightLabel mode : string =
        match mode with
        | Day -> "白天"
        | Night -> "夜晚"

    // Transition windows in float hours. Dawn lingers past 6:00 and dusk begins before
    // 20:00 so the blue hour is longer and the sky warms before it darkens; the anchors
    // still agree with Sim.isNightTick (night >= 22:00 or < 6:00) once fully dark.
    let dawnStartHour = 4.0f
    let dawnEndHour = 6.5f
    let duskStartHour = 19.5f
    let duskEndHour = 22.0f

    /// Continuous light blend: 0 = full day, 1 = full night. Deterministic pure function
    /// of the simulation tick, parameterised by the dawn/dusk windows above.
    let lightingBlend (tick: int64) : float32 =
        let hourTicks = Sim.ticksPerDay / 24L
        let hour = float32 tick / float32 hourTicks
        let clamp01 v = if v < 0.0f then 0.0f elif v > 1.0f then 1.0f else v
        if hour >= dawnEndHour && hour < duskStartHour then 0.0f
        elif hour >= duskEndHour || hour < dawnStartHour then 1.0f
        elif hour < dawnEndHour then clamp01 (1.0f - (hour - dawnStartHour) / (dawnEndHour - dawnStartHour))
        else clamp01 ((hour - duskStartHour) / (duskEndHour - duskStartHour))

    /// Golden-hour warmth (0..1): a triangular bump peaking mid-dawn and mid-dusk, zero at
    /// noon and midnight. Drives the warm sky/world tint so P17 transition frames read golden.
    let transitionWarmth (tick: int64) : float32 =
        let hour = float32 tick / float32 (Sim.ticksPerDay / 24L)
        let bump (startHour: float32) (endHour: float32) : float32 =
            if hour <= startHour || hour >= endHour then
                0.0f
            else
                let mid = (startHour + endHour) * 0.5f
                let half = (endHour - startHour) * 0.5f
                1.0f - abs (hour - mid) / half
        max (bump dawnStartHour dawnEndHour) (bump duskStartHour duskEndHour)

    let private lerp (a: int) (b: int) (blend: float32) : int =
        a + int (float32 (b - a) * blend)

    /// Blended sky/world colour plus the golden-hour warmth shift (warm channels up, blue down).
    let backgroundAtWarmth (blend: float32) (warmth: float32) : Color =
        Color(
            lerp 100 18 blend + int (52.0f * warmth),
            lerp 160 25 blend + int (14.0f * warmth),
            lerp 210 55 blend - int (34.0f * warmth))

    let worldTintAtWarmth (blend: float32) (warmth: float32) : Color =
        Color(
            lerp 255 118 blend + int (10.0f * warmth),
            lerp 248 136 blend - int (6.0f * warmth),
            lerp 224 184 blend - int (26.0f * warmth))

    /// Warmth-free base colours (kept for callers that only have a blend value).
    let backgroundAtBlend (blend: float32) : Color = backgroundAtWarmth blend 0.0f
    let worldTintAtBlend (blend: float32) : Color = worldTintAtWarmth blend 0.0f

    /// Pure day-phase lighting: deterministic tint/background/warmth plus lantern glow.
    let lightingAtTick (tick: int64) : M6RenderProfile =
        let blend = lightingBlend tick
        let warmth = transitionWarmth tick
        { Mode = if blend < 0.5f then Day else Night
          Background = backgroundAtWarmth blend warmth
          Blend = blend
          WorldTint = worldTintAtWarmth blend warmth
          LanternGlow = blend
          SkyWarmth = warmth }

    let profileAtTick (tick: int64) : M6RenderProfile = lightingAtTick tick

    let clockLabel (control: SimulationControl) : string =
        if control.Paused then
            "暂停"
        else
            match control.Speed with
            | OneX -> "1倍速"
            | TwoX -> "2倍速"
            | FiveX -> "5倍速"

    /// 倍速标签（语义别名，HUD 用）。
    let speedLabel (control: SimulationControl) : string = clockLabel control

    let private hourOf (tick: int64) : int =
        int ((tick / (Sim.ticksPerDay / 24L)) % 24L)

    /// 24 小时制的模拟时钟（HH:MM），由 tick 纯函数导出。
    let clockTimeLabel (tick: int64) : string =
        let hourTicks = Sim.ticksPerDay / 24L
        let hour = hourOf tick
        let minute = int ((tick % hourTicks) * 60L / hourTicks)
        sprintf "%02d:%02d" hour minute

    /// 时段标签：清晨/白天/黄昏/夜晚，与实际 tick 一致（纯函数）。
    let timePeriodLabel (tick: int64) : string =
        let hour = hourOf tick
        if hour < 5 then "夜晚"
        elif hour < 8 then "清晨"
        elif hour < 17 then "白天"
        elif hour < 20 then "黄昏"
        else "夜晚"