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 so the blue hour is long.
    // Dusk keeps two independent ramps: the darkening ramp 20:00 -> 22:00 (still agrees with
    // Sim.isNightTick at 22:00), and a wider golden-hour warmth bump peaking at 20:30. Keeping
    // them separate is what makes the orange dusk visible: at 20:45 the scene is still only
    // ~0.37 dark (Day mode) while warmth is high.
    let dawnStartHour = 4.0f
    let dawnEndHour = 6.5f
    let duskStartHour = 20.0f
    let duskEndHour = 22.0f
    let duskWarmthStartHour = 19.25f
    let duskWarmthEndHour = 21.75f

    /// 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 duskWarmthStartHour duskWarmthEndHour)

    /// Additive golden-hour veil alpha (0 at noon/midnight, peaks ~150 at dawn/dusk mid).
    /// Multiplicative WorldTint alone cannot warm green foliage, so the renderer layers this
    /// premultiplied orange wash over the finished world scene.
    let goldenVeilAlpha (tick: int64) : int =
        int (150.0f * transitionWarmth tick)

    /// Cool moonlight wash applied as a premultiplied veil over the finished night scene.
    /// Multiplicative night tint can only darken, so this additive cool layer is what makes deep
    /// night read moon-blue. It is zero whenever the sun lights the scene (blend 0) and is
    /// suppressed through the warm dawn/dusk windows (warmth), so it never competes with the
    /// golden veil. Purely desktop render state; the Kernel never sees it.
    let moonlightRgb : int * int * int = (120, 170, 235)

    let moonlightVeilAlpha (tick: int64) : int =
        let blend = lightingBlend tick
        let warmth = transitionWarmth tick
        int (72.0f * blend * (1.0f - warmth))

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

    /// Blended sky colour plus a strong golden-hour shift: at dusk this reads as a warm orange
    /// horizon (red up hard, blue down hard) rather than the old muted blue-grey twilight.
    let backgroundAtWarmth (blend: float32) (warmth: float32) : Color =
        Color(
            lerp 100 18 blend + int (120.0f * warmth),
            lerp 160 25 blend + int (20.0f * warmth),
            lerp 210 55 blend - int (90.0f * warmth))

    /// World tint multiplies the whole scene. The day baseline is neutral white so noon keeps
    /// a true white balance (the old day base 255/248/224 clipped blue by ~12% and made daylight
    /// look yellow); night stays cool, and the golden shade only appears through `warmth`, which
    /// is a pure function that is zero at noon and outside the dawn/dusk windows.
    let worldTintAtWarmth (blend: float32) (warmth: float32) : Color =
        Color(
            lerp 255 118 blend + int (70.0f * warmth),
            lerp 255 136 blend - int (10.0f * warmth),
            lerp 255 184 blend - int (75.0f * 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
          // Lanterns glow through the golden hour too, so dusk reads as warm lanterns at a
          // warm sunset rather than only a local night point-light.
          LanternGlow = max blend (warmth * 0.8f)
          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

    /// Deterministic start tick for a wall-clock hour (evidence harness): 20.75 -> 20:45.
    let startTickForHour (hour: float) : int64 =
        int64 (hour * float (Sim.ticksPerDay / 24L))

    /// Start-tick decision shared by bootstrap and new-game: an explicit evidence hour wins,
    /// else daylight starts at 6:00, else midnight. Pure function, no side effects.
    let resolveStartTick (startHour: float option) (startAtDaylight: bool) : int64 =
        match startHour with
        | Some hour -> startTickForHour hour
        | None -> if startAtDaylight then 6L * Sim.ticksPerDay / 24L else 0L

    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）。
    /// 黄昏覆盖到 21:00，与 dusk 暖色窗口（峰值 20:30）对齐；22:00 起才是夜晚。
    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 < 21 then "黄昏"
        else "夜晚"