namespace LivingVillage.Desktop

open System
open Microsoft.Xna.Framework
open Microsoft.Xna.Framework.Graphics
open LivingVillage.Kernel

/// P47 场景细节渲染层：把 `SceneDetail` 的纯函数结果落成画面。
/// 倒影为每个光源正下方一条暖色垂直光柱（核心 + 外晕，离光源越远越淡），
/// 岸芦苇/漂浮元素用既有瓦片精灵与原创点阵图集，近景屋顶按统一光源分受光面/背光面。
/// 全部只读，不改瓦片/可达性。
module SceneDetailRender =

    let private tileX (camera: Vector2) (x: int) = x * Sim.tilePixels - int camera.X
    let private tileY (camera: Vector2) (y: int) = y * Sim.tilePixels - int camera.Y

    /// 河道倒影：每个光源在正下方水面格画一段暖色垂直光柱（外晕 20px + 核心 10px），
    /// alpha 随离光源距离递减、逐格 ±1px 微抖，连成一条可辨认的暖色垂直条纹
    /// （明显区别于蓝灰横向波纹）。
    let private drawReflections
        (spriteBatch: SpriteBatch)
        (pixel: Texture2D)
        (camera: Vector2)
        (map: MapGen.Result)
        (tick: int64) =
        for (x, y, alpha, _) in SceneDetail.reflectionStreaks map do
            let wobble = SceneDetail.reflectionWobbleAt tick x y
            let cx = tileX camera x
            let cy = tileY camera y
            let halo = VillageArt.premultiply 255 150 70 (alpha * 3 / 5)
            let core = VillageArt.premultiply 255 208 120 alpha
            spriteBatch.Draw(pixel, Rectangle(cx + 4 + wobble, cy, 24, Sim.tilePixels), halo)
            spriteBatch.Draw(pixel, Rectangle(cx + 10 + wobble, cy, 12, Sim.tilePixels), core)

    /// 岸边芦苇加密度：用既有芦苇精灵补绘一层贴水芦苇。
    let private drawBankReeds (spriteBatch: SpriteBatch) (textures: VillageArt.ArtTextures) (camera: Vector2) (map: MapGen.Result) =
        match textures.Cc0TileAtlas with
        | Some cc0 ->
            for (x, y) in SceneDetail.bankReedTiles map do
                spriteBatch.Draw(cc0, Rectangle(tileX camera x, tileY camera y, Sim.tilePixels, Sim.tilePixels), Nullable(VillageArt.cc0TileRect VillageArt.cc0TileIndexReeds), Color.White)
        | None ->
            let source = VillageArt.atlasTileRectangle 18
            for (x, y) in SceneDetail.bankReedTiles map do
                spriteBatch.Draw(textures.TileAtlas, Rectangle(tileX camera x, tileY camera y, Sim.tilePixels, Sim.tilePixels), Nullable(source), Color.White)

    /// 漂浮元素：原创点阵鸭/叶，按 tick 慢漂移。
    let private drawFloaters (spriteBatch: SpriteBatch) (textures: VillageArt.ArtTextures) (camera: Vector2) (map: MapGen.Result) (tick: int64) =
        for (x, y, kind) in SceneDetail.floatingProps map do
            let seed = x * 31 + y * 7
            let dx, dy = SceneDetail.floatDrift tick seed
            let frame = SceneDetail.floatFrame tick seed
            let kindIndex =
                match kind with
                | SceneDetail.DuckFloat -> FloaterArt.duckIndex
                | SceneDetail.FallenLeaf -> FloaterArt.leafIndex
            let source = FloaterArt.sourceRectangle kindIndex frame
            spriteBatch.Draw(
                textures.FloaterAtlas,
                Rectangle(tileX camera x + dx + (Sim.tilePixels - FloaterArt.cellWidth) / 2, tileY camera y + dy + (Sim.tilePixels - FloaterArt.cellHeight) / 2, FloaterArt.cellWidth, FloaterArt.cellHeight),
                Nullable(source),
                Color.White)

    /// 近景楼层层错落：屏幕空间前景屋顶带。统一光源来自左上，故每段屋顶
    /// 左半受光（暖亮）、右半背光（压暗），并整体投影到右下（shadowOffsetPx）。
    let private drawForeground (spriteBatch: SpriteBatch) (textures: VillageArt.ArtTextures) (pixel: Texture2D) (viewportWidth: int) (viewportHeight: int) (tick: int64) =
        let ridgeSource = VillageArt.atlasTileRectangle 8
        let eaveSource = VillageArt.atlasTileRectangle 9
        let shadowColor = VillageArt.premultiply 8 12 18 120
        let litColor = VillageArt.premultiply 255 236 196 46
        let darkColor = VillageArt.premultiply 6 10 18 110
        let dx, dy = SceneDetail.shadowOffsetPx
        for (x, y, w) in SceneDetail.foregroundRooftops viewportWidth viewportHeight tick do
            // 统一方向的投影：先把 eave 的暗色镜像平移一份到右下，再画本体。
            spriteBatch.Draw(textures.TileAtlas, Rectangle(x + dx, y + dy, w, Sim.tilePixels), Nullable(eaveSource), shadowColor)
            spriteBatch.Draw(textures.TileAtlas, Rectangle(x, y - Sim.tilePixels, w, Sim.tilePixels), Nullable(ridgeSource), Color.White)
            spriteBatch.Draw(textures.TileAtlas, Rectangle(x, y, w, Sim.tilePixels), Nullable(eaveSource), Color.White)
            // 受光面 / 背光面：左半加暖亮、右半压暗，形成两档以上 luma 差。
            let half = max 1 (w / 2)
            spriteBatch.Draw(pixel, Rectangle(x, y - Sim.tilePixels, half, 2 * Sim.tilePixels), litColor)
            spriteBatch.Draw(pixel, Rectangle(x + half, y - Sim.tilePixels, w - half, 2 * Sim.tilePixels), darkColor)

    /// 一次性绘制全部 P47 场景细节（倒影 → 岸边芦苇 → 漂浮元素 → 近景前景层）。
    let draw
        (spriteBatch: SpriteBatch)
        (textures: VillageArt.ArtTextures)
        (pixel: Texture2D)
        (camera: Vector2)
        (viewportWidth: int)
        (viewportHeight: int)
        (map: MapGen.Result)
        (tick: int64) =
        drawReflections spriteBatch pixel camera map tick
        drawBankReeds spriteBatch textures camera map
        drawFloaters spriteBatch textures camera map tick
        drawForeground spriteBatch textures pixel viewportWidth viewportHeight tick