// The one GPU owner for panel transitions and persistent scene effects.
// CoreText remains the renderer: while either exists PardesView draws its
// complete ordinary frame into this retained bitmap, then Core Image runs the
// standalone shaders/crt.ci.metal kernels over it. With neither, the view
// bypasses this object entirely.

import CoreGraphics
import CoreImage
import Darwin
import Metal

final class ScenePostprocessor {
    enum CompositeOutcome {
        case presented
        case retry
        case unavailable
    }

    private let colorSpace: CGColorSpace
    private let sceneKernel: CIKernel
    private let panelClearKernel: CIKernel
    private let panelKernel: CIKernel
    private let context: CIContext
    private var raster: CGContext?
    private var previousRaster: CGContext?
    private var rasterWidth = 0
    private var rasterHeight = 0
    private var rasterScale: CGFloat = 0

    init?() {
        let colorSpace = CGColorSpace(name: CGColorSpace.sRGB)
            ?? CGColorSpaceCreateDeviceRGB()
        guard let source = ScenePostprocessor.kernelSource(),
              let device = MTLCreateSystemDefaultDevice(),
              let made = try? CIKernel.kernels(withMetalString: source),
              let sceneKernel = made.first(where: { $0.name == "pardesScene" }),
              let panelClearKernel = made.first(where: { $0.name == "pardesPanelClear" }),
              let panelKernel = made.first(where: { $0.name == "pardesPanel" })
        else { return nil }
        self.colorSpace = colorSpace
        self.sceneKernel = sceneKernel
        self.panelClearKernel = panelClearKernel
        self.panelKernel = panelKernel
        self.context = CIContext(mtlDevice: device, options: [
            .workingColorSpace: colorSpace,
            .outputColorSpace: colorSpace,
            .cacheIntermediates: false,
        ])
    }

    private static func kernelSource() -> String? {
        var candidates: [URL] = []
        if let resources = Bundle.main.resourceURL {
            candidates.append(resources.appendingPathComponent("crt.ci.metal"))
        }
        // An unbundled e2e executable has no Contents/Resources. Its build
        // puts the asset next to the binary, and this explicit candidate keeps
        // that dev loop independent of Bundle's treatment of command tools.
        if let executable = Bundle.main.executableURL {
            candidates.append(executable.deletingLastPathComponent()
                .appendingPathComponent("crt.ci.metal"))
        }
        for url in candidates {
            if let source = try? String(contentsOf: url, encoding: .utf8) {
                return source
            }
        }
        return nil
    }

    /// A body-font-sized, top-left-origin CGContext matching the view's own
    /// coordinate system. It is retained across frames; only a resize or a
    /// backing-scale move reallocates the pixel storage.
    func renderContext(size: CGSize, scale: CGFloat) -> CGContext? {
        let scale = max(1, scale)
        let width = max(1, Int((size.width * scale).rounded(.up)))
        let height = max(1, Int((size.height * scale).rounded(.up)))
        if raster == nil || width != rasterWidth || height != rasterHeight || scale != rasterScale {
            let info = CGBitmapInfo.byteOrder32Big.rawValue
                | CGImageAlphaInfo.premultipliedLast.rawValue
            guard let next = CGContext(
                data: nil, width: width, height: height,
                bitsPerComponent: 8, bytesPerRow: width * 4,
                space: colorSpace, bitmapInfo: info)
            else { return nil }
            next.translateBy(x: 0, y: CGFloat(height))
            next.scaleBy(x: scale, y: -scale)
            raster = next
            // The old and new snapshots must have identical extents. Lazily
            // rebuild the old owner only if an effect actually needs it.
            previousRaster = nil
            rasterWidth = width
            rasterHeight = height
            rasterScale = scale
        }
        return raster
    }

    /// A second complete CoreText raster for the frozen old grid. It is
    /// intentionally a peer of `raster`, not a collection of per-pane image
    /// pointers: deleted PDF/image panes have already released their core
    /// bytes, while PardesView's frozen CGImages remain safe to draw here.
    func previousRenderContext(size: CGSize, scale: CGFloat) -> CGContext? {
        guard renderContext(size: size, scale: scale) != nil else { return nil }
        if previousRaster == nil {
            let info = CGBitmapInfo.byteOrder32Big.rawValue
                | CGImageAlphaInfo.premultipliedLast.rawValue
            guard let next = CGContext(
                data: nil, width: rasterWidth, height: rasterHeight,
                bitsPerComponent: 8, bytesPerRow: rasterWidth * 4,
                space: colorSpace, bitmapInfo: info)
            else { return nil }
            next.translateBy(x: 0, y: CGFloat(rasterHeight))
            next.scaleBy(x: rasterScale, y: -rasterScale)
            previousRaster = next
        }
        return previousRaster
    }

    /// Run the one scene kernel and copy its result into the flipped NSView
    /// context. Allocation/device failures may be retried briefly. A kernel
    /// rejecting its fixed argument layout is permanent for this executable,
    /// so the caller can turn the advertised effects back off instead of
    /// silently spinning a display clock forever.
    func composite(
        scene: pardes_scene_s,
        tracks: UnsafeBufferPointer<pardes_panel_track_s>,
        changedCells: UnsafePointer<UInt8>?,
        changedAttachmentRects: [CGRect],
        gridSize: (cols: Int, rows: Int),
        cellSize: CGSize,
        ground: UInt32?,
        size: CGSize,
        into destination: CGContext
    ) -> CompositeOutcome {
        guard let raster, let sourceImage = raster.makeImage() else { return .retry }
        let extent = CGRect(x: 0, y: 0, width: rasterWidth, height: rasterHeight)
        let current = CIImage(cgImage: sourceImage, options: [.colorSpace: colorSpace])
        let old: CIImage
        if let previousImage = previousRaster?.makeImage() {
            old = CIImage(cgImage: previousImage, options: [.colorSpace: colorSpace])
        } else {
            old = current
        }
        let mask = changeMask(
            changedCells, attachmentRects: changedAttachmentRects,
            gridSize: gridSize, cellSize: cellSize) ??
            CIImage(color: CIColor(red: 0, green: 0, blue: 0, alpha: 1))
                .cropped(to: CGRect(x: 0, y: 0, width: 1, height: 1))
        var filtered = current

        // Geometric targets are prepared before any presented panel is drawn.
        // Horizontal slide/zoom use the theme ground; a vertical opener uses
        // the exact old frame inside its fixed clip. Data effects and closing
        // tombstones leave the canonical current frame untouched underneath.
        let clear = ground.map { encoded in
            CIColor(
                red: CGFloat((encoded >> 16) & 0xFF) / 255,
                green: CGFloat((encoded >> 8) & 0xFF) / 255,
                blue: CGFloat(encoded & 0xFF) / 255,
                alpha: 1)
        } ?? CIColor(red: 0, green: 0, blue: 0, alpha: 0)
        for track in tracks {
            let content = track.phase == UInt8(PARDES_PANEL_CLOSING) ? track.from : track.to
            guard let next = panelClearKernel.apply(
                extent: extent,
                roiCallback: { _, _ in extent },
                arguments: [
                    filtered, old,
                    pixelBox(content, cellSize: cellSize), clear,
                    Float(track.effect), Float(track.phase),
                ])
            else { return .unavailable }
            filtered = next
        }

        // libpardes orders moving, opening, then closing tombstones. Each pass
        // samples immutable old/new rasters and composes over the prior pass,
        // so a deleted pane can safely outlive its core Pane allocation.
        let pixelCell = CIVector(
            x: cellSize.width * rasterScale,
            y: cellSize.height * rasterScale)
        for track in tracks {
            let content = track.phase == UInt8(PARDES_PANEL_CLOSING) ? track.from : track.to
            guard let next = panelKernel.apply(
                extent: extent,
                roiCallback: { _, _ in extent },
                arguments: [
                    current, old, mask, filtered,
                    pixelBox(content, cellSize: cellSize),
                    pixelBox(track.from, cellSize: cellSize),
                    pixelBox(track.to, cellSize: cellSize),
                    Float(track.effect), Float(track.phase), Float(track.frame),
                    CIVector(
                        x: CGFloat(track.serial & 0xFFFF),
                        y: CGFloat(track.serial >> 16)),
                    pixelCell,
                    CIVector(
                        x: 0,
                        y: extent.height - CGFloat(gridSize.rows) * pixelCell.y),
                ])
            else { return .unavailable }
            filtered = next
        }

        if scene.flags != 0 {
            let crt: Float = scene.flags & UInt32(PARDES_SCENE_CRT) != 0 ? 1 : 0
            let ripple: Float = scene.flags & UInt32(PARDES_SCENE_RIPPLE) != 0 ? 1 : 0
            let glitch: Float = scene.flags & UInt32(PARDES_SCENE_GLITCH) != 0 ? 1 : 0
            // SDL samples the scene with CLAMP_TO_EDGE. A finite Core Image
            // instead supplies transparent black outside its extent, which
            // would make ripple/glitch tear dark seams at the window edge.
            // Clamp the input only; the kernel still emits true black before
            // sampling when a destination lies outside the CRT tube.
            let sceneInput = filtered.clampedToExtent()
            guard let next = sceneKernel.apply(
                extent: extent,
                roiCallback: { _, _ in extent },
                arguments: [
                    sceneInput, scene.time_seconds, Float(scene.frame),
                    crt, ripple, glitch,
                    CIVector(x: extent.width, y: extent.height),
                    CIVector(x: extent.minX, y: extent.minY),
                ])
            else { return .unavailable }
            filtered = next
        }

        guard let presented = context.createCGImage(filtered, from: extent) else { return .retry }

        destination.clear(CGRect(origin: .zero, size: size))
        destination.saveGState()
        destination.translateBy(x: 0, y: size.height)
        destination.scaleBy(x: 1, y: -1)
        destination.interpolationQuality = .none
        destination.draw(presented, in: CGRect(origin: .zero, size: size))
        destination.restoreGState()
        return .presented
    }

    /// Byte-per-cell mask from the core. Zig expands true to 255 so the image
    /// is a literal normalized 0/1 texture; sampling cell centres below keeps
    /// adjacent values from interpolating at pane/cell boundaries.
    private func changeMask(
        _ cells: UnsafePointer<UInt8>?,
        attachmentRects: [CGRect],
        gridSize: (cols: Int, rows: Int),
        cellSize: CGSize
    ) -> CIImage? {
        let count = gridSize.cols * gridSize.rows
        guard count > 0, let cells, cellSize.width > 0, cellSize.height > 0 else { return nil }
        var bytes = Array(UnsafeBufferPointer(start: cells, count: count))
        for rect in attachmentRects where !rect.isNull && !rect.isEmpty {
            let x0 = max(0, Int((rect.minX / cellSize.width).rounded(.down)))
            let x1 = min(gridSize.cols, Int((rect.maxX / cellSize.width).rounded(.up)))
            let y0 = max(0, Int((rect.minY / cellSize.height).rounded(.down)))
            let y1 = min(gridSize.rows, Int((rect.maxY / cellSize.height).rounded(.up)))
            guard x0 < x1, y0 < y1 else { continue }
            for row in y0..<y1 {
                for col in x0..<x1 { bytes[row * gridSize.cols + col] = 255 }
            }
        }
        return bytes.withUnsafeBufferPointer { buffer in
            guard let base = buffer.baseAddress,
                  let data = CFDataCreate(nil, base, count),
                  let provider = CGDataProvider(data: data),
                  let gray = CGColorSpace(name: CGColorSpace.linearGray),
                  let image = CGImage(
                    width: gridSize.cols, height: gridSize.rows,
                    bitsPerComponent: 8, bitsPerPixel: 8,
                    bytesPerRow: gridSize.cols, space: gray,
                    bitmapInfo: CGBitmapInfo(rawValue: CGImageAlphaInfo.none.rawValue),
                    provider: provider, decode: nil,
                    shouldInterpolate: false, intent: .defaultIntent)
            else { return nil }
            return CIImage(cgImage: image, options: [.colorSpace: gray])
        }
    }

    /// Convert the core's top-left logical-cell box to Core Image's
    /// bottom-left backing-pixel rectangle.
    private func pixelBox(_ box: pardes_panel_box_s, cellSize: CGSize) -> CIVector {
        let cellW = cellSize.width * rasterScale
        let cellH = cellSize.height * rasterScale
        let x = CGFloat(box.x) * cellW
        let w = CGFloat(box.w) * cellW
        let h = CGFloat(box.h) * cellH
        let y = CGFloat(rasterHeight) - (CGFloat(box.y) + CGFloat(box.h)) * cellH
        return CIVector(x: x, y: y, z: w, w: h)
    }

    /// The scene kernel is a destination-to-source mapping. Pointer input must
    /// apply that same mapping before the grid and its panel tracks see a cell,
    /// otherwise a visible word under ripple/glitch is not the word Look gets.
    static func sourcePoint(
        _ point: CGPoint,
        size: CGSize,
        scene: pardes_scene_s
    ) -> CGPoint? {
        guard size.width > 0, size.height > 0 else { return nil }
        if scene.flags == 0 { return point }

        var uvX = Float(point.x / size.width)
        var uvY = 1 - Float(point.y / size.height) // Core Image is bottom-up
        var ccX = uvX * 2 - 1
        var ccY = uvY * 2 - 1
        let crt: Float = scene.flags & UInt32(PARDES_SCENE_CRT) != 0 ? 1 : 0
        let radius2 = ccX * ccX + ccY * ccY
        let barrel = 1 + 0.016 * radius2 * crt
        ccX *= barrel
        ccY *= barrel
        uvX = ccX * 0.5 + 0.5
        uvY = ccY * 0.5 + 0.5
        // Only CRT has a black tube. Ripple/glitch without CRT sample through
        // the texture's clamp-to-edge policy and remain clickable there.
        if crt > 0.5 && min(min(uvX, uvY), min(1 - uvX, 1 - uvY)) <= 0 { return nil }

        let time = scene.time_seconds
        if scene.flags & UInt32(PARDES_SCENE_RIPPLE) != 0 {
            let centeredX = uvX - 0.5
            let centeredY = uvY - 0.5
            let radius = sqrtf(centeredX * centeredX + centeredY * centeredY)
            let envelope = 1 - smoothstep(0.04, 0.72, radius)
            let wave = sinf(radius * 42 - time * 5.2)
            let travel = wave * envelope * 0.0032 / max(radius, 0.00001)
            uvX += centeredX * travel
            uvY += centeredY * travel
        }
        if scene.flags & UInt32(PARDES_SCENE_GLITCH) != 0 {
            let band = floorf(uvY * 96)
            let seed = noise(band, floorf(time * 13))
            let tear = smoothstep(0.955, 1, seed)
            uvX += (noise(seed, band) - 0.5) * tear * 0.020
        }
        uvX = min(max(uvX, 0), max(0, 1 - 1 / Float(size.width)))
        uvY = min(max(uvY, 0), max(0, 1 - 1 / Float(size.height)))
        return CGPoint(
            x: CGFloat(uvX) * size.width,
            y: CGFloat(1 - uvY) * size.height)
    }

    private static func smoothstep(_ edge0: Float, _ edge1: Float, _ x: Float) -> Float {
        let t = min(max((x - edge0) / (edge1 - edge0), 0), 1)
        return t * t * (3 - 2 * t)
    }

    /// Scalar spelling of pardesNoise in crt.ci.metal. Float arithmetic is
    /// deliberate: the shader's band decision must not move at a Double round.
    private static func noise(_ x: Float, _ y: Float) -> Float {
        var qx = fract(x * 0.1031)
        var qy = fract(y * 0.1031)
        var qz = fract(x * 0.1031)
        let d = qx * (qy + 33.33) + qy * (qz + 33.33) + qz * (qx + 33.33)
        qx += d
        qy += d
        qz += d
        return fract((qx + qy) * qz)
    }

    private static func fract(_ x: Float) -> Float { x - floorf(x) }
}