internal import CPlaydate

extension JSON {
    /// A streaming JSON encoder into a string. Wraps `json_encoder`.
    /// Does not validate: the caller must emit well-formed JSON.
    public final class Encoder {
        /// A class so the write callback's userdata pointer stays stable.
        private final class Output {
            var bytes: [UInt8] = []
        }

        private var encoder = json_encoder()
        private let output = Output()

        /// `pretty` adds human-readable formatting.
        public init(pretty: Bool = false) {
            jsonAPI.pointee.initEncoder.unsafelyUnwrapped(&encoder, { userdata, string, length in
                guard let userdata, let string else { return }
                let output = Unmanaged<Output>.fromOpaque(userdata).takeUnretainedValue()
                output.bytes.append(contentsOf: UnsafeRawBufferPointer(start: string, count: Int(length)))
            }, Unmanaged.passUnretained(output).toOpaque(), pretty ? 1 : 0)
        }

        /// The JSON produced so far.
        public var json: String { String(decoding: output.bytes, as: UTF8.self) }

        public func startArray() {
            withUnsafeMutablePointer(to: &encoder) { $0.pointee.startArray.unsafelyUnwrapped($0) }
        }

        /// Call before writing each array element.
        public func addArrayMember() {
            withUnsafeMutablePointer(to: &encoder) { $0.pointee.addArrayMember.unsafelyUnwrapped($0) }
        }

        public func endArray() {
            withUnsafeMutablePointer(to: &encoder) { $0.pointee.endArray.unsafelyUnwrapped($0) }
        }

        /// Starts a JSON object.
        public func startTable() {
            withUnsafeMutablePointer(to: &encoder) { $0.pointee.startTable.unsafelyUnwrapped($0) }
        }

        /// Call before writing member `name`'s value.
        public func addTableMember(name: String) {
            name.withCString { cString in
                withUnsafeMutablePointer(to: &encoder) {
                    $0.pointee.addTableMember.unsafelyUnwrapped(
                        $0, cString, Int32(name.utf8.count))
                }
            }
        }

        public func endTable() {
            withUnsafeMutablePointer(to: &encoder) { $0.pointee.endTable.unsafelyUnwrapped($0) }
        }

        public func writeNull() {
            withUnsafeMutablePointer(to: &encoder) { $0.pointee.writeNull.unsafelyUnwrapped($0) }
        }

        public func writeBool(_ value: Bool) {
            withUnsafeMutablePointer(to: &encoder) {
                (value ? $0.pointee.writeTrue : $0.pointee.writeFalse).unsafelyUnwrapped($0)
            }
        }

        /// `value` must fit in `Int32`.
        public func writeInt(_ value: Int) {
            withUnsafeMutablePointer(to: &encoder) { $0.pointee.writeInt.unsafelyUnwrapped($0, Int32(value)) }
        }

        public func writeDouble(_ value: Double) {
            withUnsafeMutablePointer(to: &encoder) { $0.pointee.writeDouble.unsafelyUnwrapped($0, value) }
        }

        public func writeString(_ value: String) {
            value.withCString { cString in
                withUnsafeMutablePointer(to: &encoder) {
                    $0.pointee.writeString.unsafelyUnwrapped(
                        $0, cString, Int32(value.utf8.count))
                }
            }
        }

        /// Writes a whole `Value` tree; `.float` as `Double`, keys in `Dictionary` order.
        public func write(_ value: Value) {
            switch value {
            case .null:
                writeNull()
            case .bool(let bool):
                writeBool(bool)
            case .int(let int):
                writeInt(int)
            case .float(let float):
                writeDouble(Double(float))
            case .string(let string):
                writeString(string)
            case .array(let items):
                startArray()
                for item in items {
                    addArrayMember()
                    write(item)
                }
                endArray()
            case .table(let entries):
                startTable()
                for (key, entry) in entries {
                    addTableMember(name: key)
                    write(entry)
                }
                endTable()
            }
        }
    }
}