dispatch.vsl

// @mock(ui32)
// @dynamic(false)
// private class JSReference {
//     deinit {
//         freeReference(index: UInt32::self)
//     }
// }
//
// private typealias WDSFrame = UInt32
// private const WDS_HEADER_SIZE: UInt64 = 4
// private const WDS_PARAM_TYPE_SIZE: UInt64 = 1
// private const WDS_PARAM_VALUE_SIZE: UInt64 = 4
//
// private const WDS_PARAM_TYPE_OBJREF = 0x01
// private const WDS_PARAM_TYPE_STRING = 0x00

private func metaGlobal() -> UInt32 external("meta.__objectheap_global");
private func metaUndefined() -> UInt32 external("meta.__objectheap_undefined");
private func metaNull() -> UInt32 external("meta.__objectheap_null");

// Constants
public const JS_GLOBAL: JSValue = JSValue::metaGlobal();
public const JS_UNDEFINED: JSValue = JSValue::metaUndefined();
public const JS_NULL: JSValue = JSValue::metaNull();

public lazy const JS_ARRAY: JSValue = JS_GLOBAL.dispatchAccess("Array");
public lazy const JS_STRING: JSValue = JS_GLOBAL.dispatchAccess("String");

// JS bridging class
typealias WASMDispatchStackFrame = Pointer<UInt8>

@mock(ui32)
@dynamic(false)
public class JSValue {

    /// Creates a JSValue encapsulating a VSL string. These does not create any
    /// reference, instead creates a copy in the JS context.
    public static func from(string: String) -> JSValue external("meta.objectheap.fromString");

    /// Creates a JSValue encapsulating a VSL number. These does not create any
    /// reference, instead creates a copy in the JS context. Use of this is not
    /// recommended, instead to directly pass the number to the JS interface.
    public static func from(uint8: UInt8) -> JSValue external("meta.objectheap.fromNumber");

    /// Creates a JSValue encapsulating a VSL number. These does not create any
    /// reference, instead creates a copy in the JS context. Use of this is not
    /// recommended, instead to directly pass the number to the JS interface.
    public static func from(uint16: UInt16) -> JSValue external("meta.objectheap.fromNumber");

    /// Creates a JSValue encapsulating a VSL number. These does not create any
    /// reference, instead creates a copy in the JS context. Use of this is not
    /// recommended, instead to directly pass the number to the JS interface.
    public static func from(uint32: UInt32) -> JSValue external("meta.objectheap.fromNumber");

    /// Creates a JSValue encapsulating a VSL number. These does not create any
    /// reference, instead creates a copy in the JS context. Use of this is not
    /// recommended, instead to directly pass the number to the JS interface.
    public static func from(int8: Int8) -> JSValue external("meta.objectheap.fromNumber");

    /// Creates a JSValue encapsulating a VSL number. These does not create any
    /// reference, instead creates a copy in the JS context. Use of this is not
    /// recommended, instead to directly pass the number to the JS interface.
    public static func from(int16: Int16) -> JSValue external("meta.objectheap.fromNumber");

    /// Creates a JSValue encapsulating a VSL number. These does not create any
    /// reference, instead creates a copy in the JS context. Use of this is not
    /// recommended, instead to directly pass the number to the JS interface.
    public static func from(int32: Int32) -> JSValue external("meta.objectheap.fromNumber");

    /// Creates a copy of the (assumed to be) JS string reference in the VSL
    /// heap. Undefined behavior if the value is not actually a JS value. Use
    /// the `checked: true` parameter for safe operations.
    public func toString(free: Bool = false, checked: Bool = false) -> String {
        if checked {
            // Get the 'String' class from the global object and use that.
            assert(self.dispatchInstanceOf(jsClass: JS_STRING), "invalid attempt to cast non-string to string")
        }

        let stringLength = UInt64::self.dispatchGetStringLength()
        let ptr = Pointer<UInt8>.alloc(count: stringLength + 1)

        // Set null byte at end
        ptr.offset(by: Int64::stringLength).store(value: 0x00)

        // Copy the string from JS -> VSL
        self.dispatchCopyString(to: ptr)

        if free {
            self.dispatchFree()
        }

        return String(value: ptr, byteLength: UInt::stringLength)
    }

    private func dispatchGetStringLength() -> UInt32 external("dispatch.readStringLength");
    private func dispatchCopyString(to pointer: Pointer<UInt8>) external("dispatch.copyString");

    public func dispatchInstanceOf(jsClass: JSValue) -> Bool external("dispatch.instanceOf");
    public func dispatchFree() external("dispatch.freeReference");
    public func dispatchAccess(target: String) -> JSValue external("dispatch.access");
    public func dispatchAnon(target: String) -> JSValue external("dispatch.anon");
    public func dispatch(target: String, stackFrame: WASMDispatchStackFrame) -> JSValue external("dispatch.dispatch");

    deinit { self.dispatchFree() }
}