Livt.Net

src/services/ServiceChain.lvt

namespace Livt.Net

/**
 * Identifies the selected fixed handler without runtime component references.
 */
enum ServiceSelection
{
	None
	First
	Second
}

/**
 * Deterministic priority chain. Only Ignored falls through to the second handler.
 * Owns selection metadata; borrows two independent response services. Neither
 * child may be driven separately while the chain owns its lifecycle.
 */
component ServiceChain<F: IResponseService, N: IResponseService> : IResponseService
{
	// Fixed handlers and current response selection.
	first: F
	second: N
	selection: ServiceSelection

	/**
	 * Binds idle handlers; the caller constructs their request sources and policies.
	 */
	new(first: F, second: N)
	{
		this.first = first
		this.second = second
	}

	/**
	 * Visits handlers in priority order and retains the selected graph until release.
	 */
	override fn TryHandle() ServiceResult
	{
		if (this.selection != ServiceSelection.None) {
			return ServiceResult.Busy
		}

		var result = this.first.TryHandle()

		if (result == ServiceResult.Prepared) {
			this.selection = ServiceSelection.First;
			return result
		}

		if (result != ServiceResult.Ignored) {
			return result
		}

		result = this.second.TryHandle()

		if (result == ServiceResult.Prepared) {
			this.selection = ServiceSelection.Second
		}

		return result
	}

	/**
	 * Returns the selected handler for application-specific diagnostics.
	 */
	public fn GetSelection() ServiceSelection
	{
		return this.selection
	}

	/**
	 * Releases only the selected child after the caller has ended response borrows.
	 */
	override fn TryReleaseResponse() PacketDataResult
	{
		var result = PacketDataResult.Invalid

		if (this.selection == ServiceSelection.First) {
			result = this.first.TryReleaseResponse()
		}
		elif (this.selection == ServiceSelection.Second) {
			result = this.second.TryReleaseResponse()
		}

		if (result == PacketDataResult.Success) {
			this.selection = ServiceSelection.None
		}

		return result
	}

	/**
	 * Reports a selected, published response.
	 */
	override fn IsReady() bool
	{
		return this.selection != ServiceSelection.None
	}

	/**
	 * Returns the selected complete frame length, or zero with no selection.
	 */
	override fn GetAvailableLength() int
	{
		if (this.selection == ServiceSelection.First) {
			return this.first.GetAvailableLength()
		}

		if (this.selection == ServiceSelection.Second) {
			return this.second.GetAvailableLength()
		}

		return 0
	}

	/**
	 * Delegates bounded reads to the selected graph. No packet bytes are copied here.
	 */
	override fn TryRead(index: int, value: out byte) PacketDataResult
	{
		value = 0x00

		if (this.selection == ServiceSelection.First) {
			return this.first.TryRead(index, value)
		}

		if (this.selection == ServiceSelection.Second) {
			return this.second.TryRead(index, value)
		}

		return PacketDataResult.NotReady
	}
}