//
//  ComponentIdentifier.swift
//  FirebladeECS
//
//  Created by Christian Treffs on 20.08.19.
//

/// Identifies a component by it's meta type
public struct ComponentIdentifier {
    public typealias Identifier = Int
    public let id: Identifier
}

extension ComponentIdentifier {
    @usableFromInline
    init(_ componentType: (some Component).Type) {
        id = Self.makeRuntimeHash(componentType)
    }

    /// object identifier hash (only stable during runtime) - arbitrary hash is ok.
    static func makeRuntimeHash(_ componentType: (some Component).Type) -> Identifier {
        ObjectIdentifier(componentType).hashValue
    }

    typealias StableId = UInt64
    static func makeStableTypeHash(component: Component) -> StableId {
        let componentTypeString = String(describing: type(of: component))
        return StringHashing.singer_djb2(componentTypeString)
    }

    static func makeStableInstanceHash(component: Component, entityId: EntityIdentifier) -> StableId {
        let componentTypeString = String(describing: type(of: component)) + String(entityId.id)
        return StringHashing.singer_djb2(componentTypeString)
    }
}

extension ComponentIdentifier: Equatable {}
extension ComponentIdentifier: Hashable {}