//
//  Nexus.swift
//  FirebladeECS
//
//  Created by Christian Treffs on 09.10.17.
//

public final class Nexus {
    /// - Key: ComponentIdentifier aka component type.
    /// - Value: Array of component instances of same type (uniform).
    ///          New component instances are appended.
    @usableFromInline final var componentsByType: [ComponentIdentifier: ManagedContiguousArray<Component>]

    /// - Key: EntityIdentifier aka entity index
    /// - Value: Set of unique component types (ComponentIdentifier).
    ///          Each element is a component identifier associated with this entity.
    @usableFromInline final var componentIdsByEntity: [EntityIdentifier: Set<ComponentIdentifier>]

    /// - Key: FamilyTraitSet aka component types that make up one distinct family.
    /// - Value: Tightly packed EntityIdentifiers that represent the association of an entity to the family.
    @usableFromInline final var familyMembersByTraits: [FamilyTraitSet: UnorderedSparseSet<EntityIdentifier, EntityIdentifier.Identifier>]

    /// The entity identifier generator responsible for providing unique ids for entities during runtime.
    ///
    /// Provide a custom implementation prior to entity creation.
    /// Defaults to `DefaultEntityIdGenerator`.
    public final var entityIdGenerator: EntityIdentifierGenerator

    /// The coding strategy used to encode/decode entities from/into families.
    ///
    /// Provide a custom implementation prior to encoding/decoding.
    /// Defaults to `DefaultCodingStrategy`.
    public final var codingStrategy: CodingStrategy

    public final weak var delegate: NexusEventDelegate?

    public convenience init() {
        self.init(componentsByType: [:],
                  componentsByEntity: [:],
                  entityIdGenerator: DefaultEntityIdGenerator(),
                  familyMembersByTraits: [:],
                  codingStrategy: DefaultCodingStrategy())
    }

    init(componentsByType: [ComponentIdentifier: ManagedContiguousArray<Component>],
         componentsByEntity: [EntityIdentifier: Set<ComponentIdentifier>],
         entityIdGenerator: EntityIdentifierGenerator,
         familyMembersByTraits: [FamilyTraitSet: UnorderedSparseSet<EntityIdentifier, EntityIdentifier.Identifier>],
         codingStrategy: CodingStrategy)
    {
        self.componentsByType = componentsByType
        componentIdsByEntity = componentsByEntity
        self.familyMembersByTraits = familyMembersByTraits
        self.entityIdGenerator = entityIdGenerator
        self.codingStrategy = codingStrategy
    }

    deinit {
        clear()
    }

    public final func clear() {
        componentsByType.removeAll()
        componentIdsByEntity.removeAll()
        familyMembersByTraits.removeAll()
    }
}

// MARK: - CustomDebugStringConvertible

extension Nexus: CustomDebugStringConvertible {
    public var debugDescription: String {
        "<Nexus entities:\(numEntities) components:\(numComponents) families:\(numFamilies)>"
    }
}

// MARK: - default coding strategy

public struct DefaultCodingStrategy: CodingStrategy {
    public init() {}

    public func codingKey<C>(for componentType: C.Type) -> DynamicCodingKey where C: Component {
        DynamicCodingKey(stringValue: "\(C.self)").unsafelyUnwrapped
    }
}