// Sources/SwiftProtobuf/MessageExtension.swift - Extension support

//

// Copyright (c) 2014 - 2016 Apple Inc. and the project authors

// Licensed under Apache License v2.0 with Runtime Library Exception

//

// See LICENSE.txt for license information:

// https://github.com/apple/swift-protobuf/blob/main/LICENSE.txt

//

// -----------------------------------------------------------------------------

///

/// A 'Message Extension' is an immutable class object that describes

/// a particular extension field, including string and number

/// identifiers, serialization details, and the identity of the

/// message that is being extended.

///

// -----------------------------------------------------------------------------

/// Type-erased MessageExtension field implementation.

@preconcurrency

public protocol AnyMessageExtension: Sendable {

    var fieldNumber: Int { get }

    var fieldName: String { get }

    var messageType: any Message.Type { get }

    func _protobuf_newField<D: Decoder>(decoder: inout D) throws -> (any AnyExtensionField)?

}

/// A "Message Extension" relates a particular extension field to

/// a particular message.  The generic constraints allow

/// compile-time compatibility checks.

public final class MessageExtension<FieldType: ExtensionField, MessageType: Message>: AnyMessageExtension {

    public let fieldNumber: Int

    public let fieldName: String

    public let messageType: any Message.Type

    public init(_protobuf_fieldNumber: Int, fieldName: String) {

        self.fieldNumber = _protobuf_fieldNumber

        self.fieldName = fieldName

        self.messageType = MessageType.self

    }

    public func _protobuf_newField<D: Decoder>(decoder: inout D) throws -> (any AnyExtensionField)? {

        try FieldType(protobufExtension: self, decoder: &decoder)

    }

}