Sources/ApacheBeam/Internal/PipelineProto+Initializers.swift

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 *  License); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an  AS IS BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/// An enumeration for representing various elements of a pipeline protocol buffer. This enum is used
/// when constructing the pipeline for submission to a portable runner.
enum PipelineComponent {
    case none
    case transform(String, PTransformProto)
    case collection(String, PCollectionProto)
    case coder(String, CoderProto)
    case windowingStrategy(String, WindowingStrategyProto)
    case environment(String, EnvironmentProto)
    
    /// The name of the pipeline component. Most components in the protocol buffer have a name used to reference the component throughout the pipeline structure.
    var name: String {
        switch self {
        case .none:
            fatalError("PipelineComponent not properly initialized")
        case let .transform(n, _):
            n
        case let .collection(n, _):
            n
        case let .coder(n, _):
            n
        case let .windowingStrategy(n, _):
            n
        case let .environment(n, _):
            n
        }
    }

    
    /// The PTransfrom protocol buffer for this component. Returns ``nil`` for everything except a ``transform`` type.
    var transform: PTransformProto? {
        if case let .transform(_, pTransformProto) = self {
            return pTransformProto
        } else {
            return nil
        }
    }
}

// Convenience function for creating new pipeline elements. Note that these shouldn't be accessed concurrently
// but this isn't a problem itself since trying to access the proto concurrently throws an error.
extension PipelineProto {
    
    /// Adds a new `PTransform` protocol buffer to the pipeline along with an internal reference name to be used by other parts of the pipeline.
    /// - Parameter mapper: A closure that returns the `PTransform` protocol buffer. Includes the reference id as a parameter in case it is needed.
    /// - Returns: A ``PipelineComponent`` representing this `PTransform`
    mutating func transform(_ mapper: @escaping (String) throws -> PTransformProto) throws -> PipelineComponent {
        let name = "ref_PTransform_\(components.transforms.count + 1)"
        let proto = try mapper(name)
        components.transforms[name] = proto
        return .transform(name, proto)
    }
    
    /// Adds a new `PCollection` protocol buffer to the pipeline along with an internal reference name to be used elsewhere (e.g. `PTransform`s)
    /// - Parameter mapper: A closure that returns the `PCollection` protocol buffer. It is passed the reference name in case that is useful
    /// - Returns: A ``PipelineComponent`` representing the `PCollection`
    mutating func collection(_ mapper: @escaping (String) throws -> PCollectionProto) throws -> PipelineComponent {
        let name = "ref_PCollection_\(components.pcollections.count + 1)"
        let proto = try mapper(name)
        components.pcollections[name] = proto
        return .collection(name, proto)
    }

    mutating func coder(_ mapper: @escaping (String) -> CoderProto) -> PipelineComponent {
        let name = "ref_Coder_\(components.coders.count + 1)"
        let proto = mapper(name)
        components.coders[name] = proto
        return .coder(name, proto)
    }

    mutating func windowingStrategy(_ mapper: @escaping (String) -> WindowingStrategyProto) -> PipelineComponent {
        let name = "ref_WindowingStrategy_\(components.coders.count + 1)"
        let proto = mapper(name)
        components.windowingStrategies[name] = proto
        return .windowingStrategy(name, proto)
    }

    mutating func environment(_ mapper: @escaping (String) throws -> EnvironmentProto) throws -> PipelineComponent {
        let name = "ref_Environment_\(components.coders.count + 1)"
        let proto = try mapper(name)
        components.environments[name] = proto
        return .environment(name, proto)
    }
}