/*
 * Copyright 2022, gRPC Authors All rights reserved.
 *
 * Licensed 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.
 */

import Foundation
import PackagePlugin

@main
struct GRPCSwiftPlugin: BuildToolPlugin {
  /// Errors thrown by the `GRPCSwiftPlugin`
  enum PluginError: Error {
    /// Indicates that the target where the plugin was applied to was not `SourceModuleTarget`.
    case invalidTarget
    /// Indicates that the file extension of an input file was not `.proto`.
    case invalidInputFileExtension
  }

  /// The configuration of the plugin.
  struct Configuration: Codable {
    /// Encapsulates a single invocation of protoc.
    struct Invocation: Codable {
      /// The visibility of the generated files.
      enum Visibility: String, Codable {
        /// The generated files should have `internal` access level.
        case `internal`
        /// The generated files should have `public` access level.
        case `public`
      }

      /// An array of paths to `.proto` files for this invocation.
      var protoFiles: [String]
      /// The visibility of the generated files.
      var visibility: Visibility?
      /// Whether server code is generated.
      var server: Bool?
      /// Whether client code is generated.
      var client: Bool?
      /// Determines whether the casing of generated function names is kept.
      var keepMethodCasing: Bool?
    }

    /// The path to the `protoc` binary.
    ///
    /// If this is not set, SPM will try to find the tool itself.
    var protocPath: String?

    /// A list of invocations of `protoc` with the `GRPCSwiftPlugin`.
    var invocations: [Invocation]
  }

  static let configurationFileName = "grpc-swift-config.json"

  func createBuildCommands(context: PluginContext, target: Target) throws -> [Command] {
    // Let's check that this is a source target
    guard let target = target as? SourceModuleTarget else {
      throw PluginError.invalidTarget
    }

    // We need to find the configuration file at the root of the target
    let configurationFilePath = target.directory.appending(subpath: Self.configurationFileName)
    let data = try Data(contentsOf: URL(fileURLWithPath: "\(configurationFilePath)"))
    let configuration = try JSONDecoder().decode(Configuration.self, from: data)

    try self.validateConfiguration(configuration)

    // We need to find the path of protoc and protoc-gen-grpc-swift
    let protocPath: Path
    if let configuredProtocPath = configuration.protocPath {
      protocPath = Path(configuredProtocPath)
    } else if let environmentPath = ProcessInfo.processInfo.environment["PROTOC_PATH"] {
      // The user set the env variable, so let's take that
      protocPath = Path(environmentPath)
    } else {
      // The user didn't set anything so let's try see if SPM can find a binary for us
      protocPath = try context.tool(named: "protoc").path
    }
    let protocGenGRPCSwiftPath = try context.tool(named: "protoc-gen-grpc-swift").path

    // This plugin generates its output into GeneratedSources
    let outputDirectory = context.pluginWorkDirectory

    return configuration.invocations.map { invocation in
      self.invokeProtoc(
        target: target,
        invocation: invocation,
        protocPath: protocPath,
        protocGenGRPCSwiftPath: protocGenGRPCSwiftPath,
        outputDirectory: outputDirectory
      )
    }
  }

  /// Invokes `protoc` with the given inputs
  ///
  /// - Parameters:
  ///   - target: The plugin's target.
  ///   - invocation: The `protoc` invocation.
  ///   - protocPath: The path to the `protoc` binary.
  ///   - protocGenSwiftPath: The path to the `protoc-gen-swift` binary.
  ///   - outputDirectory: The output directory for the generated files.
  /// - Returns: The build command.
  private func invokeProtoc(
    target: Target,
    invocation: Configuration.Invocation,
    protocPath: Path,
    protocGenGRPCSwiftPath: Path,
    outputDirectory: Path
  ) -> Command {
    // Construct the `protoc` arguments.
    var protocArgs = [
      "--plugin=protoc-gen-grpc-swift=\(protocGenGRPCSwiftPath)",
      "--grpc-swift_out=\(outputDirectory)",
      // We include the target directory as a proto search path
      "-I",
      "\(target.directory)",
    ]

    if let visibility = invocation.visibility {
      protocArgs.append("--grpc-swift_opt=Visibility=\(visibility.rawValue.capitalized)")
    }

    if let generateServerCode = invocation.server {
      protocArgs.append("--grpc-swift_opt=Server=\(generateServerCode)")
    }

    if let generateClientCode = invocation.client {
      protocArgs.append("--grpc-swift_opt=Client=\(generateClientCode)")
    }

    if let keepMethodCasingOption = invocation.keepMethodCasing {
      protocArgs.append("--grpc-swift_opt=KeepMethodCasing=\(keepMethodCasingOption)")
    }

    var inputFiles = [Path]()
    var outputFiles = [Path]()

    for var file in invocation.protoFiles {
      // Append the file to the protoc args so that it is used for generating
      protocArgs.append("\(file)")
      inputFiles.append(target.directory.appending(file))

      // The name of the output file is based on the name of the input file.
      // We validated in the beginning that every file has the suffix of .proto
      // This means we can just drop the last 5 elements and append the new suffix
      file.removeLast(5)
      file.append("grpc.swift")
      let protobufOutputPath = outputDirectory.appending(file)

      // Add the outputPath as an output file
      outputFiles.append(protobufOutputPath)
    }

    // Construct the command. Specifying the input and output paths lets the build
    // system know when to invoke the command. The output paths are passed on to
    // the rule engine in the build system.
    return Command.buildCommand(
      displayName: "Generating gRPC Swift files from proto files",
      executable: protocPath,
      arguments: protocArgs,
      inputFiles: inputFiles + [protocGenGRPCSwiftPath],
      outputFiles: outputFiles
    )
  }

  /// Validates the configuration file for various user errors.
  private func validateConfiguration(_ configuration: Configuration) throws {
    for invocation in configuration.invocations {
      for protoFile in invocation.protoFiles {
        if !protoFile.hasSuffix(".proto") {
          throw PluginError.invalidInputFileExtension
        }
      }
    }
  }
}