// Sources/SwiftProtobufPluginLibrary/CodeGenerator.swift
//
// Copyright (c) 2014 - 2023 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
//
// -----------------------------------------------------------------------------
///
/// This provides the basic interface for writing a CodeGenerator.
///
// -----------------------------------------------------------------------------

import Foundation
import SwiftProtobuf

/// A protocol that generator should conform to then get easy support for
/// being a protocol buffer compiler pluign.
public protocol CodeGenerator {
    init()

    /// Generates code for the given proto files.
    ///
    /// - Parameters:
    ///   - parameter: The parameter (or paramenters) passed for the generator.
    ///       This is for parameters specific to this generator,
    ///       `parse(parameter:)` (below) can be used to split back out
    ///       multiple parameters into the combined for the protocol buffer
    ///       compiler uses.
    ///   - protoCompilerContext: Context information about the protocol buffer
    ///       compiler being used.
    ///   - generatorOutputs: A object that can be used to send back the
    ///       generated outputs.
    ///
    /// - Throws: Can throw any `Error` to fail generate. `String(describing:)`
    ///       will be called on the error to provide the error string reported
    ///       to the user attempting to generate sources.
    func generate(
        files: [FileDescriptor],
        parameter: any CodeGeneratorParameter,
        protoCompilerContext: any ProtoCompilerContext,
        generatorOutputs: any GeneratorOutputs
    ) throws

    /// The list of features this CodeGenerator support to be reported back to
    /// the protocol buffer compiler.
    var supportedFeatures: [Google_Protobuf_Compiler_CodeGeneratorResponse.Feature] { get }

    /// The Protobuf Edition range that this generator can handle. Attempting
    /// to generate for an Edition outside this range will cause protoc to
    /// error.
    var supportedEditionRange: ClosedRange<Google_Protobuf_Edition> { get }

    /// A list of extensions that define Custom Options
    /// (https://protobuf.dev/programming-guides/proto2/#customoptions) for this generator so
    /// they will be exposed on the `Descriptor` options.
    var customOptionExtensions: [any AnyMessageExtension] { get }

    /// If provided, the argument parsing will support `--version` and report
    /// this value.
    var version: String? { get }

    /// If provided and `printHelp` isn't provide, this value will be including in
    /// default output for the `--help` output.
    var projectURL: String? { get }

    /// If provided and `printHelp` isn't provide, this value will be including in
    /// default output for the `--help` output.
    var copyrightLine: String? { get }

    /// Will be called for `-h` or `--help`, should `print()` out whatever is
    /// desired; there is a default implementation that uses the above info
    /// when provided.
    func printHelp()
}

extension CommandLine {
    /// Get the command-line arguments passed to this process in a non mutable
    /// form. Idea from https://github.com/swiftlang/swift/issues/66213
    ///
    /// - Returns: An array of command-line arguments.
    fileprivate static let safeArguments: [String] =
        UnsafeBufferPointer(start: unsafeArgv, count: Int(argc)).compactMap {
            String(validatingUTF8: $0!)
        }
}

extension CodeGenerator {
    var programName: String {
        guard let name = CommandLine.safeArguments.first?.split(separator: "/").last else {
            return "<plugin>"
        }
        return String(name)
    }

    /// Runs as a protocol buffer compiler plugin based on the given arguments
    /// or falls back to `CommandLine.arguments`.
    public func main(_ args: [String]?) {
        let args = args ?? Array(CommandLine.safeArguments.dropFirst())

        for arg in args {
            if arg == "--version", let version = version {
                print("\(programName) \(version)")
                return
            }
            if arg == "-h" || arg == "--help" {
                printHelp()
                return
            }
            // Could look at bringing back the support for recorded requests, but
            // haven't needed it in a long time.
            var stderr = StandardErrorOutputStream()
            print("Unknown argument: \(arg)", to: &stderr)
            return
        }

        var extensionMap = SimpleExtensionMap()
        if !customOptionExtensions.isEmpty {
            for e in customOptionExtensions {
                // Don't include Google_Protobuf_FeatureSet, that will be handing via custom features.
                precondition(
                    e.messageType == Google_Protobuf_EnumOptions.self
                        || e.messageType == Google_Protobuf_EnumValueOptions.self
                        || e.messageType == Google_Protobuf_ExtensionRangeOptions.self
                        || e.messageType == Google_Protobuf_FieldOptions.self
                        || e.messageType == Google_Protobuf_FileOptions.self
                        || e.messageType == Google_Protobuf_MessageOptions.self
                        || e.messageType == Google_Protobuf_MethodOptions.self
                        || e.messageType == Google_Protobuf_OneofOptions.self
                        || e.messageType == Google_Protobuf_ServiceOptions.self,
                    "CodeGenerator `customOptionExtensions` must only extend the descriptor.proto 'Options' messages \(e.messageType)."
                )
            }
            extensionMap.insert(contentsOf: customOptionExtensions)
        }

        let request: Google_Protobuf_Compiler_CodeGeneratorRequest
        do {
            request = try Google_Protobuf_Compiler_CodeGeneratorRequest(
                serializedBytes: FileHandle.standardInput.readDataToEndOfFile(),
                extensions: extensionMap
            )
        } catch let e {
            var stderr = StandardErrorOutputStream()
            print("\(programName): Received an unparsable request from the compiler: \(e)", to: &stderr)
            return
        }

        let response = generateCode(request: request, generator: self)
        let serializedResponse: Data
        do {
            serializedResponse = try response.serializedBytes()
        } catch let e {
            var stderr = StandardErrorOutputStream()
            print("\(programName): Failure while serializing response: \(e)", to: &stderr)
            return
        }
        FileHandle.standardOutput.write(serializedResponse)
    }

    /// Runs as a protocol buffer compiler plugin; reading the generation request
    /// off stdin and sending the response on stdout.
    ///
    /// Instead of calling this, just add `@main` to your `CodeGenerator`.
    public static func main() {
        let generator = Self()
        generator.main(nil)
    }
}

// Provide default implementation for things so `CodeGenerator`s only have to
// provide them if they wish too.
extension CodeGenerator {
    public var supportedEditionRange: ClosedRange<Google_Protobuf_Edition> {
        // Default impl of unknown so generator don't have to provide this until
        // they support editions.
        Google_Protobuf_Edition.unknown...Google_Protobuf_Edition.unknown
    }
    public var customOptionExtensions: [any AnyMessageExtension] { [] }
    public var version: String? { nil }
    public var projectURL: String? { nil }
    public var copyrightLine: String? { nil }

    public func printHelp() {
        print("\(programName): A plugin for protoc and should not normally be run directly.")
        if let copyright = copyrightLine {
            print("\(copyright)")
        }
        if let projectURL = projectURL {
            print(
                """

                For more information on the usage of this plugin, please see:
                  \(projectURL)

                """
            )
        }
    }
}

/// Uses the given `Google_Protobuf_Compiler_CodeGeneratorRequest` and
/// `CodeGenerator` to get code generated and create the
/// `Google_Protobuf_Compiler_CodeGeneratorResponse`. If there is a failure,
/// the failure will be used in the response to be returned to the protocol
/// buffer compiler to then be reported.
///
/// - Parameters:
///   - request: The request proto as generated by the protocol buffer compiler.
///   - geneator: The `CodeGenerator` to use for generation.
///
/// - Returns a filled out response with the success or failure of the
///    generation.
public func generateCode(
    request: Google_Protobuf_Compiler_CodeGeneratorRequest,
    generator: any CodeGenerator
) -> Google_Protobuf_Compiler_CodeGeneratorResponse {

    var response = Google_Protobuf_Compiler_CodeGeneratorResponse()

    // TODO: Could supportedFeatures be completely handled within library?
    // - The only "hard" part around hiding the proto3 optional support is making
    //   sure the oneof index related bits aren't leaked from FieldDescriptors.
    //   Otherwise the oneof related apis could likely take over the "realOneof"
    //   jobs and just never vend the synthetic information.
    // - The editions support bit likely could be computed based on the values
    //   `supportedEditionRange` having been overridden.
    let supportedFeatures = generator.supportedFeatures
    response.supportedFeatures = supportedFeatures.reduce(0) { $0 | UInt64($1.rawValue) }

    if supportedFeatures.contains(.supportsEditions) {
        let supportedEditions = generator.supportedEditionRange
        precondition(
            supportedEditions.upperBound != .unknown,
            "For a CodeGenerator to support Editions, it must override `supportedEditionRange`"
        )
        precondition(
            DescriptorSet.bundledEditionsSupport.contains(supportedEditions.lowerBound),
            "A CodeGenerator can't claim to support an Edition before what the library supports: \(supportedEditions.lowerBound) vs \(DescriptorSet.bundledEditionsSupport)"
        )
        precondition(
            DescriptorSet.bundledEditionsSupport.contains(supportedEditions.upperBound),
            "A CodeGenerator can't claim to support an Edition after what the library supports: \(supportedEditions.upperBound) vs \(DescriptorSet.bundledEditionsSupport)"
        )
        response.minimumEdition = Int32(supportedEditions.lowerBound.rawValue)
        response.maximumEdition = Int32(supportedEditions.upperBound.rawValue)
    }

    // TODO: This will need update to language specific features.

    let descriptorSet = DescriptorSet(protos: request.protoFile)

    var files = [FileDescriptor]()
    for name in request.fileToGenerate {
        guard let fileDescriptor = descriptorSet.fileDescriptor(named: name) else {
            response.error =
                "protoc asked plugin to generate a file but did not provide a descriptor for the file: \(name)"
            return response
        }
        files.append(fileDescriptor)
    }

    let context = InternalProtoCompilerContext(request: request)
    let outputs = InternalGeneratorOutputs()
    let parameter = InternalCodeGeneratorParameter(request.parameter)

    do {
        try generator.generate(
            files: files,
            parameter: parameter,
            protoCompilerContext: context,
            generatorOutputs: outputs
        )
        response.file = outputs.files
    } catch let e {
        // Use the description from whatever the Generator threw as the error message.
        response.error = String(describing: e)
    }

    return response
}

// MARK: Internal supporting types

/// Internal implementation of `CodeGeneratorParameter` for
/// `generateCode(request:generator:)`
struct InternalCodeGeneratorParameter: CodeGeneratorParameter {
    let parameter: String

    init(_ parameter: String) {
        self.parameter = parameter
    }

    var parsedPairs: [(key: String, value: String)] {
        guard !parameter.isEmpty else {
            return []
        }
        let parts = parameter.components(separatedBy: ",")
        return parts.map { s -> (key: String, value: String) in
            guard let index = s.range(of: "=")?.lowerBound else {
                // Key only, no value ("baz" in example).
                return (trimWhitespace(s), "")
            }
            return (
                key: trimWhitespace(s[..<index]),
                value: trimWhitespace(s[s.index(after: index)...])
            )
        }
    }
}

/// Internal implementation of `ProtoCompilerContext` for
/// `generateCode(request:generator:)`
private struct InternalProtoCompilerContext: ProtoCompilerContext {
    let version: Google_Protobuf_Compiler_Version?

    init(request: Google_Protobuf_Compiler_CodeGeneratorRequest) {
        self.version = request.hasCompilerVersion ? request.compilerVersion : nil
    }
}

/// Internal implementation of `GeneratorOutputs` for
/// `generateCode(request:generator:)`
private final class InternalGeneratorOutputs: GeneratorOutputs {

    enum OutputError: Error, CustomStringConvertible {
        /// Attempt to add two files with the same name.
        case duplicateName(String)

        var description: String {
            switch self {
            case .duplicateName(let name):
                return "Generator tried to generate two files named \(name)."
            }
        }
    }

    var files: [Google_Protobuf_Compiler_CodeGeneratorResponse.File] = []
    private var fileNames: Set<String> = []

    func add(fileName: String, contents: String) throws {
        guard !fileNames.contains(fileName) else {
            throw OutputError.duplicateName(fileName)
        }
        fileNames.insert(fileName)
        files.append(
            Google_Protobuf_Compiler_CodeGeneratorResponse.File(
                name: fileName,
                content: contents
            )
        )
    }
}