//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

import Foundation
import LSPLogging
import LanguageServerProtocol
import SKSupport

import struct TSCBasic.AbsolutePath
import protocol TSCBasic.FileSystem
import struct TSCBasic.RelativePath
import var TSCBasic.localFileSystem
import func TSCBasic.resolveSymlinks

/// A single compilation database command.
///
/// See https://clang.llvm.org/docs/JSONCompilationDatabase.html
public struct CompilationDatabaseCompileCommand: Equatable {

  /// The working directory for the compilation.
  public var directory: String

  /// The path of the main file for the compilation, which may be relative to `directory`.
  public var filename: String

  /// The compile command as a list of strings, with the program name first.
  public var commandLine: [String]

  /// The name of the build output, or nil.
  public var output: String? = nil

  public init(directory: String, filename: String, commandLine: [String], output: String? = nil) {
    self.directory = directory
    self.filename = filename
    self.commandLine = commandLine
    self.output = output
  }
}

extension CompilationDatabase.Command {

  /// The `DocumentURI` for this file. If `filename` is relative and `directory` is
  /// absolute, returns the concatenation. However, if both paths are relative,
  /// it falls back to `filename`, which is more likely to be the identifier
  /// that a caller will be looking for.
  public var uri: DocumentURI {
    if filename.hasPrefix("/") || !directory.hasPrefix("/") {
      return DocumentURI(filePath: filename, isDirectory: false)
    } else {
      return DocumentURI(URL(fileURLWithPath: directory).appendingPathComponent(filename, isDirectory: false))
    }
  }
}

/// A clang-compatible compilation database.
///
/// See https://clang.llvm.org/docs/JSONCompilationDatabase.html
public protocol CompilationDatabase {
  typealias Command = CompilationDatabaseCompileCommand
  subscript(_ uri: DocumentURI) -> [Command] { get }
  var allCommands: AnySequence<Command> { get }
}

/// Loads the compilation database located in `directory`, if one can be found in `additionalSearchPaths` or in the default search paths of "." and "build".
public func tryLoadCompilationDatabase(
  directory: AbsolutePath,
  additionalSearchPaths: [RelativePath] = [],
  _ fileSystem: FileSystem = localFileSystem
) -> CompilationDatabase? {
  let searchPaths =
    additionalSearchPaths + [
      // These default search paths match the behavior of `clangd`
      try! RelativePath(validating: "."),
      try! RelativePath(validating: "build"),
    ]
  return
    searchPaths
    .lazy
    .map { directory.appending($0) }
    .compactMap { searchPath in
      orLog("Failed to load compilation database") { () -> CompilationDatabase? in
        if let compDb = try JSONCompilationDatabase(directory: searchPath, fileSystem) {
          return compDb
        }
        if let compDb = try FixedCompilationDatabase(directory: searchPath, fileSystem) {
          return compDb
        }
        return nil
      }
    }
    .first
}

/// Fixed clang-compatible compilation database (compile_flags.txt).
///
/// Each line in the file becomes a command line argument. Example:
/// ```
/// -xc++
/// -I
/// libwidget/include/
/// ```
///
/// See https://clang.llvm.org/docs/JSONCompilationDatabase.html under Alternatives
public struct FixedCompilationDatabase: CompilationDatabase, Equatable {
  public var allCommands: AnySequence<CompilationDatabaseCompileCommand> { AnySequence([]) }

  private let fixedArgs: [String]
  private let directory: String

  public subscript(path: DocumentURI) -> [CompilationDatabaseCompileCommand] {
    [Command(directory: directory, filename: path.pseudoPath, commandLine: fixedArgs + [path.pseudoPath])]
  }
}

extension FixedCompilationDatabase {
  /// Loads the compilation database located in `directory`, if any.
  /// - Returns: `nil` if `compile_flags.txt` was not found
  public init?(directory: AbsolutePath, _ fileSystem: FileSystem = localFileSystem) throws {
    let path = directory.appending(component: "compile_flags.txt")
    try self.init(file: path, fileSystem)
  }

  /// Loads the compilation database from `file`
  /// - Returns: `nil` if the file does not exist
  public init?(file: AbsolutePath, _ fileSystem: FileSystem = localFileSystem) throws {
    self.directory = file.dirname

    guard fileSystem.exists(file) else {
      return nil
    }
    let bytes = try fileSystem.readFileContents(file)

    var fixedArgs: [String] = ["clang"]
    try bytes.withUnsafeData { data in
      guard let fileContents = String(data: data, encoding: .utf8) else {
        throw CompilationDatabaseDecodingError.fixedDatabaseDecodingError
      }

      fileContents.enumerateLines { line, _ in
        fixedArgs.append(line.trimmingCharacters(in: .whitespacesAndNewlines))
      }
    }
    self.fixedArgs = fixedArgs
  }
}

/// The JSON clang-compatible compilation database.
///
/// Example:
///
/// ```
/// [
///   {
///     "directory": "/src",
///     "file": "/src/file.cpp",
///     "command": "clang++ file.cpp"
///   }
/// ]
/// ```
///
/// See https://clang.llvm.org/docs/JSONCompilationDatabase.html
public struct JSONCompilationDatabase: CompilationDatabase, Equatable {
  var pathToCommands: [DocumentURI: [Int]] = [:]
  var commands: [CompilationDatabaseCompileCommand] = []

  public init(_ commands: [CompilationDatabaseCompileCommand] = []) {
    for command in commands {
      add(command)
    }
  }

  public subscript(_ uri: DocumentURI) -> [CompilationDatabaseCompileCommand] {
    if let indices = pathToCommands[uri] {
      return indices.map { commands[$0] }
    }
    if let fileURL = uri.fileURL, let indices = pathToCommands[DocumentURI(fileURL.resolvingSymlinksInPath())] {
      return indices.map { commands[$0] }
    }
    return []
  }

  public var allCommands: AnySequence<CompilationDatabaseCompileCommand> { AnySequence(commands) }

  public mutating func add(_ command: CompilationDatabaseCompileCommand) {
    let uri = command.uri
    pathToCommands[uri, default: []].append(commands.count)

    if let fileURL = uri.fileURL,
      let symlinksResolved = try? resolveSymlinks(AbsolutePath(validating: fileURL.path))
    {
      let canonical = DocumentURI(filePath: symlinksResolved.pathString, isDirectory: false)
      if canonical != uri {
        pathToCommands[canonical, default: []].append(commands.count)
      }
    }

    commands.append(command)
  }
}

extension JSONCompilationDatabase: Codable {
  public init(from decoder: Decoder) throws {
    var container = try decoder.unkeyedContainer()
    while !container.isAtEnd {
      self.add(try container.decode(Command.self))
    }
  }

  public func encode(to encoder: Encoder) throws {
    var container = encoder.unkeyedContainer()
    try commands.forEach { try container.encode($0) }
  }
}

extension JSONCompilationDatabase {
  /// Loads the compilation database located in `directory`, if any.
  ///
  /// - Returns: `nil` if `compile_commands.json` was not found
  public init?(directory: AbsolutePath, _ fileSystem: FileSystem = localFileSystem) throws {
    let path = directory.appending(component: "compile_commands.json")
    try self.init(file: path, fileSystem)
  }

  /// Loads the compilation database from `file`
  /// - Returns: `nil` if the file does not exist
  public init?(file: AbsolutePath, _ fileSystem: FileSystem = localFileSystem) throws {
    guard fileSystem.exists(file) else {
      return nil
    }
    let bytes = try fileSystem.readFileContents(file)
    try bytes.withUnsafeData { data in
      self = try JSONDecoder().decode(JSONCompilationDatabase.self, from: data)
    }
  }
}

enum CompilationDatabaseDecodingError: Error {
  case missingCommandOrArguments
  case fixedDatabaseDecodingError
}

extension CompilationDatabase.Command: Codable {
  private enum CodingKeys: String, CodingKey {
    case directory
    case file
    case command
    case arguments
    case output
  }

  public init(from decoder: Decoder) throws {
    let container = try decoder.container(keyedBy: CodingKeys.self)
    self.directory = try container.decode(String.self, forKey: .directory)
    self.filename = try container.decode(String.self, forKey: .file)
    self.output = try container.decodeIfPresent(String.self, forKey: .output)
    if let arguments = try container.decodeIfPresent([String].self, forKey: .arguments) {
      self.commandLine = arguments
    } else if let command = try container.decodeIfPresent(String.self, forKey: .command) {
      #if os(Windows)
      self.commandLine = splitWindowsCommandLine(command, initialCommandName: true)
      #else
      self.commandLine = splitShellEscapedCommand(command)
      #endif
    } else {
      throw CompilationDatabaseDecodingError.missingCommandOrArguments
    }
  }

  public func encode(to encoder: Encoder) throws {
    var container = encoder.container(keyedBy: CodingKeys.self)
    try container.encode(directory, forKey: .directory)
    try container.encode(filename, forKey: .file)
    try container.encode(commandLine, forKey: .arguments)
    try container.encodeIfPresent(output, forKey: .output)
  }
}