const fs = require('fs')
const { Directory } = require('pathwatcher')
const GitRepository = require('./git-repository')

const GIT_FILE_REGEX = RegExp('^gitdir: (.+)')

// Returns the .gitdir path in the agnostic Git symlink .git file given, or
// null if the path is not a valid gitfile.
//
// * `gitFile` {String} path of gitfile to parse
function pathFromGitFileSync (gitFile) {
  try {
    const gitFileBuff = fs.readFileSync(gitFile, 'utf8')
    return gitFileBuff != null ? gitFileBuff.match(GIT_FILE_REGEX)[1] : null
  } catch (error) {}
}

// Returns a {Promise} that resolves to the .gitdir path in the agnostic
// Git symlink .git file given, or null if the path is not a valid gitfile.
//
// * `gitFile` {String} path of gitfile to parse
function pathFromGitFile (gitFile) {
  return new Promise(resolve => {
    fs.readFile(gitFile, 'utf8', (err, gitFileBuff) => {
      if (err == null && gitFileBuff != null) {
        const result = gitFileBuff.toString().match(GIT_FILE_REGEX)
        resolve(result != null ? result[1] : null)
      } else {
        resolve(null)
      }
    })
  })
}

// Checks whether a valid `.git` directory is contained within the given
// directory or one of its ancestors. If so, a Directory that corresponds to the
// `.git` folder will be returned. Otherwise, returns `null`.
//
// * `directory` {Directory} to explore whether it is part of a Git repository.
function findGitDirectorySync (directory) {
  // TODO: Fix node-pathwatcher/src/directory.coffee so the following methods
  // can return cached values rather than always returning new objects:
  // getParent(), getFile(), getSubdirectory().
  let gitDir = directory.getSubdirectory('.git')
  if (typeof gitDir.getPath === 'function') {
    const gitDirPath = pathFromGitFileSync(gitDir.getPath())
    if (gitDirPath) {
      gitDir = new Directory(directory.resolve(gitDirPath))
    }
  }
  if (
    typeof gitDir.existsSync === 'function' &&
    gitDir.existsSync() &&
    isValidGitDirectorySync(gitDir)
  ) {
    return gitDir
  } else if (directory.isRoot()) {
    return null
  } else {
    return findGitDirectorySync(directory.getParent())
  }
}

// Checks whether a valid `.git` directory is contained within the given
// directory or one of its ancestors. If so, a Directory that corresponds to the
// `.git` folder will be returned. Otherwise, returns `null`.
//
// Returns a {Promise} that resolves to
// * `directory` {Directory} to explore whether it is part of a Git repository.
async function findGitDirectory (directory) {
  // TODO: Fix node-pathwatcher/src/directory.coffee so the following methods
  // can return cached values rather than always returning new objects:
  // getParent(), getFile(), getSubdirectory().
  let gitDir = directory.getSubdirectory('.git')
  if (typeof gitDir.getPath === 'function') {
    const gitDirPath = await pathFromGitFile(gitDir.getPath())
    if (gitDirPath) {
      gitDir = new Directory(directory.resolve(gitDirPath))
    }
  }
  if (
    typeof gitDir.exists === 'function' &&
    (await gitDir.exists()) &&
    isValidGitDirectory(gitDir)
  ) {
    return gitDir
  } else if (directory.isRoot()) {
    return null
  } else {
    return await findGitDirectory(directory.getParent())
  }
}

// Returns a boolean indicating whether the specified directory represents a Git
// repository.
//
// * `directory` {Directory} whose base name is `.git`.
function isValidGitDirectorySync (directory) {
  // To decide whether a directory has a valid .git folder, we use
  // the heuristic adopted by the valid_repository_path() function defined in
  // node_modules/git-utils/deps/libgit2/src/repository.c.
  return (
    directory.getSubdirectory('objects').existsSync() &&
    directory.getFile('HEAD').existsSync() &&
    directory.getSubdirectory('refs').existsSync()
  )
}

// Returns a {Promise} that resolves to a {Boolean} indicating whether the
// specified directory represents a Git repository.
//
// * `directory` {Directory} whose base name is `.git`.
async function isValidGitDirectory (directory) {
  // To decide whether a directory has a valid .git folder, we use
  // the heuristic adopted by the valid_repository_path() function defined in
  // node_modules/git-utils/deps/libgit2/src/repository.c.
  return (
    (await directory.getSubdirectory('objects').exists()) &&
    (await directory.getFile('HEAD').exists()) &&
    (await directory.getSubdirectory('refs').exists())
  )
}

// Provider that conforms to the atom.repository-provider@0.1.0 service.
class GitRepositoryProvider {
  constructor (project, config) {
    // Keys are real paths that end in `.git`.
    // Values are the corresponding GitRepository objects.
    this.project = project
    this.config = config
    this.pathToRepository = {}
  }

  // Returns a {Promise} that resolves with either:
  // * {GitRepository} if the given directory has a Git repository.
  // * `null` if the given directory does not have a Git repository.
  async repositoryForDirectory (directory) {
    // Only one GitRepository should be created for each .git folder. Therefore,
    // we must check directory and its parent directories to find the nearest
    // .git folder.
    const gitDir = await findGitDirectory(directory)
    return this.repositoryForGitDirectory(gitDir)
  }

  // Returns either:
  // * {GitRepository} if the given directory has a Git repository.
  // * `null` if the given directory does not have a Git repository.
  repositoryForDirectorySync (directory) {
    // Only one GitRepository should be created for each .git folder. Therefore,
    // we must check directory and its parent directories to find the nearest
    // .git folder.
    const gitDir = findGitDirectorySync(directory)
    return this.repositoryForGitDirectory(gitDir)
  }

  // Returns either:
  // * {GitRepository} if the given Git directory has a Git repository.
  // * `null` if the given directory does not have a Git repository.
  repositoryForGitDirectory (gitDir) {
    if (!gitDir) {
      return null
    }

    const gitDirPath = gitDir.getPath()
    let repo = this.pathToRepository[gitDirPath]
    if (!repo) {
      repo = GitRepository.open(gitDirPath, { project: this.project, config: this.config })
      if (!repo) {
        return null
      }
      repo.onDidDestroy(() => delete this.pathToRepository[gitDirPath])
      this.pathToRepository[gitDirPath] = repo
      repo.refreshIndex()
      repo.refreshStatus()
    }
    return repo
  }
}

module.exports = GitRepositoryProvider
