# Git Pivotal Tracker Integration
# Copyright (c) 2013 the original author or authors.
#
# 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.

require 'git-pivotal-tracker-integration/util/shell'
require 'git-pivotal-tracker-integration/util/util'

# Utilities for dealing with Git
class GitPivotalTrackerIntegration::Util::Git

  # Adds a Git hook to the current repository
  #
  # @param [String] name the name of the hook to add
  # @param [String] source the file to use as the source for the created hook
  # @param [Boolean] overwrite whether to overwrite the hook if it already exists
  # @return [void]
  def self.add_hook(name, source, overwrite = false)
    hooks_directory =  File.join repository_root, '.git', 'hooks'
    hook = File.join hooks_directory, name

    if overwrite || !File.exist?(hook)
      print "Creating Git hook #{name}...  "

      FileUtils.mkdir_p hooks_directory
      File.open(source, 'r') do |input|
        File.open(hook, 'w') do |output|
          output.write(input.read)
          output.chmod(0755)
        end
      end

      puts 'OK'
    end
  end

  # Returns the name of the currently checked out branch
  #
  # @return [String] the name of the currently checked out branch
  def self.branch_name
    GitPivotalTrackerIntegration::Util::Shell.exec('git branch').scan(/\* (.*)/)[0][0]
  end

  # Creates a branch with a given +name+.  First pulls the current branch to
  # ensure that it is up to date and then creates and checks out the new
  # branch.  If specified, sets branch-specific properties that are passed in.
  #
  # @param [String] name the name of the branch to create
  # @param [Boolean] print_messages whether to print messages
  # @return [void]
  def self.create_branch(name, print_messages = true)
    root_branch = branch_name
    root_remote = get_config KEY_REMOTE, :branch

    if print_messages; print "Pulling #{root_branch}... " end
    GitPivotalTrackerIntegration::Util::Shell.exec 'git pull --quiet --ff-only'
    if print_messages; puts 'OK'
    end

    if print_messages; print "Creating and checking out #{name}... " end
    GitPivotalTrackerIntegration::Util::Shell.exec "git checkout --quiet -b #{name}"
    set_config KEY_ROOT_BRANCH, root_branch, :branch
    set_config KEY_ROOT_REMOTE, root_remote, :branch
    if print_messages; puts 'OK'
    end
  end

  # Creates a commit with a given message.  The commit includes all change
  # files.
  #
  # @param [String] message The commit message, which will be appended with
  #   +[#<story-id]+
  # @param [PivotalTracker::Story] story the story associated with the current
  #   commit
  # @return [void]
  def self.create_commit(message, story)
    GitPivotalTrackerIntegration::Util::Shell.exec "git commit --quiet --all --allow-empty --message \"#{message}\n\n[##{story.id}]\""
  end

  # Creates a tag with the given name.  Before creating the tag, commits all
  # outstanding changes with a commit message that reflects that these changes
  # are for a release.
  #
  # @param [String] name the name of the tag to create
  # @param [PivotalTracker::Story] story the story associated with the current
  #   tag
  # @return [void]
  def self.create_release_tag(name, story)
    root_branch = branch_name

    print "Creating tag v#{name}... "

    create_branch RELEASE_BRANCH_NAME, false
    create_commit "#{name} Release", story
    GitPivotalTrackerIntegration::Util::Shell.exec "git tag v#{name}"
    GitPivotalTrackerIntegration::Util::Shell.exec "git checkout --quiet #{root_branch}"
    GitPivotalTrackerIntegration::Util::Shell.exec "git branch --quiet -D #{RELEASE_BRANCH_NAME}"

    puts 'OK'
  end

  # Returns a Git configuration value.  This value is read using the +git
  # config+ command. The scope of the value to read can be controlled with the
  # +scope+ parameter.
  #
  # @param [String] key the key of the configuration to retrieve
  # @param [:branch, :inherited] scope the scope to read the configuration from
  #   * +:branch+: equivalent to calling +git config branch.branch-name.key+
  #   * +:inherited+: equivalent to calling +git config key+
  # @return [String] the value of the configuration
  # @raise if the specified scope is not +:branch+ or +:inherited+
  def self.get_config(key, scope = :inherited)
    if :branch == scope
      GitPivotalTrackerIntegration::Util::Shell.exec("git config branch.#{branch_name}.#{key}", false).strip
    elsif :inherited == scope
      GitPivotalTrackerIntegration::Util::Shell.exec("git config #{key}", false).strip
    else
      raise "Unable to get Git configuration for scope '#{scope}'"
    end
  end

  # Merges the current branch to its root branch and deletes the current branch
  #
  # @param [PivotalTracker::Story] story the story associated with the current branch
  # @param [Boolean] no_complete whether to suppress the +Completes+ statement in the commit message
  # @return [void]
  def self.merge(story, no_complete)
    development_branch = branch_name
    root_branch = get_config KEY_ROOT_BRANCH, :branch

    print "Merging #{development_branch} to #{root_branch}... "
    GitPivotalTrackerIntegration::Util::Shell.exec "git checkout --quiet #{root_branch}"
    GitPivotalTrackerIntegration::Util::Shell.exec "git merge --quiet --no-ff -m \"Merge #{development_branch} to #{root_branch}\n\n[#{no_complete ? '' : 'Completes '}##{story.id}]\" #{development_branch}"
    puts 'OK'

    print "Deleting #{development_branch}... "
    GitPivotalTrackerIntegration::Util::Shell.exec "git branch --quiet -D #{development_branch}"
    puts 'OK'
  end

  # Push changes to the remote of the current branch
  #
  # @param [String] refs the explicit references to push
  # @return [void]
  def self.push(*refs)
    remote = get_config KEY_REMOTE, :branch

    print "Pushing to #{remote}... "
    GitPivotalTrackerIntegration::Util::Shell.exec "git push --quiet #{remote} " + refs.join(' ')
    puts 'OK'
  end

  # Returns the root path of the current Git repository.  The root is
  # determined by ascending the path hierarchy, starting with the current
  # working directory (+Dir#pwd+), until a directory is found that contains a
  # +.git/+ sub directory.
  #
  # @return [String] the root path of the Git repository
  # @raise if the current working directory is not in a Git repository
  def self.repository_root
    repository_root = Dir.pwd

    until Dir.entries(repository_root).any? { |child| File.directory?(child) && (child =~ /^.git$/) }
      next_repository_root = File.expand_path('..', repository_root)
      abort('Current working directory is not in a Git repository') unless repository_root != next_repository_root
      repository_root =  next_repository_root
    end

    repository_root
  end

  # Sets a Git configuration value.  This value is set using the +git config+
  # command.  The scope of the set value can be controlled with the +scope+
  # parameter.
  #
  # @param [String] key the key of configuration to store
  # @param [String] value the value of the configuration to store
  # @param [:branch, :global, :local] scope the scope to store the configuration value in.
  #   * +:branch+: equivalent to calling +git config --local branch.branch-name.key value+
  #   * +:global+: equivalent to calling +git config --global key value+
  #   * +:local+:  equivalent to calling +git config --local key value+
  # @return [void]
  # @raise if the specified scope is not +:branch+, +:global+, or +:local+
  def self.set_config(key, value, scope = :local)
    if :branch == scope
      GitPivotalTrackerIntegration::Util::Shell.exec "git config --local branch.#{branch_name}.#{key} #{value}"
    elsif :global == scope
      GitPivotalTrackerIntegration::Util::Shell.exec "git config --global #{key} #{value}"
    elsif :local == scope
      GitPivotalTrackerIntegration::Util::Shell.exec "git config --local #{key} #{value}"
    else
      raise "Unable to set Git configuration for scope '#{scope}'"
    end
  end

  # Checks whether merging the current branch back to its root branch would be
  # a trivial merge.  A trivial merge is defined as one where the net change
  # of the merge would be the same as the net change of the branch being
  # merged.  The easiest way to ensure that a merge is trivial is to rebase a
  # development branch onto the tip of its root branch.
  #
  # @return [void]
  def self.trivial_merge?
    development_branch = branch_name
    root_branch = get_config KEY_ROOT_BRANCH, :branch

    print "Checking for trivial merge from #{development_branch} to #{root_branch}... "

    GitPivotalTrackerIntegration::Util::Shell.exec "git checkout --quiet #{root_branch}"
    GitPivotalTrackerIntegration::Util::Shell.exec 'git pull --quiet --ff-only'
    GitPivotalTrackerIntegration::Util::Shell.exec "git checkout --quiet #{development_branch}"

    root_tip = GitPivotalTrackerIntegration::Util::Shell.exec "git rev-parse #{root_branch}"
    common_ancestor = GitPivotalTrackerIntegration::Util::Shell.exec "git merge-base #{root_branch} #{development_branch}"

    if root_tip != common_ancestor
      abort 'FAIL'
    end

    puts 'OK'
  end

  private

  KEY_REMOTE = 'remote'.freeze

  KEY_ROOT_BRANCH = 'root-branch'.freeze

  KEY_ROOT_REMOTE = 'root-remote'.freeze

  RELEASE_BRANCH_NAME = 'pivotal-tracker-release'.freeze

end