module Prick
  module SubCommand
    def self.create_migration(username, from_version, force: false, file: nil)
      constrain from_version, PrickVersion
      Git.clean? or raise "Won't migrate: Repository is dirty"
      Git.synchronized? or raise "Won't migrate: Repository is not synchronized"

      from_version != PrickVersion.zero or raise Prick::Error, "Can't migrate from release 0.0.0"
      to_version = Prick.state.version
      migration_dir = "#{MIGRATION_DIR}/#{from_version}"
      migration_exist = File.directory? migration_dir
      force || file || !migration_exist or raise Prick::Fail, "Migration #{from_version} exists"

      $quiet = true if file

      if file && migration_exist
        File.open(file, "w") { |file|
          for diff_file in DIFF_FILES
            file.write File.read("#{migration_dir}/#{diff_file}")
          end
        }
      else
        from_version != to_version or raise Prick::Fail, "Can't migrate to same release"
        from_version < to_version or raise Prick::Fail, "Can't migrate backwards (why not?)"

        diff = nil
        if force || !migration_exist
          from_db = "#{Prick.state.name}-#{from_version}"
          to_db = "#{Prick.state.name}-#{to_version}"

          mesg "Migrating from #{from_version} to #{to_version}"
          begin
            origin = Git.origin

            # Local repos are supported to ease testing
            if File.directory?(origin)
              origin = File.expand_path(origin)
            end

            diff = Dir.mktmpdir { |tmpdir|
                Dir.chdir(tmpdir) {
                mesg "  Building #{from_db}"
                Git.clone(origin, from_version, branch: from_version)
                Dir.chdir(from_version.to_s) { build(from_db, username, nil) }
              }

              mesg "  Building #{to_db}"
              build(to_db, username, nil)

              mesg "  Creating diff"
              Diff.new(from_db, to_db)
            }
            !diff.same? or raise Prick::Fail, "No changes"
          ensure
            drop_all(from_db)
            drop_all(to_db)
          end
        end

        diff.write(file) if file
      end

      if file
        File.open(file, "a") { |f| 
          f.puts "-- UPDATE VERSION"
          f.puts File.readlines(SCHEMA_VERSION_PATH).grep_v(/^--/)
        }
      else
        FileUtils.rm_rf migration_dir if force
        FileUtils.mkdir_p migration_dir
        Command.command "cp -a #{SHARE_PATH}/migrate/migration/. #{migration_dir}"
        Dir.chdir(migration_dir) { diff.write(*DIFF_FILES, mark: true) }
      end 
    end
  end
end