blame.rb

require_relative "./base"
require_relative "../diff"
require_relative "../rev_list"

module Command
  class Blame < Base

    def run
      @lines   = []
      @commits = []
      @chain   = nil

      revs = ::RevList.new(repo, [@args.first])

      revs.each do |commit|
        tree_diff = revs.tree_diff(commit.parent, commit.oid)
        index_commit(commit, tree_diff.values.first)
        @commits << commit
      end

      @author_width = @commits.map { |c| c.author.name.size }.max
      @number_width = @lines.size.to_s.size

      setup_pager

      @lines.each_with_index do |(commit, line), i|
        print_line(commit, i + 1, line)
      end

      exit 0
    end

    private

    def index_commit(commit, entries)
      a, b = entries.map { |entry| read_blob(entry) }

      @next_chain = {}
      ::Diff.diff(a, b).each { |edit| index_edit(commit, edit) }
      @chain = @next_chain
    end

    def read_blob(entry)
      entry ? repo.database.load(entry.oid).data : ""
    end

    def index_edit(commit, edit)
      b_number = edit.b_line&.number
      number   = @chain ? @chain[b_number] : b_number

      return unless number

      case edit.type
      when :eql
        @next_chain[edit.a_line.number] = number
      when :ins
        @lines[number - 1] = [commit, edit.b_line.text]
      end
    end

    def print_line(commit, number, line)
      puts format("%s (%-#{ @author_width }s %s %#{ @number_width }d) %s",
                  commit.oid[0..7],
                  commit.author.name,
                  commit.author.time.strftime("%Y-%m-%d %H:%M:%S %z"),
                  number, 
                  line)
    end

  end
end