require 'shellwords'

class Blamify
  PORCELAIN_COMMIT_HASH_RE = /^(?<hash>\h{40})\s/
  PORCELAIN_LINE_RE = /^\t(?<line>.*)$/
  COLORS = (237..255).to_a # Greyscale gradient

  def initialize(filename)
    @filename = filename
  end

  def print(output = $stdout)
    committer_times = blames.map { |blame| blame[:committer_time].to_i }
    min_time = committer_times.min
    max_time = committer_times.max
    timespan = max_time - min_time
    mid_time = min_time + timespan / 2

    blames.each do |blame|
      committer_time = blame[:committer_time].to_i
      offset = committer_time - min_time
      Time.at(committer_time)
      color = color_at(offset / timespan.to_f)

      author = blame.fetch(:author, "")
      output.puts format("\e[38;5;%dm%-14s: %s\e[0m", color, author[0, 14], blame[:line])
    end
  end

  private

  def color_at(x)
    x = 0 if x.nan?
    x = [[x, 0.0].max, 1.0].min # Clamp to (0.0, 1.0)
    COLORS[(x * COLORS.size.pred).floor]
  end

  def blames
    @blames ||= load_blames
  end

  def load_blames
    blame_data = {}

    load_porcelain.lines.each_with_object([]) do |line, blames|
      case line
      when PORCELAIN_COMMIT_HASH_RE
        blame_data[:commit] = $~[:hash]
      when PORCELAIN_LINE_RE
        blames << blame_data.merge(line: $~[:line])
      else # Key/value
        key, value = line.chomp.split(' ', 2)
        key.tr!('-', '_')

        blame_data[key.to_sym] = value
      end
    end
  end

  def load_porcelain
    `#{ Shellwords.shelljoin(['git', 'blame', '-p', @filename]) }`
  end
end

if file = ARGV.first
  dir = File.dirname(File.expand_path(file))

  Dir.chdir(dir) do
    Blamify.new(File.basename(file)).print
  end
end