Ruby/Rails勉強会@関西 60th #rubykansai のプレゼン用に作成した正規表現(ごく一部)の動作をステップ表示するアプリ

Gemfile

source "https://rubygems.org"
ruby "2.1.1"
gem "sinatra"

Gemfile.lock

GEM
  remote: https://rubygems.org/
  specs:
    rack (1.5.2)
    rack-protection (1.5.2)
      rack
    sinatra (1.4.4)
      rack (~> 1.4)
      rack-protection (~> 1.4)
      tilt (~> 1.3, >= 1.3.4)
    tilt (1.4.1)

PLATFORMS
  ruby

DEPENDENCIES
  sinatra

Procfile

web: bundle exec ruby regexp-201403.rb -p $PORT

regexp-201403.rb

#!/usr/bin/env ruby
# -*- coding: utf-8 -*-
require 'sinatra'

def make_link(re, str)
  require 'erb'
  %Q[<li><a href="/#{URI.encode_www_form_component(re)}/#{URI.encode_www_form_component(str)}/0">/#{ERB::Util.h(re)}/ =~ "#{ERB::Util.h(str)}"</a></li>]
end

example = [
  make_link("abc", "abracadabra"),
  make_link("ada", "abracadabra"),
  make_link("a(?=br)a", "abracadabra"),
  make_link("a(?=.r)b.a", "abracadabra"),
  make_link("foo(?=bar)", "foobar"),
  make_link("(?=foo)bar", "foobar"),
]

get '/' do
  example.join('')
end

def step(state)
  STDERR.puts state.inspect
  return state if state[:step] <= 0
  reg_range = state[:reg_range]
  str_range = state[:str_range]
  if state[:reg][reg_range.end, 3] == '(?='
    state[:outer_range] = {
      reg_range: reg_range,
      str_range: str_range,
    }
    state[:reg_range] = reg_range.end+3...reg_range.end+3
    state[:str_range] = str_range.end...str_range.end
  elsif state[:reg][reg_range.end] == ')' && state[:outer_range]
    state[:reg_range] = reg_range.end+1...reg_range.end+1
    state[:str_range] = state[:outer_range][:str_range].end...state[:outer_range][:str_range].end
  elsif state[:reg][reg_range.end] == '.'
    state[:reg_range] = reg_range.begin...reg_range.end+1
    state[:str_range] = str_range.begin...str_range.end+1
  elsif state[:reg][reg_range.end] == state[:str][str_range.end]
    state[:reg_range] = reg_range.begin...reg_range.end+1
    state[:str_range] = str_range.begin...str_range.end+1
  elsif state[:finished]
    state[:reg_range] = 0...0
    state[:str_range] = str_range.begin+1...str_range.begin+1
    state[:finished] = false
  else
    if state[:reg].length == reg_range.end
      state[:finished]  = :matched
    else
      state[:finished]  = :failed
    end
  end
  state[:step] -= 1
  step(state)
end

get '/:reg/:str/:step' do
  reg = params[:reg]
  str = params[:str]
  n = params[:step].to_i
  result = step(reg: reg, str: str, step: n, reg_range: 0...0, str_range: 0...0, finished: false)
  reg_range = result[:reg_range]
  str_range = result[:str_range]
  finished = result[:finished]
  case finished
  when :failed
    reg[reg_range.end, 1] &&= '<span class="failed">' + reg[reg_range.end, 1] + '</span>'
    str[str_range.end, 1] &&= '<span class="failed">' + str[str_range.end, 1] + '</span>'
  end
  reg[reg_range] &&= '<span class="reg-step">' + reg[reg_range] + '</span>'
  if str[str_range]
    str[str_range] &&= '<span class="str-step">' + str[str_range] + '</span>'
  else
    match_failed = true
  end
  [
    %Q[<style type="text/css">.failed{border:5px solid red} .reg-step{border:5px solid green} .str-step{border:5px solid blue}</style>],
    %Q[<p style="font-size:128px">/#{reg}/ =~ "#{str}"</p>],
    finished == :matched ? %Q[<p>matched</p>] : "",
    match_failed ? %Q[<p>failed</p>] : "",
    %Q[<p><a href="#{n-1}">prev</a> <a href="#{n+1}">next</a></p>],
    *example,
  ].join("")
end