/* gaido v1.0.0 (c) 2016~ nodegin */
!function() {
  var container = document.querySelector('#gaido');
  var script = document.querySelector('script[type="text/gaido"]').innerHTML;
  script = script.split('\n').slice(1, -1);
  var getIndentLength = function(line) {
    matches = line.match(/^\s+/);
    return matches ? matches[0].length : 0;
  };
  var raise = function(message, i) {
    throw new Error(message + (i ? ' at line ' + (i + 1) : ''));
  };
  if (script.length < 2) {
    raise('Invalid gaido script');
  }
  var trimIndent = new RegExp('^\\s{' + getIndentLength(script[0]) + '}');
  script = script.map(function(line) {
    return line.replace(trimIndent, '');
  });
  var questions = {};
  var current = null;
  var lastIndent = 0;
  var currentIndent = 0;
  var levels = [];
  var indentSpaces = getIndentLength(script[1]);
  if (indentSpaces < 1 || indentSpaces % 2 !== 0) {
    raise('Unexpected indentation at line 2');
  }
  script.forEach(function(line, _i) {
    var _choice = null;
    if (_choice = line.match(/^\d+?\:$/)) {
      current = parseInt(_choice);
      if (questions[current]) {
        raise('Duplicate key for Question #' + current);
      } else {
        questions[current] = {};
      }
    } else {
      currentIndent = getIndentLength(line);
      if (currentIndent % indentSpaces !== 0) {
        raise('Unexpected indentation', _i);
      }
      /* Parse choice */
      if (currentIndent > lastIndent) {
        // enter level
        levels.push(line);
      } else if (currentIndent < lastIndent) {
        // exit levels
        for (var i = 0; i < lastIndent / currentIndent; i++)
          levels.pop();
        levels.push(line);
      } else if (currentIndent === lastIndent) {
        // update level
        levels.pop();
        levels.push(line);
      }
      var levMessage = line.match(/message:\s"(.+?)"$/);
      var levChoices = line.match(/choices:$/);
      if (levMessage) {
        questions[current].message = levMessage[1];
      } else if (levChoices) {
        questions[current].choices = [];
      } else if (currentIndent >= lastIndent) {
        // entered from last level (>) or in same level (===)
        var lastLevel = levels[levels.length - 2];
        if (lastLevel.indexOf('choices') > -1) {
          // entered from choices, add new choice
          var matches = line.match(/^\s+?"(.+?)"\s=>\s(\d+)$/);
          if (!matches) {
            raise('Syntax error', _i);
          }
          questions[current].choices.push({
            next: +matches[2],
            text: matches[1]
          });
        }
      }
      lastIndent = currentIndent;
    }
  });
  // start building ui
  var fragment = document.createDocumentFragment();
  var currentArticle = null;
  var firstArticle = null;
  var articles = {};
  for (var q in questions) {
    var qstn = questions[q];
    var article = document.createElement('article');
    article.qid = q;
    articles[q] = article;
    var section = document.createElement('section');
    // display message
    var msgWrap = document.createElement('div');
    msgWrap.innerHTML = qstn.message;
    msgWrap.className = 'message-container';
    section.appendChild(msgWrap);
    // build buttons
    if (qstn.choices) {
      var buttonsWrap = document.createElement('div');
      buttonsWrap.className = 'buttons-container';
      qstn.choices.forEach(function(c) {
        var button = document.createElement('button');
        button.onclick = function() {
          currentArticle.style.display = 'none';
          currentArticle = articles[c.next];
          history.pushState(c.next, document.title, location.pathname);
          currentArticle.style.display = 'block';
        };
        button.appendChild(document.createTextNode(c.text));
        buttonsWrap.appendChild(button);
      });
      section.appendChild(buttonsWrap);
    }
    article.appendChild(section);
    article.style.display = 'none';
    fragment.appendChild(article);
    // show first
    if (null === currentArticle) {
      currentArticle = firstArticle = article;
    }
  }
  window.onpopstate = function(e) {
    var qid = e.state;
    if (null === qid) {
      qid = firstArticle.qid;
    }
    currentArticle.style.display = 'none';
    currentArticle = articles[qid];
    currentArticle.style.display = 'block';
  };
  container.appendChild(fragment);
  currentArticle.style.display = 'block';
}();