define(['./underscore', './defaults', './templateSettings'], function (underscore, defaults, templateSettings) {

  // When customizing `_.templateSettings`, if you don't want to define an
  // interpolation, evaluation or escaping regex, we need one that is
  // guaranteed not to match.
  var noMatch = /(.)^/;

  // Certain characters need to be escaped so that they can be put into a
  // string literal.
  var escapes = {
    "'": "'",
    '\\': '\\',
    '\r': 'r',
    '\n': 'n',
    '\u2028': 'u2028',
    '\u2029': 'u2029'
  };

  var escapeRegExp = /\\|'|\r|\n|\u2028|\u2029/g;

  function escapeChar(match) {
    return '\\' + escapes[match];
  }

  var bareIdentifier = /^\s*(\w|\$)+\s*$/;

  // JavaScript micro-templating, similar to John Resig's implementation.
  // Underscore templating handles arbitrary delimiters, preserves whitespace,
  // and correctly escapes quotes within interpolated code.
  // NB: `oldSettings` only exists for backwards compatibility.
  function template(text, settings, oldSettings) {
    if (!settings && oldSettings) settings = oldSettings;
    settings = defaults({}, settings, underscore.templateSettings);

    // Combine delimiters into one regular expression via alternation.
    var matcher = RegExp([
      (settings.escape || noMatch).source,
      (settings.interpolate || noMatch).source,
      (settings.evaluate || noMatch).source
    ].join('|') + '|$', 'g');

    // Compile the template source, escaping string literals appropriately.
    var index = 0;
    var source = "__p+='";
    text.replace(matcher, function(match, escape, interpolate, evaluate, offset) {
      source += text.slice(index, offset).replace(escapeRegExp, escapeChar);
      index = offset + match.length;

      if (escape) {
        source += "'+\n((__t=(" + escape + "))==null?'':_.escape(__t))+\n'";
      } else if (interpolate) {
        source += "'+\n((__t=(" + interpolate + "))==null?'':__t)+\n'";
      } else if (evaluate) {
        source += "';\n" + evaluate + "\n__p+='";
      }

      // Adobe VMs need the match returned to produce the correct offset.
      return match;
    });
    source += "';\n";

    var argument = settings.variable;
    if (argument) {
      if (!bareIdentifier.test(argument)) throw new Error(argument);
    } else {
      // If a variable is not specified, place data values in local scope.
      source = 'with(obj||{}){\n' + source + '}\n';
      argument = 'obj';
    }

    source = "var __t,__p='',__j=Array.prototype.join," +
      "print=function(){__p+=__j.call(arguments,'');};\n" +
      source + 'return __p;\n';

    var render;
    try {
      render = new Function(argument, '_', source);
    } catch (e) {
      e.source = source;
      throw e;
    }

    var template = function(data) {
      return render.call(this, data, underscore);
    };

    // Provide the compiled source as a convenience for precompilation.
    template.source = 'function(' + argument + '){\n' + source + '}';

    return template;
  }

  return template;

});
