var underscore = require('./underscore.js');
var defaults = require('./defaults.js');
require('./templateSettings.js');

// 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;
}

module.exports = template;
