expressions.js

var slice = Array.prototype.slice;
var strings = require('./strings');
var formatterParser = require('./formatters');
var propertyChains = require('./property-chains');
var valueProperty = '_value_';
var cache = {};

exports.globals = {};


exports.parse = function(expr, globals, formatters) {
  if (typeof expr !== 'string') {
    throw new TypeError('Invalid expr, must be type String');
  }
  var extraArgs = slice.call(arguments, 3);
  var cacheKey = expr + '|' + extraArgs.join(',');
  // Returns the cached function for this expression if it exists.
  var func = cache[cacheKey];
  if (func) {
    return func;
  }

  var original = expr;
  var isSetter = (extraArgs[0] === valueProperty);

  expr = strings.pullOutStrings(expr);
  expr = formatterParser.parseFormatters(expr);
  expr = propertyChains.parseExpression(expr, getVariables(globals, extraArgs));
  if (!isSetter) {
    var lines = expr.split('\n');
    lines[lines.length - 1] = 'return ' + lines[lines.length - 1];
    expr = lines.join('\n');
  }
  expr = strings.putInStrings(expr);
  func = compileExpression(original, expr, globals, formatters, extraArgs);
  func.expr = expr;
  cache[cacheKey] = func;
  return func;
};


exports.parseSetter = function(expr, globals, formatters, extraArgs) {
  var extraArgs = slice.call(arguments, 3);

  if (expr.charAt(0) === '!') {
    // Allow '!prop' to become 'prop = !value'
    expr = expr.slice(1).replace(/(\s*\||$)/, ' = !_value_$1');
  } else {
    expr = expr.replace(/(\s*\||$)/, ' = _value_$1');
  }

  // Add _value_ as the first extra argument
  return exports.parse.apply(exports, [expr, globals, formatters, valueProperty].concat(extraArgs));
};


function getVariables(globals, extraArgs) {
  var variables = {};

  Object.keys(exports.globals).forEach(function(key) {
    variables[key] = exports.globals[key];
  });

  if (globals) {
    Object.keys(globals).forEach(function(key) {
      variables[key] = globals[key];
    });
  }

  extraArgs.forEach(function(key) {
    variables[key] = null;
  });

  return variables;
}



function compileExpression(original, expr, globals, formatters, extraArgs) {
  var func, args = ['_globals_', '_formatters_'].concat(extraArgs).concat(expr);

  try {
    func = Function.apply(null, args);
  } catch (e) {
    // Throws an error if the expression was not valid JavaScript
    throw new Error('Bad expression: ' + original + '\n' + 'Compiled expression:\n' + expr + '\n' + e.message);
  }

  return bindArguments(func, globals, formatters);
}


// a custom "bind" function to bind arguments to a function without binding the context
function bindArguments(func) {
  function binder() {
    return func.apply(this, args.concat(slice.call(arguments)));
  }

  var args = slice.call(arguments, 1);
  return binder;
}