sprintf.js

// sprintf() for JavaScript 0.7-beta1
// http://www.diveintojavascript.com/projects/javascript-sprintf
//
// Copyright (c) Alexandru Marasteanu <alexaholic [at) gmail (dot] com>
// All rights reserved.
var strRepeat = require('./helper/strRepeat');
var toString = Object.prototype.toString;
var sprintf = (function() {
  function get_type(variable) {
    return toString.call(variable).slice(8, -1).toLowerCase();
  }

  var str_repeat = strRepeat;

  var str_format = function() {
    if (!str_format.cache.hasOwnProperty(arguments[0])) {
      str_format.cache[arguments[0]] = str_format.parse(arguments[0]);
    }
    return str_format.format.call(null, str_format.cache[arguments[0]], arguments);
  };

  str_format.format = function(parse_tree, argv) {
    var cursor = 1, tree_length = parse_tree.length, node_type = '', arg, output = [], i, k, match, pad, pad_character, pad_length;
    for (i = 0; i < tree_length; i++) {
      node_type = get_type(parse_tree[i]);
      if (node_type === 'string') {
        output.push(parse_tree[i]);
      }
      else if (node_type === 'array') {
        match = parse_tree[i]; // convenience purposes only
        if (match[2]) { // keyword argument
          arg = argv[cursor];
          for (k = 0; k < match[2].length; k++) {
            if (!arg.hasOwnProperty(match[2][k])) {
              throw new Error(sprintf('[_.sprintf] property "%s" does not exist', match[2][k]));
            }
            arg = arg[match[2][k]];
          }
        } else if (match[1]) { // positional argument (explicit)
          arg = argv[match[1]];
        }
        else { // positional argument (implicit)
          arg = argv[cursor++];
        }

        if (/[^s]/.test(match[8]) && (get_type(arg) != 'number')) {
          throw new Error(sprintf('[_.sprintf] expecting number but found %s', get_type(arg)));
        }
        switch (match[8]) {
          case 'b': arg = arg.toString(2); break;
          case 'c': arg = String.fromCharCode(arg); break;
          case 'd': arg = parseInt(arg, 10); break;
          case 'e': arg = match[7] ? arg.toExponential(match[7]) : arg.toExponential(); break;
          case 'f': arg = match[7] ? parseFloat(arg).toFixed(match[7]) : parseFloat(arg); break;
          case 'o': arg = arg.toString(8); break;
          case 's': arg = ((arg = String(arg)) && match[7] ? arg.substring(0, match[7]) : arg); break;
          case 'u': arg = Math.abs(arg); break;
          case 'x': arg = arg.toString(16); break;
          case 'X': arg = arg.toString(16).toUpperCase(); break;
        }
        arg = (/[def]/.test(match[8]) && match[3] && arg >= 0 ? '+'+ arg : arg);
        pad_character = match[4] ? match[4] == '0' ? '0' : match[4].charAt(1) : ' ';
        pad_length = match[6] - String(arg).length;
        pad = match[6] ? str_repeat(pad_character, pad_length) : '';
        output.push(match[5] ? arg + pad : pad + arg);
      }
    }
    return output.join('');
  };

  str_format.cache = {};

  str_format.parse = function(fmt) {
    var _fmt = fmt, match = [], parse_tree = [], arg_names = 0;
    while (_fmt) {
      if ((match = /^[^\x25]+/.exec(_fmt)) !== null) {
        parse_tree.push(match[0]);
      }
      else if ((match = /^\x25{2}/.exec(_fmt)) !== null) {
        parse_tree.push('%');
      }
      else if ((match = /^\x25(?:([1-9]\d*)\$|\(([^\)]+)\))?(\+)?(0|'[^$])?(-)?(\d+)?(?:\.(\d+))?([b-fosuxX])/.exec(_fmt)) !== null) {
        if (match[2]) {
          arg_names |= 1;
          var field_list = [], replacement_field = match[2], field_match = [];
          if ((field_match = /^([a-z_][a-z_\d]*)/i.exec(replacement_field)) !== null) {
            field_list.push(field_match[1]);
            while ((replacement_field = replacement_field.substring(field_match[0].length)) !== '') {
              if ((field_match = /^\.([a-z_][a-z_\d]*)/i.exec(replacement_field)) !== null) {
                field_list.push(field_match[1]);
              }
              else if ((field_match = /^\[(\d+)\]/.exec(replacement_field)) !== null) {
                field_list.push(field_match[1]);
              }
              else {
                throw new Error('[_.sprintf] huh?');
              }
            }
          }
          else {
            throw new Error('[_.sprintf] huh?');
          }
          match[2] = field_list;
        }
        else {
          arg_names |= 2;
        }
        if (arg_names === 3) {
          throw new Error('[_.sprintf] mixing positional and named placeholders is not (yet) supported');
        }
        parse_tree.push(match);
      }
      else {
        throw new Error('[_.sprintf] huh?');
      }
      _fmt = _fmt.substring(match[0].length);
    }
    return parse_tree;
  };

  return str_format;
})();

module.exports = sprintf;