BrillTransformationRulesAsFunctions

// Usage: 
// transformationRules = new BrillTransformationRules();
// transformationRules.rules.forEach(function(ruleFunction) {
//   ruleFunction(taggedSentence, i);
// });
// where taggedSentence is an array of arrays of the form:
// [[the, DET], [red, JJ], [book, NN]] and i the position to be processed

function BrillTransformationRules() {
  this.rules = [rule1, rule2, rule3, rule4, rule5, rule6, rule7, rule8];
}

BrillTransformationRules.prototype.getRule = function(index) {
  return(this.rules[index]);
};

BrillTransformationRules.prototype.setRule = function(index, rule) {
  this.rules[index] = rule;
};

BrillTransformationRules.prototype.appendRule = function(rule) {
  this.rules[this.rules.length] = rule;
};

/**
 * Indicates whether or not this string starts with the specified string.
 * @param {Object} string
 */
function startsWith($this, string) {
    if (!string) {
        return false;
    }
    return $this.indexOf(string) == 0;
}

/**
 * Indicates whether or not this string ends with the specified string.
 * @param {Object} string
 */
function endsWith($this, string) {
    if (!string || string.length > $this.length) {
        return false;
    }
    return $this.indexOf(string) == $this.length - string.length;
}

//  rule 1: DT, {VBD | VBP} --> DT, NN
function rule1(taggedSentence, index) {
  if ((index > 0) && (taggedSentence[index - 1][1] === "DT")) {
    if ((taggedSentence[index][1] === "VBD") ||
      (taggedSentence[index][1] === "VBP") ||
      (taggedSentence[index][1] === "VB")) {
      taggedSentence[index][1] = "NN";
    }
  }
}

// rule 2: convert a noun to a number (CD) if "." appears in the word
function rule2(taggedSentence, index) {
  if (startsWith(taggedSentence[index][1], "N")) {
    if (taggedSentence[index][0].indexOf(".") > -1) {
      // url if there are two contiguous alpha characters
      if (/[a-zA-Z]{2}/.test(words[i])) {
        taggedSentence[index][1] = "URL";
      }
      else {
        taggedSentence[index][1] = "CD";
      }
      // Attempt to convert into a number
      if (!isNaN(parseFloat(words[i]))) {
        taggedSentence[index][1] = "CD";
      }
    }
  }
}

// rule 3: convert a noun to a past participle if words[i] ends with "ed"
function rule3(taggedSentence, index) {
  if (startsWith(taggedSentence[index][1], "N") && endsWith(taggedSentence[index][0], "ed"))
    startsWith(taggedSentence[index][1] = "VBN";
  }
}

// rule 4: convert any type to adverb if it ends in "ly";
function rule4(taggedSentence, index) {
  if (endsWith(taggedSentence[index][0], "ly"))
    taggedSentence[index][1] = "RB";
  }
}

// rule 5: convert a common noun (NN or NNS) to a adjective if it ends with "al"
function rule5(taggedSentence, index) {
  if (startsWith(taggedSentence[index][1], "NN") && endsWith(taggedSentence[index][0], "al")) {
    taggedSentence[index][1] = "JJ";
  }
}
    
// rule 6: convert a noun to a verb if the preceding work is "would"
function rule6(taggedSentence, index) {
  if ((i > 0) && startsWith(taggedSentence[index][1], "NN") && (taggedSentence[index][0].toLowerCase() === "would")) {
    taggedSentence[index][1] = "VB";
  }
}
    
// rule 7: if a word has been categorized as a common noun and it ends with "s",
//         then set its type to plural common noun (NNS)
function rule7(taggedSentence, index) {
  if ((taggedSentence[index][1] === "NN") && (endsWith(taggedSentence[index][0], "s"))) {
    taggedSentence[index][1] = "NNS";
  }
}
    
// rule 8: convert a common noun to a present participle verb (i.e., a gerund)
function rule8(taggedSentence, index) {
  if (startsWith(taggedSentence[index][1], "NN") && endsWith(taggedSentence[index][0], "ing")) {
    taggedSentence[index][1] = "VBG";
  }
}

module.exports = BrillTransformationRules;