#!/usr/bin/env node

// An implementation of the ROT13 substitution cipher [1], replacing each letter
// with the letter 13 letters after it in the alphabet.
//
// Nearly identical to cat, except the data is transformed in-place before
// writing, and only a single input file is read.
//
// [1] https://en.wikipedia.org/wiki/ROT13

var rw = require("../");

var reader = rw.fileReader(process.argv[2] || "/dev/stdin"),
    writer = rw.fileWriter("/dev/stdout");

var CODE_A = "A".charCodeAt(0),
    CODE_Z = "Z".charCodeAt(0),
    CODE_a = "a".charCodeAt(0),
    CODE_z = "z".charCodeAt(0);

function rot13(buffer) {
  for (var i = 0, n = buffer.length, character; i < n; ++i) {
    character = buffer[i];
    if (CODE_A <= character && character <= CODE_Z) {
      buffer[i] = (character - CODE_A + 13) % 26 + CODE_A;
    } else if (CODE_a <= character && character <= CODE_z) {
      buffer[i] = (character - CODE_a + 13) % 26 + CODE_a;
    }
  }
  return buffer;
}

reader.fill(function flow(error) {
  if (error) throw error;
  var data = reader.read();
  if (data && !writer.write(rot13(data))) return writer.drain(flow);
  if (reader.ended) return writer.end();
  reader.fill(flow);
});