title: Recognize pattern matches in String with regular expression
body: <p>In short, the system I am working on has many layers. In Java, I will get a String containing a condition to evaluate. I will be receiving a string with possible occurrences of function calls to a function called "days(int)". The string may look like:</p>
  
  <pre><code>1405555200 + days(4)
  </code></pre>
  
  <p>or</p>
  
  <pre><code>1405555200 + days(param_date)
  </code></pre>
  
  <p>where the first operands are Unix timestamps. Dates in the system are converted to Unix time (Long). Essentially, this days(x) thing inside the string is just a notation for "add this many days to the timestamp". Since one day is 86400 seconds, we can simplify this notation to "add 86400 times the parameter to the other operand".</p>
  
  <p>I need to find all occurences of this pattern and turn</p>
  
  <pre><code>1405555200 + days(param_date)
  </code></pre>
  
  <p>into</p>
  
  <pre><code>1405555200 + (86400 * param_date)
  </code></pre>
  
  <p>How can I do this cleanly?</p>