Prune history of a Firepad.

prune-firepad-history.js

// This should be easier, but due to an oversight in the checkpoint id's, it's a tad tricky (you need this revision/id stuff).
// I'll rework things to be cleaner in the near future.

function pruneHistory(firepadRef) {
  var characters = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';
  function revisionToId(revision) {
    if (revision === 0) {
      return 'A0';
    }
  
    var str = '';
    while (revision > 0) {
      var digit = (revision % characters.length);
      str = characters[digit] + str;
      revision -= digit;
      revision /= characters.length;
    }
  
    // Prefix with length (starting at 'A' for length 1) to ensure the id's sort lexicographically.
    var prefix = characters[str.length + 9];
    return prefix + str;
  }
  
  function revisionFromId(revisionId) {
    var revision = 0;
    for(var i = 1; i < revisionId.length; i++) {
      revision *= characters.length;
      revision += characters.indexOf(revisionId[i]);
    }
    return revision;
  }

  firepadRef.child('checkpoint/id').once('value', function(idSnapshot) {
    var checkpointId = idSnapshot.val();
    if (checkpointId !== null) {
      var pruneBefore = revisionToId(revisionFromId(checkpointId) - 1);
      firepadRef.child('history').once('value', function(historySnapshot) {
        historySnapshot.forEach(function(itemSnapshot) {
          if (itemSnapshot.name() < pruneBefore) {
            itemSnapshot.ref().remove();
          };
        });
      });
    }
  });
}