find-prev.js

// repo is assumed to be in closure
var repo;

// commit - the hash of the current commit
// path - the path to the hash in the current commit
// callback -> the previous blob value
function findPrevious(commit, path, callback) {
  var log; // The log stream
  var currentBlob; // The current value of the blob
  var oldBlob; // The last value of the blob
  var changeCommit; // The commit that made the last change to the blob
  var oldCommit; // The previous commit

  // First get the log stream
  repo.logWalk(commit, onLog);

  function onLog(err, result) {
    if (err) return callback(err);
    log = result;
    // Read the current commit
    log.read(onCurrentCommit);
  }

  function onCurrentCommit(err, result) {
    if (err) return callback(err);
    changeCommit = result;
    // Find the file by path in the current commit
    walkPath(changeCommit.tree, path, onCurrentBlob);
  }

  function onCurrentBlob(err, result) {
    if (err) return callback(err);
    currentBlob = result;
    // Start our search loop looking for a change in the next commit
    log.read(onCommit);
  }

  function onCommit(err, result) {
    if (err) return callback(err);
    oldCommit = result
    if (oldCommit === undefined) {
      // We've reached the beginning of history, this was created in the initial commit
      return callback(null, {
        oldBlob: undefined,
        currentBlob: currentBlob,
        changeCommit: changeCommit
      });
    }
    walkPath(oldCommit.tree, path, onBlob);
  }

  function onBlob(err, result) {
    if (err) return callback(err);
    oldBlob = result;
    if ((oldBlob && oldBlob.hash) !== currentBlob.hash) {
      return callback(null, {
        oldBlob: oldBlob,
        currentBlob: currentBlob,
        changeCommit: changeCommit
      });
    }
    changeCommit = oldCommit;
    log.read(onCommit);
  }
}


function walkPath(tree, path, callback) {
  // Remove leading and trailing slashes, '.' entries, and split artifacts.
  var names = path.split("/").filter(cleanPath);
  repo.loadAs("tree", tree, onTree);

  function onTree(err, tree) {
    if (err) return callback(err);
    var name = names.shift();
    var entry = findByName(tree, name);
    // return undefined for not-found errors
    if (!entry) return callback();
    // If there are still segments left, keep reading tree paths
    if (names.length) return repo.loadAs("tree", entry.hash, onTree);
    // Otherwise, load and return the blob
    repo.loadAs("blob", entry.hash, callback);
  }
}

function findByName(tree, name) {
  for (var i = 0, l = tree.length; i < l; i++) {
    var entry = tree[i];
    if (entry.name === name) return entry;
  }
}

function cleanPath(name) {
  return name && name !== ".";
}