Add example for file history

This fixes #220
nodegit · johnhaley81 · Feb 27, 2015 · Feb 20, 2015 · Feb 27, 2015 · Feb 27, 2015
commit 74f31bff77be3a29c765dd5f2ba3753d8171d4e0
diff --git a/examples/walk-history-for-file.js b/examples/walk-history-for-file.js
@@ -0,0 +1,52 @@
+var nodegit = require("../"),
+    path = require("path");
+
+// This code walks the history of the master branch and prints results
+// that look very similar to calling `git log` from the command line
+
+nodegit.Repository.open(path.resolve(__dirname, "../.git"))
+  .then(function(repo) {
+    return repo.getMasterCommit();
+  })
+  .then(function(firstCommitOnMaster){
+    // History returns an event.
+    var history = firstCommitOnMaster.history(nodegit.Revwalk.SORT.Time);
+    var commits = [];
+
+    // History emits "commit" event for each commit in the branch's history
+    history.on("commit", function(commit) {
+      return commit.getDiff()
+      .then(function(diffList) {
+        var addCommit = diffList.reduce(function(prevVal, diff) {
+          var result = prevVal || diff.patches().reduce(function(prevValDiff, patch) {
+            var result =
+              prevValDiff ||
+              !!~patch.oldFile().path().indexOf("descriptor.json") ||
+              !!~patch.newFile().path().indexOf("descriptor.json");
+
+            return result;
+          }, false);
+
+          return result;
+        }, false);
+
+        if (addCommit) {
+          commits.push(commit);
+        }
+      });
+    });
+
+    history.on("end", function() {
+      commits.forEach(function(commit) {
+        console.log("commit " + commit.sha());
+        console.log("Author:", commit.author().name() +
+          " <" + commit.author().email() + ">");
+        console.log("Date:", commit.date());
+        console.log("\n    " + commit.message());
+      });
+    });
+
+    // Don't forget to call `start()`!
+    history.start();
+  })
+  .done();