From c671d54d6755b8e164428214216e13351f92d09c Mon Sep 17 00:00:00 2001
From: Wu Cheng-Han
Date: Fri, 18 Nov 2016 12:09:58 +0800
Subject: Add dmp worker to leverage CPU intensive calculation to child process

---
 lib/workers/dmpWorker.js | 142 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 142 insertions(+)
 create mode 100644 lib/workers/dmpWorker.js

(limited to 'lib/workers')

diff --git a/lib/workers/dmpWorker.js b/lib/workers/dmpWorker.js
new file mode 100644
index 00000000..fae36191
--- /dev/null
+++ b/lib/workers/dmpWorker.js
@@ -0,0 +1,142 @@
+// external modules
+var LZString = require('lz-string');
+var DiffMatchPatch = require('diff-match-patch');
+var dmp = new DiffMatchPatch();
+
+// core
+var config = require("../config.js");
+var logger = require("../logger.js");
+
+process.on('message', function(data) {
+    if (!data || !data.msg || !data.cacheKey) {
+        return logger.error('dmp worker error: not enough data');
+    }
+    switch (data.msg) {
+        case 'create patch':
+            if (!data.hasOwnProperty('lastDoc') || !data.hasOwnProperty('currDoc')) {
+                return logger.error('dmp worker error: not enough data on create patch');
+            }
+            try {
+                var patch = createPatch(data.lastDoc, data.currDoc);
+                process.send({
+                    msg: 'check',
+                    result: patch,
+                    cacheKey: data.cacheKey
+                });
+            } catch (err) {
+                logger.error('dmp worker error', err);
+                process.send({
+                    msg: 'error',
+                    error: err,
+                    cacheKey: data.cacheKey
+                });
+            }
+            break;
+        case 'get revision':
+            if (!data.hasOwnProperty('revisions') || !data.hasOwnProperty('count')) {
+                return logger.error('dmp worker error: not enough data on get revision');
+            }
+            try {
+                var result = getRevision(data.revisions, data.count);
+                process.send({
+                    msg: 'check',
+                    result: result,
+                    cacheKey: data.cacheKey
+                });
+            } catch (err) {
+                logger.error('dmp worker error', err);
+                process.send({
+                    msg: 'error',
+                    error: err,
+                    cacheKey: data.cacheKey
+                });
+            }
+            break;
+    }
+});
+
+function createPatch(lastDoc, currDoc) {
+    var ms_start = (new Date()).getTime();
+    var diff = dmp.diff_main(lastDoc, currDoc);
+    dmp.diff_cleanupSemantic(diff);
+    var patch = dmp.patch_make(lastDoc, diff);
+    patch = dmp.patch_toText(patch);
+    var ms_end = (new Date()).getTime();
+    if (config.debug) {
+        logger.info(patch);
+        logger.info((ms_end - ms_start) + 'ms');
+    }
+    return patch;
+}
+
+function getRevision(revisions, count) {
+    var ms_start = (new Date()).getTime();
+    var startContent = null;
+    var lastPatch = [];
+    var applyPatches = [];
+    var authorship = [];
+    if (count <= Math.round(revisions.length / 2)) {
+        // start from top to target
+        for (var i = 0; i < count; i++) {
+            var revision = revisions[i];
+            if (i == 0) {
+                startContent = LZString.decompressFromBase64(revision.content || revision.lastContent);
+            }
+            if (i != count - 1) {
+                var patch = dmp.patch_fromText(LZString.decompressFromBase64(revision.patch));
+                applyPatches = applyPatches.concat(patch);
+            }
+            lastPatch = revision.patch;
+            authorship = revision.authorship;
+        }
+        // swap DIFF_INSERT and DIFF_DELETE to achieve unpatching
+        for (var i = 0, l = applyPatches.length; i < l; i++) {
+            for (var j = 0, m = applyPatches[i].diffs.length; j < m; j++) {
+                var diff = applyPatches[i].diffs[j];
+                if (diff[0] == DiffMatchPatch.DIFF_INSERT)
+                    diff[0] = DiffMatchPatch.DIFF_DELETE;
+                else if (diff[0] == DiffMatchPatch.DIFF_DELETE)
+                    diff[0] = DiffMatchPatch.DIFF_INSERT;
+            }
+        }
+    } else {
+        // start from bottom to target
+        var l = revisions.length - 1;
+        for (var i = l; i >= count - 1; i--) {
+            var revision = revisions[i];
+            if (i == l) {
+                startContent = LZString.decompressFromBase64(revision.lastContent);
+                authorship = revision.authorship;
+            }
+            if (revision.patch) {
+                var patch = dmp.patch_fromText(LZString.decompressFromBase64(revision.patch));
+                applyPatches = applyPatches.concat(patch);
+            }
+            lastPatch = revision.patch;
+            authorship = revision.authorship;
+        }
+    }
+    try {
+        var finalContent = dmp.patch_apply(applyPatches, startContent)[0];
+    } catch (err) {
+        throw new Error(err);
+    }
+    var data = {
+        content: finalContent,
+        patch: dmp.patch_fromText(LZString.decompressFromBase64(lastPatch)),
+        authorship: authorship ? JSON.parse(LZString.decompressFromBase64(authorship)) : null
+    };
+    var ms_end = (new Date()).getTime();
+    if (config.debug) {
+        logger.info((ms_end - ms_start) + 'ms');
+    }
+    return data;
+}
+
+// log uncaught exception
+process.on('uncaughtException', function (err) {
+    logger.error('An uncaught exception has occured.');
+    logger.error(err);
+    logger.error('Process will exit now.');
+    process.exit(1);
+});
\ No newline at end of file
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