From b3ec7b79856128edc30867d48f586cc5abccbac6 Mon Sep 17 00:00:00 2001
From: Jason Morrison <jmorrison@minervaproject.com>
Date: Sat, 30 Mar 2019 00:03:17 -0700
Subject: [PATCH] Proof-of-concept of presence operators for the
 @teamwork/sharedb presence mechanics

Provides the following presence functions on the rich-text type,
copying them from the @teamwork/ot-rich-text implementation:

- createPresence
- transformPresence
- comparePresence
- isValidPresence
---
 lib/type.js | 85 ++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 81 insertions(+), 4 deletions(-)

diff --git a/lib/type.js b/lib/type.js
index b6e1a2b..b3d576b 100644
--- a/lib/type.js
+++ b/lib/type.js
@@ -1,5 +1,79 @@
 var Delta = require('quill-delta');
 
+// Slightly modified from the base rich-text implementation
+function transformCursor(cursor, delta, isOwnOp) {
+  // Rewrap in Quill Delta since we seem to get a raw ops object
+  delta = new Delta(delta);
+  return delta.transformPosition(cursor, !isOwnOp);
+}
+
+// Copied from https://github.com/Teamwork/ot-rich-text/blob/master/src/Operation.js
+function createPresence(presence) {
+  return isValidPresence(presence) ? presence : {
+    u: '',
+    c: 0,
+    s: []
+  };
+}
+
+// Copied from https://github.com/Teamwork/ot-rich-text/blob/master/src/Operation.js
+function transformPresence(presence, operation, isOwnOperation) {
+  var user = presence.u;
+  var change = presence.c;
+  var selections = presence.s;
+  var newSelections = new Array(selections.length);
+
+  for (var i = 0, l = selections.length; i < l; ++i) {
+    var selection = selections[i];
+    var newStart = transformCursor(selection[0], operation, isOwnOperation);
+    var newEnd = selection[0] === selection[1] ? newStart : transformCursor(selection[1], operation, isOwnOperation);
+    newSelections[i] = [newStart, newEnd];
+  }
+
+  return {
+    u: user,
+    c: change,
+    s: newSelections
+  };
+}
+
+// Copied from https://github.com/Teamwork/ot-rich-text/blob/master/src/Operation.js
+function comparePresence(presence1, presence2) {
+  if (presence1 === presence2) {
+    return true;
+  }
+
+  if (presence1 == null || presence2 == null || presence1.u !== presence2.u || presence1.c !== presence2.c || presence1.s.length !== presence2.s.length) {
+    return false;
+  }
+
+  for (var i = 0, l = presence1.s.length; i < l; ++i) {
+    if (presence1.s[i][0] !== presence2.s[i][0] || presence1.s[i][1] !== presence2.s[i][1]) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+// Copied from https://github.com/Teamwork/ot-rich-text/blob/master/src/Operation.js
+function isValidPresence(presence) {
+  if (presence == null || typeof presence.u !== 'string' || typeof presence.c !== 'number' || !isFinite(presence.c) || Math.floor(presence.c) !== presence.c || !Array.isArray(presence.s)) {
+    return false;
+  }
+
+  var selections = presence.s;
+
+  for (var i = 0, l = selections.length; i < l; ++i) {
+    var selection = selections[i];
+
+    if (!Array.isArray(selection) || selection.length !== 2 || selection[0] !== (selection[0] | 0) || selection[1] !== (selection[1] | 0)) {
+      return false;
+    }
+  }
+
+  return true;
+}
 
 module.exports = {
   Delta: Delta,
@@ -36,9 +110,7 @@ module.exports = {
       return delta2.transform(delta1, side === 'left');
     },
 
-    transformCursor: function(cursor, delta, isOwnOp) {
-      return delta.transformPosition(cursor, !isOwnOp);
-    },
+    transformCursor: transformCursor,
 
     normalize: function(delta) {
       return delta;   // quill-delta is already canonical
@@ -50,6 +122,11 @@ module.exports = {
 
     deserialize: function(ops) {
       return new Delta(ops);
-    }
+    },
+
+    createPresence: createPresence,
+    transformPresence: transformPresence,
+    comparePresence: comparePresence,
+    isValidPresence: isValidPresence,
   }
 };