idb sort key prototype

2018-12-21 18:09:01 +01:00 · 2018-12-21 18:09:01 +01:00 · 25a84d41a5
commit 25a84d41a5
parent 0cf9e84bdd
2 changed files with 189 additions and 1 deletions
--- a/matrix.mjs
+++ b/matrix.mjs
@ -2,7 +2,7 @@
 /*
 idb stores:
 all in one database per stored session:
-	- session
+	- session (store all sessions in localStorage object?)
 		- device id
 		- last sync token
 		- access token
@ -44,6 +44,17 @@ all in one database per stored session:
 	- members_{room_id}
 		historical?
 	- timeline_{room_id}
+		how to store timeline events in order they should be shown?
+		what's the key they should be sorted by?
+
+		start with origin_server_ts of first event as 0 and add / subtract from there
+		in case of gaps, take the max(last_ts + 1000, origin_server_ts) again to get an idea of how many
+		numbers are in between, and go down/up one again for events filling the gap
+		
+		when closing the gap, we notice there are not enough numbers between the PK
+		of both sides of the gap (because more than 1 event / millisecond was sent, or server clocks were off),
+		what do we do? floating point?
+
 	- search?

 where to store avatars?
--- a/typedarray.html
+++ b/typedarray.html
@ -0,0 +1,177 @@
+<html>
+<body>
+	<ul id="messages"></ul>
+	<script type="text/javascript">
+		class Key {
+			constructor() {
+				this._keys = new Int32Array(2);
+			}
+
+			get gapKey() {
+				return this._keys[0];
+			}
+
+			set gapKey(value) {
+				this._keys[0] = value;
+			}
+
+			get eventKey() {
+				return this._keys[1];
+			}
+
+			set eventKey(value) {
+				this._keys[1] = value;
+			}
+
+			buffer() {
+				return this._keys.buffer;
+			}
+
+			nextKeyWithGap() {
+				const k = new Key();
+				k.gapKey = this.gapKey + 1;
+				k.eventKey = 0;
+				return k;
+			}
+
+			nextKey() {
+				const k = new Key();
+				k.gapKey = this.gapKey;
+				k.eventKey = this.eventKey + 1;
+				return k;
+			}
+
+			previousKey() {
+				const k = new Key();
+				k.gapKey = this.gapKey;
+				k.eventKey = this.eventKey - 1;
+				return k;
+			}
+
+			clone() {
+				const k = new Key();
+				k.gapKey = this.gapKey;
+				k.eventKey = this.eventKey;	
+				return k;
+			}
+		}
+
+		function reqAsPromise(req) {
+		    return new Promise((resolve, reject) => {
+		        req.onsuccess = () => resolve(req);
+		        req.onerror = (err) => reject(err);
+		    });
+		}
+
+		function fetchResults(cursor, isDone, resultMapper) {
+		    return new Promise((resolve, reject) => {
+		        const results = [];
+		        cursor.onerror = (event) => {
+		            reject(new Error("Query failed: " + event.target.errorCode));
+		        };
+		        // collect results
+		        cursor.onsuccess = (event) => {
+		        	console.log("got a result");
+		            const cursor = event.target.result;
+		            if (!cursor) {
+		                resolve(results);
+		                return; // end of results
+		            }
+		            results.push(resultMapper(cursor));
+		            if (!isDone(results)) {
+		            	cursor.continue();
+		            } else {
+		            	resolve(results);
+		            }
+		        };
+		    });
+		}
+
+		class Storage {
+			constructor(databaseName) {
+				this._databaseName = databaseName;
+				this._database = null;
+			}
+
+			async open() {
+				const req = window.indexedDB.open(this._databaseName);
+				req.onupgradeneeded = async (ev) => {
+					const db = ev.target.result;
+					const oldVersion = ev.oldVersion;
+					this._createStores(db, oldVersion);
+				}; 
+				await reqAsPromise(req);
+				this._database = req.result;
+			}
+
+			_createStores(db) {
+				db.createObjectStore("timeline", {keyPath: ["roomId", "sortKey"]});
+			}
+
+			async insert(value) {
+				const tx = this._database.transaction(["timeline"], "readwrite");
+				const store = tx.objectStore("timeline");
+				await reqAsPromise(store.add(value));
+			}
+
+			async selectAt(roomId, sortKey, amount) {
+				const tx = this._database.transaction(["timeline"], "readonly");
+				const store = tx.objectStore("timeline");
+				const range = IDBKeyRange.lowerBound([roomId, sortKey.buffer()]);
+				const cursor = store.openCursor(range);
+				return await fetchResults(cursor, 
+					(results) => results.length === amount,
+					(cursor) => cursor.value);
+			}
+		}
+
+		(async () => {
+			const initialSortKey = new Key();
+			initialSortKey.gapKey = 1000;
+			const roomId = "!abc:hs.tld";
+			const storage = new Storage("mysession");
+			await storage.open();
+
+			let records = await storage.selectAt(roomId, initialSortKey, 15);
+			if (!records.length) {
+				// insert first batch backwards,
+				// to see we're not assuming insertion order to sort
+				let sortKey = initialSortKey.clone();
+				sortKey.eventKey = 10;
+				for (var i = 10; i > 0; i--) {
+					await storage.insert({
+						roomId,
+						sortKey: sortKey.buffer(),
+						message: `message ${i} before gap`
+					});
+					sortKey = sortKey.previousKey();
+				}
+				sortKey = sortKey.nextKeyWithGap();
+				await storage.insert({
+					roomId,
+					sortKey: sortKey.buffer(),
+					message: `event to represent gap!`
+				});
+				for (var i = 1; i <= 10; i++) {
+					sortKey = sortKey.nextKey();
+					await storage.insert({
+						roomId,
+						sortKey: sortKey.buffer(),
+						message: `message ${i} after gap`
+					});
+				}
+				records = await storage.selectAt(roomId, initialSortKey, 15);
+			}
+			console.log(records, "records");
+			const nodes = records.map(r => {
+				const li = document.createElement("li");
+				li.appendChild(document.createTextNode(r.message));
+				return li;
+			});
+			const parentNode = document.getElementById("messages");
+			nodes.forEach(n => parentNode.appendChild(n));
+		})();
+
+	</script>
+</body>
+</html>