Started support for FTS search

ReactNativeClient/lib/services/SearchEngine.js

@@ -0,0 +1,95 @@
+const { Logger } = require('lib/logger.js');
+
+class SearchEngine {
+
+	constructor() {
+		this.dispatch = (action) => {};
+		this.logger_ = new Logger();
+		this.db_ = null;
+	}
+	
+	async updateFtsTables() {
+		// CREATE VIRTUAL TABLE notes_fts USING fts4(content="notes", title, body);
+		// INSERT INTO notes_fts(docid, title, body) SELECT rowid, title, body FROM notes;
+		// SELECT title, offsets(notes_fts) length(offsets(notes_fts)) - length(replace(offsets(notes_fts), ' ', '')) + 1
+		// FROM notes_fts
+		// WHERE notes_fts
+		// MATCH 'test';
+
+		await this.db().exec('CREATE VIRTUAL TABLE notes_fts USING fts4(content="notes", title, body)');
+		await this.db().exec('INSERT INTO notes_fts(docid, title, body) SELECT rowid, title, body FROM notes;');
+
+		
+		const sql = `SELECT docid, title, offsets(notes_fts) as offsets FROM notes_fts WHERE notes_fts MATCH "abcd efgh" `;
+
+		const rows = await this.db().selectAll(sql);
+
+		const calculateWeight = (offsets) => {
+			// Offset doc: https://www.sqlite.org/fts3.html#offsets
+			
+			const occurenceCount = Math.floor(offsets.length / 4);
+
+			let spread = 0;
+			let previousDist = null;
+			for (let i = 0; i < occurenceCount; i++) {
+				const dist = offsets[i * 4 + 2];
+
+				if (previousDist !== null) {
+					const delta = dist - previousDist;
+					spread += delta;
+				}
+
+				previousDist = dist;
+			}
+
+			// Divide the number of occureances by the spread so even if a note has many times the searched terms
+			// but these terms are very spread appart, they'll be given a lower weight than a note that has the
+			// terms once or twice but just next to each others.
+			return occurenceCount / spread;
+		}
+
+		const orderResults = (rows) => {
+			for (let i = 0; i < rows.length; i++) {
+				const row = rows[i];
+				row.weight = calculateWeight(row.offsets.split(' ').map(o => Number(o)));
+			}
+
+			rows.sort((a, b) => {
+				if (a.weight < b.weight) return +1;
+				if (a.weight > b.weight) return -1;
+				return 0;
+			});
+		}
+
+		orderResults(rows);
+
+		console.info(rows);
+
+		// console.info(rows);
+	}
+
+	static instance() {
+		if (this.instance_) return this.instance_;
+		this.instance_ = new SearchEngine();
+		return this.instance_;
+	}
+
+	setLogger(logger) {
+		this.logger_ = logger;
+	}
+
+	logger() {
+		return this.logger_;
+	}
+
+	setDb(db) {
+		this.db_ = db;
+	}
+
+	db() {
+		return this.db_;
+	}
+
+}
+
+module.exports = SearchEngine;