Added FTS OR search

FAQ.md

@@ -693,6 +693,10 @@ to check if the searched text is contained in the file, which is a relative expe
 
 In the *miscellaneous settings* you can enable *Build search index* to significantly increase the speed of searching on the device,
 but be aware that this will increase battery usage and significantly increase storage space usage too.
+Searching using the search index is by default AND, so searching for *apple orange* will search for apple AND orange.
+Words separated by commas results in searching for OR, so for example *apple, orange* will search for apple OR orange.
+Both can be combined, so searching for *apple, orange banana* will search for apple OR (orange AND banana).
+Using the search index is a pro feature.
 
 Searching messages on the device is a free feature, searching messages on the server is a pro feature.
 

app/src/main/java/eu/faircode/email/FtsDbHelper.java

@@ -94,13 +94,26 @@ public class FtsDbHelper extends SQLiteOpenHelper {
     }
 
     static List<Long> match(SQLiteDatabase db, Long folder, String query) {
-        String[] parts = query.split("\\s+");
         StringBuilder sb = new StringBuilder();
-        for (String part : parts) {
+        for (String or : query.split(",")) {
             if (sb.length() > 0)
+                sb.append(" OR ");
+
+            boolean first = true;
+            sb.append("(");
+            for (String and : or.trim().split("\\s+")) {
+                if (first)
+                    first = false;
+                else
                     sb.append(" AND ");
-            part = part.replaceAll("\"", "\"\"");
+
-            sb.append("\"").append(part).append("\"");
+                // Escape quotes
+                String term = and.replaceAll("\"", "\"\"");
+
+                // Quote search term
+                sb.append("\"").append(term).append("\"");
+            }
+            sb.append(")");
         }
 
         String search = sb.toString();