TermHistory, a class for tracking what terms the user views

app/src/androidTest/java/net/mdln/englisc/TermHistoryTest.java

@@ -0,0 +1,31 @@
+package net.mdln.englisc;
+
+import android.content.Context;
+
+import androidx.test.platform.app.InstrumentationRegistry;
+
+import org.junit.Test;
+
+import java.util.HashSet;
+import java.util.Set;
+
+import static org.junit.Assert.assertEquals;
+
+public class TermHistoryTest {
+
+    @Test
+    public void history() {
+        Context ctx = InstrumentationRegistry.getInstrumentation().getTargetContext();
+        try (TermHistory history = new TermHistory(ctx, TermHistory.Location.IN_MEMORY, 0)) {
+            history.recordId(100, 1000);
+            history.recordId(101, 1001);
+            Set<Integer> expectedIds = new HashSet();
+            assertEquals(expectedIds, history.getIds(0));
+            expectedIds.add(101);
+            assertEquals(expectedIds, history.getIds(1));
+            expectedIds.add(100);
+            assertEquals(expectedIds, history.getIds(2));
+            assertEquals(expectedIds, history.getIds(3));
+        }
+    }
+}

app/src/main/java/net/mdln/englisc/TermHistory.java

@@ -0,0 +1,83 @@
+package net.mdln.englisc;
+
+import android.content.Context;
+import android.database.Cursor;
+import android.database.sqlite.SQLiteDatabase;
+import android.database.sqlite.SQLiteOpenHelper;
+
+import androidx.annotation.Nullable;
+
+import java.io.File;
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * Keeps track of term ids viewed and their timestamps so we can show recently viewed items
+ * in {@link MainActivity}.
+ */
+public class TermHistory implements AutoCloseable {
+
+    private static final int SCHEMA_VERSION = 1;
+
+    private final SQLiteOpenHelper databaseHelper;
+
+    TermHistory(Context ctx, Location loc, long deleteHistoryBeforeMillis) {
+        this.databaseHelper = new OpenHelper(ctx, loc, deleteHistoryBeforeMillis / 1000.0);
+    }
+
+    void recordId(int nid, long timeMillis) {
+        String sql = "INSERT INTO history (nid, timestamp_secs) VALUES (?, ?)";
+        databaseHelper.getWritableDatabase().execSQL(sql, new Object[]{nid, timeMillis / 1000.0});
+    }
+
+    Set<Integer> getIds(int limit) {
+        SQLiteDatabase db = databaseHelper.getReadableDatabase();
+        Set<Integer> ids = new HashSet<>();
+        String sql = "SELECT nid FROM history ORDER BY timestamp_secs DESC LIMIT " + limit;
+        try (Cursor cursor = db.rawQuery(sql, new String[]{})) {
+            while (cursor.moveToNext()) {
+                ids.add(cursor.getInt(0));
+            }
+        }
+        return ids;
+    }
+
+    @Override
+    public void close() {
+        databaseHelper.close();
+    }
+
+    enum Location {ON_DISK, IN_MEMORY}
+
+    private static final class OpenHelper extends SQLiteOpenHelper {
+
+        private final double deleteHistoryBeforeSecs;
+
+        public OpenHelper(Context context, Location loc, double deleteHistoryBeforeSecs) {
+            super(context, getPath(context, loc), null, SCHEMA_VERSION);
+            this.deleteHistoryBeforeSecs = deleteHistoryBeforeSecs;
+        }
+
+        @Nullable
+        private static String getPath(Context context, Location loc) {
+            return loc == Location.IN_MEMORY ? null :
+                    new File(context.getNoBackupFilesDir(), "history.db").toString();
+        }
+
+        @Override
+        public void onCreate(SQLiteDatabase db) {
+            db.execSQL("CREATE TABLE history (nid INTEGER, timestamp_secs REAL)");
+        }
+
+        @Override
+        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
+        }
+
+        @Override
+        public void onOpen(SQLiteDatabase db) {
+            if (deleteHistoryBeforeSecs > 0) {
+                db.execSQL("DELETE FROM history WHERE timestamp_secs < ?", new String[]{String.valueOf(deleteHistoryBeforeSecs)});
+            }
+        }
+    }
+}

app/src/main/java/net/mdln/englisc/WebViewStyle.java

@@ -30,7 +30,7 @@ public static void apply(Activity activity, WebView view, String html) {
     private static String styledHtml(Activity activity, String html, boolean night) {
         String headBlock = "<head><style type=\"text/css\">" + Streams.readUtf8Resource(activity, R.raw.defn) + "</style></head>";
         String styleClass = night ? "dark" : "light";
-        String bodyBlock = "<body class=\"" + styleClass + "\">" +  html + "</body>";
+        String bodyBlock = "<body class=\"" + styleClass + "\">" + html + "</body>";
         return "<html>" + headBlock + bodyBlock + "</html>";
     }
 

app/src/main/res/values/strings.xml

@@ -5,5 +5,5 @@
     <string name="close_button">Close</string>
     <string name="feedback_subject">Feedback on %s</string>
     <string name="type_feedback_here">TYPE FEEDBACK HERE</string>
-    <string name="main_help_text">Type \'th\' for \'þ\' or \'ð\', and \'ae\' for \'æ\'. You can search for Anglo-Saxon words, Modern English words, and abbreviations. Got ideas for how to make the app better? Please let me know by selecting Feedback in the ⋮ menu.</string>
+    <string name="main_help_text">Type \'th\' for \'þ\' or \'ð\', and \'ae\' for \'æ\'. You can search for Anglo-Saxon and Modern English words.</string>
 </resources>