Add card shortcuts for most recently used cards

This adds app shortcuts for the most recently used cards.
When a new card is accessed, it is added to the shortcuts list.
When the list exceeds its maximum size, the least recently
used shortcut is discarded.

Android limits the maximum number of shortcuts to 5, however
it recommends in its documentation to limit this to 4. This
commit limits this to 3, however, as that is aesthetically pleasing.

app/build.gradle

@@ -13,7 +13,7 @@ android {
     defaultConfig {
         applicationId "protect.card_locker"
         minSdkVersion 17
-        targetSdkVersion 23
+        targetSdkVersion 25
         versionCode 14
         versionName "0.13"
     }

app/src/main/java/protect/card_locker/LoyaltyCardViewActivity.java

@@ -354,6 +354,9 @@ public class LoyaltyCardViewActivity extends AppCompatActivity
 
                         DBHelper db = new DBHelper(LoyaltyCardViewActivity.this);
                         db.deleteLoyaltyCard(loyaltyCardId);
+
+                        ShortcutHelper.removeShortcut(LoyaltyCardViewActivity.this, loyaltyCardId);
+
                         finish();
                         dialog.dismiss();
                     }

app/src/main/java/protect/card_locker/MainActivity.java

@@ -7,7 +7,10 @@ import android.content.ClipboardManager;
 import android.content.SharedPreferences;
 import android.content.pm.PackageInfo;
 import android.content.pm.PackageManager;
+import android.content.pm.ShortcutInfo;
+import android.content.pm.ShortcutManager;
 import android.database.Cursor;
+import android.os.Build;
 import android.os.Bundle;
 import android.support.v7.app.AlertDialog;
 import android.support.v7.app.AppCompatActivity;
@@ -27,6 +30,7 @@ import android.widget.Toast;
 import com.google.common.collect.ImmutableMap;
 
 import java.util.Calendar;
+import java.util.List;
 import java.util.Map;
 
 import protect.card_locker.intro.IntroActivity;
@@ -93,10 +97,14 @@ public class MainActivity extends AppCompatActivity
                 LoyaltyCard loyaltyCard = LoyaltyCard.toLoyaltyCard(selected);
 
                 Intent i = new Intent(view.getContext(), LoyaltyCardViewActivity.class);
+                i.setAction("");
                 final Bundle b = new Bundle();
                 b.putInt("id", loyaltyCard.id);
                 b.putBoolean("view", true);
                 i.putExtras(b);
+
+                ShortcutHelper.updateShortcuts(MainActivity.this, loyaltyCard, i);
+
                 startActivity(i);
             }
         });

app/src/main/java/protect/card_locker/ShortcutHelper.java

@@ -0,0 +1,147 @@
+package protect.card_locker;
+
+import android.annotation.TargetApi;
+import android.content.Context;
+import android.content.Intent;
+import android.content.pm.ShortcutInfo;
+import android.content.pm.ShortcutManager;
+import android.graphics.drawable.Icon;
+import android.os.Build;
+
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.LinkedList;
+import java.util.List;
+
+class ShortcutHelper
+{
+    // Android documentation says that no more than 5 shortcuts
+    // are supported. However, that may be too many, as not all
+    // launcher will show all 5. Instead, the number is limited
+    // to 3 here, so that the most recent shortcut has a good
+    // chance of being shown.
+    private static final int MAX_SHORTCUTS = 3;
+
+    /**
+     * Add a card to the app shortcuts, and maintain a list of the most
+     * recently used cards. If there is already a shortcut for the card,
+     * the card is marked as the most recently used card. If adding this
+     * card exceeds the max number of shortcuts, then the least recently
+     * used card shortcut is discarded.
+     */
+    @TargetApi(25)
+    static void updateShortcuts(Context context, LoyaltyCard card, Intent intent)
+    {
+        if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.N_MR1)
+        {
+            ShortcutManager shortcutManager = context.getSystemService(ShortcutManager.class);
+            LinkedList<ShortcutInfo> list = new LinkedList<>(shortcutManager.getDynamicShortcuts());
+
+            String shortcutId = Integer.toString(card.id);
+
+            // Sort the shortcuts by rank, so working with the relative order will be easier.
+            // This sorts so that the lowest rank is first.
+            Collections.sort(list, new Comparator<ShortcutInfo>()
+            {
+                @Override
+                public int compare(ShortcutInfo o1, ShortcutInfo o2)
+                {
+                    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N_MR1)
+                    {
+                        return o1.getRank() - o2.getRank();
+                    }
+                    else
+                    {
+                        return 0;
+                    }
+                }
+            });
+
+            Integer foundIndex = null;
+
+            for(int index = 0; index < list.size(); index++)
+            {
+                if(list.get(index).getId().equals(shortcutId))
+                {
+                    // Found the item already
+                    foundIndex = index;
+                    break;
+                }
+            }
+
+            if(foundIndex != null)
+            {
+                // If the item is already found, then the list needs to be
+                // reordered, so that the selected item now has the lowest
+                // rank, thus letting it survive longer.
+                ShortcutInfo found = list.remove(foundIndex.intValue());
+                list.addFirst(found);
+            }
+            else
+            {
+                // The item is new to the list. First, we need to trim the list
+                // until it is able to accept a new item, then the item is
+                // inserted.
+                while(list.size() >= MAX_SHORTCUTS)
+                {
+                    list.pollLast();
+                }
+
+                ShortcutInfo shortcut = new ShortcutInfo.Builder(context, Integer.toString(card.id))
+                    .setShortLabel(card.store)
+                    .setLongLabel(card.store)
+                    .setIntent(intent)
+                    .build();
+
+                list.addFirst(shortcut);
+            }
+
+            LinkedList<ShortcutInfo> finalList = new LinkedList<>();
+
+            // The ranks are now updated; the order in the list is the rank.
+            for(int index = 0; index < list.size(); index++)
+            {
+                ShortcutInfo prevShortcut = list.get(index);
+
+                ShortcutInfo updatedShortcut = new ShortcutInfo.Builder(context, prevShortcut.getId())
+                        .setShortLabel(prevShortcut.getShortLabel())
+                        .setLongLabel(prevShortcut.getLongLabel())
+                        .setIntent(prevShortcut.getIntent())
+                        .setIcon(Icon.createWithResource(context, R.drawable.circle))
+                        .setRank(index)
+                        .build();
+
+                finalList.addLast(updatedShortcut);
+            }
+
+            shortcutManager.setDynamicShortcuts(finalList);
+        }
+    }
+
+    /**
+     * Remove the given card id from the app shortcuts, if such a
+     * shortcut exists.
+     */
+    @TargetApi(25)
+    static void removeShortcut(Context context, int cardId)
+    {
+        if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.N_MR1)
+        {
+            ShortcutManager shortcutManager = context.getSystemService(ShortcutManager.class);
+            List<ShortcutInfo> list = shortcutManager.getDynamicShortcuts();
+
+            String shortcutId = Integer.toString(cardId);
+
+            for(int index = 0; index < list.size(); index++)
+            {
+                if(list.get(index).getId().equals(shortcutId))
+                {
+                    list.remove(index);
+                    break;
+                }
+            }
+
+            shortcutManager.setDynamicShortcuts(list);
+        }
+    }
+}