/* -*- Mode: Java; c-basic-offset: 4; tab-width: 20; indent-tabs-mode: nil; -*-
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

package org.mozilla.gecko.home;

import static org.mozilla.gecko.home.HomeConfig.createBuiltinPanelConfig;

import java.util.ArrayList;
import java.util.EnumSet;
import java.util.Locale;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import org.mozilla.gecko.GeckoSharedPrefs;
import org.mozilla.gecko.home.HomeConfig.HomeConfigBackend;
import org.mozilla.gecko.home.HomeConfig.OnReloadListener;
import org.mozilla.gecko.home.HomeConfig.PanelConfig;
import org.mozilla.gecko.home.HomeConfig.PanelType;
import org.mozilla.gecko.home.HomeConfig.State;
import org.mozilla.gecko.util.HardwareUtils;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.SharedPreferences;
import android.support.annotation.CheckResult;
import android.support.annotation.VisibleForTesting;
import android.support.v4.content.LocalBroadcastManager;
import android.text.TextUtils;
import android.util.Log;

public class HomeConfigPrefsBackend implements HomeConfigBackend {
    private static final String LOGTAG = "GeckoHomeConfigBackend";

    // Increment this to trigger a migration.
    @VisibleForTesting
    static final int VERSION = 8;

    // This key was originally used to store only an array of panel configs.
    public static final String PREFS_CONFIG_KEY_OLD = "home_panels";

    // This key is now used to store a version number with the array of panel configs.
    public static final String PREFS_CONFIG_KEY = "home_panels_with_version";

    // Keys used with JSON object stored in prefs.
    private static final String JSON_KEY_PANELS = "panels";
    private static final String JSON_KEY_VERSION = "version";

    private static final String PREFS_LOCALE_KEY = "home_locale";

    private static final String RELOAD_BROADCAST = "HomeConfigPrefsBackend:Reload";

    private final Context mContext;
    private ReloadBroadcastReceiver mReloadBroadcastReceiver;
    private OnReloadListener mReloadListener;

    private static boolean sMigrationDone;

    public HomeConfigPrefsBackend(Context context) {
        mContext = context;
    }

    private SharedPreferences getSharedPreferences() {
        return GeckoSharedPrefs.forProfile(mContext);
    }

    private State loadDefaultConfig() {
        final ArrayList<PanelConfig> panelConfigs = new ArrayList<PanelConfig>();

        panelConfigs.add(createBuiltinPanelConfig(mContext, PanelType.TOP_SITES,
                                                  EnumSet.of(PanelConfig.Flags.DEFAULT_PANEL)));

        panelConfigs.add(createBuiltinPanelConfig(mContext, PanelType.BOOKMARKS));
        panelConfigs.add(createBuiltinPanelConfig(mContext, PanelType.COMBINED_HISTORY));


        return new State(panelConfigs, true);
    }

    /**
     * Iterate through the panels to check if they are all disabled.
     */
    private static boolean allPanelsAreDisabled(JSONArray jsonPanels) throws JSONException {
        final int count = jsonPanels.length();
        for (int i = 0; i < count; i++) {
            final JSONObject jsonPanelConfig = jsonPanels.getJSONObject(i);

            if (!jsonPanelConfig.optBoolean(PanelConfig.JSON_KEY_DISABLED, false)) {
                return false;
            }
        }

        return true;
    }

    protected enum Position {
        NONE, // Not present.
        FRONT, // At the front of the list of panels.
        BACK, // At the back of the list of panels.
    }

    /**
     * Create and insert a built-in panel configuration.
     *
     * @param context Android context.
     * @param jsonPanels array of JSON panels to update in place.
     * @param panelType to add.
     * @param positionOnPhones where to place the new panel on phones.
     * @param positionOnTablets where to place the new panel on tablets.
     * @throws JSONException
     */
    protected static void addBuiltinPanelConfig(Context context, JSONArray jsonPanels,
            PanelType panelType, Position positionOnPhones, Position positionOnTablets) throws JSONException {
        // Add the new panel.
        final JSONObject jsonPanelConfig =
                createBuiltinPanelConfig(context, panelType).toJSON();

        // If any panel is enabled, then we should make the new panel enabled.
        jsonPanelConfig.put(PanelConfig.JSON_KEY_DISABLED,
                                 allPanelsAreDisabled(jsonPanels));

        final boolean isTablet = HardwareUtils.isTablet();
        final boolean isPhone = !isTablet;

        // Maybe add the new panel to the front of the array.
        if ((isPhone && positionOnPhones == Position.FRONT) ||
            (isTablet && positionOnTablets == Position.FRONT)) {
            // This is an inefficient way to stretch [a, b, c] to [a, a, b, c].
            for (int i = jsonPanels.length(); i >= 1; i--) {
                jsonPanels.put(i, jsonPanels.get(i - 1));
            }
            // And this inserts [d, a, b, c].
            jsonPanels.put(0, jsonPanelConfig);
        }

        // Maybe add the new panel to the back of the array.
        if ((isPhone && positionOnPhones == Position.BACK) ||
            (isTablet && positionOnTablets == Position.BACK)) {
            jsonPanels.put(jsonPanelConfig);
        }
    }

    /**
     * Updates the panels to combine the History and Sync panels into the (Combined) History panel.
     *
     * Tries to replace the History panel with the Combined History panel if visible, or falls back to
     * replacing the Sync panel if it's visible. That way, we minimize panel reordering during a migration.
     * @param context Android context
     * @param jsonPanels array of original JSON panels
     * @return new array of updated JSON panels
     * @throws JSONException
     */
    private static JSONArray combineHistoryAndSyncPanels(Context context, JSONArray jsonPanels) throws JSONException {
        EnumSet<PanelConfig.Flags> historyFlags = null;
        EnumSet<PanelConfig.Flags> syncFlags = null;

        int historyIndex = -1;
        int syncIndex = -1;

        // Determine state and location of History and Sync panels.
        for (int i = 0; i < jsonPanels.length(); i++) {
            JSONObject panelObj = jsonPanels.getJSONObject(i);
            final PanelConfig panelConfig = new PanelConfig(panelObj);
            final PanelType type = panelConfig.getType();
            if (type == PanelType.DEPRECATED_HISTORY) {
                historyIndex = i;
                historyFlags = panelConfig.getFlags();
            } else if (type == PanelType.DEPRECATED_REMOTE_TABS) {
                syncIndex = i;
                syncFlags = panelConfig.getFlags();
            } else if (type == PanelType.COMBINED_HISTORY) {
                // Partial landing of bug 1220928 combined the History and Sync panels of users who didn't
                // have home panel customizations (including new users), thus they don't this migration.
                return jsonPanels;
            }
        }

        if (historyIndex == -1 || syncIndex == -1) {
            throw new IllegalArgumentException("Expected both History and Sync panels to be present prior to Combined History.");
        }

        PanelConfig newPanel;
        int replaceIndex;
        int removeIndex;

        if (historyFlags.contains(PanelConfig.Flags.DISABLED_PANEL) && !syncFlags.contains(PanelConfig.Flags.DISABLED_PANEL)) {
            // Replace the Sync panel if it's visible and the History panel is disabled.
            replaceIndex = syncIndex;
            removeIndex = historyIndex;
            newPanel = createBuiltinPanelConfig(context, PanelType.COMBINED_HISTORY, syncFlags);
        } else {
            // Otherwise, just replace the History panel.
            replaceIndex = historyIndex;
            removeIndex = syncIndex;
            newPanel = createBuiltinPanelConfig(context, PanelType.COMBINED_HISTORY, historyFlags);
        }

        // Copy the array with updated panel and removed panel.
        final JSONArray newArray = new JSONArray();
        for (int i = 0; i < jsonPanels.length(); i++) {
            if (i == replaceIndex) {
                newArray.put(newPanel.toJSON());
            } else if (i == removeIndex) {
                continue;
            } else {
                newArray.put(jsonPanels.get(i));
            }
        }

        return newArray;
    }

    /**
     * Iterate over all homepanels to verify that there is at least one default panel. If there is
     * no default panel, set History as the default panel. (This is only relevant for two botched
     * migrations where the history panel should have been made the default panel, but wasn't.)
     */
    private static void ensureDefaultPanelForV5orV8(Context context, JSONArray jsonPanels) throws JSONException {
        int historyIndex = -1;

        // If all panels are disabled, there is no default panel - this is the only valid state
        // that has no default. We can use this flag to track whether any visible panels have been
        // found.
        boolean enabledPanelsFound = false;

        for (int i = 0; i < jsonPanels.length(); i++) {
            final PanelConfig panelConfig = new PanelConfig(jsonPanels.getJSONObject(i));
            if (panelConfig.isDefault()) {
                return;
            }

            if (!panelConfig.isDisabled()) {
                enabledPanelsFound = true;
            }

            if (panelConfig.getType() == PanelType.COMBINED_HISTORY) {
                historyIndex = i;
            }
        }

        if (!enabledPanelsFound) {
            // No panels are enabled, hence there can be no default (see noEnabledPanelsFound declaration
            // for more information).
            return;
        }

        // Make the History panel default. We can't modify existing PanelConfigs, so make a new one.
        final PanelConfig historyPanelConfig = createBuiltinPanelConfig(context, PanelType.COMBINED_HISTORY, EnumSet.of(PanelConfig.Flags.DEFAULT_PANEL));
        jsonPanels.put(historyIndex, historyPanelConfig.toJSON());
    }

    /**
     * Removes a panel from the home panel config.
     * If the removed panel was set as the default home panel, we provide a replacement for it.
     *
     * @param context Android context
     * @param jsonPanels array of original JSON panels
     * @param panelToRemove The home panel to be removed.
     * @param replacementPanel The panel which will replace it if the removed panel
     *                         was the default home panel.
     * @param alwaysUnhide If true, the replacement panel will always be unhidden,
     *                     otherwise only if we turn it into the new default panel.
     * @return new array of updated JSON panels
     * @throws JSONException
     */
    private static JSONArray removePanel(Context context, JSONArray jsonPanels,
                                         PanelType panelToRemove, PanelType replacementPanel, boolean alwaysUnhide) throws JSONException {
        boolean wasDefault = false;
        boolean wasDisabled = false;
        int replacementPanelIndex = -1;
        boolean replacementWasDefault = false;

        // JSONArrary doesn't provide remove() for API < 19, therefore we need to manually copy all
        // the items we don't want deleted into a new array.
        final JSONArray newJSONPanels = new JSONArray();

        for (int i = 0; i < jsonPanels.length(); i++) {
            final JSONObject panelJSON = jsonPanels.getJSONObject(i);
            final PanelConfig panelConfig = new PanelConfig(panelJSON);

            if (panelConfig.getType() == panelToRemove) {
                // If this panel was the default we'll need to assign a new default:
                wasDefault = panelConfig.isDefault();
                wasDisabled = panelConfig.isDisabled();
            } else {
                if (panelConfig.getType() == replacementPanel) {
                    replacementPanelIndex = newJSONPanels.length();
                    if (panelConfig.isDefault()) {
                        replacementWasDefault = true;
                    }
                }

                newJSONPanels.put(panelJSON);
            }
        }

        // Unless alwaysUnhide is true, we make the replacement panel visible only if it is going
        // to be the new default panel, since a hidden default panel doesn't make sense.
        // This is to allow preserving the behaviour of the original reading list migration function.
        if ((wasDefault || alwaysUnhide) && !wasDisabled) {
            final JSONObject replacementPanelConfig;
            if (wasDefault) {
                // If the removed panel was the default, the replacement has to be made the new default
                replacementPanelConfig = createBuiltinPanelConfig(context, replacementPanel, EnumSet.of(PanelConfig.Flags.DEFAULT_PANEL)).toJSON();
            } else {
                final EnumSet<HomeConfig.PanelConfig.Flags> flags;
                if (replacementWasDefault) {
                    // However if the replacement panel was already default, we need to preserve it's default status
                    // (By rewriting the PanelConfig, we lose all existing flags, so we need to make sure desired
                    // flags are retained - in this case there's only DEFAULT_PANEL, which is mutually
                    // exclusive with the DISABLE_PANEL case).
                    flags = EnumSet.of(PanelConfig.Flags.DEFAULT_PANEL);
                } else {
                    flags = EnumSet.noneOf(PanelConfig.Flags.class);
                }

                // The panel is visible since we don't set Flags.DISABLED_PANEL.
                replacementPanelConfig = createBuiltinPanelConfig(context, replacementPanel, flags).toJSON();
            }

            if (replacementPanelIndex != -1) {
                newJSONPanels.put(replacementPanelIndex, replacementPanelConfig);
            } else {
                newJSONPanels.put(replacementPanelConfig);
            }
        }

        return newJSONPanels;
    }

    /**
     * Checks to see if the reading list panel already exists.
     *
     * @param jsonPanels JSONArray array representing the curent set of panel configs.
     *
     * @return boolean Whether or not the reading list panel exists.
     */
    private static boolean readingListPanelExists(JSONArray jsonPanels) {
        final int count = jsonPanels.length();
        for (int i = 0; i < count; i++) {
            try {
                final JSONObject jsonPanelConfig = jsonPanels.getJSONObject(i);
                final PanelConfig panelConfig = new PanelConfig(jsonPanelConfig);
                if (panelConfig.getType() == PanelType.DEPRECATED_READING_LIST) {
                    return true;
                }
            } catch (Exception e) {
                // It's okay to ignore this exception, since an invalid reading list
                // panel config is equivalent to no reading list panel.
                Log.e(LOGTAG, "Exception loading PanelConfig from JSON", e);
            }
        }
        return false;
    }

    @CheckResult
    static synchronized JSONArray migratePrefsFromVersionToVersion(final Context context, final int currentVersion, final int newVersion,
                                                              final JSONArray jsonPanelsIn, final SharedPreferences.Editor prefsEditor) throws JSONException {

        JSONArray jsonPanels = jsonPanelsIn;

        for (int v = currentVersion + 1; v <= newVersion; v++) {
            Log.d(LOGTAG, "Migrating to version = " + v);

            switch (v) {
                case 1:
                    // Add "Recent Tabs" panel.
                    addBuiltinPanelConfig(context, jsonPanels,
                            PanelType.DEPRECATED_RECENT_TABS, Position.FRONT, Position.BACK);

                    // Remove the old pref key.
                    prefsEditor.remove(PREFS_CONFIG_KEY_OLD);
                    break;

                case 2:
                    // Add "Remote Tabs"/"Synced Tabs" panel.
                    addBuiltinPanelConfig(context, jsonPanels,
                            PanelType.DEPRECATED_REMOTE_TABS, Position.FRONT, Position.BACK);
                    break;

                case 3:
                    // Add the "Reading List" panel if it does not exist. At one time,
                    // the Reading List panel was shown only to devices that were not
                    // considered "low memory". Now, we expose the panel to all devices.
                    // This migration should only occur for "low memory" devices.
                    // Note: This will not agree with the default configuration, which
                    // has DEPRECATED_REMOTE_TABS after DEPRECATED_READING_LIST on some devices.
                    if (!readingListPanelExists(jsonPanels)) {
                        addBuiltinPanelConfig(context, jsonPanels,
                                PanelType.DEPRECATED_READING_LIST, Position.BACK, Position.BACK);
                    }
                    break;

                case 4:
                    // Combine the History and Sync panels. In order to minimize an unexpected reordering
                    // of panels, we try to replace the History panel if it's visible, and fall back to
                    // the Sync panel if that's visible.
                    jsonPanels = combineHistoryAndSyncPanels(context, jsonPanels);
                    break;

                case 5:
                    // This is the fix for bug 1264136 where we lost track of the default panel during some migrations.
                    ensureDefaultPanelForV5orV8(context, jsonPanels);
                    break;

                case 6:
                    jsonPanels = removePanel(context, jsonPanels,
                            PanelType.DEPRECATED_READING_LIST, PanelType.BOOKMARKS, false);
                    break;

                case 7:
                    jsonPanels = removePanel(context, jsonPanels,
                            PanelType.DEPRECATED_RECENT_TABS, PanelType.COMBINED_HISTORY, true);
                    break;

                case 8:
                    // Similar to "case 5" above, this time 1304777 - once again we lost track
                    // of the history panel
                    ensureDefaultPanelForV5orV8(context, jsonPanels);
                    break;
            }
        }

        return jsonPanels;
    }

    /**
     * Migrates JSON config data storage.
     *
     * @param context Context used to get shared preferences and create built-in panel.
     * @param jsonString String currently stored in preferences.
     *
     * @return JSONArray array representing new set of panel configs.
     */
    private static synchronized JSONArray maybePerformMigration(Context context, String jsonString) throws JSONException {
        // If the migration is already done, we're at the current version.
        if (sMigrationDone) {
            final JSONObject json = new JSONObject(jsonString);
            return json.getJSONArray(JSON_KEY_PANELS);
        }

        // Make sure we only do this version check once.
        sMigrationDone = true;

        JSONArray jsonPanels;
        final int version;

        final SharedPreferences prefs = GeckoSharedPrefs.forProfile(context);
        if (prefs.contains(PREFS_CONFIG_KEY_OLD)) {
            // Our original implementation did not contain versioning, so this is implicitly version 0.
            jsonPanels = new JSONArray(jsonString);
            version = 0;
        } else {
            final JSONObject json = new JSONObject(jsonString);
            jsonPanels = json.getJSONArray(JSON_KEY_PANELS);
            version = json.getInt(JSON_KEY_VERSION);
        }

        if (version == VERSION) {
            return jsonPanels;
        }

        Log.d(LOGTAG, "Performing migration");

        final SharedPreferences.Editor prefsEditor = prefs.edit();

        jsonPanels = migratePrefsFromVersionToVersion(context, version, VERSION, jsonPanels, prefsEditor);

        // Save the new panel config and the new version number.
        final JSONObject newJson = new JSONObject();
        newJson.put(JSON_KEY_PANELS, jsonPanels);
        newJson.put(JSON_KEY_VERSION, VERSION);

        prefsEditor.putString(PREFS_CONFIG_KEY, newJson.toString());
        prefsEditor.apply();

        return jsonPanels;
    }

    private State loadConfigFromString(String jsonString) {
        final JSONArray jsonPanelConfigs;
        try {
            jsonPanelConfigs = maybePerformMigration(mContext, jsonString);
            updatePrefsFromConfig(jsonPanelConfigs);
        } catch (JSONException e) {
            Log.e(LOGTAG, "Error loading the list of home panels from JSON prefs", e);

            // Fallback to default config
            return loadDefaultConfig();
        }

        final ArrayList<PanelConfig> panelConfigs = new ArrayList<PanelConfig>();

        final int count = jsonPanelConfigs.length();
        for (int i = 0; i < count; i++) {
            try {
                final JSONObject jsonPanelConfig = jsonPanelConfigs.getJSONObject(i);
                final PanelConfig panelConfig = new PanelConfig(jsonPanelConfig);
                panelConfigs.add(panelConfig);
            } catch (Exception e) {
                Log.e(LOGTAG, "Exception loading PanelConfig from JSON", e);
            }
        }

        return new State(panelConfigs, false);
    }

    @Override
    public State load() {
        final SharedPreferences prefs = getSharedPreferences();

        final String key = (prefs.contains(PREFS_CONFIG_KEY_OLD) ? PREFS_CONFIG_KEY_OLD : PREFS_CONFIG_KEY);
        final String jsonString = prefs.getString(key, null);

        final State configState;
        if (TextUtils.isEmpty(jsonString)) {
            configState = loadDefaultConfig();
        } else {
            configState = loadConfigFromString(jsonString);
        }

        return configState;
    }

    @Override
    public void save(State configState) {
        final SharedPreferences prefs = getSharedPreferences();
        final SharedPreferences.Editor editor = prefs.edit();

        // No need to save the state to disk if it represents the default
        // HomeConfig configuration. Simply force all existing HomeConfigLoader
        // instances to refresh their contents.
        if (!configState.isDefault()) {
            final JSONArray jsonPanelConfigs = new JSONArray();

            for (PanelConfig panelConfig : configState) {
                try {
                    final JSONObject jsonPanelConfig = panelConfig.toJSON();
                    jsonPanelConfigs.put(jsonPanelConfig);
                } catch (Exception e) {
                    Log.e(LOGTAG, "Exception converting PanelConfig to JSON", e);
                }
            }

            try {
                final JSONObject json = new JSONObject();
                json.put(JSON_KEY_PANELS, jsonPanelConfigs);
                json.put(JSON_KEY_VERSION, VERSION);

                editor.putString(PREFS_CONFIG_KEY, json.toString());
            } catch (JSONException e) {
                Log.e(LOGTAG, "Exception saving PanelConfig state", e);
            }
        }

        editor.putString(PREFS_LOCALE_KEY, Locale.getDefault().toString());
        editor.apply();

        // Trigger reload listeners on all live backend instances
        sendReloadBroadcast();
    }

    @Override
    public String getLocale() {
        final SharedPreferences prefs = getSharedPreferences();

        String locale = prefs.getString(PREFS_LOCALE_KEY, null);
        if (locale == null) {
            // Initialize config with the current locale
            final String currentLocale = Locale.getDefault().toString();

            final SharedPreferences.Editor editor = prefs.edit();
            editor.putString(PREFS_LOCALE_KEY, currentLocale);
            editor.apply();

            // If the user has saved HomeConfig before, return null this
            // one time to trigger a refresh and ensure we use the
            // correct locale for the saved state. For more context,
            // see HomePanelsManager.onLocaleReady().
            if (!prefs.contains(PREFS_CONFIG_KEY)) {
                locale = currentLocale;
            }
        }

        return locale;
    }

    @Override
    public void setOnReloadListener(OnReloadListener listener) {
        if (mReloadListener != null) {
            unregisterReloadReceiver();
            mReloadBroadcastReceiver = null;
        }

        mReloadListener = listener;

        if (mReloadListener != null) {
            mReloadBroadcastReceiver = new ReloadBroadcastReceiver();
            registerReloadReceiver();
        }
    }

    /**
     * Update prefs that depend on home panels state.
     *
     * This includes the prefs that keep track of whether bookmarks or history are enabled, which are
     * used to control the visibility of the corresponding menu items.
     */
    private void updatePrefsFromConfig(JSONArray panelsArray) {
        final SharedPreferences prefs = GeckoSharedPrefs.forProfile(mContext);
        if (!prefs.contains(HomeConfig.PREF_KEY_BOOKMARKS_PANEL_ENABLED)
                || !prefs.contains(HomeConfig.PREF_KEY_HISTORY_PANEL_ENABLED)) {

            final String bookmarkType = PanelType.BOOKMARKS.toString();
            final String historyType = PanelType.COMBINED_HISTORY.toString();
            try {
                for (int i = 0; i < panelsArray.length(); i++) {
                    final JSONObject panelObj = panelsArray.getJSONObject(i);
                    final String panelType = panelObj.optString(PanelConfig.JSON_KEY_TYPE, null);
                    if (panelType == null) {
                        break;
                    }
                    final boolean isDisabled = panelObj.optBoolean(PanelConfig.JSON_KEY_DISABLED, false);
                    if (bookmarkType.equals(panelType)) {
                        prefs.edit().putBoolean(HomeConfig.PREF_KEY_BOOKMARKS_PANEL_ENABLED, !isDisabled).apply();
                    } else if (historyType.equals(panelType)) {
                        prefs.edit().putBoolean(HomeConfig.PREF_KEY_HISTORY_PANEL_ENABLED, !isDisabled).apply();
                    }
                }
            } catch (JSONException e) {
                Log.e(LOGTAG, "Error fetching panel from config to update prefs");
            }
        }
    }


    private void sendReloadBroadcast() {
        final LocalBroadcastManager lbm = LocalBroadcastManager.getInstance(mContext);
        final Intent reloadIntent = new Intent(RELOAD_BROADCAST);
        lbm.sendBroadcast(reloadIntent);
    }

    private void registerReloadReceiver() {
        final LocalBroadcastManager lbm = LocalBroadcastManager.getInstance(mContext);
        lbm.registerReceiver(mReloadBroadcastReceiver, new IntentFilter(RELOAD_BROADCAST));
    }

    private void unregisterReloadReceiver() {
        final LocalBroadcastManager lbm = LocalBroadcastManager.getInstance(mContext);
        lbm.unregisterReceiver(mReloadBroadcastReceiver);
    }

    private class ReloadBroadcastReceiver extends BroadcastReceiver {
        @Override
        public void onReceive(Context context, Intent intent) {
            mReloadListener.onReload();
        }
    }
}