/*
 * Copyright (C) 2022 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.server.healthconnect.common.preferences;

import static com.android.server.healthconnect.storage.request.UpsertTableRequest.TYPE_STRING;
import static com.android.server.healthconnect.storage.utils.StorageUtils.TEXT_NOT_NULL_UNIQUE;
import static com.android.server.healthconnect.storage.utils.StorageUtils.TEXT_NULL;

import android.annotation.Nullable;
import android.content.ContentValues;
import android.database.Cursor;
import android.util.Pair;

import com.android.server.healthconnect.storage.DatabaseHelper;
import com.android.server.healthconnect.storage.TransactionManager;
import com.android.server.healthconnect.storage.request.CreateTableRequest;
import com.android.server.healthconnect.storage.request.DeleteTableRequest;
import com.android.server.healthconnect.storage.request.ReadTableRequest;
import com.android.server.healthconnect.storage.request.UpsertTableRequest;
import com.android.server.healthconnect.storage.utils.StorageUtils;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

/**
 * A helper class to store user preferences, set in UI APK for the platform.
 *
 * @hide
 */
// TODO(b/303023796): Make this final.
public class PreferenceHelper extends DatabaseHelper {
    private static final String TAG = "PreferenceHelper";
    private static final String TABLE_NAME = "preference_table";
    private static final String KEY_COLUMN_NAME = "key";
    public static final List<Pair<String, Integer>> UNIQUE_COLUMN_INFO =
            Collections.singletonList(new Pair<>(KEY_COLUMN_NAME, TYPE_STRING));
    private static final String VALUE_COLUMN_NAME = "value";
    private final TransactionManager mTransactionManager;

    /**
     * Key to store timestamp of the last time any PHR <b>read medical resources</b> API is called.
     */
    private static final String PREFS_KEY_PHR_LAST_READ_MEDICAL_RESOURCES_API =
            "phr_last_read_medical_resources_api";

    @Nullable protected volatile ConcurrentHashMap<String, String> mPreferences;

    public PreferenceHelper(
            TransactionManager transactionManager, DatabaseHelpers databaseHelpers) {
        super(databaseHelpers);
        mTransactionManager = transactionManager;
    }

    /** Note: Overrides existing preference (if it exists) with the new value */
    public synchronized void insertOrReplacePreference(String key, String value) {
        mTransactionManager.insertOrReplaceOnConflict(
                new UpsertTableRequest(
                        TABLE_NAME, getContentValues(key, value), UNIQUE_COLUMN_INFO));
        getPreferences().put(key, value);
    }

    /** Removes key entry from the table */
    public synchronized void removeKey(String id) {
        mTransactionManager.delete(new DeleteTableRequest(TABLE_NAME).setId(KEY_COLUMN_NAME, id));
        getPreferences().remove(id);
    }

    /** Inserts multiple preferences together in a transaction */
    public synchronized void insertOrReplacePreferencesTransaction(
            HashMap<String, String> keyValues) {
        List<UpsertTableRequest> requests = new ArrayList<>();
        keyValues.forEach(
                (key, value) ->
                        requests.add(
                                new UpsertTableRequest(
                                        TABLE_NAME,
                                        getContentValues(key, value),
                                        UNIQUE_COLUMN_INFO)));
        mTransactionManager.insertOrReplaceAllOnConflict(requests);
        getPreferences().putAll(keyValues);
    }

    public static CreateTableRequest getCreateTableRequest() {
        return new CreateTableRequest(TABLE_NAME, getColumnInfo());
    }

    /** Get the preference for the given key. */
    @Nullable
    public String getPreference(String key) {
        return getPreferences().get(key);
    }

    @Override
    public synchronized void clearCache() {
        mPreferences = null;
    }

    @Override
    protected String getMainTableName() {
        return TABLE_NAME;
    }

    /** Fetch preferences into memory. */
    public void initializePreferences() {
        populatePreferences();
    }

    protected Map<String, String> getPreferences() {
        ConcurrentHashMap<String, String> preferences = mPreferences;
        if (preferences == null) {
            preferences = populatePreferences();
        }
        return preferences;
    }

    private ContentValues getContentValues(String key, String value) {
        ContentValues contentValues = new ContentValues();
        contentValues.put(KEY_COLUMN_NAME, key);
        contentValues.put(VALUE_COLUMN_NAME, value);
        return contentValues;
    }

    private synchronized ConcurrentHashMap<String, String> populatePreferences() {
        ConcurrentHashMap<String, String> preferences = mPreferences;
        if (preferences != null) {
            return preferences;
        }

        preferences = new ConcurrentHashMap<>();
        try (Cursor cursor = mTransactionManager.read(new ReadTableRequest(TABLE_NAME))) {
            while (cursor.moveToNext()) {
                String key = StorageUtils.getCursorString(cursor, KEY_COLUMN_NAME);
                String value = StorageUtils.getCursorString(cursor, VALUE_COLUMN_NAME);
                preferences.put(key, value);
            }
        }
        mPreferences = preferences;
        return preferences;
    }

    private static List<Pair<String, String>> getColumnInfo() {
        ArrayList<Pair<String, String>> columnInfo = new ArrayList<>();
        columnInfo.add(new Pair<>(KEY_COLUMN_NAME, TEXT_NOT_NULL_UNIQUE));
        columnInfo.add(new Pair<>(VALUE_COLUMN_NAME, TEXT_NULL));

        return columnInfo;
    }
}