package com.wireguard.android;

import android.app.Service;
import android.content.Intent;
import android.content.SharedPreferences;
import android.databinding.ObservableArrayMap;
import android.os.AsyncTask;
import android.os.Binder;
import android.os.IBinder;
import android.preference.PreferenceManager;
import android.util.Log;

import com.wireguard.config.Config;

import java.io.File;
import java.io.FileOutputStream;
import java.io.FilenameFilter;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;

/**
 * Service that handles config state coordination and all background processing for the application.
 */

public class VpnService extends Service
        implements SharedPreferences.OnSharedPreferenceChangeListener {
    private static final String KEY_PRIMARY_CONFIG = "primary_config";
    private static final String TAG = "VpnService";

    private static VpnService instance;

    public static VpnService getInstance() {
        return instance;
    }

    private final IBinder binder = new Binder();
    private final ObservableArrayMap<String, Config> configurations = new ObservableArrayMap<>();
    private SharedPreferences preferences;
    private Config primaryConfig;
    private RootShell rootShell;

    /**
     * Add a new configuration to the set of known configurations. The configuration will initially
     * be disabled. The configuration's name must be unique within the set of known configurations.
     *
     * @param config The configuration to add.
     */
    public void add(final Config config) {
        new ConfigUpdater(null, config, false).execute();
    }

    /**
     * Attempt to disable and tear down an interface for this configuration. The configuration's
     * enabled state will be updated the operation is successful. If this configuration is already
     * disconnected, or it is not a known configuration, no changes will be made.
     *
     * @param name The name of the configuration (in the set of known configurations) to disable.
     */
    public void disable(final String name) {
        final Config config = configurations.get(name);
        if (config == null || !config.isEnabled())
            return;
        new ConfigDisabler(config).execute();
    }

    /**
     * Attempt to set up and enable an interface for this configuration. The configuration's enabled
     * state will be updated if the operation is successful. If this configuration is already
     * enabled, or it is not a known configuration, no changes will be made.
     *
     * @param name The name of the configuration (in the set of known configurations) to enable.
     */
    public void enable(final String name) {
        final Config config = configurations.get(name);
        if (config == null || config.isEnabled())
            return;
        new ConfigEnabler(config).execute();
    }

    /**
     * Retrieve a configuration known and managed by this service. The returned object must not be
     * modified directly.
     *
     * @param name The name of the configuration (in the set of known configurations) to retrieve.
     * @return An object representing the configuration. This object must not be modified.
     */
    public Config get(final String name) {
        return configurations.get(name);
    }

    /**
     * Retrieve the set of configurations known and managed by the service. Configurations in this
     * set must not be modified directly. If a configuration is to be updated, first create a copy
     * of it by calling getCopy().
     *
     * @return The set of known configurations.
     */
    public ObservableArrayMap<String, Config> getConfigs() {
        return configurations;
    }

    @Override
    public IBinder onBind(final Intent intent) {
        instance = this;
        return binder;
    }

    @Override
    public void onCreate() {
        // Ensure the service sticks around after being unbound. This only needs to happen once.
        startService(new Intent(this, getClass()));
        rootShell = new RootShell(this);
        new ConfigLoader().execute(getFilesDir().listFiles(new FilenameFilter() {
            @Override
            public boolean accept(final File dir, final String name) {
                return name.endsWith(".conf");
            }
        }));
        preferences = PreferenceManager.getDefaultSharedPreferences(this);
        preferences.registerOnSharedPreferenceChangeListener(this);
    }

    @Override
    public void onSharedPreferenceChanged(final SharedPreferences preferences,
                                          final String key) {
        Log.i(TAG, "Preference change trigger!");
        if (!KEY_PRIMARY_CONFIG.equals(key))
            return;
        final String name = preferences.getString(key, null);
        if (primaryConfig != null && !primaryConfig.getName().equals(name)) {
            primaryConfig.setIsPrimary(false);
            primaryConfig = null;
        }
        if (primaryConfig == null && name != null) {
            primaryConfig = configurations.get(name);
            if (primaryConfig != null)
                primaryConfig.setIsPrimary(true);
        }
    }

    @Override
    public int onStartCommand(final Intent intent, final int flags, final int startId) {
        instance = this;
        return START_STICKY;
    }

    /**
     * Remove a configuration from being managed by the service. If it is currently enabled, the
     * the configuration will be disabled before removal. If successful, the configuration will be
     * removed from persistent storage. If the configuration is not known to the service, no changes
     * will be made.
     *
     * @param name The name of the configuration (in the set of known configurations) to remove.
     */
    public void remove(final String name) {
        final Config config = configurations.get(name);
        if (config == null)
            return;
        if (config.isEnabled())
            new ConfigDisabler(config).execute();
        new ConfigRemover(config).execute();
    }

    /**
     * Update the attributes of the named configuration. If the configuration is currently enabled,
     * it will be disabled before the update, and the service will attempt to re-enable it
     * afterward. If successful, the updated configuration will be saved to persistent storage.
     *
     * @param name   The name of an existing configuration to update.
     * @param config A copy of the configuration, with updated attributes.
     */
    public void update(final String name, final Config config) {
        if (name == null)
            return;
        if (configurations.containsValue(config))
            throw new IllegalArgumentException("Config " + config.getName() + " modified directly");
        final Config oldConfig = configurations.get(name);
        if (oldConfig == null)
            return;
        final boolean wasEnabled = oldConfig.isEnabled();
        if (wasEnabled)
            new ConfigDisabler(oldConfig).execute();
        new ConfigUpdater(oldConfig, config, wasEnabled).execute();
    }

    private class ConfigDisabler extends AsyncTask<Void, Void, Boolean> {
        private final Config config;

        private ConfigDisabler(final Config config) {
            this.config = config;
        }

        @Override
        protected Boolean doInBackground(final Void... voids) {
            Log.i(TAG, "Running wg-quick down for " + config.getName());
            final File configFile = new File(getFilesDir(), config.getName() + ".conf");
            return rootShell.run(null, "wg-quick down '" + configFile.getPath() + "'") == 0;
        }

        @Override
        protected void onPostExecute(final Boolean result) {
            if (!result)
                return;
            config.setIsEnabled(false);
        }
    }

    private class ConfigEnabler extends AsyncTask<Void, Void, Boolean> {
        private final Config config;

        private ConfigEnabler(final Config config) {
            this.config = config;
        }

        @Override
        protected Boolean doInBackground(final Void... voids) {
            Log.i(TAG, "Running wg-quick up for " + config.getName());
            final File configFile = new File(getFilesDir(), config.getName() + ".conf");
            return rootShell.run(null, "wg-quick up '" + configFile.getPath() + "'") == 0;
        }

        @Override
        protected void onPostExecute(final Boolean result) {
            if (!result)
                return;
            config.setIsEnabled(true);
        }
    }

    private class ConfigLoader extends AsyncTask<File, Void, List<Config>> {
        @Override
        protected List<Config> doInBackground(final File... files) {
            final List<Config> configs = new LinkedList<>();
            final List<String> interfaces = new LinkedList<>();
            final String command = "wg show interfaces";
            if (rootShell.run(interfaces, command) == 0 && interfaces.size() == 1) {
                // wg puts all interface names on the same line. Split them into separate elements.
                final String nameList = interfaces.get(0);
                Collections.addAll(interfaces, nameList.split(" "));
                interfaces.remove(0);
            } else {
                interfaces.clear();
                Log.w(TAG, "No existing WireGuard interfaces found. Maybe they are all disabled?");
            }
            for (final File file : files) {
                if (isCancelled())
                    return null;
                final String fileName = file.getName();
                final String configName = fileName.substring(0, fileName.length() - 5);
                Log.v(TAG, "Attempting to load config " + configName);
                try {
                    final Config config = new Config();
                    config.parseFrom(openFileInput(fileName));
                    config.setIsEnabled(interfaces.contains(configName));
                    config.setName(configName);
                    configs.add(config);
                } catch (IllegalArgumentException | IOException e) {
                    Log.w(TAG, "Failed to load config from " + fileName, e);
                }
            }
            return configs;
        }

        @Override
        protected void onPostExecute(final List<Config> configs) {
            if (configs == null)
                return;
            for (final Config config : configs)
                configurations.put(config.getName(), config);
            final String primaryName = preferences.getString(KEY_PRIMARY_CONFIG, null);
            if (primaryName != null) {
                primaryConfig = configurations.get(primaryName);
                if (primaryConfig != null)
                    primaryConfig.setIsPrimary(true);
            }
        }
    }

    private class ConfigRemover extends AsyncTask<Void, Void, Boolean> {
        private final Config config;

        private ConfigRemover(final Config config) {
            this.config = config;
        }

        @Override
        protected Boolean doInBackground(final Void... voids) {
            Log.i(TAG, "Removing config " + config.getName());
            final File configFile = new File(getFilesDir(), config.getName() + ".conf");
            if (configFile.delete()) {
                return true;
            } else {
                Log.e(TAG, "Could not delete configuration for config " + config.getName());
                return false;
            }
        }

        @Override
        protected void onPostExecute(final Boolean result) {
            if (!result)
                return;
            configurations.remove(config.getName());
            // This will get picked up by the preference change listener.
            if (primaryConfig == config)
                preferences.edit().putString(KEY_PRIMARY_CONFIG, null).apply();
        }
    }

    private class ConfigUpdater extends AsyncTask<Void, Void, Boolean> {
        private Config newConfig;
        private final String newName;
        private final Config oldConfig;
        private final String oldName;
        private final Boolean shouldConnect;

        private ConfigUpdater(final Config oldConfig, final Config newConfig,
                              final Boolean shouldConnect) {
            super();
            this.newConfig = newConfig;
            this.oldConfig = oldConfig;
            this.shouldConnect = shouldConnect;
            newName = newConfig.getName();
            // When adding a config, "old file" and "new file" are the same thing.
            oldName = oldConfig != null ? oldConfig.getName() : newName;
            if (isAddOrRename() && configurations.containsKey(newName))
                throw new IllegalStateException("Config " + newName + " already exists");
        }

        @Override
        protected Boolean doInBackground(final Void... voids) {
            Log.i(TAG, (oldConfig == null ? "Adding" : "Updating") + " config " + newName);
            final File newFile = new File(getFilesDir(), newName + ".conf");
            final File oldFile = new File(getFilesDir(), oldName + ".conf");
            if (isAddOrRename() && newFile.exists()) {
                Log.w(TAG, "Refusing to overwrite existing config configuration");
                return false;
            }
            try {
                final FileOutputStream stream = openFileOutput(oldFile.getName(), MODE_PRIVATE);
                stream.write(newConfig.toString().getBytes(StandardCharsets.UTF_8));
                stream.close();
            } catch (final IOException e) {
                Log.e(TAG, "Could not save configuration for config " + oldName, e);
                return false;
            }
            if (isRename() && !oldFile.renameTo(newFile)) {
                Log.e(TAG, "Could not rename " + oldFile.getName() + " to " + newFile.getName());
                return false;
            }
            return true;
        }

        private boolean isAddOrRename() {
            return oldConfig == null || !newName.equals(oldName);
        }

        private boolean isRename() {
            return oldConfig != null && !newName.equals(oldName);
        }

        @Override
        protected void onPostExecute(final Boolean result) {
            if (!result)
                return;
            if (oldConfig != null) {
                configurations.remove(oldName);
                oldConfig.copyFrom(newConfig);
                newConfig = oldConfig;
            }
            newConfig.setIsEnabled(false);
            configurations.put(newName, newConfig);
            if (shouldConnect)
                new ConfigEnabler(newConfig).execute();
        }
    }
}