Eula.java

package net.everythingandroid.smspopup.util;

import java.io.BufferedReader;
import java.io.Closeable;
import java.io.IOException;
import java.io.InputStreamReader;

import net.everythingandroid.smspopup.R;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.SharedPreferences;
import android.net.Uri;

/**
 * Displays an EULA ("End User License Agreement") that the user has to accept before using the
 * application. Your application should call {@link Eula#show(android.app.Activity)} in the
 * onCreate() method of the first activity. If the user accepts the EULA, it will never be shown
 * again. If the user refuses, {@link android.app.Activity#finish()} is invoked on your activity.
 */
public class Eula {
    private static final String ASSET_EULA = "eula.txt";
    private static final String PREFERENCE_EULA_ACCEPTED = "eula.accepted";
    private static final String PREFERENCES_EULA = "eula";

    /**
     * callback to let the activity know when the user has accepted the EULA.
     */
    static interface OnEulaAgreedTo {

        /**
         * Called when the user has accepted the eula and the dialog closes.
         */
        void onEulaAgreedTo();
    }

    /**
     * callback to let the activity know when the user has not accepted the EULA.
     */
    static interface OnEulaNotAgreedTo {

        /**
         * Called when the user has not accepted the eula and the dialog closes.
         */
        void onEulaNotAgreedTo();
    }

    /**
     * Displays the EULA if necessary. This method should be called from the onCreate() method of
     * your main Activity.
     * 
     * @param activity
     *            The Activity to finish if the user rejects the EULA.
     * @return Whether the user has agreed already.
     */
    public static boolean show(final Activity activity) {
        final SharedPreferences preferences = activity.getSharedPreferences(PREFERENCES_EULA,
                Activity.MODE_PRIVATE);
        if (!preferences.getBoolean(PREFERENCE_EULA_ACCEPTED, false)) {
            final AlertDialog.Builder builder = new AlertDialog.Builder(activity);
            builder.setTitle(R.string.eula_title);
            builder.setCancelable(true);
            builder.setPositiveButton(R.string.eula_accept, new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int which) {
                    accept(preferences);
                    if (activity instanceof OnEulaAgreedTo) {
                        ((OnEulaAgreedTo) activity).onEulaAgreedTo();
                    }
                }
            });
            builder.setNegativeButton(R.string.eula_refuse, new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int which) {
                    refuse(activity);
                }
            });
            builder.setOnCancelListener(new DialogInterface.OnCancelListener() {
                public void onCancel(DialogInterface dialog) {
                    refuse(activity);
                }
            });
            builder.setMessage(readEula(activity));
            builder.create().show();
            return false;
        }
        return true;
    }

    private static void accept(SharedPreferences preferences) {
        preferences.edit().putBoolean(PREFERENCE_EULA_ACCEPTED, true).commit();
    }

    private static void refuse(Activity activity) {
        final Uri packageUri = Uri.parse("package:net.everythingandroid.smspopup");
        Intent uninstallIntent = new Intent(Intent.ACTION_DELETE, packageUri);
        activity.startActivity(uninstallIntent);

        activity.finish();
    }

    private static CharSequence readEula(Activity activity) {
        BufferedReader in = null;
        try {
            in = new BufferedReader(new InputStreamReader(activity.getAssets().open(ASSET_EULA)));
            String line;
            StringBuilder buffer = new StringBuilder();
            while ((line = in.readLine()) != null)
                buffer.append(line).append('\n');
            return buffer;
        } catch (IOException e) {
            return "";
        } finally {
            closeStream(in);
        }
    }

    /**
     * Closes the specified stream.
     * 
     * @param stream
     *            The stream to close.
     */
    private static void closeStream(Closeable stream) {
        if (stream != null) {
            try {
                stream.close();
            } catch (IOException e) {
                // Ignore
            }
        }
    }
}