Activity-only navigator for Cicerone

SupportActivityNavigator.kt

package net.broachcutter.vendorapp.util

import android.content.Context
import android.content.Intent
import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import android.widget.Toast
import ru.terrakok.cicerone.Navigator
import ru.terrakok.cicerone.commands.*

@Suppress("UNUSED_PARAMETER")
abstract class SupportActivityNavigator(val activity: AppCompatActivity) : Navigator {

    override fun applyCommands(commands: Array<out Command>) {
        for (command in commands) {
            applyCommand(command)
        }
    }

    /**
     * Perform transition described by the navigation command
     *
     * @param command the navigation command to apply
     */
    private fun applyCommand(command: Command) {
        when (command) {
            is Forward -> forward(command)
            is Back -> back()
            is Replace -> replace(command)
            is BackTo -> backTo(command)
            is SystemMessage -> showSystemMessage(command.message)
        }
    }

    private fun backTo(command: BackTo) {
        TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
    }

    /**
     * Override this method to create option for start activity
     *
     * @param command        current navigation command. Will be only [Forward] or [Replace]
     * @param activityIntent activity intent
     * @return transition options
     */
    private fun createStartActivityOptions(command: Command, activityIntent: Intent): Bundle? {
        return null
    }

    private fun back() {
        exit()
    }

    private fun forward(command: Forward) {
        val activityIntent =
            createActivityIntent(activity, command.screenKey, command.transitionData)

        // Start activity
        if (activityIntent != null) {
            val options = createStartActivityOptions(command, activityIntent)
            checkAndStartActivity(command.screenKey, activityIntent, options)
        }
    }

    private fun replace(command: Replace) {
        val activityIntent =
            createActivityIntent(activity, command.screenKey, command.transitionData)

        // Replace activity
        if (activityIntent != null) {
            val options = createStartActivityOptions(command, activityIntent)
            checkAndStartActivity(command.screenKey, activityIntent, options)
            activity.finish()
        }
    }

    private fun checkAndStartActivity(screenKey: String, activityIntent: Intent, options: Bundle?) {
        // Check if we can start activity
        if (activityIntent.resolveActivity(activity.packageManager) != null) {
            activity.startActivity(activityIntent, options)
        } else {
            unexistingActivity(screenKey, activityIntent)
        }
    }

    /**
     * Called when there is no activity to open `screenKey`.
     *
     * @param screenKey screen key
     * @param activityIntent intent passed to start Activity for the `screenKey`
     */
    private fun unexistingActivity(screenKey: String, activityIntent: Intent) {
        // Do nothing by default
    }

    /**
     * Creates Intent to start Activity for `screenKey`.
     *
     *
     * **Warning:** This method does not work with [BackTo] command.
     *
     *
     * @param screenKey screen key
     * @param data      initialization data, can be null
     * @return intent to start Activity for the passed screen key
     */
    protected abstract fun createActivityIntent(
        context: Context,
        screenKey: String,
        data: Any
    ): Intent?

    private fun showSystemMessage(message: String) {
        // Toast by default
        Toast.makeText(activity, message, Toast.LENGTH_SHORT).show()
    }

    private fun exit() {
        // Finish by default
        activity.finish()
    }
}