Kotlin Multiplatform Configuration Recipe

Just the facts please...

So my implementation of the Kotlin Multiplatform project configuration so far is this:

which looks like this in the heirarchy:

commonMain/kotlin/config/Config.kt

commonMain/kotlin/config/ConfigProvider.kt

desktopMain/kotlin/config/DesktopConfigProvider.kt

androidMain/kotlin/config/AndroidConfigProvider.kt

our Config.kt:

class Config(val configProvider: ConfigProvider) {
    var lastDepth by configProvider::lastDepth
}

our ConfigProvider.kt:

interface ConfigProvider {
    var lastDepth: Double
}

our DesktopConfigProvider.kt:

import java.util.prefs.Preferences

class DesktopConfigProvider : ConfigProvider {
    private val preferences = Preferences.userNodeForPackage(this::class.java)

    override var lastDepth: Double
        get() = preferences.getDouble("lastDepth", 0.0)
        set(value) {
            preferences.putDouble("lastDepth", value)
        }
}

and our AndroidConfigProvider.kt:

mport android.content.Context

private const val CONFIG_KEY = "DA_MON_CONFIG"
private const val LAST_DEPTH_KEY = "LAST_DEPTH"
class AndroidConfigProvider(context: Context) : ConfigProvider {
    private val sharedPreferences = context.getSharedPreferences(
        CONFIG_KEY,
        Context.MODE_PRIVATE
    )
    override var lastDepth: Double
        get() = getSharedLastDepth()
        set(value) {
            setSharedLastDepth(value)
        }

    private fun setSharedLastDepth(value: Double) {
        sharedPreferences?.edit()
            ?.putString(LAST_DEPTH_KEY, value.toString())
            ?.apply()
    }

    private fun getSharedLastDepth(): Double {
        return (sharedPreferences?.getString(LAST_DEPTH_KEY, "0.0")
            ?.toDouble()
            ?: 0.0)
    }
}

and here is an example test that makes a config:

import androidx.test.platform.app.InstrumentationRegistry
import io.kotest.matchers.doubles.shouldBeExactly
import org.junit.Test

class AndroidConfigProviderPersistsDepthTest {

    @Test
    fun configProviderPersistsDepthTest() {
        val depth = 1.3
        val context = InstrumentationRegistry.getInstrumentation()
                                             .targetContext
        val androidConfigProvider = AndroidConfigProvider(context)
        Config(androidConfigProvider).lastDepth = depth

        Config(AndroidConfigProvider(context))
            .lastDepth
            .shouldBeExactly(depth)
    }
}

though most tests should simply make a TestConfigProvider that controls the configuration exactly as you want it for the test.

The only thing remaining is the ios and perhaps web-based projects - we will update this as we encounter those projects later.