TimberDelegate.kt

import timber.log.Timber
import kotlin.properties.ReadOnlyProperty
import kotlin.reflect.KProperty

class MyClass {
    // This will automatically have the TAG "MyClass"
    private val log by timber()
    
    fun logSomething() {
        log.i("Hello")
        log.w(Exception(), "World")
    }
}

/**
 * Use this delegate to have easy access to Timber logging in your class.
 * Add `private val log by timber()` to your class. It will automatically use your class name as a tag,
 * trim it to 23 characters and replace Fragment with Frag and ViewModel to VM by default if it is too long,
 * finally, just truncating the class name if needed.
 * If the default option is not good enough, you can pass in a custom tag.
 */
inline fun <reified T : Any> T.timber(tag: String? = null) = TimberLoggerProperty<T>(tag)

class TimberLoggerProperty<T : Any>(private val tag: String? = null) : ReadOnlyProperty<T, TimberLogger> {

    @Volatile var logger: TimberLogger? = null

    override fun getValue(thisRef: T, property: KProperty<*>): TimberLogger {
        logger?.let { return it }
        logger = TimberLogger(thisRef, tag)
        return logger!!
    }
}

class TimberLogger(thisRef: Any, tag: String? = null) : Timber.Tree() {

    private val tag = tag ?: thisRef.toTag()

    override fun log(priority: Int, tag: String?, message: String, t: Throwable?) {
        Timber.tag(tag ?: this.tag).log(priority, t, message)
    }

    private fun Any.toTag(): String {
        val str = this::class.java.simpleName
            .run { if (endsWith("Impl")) substring(0, length - 4) else this }
        if (str.length <= 23) {
            return str
        }
        return str
            .replace("Fragment", "Frag")
            .replace("ViewModel", "VM")
            .replace("Controller", "Ctrl")
            .replace("Manager", "Mgr")
            .take(23)
    }
}