composition time logger

CompositionTimeLogger.kt

package net.ppldo.comment.android.messages.content

interface CompositionTimeLogger {
    fun start()
    fun logNext(name: String)
    fun logAll()
}

class DummyCompositionTimeLogger : CompositionTimeLogger {
    override fun start() {
        // no op
    }

    override fun logNext(name: String) {
        // no op
    }

    override fun logAll() {
        // no op
    }
}

CompositionTimeLoggerImpl.kt

package net.ppldo.comment.android.messages.content

class CompositionTimeLoggerImpl(
    private val tag: String,
    private val maxNameLength: Int = MAX_NAME_LENGTH,
) : CompositionTimeLogger {

    private var lastTime = current()
    private val map = mutableMapOf<String, Long>()

    override fun start() {
        lastTime = current()
    }

    override fun logNext(name: String) {
        val currentTime = current()
        val millis = currentTime - lastTime
        map[name] = map.getOrDefault(name, 0) + millis
        println("$tag: ${formatName(name)}: $millis ms " + visualizeMillis(millis))
        lastTime = current()
    }

    override fun logAll() {
        val log = buildString {
            append(tag)
            append(" result: ")
            map.forEach { (t, u) ->
                append(t)
                append(':')
                append(u)
                append(", ")
            }
        }

        println(log)
    }

    private fun current() = System.currentTimeMillis()

    private fun formatName(name: String) =
        if (name.length < MAX_NAME_LENGTH) {
            buildString {
                repeat(maxNameLength - name.length) {
                    append(' ')
                }
                append(name)
            }
        } else {
            name.substring(name.length - maxNameLength)
        }

    private fun visualizeMillis(millis: Long): String {
        if (millis == 0L) return ""

        return buildString {
            repeat(millis.toInt()) {
                append('*')
            }
        }
    }
}

private const val MAX_NAME_LENGTH = 20