Add Utilities to trace flow values

/*

 * Copyright (C) 2023 The Android Open Source Project

 *

 * Licensed under the Apache License, Version 2.0 (the "License");

 * you may not use this file except in compliance with the License.

 * You may obtain a copy of the License at

 *

 *      http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.android.app.tracing

import kotlinx.coroutines.flow.Flow

import kotlinx.coroutines.flow.onEach

/** Utilities to trace Flows */

object FlowTracing {

    /** Logs each flow element to a trace. */

    inline fun <T> Flow<T>.traceEach(

            flowName: String,

            logcat: Boolean = false,

            crossinline valueToString: (T) -> String = { it.toString() }

    ): Flow<T> {

        val stateLogger = TraceStateLogger(flowName, logcat = logcat)

        return onEach { stateLogger.log(valueToString(it)) }

    }

}

package com.android.app.tracing

import android.os.Trace

import android.util.Log

/**

 * Utility class used to log state changes easily in a track with a custom name.

class TraceStateLogger(

    private val trackName: String,

    private val logOnlyIfDifferent: Boolean = true,

    private val instantEvent: Boolean = true

    private val instantEvent: Boolean = true,

    private val logcat: Boolean = false,

) {

    private var previousValue: String? = null

        if (logOnlyIfDifferent && previousValue == newValue) return

        Trace.asyncTraceForTrackEnd(Trace.TRACE_TAG_APP, trackName, 0)

        Trace.asyncTraceForTrackBegin(Trace.TRACE_TAG_APP, trackName, newValue, 0)

        if (logcat) {

            Log.d(trackName, "newValue: $newValue")

        }

        previousValue = newValue

    }

}