1 /*
2  * Copyright (C) 2023 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 package com.android.app.tracing
18 
19 import android.util.Log
20 
21 /**
22  * Utility class used to log state changes easily in a track with a custom name.
23  *
24  * Example of usage:
25  * ```kotlin
26  * class MyClass {
27  *    val screenStateLogger = TraceStateLogger("Screen state")
28  *
29  *    fun onTurnedOn() { screenStateLogger.log("on") }
30  *    fun onTurnedOff() { screenStateLogger.log("off") }
31  * }
32  * ```
33  *
34  * This creates a new slice in a perfetto trace only if the state is different than the previous
35  * one.
36  */
37 class TraceStateLogger(
38     private val trackName: String,
39     private val logOnlyIfDifferent: Boolean = true,
40     private val instantEvent: Boolean = true,
41     private val logcat: Boolean = false,
42 ) {
43 
44     private var previousValue: String? = null
45 
46     /** If needed, logs the value to a track with name [trackName]. */
lognull47     fun log(newValue: String) {
48         if (instantEvent) {
49             instantForTrack(trackName, newValue)
50         }
51         if (logOnlyIfDifferent && previousValue == newValue) return
52         previousValue?.let { asyncTraceForTrackEnd(trackName, it, 0) }
53         asyncTraceForTrackBegin(trackName, newValue, 0)
54         if (logcat) {
55             Log.d(trackName, "newValue: $newValue")
56         }
57         previousValue = newValue
58     }
59 }
60