build-system/gradle-core/src/main/java/com/android/build/gradle/internal/dependency/PlatformAttrTransform.kt

/*
 * Copyright (C) 2018 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.build.gradle.internal.dependency

import com.android.build.gradle.internal.tasks.recordArtifactTransformSpan
import com.android.tools.build.gradle.internal.profile.GradleTransformExecutionType
import com.google.common.collect.Lists
import org.gradle.api.artifacts.transform.InputArtifact
import org.gradle.api.artifacts.transform.TransformAction
import org.gradle.api.artifacts.transform.TransformOutputs
import org.gradle.api.file.FileSystemLocation
import org.gradle.api.provider.Provider
import org.gradle.api.tasks.Classpath
import org.objectweb.asm.ClassReader
import org.objectweb.asm.ClassVisitor
import org.objectweb.asm.FieldVisitor
import org.objectweb.asm.Opcodes
import java.io.FileWriter
import java.util.zip.ZipFile

/**
 * Extract attr IDs from a jar file and puts it in a R.txt
 */
abstract class PlatformAttrTransform : TransformAction<GenericTransformParameters> {
    @get:Classpath
    @get:InputArtifact
    abstract val primaryInput: Provider<FileSystemLocation>

    override fun transform(outputs: TransformOutputs) {
        recordArtifactTransformSpan(
            parameters.projectName.get(),
            GradleTransformExecutionType.PLATFORM_ATTR_ARTIFACT_TRANSFORM) {

            val outputFile = outputs.file("R.txt")

            val attributes = ZipFile(primaryInput.get().asFile).use { zip ->
                // return from let{} is passed as return for use{}
                zip.getEntry("android/R\$attr.class")?.let {
                    val stream = zip.getInputStream(it)!! // this method does not return null.

                    val customClassVisitor = CustomClassVisitor()
                    ClassReader(stream).accept(customClassVisitor, 0)

                    customClassVisitor.attributes
                }
            }

            if (attributes == null || attributes.isEmpty()) {
                error("Missing attr resources in android.jar, the file might be corrupted: $primaryInput")
            } else {
                FileWriter(outputFile).use { writer ->
                    for ((name, value) in attributes) {
                        writer.write("int attr $name 0x${String.format("%08x", value)}\n")
                    }
                }
            }
        }
    }
}

data class AttributeValue(val name: String, val value: Int)

class CustomClassVisitor : ClassVisitor(Opcodes.ASM5) {

    val attributes: MutableList<AttributeValue> = Lists.newArrayList()

    override fun visitField(
        access: Int,
        name: String?,
        desc: String?,
        signature: String?,
        value: Any?
    ): FieldVisitor? {
        if (value is Int) {
            attributes.add(AttributeValue(name!!, value))
        }
        return null
    }
}