lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/StorageDetector.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.tools.lint.checks

import com.android.tools.lint.detector.api.Category
import com.android.tools.lint.detector.api.Detector
import com.android.tools.lint.detector.api.Implementation
import com.android.tools.lint.detector.api.Issue
import com.android.tools.lint.detector.api.JavaContext
import com.android.tools.lint.detector.api.Scope
import com.android.tools.lint.detector.api.Severity
import com.android.tools.lint.detector.api.SourceCodeScanner
import com.intellij.psi.PsiMethod
import org.jetbrains.uast.UCallExpression
import org.jetbrains.uast.visitor.AbstractUastVisitor

/**
 * Checks related to using the StorageManager APIs correctly
 */
class StorageDetector : Detector(), SourceCodeScanner {

    override fun getApplicableMethodNames(): List<String>? {
        return listOf("getUsableSpace")
    }

    override fun visitMethodCall(
        context: JavaContext,
        node: UCallExpression,
        method: PsiMethod
    ) {
        if (!context.evaluator.isMemberInClass(method, "java.io.File")) {
            return
        }

        // See if we're already referencing getAllocatableBytes in the same compilation unit
        var found = false
        context.uastFile?.accept(object : AbstractUastVisitor() {
            override fun visitCallExpression(node: UCallExpression): Boolean {
                if (node.methodName == "getAllocatableBytes") {
                    found = true
                }
                return super.visitCallExpression(node)
            }
        })
        if (!found) {
            val location = context.getCallLocation(node, false, false)
            val message = "Consider also using `StorageManager#getAllocatableBytes` and " +
                    "`allocateBytes` which will consider clearable cached data"
            context.report(ISSUE, node, location, message)
        }
    }

    companion object {
        @JvmField
        val ISSUE = Issue.create(
            id = "UsableSpace",
            briefDescription = "Using getUsableSpace()",
            explanation = """
                When you need to allocate disk space for large files, consider using the new \
                `allocateBytes(FileDescriptor, long)` API, which will automatically clear \
                cached files belonging to other apps (as needed) to meet your request.

                When deciding if the device has enough disk space to hold your new data, \
                call `getAllocatableBytes(UUID)` instead of using `getUsableSpace()`, since \
                the former will consider any cached data that the system is willing to \
                clear on your behalf.

                Note that these methods require API level 26. If your app is running on \
                older devices, you will probably need to use both APIs, conditionally switching \
                on `Build.VERSION.SDK_INT`. Lint only looks in the same compilation unit to \
                see if you are already using both APIs, so if it warns even though you are \
                already using the new API, consider moving the calls to the same file or \
                suppressing the warning.
                """,
            category = Category.PERFORMANCE,
            priority = 3,
            severity = Severity.WARNING,
            androidSpecific = true,
            implementation = Implementation(
                StorageDetector::class.java,
                Scope.JAVA_FILE_SCOPE
            )
        )
    }
}