build.gradle.kts: tests and docs for LastModifiedFiles collection

idea/idea-gradle/src/org/jetbrains/kotlin/idea/scripting/gradle/GradleScriptInputsWatcher.kt

@@ -14,6 +14,8 @@ import com.intellij.openapi.vfs.newvfs.BulkFileListener
 import com.intellij.openapi.vfs.newvfs.events.VFileEvent
 import com.intellij.util.PathUtil
 import org.jetbrains.annotations.TestOnly
+import org.junit.Assert.assertEquals
+import org.junit.Test
 
 @State(
     name = "KotlinBuildScriptsModificationInfo",
@@ -44,43 +46,17 @@ class GradleScriptInputsWatcher(val project: Project) : PersistentStateComponent
         return storage.lastModifiedTimeStampExcept(file) < timeStamp
     }
 
-    class Storage(
-        private var lastModifiedTS: Long = 0,
-        private var lastModifiedFiles: MutableSet<String> = hashSetOf(),
-        private var previousModifiedTS: Long = 0,
-        private var previousModifiedFiles: MutableSet<String> = hashSetOf()
-    ) {
+    class Storage {
+        private val lastModifiedFiles = LastModifiedFiles()
+
         fun lastModifiedTimeStampExcept(file: VirtualFile): Long {
             val fileId = getFileId(file)
-            synchronized(this) {
-                if (lastModifiedFiles.contains(fileId) && lastModifiedFiles.size == 1) {
-                    return previousModifiedTS
-                }
-                return lastModifiedTS
-            }
-
+            return lastModifiedFiles.lastModifiedTimeStampExcept(fileId)
         }
 
         fun fileChanged(file: VirtualFile, ts: Long) {
             val fileId = getFileId(file)
-            synchronized(this) {
-                when {
-                    ts > lastModifiedTS -> {
-                        previousModifiedFiles = lastModifiedFiles
-                        previousModifiedTS = lastModifiedTS
-
-                        lastModifiedFiles = hashSetOf(fileId)
-                        lastModifiedTS = ts
-                    }
-                    ts == lastModifiedTS -> {
-                        lastModifiedFiles.add(fileId)
-                    }
-                    ts == previousModifiedTS -> {
-                        previousModifiedFiles.add(fileId)
-                    }
-                    else -> {}
-                }
-            }
+            lastModifiedFiles.fileChanged(ts, fileId)
         }
 
         private fun getFileId(file: VirtualFile): String {

idea/idea-gradle/src/org/jetbrains/kotlin/idea/scripting/gradle/LastModifiedFiles.kt

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.idea.scripting.gradle
+
+/**
+ * Optimized collection for storing last modified files with ability to
+ * get time of last modified file expect given one ([lastModifiedTimeStampExcept]).
+ *
+ * This is required since Gradle scripts configurations should be updated on
+ * each other script changes (but not on the given script changes itself).
+ *
+ * Actually works by storing two last timestamps with the set of files modified at this times.
+ */
+class LastModifiedFiles {
+    private var last: SimultaneouslyChangedFiles = SimultaneouslyChangedFiles()
+    private var previous: SimultaneouslyChangedFiles = SimultaneouslyChangedFiles()
+
+    class SimultaneouslyChangedFiles(
+        val ts: Long = Long.MIN_VALUE,
+        val fileIds: MutableSet<String> = mutableSetOf()
+    )
+
+    @Synchronized
+    fun fileChanged(ts: Long, fileId: String) {
+        when {
+            ts > last.ts -> {
+                previous = last
+                last = SimultaneouslyChangedFiles(ts, hashSetOf(fileId))
+            }
+            ts == last.ts -> last.fileIds.add(fileId)
+            ts == previous.ts -> previous.fileIds.add(fileId)
+        }
+    }
+
+    @Synchronized
+    fun lastModifiedTimeStampExcept(fileId: String): Long = when {
+        last.fileIds.size == 1 && last.fileIds.contains(fileId) -> previous.ts
+        else -> last.ts
+    }
+}

idea/idea-gradle/tests/org/jetbrains/kotlin/idea/scripting/gradle/LastModifiedFilesTest.kt

@@ -0,0 +1,75 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.idea.scripting.gradle
+
+import org.junit.Test
+import kotlin.test.assertEquals
+
+class LastModifiedFilesTest {
+    val files = LastModifiedFiles()
+
+    @Test
+    fun testSimple0() {
+        assertEquals(Long.MIN_VALUE, files.lastModifiedTimeStampExcept("x"))
+    }
+
+    @Test
+    fun testSimple1() {
+        files.fileChanged(1, "x")
+        assertEquals(Long.MIN_VALUE, files.lastModifiedTimeStampExcept("x"))
+        assertEquals(1, files.lastModifiedTimeStampExcept("y"))
+    }
+
+    @Test
+    fun testSimple2() {
+        files.fileChanged(1, "x")
+        files.fileChanged(2, "y")
+        assertEquals(2, files.lastModifiedTimeStampExcept("x"))
+        assertEquals(1, files.lastModifiedTimeStampExcept("y"))
+    }
+
+    @Test
+    fun testSimple3() {
+        files.fileChanged(1, "x")
+        files.fileChanged(2, "y")
+        files.fileChanged(3, "z")
+        assertEquals(3, files.lastModifiedTimeStampExcept("x"))
+        assertEquals(3, files.lastModifiedTimeStampExcept("y"))
+        assertEquals(2, files.lastModifiedTimeStampExcept("z"))
+    }
+
+    @Test
+    fun testSame2() {
+        files.fileChanged(1, "x")
+        files.fileChanged(1, "y")
+        assertEquals(1, files.lastModifiedTimeStampExcept("x"))
+        assertEquals(1, files.lastModifiedTimeStampExcept("y"))
+    }
+
+    @Test
+    fun testSame3() {
+        files.fileChanged(1, "x")
+        files.fileChanged(1, "y")
+        files.fileChanged(2, "z")
+        assertEquals(2, files.lastModifiedTimeStampExcept("x"))
+        assertEquals(2, files.lastModifiedTimeStampExcept("y"))
+        assertEquals(1, files.lastModifiedTimeStampExcept("z"))
+    }
+
+    @Test
+    fun testSame4() {
+        files.fileChanged(1, "x")
+        files.fileChanged(1, "y")
+        files.fileChanged(2, "z")
+        files.fileChanged(3, "a")
+        files.fileChanged(3, "b")
+        assertEquals(3, files.lastModifiedTimeStampExcept("x"))
+        assertEquals(3, files.lastModifiedTimeStampExcept("y"))
+        assertEquals(3, files.lastModifiedTimeStampExcept("z"))
+        assertEquals(3, files.lastModifiedTimeStampExcept("a"))
+        assertEquals(3, files.lastModifiedTimeStampExcept("b"))
+    }
+}