Reload .autocp when modified externally

src/main/kotlin/com/github/pushpavel/autocp/database/AutoCpDatabase.kt

@@ -10,13 +10,22 @@ class AutoCpDatabase(
 ) {
     val problems get() = problemsFlow.value
 
+    /**
+     * true once the in-memory state diverged from what was loaded from disk,
+     * so an intentionally emptied database is distinguishable from a never-populated one
+     */
+    @Volatile
+    var mutated = false
+
     fun updateProblem(problem: Problem) {
+        mutated = true
         val group = this.problems[problem.groupName]?.toMutableMap() ?: mutableMapOf()
         group[problem.name] = problem
         this.problemsFlow.value = problems.toMutableMap().apply { this[problem.groupName] = group }
     }
 
     fun modifySolutionFiles(action: MutableMap<String, SolutionFile>.() -> Unit) {
+        mutated = true
         solutionFilesFlow.value = solutionFilesFlow.value.toMutableMap().apply(action)
     }
 }

src/main/kotlin/com/github/pushpavel/autocp/database/AutoCpExternalReloader.kt

@@ -0,0 +1,36 @@
+package com.github.pushpavel.autocp.database
+
+import com.intellij.openapi.application.ApplicationManager
+import com.intellij.openapi.components.service
+import com.intellij.openapi.project.ProjectManager
+import com.intellij.openapi.util.io.FileUtil
+import com.intellij.openapi.vfs.newvfs.BulkFileListener
+import com.intellij.openapi.vfs.newvfs.events.VFileContentChangeEvent
+import com.intellij.openapi.vfs.newvfs.events.VFileCreateEvent
+import com.intellij.openapi.vfs.newvfs.events.VFileEvent
+
+class AutoCpExternalReloader : BulkFileListener {
+
+    override fun after(events: List<VFileEvent>) {
+        val autocpEvents = events.asSequence()
+            .filter { it is VFileCreateEvent || (it is VFileContentChangeEvent && !it.isFromSave) }
+            .filter { it.path.endsWith("/.autocp") }
+            .toList()
+        if (autocpEvents.isEmpty()) return
+
+        val openProjects = ProjectManager.getInstanceIfCreated()?.openProjects ?: return
+        val affectedProjects = autocpEvents
+            .map { it.path.removeSuffix("/.autocp") }
+            .flatMap { parentPath ->
+                openProjects.filter { !it.isDefault && FileUtil.pathsEqual(it.basePath, parentPath) }
+            }
+            .toSet()
+
+        // defer disk I/O out of the write action that delivered the VFS events
+        for (project in affectedProjects) {
+            ApplicationManager.getApplication().invokeLater({
+                project.service<AutoCpStorage>().reloadFromDisk()
+            }, project.disposed)
+        }
+    }
+}

src/main/kotlin/com/github/pushpavel/autocp/database/AutoCpStorage.kt

@@ -28,7 +28,7 @@ class AutoCpStorage(val project: Project) {
 
     val log = Logger.getInstance(AutoCpStorage::class.java)
 
-    val database by lazy {
+    private val databaseDelegate = lazy {
         if(!project.isDefault){
             val converter = AutoCpFileConversion(project)
             converter.convert()
@@ -51,6 +51,25 @@ class AutoCpStorage(val project: Project) {
         AutoCpDatabase(MutableStateFlow(db.problems), MutableStateFlow(db.solutionFiles))
     }
 
+    val database by databaseDelegate
+
+    fun reloadFromDisk() {
+        if (project.isDefault) return
+        if (!databaseDelegate.isInitialized()) return
+        val path = Paths.get(project.basePath!!, ".autocp")
+        if (!path.exists()) return
+        try {
+            val newDb = Migrations.migrateDB(runReadAction {
+                Json.parseToJsonElement(path.readText())
+            })
+            database.problemsFlow.value = newDb.problems
+            database.solutionFilesFlow.value = newDb.solutionFiles
+            database.mutated = false
+        } catch (e: Exception) {
+            log.warn("Failed to reload .autocp from disk", e)
+        }
+    }
+
     val serializableDatabase
         get() = database.run {
             AutoCpDB(
@@ -70,7 +89,8 @@ class AutoCpStorageSaver : FileDocumentManagerListener {
                 return
             val path = Paths.get(Path(project.basePath!!).pathString, ".autocp")
             var virtualFile = VfsUtil.findFile(path, true)
-            val db = project.service<AutoCpStorage>().serializableDatabase
+            val storage = project.service<AutoCpStorage>()
+            val db = storage.serializableDatabase
 
 
             if (virtualFile?.isValid != true && DEFAULT_AUTO_CP_DB != db) {
@@ -93,8 +113,15 @@ class AutoCpStorageSaver : FileDocumentManagerListener {
                     R.notify.couldNotWriteToAutoCpFile()
                     return@runReadAction
                 }
+                // in-memory state was never populated, prefer the on-disk content over clobbering it
+                if (!storage.database.mutated && db == DEFAULT_AUTO_CP_DB && document.text.isNotBlank()) {
+                    storage.reloadFromDisk()
+                    return@runReadAction
+                }
+                val newText = Json.encodeToString(db)
+                if (document.text == newText) return@runReadAction
                 runWriteAction {
-                    document.setText(Json.encodeToString(db))
+                    document.setText(newText)
                 }
             }
         }

src/main/resources/META-INF/plugin.xml

@@ -62,6 +62,10 @@
         <programRunner implementation="com.github.pushpavel.autocp.config.AutoCpProgramRunner"/>
         <executionTargetProvider implementation="com.github.pushpavel.autocp.config.AutoCpExecutionTargetProvider"/>
     </extensions>
+    <applicationListeners>
+        <listener class="com.github.pushpavel.autocp.database.AutoCpExternalReloader"
+                  topic="com.intellij.openapi.vfs.newvfs.BulkFileListener"/>
+    </applicationListeners>
     <projectListeners>
         <listener class="com.github.pushpavel.autocp.extend.cmake.CMakeAddExecutable"
                   topic="com.github.pushpavel.autocp.gather.filegen.FileGenerationListener"/>