fix: Impede concurrent session execution

- Move teardown to top-level code

src/main.ts

@@ -1,6 +1,6 @@
-import { StateField } from "@codemirror/state";
-import { Editor, MarkdownView, Plugin } from "obsidian";
+import { Editor, MarkdownView, Notice, Plugin } from "obsidian";
 import { startSession, abortSession } from "./perilous";
+import { canStartScheduler, Scheduler } from "./perilous/scheduler";
 import {
   DEFAULT_SETTINGS,
   PerilousWritingSettings,
@@ -10,7 +10,7 @@ import { log } from "./utilities";
 
 export default class PerilousWritingPlugin extends Plugin {
   settings: PerilousWritingSettings;
-  cmExtensions: Array<StateField<unknown>> = [];
+  scheduler: Scheduler | undefined;
 
   async onload() {
     await this.loadSettings();
@@ -20,27 +20,33 @@ export default class PerilousWritingPlugin extends Plugin {
       id: "short-session",
       name: `Begin short session`,
       editorCallback: (editor: Editor, view: MarkdownView) => {
-        startSession(editor, view, this, this.cmExtensions, "short");
+        if (canStartScheduler(this.scheduler)) {
+          this.scheduler = startSession(editor, view, this, "short");
+        } else {
+          new Notice("A session is already in progress.");
+        }
       },
     });
 
     this.addCommand({
       id: "long-session",
       name: `Begin long session`,
       editorCallback: (editor: Editor, view: MarkdownView) => {
-        startSession(editor, view, this, this.cmExtensions, "long");
+        if (canStartScheduler(this.scheduler)) {
+          this.scheduler = startSession(editor, view, this, "long");
+        } else {
+          new Notice("A session is already in progress.");
+        }
       },
     });
 
     log("Loaded plugin");
   }
 
   onunload() {
-    abortSession();
-    // Remove the CodeMirror transaction handler, if it still exists.
-    if (this.cmExtensions.length > 0) {
-      this.cmExtensions.pop();
-      this.app.workspace.updateOptions();
+    if (this.scheduler !== undefined) {
+      this.scheduler.teardown();
+      abortSession();
     }
     log("Unloaded plugin");
   }

src/perilous/perilous.ts

@@ -18,7 +18,6 @@ export function startSession(
   editor: Editor,
   view: MarkdownView,
   plugin: PerilousWritingPlugin,
-  cmExtensions: Array<StateField<unknown>>,
   sessionType: SessionType
 ) {
   const sessionLength =
@@ -27,9 +26,10 @@ export function startSession(
       : plugin.settings.longSessionLength) * MILLISECONDS_PER_MINUTE;
   log(`Session length: ${sessionLength / MILLISECONDS_PER_MINUTE}m`);
 
+  const cmExtensions: Array<StateField<unknown>> = [];
   const [initialContent, initialCursor] = getSnapshot(editor);
   removeProgressBar();
-  addProgressBar(editor, sessionLength);
+  addProgressBar(view, sessionLength);
 
   const hooks: SchedulerHooks = {
     onInitialisation: () => {
@@ -88,6 +88,8 @@ export function startSession(
     plugin.registerEditorExtension(cmExtensions);
     log("Registered CodeMirror hook");
   });
+
+  return scheduler;
 }
 
 export function abortSession() {

src/perilous/scheduler.ts

@@ -1,3 +1,5 @@
+type SchedulerState = "initialised" | "running" | "success" | "failure";
+
 export type SchedulerHooks = {
   /* The first entry point in to the application; a session has been requested. */
   onInitialisation: () => void;
@@ -26,6 +28,9 @@ export class Scheduler {
   // Event hooks
   hooks: SchedulerHooks;
 
+  // Scheduler state
+  schedulerState: SchedulerState = "initialised";
+
   // Internals
   elapsedTime: number = 0;
   sinceLastEvent: number = 0;
@@ -83,6 +88,7 @@ export class Scheduler {
         this.tickLength
       );
       this.startedScheduler = true;
+      this.schedulerState = "running";
       this.hooks.onStart(this.intervalId);
     } else {
       this.sinceLastEvent = 0;
@@ -91,6 +97,7 @@ export class Scheduler {
   }
 
   succeed() {
+    this.schedulerState = "success";
     this.hooks.onSuccess();
     this.teardown();
   }
@@ -105,6 +112,7 @@ export class Scheduler {
   }
 
   fail() {
+    this.schedulerState = "failure";
     this.hooks.onFailure();
     this.teardown();
   }
@@ -114,3 +122,15 @@ export class Scheduler {
     clearInterval(this.intervalId);
   }
 }
+
+/**
+ * A scheduler can be requested if (1) there is no current scheduler, or (2)
+ * the previous scheduler is not in progress.
+ */
+export function canStartScheduler(scheduler: Scheduler | undefined): boolean {
+  return (
+    scheduler === undefined ||
+    (scheduler.schedulerState !== "initialised" &&
+      scheduler.schedulerState !== "running")
+  );
+}