Show warning if post is empty

This fixes #10.

src/MicroPlugin.ts

@@ -1,3 +1,4 @@
+import { ErrorView } from '@views/ErrorView'
 import { Notice, Plugin } from 'obsidian'
 import { MicroPluginContainerInterface, MicroPluginContainer } from '@base/MicroPluginContainer'
 import { MicroPluginSettingsView } from '@views/MicroPluginSettingsView'
@@ -32,12 +33,18 @@ export default class MicroPlugin extends Plugin {
             id: 'microblog-publish-command',
             name: 'Post to Micro.blog',
             editorCallback: (editor, markdownView) => {
-                new PublishView(
-                    this.viewModelFactory.makePublishViewModel(
-                        markdownView.file.basename,
-                        editor.getValue()
-                    )
-                ).open()
+                if (editor.getValue().trim().length == 0) {
+                    new ErrorView(
+                        this.viewModelFactory.makeEmptyPostErrorViewModel()
+                    ).open()
+                } else {
+                    new PublishView(
+                        this.viewModelFactory.makePublishViewModel(
+                            markdownView.file.basename,
+                            editor.getValue()
+                        )
+                    ).open()
+                }
             }
         })
 

src/factories/ViewModelFactory.ts

@@ -1,6 +1,7 @@
 import { MicroPluginSettingsViewModel } from '@views/MicroPluginSettingsViewModel'
 import { PublishViewModel } from '@views/PublishViewModel'
 import { TagSuggestionViewModel, TagSuggestionDelegate } from '@views/TagSuggestionViewModel'
+import { ErrorViewModel } from '@views/ErrorViewModel'
 import { MicroPluginContainerInterface } from '@base/MicroPluginContainer'
 
 export interface ViewModelFactoryInterface {
@@ -21,6 +22,9 @@ export interface ViewModelFactoryInterface {
         excluding: Array<string>,
         delegate?: TagSuggestionDelegate
     ): TagSuggestionViewModel
+
+    // Builds the Empty Post Error View Model.
+    makeEmptyPostErrorViewModel(): ErrorViewModel
 }
 
 /*
@@ -87,4 +91,11 @@ export class ViewModelFactory implements ViewModelFactoryInterface {
 
         return viewModel
     }
-}
+
+    public makeEmptyPostErrorViewModel(): ErrorViewModel {
+        return new ErrorViewModel(
+            "Oops",
+            "Micro.blog doesn't support blank posts. Write something first and try again."
+        )
+    }
+}

src/views/ErrorView.ts

@@ -0,0 +1,42 @@
+import { Modal } from 'obsidian'
+import { ErrorViewModel } from '@views/ErrorViewModel'
+
+/*
+ * Error View subclasses Modal.
+ */
+export class ErrorView extends Modal {
+
+    // Properties
+
+    private viewModel: ErrorViewModel
+
+    // Life cycle
+
+    constructor(
+        viewModel: ErrorViewModel
+    ) {
+        super(app)
+
+        this.viewModel = viewModel
+    }
+
+    // Public
+
+    public onOpen() {
+        super.onOpen()
+
+        const { contentEl } = this
+
+        contentEl.empty()
+        contentEl.createEl('h2', { text: this.viewModel.title })
+        contentEl.createEl('p', { text: this.viewModel.message })
+    }
+
+    public onClose() {
+        super.onClose()
+
+        const { contentEl } = this
+
+        contentEl.empty()
+    }
+}

src/views/ErrorViewModel.ts

@@ -0,0 +1,21 @@
+/*
+ * This view model drives the content and interactions with the
+ * error view.
+ */
+export class ErrorViewModel {
+
+    // Properties
+
+    readonly title: string
+    readonly message: string
+
+    // Life cycle
+
+    constructor(
+        title: string,
+        message: string
+    ) {
+        this.title = title
+        this.message = message
+    }
+}