Add view engine unit - handlebars - and response helpers

lib/src/unit/ViewEngine.ts

@@ -0,0 +1,60 @@
+import LifecycleUnit from '../lifecycle/Unit.ts'
+import {Unit} from '../lifecycle/decorators.ts'
+import {Handlebars} from '../external/http.ts'
+import {Logging} from '../service/logging/Logging.ts'
+import {fs} from '../external/std.ts'
+
+@Unit()
+export default class ViewEngine extends LifecycleUnit {
+    protected _handlebars!: Handlebars
+
+    // TODO include basic app info in view data
+
+    constructor(
+        protected readonly logger: Logging,
+    ) {
+        super()
+    }
+
+    async up() {
+        this.logger.info(`Setting views base dir: ${this.app.app_path('http', 'views')}`)
+        this._handlebars = new Handlebars({
+            baseDir: this.app.app_path('http', 'views'),
+            extname: '.hbs',
+            layoutsDir: 'layouts',
+            partialsDir: 'partials',
+            defaultLayout: 'main',
+            helpers: undefined,
+            compilerOptions: undefined,
+        })
+
+        const main_layout_path = this.app.app_path('http', 'views', 'layouts', 'main.hbs')
+        if ( !(await fs.exists(main_layout_path)) ) {
+            this.logger.warn(`Unable to open main view layout file: ${main_layout_path}`)
+            this.logger.warn(`Unless you are using a custom layout, this could cause errors.`)
+        }
+
+        const partials_path = this.app.app_path('http', 'views', 'partials')
+        if ( !(await fs.exists(partials_path)) ) {
+            this.logger.warn(`Unable to open view partials directory: ${partials_path}`)
+            this.logger.warn(`This directory must exist for the view engine to function, even if it is empty.`)
+        }
+    }
+
+    get handlebars(): Handlebars {
+        return this._handlebars
+    }
+
+    async render(view: string, args?: any, layout?: string): Promise<string> {
+        this.logger.debug(`Rendering view: ${view}`)
+        return this.handlebars.renderView(view, args, layout)
+    }
+
+    async partial(view: string, args?: any) {
+        const parts = `${view}.hbs`.split(':')
+        const resolved = this.app.app_path('http', 'views', ...parts)
+
+        this.logger.debug(`Rendering partial: ${view} from ${resolved}`)
+        return this.handlebars.render(resolved, args)
+    }
+}