feat: add layouts, partials apart from root, #395

src/fs/loader.ts

@@ -0,0 +1,48 @@
+import { FS } from './fs'
+
+interface LoaderOptions {
+  fs: FS;
+  extname: string;
+  root: string[];
+  partials: string[];
+  layouts: string[];
+}
+export enum LookupType {
+  Partials = 'partials',
+  Layouts = 'layouts',
+  Root = 'root'
+}
+export class Loader {
+  private options: LoaderOptions
+
+  constructor (options: LoaderOptions) {
+    this.options = options
+  }
+
+  public * lookup (file: string, type: LookupType, sync?: boolean) {
+    const { fs, root } = this.options
+    for (const filepath of this.candidates(file, type)) {
+      if (sync ? fs.existsSync(filepath) : yield fs.exists(filepath)) return filepath
+    }
+    throw this.lookupError(file, root)
+  }
+
+  private * candidates (file: string, type: LookupType) {
+    const { fs, extname } = this.options
+    const dirs = this.options[type]
+    for (const dir of dirs) {
+      yield fs.resolve(dir, file, extname)
+    }
+    if (fs.fallback !== undefined) {
+      const filepath = fs.fallback(file)
+      if (filepath !== undefined) yield filepath
+    }
+  }
+
+  private lookupError (file: string, roots: string[]) {
+    const err = new Error('ENOENT') as any
+    err.message = `ENOENT: Failed to lookup "${file}" in "${roots}"`
+    err.code = 'ENOENT'
+    return err
+  }
+}