feat: support in-memory template mapping, inspired by @jg-rp #714

src/fs/map-fs.ts

@@ -0,0 +1,43 @@
+import { isNil } from '../util'
+
+export class MapFS {
+  constructor (private mapping: {[key: string]: string}) {}
+
+  public sep = '/'
+
+  async exists (filepath: string) {
+    return this.existsSync(filepath)
+  }
+
+  existsSync (filepath: string) {
+    return !isNil(this.mapping[filepath])
+  }
+
+  async readFile (filepath: string) {
+    return this.readFileSync(filepath)
+  }
+
+  readFileSync (filepath: string) {
+    const content = this.mapping[filepath]
+    if (isNil(content)) throw new Error(`ENOENT: ${filepath}`)
+    return content
+  }
+
+  dirname (filepath: string) {
+    const segments = filepath.split(this.sep)
+    segments.pop()
+    return segments.join(this.sep)
+  }
+
+  resolve (dir: string, file: string, ext: string) {
+    file += ext
+    if (dir === '.') return file
+    const segments = dir.split(this.sep)
+    for (const segment of file.split(this.sep)) {
+      if (segment === '.' || segment === '') continue
+      else if (segment === '..') segments.pop()
+      else segments.push(segment)
+    }
+    return segments.join(this.sep)
+  }
+}