treegen: Add a utility FileWriter class

treegen/src/util.ts

@@ -0,0 +1,49 @@
+
+function isWhiteSpace(ch: string) {
+  return /[\r\t ]/.test(ch);
+}
+
+export interface FileWriterOptions {
+  indentStr?: string;
+  startIndent?: number;
+  indentWidth?: number;
+}
+
+export class FileWriter {
+
+  public currentText = '';
+
+  private atBlankLine = true;
+  private currentIndent: number;
+  private indentStr: string;
+  private indentWidth: number;
+
+  constructor(opts: FileWriterOptions = {}) {
+    this.indentStr = opts.indentStr ?? ' ';
+    this.indentWidth = opts.indentWidth ?? 2;
+    this.currentIndent = (opts.startIndent ?? 0) * this.indentWidth;
+  }
+
+  public indent(count = 1) {
+    this.currentIndent += this.indentWidth * count;
+  }
+
+  public dedent(count = 1) {
+    this.currentIndent -= this.indentWidth * count;
+  }
+
+  public write(str: string) {
+    for (const ch of str) {
+      if (ch === '\n') {
+        this.atBlankLine = true;
+      } else if (!(this.atBlankLine && isWhiteSpace(ch))) {
+        if (this.atBlankLine) {
+          this.currentText += this.indentStr.repeat(this.currentIndent)
+        }
+        this.atBlankLine = false;
+      }
+      this.currentText += ch;
+    }
+  }
+
+}