typia/src/factories/TemplateFactory.ts

Superfast runtime validators with only one line

import ts from "typescript";

export namespace TemplateFactory {
  export const generate = (expressions: ts.Expression[]): ts.Expression => {
    if (expressions.every((exp) => ts.isStringLiteral(exp)))
      return ts.factory.createStringLiteral(
        (expressions as ts.StringLiteral[]).map((str) => str.text).join(""),
      );

    const it: IIterator = {
      value: "",
      index: 0,
    };
    gather(expressions)(it);

    const head: ts.TemplateHead = ts.factory.createTemplateHead(it.value);
    const spans: ts.TemplateSpan[] = [];

    while (true) {
      const elem: ts.Expression = expressions[it.index++]!;
      gather(expressions)(it);

      const broken: boolean = it.index === expressions.length;
      spans.push(
        ts.factory.createTemplateSpan(
          elem,
          broken
            ? ts.factory.createTemplateTail(it.value)
            : ts.factory.createTemplateMiddle(it.value),
        ),
      );
      if (broken === true) break;
    }
    return ts.factory.createTemplateExpression(head, spans);
  };

  const gather =
    (expressions: ts.Expression[]) =>
    (it: IIterator): void => {
      const found: number = expressions.findIndex(
        (elem, index) => index >= it.index && !ts.isStringLiteral(elem),
      );

      const last: number = found !== -1 ? found : expressions.length;
      it.value = expressions
        .slice(it.index, last)
        .map((elem) => (elem as ts.StringLiteral).text)
        .reduce((x, y) => x + y, "");
      it.index = last;
    };

  interface IIterator {
    value: string;
    index: number;
  }
}