import path from "path";
import ts from "typescript";

export namespace ImportTransformer {
  export const transform =
    (from: string) =>
    (to: string) =>
    (context: ts.TransformationContext) =>
    (file: ts.SourceFile) =>
      transform_file(from)(to)(context)(file);

  const transform_file =
    (top: string) =>
    (to: string) =>
    (context: ts.TransformationContext) =>
    (file: ts.SourceFile): ts.SourceFile => {
      if (file.isDeclarationFile) return file;

      const from: string = get_directory_path(
        path.resolve(file.getSourceFile().fileName),
      );
      to = from.replace(top, to);

      return ts.visitEachChild(
        file,
        (node) => transform_node(top)(from)(to)(node),
        context,
      );
    };

  const transform_node =
    (top: string) => (from: string) => (to: string) => (node: ts.Node) => {
      if (
        !ts.isImportDeclaration(node) ||
        !ts.isStringLiteral(node.moduleSpecifier)
      )
        return node;

      const text: string = node.moduleSpecifier.text;
      if (text[0] !== ".") return node;

      const location: string = path.resolve(from, text);
      if (location.indexOf(top) === 0) return node;

      const replaced: string = (() => {
        const simple: string = path
          .relative(to, location)
          .split(path.sep)
          .join("/");
        return simple[0] === "." ? simple : `./${simple}`;
      })();

      return ts.factory.createImportDeclaration(
        undefined,
        node.importClause,
        ts.factory.createStringLiteral(replaced),
        node.assertClause,
      );
    };
}

const get_directory_path = (file: string): string => {
  const splitted: string[] = path.resolve(file).split(path.sep);
  splitted.pop();
  return path.resolve(splitted.join(path.sep));
};