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// This script checks `import`s in TypeScript files under `src/` have ".js"
// file extension in its import path. In Node.js ESM, import path must have
// a file extension, while TypeScript has been using extension-less import
// even with Node.js ESM module setting. That means, runtime error happens
// when importing an ESM module TypeScript deliberately emitted.
//
// (OK) import "./foo.js";
// (NG) import "./foo";     ... Runtime error, both in Node.js and basic file server.
// (NG) import "./foo.ts";  ... ".ts" remains in emitted JS files.
// (NG) require("./foo");   ... Enough.
// (NG) import("./foo.js"); ... This package should be minimal set of functions.

import { file, Transpiler } from "bun";
import chalk from "chalk";
import { readdirSync } from "node:fs";
import { relative } from "node:path";

export enum RuleViolationKind {
  ExtensionLessImport,
  CJS,
  DynamicImport,
}

export interface ImportRuleViolation {
  kind: RuleViolationKind;

  importPath: string;
}

export interface OffendingFile {
  url: URL;

  violations: readonly ImportRuleViolation[];
}

export interface CheckResult {
  checkedFiles: number;

  offendingFiles: readonly OffendingFile[];
}

async function checkFile(
  t: Transpiler,
  url: URL,
): Promise<readonly ImportRuleViolation[]> {
  const contents = await file(url).arrayBuffer();

  const imports = t.scanImports(contents);

  return imports
    .map<ImportRuleViolation | null>((i) => {
      switch (i.kind) {
        case "dynamic-import":
          return {
            kind: RuleViolationKind.DynamicImport,
            importPath: i.path,
          };
        case "require-call":
        case "require-resolve":
          return {
            kind: RuleViolationKind.CJS,
            importPath: i.path,
          };
        case "import-statement": {
          if (!i.path.endsWith(".js")) {
            return {
              kind: RuleViolationKind.ExtensionLessImport,
              importPath: i.path,
            };
          }

          return null;
        }
        default: {
          return null;
        }
      }
    })
    .filter((v): v is ImportRuleViolation => v !== null);
}

async function checkDir(t: Transpiler, dir: URL): Promise<CheckResult> {
  let checkedFiles = 0;
  const offendingFiles: OffendingFile[] = [];

  for (const entry of readdirSync(dir, { withFileTypes: true })) {
    if (entry.isDirectory()) {
      const result = await checkDir(t, new URL(entry.name + "/", dir));

      checkedFiles += result.checkedFiles;
      offendingFiles.push(...result.offendingFiles);
      continue;
    }

    if (!entry.isFile() || !entry.name.endsWith(".ts")) {
      continue;
    }

    checkedFiles += 1;

    const fileUrl = new URL(entry.name, dir);

    const violations = await checkFile(t, fileUrl);
    if (violations.length === 0) {
      continue;
    }

    offendingFiles.push({
      url: fileUrl,
      violations,
    });
  }

  return {
    checkedFiles,
    offendingFiles,
  };
}

export async function checkImports(srcDir: URL): Promise<CheckResult> {
  const transpiler = new Transpiler({
    loader: "ts",
  });

  return checkDir(transpiler, srcDir);
}

function kindToLabel(kind: RuleViolationKind): string {
  switch (kind) {
    case RuleViolationKind.CJS:
      return "CommonJS import is not allowed.";
    case RuleViolationKind.DynamicImport:
      return "Dynamic import is not allowed.";
    case RuleViolationKind.ExtensionLessImport:
      return `Import path must end with ".js".`;
  }
}

if (import.meta.main) {
  const result = await checkImports(new URL("../src/", import.meta.url));

  console.error(
    chalk.white(`Checked ${chalk.bold("%s")} files.`),
    result.checkedFiles,
  );

  if (result.offendingFiles.length === 0) {
    console.error(chalk.white("No import rule violations found."));
    process.exit(0);
  }

  console.error(
    chalk.red("%s have import rule violations."),
    result.offendingFiles.length > 1
      ? result.offendingFiles.length + " files"
      : "1 file",
  );

  for (const file of result.offendingFiles) {
    console.error(
      chalk.white(`[%s]`),
      relative(process.cwd(), file.url.pathname),
    );

    for (const violation of file.violations) {
      console.error(
        chalk.white(` %s: %s`),
        chalk.yellow(`"${violation.importPath}"`),
        chalk.red(kindToLabel(violation.kind)),
      );
    }
  }

  process.exit(1);
}