// Generates src/types/api.ts, the TypeScript types of the backend's API, from
// its OpenAPI 3.1 description:
//
//   npm run generate:api [-- <path or URL of openapi.json>]
//
// The default is the backend's generated file, ../internal/api/openapi/
// swagger.json (run go generate ./... in the repository first); a running
// server's http://localhost:9393/api/openapi.json works too.
//
// swag marks a Go field that can be null (a pointer, or a slice that can be
// nil) with the x-nullable extension, which openapi-typescript ignores, so
// those properties are rewritten into OpenAPI 3.1's own form first.
import { readFile, writeFile } from 'node:fs/promises';
import type { OpenAPI3 } from 'openapi-typescript';
import openapiTS, { astToString } from 'openapi-typescript';

const defaultSource = '../internal/api/openapi/swagger.json';
const output = 'src/types/api.ts';

const header = `// Code generated by npm run generate:api from the backend's OpenAPI
// description. DO NOT EDIT: change the Go types or handlers, then
// regenerate (see scripts/generateApiTypes.ts).

`;

type Schema = Record<string, unknown>;

/** Rewrites every x-nullable property of the description's schemas so it allows null. */
function allowNulls(description: OpenAPI3): void {
  const schemas = (description.components?.schemas ?? {}) as Record<string, Schema>;
  for (const schema of Object.values(schemas)) {
    const properties = (schema.properties ?? {}) as Record<string, Schema>;
    for (const [name, property] of Object.entries(properties)) {
      if (property['x-nullable'] !== true) continue;
      delete property['x-nullable'];
      properties[name] =
        typeof property.type === 'string' && property.type !== 'array'
          ? { ...property, type: [property.type, 'null'] }
          : { oneOf: [property, { type: 'null' }] };
    }
  }
}

async function readDescription(source: string): Promise<OpenAPI3> {
  const text = /^https?:\/\//.test(source)
    ? await (await fetch(source)).text()
    : await readFile(source, 'utf8');
  return JSON.parse(text) as OpenAPI3;
}

const source = process.argv[2] ?? defaultSource;
const description = await readDescription(source);
allowNulls(description);
const types = astToString(await openapiTS(description));
await writeFile(output, header + types);
console.log(`Wrote ${output} from ${source}`);