import { mkdir, readFile, writeFile } from 'node:fs/promises';
import { dirname, join } from 'node:path';
import {
  validateProjectTemplateSnapshot,
  type ProjectTemplateSnapshot,
} from '../../shared/project-template';

export const PROJECT_TEMPLATE_SNAPSHOT_PATH = '.niancode/project-template.json';

export type ProjectTemplateSnapshotReadResult =
  | { status: 'missing' }
  | { status: 'valid'; snapshot: ProjectTemplateSnapshot }
  | { status: 'invalid'; error: string };

export function getProjectTemplateSnapshotPath(projectPath: string): string {
  return join(projectPath, '.niancode', 'project-template.json');
}

export async function readProjectTemplateSnapshot(projectPath: string): Promise<ProjectTemplateSnapshotReadResult> {
  const snapshotPath = getProjectTemplateSnapshotPath(projectPath);
  let raw: string;
  try {
    raw = await readFile(snapshotPath, 'utf8');
  } catch (error) {
    if ((error as NodeJS.ErrnoException).code === 'ENOENT') {
      return { status: 'missing' };
    }
    return { status: 'invalid', error: `${PROJECT_TEMPLATE_SNAPSHOT_PATH}: ${String(error)}` };
  }

  let parsed: unknown;
  try {
    parsed = JSON.parse(raw);
  } catch (error) {
    return { status: 'invalid', error: `${PROJECT_TEMPLATE_SNAPSHOT_PATH}: invalid JSON (${String(error)})` };
  }

  const validation = validateProjectTemplateSnapshot(parsed);
  if (!validation.ok) {
    return { status: 'invalid', error: `${PROJECT_TEMPLATE_SNAPSHOT_PATH}: ${validation.error}` };
  }
  return { status: 'valid', snapshot: validation.snapshot };
}

export async function writeProjectTemplateSnapshot(
  projectPath: string,
  snapshot: ProjectTemplateSnapshot,
): Promise<ProjectTemplateSnapshot> {
  const validation = validateProjectTemplateSnapshot(snapshot);
  if (!validation.ok) {
    throw new Error(validation.error);
  }
  const snapshotPath = getProjectTemplateSnapshotPath(projectPath);
  await mkdir(dirname(snapshotPath), { recursive: true });
  try {
    await writeFile(snapshotPath, `${JSON.stringify(validation.snapshot, null, 2)}\n`, {
      encoding: 'utf8',
      flag: 'wx',
    });
  } catch (error) {
    if ((error as NodeJS.ErrnoException).code === 'EEXIST') {
      throw new Error(`${PROJECT_TEMPLATE_SNAPSHOT_PATH} already exists and cannot be replaced`, { cause: error });
    }
    throw error;
  }
  return validation.snapshot;
}