import { getLatestVersion } from 'fast-npm-meta'
import { createError } from 'h3'
import validatePackageName from 'validate-npm-package-name'

const NPM_USERNAME_RE = /^[a-z0-9](?:[a-z0-9-]*[a-z0-9])?$/i
const NPM_USERNAME_MAX_LENGTH = 50

/**
 * Encode package name for URL usage.
 * Scoped packages need special handling (@scope/name → @scope%2Fname)
 */
export function encodePackageName(name: string): string {
  if (name.startsWith('@')) {
    return `@${encodeURIComponent(name.slice(1))}`
  }
  return encodeURIComponent(name)
}

/**
 * Fetch the latest version of a package using fast-npm-meta API.
 * This is a lightweight alternative to fetching the full packument.
 *
 * @param name Package name
 * @returns Latest version string or null if not found
 * @see https://github.com/antfu/fast-npm-meta
 */
export async function fetchLatestVersion(name: string): Promise<string | null> {
  try {
    const meta = await getLatestVersion(name)
    return meta.version
  } catch {
    return null
  }
}

/**
 * Validate an npm package name and throw an HTTP error if invalid.
 * Uses validate-npm-package-name to check against npm naming rules.
 */
export function assertValidPackageName(name: string): void {
  const result = validatePackageName(name)
  if (!result.validForNewPackages && !result.validForOldPackages) {
    const errors = [...(result.errors ?? []), ...(result.warnings ?? [])]
    throw createError({
      // TODO: throwing 404 rather than 400 as it's cacheable
      statusCode: 404,
      message: `Invalid package name: ${errors[0] ?? 'unknown error'}`,
    })
  }
}

/**
 * Validate an npm username and throw an HTTP error if invalid.
 * Uses a regular expression to check against npm naming rules.
 * @public
 */
export function assertValidUsername(username: string): void {
  if (!username || username.length > NPM_USERNAME_MAX_LENGTH || !NPM_USERNAME_RE.test(username)) {
    throw createError({
      // TODO: throwing 404 rather than 400 as it's cacheable
      statusCode: 404,
      message: `Invalid username: ${username}`,
    })
  }
}