import * as v from 'valibot'
import { PackageRouteParamsSchema } from '#shared/schemas/package'
import {
  CACHE_MAX_AGE_ONE_HOUR,
  NPM_MISSING_README_SENTINEL,
  NPM_README_TRUNCATION_THRESHOLD,
} from '#shared/utils/constants'

/** Standard README filenames to try when fetching from jsdelivr (case-sensitive CDN) */
const standardReadmeFilenames = [
  'README.md',
  'readme.md',
  'Readme.md',
  'README',
  'readme',
  'README.markdown',
  'readme.markdown',
]

/** Matches standard README filenames (case-insensitive, for checking registry metadata) */
const standardReadmePattern = /^readme(?:\.md|\.markdown)?$/i

export function isStandardReadme(filename: string | undefined): boolean {
  return !!filename && standardReadmePattern.test(filename)
}

/**
 * Fetch README from jsdelivr CDN for a specific package version.
 * Falls back through common README filenames.
 */
export async function fetchReadmeFromJsdelivr(
  packageName: string,
  readmeFilenames: string[],
  version?: string,
): Promise<string | null> {
  const versionSuffix = version ? `@${version}` : ''

  for (const filename of readmeFilenames) {
    try {
      const url = `https://cdn.jsdelivr.net/npm/${packageName}${versionSuffix}/${filename}`
      const response = await fetch(url)
      if (response.ok) {
        return await response.text()
      }
    } catch {
      // Try next filename
    }
  }

  return null
}

export const resolvePackageReadmeSource = defineCachedFunction(
  async (packagePath: string) => {
    const pkgParamSegments = packagePath.split('/')

    const { rawPackageName, rawVersion } = parsePackageParams(pkgParamSegments)

    const { packageName, version } = v.parse(PackageRouteParamsSchema, {
      packageName: rawPackageName,
      version: rawVersion,
    })

    const packageData = await fetchNpmPackage(packageName)

    let readmeContent: string | undefined
    let readmeFilename: string | undefined

    if (version) {
      const versionData = packageData.versions[version]
      if (versionData) {
        readmeContent = versionData.readme
        readmeFilename = versionData.readmeFilename
      }
    } else {
      readmeContent = packageData.readme
      readmeFilename = packageData.readmeFilename
    }

    const hasValidNpmReadme = readmeContent && readmeContent !== NPM_MISSING_README_SENTINEL

    if (
      !hasValidNpmReadme ||
      !isStandardReadme(readmeFilename) ||
      readmeContent!.length >= NPM_README_TRUNCATION_THRESHOLD
    ) {
      const resolvedVersion = version ?? packageData['dist-tags']?.latest
      const jsdelivrReadme = await fetchReadmeFromJsdelivr(
        packageName,
        standardReadmeFilenames,
        resolvedVersion,
      )
      if (jsdelivrReadme) {
        readmeContent = jsdelivrReadme
      }
    }

    if (!readmeContent || readmeContent === NPM_MISSING_README_SENTINEL) {
      return {
        packageName,
        version,
        markdown: undefined,
        repoInfo: undefined,
      }
    }

    const repoInfo = parseRepositoryInfo(packageData.repository)

    return {
      packageName,
      version,
      markdown: readmeContent,
      repoInfo,
    }
  },
  {
    maxAge: CACHE_MAX_AGE_ONE_HOUR,
    swr: true,
    getKey: (packagePath: string) => packagePath,
  },
)