@jsenv/node-module-import-map/src/internal/resolveFile.js

Generate importmap for node_modules.

import { resolveUrl, readFileSystemNodeStat, urlToFilename, urlToExtension } from "@jsenv/util"
import { firstOperationMatching } from "@jsenv/cancellation"

export const resolveFile = async (fileUrl, { magicExtensions }) => {
  const fileStat = await readFileSystemNodeStat(fileUrl, {
    nullIfNotFound: true,
  })

  // file found
  if (fileStat && fileStat.isFile()) {
    return fileUrl
  }

  // directory found
  if (fileStat && fileStat.isDirectory()) {
    const indexFileSuffix = fileUrl.endsWith("/") ? "index" : "/index"
    const indexFileUrl = `${fileUrl}${indexFileSuffix}`
    const extensionLeadingToAFile = await findExtensionLeadingToFile(indexFileUrl, magicExtensions)
    if (extensionLeadingToAFile === null) {
      return null
    }
    return `${indexFileUrl}${extensionLeadingToAFile}`
  }

  // file not found and it has an extension
  const extension = urlToExtension(fileUrl)
  if (extension !== "") {
    return null
  }

  const extensionLeadingToAFile = await findExtensionLeadingToFile(fileUrl, magicExtensions)
  // magic extension not found
  if (extensionLeadingToAFile === null) {
    return null
  }

  // magic extension worked
  return `${fileUrl}${extensionLeadingToAFile}`
}

const findExtensionLeadingToFile = async (fileUrl, magicExtensions) => {
  const urlDirectoryUrl = resolveUrl("./", fileUrl)
  const urlFilename = urlToFilename(fileUrl)
  const extensionLeadingToFile = await firstOperationMatching({
    array: magicExtensions,
    start: async (extensionCandidate) => {
      const urlCandidate = `${urlDirectoryUrl}${urlFilename}${extensionCandidate}`
      const stats = await readFileSystemNodeStat(urlCandidate, { nullIfNotFound: true })
      return stats && stats.isFile() ? extensionCandidate : null
    },
    predicate: (extension) => Boolean(extension),
  })
  return extensionLeadingToFile || null
}