const { satisfies } = require('bare-semver')
const errors = require('./lib/errors')

module.exports = exports = function resolve(specifier, parentURL, opts, readPackage) {
  if (typeof opts === 'function') {
    readPackage = opts
    opts = {}
  } else if (typeof readPackage !== 'function') {
    readPackage = defaultReadPackage
  }

  return {
    *[Symbol.iterator]() {
      const generator = exports.module(specifier, parentURL, opts)

      let next = generator.next()

      while (next.done !== true) {
        const value = next.value

        if (value.package) {
          next = generator.next(readPackage(value.package))
        } else {
          next = generator.next(yield value.resolution)
        }
      }

      return next.value
    },

    async *[Symbol.asyncIterator]() {
      const generator = exports.module(specifier, parentURL, opts)

      let next = generator.next()

      while (next.done !== true) {
        const value = next.value

        if (value.package) {
          next = generator.next(await readPackage(value.package))
        } else {
          next = generator.next(yield value.resolution)
        }
      }

      return next.value
    }
  }
}

function defaultReadPackage() {
  return null
}

// No resolution candidate was yielded
const UNRESOLVED = 0x0
// At least 1 resolution candidate was yielded
const YIELDED = 0x1
// At least 1 resolution candidate was yielded and resolved
const RESOLVED = YIELDED | 0x2

exports.constants = {
  UNRESOLVED,
  YIELDED,
  RESOLVED
}

exports.module = function* (specifier, parentURL, opts = {}) {
  const { resolutions = null, imports = null } = opts

  if (exports.startsWithWindowsDriveLetter(specifier)) {
    specifier = '/' + specifier
  }

  let status

  if (resolutions) {
    status = yield* exports.preresolved(specifier, resolutions, parentURL, opts)

    if (status) return status
  }

  status = yield* exports.url(specifier, parentURL, opts)

  if (status) return status

  status = yield* exports.packageImports(specifier, parentURL, opts)

  if (status) return status

  if (
    specifier === '.' ||
    specifier === '..' ||
    specifier[0] === '/' ||
    specifier[0] === '\\' ||
    specifier.startsWith('./') ||
    specifier.startsWith('.\\') ||
    specifier.startsWith('../') ||
    specifier.startsWith('..\\')
  ) {
    if (imports) {
      status = yield* exports.packageImportsExports(specifier, imports, parentURL, true, opts)

      if (status) return status
    }

    status = yield* exports.deferred(specifier, opts)

    if (status) return status

    status = yield* exports.file(specifier, parentURL, false, opts)

    if (status === RESOLVED) return status

    return yield* exports.directory(specifier, parentURL, opts)
  }

  return yield* exports.package(specifier, parentURL, opts)
}

exports.url = function* (url, parentURL, opts = {}) {
  const { imports = null, deferredProtocol = 'deferred:', resolutions = null } = opts

  let resolution
  try {
    resolution = new URL(url)
  } catch {
    return UNRESOLVED
  }

  if (imports) {
    const status = yield* exports.packageImportsExports(
      resolution.href,
      imports,
      parentURL,
      true,
      opts
    )

    if (status) return status
  }

  if (resolution.protocol === deferredProtocol) {
    const specifier = resolution.pathname

    if (resolutions) {
      const imports = resolutions[parentURL.href]

      if (typeof imports === 'object' && imports !== null) {
        opts = {
          ...opts,
          resolutions: { ...resolutions, [parentURL.href]: { ...imports, [specifier]: null } }
        }
      }
    }

    return yield* exports.module(specifier, parentURL, opts)
  }

  if (resolution.protocol === 'node:') {
    const specifier = resolution.pathname

    if (
      specifier === '.' ||
      specifier === '..' ||
      specifier[0] === '/' ||
      specifier.startsWith('./') ||
      specifier.startsWith('../')
    ) {
      throw errors.INVALID_MODULE_SPECIFIER(`Module specifier '${url}' is not a valid package name`)
    }

    return yield* exports.package(specifier, parentURL, opts)
  }

  const resolved = yield { resolution }

  return resolved ? RESOLVED : YIELDED
}

exports.preresolved = function* (specifier, resolutions, parentURL, opts = {}) {
  const imports = resolutions[parentURL.href]

  if (typeof imports === 'object' && imports !== null) {
    return yield* exports.packageImportsExports(specifier, imports, parentURL, true, opts)
  }

  return UNRESOLVED
}

exports.deferred = function* (specifier, opts = {}) {
  const { deferredProtocol = 'deferred:', defer = [] } = opts

  if (defer.includes(specifier)) {
    const resolved = yield { resolution: new URL(deferredProtocol + specifier) }

    return resolved ? RESOLVED : YIELDED
  }

  return UNRESOLVED
}

exports.package = function* (packageSpecifier, parentURL, opts = {}) {
  const { builtins = [] } = opts

  if (packageSpecifier === '') {
    throw errors.INVALID_MODULE_SPECIFIER(
      `Module specifier '${packageSpecifier}' is not a valid package name`
    )
  }

  let packageName

  if (packageSpecifier[0] !== '@') {
    packageName = packageSpecifier.split('/', 1).join()
  } else {
    if (!packageSpecifier.includes('/')) {
      throw errors.INVALID_MODULE_SPECIFIER(
        `Module specifier '${packageSpecifier}' is not a valid package name`
      )
    }

    packageName = packageSpecifier.split('/', 2).join('/')
  }

  if (packageName[0] === '.' || packageName.includes('\\') || packageName.includes('%')) {
    throw errors.INVALID_MODULE_SPECIFIER(
      `Module specifier '${packageSpecifier}' is not a valid package name`
    )
  }

  let status

  status = yield* exports.builtinTarget(packageSpecifier, null, builtins, opts)

  if (status) return status

  status = yield* exports.deferred(packageSpecifier, opts)

  if (status) return status

  let packageSubpath = '.' + packageSpecifier.substring(packageName.length)

  status = yield* exports.packageSelf(packageName, packageSubpath, parentURL, opts)

  if (status) return status

  parentURL = new URL(parentURL.href)

  for (const packageURL of exports.lookupPackageRoot(packageName, parentURL)) {
    const info = yield { package: packageURL }

    if (info) {
      if (info.engines) exports.validateEngines(packageURL, info.engines, opts)

      if (info.exports) {
        return yield* exports.packageExports(packageURL, packageSubpath, info.exports, opts)
      }

      if (packageSubpath === '.') {
        if (typeof info.main === 'string' && info.main !== '') {
          packageSubpath = info.main
        } else {
          return yield* exports.file('index', packageURL, true, opts)
        }
      }

      status = yield* exports.file(packageSubpath, packageURL, false, opts)

      if (status === RESOLVED) return status

      return yield* exports.directory(packageSubpath, packageURL, opts)
    }
  }

  return UNRESOLVED
}

exports.packageSelf = function* (packageName, packageSubpath, parentURL, opts = {}) {
  for (const packageURL of exports.lookupPackageScope(parentURL, opts)) {
    const info = yield { package: packageURL }

    if (info) {
      if (info.name !== packageName) return false

      if (info.exports) {
        return yield* exports.packageExports(packageURL, packageSubpath, info.exports, opts)
      }

      if (packageSubpath === '.') {
        if (typeof info.main === 'string' && info.main !== '') {
          packageSubpath = info.main
        } else {
          return yield* exports.file('index', packageURL, true, opts)
        }
      }

      const status = yield* exports.file(packageSubpath, packageURL, false, opts)

      if (status === RESOLVED) return status

      return yield* exports.directory(packageSubpath, packageURL, opts)
    }
  }

  return UNRESOLVED
}

exports.packageExports = function* (packageURL, subpath, packageExports, opts = {}) {
  if (subpath === '.') {
    let mainExport

    if (typeof packageExports === 'string' || Array.isArray(packageExports)) {
      mainExport = packageExports
    } else if (typeof packageExports === 'object' && packageExports !== null) {
      const keys = Object.keys(packageExports)

      if (keys.some((key) => key.startsWith('.'))) {
        if ('.' in packageExports) mainExport = packageExports['.']
      } else {
        mainExport = packageExports
      }
    }

    if (mainExport) {
      const status = yield* exports.packageTarget(packageURL, mainExport, null, false, opts)

      if (status) return status
    }
  } else if (typeof packageExports === 'object' && packageExports !== null) {
    const keys = Object.keys(packageExports)

    if (keys.every((key) => key.startsWith('.'))) {
      const status = yield* exports.packageImportsExports(
        subpath,
        packageExports,
        packageURL,
        false,
        opts
      )

      if (status) return status
    }
  }

  throw errors.PACKAGE_PATH_NOT_EXPORTED(
    `Package subpath '${subpath}' is not defined by "exports" in '${packageURL}'`
  )
}

exports.packageImports = function* (specifier, parentURL, opts = {}) {
  const { imports = null } = opts

  if (specifier === '#' || specifier.startsWith('#/')) {
    throw errors.INVALID_MODULE_SPECIFIER(
      `Module specifier '${specifier}' is not a valid internal imports specifier`
    )
  }

  for (const packageURL of exports.lookupPackageScope(parentURL, opts)) {
    const info = yield { package: packageURL }

    if (info) {
      if (info.imports) {
        const status = yield* exports.packageImportsExports(
          specifier,
          info.imports,
          packageURL,
          true,
          opts
        )

        if (status) return status
      }

      if (specifier.startsWith('#')) {
        throw errors.PACKAGE_IMPORT_NOT_DEFINED(
          `Package import specifier '${specifier}' is not defined by "imports" in '${packageURL}'`
        )
      }

      break
    }
  }

  if (imports) {
    const status = yield* exports.packageImportsExports(specifier, imports, parentURL, true, opts)

    if (status) return status
  }

  return UNRESOLVED
}

exports.packageImportsExports = function* (
  matchKey,
  matchObject,
  packageURL,
  isImports,
  opts = {}
) {
  if (matchKey in matchObject && !matchKey.includes('*')) {
    const target = matchObject[matchKey]

    return yield* exports.packageTarget(packageURL, target, null, isImports, opts)
  }

  const expansionKeys = Object.keys(matchObject)
    .filter((key) => key.includes('*'))
    .sort(exports.patternKeyCompare)

  for (const expansionKey of expansionKeys) {
    const patternIndex = expansionKey.indexOf('*')
    const patternBase = expansionKey.substring(0, patternIndex)

    if (matchKey.startsWith(patternBase) && matchKey !== patternBase) {
      const patternTrailer = expansionKey.substring(patternIndex + 1)

      if (
        patternTrailer === '' ||
        (matchKey.endsWith(patternTrailer) && matchKey.length >= expansionKey.length)
      ) {
        const target = matchObject[expansionKey]

        const patternMatch = matchKey.substring(
          patternBase.length,
          matchKey.length - patternTrailer.length
        )

        return yield* exports.packageTarget(packageURL, target, patternMatch, isImports, opts)
      }
    }
  }

  return UNRESOLVED
}

exports.validateEngines = function validateEngines(packageURL, packageEngines, opts = {}) {
  const { engines = {} } = opts

  for (const [engine, range] of Object.entries(packageEngines)) {
    if (engine in engines) {
      const version = engines[engine]

      if (!satisfies(version, range)) {
        throw errors.UNSUPPORTED_ENGINE(
          `Package not compatible with engine '${engine}' ${version}, requires range '${range}' defined by "engines" in '${packageURL}'`
        )
      }
    }
  }
}

exports.patternKeyCompare = function patternKeyCompare(keyA, keyB) {
  const patternIndexA = keyA.indexOf('*')
  const patternIndexB = keyB.indexOf('*')
  const baseLengthA = patternIndexA === -1 ? keyA.length : patternIndexA + 1
  const baseLengthB = patternIndexB === -1 ? keyB.length : patternIndexB + 1
  if (baseLengthA > baseLengthB) return -1
  if (baseLengthB > baseLengthA) return 1
  if (patternIndexA === -1) return 1
  if (patternIndexB === -1) return -1
  if (keyA.length > keyB.length) return -1
  if (keyB.length > keyA.length) return 1
  return 0
}

exports.packageTarget = function* (packageURL, target, patternMatch, isImports, opts = {}) {
  const { conditions = [], matchedConditions = [] } = opts

  if (typeof target === 'string') {
    if (!target.startsWith('./') && !isImports) {
      throw errors.INVALID_PACKAGE_TARGET(
        `Invalid target '${target}' defined by "exports" in '${packageURL}'`
      )
    }

    if (patternMatch !== null) {
      target = target.replaceAll('*', patternMatch)
    }

    const status = yield* exports.url(target, packageURL, opts)

    if (status) return status

    if (
      target === '.' ||
      target === '..' ||
      target[0] === '/' ||
      target.startsWith('./') ||
      target.startsWith('../')
    ) {
      const resolved = yield { resolution: new URL(target, packageURL) }

      return resolved ? RESOLVED : YIELDED
    }

    return yield* exports.package(target, packageURL, opts)
  }

  if (Array.isArray(target)) {
    for (const targetValue of target) {
      const status = yield* exports.packageTarget(
        packageURL,
        targetValue,
        patternMatch,
        isImports,
        opts
      )

      if (status) return status
    }
  } else if (typeof target === 'object' && target !== null) {
    let status = UNRESOLVED

    for (const [condition, targetValue, subset] of exports.conditionMatches(
      target,
      conditions,
      opts
    )) {
      matchedConditions.push(condition)

      status |= yield* exports.packageTarget(packageURL, targetValue, patternMatch, isImports, {
        ...opts,
        conditions: subset
      })

      matchedConditions.pop()
    }

    if (status) return status
  }

  return UNRESOLVED
}

exports.builtinTarget = function* (packageSpecifier, packageVersion, target, opts = {}) {
  const { builtinProtocol = 'builtin:', conditions = [], matchedConditions = [] } = opts

  if (typeof target === 'string') {
    const targetParts = target.split('@')

    let targetName
    let targetVersion

    if (target[0] !== '@') {
      targetName = targetParts[0]
      targetVersion = targetParts[1] || null
    } else {
      targetName = targetParts.slice(0, 2).join('@')
      targetVersion = targetParts[2] || null
    }

    if (packageSpecifier === targetName) {
      if (packageVersion === null && targetVersion === null) {
        const resolved = yield {
          resolution: new URL(builtinProtocol + packageSpecifier)
        }

        return resolved ? RESOLVED : YIELDED
      }

      let version = null

      if (packageVersion === null) {
        version = targetVersion
      } else if (targetVersion === null || packageVersion === targetVersion) {
        version = packageVersion
      }

      if (version !== null) {
        const resolved = yield {
          resolution: new URL(builtinProtocol + packageSpecifier + '@' + version)
        }

        return resolved ? RESOLVED : YIELDED
      }
    }
  } else if (Array.isArray(target)) {
    for (const targetValue of target) {
      const status = yield* exports.builtinTarget(
        packageSpecifier,
        packageVersion,
        targetValue,
        opts
      )

      if (status) return status
    }
  } else if (typeof target === 'object' && target !== null) {
    let status = UNRESOLVED

    for (const [condition, targetValue, subset] of exports.conditionMatches(
      target,
      conditions,
      opts
    )) {
      matchedConditions.push(condition)

      status |= yield* exports.builtinTarget(packageSpecifier, packageVersion, targetValue, {
        ...opts,
        conditions: subset
      })

      matchedConditions.pop()
    }

    if (status) return status
  }

  return UNRESOLVED
}

exports.conditionMatches = function* conditionMatches(target, conditions, opts = {}) {
  if (conditions.every((condition) => typeof condition === 'string')) {
    const keys = Object.keys(target)

    for (const condition of keys) {
      if (condition === 'default' || conditions.includes(condition)) {
        yield [condition, target[condition], conditions]

        return true
      }
    }

    return false
  }

  let yielded = false

  for (const subset of conditions) {
    if (yield* conditionMatches(target, subset, opts)) {
      yielded = true
    }
  }

  return yielded
}

exports.lookupPackageRoot = function* (packageName, parentURL) {
  parentURL = new URL(parentURL.href)

  do {
    const packageURL = new URL('node_modules/' + packageName + '/', parentURL)

    const info = yield new URL('package.json', packageURL)

    if (info) return info

    parentURL.pathname = parentURL.pathname.substring(0, parentURL.pathname.lastIndexOf('/'))

    if (
      parentURL.pathname.length === 3 &&
      exports.isWindowsDriveLetter(parentURL.pathname.substring(1))
    ) {
      break
    }
  } while (parentURL.pathname !== '' && parentURL.pathname !== '/')

  return null
}

exports.lookupPackageScope = function* lookupPackageScope(scopeURL, opts = {}) {
  const { resolutions = null } = opts

  if (resolutions) {
    for (const { resolution } of exports.preresolved('#package', resolutions, scopeURL, opts)) {
      if (resolution) return yield resolution
    }
  }

  scopeURL = new URL(scopeURL.href)

  do {
    if (scopeURL.pathname.endsWith('/node_modules')) break

    const info = yield new URL('package.json', scopeURL)

    if (info) return info

    scopeURL.pathname = scopeURL.pathname.substring(0, scopeURL.pathname.lastIndexOf('/'))

    if (
      scopeURL.pathname.length === 3 &&
      exports.isWindowsDriveLetter(scopeURL.pathname.substring(1))
    ) {
      break
    }
  } while (scopeURL.pathname !== '' && scopeURL.pathname !== '/')

  return null
}

exports.file = function* (filename, parentURL, isIndex, opts = {}) {
  if (
    filename === '.' ||
    filename === '..' ||
    filename[filename.length - 1] === '/' ||
    filename[filename.length - 1] === '\\'
  ) {
    return UNRESOLVED
  }

  if (parentURL.protocol === 'file:' && /%2f|%5c/i.test(filename)) {
    throw errors.INVALID_MODULE_SPECIFIER(`Module specifier '${filename}' is invalid`)
  }

  const { extensions = [] } = opts

  let status = UNRESOLVED

  if (!isIndex) {
    if (yield { resolution: new URL(filename, parentURL) }) {
      return RESOLVED
    }

    status = YIELDED
  }

  for (const ext of extensions) {
    if (filename.endsWith(ext)) continue

    if (yield { resolution: new URL(filename + ext, parentURL) }) {
      return RESOLVED
    }

    status = YIELDED
  }

  return status
}

exports.directory = function* (dirname, parentURL, opts = {}) {
  let directoryURL

  if (dirname[dirname.length - 1] === '/' || dirname[dirname.length - 1] === '\\') {
    directoryURL = new URL(dirname, parentURL)
  } else {
    directoryURL = new URL(dirname + '/', parentURL)
  }

  const info = yield { package: new URL('package.json', directoryURL) }

  if (info) {
    if (info.exports) {
      return yield* exports.packageExports(directoryURL, '.', info.exports, opts)
    }

    if (typeof info.main === 'string' && info.main !== '') {
      const status = yield* exports.file(info.main, directoryURL, false, opts)

      if (status === RESOLVED) return status

      return yield* exports.directory(info.main, directoryURL, opts)
    }
  }

  return yield* exports.file('index', directoryURL, true, opts)
}

// https://infra.spec.whatwg.org/#ascii-upper-alpha
function isASCIIUpperAlpha(c) {
  return c >= 0x41 && c <= 0x5a
}

// https://infra.spec.whatwg.org/#ascii-lower-alpha
function isASCIILowerAlpha(c) {
  return c >= 0x61 && c <= 0x7a
}

// https://infra.spec.whatwg.org/#ascii-alpha
function isASCIIAlpha(c) {
  return isASCIIUpperAlpha(c) || isASCIILowerAlpha(c)
}

// https://url.spec.whatwg.org/#windows-drive-letter
exports.isWindowsDriveLetter = function isWindowsDriveLetter(input) {
  return (
    input.length >= 2 &&
    isASCIIAlpha(input.charCodeAt(0)) &&
    (input.charCodeAt(1) === 0x3a || input.charCodeAt(1) === 0x7c)
  )
}

// https://url.spec.whatwg.org/#start-with-a-windows-drive-letter
exports.startsWithWindowsDriveLetter = function startsWithWindowsDriveLetter(input) {
  return (
    input.length >= 2 &&
    exports.isWindowsDriveLetter(input) &&
    (input.length === 2 ||
      input.charCodeAt(2) === 0x2f ||
      input.charCodeAt(2) === 0x5c ||
      input.charCodeAt(2) === 0x3f ||
      input.charCodeAt(2) === 0x23)
  )
}