// Copyright 2018 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Package syserror contains syscall error codes exported as error interface
// instead of Errno. This allows for fast comparison and returns when the
// comparand or return value is of type error because there is no need to
// convert from Errno to an interface, i.e., runtime.convT2I isn't called.
package syserror

import (
	"errors"
	"syscall"
)

// The following variables have the same meaning as their syscall equivalent.
var (
	E2BIG        = error(syscall.E2BIG)
	EACCES       = error(syscall.EACCES)
	EAGAIN       = error(syscall.EAGAIN)
	EBADF        = error(syscall.EBADF)
	EBUSY        = error(syscall.EBUSY)
	ECHILD       = error(syscall.ECHILD)
	ECONNREFUSED = error(syscall.ECONNREFUSED)
	ECONNRESET   = error(syscall.ECONNRESET)
	EEXIST       = error(syscall.EEXIST)
	EFAULT       = error(syscall.EFAULT)
	EFBIG        = error(syscall.EFBIG)
	EIDRM        = error(syscall.EIDRM)
	EINTR        = error(syscall.EINTR)
	EINVAL       = error(syscall.EINVAL)
	EIO          = error(syscall.EIO)
	EISDIR       = error(syscall.EISDIR)
	ELIBBAD      = error(syscall.ELIBBAD)
	ELOOP        = error(syscall.ELOOP)
	EMFILE       = error(syscall.EMFILE)
	EMSGSIZE     = error(syscall.EMSGSIZE)
	ENAMETOOLONG = error(syscall.ENAMETOOLONG)
	ENOATTR      = ENODATA
	ENODATA      = error(syscall.ENODATA)
	ENODEV       = error(syscall.ENODEV)
	ENOENT       = error(syscall.ENOENT)
	ENOEXEC      = error(syscall.ENOEXEC)
	ENOLCK       = error(syscall.ENOLCK)
	ENOLINK      = error(syscall.ENOLINK)
	ENOMEM       = error(syscall.ENOMEM)
	ENOSPC       = error(syscall.ENOSPC)
	ENOSYS       = error(syscall.ENOSYS)
	ENOTDIR      = error(syscall.ENOTDIR)
	ENOTEMPTY    = error(syscall.ENOTEMPTY)
	ENOTSUP      = error(syscall.ENOTSUP)
	ENOTTY       = error(syscall.ENOTTY)
	ENXIO        = error(syscall.ENXIO)
	EOPNOTSUPP   = error(syscall.EOPNOTSUPP)
	EOVERFLOW    = error(syscall.EOVERFLOW)
	EPERM        = error(syscall.EPERM)
	EPIPE        = error(syscall.EPIPE)
	ERANGE       = error(syscall.ERANGE)
	EROFS        = error(syscall.EROFS)
	ESPIPE       = error(syscall.ESPIPE)
	ESRCH        = error(syscall.ESRCH)
	ETIMEDOUT    = error(syscall.ETIMEDOUT)
	EUSERS       = error(syscall.EUSERS)
	EWOULDBLOCK  = error(syscall.EWOULDBLOCK)
	EXDEV        = error(syscall.EXDEV)
)

var (
	// ErrWouldBlock is an internal error used to indicate that an operation
	// cannot be satisfied immediately, and should be retried at a later
	// time, possibly when the caller has received a notification that the
	// operation may be able to complete. It is used by implementations of
	// the kio.File interface.
	ErrWouldBlock = errors.New("request would block")

	// ErrInterrupted is returned if a request is interrupted before it can
	// complete.
	ErrInterrupted = errors.New("request was interrupted")

	// ErrExceedsFileSizeLimit is returned if a request would exceed the
	// file's size limit.
	ErrExceedsFileSizeLimit = errors.New("exceeds file size limit")
)

// errorMap is the map used to convert generic errors into errnos.
var errorMap = map[error]syscall.Errno{}

// errorUnwrappers is an array of unwrap functions to extract typed errors.
var errorUnwrappers = []func(error) (syscall.Errno, bool){}

// AddErrorTranslation allows modules to populate the error map by adding their
// own translations during initialization. Returns if the error translation is
// accepted or not. A pre-existing translation will not be overwritten by the
// new translation.
func AddErrorTranslation(from error, to syscall.Errno) bool {
	if _, ok := errorMap[from]; ok {
		return false
	}

	errorMap[from] = to
	return true
}

// AddErrorUnwrapper registers an unwrap method that can extract a concrete error
// from a typed, but not initialized, error.
func AddErrorUnwrapper(unwrap func(e error) (syscall.Errno, bool)) {
	errorUnwrappers = append(errorUnwrappers, unwrap)
}

// TranslateError translates errors to errnos, it will return false if
// the error was not registered.
func TranslateError(from error) (syscall.Errno, bool) {
	err, ok := errorMap[from]
	if ok {
		return err, ok
	}
	// Try to unwrap the error if we couldn't match an error
	// exactly.  This might mean that a package has its own
	// error type.
	for _, unwrap := range errorUnwrappers {
		err, ok := unwrap(from)
		if ok {
			return err, ok
		}
	}
	return 0, false
}

// ConvertIntr converts the provided error code (err) to another one (intr) if
// the first error corresponds to an interrupted operation.
func ConvertIntr(err, intr error) error {
	if err == ErrInterrupted {
		return intr
	}
	return err
}

func init() {
	AddErrorTranslation(ErrWouldBlock, syscall.EWOULDBLOCK)
	AddErrorTranslation(ErrInterrupted, syscall.EINTR)
	AddErrorTranslation(ErrExceedsFileSizeLimit, syscall.EFBIG)
}