/*
Copyright 2013 CoreOS 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 journal provides write bindings to the systemd journal
package journal

import (
	"bytes"
	"encoding/binary"
	"errors"
	"fmt"
	"io"
	"io/ioutil"
	"net"
	"os"
	"strconv"
	"strings"
	"syscall"
)

// Priority of a journal message
type Priority int

const (
	PriEmerg Priority = iota
	PriAlert
	PriCrit
	PriErr
	PriWarning
	PriNotice
	PriInfo
	PriDebug
)

var conn net.Conn

func init() {
	var err error
	conn, err = net.Dial("unixgram", "/run/systemd/journal/socket")
	if err != nil {
		conn = nil
	}
}

// Enabled returns true iff the systemd journal is available for logging
func Enabled() bool {
	return conn != nil
}

// Send a message to the systemd journal. vars is a map of journald fields to
// values.  Fields must be composed of uppercase letters, numbers, and
// underscores, but must not start with an underscore. Within these
// restrictions, any arbitrary field name may be used.  Some names have special
// significance: see the journalctl documentation
// (http://www.freedesktop.org/software/systemd/man/systemd.journal-fields.html)
// for more details.  vars may be nil.
func Send(message string, priority Priority, vars map[string]string) error {
	if conn == nil {
		return journalError("could not connect to journald socket")
	}

	data := new(bytes.Buffer)
	appendVariable(data, "PRIORITY", strconv.Itoa(int(priority)))
	appendVariable(data, "MESSAGE", message)
	for k, v := range vars {
		appendVariable(data, k, v)
	}

	_, err := io.Copy(conn, data)
	if err != nil && isSocketSpaceError(err) {
		file, err := tempFd()
		if err != nil {
			return journalError(err.Error())
		}
		_, err = io.Copy(file, data)
		if err != nil {
			return journalError(err.Error())
		}

		rights := syscall.UnixRights(int(file.Fd()))

		/* this connection should always be a UnixConn, but better safe than sorry */
		unixConn, ok := conn.(*net.UnixConn)
		if !ok {
			return journalError("can't send file through non-Unix connection")
		}
		unixConn.WriteMsgUnix([]byte{}, rights, nil)
	} else if err != nil {
		return journalError(err.Error())
	}
	return nil
}

func appendVariable(w io.Writer, name, value string) {
	if !validVarName(name) {
		journalError("variable name contains invalid character, ignoring")
	}
	if strings.ContainsRune(value, '\n') {
		/* When the value contains a newline, we write:
		 * - the variable name, followed by a newline
		 * - the size (in 64bit little endian format)
		 * - the data, followed by a newline
		 */
		fmt.Fprintln(w, name)
		binary.Write(w, binary.LittleEndian, uint64(len(value)))
		fmt.Fprintln(w, value)
	} else {
		/* just write the variable and value all on one line */
		fmt.Fprintf(w, "%s=%s\n", name, value)
	}
}

func validVarName(name string) bool {
	/* The variable name must be in uppercase and consist only of characters,
	 * numbers and underscores, and may not begin with an underscore. (from the docs)
	 */

	valid := name[0] != '_'
	for _, c := range name {
		valid = valid && ('A' <= c && c <= 'Z') || ('0' <= c && c <= '9') || c == '_'
	}
	return valid
}

func isSocketSpaceError(err error) bool {
	opErr, ok := err.(*net.OpError)
	if !ok {
		return false
	}

	sysErr, ok := opErr.Err.(syscall.Errno)
	if !ok {
		return false
	}

	return sysErr == syscall.EMSGSIZE || sysErr == syscall.ENOBUFS
}

func tempFd() (*os.File, error) {
	file, err := ioutil.TempFile("/dev/shm/", "journal.XXXXX")
	if err != nil {
		return nil, err
	}
	syscall.Unlink(file.Name())
	if err != nil {
		return nil, err
	}
	return file, nil
}

func journalError(s string) error {
	s = "journal error: " + s
	fmt.Fprintln(os.Stderr, s)
	return errors.New(s)
}