// Copyright 2020 The Prometheus Authors
// 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 procfs

import (
	"bufio"
	"encoding/hex"
	"fmt"
	"io"
	"net"
	"os"
	"strconv"
	"strings"
)

const (
	// readLimit is used by io.LimitReader while reading the content of the
	// /proc/net/udp{,6} files. The number of lines inside such a file is dynamic
	// as each line represents a single used socket.
	// In theory, the number of available sockets is 65535 (2^16 - 1) per IP.
	// With e.g. 150 Byte per line and the maximum number of 65535,
	// the reader needs to handle 150 Byte * 65535 =~ 10 MB for a single IP.
	readLimit = 4294967296 // Byte -> 4 GiB
)

type (
	// NetUDP represents the contents of /proc/net/udp{,6} file without the header.
	NetUDP []*netUDPLine

	// NetUDPSummary provides already computed values like the total queue lengths or
	// the total number of used sockets. In contrast to NetUDP it does not collect
	// the parsed lines into a slice.
	NetUDPSummary struct {
		// TxQueueLength shows the total queue length of all parsed tx_queue lengths.
		TxQueueLength uint64
		// RxQueueLength shows the total queue length of all parsed rx_queue lengths.
		RxQueueLength uint64
		// UsedSockets shows the total number of parsed lines representing the
		// number of used sockets.
		UsedSockets uint64
	}

	// netUDPLine represents the fields parsed from a single line
	// in /proc/net/udp{,6}. Fields which are not used by UDP are skipped.
	// For the proc file format details, see https://linux.die.net/man/5/proc.
	netUDPLine struct {
		Sl        uint64
		LocalAddr net.IP
		LocalPort uint64
		RemAddr   net.IP
		RemPort   uint64
		St        uint64
		TxQueue   uint64
		RxQueue   uint64
		UID       uint64
	}
)

// NetUDP returns the IPv4 kernel/networking statistics for UDP datagrams
// read from /proc/net/udp.
func (fs FS) NetUDP() (NetUDP, error) {
	return newNetUDP(fs.proc.Path("net/udp"))
}

// NetUDP6 returns the IPv6 kernel/networking statistics for UDP datagrams
// read from /proc/net/udp6.
func (fs FS) NetUDP6() (NetUDP, error) {
	return newNetUDP(fs.proc.Path("net/udp6"))
}

// NetUDPSummary returns already computed statistics like the total queue lengths
// for UDP datagrams read from /proc/net/udp.
func (fs FS) NetUDPSummary() (*NetUDPSummary, error) {
	return newNetUDPSummary(fs.proc.Path("net/udp"))
}

// NetUDP6Summary returns already computed statistics like the total queue lengths
// for UDP datagrams read from /proc/net/udp6.
func (fs FS) NetUDP6Summary() (*NetUDPSummary, error) {
	return newNetUDPSummary(fs.proc.Path("net/udp6"))
}

// newNetUDP creates a new NetUDP{,6} from the contents of the given file.
func newNetUDP(file string) (NetUDP, error) {
	f, err := os.Open(file)
	if err != nil {
		return nil, err
	}
	defer f.Close()

	netUDP := NetUDP{}

	lr := io.LimitReader(f, readLimit)
	s := bufio.NewScanner(lr)
	s.Scan() // skip first line with headers
	for s.Scan() {
		fields := strings.Fields(s.Text())
		line, err := parseNetUDPLine(fields)
		if err != nil {
			return nil, err
		}
		netUDP = append(netUDP, line)
	}
	if err := s.Err(); err != nil {
		return nil, err
	}
	return netUDP, nil
}

// newNetUDPSummary creates a new NetUDP{,6} from the contents of the given file.
func newNetUDPSummary(file string) (*NetUDPSummary, error) {
	f, err := os.Open(file)
	if err != nil {
		return nil, err
	}
	defer f.Close()

	netUDPSummary := &NetUDPSummary{}

	lr := io.LimitReader(f, readLimit)
	s := bufio.NewScanner(lr)
	s.Scan() // skip first line with headers
	for s.Scan() {
		fields := strings.Fields(s.Text())
		line, err := parseNetUDPLine(fields)
		if err != nil {
			return nil, err
		}
		netUDPSummary.TxQueueLength += line.TxQueue
		netUDPSummary.RxQueueLength += line.RxQueue
		netUDPSummary.UsedSockets++
	}
	if err := s.Err(); err != nil {
		return nil, err
	}
	return netUDPSummary, nil
}

// parseNetUDPLine parses a single line, represented by a list of fields.
func parseNetUDPLine(fields []string) (*netUDPLine, error) {
	line := &netUDPLine{}
	if len(fields) < 8 {
		return nil, fmt.Errorf(
			"cannot parse net udp socket line as it has less then 8 columns: %s",
			strings.Join(fields, " "),
		)
	}
	var err error // parse error

	// sl
	s := strings.Split(fields[0], ":")
	if len(s) != 2 {
		return nil, fmt.Errorf(
			"cannot parse sl field in udp socket line: %s", fields[0])
	}

	if line.Sl, err = strconv.ParseUint(s[0], 0, 64); err != nil {
		return nil, fmt.Errorf("cannot parse sl value in udp socket line: %s", err)
	}
	// local_address
	l := strings.Split(fields[1], ":")
	if len(l) != 2 {
		return nil, fmt.Errorf(
			"cannot parse local_address field in udp socket line: %s", fields[1])
	}
	if line.LocalAddr, err = hex.DecodeString(l[0]); err != nil {
		return nil, fmt.Errorf(
			"cannot parse local_address value in udp socket line: %s", err)
	}
	if line.LocalPort, err = strconv.ParseUint(l[1], 16, 64); err != nil {
		return nil, fmt.Errorf(
			"cannot parse local_address port value in udp socket line: %s", err)
	}

	// remote_address
	r := strings.Split(fields[2], ":")
	if len(r) != 2 {
		return nil, fmt.Errorf(
			"cannot parse rem_address field in udp socket line: %s", fields[1])
	}
	if line.RemAddr, err = hex.DecodeString(r[0]); err != nil {
		return nil, fmt.Errorf(
			"cannot parse rem_address value in udp socket line: %s", err)
	}
	if line.RemPort, err = strconv.ParseUint(r[1], 16, 64); err != nil {
		return nil, fmt.Errorf(
			"cannot parse rem_address port value in udp socket line: %s", err)
	}

	// st
	if line.St, err = strconv.ParseUint(fields[3], 16, 64); err != nil {
		return nil, fmt.Errorf(
			"cannot parse st value in udp socket line: %s", err)
	}

	// tx_queue and rx_queue
	q := strings.Split(fields[4], ":")
	if len(q) != 2 {
		return nil, fmt.Errorf(
			"cannot parse tx/rx queues in udp socket line as it has a missing colon: %s",
			fields[4],
		)
	}
	if line.TxQueue, err = strconv.ParseUint(q[0], 16, 64); err != nil {
		return nil, fmt.Errorf("cannot parse tx_queue value in udp socket line: %s", err)
	}
	if line.RxQueue, err = strconv.ParseUint(q[1], 16, 64); err != nil {
		return nil, fmt.Errorf("cannot parse rx_queue value in udp socket line: %s", err)
	}

	// uid
	if line.UID, err = strconv.ParseUint(fields[7], 0, 64); err != nil {
		return nil, fmt.Errorf(
			"cannot parse uid value in udp socket line: %s", err)
	}

	return line, nil
}