package fs

import (
	"bufio"
	"bytes"
	"fmt"
	"io"
	"os"
	"regexp"
	"strconv"
	"strings"
)

// copy from github.com/prometheus/procfs@v0.8.0/slab.go

var (
	slabSpace  = regexp.MustCompile(`\s+`)
	slabVer    = regexp.MustCompile(`slabinfo -`)
	slabHeader = regexp.MustCompile(`# name`)
)

// Slab represents a slab pool in the kernel.
type Slab struct {
	Name         string
	ObjActive    int64
	ObjNum       int64
	ObjSize      int64
	ObjPerSlab   int64
	PagesPerSlab int64
	// tunables
	Limit        int64
	Batch        int64
	SharedFactor int64
	SlabActive   int64
	SlabNum      int64
	SharedAvail  int64
	// custom
	Cache int64 // ObjNum * ObjSize
}

// SlabInfo represents info for all slabs.
type SlabInfo struct {
	Slabs []*Slab
}

func (s SlabInfo) Len() int {
	return len(s.Slabs)
}

func (s SlabInfo) Less(i, j int) bool {
	return s.Slabs[i].Cache > s.Slabs[j].Cache
}

func (s SlabInfo) Swap(i, j int) {
	s.Slabs[i], s.Slabs[j] = s.Slabs[j], s.Slabs[i]
}

func shouldParseSlab(line string) bool {
	if slabVer.MatchString(line) {
		return false
	}
	if slabHeader.MatchString(line) {
		return false
	}
	return true
}

// parseV21SlabEntry is used to parse a line from /proc/slabinfo version 2.1.
func parseV21SlabEntry(line string) (*Slab, error) {
	// First cleanup whitespace.
	l := slabSpace.ReplaceAllString(line, " ")
	s := strings.Split(l, " ")
	if len(s) != 16 {
		return nil, fmt.Errorf("unable to parse: %q", line)
	}
	var err error
	i := &Slab{Name: s[0]}
	i.ObjActive, err = strconv.ParseInt(s[1], 10, 64)
	if err != nil {
		return nil, err
	}
	i.ObjNum, err = strconv.ParseInt(s[2], 10, 64)
	if err != nil {
		return nil, err
	}
	i.ObjSize, err = strconv.ParseInt(s[3], 10, 64)
	if err != nil {
		return nil, err
	}
	i.ObjPerSlab, err = strconv.ParseInt(s[4], 10, 64)
	if err != nil {
		return nil, err
	}
	i.PagesPerSlab, err = strconv.ParseInt(s[5], 10, 64)
	if err != nil {
		return nil, err
	}
	i.Limit, err = strconv.ParseInt(s[8], 10, 64)
	if err != nil {
		return nil, err
	}
	i.Batch, err = strconv.ParseInt(s[9], 10, 64)
	if err != nil {
		return nil, err
	}
	i.SharedFactor, err = strconv.ParseInt(s[10], 10, 64)
	if err != nil {
		return nil, err
	}
	i.SlabActive, err = strconv.ParseInt(s[13], 10, 64)
	if err != nil {
		return nil, err
	}
	i.SlabNum, err = strconv.ParseInt(s[14], 10, 64)
	if err != nil {
		return nil, err
	}
	i.SharedAvail, err = strconv.ParseInt(s[15], 10, 64)
	if err != nil {
		return nil, err
	}
	// custom
	i.Cache = i.ObjNum * i.ObjSize
	return i, nil
}

// parseSlabInfo21 is used to parse a slabinfo 2.1 file.
func parseSlabInfo21(r *bytes.Reader) (SlabInfo, error) {
	scanner := bufio.NewScanner(r)
	s := SlabInfo{Slabs: []*Slab{}}
	for scanner.Scan() {
		line := scanner.Text()
		if !shouldParseSlab(line) {
			continue
		}
		slab, err := parseV21SlabEntry(line)
		if err != nil {
			return s, err
		}
		s.Slabs = append(s.Slabs, slab)
	}
	return s, nil
}

// ParseSlabInfo reads data from slabinfo file
func ParseSlabInfo(filename string) (SlabInfo, error) {
	// TODO: Consider passing options to allow for parsing different
	// slabinfo versions. However, slabinfo 2.1 has been stable since
	// kernel 2.6.10 and later.
	data, err := ReadFileNoStat(filename)
	if err != nil {
		return SlabInfo{}, err
	}

	return parseSlabInfo21(bytes.NewReader(data))
}

// ReadFileNoStat uses io.ReadAll to read contents of entire file.
// This is similar to os.ReadFile but without the call to os.Stat, because
// many files in /proc and /sys report incorrect file sizes (either 0 or 4096).
// Reads a max file size of 1024kB.  For files larger than this, a scanner
// should be used.
func ReadFileNoStat(filename string) ([]byte, error) {
	const maxBufferSize = 1024 * 1024

	f, err := os.Open(filename)
	if err != nil {
		return nil, err
	}
	defer f.Close()

	reader := io.LimitReader(f, maxBufferSize)
	return io.ReadAll(reader)
}