package symbolyze

import (
	"bufio"
	"debug/elf"
	"fmt"
	"log"
	"os"
	"path/filepath"
	"strconv"
	"strings"
)

type Finder struct {
	symbol   string
	pathglob string
	cache    map[string]uint64
	finds    map[int]uint64
	ownpid   int
	observer func(key int, value uint64) error

	*log.Logger
	debugf  func(format string, v ...interface{})
	debugln func(v ...interface{})

	err error
}

var (
	nodebugf  = func(string, ...interface{}) {}
	nodebugln = func(...interface{}) {}
)

func New(symbol, pathglob string) *Finder {
	return &Finder{
		symbol:   symbol,
		pathglob: pathglob,
		cache:    map[string]uint64{},
		finds:    map[int]uint64{},
		ownpid:   os.Getpid(),

		Logger:  log.New(os.Stdout, "[symbolyze] ", log.LstdFlags),
		debugf:  nodebugf,
		debugln: nodebugln,
	}
}

// not threadsafe
func (F *Finder) Debug(on bool) {
	if on {
		F.debugf = F.Printf
		F.debugln = F.Println
		F.debugln("starting in debug-mode")
	} else {
		F.debugf = nodebugf
		F.debugln = nodebugln
	}
}

func (F *Finder) setErrorf(format string, a ...interface{}) {
	F.err = fmt.Errorf(format, a)
	F.Printf(format, a)
}

type Observer func(int, uint64) error

// not threadsafe
func (F *Finder) OnFound(fun Observer) {
	F.observer = fun
	return
}

func (F *Finder) Run() error {
	if F.err != nil {
		return F.err
	}

	proc, err := os.Open("/proc")
	if err != nil {
		F.setErrorf("Failed to open /proc: %w\n", err)
		return F.err
	}

	infos, err := proc.Readdir(-1)
	if err != nil {
		F.setErrorf("Failed to read /proc: %w\n", err)
		return F.err
	}

	proc.Close()

	for _, pinfo := range infos {
		var pid_s = pinfo.Name()

		// The entry /proc/NNN/ must be a directory with integer name
		if !pinfo.IsDir() {
			continue
		} else if pid, err := strconv.Atoi(pid_s); err != nil {
			continue
		} else if pid == F.ownpid { // skip our own pid
			continue
		} else if offset, found := F.searchSymbolIn(pid); !found {
			continue
		} else {
			F.finds[pid] = uint64(offset)
			if F.observer != nil {
				// TODO: accumulate errors?
				err = F.observer(pid, uint64(offset))
				if err != nil {
					F.debugf("F.observer error: %w", err)
				}
			}
		}
	}
	return nil
}

func (F *Finder) searchSymbolIn(pid int) (offset uint64, ok bool) {
	// read the maps file for the binary and shared libraries
	path := filepath.Join("/proc", strconv.Itoa(pid), "maps")
	maps, err := os.Open(path)
	if err != nil {
		// fmt.Printf("Warning: Failed to read %#q: %v\n", path, err)
		return
	}

	scanner := bufio.NewScanner(maps)
	for scanner.Scan() {
		// 0                         1     2       3     4           5
		// address                   perms offset  dev   inode       pathname
		// 7fdd8fece000-7fdd8ff74000 rw-p 00423000 fd:01 14156759    /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0

		fields := strings.Fields(scanner.Text())

		// TODO: we assume that the pathname contains no spaces so
		// bytes.Fields splits the line excactly into six fields

		if len(fields) != 6 {
			continue
		}

		pathname := fields[5]

		if !strings.HasPrefix(pathname, "/") { // Not a pathname
			continue
		}

		filename := filepath.Base(pathname)
		ok, err := filepath.Match(F.pathglob, filename)
		if err != nil || !ok {
			continue
		}

		if fields[1] != "rw-p" { // symbol needs to be writable
			continue
		}

		memOffset, found := F.findSymbol(pathname)
		if !found {
			continue
		}

		start, _, err := parseRange(fields[0])
		if err != nil {
			fmt.Printf("%w\n", err)
			continue
		}

		fileoffset, err := strconv.ParseUint(fields[2], 16, 64)
		if err != nil {
			fmt.Printf("Error while parsing fileoffset %#q: %w\n", fields[2], err)
			continue
		}

		F.finds[pid] = start + memOffset - fileoffset

		return start + memOffset - fileoffset, true

	}

	return 0, false
}

func (F *Finder) findSymbol(pathname string) (offset uint64, found bool) {

	if offset, found = F.cache[pathname]; found {
		return offset, found
	}

	file, err := elf.Open(pathname)
	if err != nil {
		F.setErrorf("elf.Open(%s): %w", pathname, err)
		return 0, false
	}

	defer file.Close()

	symbols, err := file.DynamicSymbols()
	if err != nil {
		F.setErrorf("file.DynamicSymbols(): %w", err)
		return 0, false
	}

	var sym *elf.Symbol

	for _, s := range symbols {
		if s.Name == F.symbol {
			F.debugf("Found symbol %#v in %s: %#v\n", sym, pathname, s)
			sym = &s
			break
		}
	}

	if sym == nil {
		F.debugf("symbol %q not found in %s\n", sym, pathname)
		return 0, false
	}

	if len(file.Sections) < int(sym.Section) {
		F.debugf("len(file.Section) < int(sym.Section) for symbol %q in %s\n", sym, pathname)
		return 0, false
	}

	section := file.Sections[sym.Section]
	if section == nil {
		F.debugf("Section %v not found for ELF-Header %q in %s\n", sym.Section, pathname)
		return 0, false
	}

	header := &section.SectionHeader

	memoffset := sym.Value - header.Addr + alignedOffset(header)

	F.cache[pathname] = memoffset

	return memoffset, true
}

func parseRange(input string) (start, end uint64, e error) {
	// 7fdd8fece000-7fdd8ff74000
	parts := strings.Split(input, "-")

	if len(parts) != 2 {
		e = fmt.Errorf("[parseRange] unrecognized format for region: %#q", input)
		return 0, 0, e
	}

	start, e = strconv.ParseUint(parts[0], 16, 64)
	if e != nil {
		e = fmt.Errorf("[parseRange] couldn't parse start-address %#q in %#q: %w", parts[0], input, e)
		return 0, 0, e
	}

	end, e = strconv.ParseUint(parts[1], 16, 64)
	if e != nil {
		e = fmt.Errorf("[parseRange] couldn't parse end-address %#q in %#q: %w", parts[1], input, e)
		return 0, 0, e
	}

	return start, end, e
}

func alignedOffset(section *elf.SectionHeader) uint64 {
	mask := section.Addralign - 1
	return (section.Offset + mask) & (^mask)
}