package firmware

import (
	"bytes"
	"encoding/binary"
	"errors"
	"github.com/go-playground/log/v8"
	"hash/crc32"
	"io"
	"io/ioutil"
	"os"
	"path"
)

// FwExists  check if file exists
func FwExists(path string) bool {
	_, err := os.Stat(path)
	return !errors.Is(err, os.ErrNotExist)
}

// ChkHeader: runs header and CRC checks on the firmware file
func ChkHeader(fwfile string) error {
	log.Info("checking ", fwfile)
	// SCS has two different file layouts, one for the "Dragons", the other for any older modem
	var offset uint32
	if path.Ext(fwfile) == ".dr7" {
		offset = 0
	} else {
		offset = 4
	}
	r, err := os.Open(fwfile)
	if err != nil {
		return err
	}
	defer r.Close()

	var header [2]byte
	_, err = io.ReadFull(r, header[:])
	if err != nil {
		return err
	}

	if offset == 0 {
		if header != [2]byte{0x50, 0x34} {
			return errors.New("ERROR: wrong firmware header")
		}
	} else {
		if header != [2]byte{0x60, 0xea} {
			return errors.New("ERROR: wrong firmware header")
		}
	}

	r.Close()
	firmware, err := ioutil.ReadFile(fwfile)
	if err != nil {
		return errors.New("ERROR: ReadFile operation failed")
	}

	var size uint32
	if offset == 0 {
		size = binary.LittleEndian.Uint32(firmware[4:8]) // Dragons
	} else {
		size = uint32(binary.LittleEndian.Uint16(firmware[2:4])) // PTC-3 and Co
	}
	a := make([]byte, 4)
	binary.LittleEndian.PutUint32(a, crc32.ChecksumIEEE(firmware[offset:offset+size]))
	if bytes.Equal(a, firmware[offset+size:offset+size+4]) {
		log.Info("CRC checksum ok!")
	} else {
		return errors.New("CRC checksum NOT ok!")
	}
	return nil
}