package main

import (
	"bufio"
	"encoding/binary"
	"encoding/hex"
	"errors"
	"flag"
	"fmt"
	"io"
	"os"
	"strconv"
	"strings"
	"time"
)

func optPanic(msg string, err error) {
	if err != nil {
		panic(errors.New(msg + ": " + err.Error()))
	}
}

type handling struct {
	bytes    int64
	readFrom func(io.Reader, binary.ByteOrder) string
	writeTo  func(io.Writer, binary.ByteOrder, string)
}

func binaryRead(r io.Reader, order binary.ByteOrder, pointerTo interface{}) {
	err := binary.Read(r, order, pointerTo)
	optPanic(fmt.Sprintf("binary conversion failed (%T)", pointerTo), err)
}

func binaryWrite(w io.Writer, order binary.ByteOrder, pointerTo interface{}) {
	err := binary.Write(w, order, pointerTo)
	optPanic(fmt.Sprintf("binary write failed (%T)", pointerTo), err)
}

var handlings = map[string]handling{
	"int8": handling{1,
		func(r io.Reader, bo binary.ByteOrder) string {
			var i int8
			binaryRead(r, bo, &i)
			return strconv.FormatInt(int64(i), 10)
		},
		func(w io.Writer, bo binary.ByteOrder, s string) {
			i, err := strconv.ParseInt(s, 0, 8)
			optPanic("conversion of "+s+" to int8 failed", err)
			binaryWrite(w, bo, int8(i))
		}},
	"uint8": handling{1,
		func(r io.Reader, bo binary.ByteOrder) string {
			var i uint8
			binaryRead(r, bo, &i)
			return strconv.FormatUint(uint64(i), 10)
		},
		func(w io.Writer, bo binary.ByteOrder, s string) {
			i, err := strconv.ParseUint(s, 0, 8)
			optPanic("conversion of "+s+" to uint8 failed", err)
			binaryWrite(w, bo, uint8(i))
		}},
	"int16": handling{2,
		func(r io.Reader, bo binary.ByteOrder) string {
			var i int16
			binaryRead(r, bo, &i)
			return strconv.FormatInt(int64(i), 10)
		},
		func(w io.Writer, bo binary.ByteOrder, s string) {
			i, err := strconv.ParseInt(s, 0, 16)
			optPanic("conversion of "+s+" to int16 failed", err)
			binaryWrite(w, bo, int16(i))
		}},
	"uint16": handling{2,
		func(r io.Reader, bo binary.ByteOrder) string {
			var i uint16
			binaryRead(r, bo, &i)
			return strconv.FormatUint(uint64(i), 10)
		},
		func(w io.Writer, bo binary.ByteOrder, s string) {
			i, err := strconv.ParseUint(s, 0, 16)
			optPanic("conversion of "+s+" to uint16 failed", err)
			binaryWrite(w, bo, uint16(i))
		}},
	"int32": handling{4,
		func(r io.Reader, bo binary.ByteOrder) string {
			var i int32
			binaryRead(r, bo, &i)
			return strconv.FormatInt(int64(i), 10)
		},
		func(w io.Writer, bo binary.ByteOrder, s string) {
			i, err := strconv.ParseInt(s, 0, 32)
			optPanic("conversion of "+s+" to int32 failed", err)
			binaryWrite(w, bo, int32(i))
		}},
	"uint32": handling{4,
		func(r io.Reader, bo binary.ByteOrder) string {
			var i uint32
			binaryRead(r, bo, &i)
			return strconv.FormatUint(uint64(i), 10)
		},
		func(w io.Writer, bo binary.ByteOrder, s string) {
			i, err := strconv.ParseUint(s, 0, 32)
			optPanic("conversion of "+s+" to uint32 failed", err)
			binaryWrite(w, bo, uint32(i))
		}},
	"int64": handling{8,
		func(r io.Reader, bo binary.ByteOrder) string {
			var i int64
			binaryRead(r, bo, &i)
			return strconv.FormatInt(i, 10)
		},
		func(w io.Writer, bo binary.ByteOrder, s string) {
			i, err := strconv.ParseInt(s, 0, 64)
			optPanic("conversion of "+s+" to int64 failed", err)
			binaryWrite(w, bo, i)
		}},
	"uint64": handling{8,
		func(r io.Reader, bo binary.ByteOrder) string {
			var i uint64
			binaryRead(r, bo, &i)
			return strconv.FormatUint(i, 10)
		},
		func(w io.Writer, bo binary.ByteOrder, s string) {
			i, err := strconv.ParseUint(s, 0, 64)
			optPanic("conversion of "+s+" to uint64 failed", err)
			binaryWrite(w, bo, i)
		}},
	"float32": handling{4,
		func(r io.Reader, bo binary.ByteOrder) string {
			var f float32
			binaryRead(r, bo, &f)
			return strconv.FormatFloat(float64(f), 'f', -1, 64)
		},
		func(w io.Writer, bo binary.ByteOrder, s string) {
			f, err := strconv.ParseFloat(s, 32)
			optPanic("conversion of "+s+" to float32 failed", err)
			binaryWrite(w, bo, float32(f))
		}},
	"float64": handling{8,
		func(r io.Reader, bo binary.ByteOrder) string {
			var f float64
			binaryRead(r, bo, &f)
			return strconv.FormatFloat(f, 'f', -1, 64)
		},
		func(w io.Writer, bo binary.ByteOrder, s string) {
			f, err := strconv.ParseFloat(s, 64)
			optPanic("conversion of "+s+" to float64 failed", err)
			binaryWrite(w, bo, float64(f))
		}},
}

type filePart struct {
	name     string
	parttype string
	handling handling
}

func (part *filePart) Line() string {
	return part.name + " : " + part.parttype
}

func (part *filePart) setHandling() {
	if strings.HasPrefix(part.parttype, "byte") {
		tmp := strings.TrimRight(strings.TrimLeft(part.parttype, "byte["), "]")
		bytes, err := strconv.ParseInt(tmp, 10, 64)
		optPanic(part.name, err)
		readFrom := func(r io.Reader, bo binary.ByteOrder) string {
			buf := make([]byte, bytes)
			var i int64
			for i = 0; i < bytes; i++ {
				binaryRead(r, bo, &buf[i])
			}
			return hex.EncodeToString(buf)
		}
		writeTo := func(w io.Writer, bo binary.ByteOrder, s string) {
			buf, err := hex.DecodeString(s)
			optPanic("invalid string of hex values: "+s, err)
			if int64(len(buf)) > bytes {
				panic(fmt.Sprintf("string %s is too long for byte array %s : want %d bytes", s, part.name, bytes))
			}
			binaryWrite(w, bo, buf)
		}
		part.handling = handling{bytes, readFrom, writeTo}

	} else {
		if handling, ok := handlings[part.parttype]; !ok {
			panic(part.Line() + ": Don't know type")
		} else {
			part.handling = handling
		}
	}
}

type fileDescription struct {
	byteOrder binary.ByteOrder
	parts     []filePart
}

func trim(s string) string {
	return strings.TrimSpace(s)
}

var debug bool

func info(i string, s string) {
	if debug {
		fmt.Fprintln(os.Stderr, i, "-->", s)
	}
}

func readPart(line string) *filePart {
	part := &filePart{}
	splitline := strings.Split(line, ":")
	if len(splitline) != 2 {
		panic("invalid definition: " + line)
	}
	part.name = trim(splitline[0])
	part.parttype = trim(splitline[1])
	info("definition", part.Line())
	part.setHandling()
	return part
}

func readFileDescription(path string) fileDescription {
	errmsg := "read format file"
	descr := fileDescription{}
	f, err := os.Open(path)
	defer f.Close()
	optPanic("open format file", err)
	buf := bufio.NewReader(f)
	/*----------------------------------*/
	line, err := buf.ReadString('\n')
	optPanic(errmsg, err)
	line = trim(line)
	for strings.HasPrefix(line, "#") {
		info("comment", line)
		line, err = buf.ReadString('\n')
		optPanic(errmsg, err)
		line = trim(line)
	}
	/*----------------------------------*/
	line = trim(line)
	if line == "big endian" {
		descr.byteOrder = binary.BigEndian
	} else if line == "little endian" {
		descr.byteOrder = binary.LittleEndian
	} else {
		panic(errmsg + ": expected endianness ('little endian' or 'big endian'), got :" + line)
	}
	info("endianness", line)
	/*----------------------------------*/
	line, err = buf.ReadString('\n')
	optPanic(errmsg, err)
	line = trim(line)
	for err != io.EOF && line != "" {
		part := readPart(line)
		descr.parts = append(descr.parts, *part)
		line, err = buf.ReadString('\n')
		line = trim(line)
	}
	line = trim(line)
	if err == io.EOF && line != "" {
		descr.parts = append(descr.parts, *readPart(line))
	} else if err != io.EOF {
		optPanic(errmsg, err)
	}
	return descr
}

func readAssignments(descr fileDescription, s string) map[string]string {
	assignments := strings.Split(s, ",")
	m := make(map[string]string)
	for _, assignment := range assignments {
		kv := strings.Split(assignment, "=")
		if len(kv) != 2 {
			panic("weird parameters in set: " + assignment + "\nWant list of comma-separated key=value assignments")
		}
		key := trim(kv[0])
		value := trim(kv[1])
		found := false
		for _, part := range descr.parts {
			if key == part.name {
				found = true
			}
		}
		if found {
			m[key] = value
		} else {
			panic("unknown key: " + key)
		}
	}
	return m
}

func backup(binpath string) {
	bin, err := os.Open(binpath)
	defer bin.Close()
	optPanic("failed to open binary", err)
	timestamp := time.Now().Format("20060102150405")
	fi, err := bin.Stat()
	optPanic("failed to get permissions of binary", err)
	backuppath := binpath + ".bak" + timestamp
	backup, err := os.OpenFile(backuppath, os.O_RDWR|os.O_CREATE, fi.Mode())
	defer backup.Close()
	_, err = io.Copy(backup, bin)
	optPanic("failed to create backup", err)
	backup.Chmod(fi.Mode())
	fmt.Println("Created backup " + backuppath + "\n")
}

func seekErr(i int, name string, inner error) string {
	if inner != nil {
		namepart := ""
		if name != "" {
			namepart = " name: " + name
		}
		return fmt.Sprintf("could not advance in file (stuck at part %d%s)", i, namepart)
	} else {
		return ""
	}
}

func setValues(descr fileDescription, binpath string, vals map[string]string) {
	backup(binpath)
	f, err := os.OpenFile(binpath, os.O_RDWR, 0666)
	optPanic("failed to write-open binary", err)
	defer f.Close()
	for i, part := range descr.parts {
		needSeek := true
		if part.name != "" {
			if val, ok := vals[part.name]; ok {
				part.handling.writeTo(f, descr.byteOrder, val)
				needSeek = false
			}
		}
		if needSeek {
			_, err = f.Seek(part.handling.bytes, 1)
			optPanic(seekErr(i, part.name, err), err)
		}
	}
}

func getValues(descr fileDescription, binpath string) map[string]string {
	vals := make(map[string]string)
	f, err := os.Open(binpath)
	defer f.Close()
	optPanic("failed to open binary", err)
	for i, part := range descr.parts {
		if part.name == "" {
			_, err = f.Seek(part.handling.bytes, 1)
			optPanic(seekErr(i, part.name, err), err)
		} else {
			vals[part.name] = part.handling.readFrom(f, descr.byteOrder)
		}
	}
	return vals
}

func fmtPadding(descr fileDescription) string {
	pad := 0
	for _, part := range descr.parts {
		if n := len(part.name); n > pad {
			pad = n
		}
	}
	return strconv.Itoa(pad)
}

func printValues(descr fileDescription, vals map[string]string) {
	for _, part := range descr.parts {
		if part.name != "" {
			fmt.Printf("%"+fmtPadding(descr)+"s = %s\n", part.name, vals[part.name])
		}
	}
}

func printUsage() {
	fmt.Fprintf(os.Stderr, "Usage: %s [Options] FORMATFILE BINARY\n", os.Args[0])
	flag.PrintDefaults()
}

func main() {
	var assignments string
	flag.StringVar(&assignments, "set", "", "key=value pairs (e.g. \"key1=value1,key2=value2\")")
	flag.BoolVar(&debug, "debug", false, "print recognized parts of the format file")
	flag.Parse()
	args := flag.Args()
	if len(args) != 2 {
		printUsage()
		os.Exit(-1)
	}
	descr := readFileDescription(args[0])
	if assignments != "" {
		setValues(descr, args[1], readAssignments(descr, assignments))
	}
	printValues(descr, getValues(descr, args[1]))
}