package main

import (
	"encoding/binary"
	"os"
)

type PathPair struct {
	input  string
	output string
}

var byteOrder binary.ByteOrder = binary.NativeEndian

func main() {
	var inputFiles []PathPair
	for i, arg := range os.Args[1:] {
		switch arg {
		case "-b":
			byteOrder = binary.BigEndian
		case "-l":
			byteOrder = binary.LittleEndian
		case "-o":
			inputFiles = append(inputFiles, PathPair{os.Args[i+3], os.Args[i+2]})
		}
	}

	for _, p := range inputFiles {
		AssembleFile(p)
	}
}

func AssembleFile(path PathPair) {
	tempData, err := os.CreateTemp("", "data*")
	Check(err)
	dName := tempData.Name()
	defer os.Remove(dName)

	tempRoData, err := os.CreateTemp("", "rodata*")
	Check(err)
	rName := tempRoData.Name()
	defer os.Remove(rName)

	tempText, err := os.CreateTemp("", "text*")
	Check(err)
	tName := tempText.Name()
	defer os.Remove(tName)

	// First pass to find the address of all labels and encode the data
	LabelFind(path.input, tempData, tempRoData)

	var names [3]string
	var PHeaders [4]ProgramHeader
	i := 0
	n := 0

	if SectionPos[TEXT] > 0 {
		PHeaders[i] = ProgramHeader{PT_LOAD, 0, 0, 0,
			uint32(SectionPos[TEXT]), uint32(SectionPos[TEXT]), PF_READ +
				PF_EXEC, 0}
		names[i] = tName
		i++
		n++
		// Second pass to assemble the instructions.
		Assemble(path.input, tempText)
	}

	if SectionPos[DATA] > 0 {
		PHeaders[i] = ProgramHeader{PT_LOAD, 0, 0, 0,
			uint32(SectionPos[DATA]), uint32(SectionPos[DATA]), PF_READ +
				PF_WRITE, 0}
		names[i] = dName
		i++
		n++
	}

	if SectionPos[RODATA] > 0 {
		PHeaders[i] = ProgramHeader{PT_LOAD, 0, 0, 0,
			uint32(SectionPos[RODATA]), uint32(SectionPos[RODATA]), PF_READ, 0}
		names[i] = rName
		i++
		n++
	}

	if SectionPos[BSS] > 0 {
		PHeaders[i] = ProgramHeader{PT_LOAD, 0, 0, 0, 0,
			uint32(SectionPos[BSS]), PF_READ + PF_WRITE, 0}
		i++
	}

	var fOffset, mOffset uint32 = 0, 0
	for j, p := range PHeaders[:i] {
		PHeaders[j].offset = uint32(i*PHENSIZE) + fOffset + EHSIZE
		fOffset += p.filesz
		PHeaders[j].vaddr = mOffset
		mOffset += p.memsz
	}

	EHeader := EHInit(0, uint16(i))
	WriteBinary(path, EHeader, PHeaders[:i], names[:n])

}

func WriteBinary(path PathPair, e ElfHeader, ps []ProgramHeader, ns []string) {
	out, err := os.Create(path.output)
	Check(err)
	defer out.Close()
	_, err = out.Write(e.ToBytes())
	Check(err)
	for _, p := range ps {
		_, err = out.Write(p.ToBytes())
		Check(err)
	}
	for _, name := range ns {
		b, err := os.ReadFile(name)
		Check(err)
		_, err = out.Write(b)
		Check(err)
	}
}

func Check(err error) {
	if err != nil {
		panic(err)
	}
}