package proc

import (
	"encoding/binary"
	"rsc.io/x86/x86asm"
)

type ArchInst x86asm.Inst

func asmDecode(mem []byte, pc uint64) (*ArchInst, error) {
	inst, err := x86asm.Decode(mem, 64)
	if err != nil {
		return nil, err
	}
	patchPCRel(pc, &inst)
	r := ArchInst(inst)
	return &r, nil
}

func (inst *ArchInst) Size() int {
	return inst.Len
}

// converts PC relative arguments to absolute addresses
func patchPCRel(pc uint64, inst *x86asm.Inst) {
	for i := range inst.Args {
		rel, isrel := inst.Args[i].(x86asm.Rel)
		if isrel {
			inst.Args[i] = x86asm.Imm(int64(pc) + int64(rel) + int64(inst.Len))
		}
	}
	return
}

func (inst *AsmInstruction) Text(flavour AssemblyFlavour) string {
	if inst.Inst == nil {
		return "?"
	}

	var text string

	switch flavour {
	case GNUFlavour:
		text = x86asm.GNUSyntax(x86asm.Inst(*inst.Inst))
	case IntelFlavour:
		fallthrough
	default:
		text = x86asm.IntelSyntax(x86asm.Inst(*inst.Inst))
	}

	if inst.IsCall() && inst.DestLoc != nil && inst.DestLoc.Fn != nil {
		text += " " + inst.DestLoc.Fn.Name
	}

	return text
}

func (inst *AsmInstruction) IsCall() bool {
	return inst.Inst.Op == x86asm.CALL || inst.Inst.Op == x86asm.LCALL
}

func (thread *Thread) resolveCallArg(inst *ArchInst, currentGoroutine bool, regs Registers) *Location {
	if inst.Op != x86asm.CALL && inst.Op != x86asm.LCALL {
		return nil
	}

	var pc uint64
	var err error

	switch arg := inst.Args[0].(type) {
	case x86asm.Imm:
		pc = uint64(arg)
	case x86asm.Reg:
		if !currentGoroutine || regs == nil {
			return nil
		}
		pc, err = regs.Get(int(arg))
		if err != nil {
			return nil
		}
	case x86asm.Mem:
		if !currentGoroutine || regs == nil {
			return nil
		}
		if arg.Segment != 0 {
			return nil
		}
		regs, err := thread.Registers()
		if err != nil {
			return nil
		}
		base, err1 := regs.Get(int(arg.Base))
		index, err2 := regs.Get(int(arg.Index))
		if err1 != nil || err2 != nil {
			return nil
		}
		addr := uintptr(int64(base) + int64(index*uint64(arg.Scale)) + arg.Disp)
		//TODO: should this always be 64 bits instead of inst.MemBytes?
		pcbytes, err := thread.readMemory(addr, inst.MemBytes)
		if err != nil {
			return nil
		}
		pc = binary.LittleEndian.Uint64(pcbytes)
	default:
		return nil
	}

	file, line, fn := thread.dbp.PCToLine(pc)
	if fn == nil {
		return nil
	}
	return &Location{PC: pc, File: file, Line: line, Fn: fn}
}