package asm

import "fmt"
import "math"
import "strings"

import "github.com/firestuff/subcoding/vm"
import "github.com/pkg/errors"

// Lots of manual yaml assembly because the yaml package is missing features (flow in nested arrays)

func Disassemble(prog *vm.Program) (string, error) {
	fncs := []string{}

	for f, fnc := range prog.Functions {
		dis, err := disassembleFunction(fnc)
		if err != nil {
			return "", errors.Wrapf(err, "At function index %d", f)
		}

		fncs = append(fncs, dis)
	}

	return fmt.Sprintf(`global_memory_size: %d
function_memory_size: %d
functions:
%s`,
		prog.GlobalMemorySize,
		prog.FunctionMemorySize,
		strings.Join(fncs, ""),
	), nil
}

func disassembleFunction(fnc *vm.Function) (string, error) {
	instrs := []string{}

	for i, instr := range fnc.Instructions {
		dis, err := disassembleInstruction(instr)
		if err != nil {
			return "", errors.Wrapf(err, "At instruction index %d", i)
		}

		instrs = append(instrs, dis)
	}

	return fmt.Sprintf("- - %s\n", strings.Join(instrs, "\n  - ")), nil
}

func disassembleInstruction(in *vm.Instruction) (string, error) {
	parts := []string{
		nameByOpCode[in.OpCode],
	}

	for i, t := range vm.OperandsByOpCode[in.OpCode] {
		op, err := disassembleOperand(in.Operands[i], t)
		if err != nil {
			return "", err
		}

		parts = append(parts, op)
	}

	encoded := fmt.Sprintf("[%s]", strings.Join(parts, ", "))

	return encoded, nil
}

func disassembleOperand(op *vm.Operand, t vm.OperandNumericType) (string, error) {
	switch op.Type {
	case vm.GlobalMemoryIndex:
		return fmt.Sprintf("g%d", op.Value), nil

	case vm.FunctionMemoryIndex:
		return fmt.Sprintf("f%d", op.Value), nil

	case vm.Literal:
		switch t {
		case vm.OperandUnsigned:
			return fmt.Sprintf("%d", op.Value), nil

		case vm.OperandSigned:
			return fmt.Sprintf("%+d", int64(op.Value)), nil

		case vm.OperandSignedOrUnsigned:
			// Take our best guess
			if op.Value > math.MaxInt64 {
				return fmt.Sprintf("%+d", int64(op.Value)), nil
			} else {
				return fmt.Sprintf("%d", op.Value), nil
			}
		default:
			return "", fmt.Errorf("Invalid operand assembler type: %d", t)
		}

	default:
		return "", fmt.Errorf("Invalid operand type: %d", op.Type)
	}
}