package load

import "bytes"

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

const instructionBytes = 32

func Load(byteCodes [][]byte) ([][]*vm.Instruction, error) {
	fncs := [][]*vm.Instruction{}

	for i, byteCode := range byteCodes {
		instrs, err := loadFunction(byteCode)
		if err != nil {
			return nil, errors.Wrapf(err, "At function index %d", i)
		}

		fncs = append(fncs, instrs)
	}

	return fncs, nil
}

func loadFunction(byteCode []byte) ([]*vm.Instruction, error) {
	instrs := []*vm.Instruction{}

	for start := 0; start < len(byteCode); start += instructionBytes {
		chunk := byteCode[start : start+instructionBytes]

		instr, err := loadInstruction(chunk)
		if err != nil {
			return nil, errors.Wrapf(err, "At byte offset %d", start)
		}

		instrs = append(instrs, instr)
	}

	return instrs, nil
}

func loadInstruction(byteCode []byte) (*vm.Instruction, error) {
	instr := &vm.Instruction{}

	reader := bytes.NewReader(byteCode)

	err := struc.Unpack(reader, instr)
	if err != nil {
		return nil, errors.Wrap(err, "Error decoding instruction")
	}

	return instr, nil
}