package grow

import "math/rand"

import "github.com/firestuff/subcoding/gen"
import "github.com/firestuff/subcoding/vm"

const instructionsPerFunctionMean = 15
const instrucitonsPerFunctionStdDev = 10

func Mutate(prog *vm.Program) {
	target := int(rand.NormFloat64()*instrucitonsPerFunctionStdDev+instructionsPerFunctionMean)

	if len(prog.Functions[0].Instructions) < target {
		addInstruction(prog, prog.Functions[0])
	} else {
		removeInstruction(prog, prog.Functions[0])
	}
}

func addInstruction(prog *vm.Program, fnc *vm.Function) {
	if len(fnc.Instructions) == 0 {
		fnc.Instructions = append(fnc.Instructions, gen.RandInstruction(prog))
	} else {
		i := rand.Intn(len(fnc.Instructions))
		fnc.Instructions = append(fnc.Instructions[:i+1], fnc.Instructions[i:]...)
		fnc.Instructions[i] = gen.RandInstruction(prog)
	}
}

func removeInstruction(prog *vm.Program, fnc *vm.Function) {
	if len(fnc.Instructions) == 0 {
		return
	}

	i := rand.Intn(len(fnc.Instructions))
	fnc.Instructions = append(fnc.Instructions[:i], fnc.Instructions[i+1:]...)
}