package main

import (
	"errors"
	"fmt"
)

func Run(code []int16) error {
	if len(code) != 100 {
		return errors.New("Code must be exactly 100 mailboxes long")
	}

	//	for i, x := range code {
	//		fmt.Printf("%d: %d\n", i, x)
	//	}
	//	fmt.Println()

	var accumulator int16 = 0

	pc := 0
	for pc >= 0 && pc < len(code) {
		i := code[pc]
		pc++
		switch i / 100 {
		case IHALT:
			return nil
		case IADD:
			accumulator += code[i%100]
		case ISUBTRACT:
			accumulator -= code[i%100]
		case ISTORE:
			code[i%100] = accumulator
		case ILOAD:
			accumulator = code[i%100]
		case IBRANCH:
			pc = int(i % 100)
		case IBRANCH_IF_ZERO:
			if accumulator == 0 {
				pc = int(i % 100)
			}
		case IBRANCH_IF_POSITIVE:
			if accumulator > 0 {
				pc = int(i % 100)
			}
		default:
			switch i {
			case 901:
				fmt.Printf("Input: ")
				fmt.Scanf("%d\n", &accumulator)
			case 902:
				fmt.Printf("Output: %d\n", accumulator)
			default:
				e := fmt.Sprintf("Unsupported instruction %d at %d", i, pc)
				return errors.New(e)
			}
		}
	}
	return errors.New("Program counter ran away")
}