package main

import "fmt"

// Memory provides an addressable map of integer cells
type Memory struct {
	intern   map[int]int
	nextFree int
}

// Read takes a starting address and a count of cells to read after it;
// (0, 2) reads the first two cells out of memory, for example.
func (m *Memory) Read(addr int, count int) []int {
	r := []int{}
	for i := 0; i < count; i++ {
		r = append(r, m.intern[addr+i])
	}
	return r
}

// Write inserts the given values into memory, overwriting any existing contents,
// starting at the provided memory address and incrementing upward.
func (m *Memory) Write(addr int, values []int) error {
	if addr < 0 {
		return fmt.Errorf("addr out of range")
	}
	for i := range values {
		m.intern[addr+i] = values[i]
	}
	// we've written past our marker, note that
	if m.nextFree < addr+len(values) {
		m.nextFree = addr + len(values)
	}
	return nil
}

// NextFreeAddress provides the furthest "out" address, beyond which is uninitialized memory.
// Old memory is never "reclaimed", even if the program manually 0s it out.
// If you want to build your own GC, knock yourself out.
func (m *Memory) NextFreeAddress() int {
	return m.nextFree
}