package mem

type Mem struct {
	cells []cell
	free  []int
}

func New() Mem {
	return Mem{
		cells: make([]cell, 0),
		free:  make([]int, 0),
	}
}

func (m *Mem) Allocate(kind CellKind) Ptr {
	if len(m.free) > 0 {
		idx := m.free[len(m.free)-1]
		m.free = m.free[:len(m.free)-1]

		if m.cells[idx].kind != CellKindEmpty {
			panic("invalid free cell")
		}

		m.cells[idx].kind = kind
		return Ptr(idx)
	} else {
		idx := len(m.cells)
		m.cells = append(m.cells, cell{kind: kind})
		return Ptr(idx)
	}

}

func (m *Mem) Set(ptr Ptr, v any) {
	if ptr >= Ptr(len(m.cells)) {
		panic("out of bounds")
	}

	m.cells[ptr].data = v
}

func (m *Mem) Get(ptr Ptr) any {
	if ptr >= Ptr(len(m.cells)) {
		panic("out of bounds")
	}

	return m.cells[ptr].data
}

func (m *Mem) Retain(ptr Ptr) {
	if ptr >= Ptr(len(m.cells)) {
		panic("out of bounds")
	}

	m.cells[ptr].refs++
}

func (m *Mem) Release(ptr Ptr) {
	if ptr >= Ptr(len(m.cells)) {
		panic("out of bounds")
	}

	m.cells[ptr].refs--
	if m.cells[ptr].refs == 0 {
		m.cells[ptr].kind = CellKindEmpty
		m.free = append(m.free, int(ptr))
	}
}