package game

// Rng is the original Rogue linear congruential generator. The C RN macro is
//
//	#define RN (((seed = seed*11109+13849) >> 16) & 0xffff)
//
// with `seed` a C int; Seed is int32 so the multiplication wraps exactly the
// way 32-bit C arithmetic does. A given seed therefore produces the same
// dungeon as the C game.
type Rng struct {
	Seed int32
}

// Rnd picks a very random number in [0, rng) (main.c rnd).
func (r *Rng) Rnd(rng int) int {
	if rng == 0 {
		return 0
	}

	v := r.next()
	if v < 0 {
		v = -v
	}

	return v % rng
}

// Roll rolls a number of dice (main.c roll).
func (r *Rng) Roll(number, sides int) int {
	dtotal := 0
	for ; number > 0; number-- {
		dtotal += r.Rnd(sides) + 1
	}

	return dtotal
}

// next steps the generator and returns the next raw value (the RN macro).
func (r *Rng) next() int {
	r.Seed = r.Seed*11109 + 13849

	return int(r.Seed>>16) & 0xffff
}

// rnd is the ported code's spelling of C rnd(): every call site in the C
// sources reads rnd(x), and keeping that shape makes cross-checking easy.
func (g *RogueGame) rnd(rng int) int { return g.Rng.Rnd(rng) }

// roll is C roll().
func (g *RogueGame) roll(number, sides int) int { return g.Rng.Roll(number, sides) }

// spread gives a fuzzy number centered on nm (misc.c spread).
func (g *RogueGame) spread(nm int) int {
	return nm - nm/20 + g.rnd(nm/10)
}