From b806264154aa8ebdb06c4051df65a19cdbb09ee4 Mon Sep 17 00:00:00 2001
From: Kistaro Windrider <kistaro@gmail.com>
Date: Sat, 1 Apr 2023 19:23:14 -0700
Subject: [PATCH] Fraction-specified shufflers.

Convenience methods for "shuffle the bottom third of the deck" and stuff like that.
---
 cardsim/deck.go | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/cardsim/deck.go b/cardsim/deck.go
index cca7381..28214a6 100644
--- a/cardsim/deck.go
+++ b/cardsim/deck.go
@@ -238,3 +238,35 @@ func (d *Deck[C]) ShufflePart(loc, n int) error {
 	ShufflePart(d.cards, d.rand, loc, n)
 	return nil
 }
+
+// ShuffleRange shuffles the cards between the specified fractions of
+// the deck; the top of the deck is 0.0 and the bottom of the deck is
+// 1.0. This rounds "outward" -- "partial" cards at each end are counted.
+// This can return the same warnings ShufflePart can in the same circumstances
+// and may also complain about a backwards range.
+func (d *Deck[C]) ShuffleRange(loFrac, hiFrac float64) error {
+	var errs ErrorCollector
+	if loFrac > hiFrac {
+		errs.Add(Warningf("%w: %f > %f", WarningBackwardsRange, loFrac, hiFrac))
+		loFrac, hiFrac = hiFrac, loFrac
+	}
+	low := int(math.Floor(loFrac * float64(d.Len())))
+	high := int(math.Ceil(hiFrac * float64(d.Len())))
+	n := 1 + high - low
+	errs.Add(d.ShufflePart(low, n))
+	return errs.Emit()
+}
+
+// ShuffleTop uses ShuffleRange to shuffle the top frac (between 0.0 and 1.0)
+// of the deck. See ShuffleRange and ShufflePart for information on
+// rounding and warnings.
+func (d *Deck[C]) ShuffleTop(frac float64) error {
+	return d.ShuffleRange(0.0, frac)
+}
+
+// Shufflebottom uses ShuffleRange to shuffle the bottom frac (between 0.0 and
+// 1.0) of the deck. See ShuffleRange and ShufflePart for information on
+// rounding and warnings.
+func (d *Deck[C]) ShuffleBottom(frac float64) error {
+	return d.ShuffleRange(frac, 1.0)
+}