modes:triple: new file encoding a Triple with new implemented

Not a difficult function to think about: we just don't want a
situation where we have all jokers.

src/modes/triple.rs

@@ -0,0 +1,32 @@
+use crate::{
+    card::{Card, PlayingCard},
+    helper::ordered,
+};
+
+#[derive(Debug, Copy, Clone)]
+pub struct Triple(Card, Card, Card);
+
+impl Triple {
+    fn new(c1: Card, c2: Card, c3: Card) -> Option<Triple> {
+        let [c1, c2, c3] = ordered([c1, c2, c3]);
+
+        match (c1, c2, c3) {
+            (Card::Joker(_), Card::Joker(_), Card::Joker(_)) => None,
+            // NOTE: c3 should not be a joker now.
+            (Card::Joker(_), Card::Joker(_), _) => Some(Triple(c1, c2, c3)),
+            (
+                Card::Joker(_),
+                Card::PlayingCard(PlayingCard { rank: r1, .. }),
+                Card::PlayingCard(PlayingCard { rank: r2, .. }),
+            ) if r1 == r2 => Some(Triple(c1, c2, c3)),
+
+            (
+                Card::PlayingCard(PlayingCard { rank: r1, .. }),
+                Card::PlayingCard(PlayingCard { rank: r2, .. }),
+                Card::PlayingCard(PlayingCard { rank: r3, .. }),
+            ) if r1 == r2 && r2 == r3 => Some(Triple(c1, c2, c3)),
+
+            _ => None,
+        }
+    }
+}