add old man simulation

src/main.rs

@@ -5,7 +5,9 @@ use std::io;
 use std::io::prelude::*;
 
 fn main() {
+    // TODO: CLI flags to choose how to play
     interactive_play();
+    // old_man();
 }
 
 fn interactive_play() {
@@ -102,6 +104,62 @@ fn interactive_decision(hand: &Hand, dealer_showing: &Card) -> PlayerChoice {
     choice
 }
 
+fn basic_strategy(hand: &Hand, dealer_showing: &Card) -> PlayerChoice {
+    // Source: https://en.wikipedia.org/wiki/Blackjack#Basic_strategy
+    // TODO: Add doubling when it's supported
+    let dealer_val = u8::from(dealer_showing);
+    if hand.has_ace() {
+        match hand.value() {
+            v if v >= 19 => PlayerChoice::Stand,
+            v if v == 18 && dealer_val < 9 => PlayerChoice::Stand,
+            _ => PlayerChoice::Hit,
+        }
+    } else {
+        match hand.value() {
+            v if v >= 17 => PlayerChoice::Stand,
+            v if v > 12 && dealer_val < 7 => PlayerChoice::Stand,
+            v if v == 12 && (4..=6).contains(&dealer_val) => PlayerChoice::Stand,
+            _ => PlayerChoice::Hit,
+        }
+    }
+}
+
+/// An cab driver to the LAS airport was a former dealer and told me about this retired guy who
+/// would come play Blackjack every day at 7am like clockwork. He'd bring $400 to the table, play
+/// basic strategy, and would walk away once he was $100 up. He made about $3000/mo off of this, in
+/// addition to points/comps which he would use to eat brunch for free.
+///
+/// Does this actually work, or was the driver full of it?
+fn old_man() {
+    let mut bank: u64 = 100_000;
+    const PER_DAY: u32 = 400;
+    const MIN_BET: u32 = 15;
+    // Walk away when we're up by this much
+    const WALK_AWAY: u32 = 100;
+    const DAYS: u8 = 30;
+
+    println!("Starting with bank: ${bank}");
+    // Let's simulate this for 30 days
+    for day in 1..=DAYS {
+        let mut in_hand: u32 = PER_DAY;
+        bank -= in_hand as u64;
+
+        let mut game = Game::new().with_decks(6);
+        let mut rounds = 0;
+        while in_hand > MIN_BET && in_hand < (PER_DAY + WALK_AWAY) {
+            let bet = MIN_BET;
+            in_hand -= bet;
+            let result = game.play(bet, basic_strategy);
+            in_hand += u32::try_from(result.player_winnings).unwrap();
+            rounds += 1;
+        }
+        println!("Day {day}, after {rounds} rounds, in-hand: ${in_hand}");
+        bank += in_hand as u64;
+    }
+
+    println!("Ending with: ${bank}");
+}
+
 fn read_input() -> String {
     let mut buf = String::new();
     io::stdin().read_line(&mut buf).unwrap();