implement cactus kev's poker hand evaluator

src/inc/handranker.mjs

@@ -1,6 +1,44 @@
+import fs from 'node:fs';
+
 export default new class handranker {
+  #ranks;
+
   constructor() {
-    return this;
+    this.#ranks = fs.readFileSync('./data/HandRanks.dat');
+
+    this.handtypes = [
+      "InvalidHand", "HighCard", "Pair",
+      "TwoPairs", "ThreeOfAKind", "Straight",
+      "Flush", "FullHouse", "FourOfAKind",
+      "StraightFlush"
+    ];
+
+    this.cards = [''];
+    for(const cv of [..."23456789TJQKA"])
+      for(const cs of [..."CDHS"])
+        this.cards.push(cv + cs);
+  };
+  evalHand(cards) {
+    if(!this.#ranks)
+      throw new Error("HandRanks.dat not loaded, run 'npm run build' first!");
+
+    if(![7,6,5,3].includes(cards.length))
+      throw new Error("Hand must be 3, 5, 6, or 7 cards");
+
+    cards = cards.map(c => this.cards.indexOf(c));
+
+    let p = 53;
+    for(let i = 0; i < cards.length; i++)
+      p = this.#ranks.readUInt32LE((p + cards[i]) * 4);
+
+    if(cards.length == 5 || cards.length == 6)
+      p = this.#ranks.readUInt32LE(p * 4);
+
+    return {
+      handType: p >> 12,
+      handRank: p & 0x00000fff,
+      value: p,
+      handName: this.handtypes[p >> 12]
+    };
   };
-  
 };