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docs/api.md

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+# API Documentation
+
+## Core Types
+
+### `LookupHandEvaluator`
+
+The main hand evaluation engine that uses precomputed lookup tables for O(1) hand evaluation.
+
+#### Constructor
+
+```rust
+pub fn new() -> io::Result<Self>
+```
+
+Creates a new evaluator instance. On first use, generates evaluation tables if they don't exist.
+
+**Returns:**
+- `Ok(LookupHandEvaluator)` - Successfully initialized evaluator
+- `Err(io::Error)` - Failed to load or generate tables
+
+#### Methods
+
+##### `rank_hand(&self, hand: &Hand) -> u32`
+
+Evaluates any poker hand (5, 6, or 7 cards) and returns its rank value.
+
+```rust
+let rank = evaluator.rank_hand(&hand);
+```
+
+**Parameters:**
+- `hand: &Hand` - Poker hand containing 5-7 cards
+
+**Returns:**
+- `u32` - Hand rank (higher values = stronger hands)
+
+##### `rank_hand5(&self, hand: &Hand) -> u32`
+
+Optimized evaluation for exactly 5-card hands.
+
+```rust
+let rank = evaluator.rank_hand5(&hand);
+```
+
+**Parameters:**
+- `hand: &Hand` - Poker hand containing exactly 5 cards
+
+**Returns:**
+- `u32` - Hand rank value
+
+##### `rank_hand6(&self, cards: &[u32]) -> u32`
+
+Evaluates a 6-card hand by finding the best 5-card combination.
+
+```rust
+let rank = evaluator.rank_hand6(&card_indices);
+```
+
+**Parameters:**
+- `cards: &[u32]` - Array of 6 card indices
+
+**Returns:**
+- `u32` - Best possible 5-card hand rank
+
+##### `rank_hand7(&self, cards: &[u32]) -> u32`
+
+Evaluates a 7-card hand by finding the best 5-card combination.
+
+```rust
+let rank = evaluator.rank_hand7(&card_indices);
+```
+
+**Parameters:**
+- `cards: &[u32]` - Array of 7 card indices
+
+**Returns:**
+- `u32` - Best possible 5-card hand rank
+
+### `HandEval` Trait
+
+Standardized interface for poker hand evaluators.
+
+#### Constants
+
+```rust
+const HAND_CATEGORY_SHIFT: u32 = 24;
+const HAND_CATEGORY_MASK: u32 = 0xF << Self::HAND_CATEGORY_SHIFT;
+const VALUE_MASK: u32 = 0x000FFFFF;
+```
+
+#### Methods
+
+##### `rank_hand(&self, hand: &Hand) -> u32`
+
+Evaluates a poker hand of any supported size.
+
+##### `rank_hand7(&self, cards: &[Card; 7]) -> u32`
+
+Evaluates exactly 7 cards.
+
+##### `hand_description(&self, hand_value: u32) -> String`
+
+Returns human-readable description of a hand rank.
+
+##### `hand_description_hand(&self, hand: &Hand) -> String`
+
+Describes a hand by evaluating it first.
+
+##### `hand_description7(&self, cards: &[Card; 7]) -> String`
+
+Describes the best 5-card hand from 7 cards.
+
+## Supporting Types
+
+### `Hand`
+
+Collection of cards that can be evaluated.
+
+#### Key Methods
+
+```rust
+// Construction
+let mut hand = Hand::new();
+hand.add_card(card).unwrap();
+
+// Information
+let size = hand.size();
+let is_valid = hand.size() >= 5;
+
+// String representation
+println!("{}", hand.to_string()); // "As Ks Qs Js Ts"
+```
+
+### `Card`
+
+Individual playing card representation.
+
+#### Construction
+
+```rust
+// From string notation
+let card = Card::from_string("As").unwrap();
+let card = Card::from_string("Kh").unwrap();
+
+// String representation
+assert_eq!(card.to_string(), "As");
+```
+
+#### Properties
+
+```rust
+let rank = card.rank();  // Card rank (0-12)
+let suit = card.suit();  // Card suit (0-3)
+let index = card.index(); // Unique card index (0-51)
+```
+
+## Hand Ranking Values
+
+### Category Extraction
+
+```rust
+// Extract hand category (bits 24-27)
+let category = (hand_value & HandEval::HAND_CATEGORY_MASK) >> HandEval::HAND_CATEGORY_SHIFT;
+
+// Extract relative value (bits 0-23)
+let value = hand_value & HandEval::VALUE_MASK;
+```
+
+### Hand Categories
+
+| Category | Value | Description |
+|----------|-------|-------------|
+| Straight Flush | 9 | Five cards in sequence, same suit |
+| Four of a Kind | 8 | Four cards of same rank |
+| Full House | 7 | Three of a kind + pair |
+| Flush | 6 | Five cards, same suit |
+| Straight | 5 | Five cards in sequence |
+| Three of a Kind | 4 | Three cards of same rank |
+| Two Pair | 3 | Two different pairs |
+| One Pair | 2 | Two cards of same rank |
+| High Card | 1 | No matching cards |
+
+### Rank Value Ranges
+
+| Hand Type | Rank Range | Count |
+|-----------|------------|-------|
+| Straight Flush | 368,793,253 - 371,292,191 | 40 |
+| Four of a Kind | 184,396,629 - 368,793,252 | 624 |
+| Full House | 92,198,315 - 184,396,628 | 3,744 |
+| Flush | 46,099,158 - 92,198,314 | 5,108 |
+| Straight | 23,049,579 - 46,099,157 | 10,200 |
+| Three of a Kind | 11,524,790 - 23,049,578 | 54,912 |
+| Two Pair | 5,762,395 - 11,524,789 | 123,552 |
+| One Pair | 2,881,198 - 5,762,394 | 1,098,240 |
+| High Card | 1 - 2,881,197 | 1,302,540 |
+
+## Performance Characteristics
+
+### Time Complexity
+
+| Operation | Time Complexity | Notes |
+|-----------|----------------|-------|
+| 5-Card evaluation | O(1) | Direct table lookup |
+| 6-Card evaluation | O(1) | 6 table lookups |
+| 7-Card evaluation | O(1) | 21 table lookups |
+| Table generation | O(N) | N = 32M combinations |
+
+### Memory Usage
+
+| Component | Size | Description |
+|-----------|------|-------------|
+| Hand ranks table | ~128 MB | Complete evaluation table |
+| Working tables | ~2.4 MB | Generation workspace |
+| Code size | ~50 KB | Compiled binary |
+
+### Cache Performance
+
+The lookup table design provides excellent cache performance:
+
+- **Sequential Access**: Table generation processes data sequentially
+- **Compact Encoding**: Cards encoded in 8 bits each
+- **Prefetch Friendly**: Linear table layout enables hardware prefetching
+- **Low Branch Misprediction**: Perfect hash eliminates conditional logic
+
+## Error Handling
+
+### Common Error Cases
+
+```rust
+// Invalid hand size
+let rank = evaluator.rank_hand(&hand); // Returns 0 for < 5 cards
+
+// Card parsing errors
+let card = Card::from_string("XX"); // Returns Err
+
+// Table loading errors
+let evaluator = LookupHandEvaluator::new(); // May fail if disk full
+```
+
+### Error Types
+
+- `io::Error` - File system errors during table loading/generation
+- `CardParseError` - Invalid card string format
+- `HandFullError` - Attempting to add cards to full hand
+
+## Thread Safety
+
+The `LookupHandEvaluator` is designed for read-only usage after construction:
+
+```rust
+// Safe: Read-only evaluator
+let evaluator = LookupHandEvaluator::new().unwrap();
+
+// Multiple threads can use the same evaluator
+let rank1 = evaluator.rank_hand(&hand1);
+let rank2 = evaluator.rank_hand(&hand2);
+
+// NOT safe: Modifying evaluator during use
+// (evaluator is not Sync + Send for mutation)
+```
+
+## Integration Examples
+
+### Texas Hold'em Engine
+
+```rust
+use poker_api::hand_evaluator::LookupHandEvaluator;
+use poker_api::api::{hand::Hand, card::Card};
+
+struct HoldemEngine {
+    evaluator: LookupHandEvaluator,
+}
+
+impl HoldemEngine {
+    fn evaluate_board(&self, hole_cards: &[Card; 2], board: &[Card; 5]) -> u32 {
+        let mut all_cards = Vec::new();
+        all_cards.extend_from_slice(hole_cards);
+        all_cards.extend_from_slice(board);
+
+        let mut hand = Hand::new();
+        for card in all_cards {
+            hand.add_card(card).unwrap();
+        }
+
+        self.evaluator.rank_hand(&hand)
+    }
+}
+```
+
+### Hand Range Analysis
+
+```rust
+use poker_api::hand_evaluator::LookupHandEvaluator;
+
+struct RangeAnalyzer {
+    evaluator: LookupHandEvaluator,
+}
+
+impl RangeAnalyzer {
+    fn compare_hands(&self, hand1: &Hand, hand2: &Hand) -> std::cmp::Ordering {
+        let rank1 = self.evaluator.rank_hand(hand1);
+        let rank2 = self.evaluator.rank_hand(hand2);
+        rank1.cmp(&rank2)
+    }
+}
+```
+
+## Testing Integration
+
+### Unit Tests
+
+```rust
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use poker_api::hand_evaluator::LookupHandEvaluator;
+
+    #[test]
+    fn test_royal_flush() {
+        let evaluator = LookupHandEvaluator::new().unwrap();
+        let mut hand = Hand::new();
+        // Add A,K,Q,J,10 of same suit
+        let rank = evaluator.rank_hand(&hand);
+        assert!(rank > 368_793_253); // Royal flush range
+    }
+}
+```
+
+### Benchmark Tests
+
+```rust
+#[cfg(test)]
+mod benchmarks {
+    use super::*;
+    use std::time::Instant;
+
+    #[test]
+    fn benchmark_evaluation() {
+        let evaluator = LookupHandEvaluator::new().unwrap();
+        let hand = create_test_hand();
+
+        let start = Instant::now();
+        for _ in 0..1_000_000 {
+            let _rank = evaluator.rank_hand(&hand);
+        }
+        let duration = start.elapsed();
+
+        println!("1M evaluations in {:?}", duration);
+    }
+}
+```
+
+## Advanced Configuration
+
+### Custom Table Paths
+
+The evaluator uses default paths, but this can be customized by modifying the source:
+
+```rust
+// In hand_evaluator.rs
+const FILE_NAME: &'static str = "custom/path/HandRanks.dat";
+```
+
+### Memory Management
+
+For systems with limited memory, consider:
+
+```rust
+// Use Box<[u32]> for heap allocation control
+let hand_ranks: Box<[u32]> = vec![0; SIZE].into_boxed_slice();
+
+// Monitor memory usage
+println!("Table memory usage: {} MB",
+         std::mem::size_of_val(&*hand_ranks) / 1_048_576);
+```
+
+### Performance Tuning
+
+For maximum performance:
+
+```rust
+// Use release mode
+cargo build --release
+
+// Consider SIMD optimizations for batch evaluation
+// (requires custom implementation)
+```
+
+This API documentation covers the complete public interface for poker hand evaluation. For implementation details, see the source code comments and the developer guide.