// hakmem_elo.h - ELO Rating Strategy Selection (Box Theory)
//
// Priority 1 optimization from ChatGPT Pro feedback:
// ELO-based strategy selection for multi-objective optimization
//
// Why ELO beats UCB1:
// - UCB1 assumes independent arms
// - ELO handles transitivity (if A>B and B>C, then A>C)
// - Better for multi-objective scoring (CPU + memory + page faults)
//
// Expected Gain: +10-20% on VM scenario (close gap with mimalloc)

#pragma once
#include <stddef.h>
#include <stdint.h>

// Configuration
#define ELO_K_FACTOR 32.0           // ELO K-factor (higher = faster learning)
#define ELO_INITIAL_RATING 1500.0   // Starting ELO rating
#define ELO_MAX_STRATEGIES 12       // Max candidate strategies
#define ELO_EPSILON 0.1             // Epsilon-greedy exploration (10%)
#define ELO_MIN_SAMPLES 50          // Min samples before ELO update
#define ELO_SURVIVAL_COUNT 6        // Top-M strategies survive

// Strategy Candidate
typedef struct {
    int strategy_id;             // Unique strategy ID
    double elo_rating;           // Current ELO rating (starts at 1500)
    uint64_t wins;               // Number of wins
    uint64_t losses;             // Number of losses
    uint64_t draws;              // Number of draws
    uint64_t samples;            // Total samples collected
    size_t threshold_bytes;      // mmap threshold for this strategy
    int active;                  // 1 if strategy is active
} EloStrategyCandidate;

// Allocation Statistics (for comparison)
typedef struct {
    uint64_t cpu_ns;             // CPU time (nanoseconds)
    uint64_t page_faults;        // Number of page faults
    uint64_t bytes_live;         // Live memory bytes
    uint64_t alloc_count;        // Number of allocations
} EloAllocStats;

// ELO System API (Box Interface)
void hak_elo_init(void);
void hak_elo_shutdown(void);

// Strategy selection (epsilon-greedy)
int hak_elo_select_strategy(void);
size_t hak_elo_get_threshold(int strategy_id);

// Record allocation result
void hak_elo_record_alloc(int strategy_id, size_t size, uint64_t duration_ns);

// Trigger ELO evolution (pairwise comparison)
void hak_elo_trigger_evolution(void);

// Statistics
void hak_elo_print_stats(void);
void hak_elo_print_leaderboard(void);

// Internal helpers (exposed for testing)
double hak_elo_compute_score(const EloAllocStats* stats);
void hak_elo_update_ratings(EloStrategyCandidate* a, EloStrategyCandidate* b, double score_diff);