Add pow config

internal/pow/challenge/config.go

@@ -0,0 +1,147 @@
+package challenge
+
+import (
+	"crypto/rand"
+	"fmt"
+	"time"
+)
+
+// Config holds configuration for the PoW system
+type Config struct {
+	DefaultDifficulty     int           // Default difficulty in bits (e.g., 4)
+	MaxDifficulty         int           // Maximum allowed difficulty (e.g., 10)
+	MinDifficulty         int           // Minimum allowed difficulty (e.g., 3)
+	ChallengeTTL          time.Duration // Time-to-live for challenges (e.g., 5 minutes)
+	HMACSecret            []byte        // Secret key for HMAC signing
+	Resource              string        // Resource identifier (e.g., "quotes")
+	RandomBytes           int           // Number of random bytes in challenge (e.g., 6)
+	LoadAdjustmentBits    int           // Extra difficulty bits when server under load
+	FailurePenaltyBits    int           // Extra difficulty bits per failure group
+	MaxFailurePenaltyBits int           // Maximum failure penalty bits
+}
+
+// configOption represents a functional option for Config
+type configOption func(*Config)
+
+// WithDefaultDifficulty sets the default difficulty
+func WithDefaultDifficulty(difficulty int) configOption {
+	return func(c *Config) {
+		c.DefaultDifficulty = difficulty
+	}
+}
+
+// WithMaxDifficulty sets the maximum difficulty
+func WithMaxDifficulty(difficulty int) configOption {
+	return func(c *Config) {
+		c.MaxDifficulty = difficulty
+	}
+}
+
+// WithMinDifficulty sets the minimum difficulty
+func WithMinDifficulty(difficulty int) configOption {
+	return func(c *Config) {
+		c.MinDifficulty = difficulty
+	}
+}
+
+// WithChallengeTTL sets the challenge time-to-live
+func WithChallengeTTL(ttl time.Duration) configOption {
+	return func(c *Config) {
+		c.ChallengeTTL = ttl
+	}
+}
+
+// WithHMACSecret sets the HMAC secret
+func WithHMACSecret(secret []byte) configOption {
+	return func(c *Config) {
+		c.HMACSecret = secret
+	}
+}
+
+// WithResource sets the resource identifier
+func WithResource(resource string) configOption {
+	return func(c *Config) {
+		c.Resource = resource
+	}
+}
+
+// WithRandomBytes sets the number of random bytes
+func WithRandomBytes(bytes int) configOption {
+	return func(c *Config) {
+		c.RandomBytes = bytes
+	}
+}
+
+// WithLoadAdjustmentBits sets the load adjustment bits
+func WithLoadAdjustmentBits(bits int) configOption {
+	return func(c *Config) {
+		c.LoadAdjustmentBits = bits
+	}
+}
+
+// WithFailurePenaltyBits sets the failure penalty bits
+func WithFailurePenaltyBits(bits int) configOption {
+	return func(c *Config) {
+		c.FailurePenaltyBits = bits
+	}
+}
+
+// WithMaxFailurePenaltyBits sets the maximum failure penalty bits
+func WithMaxFailurePenaltyBits(bits int) configOption {
+	return func(c *Config) {
+		c.MaxFailurePenaltyBits = bits
+	}
+}
+
+// NewConfig creates and validates a new PoW configuration with defaults
+func NewConfig(opts ...configOption) (*Config, error) {
+	// Generate default HMAC secret
+	secret := make([]byte, 32)
+	rand.Read(secret)
+
+	// Create config with defaults
+	config := &Config{
+		DefaultDifficulty:     4,
+		MaxDifficulty:         10,
+		MinDifficulty:         3,
+		ChallengeTTL:          5 * time.Minute,
+		HMACSecret:            secret,
+		Resource:              "quotes",
+		RandomBytes:           6,
+		LoadAdjustmentBits:    1,
+		FailurePenaltyBits:    2,
+		MaxFailurePenaltyBits: 6,
+	}
+
+	// Apply options
+	for _, opt := range opts {
+		opt(config)
+	}
+
+	// Validate configuration
+	if config.RandomBytes <= 0 || config.RandomBytes > 32 {
+		return nil, fmt.Errorf("%w: random bytes must be between 1-32, got %d", ErrInvalidConfig, config.RandomBytes)
+	}
+
+	if config.MinDifficulty < 1 {
+		return nil, fmt.Errorf("%w: minimum difficulty must be >= 1, got %d", ErrInvalidConfig, config.MinDifficulty)
+	}
+
+	if config.MaxDifficulty < config.MinDifficulty {
+		return nil, fmt.Errorf("%w: maximum difficulty (%d) must be >= minimum difficulty (%d)", ErrInvalidConfig, config.MaxDifficulty, config.MinDifficulty)
+	}
+
+	if config.DefaultDifficulty < config.MinDifficulty || config.DefaultDifficulty > config.MaxDifficulty {
+		return nil, fmt.Errorf("%w: default difficulty (%d) must be between min (%d) and max (%d)", ErrInvalidConfig, config.DefaultDifficulty, config.MinDifficulty, config.MaxDifficulty)
+	}
+
+	if len(config.HMACSecret) == 0 {
+		return nil, fmt.Errorf("%w: HMAC secret cannot be empty", ErrInvalidConfig)
+	}
+
+	if config.ChallengeTTL <= 0 {
+		return nil, fmt.Errorf("%w: challenge TTL must be positive, got %v", ErrInvalidConfig, config.ChallengeTTL)
+	}
+
+	return config, nil
+}