/**
 * @file se050_blake2s.h
 * @brief BLAKE2s Hash Function Implementation
 * 
 * Based on RFC 7693. Supports variable-length keys and outputs.
 * Used in WireGuard for key derivation.
 * 
 * License: MIT (Clean-room implementation)
 */

#ifndef SE050_BLAKE2S_H
#define SE050_BLAKE2S_H

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

#ifdef __cplusplus
extern "C" {
#endif

/* ============================================================================
 * Constants
 * ============================================================================ */

#define BLAKE2S_BLOCK_SIZE    64
#define BLAKE2S_DIGEST_SIZE   32
#define BLAKE2S_KEY_SIZE      64
#define BLAKE2S_MIN_KEY_SIZE  1
#define BLAKE2S_MAX_KEY_SIZE  64
#define BLAKE2S_MIN_OUTLEN    1
#define BLAKE2S_MAX_OUTLEN    32

/* ============================================================================
 * Type Definitions
 * ============================================================================ */

/**
 * @brief BLAKE2s context
 */
typedef struct {
    uint32_t h[8];          /* Hash state */
    uint32_t t[2];          /* Counter */
    uint32_t f[2];          /* Block flag */
    uint8_t  buf[BLAKE2S_BLOCK_SIZE];  /* Input buffer */
    size_t   buflen;        /* Current buffer size */
    size_t   outlen;        /* Desired output length */
    uint8_t  last_node;     /* Last node flag */
} se050_blake2s_ctx_t;

/* ============================================================================
 * API Functions
 * ============================================================================ */

/**
 * @brief Initialize BLAKE2s context
 * 
 * @param ctx Context to initialize
 * @param outlen Output length (1-32 bytes)
 * @return 0 on success, -1 on error
 */
int se050_blake2s_init(se050_blake2s_ctx_t *ctx, size_t outlen);

/**
 * @brief Initialize BLAKE2s with key
 * 
 * @param ctx Context to initialize
 * @param outlen Output length (1-32 bytes)
 * @param key Key (1-64 bytes)
 * @param keylen Key length
 * @return 0 on success, -1 on error
 */
int se050_blake2s_init_key(se050_blake2s_ctx_t *ctx, size_t outlen,
                           const void *key, size_t keylen);

/**
 * @brief Update hash with data
 * 
 * @param ctx Context
 * @param data Data to hash
 * @param len Data length
 * @return 0 on success, -1 on error
 */
int se050_blake2s_update(se050_blake2s_ctx_t *ctx, const void *data, size_t len);

/**
 * @brief Finalize hash and get digest
 * 
 * @param ctx Context
 * @param out Output buffer (at least outlen bytes)
 * @param outlen Output length
 * @return 0 on success, -1 on error
 */
int se050_blake2s_final(se050_blake2s_ctx_t *ctx, void *out, size_t outlen);

/**
 * @brief Compute BLAKE2s hash (one-shot)
 * 
 * @param out Output buffer (at least outlen bytes)
 * @param outlen Output length
 * @param data Data to hash
 * @param len Data length
 * @return 0 on success, -1 on error
 */
int se050_blake2s(void *out, size_t outlen, const void *data, size_t len);

/**
 * @brief Compute BLAKE2s hash with key (one-shot)
 * 
 * @param out Output buffer (at least outlen bytes)
 * @param outlen Output length
 * @param key Key
 * @param keylen Key length
 * @param data Data to hash
 * @param len Data length
 * @return 0 on success, -1 on error
 */
int se050_blake2s_keyed(void *out, size_t outlen, const void *key, size_t keylen,
                        const void *data, size_t len);

/**
 * @brief Securely zeroize context
 * 
 * @param ctx Context to zeroize
 */
void se050_blake2s_zeroize(se050_blake2s_ctx_t *ctx);

/* ============================================================================
 * WireGuard-Specific Functions
 * ============================================================================ */

/**
 * @brief WireGuard key derivation using BLAKE2s
 * 
 * Computes: BLAKE2s("wireguard key derivation", input, 32)
 * 
 * @param out Output (32 bytes)
 * @param input Input data
 * @param inlen Input length
 * @return 0 on success, -1 on error
 */
int se050_wireguard_derive_key(uint8_t out[32], const uint8_t *input, size_t inlen);

/**
 * @brief WireGuard secret key generation
 * 
 * @param out Output (32 bytes)
 * @param input Input data
 * @param inlen Input length
 * @return 0 on success, -1 on error
 */
int se050_wireguard_generate_secret(uint8_t out[32], const uint8_t *input, size_t inlen);

#ifdef __cplusplus
}
#endif

#endif /* SE050_BLAKE2S_H */