// etcp.h - Extended Transmission Control Protocol
#ifndef ETCP_H
#define ETCP_H

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

#ifdef __cplusplus
extern "C" {
#endif

// Forward declarations
typedef struct epkt epkt_t;

// Callback type for sending packets via UDP
typedef void (*etcp_tx_callback_t)(epkt_t* epkt, uint8_t* pkt, uint16_t len, void* arg);

// Main ETCP structure
struct epkt {
    // Queues
    ll_queue_t* tx_queue;          // Queue of data to send
    ll_queue_t* output_queue;      // Output queue (reassembled data)
    
    // Received packets sorted linked list
    struct rx_packet* rx_list;
    
    // Sent packets (for retransmission)
    struct sent_packet* sent_list;
    
    // Metrics
    uint16_t rtt_last;             // Last RTT (timebase 0.1us)
    uint16_t rtt_avg_10;           // Average RTT last 10 packets
    uint16_t rtt_avg_100;          // Average RTT last 100 packets
    uint16_t jitter;               // Jitter (averaged)
    uint16_t bandwidth;            // Current bandwidth (bytes per timebase)
    uint32_t bytes_sent_total;     // Total bytes sent
    uint16_t last_sent_timestamp;  // Timestamp of last sent packet
    uint32_t bytes_allowed;        // Calculated bytes allowed to send
    
    // State
    uint16_t next_tx_id;           // Next ID for transmission
    uint16_t last_rx_id;           // Last received ID (for ACK)
    uint16_t last_delivered_id;    // Last delivered to output_queue ID
    
    // Timers
    void* next_tx_timer;           // Timer for next transmission
    void* retransmit_timer;        // Timer for retransmissions
    
    // Callback
    etcp_tx_callback_t tx_callback;
    void* tx_callback_arg;
    
    // RTT history for averaging
    uint16_t rtt_history[100];
    uint8_t rtt_history_idx;
    uint8_t rtt_history_count;
    
    // Pending ACKs
    uint16_t pending_ack_ids[32];
    uint16_t pending_ack_timestamps[32];
    uint8_t pending_ack_count;
    
    // Pending retransmission requests
    uint16_t pending_retransmit_ids[32];
    uint8_t pending_retransmit_count;
    
    // Window management
    uint32_t unacked_bytes;           // Number of bytes sent but not yet acknowledged
    uint32_t window_size;             // Current window size in bytes (calculated)
    uint16_t last_acked_id;           // Last acknowledged packet ID
    uint16_t last_rx_ack_id;          // Latest received ACK ID from receiver
    uint16_t retrans_timer_period;    // Current retransmission timer period (timebase)
    uint16_t next_retrans_time;       // Time of next retransmission check
    uint8_t window_blocked;           // Flag: transmission blocked by window limit
};

// API Functions

/**
 * @brief Initialize new ETCP instance
 * @return Pointer to new instance or NULL on error
 */
epkt_t* etcp_init(void);

/**
 * @brief Free ETCP instance and all associated resources
 * @param epkt Instance to free
 */
void etcp_free(epkt_t* epkt);

/**
 * @brief Set callback for sending packets via UDP
 * @param epkt ETCP instance
 * @param cb Callback function
 * @param arg User argument passed to callback
 */
void etcp_set_callback(epkt_t* epkt, etcp_tx_callback_t cb, void* arg);

/**
 * @brief Process received UDP packet
 * @param epkt ETCP instance
 * @param pkt Packet data
 * @param len Packet length
 * @return 0 on success, -1 on error
 */
int etcp_rx_input(epkt_t* epkt, uint8_t* pkt, uint16_t len);

/**
 * @brief Get total number of packets waiting in transmission queues
 * @param epkt ETCP instance
 * @return Number of packets
 */
int etcp_tx_queue_size(epkt_t* epkt);

/**
 * @brief Put data into transmission queue
 * @param epkt ETCP instance
 * @param data Data to send
 * @param len Data length
 * @return 0 on success, -1 on error
 */
int etcp_tx_put(epkt_t* epkt, uint8_t* data, uint16_t len);

/**
 * @brief Get output queue for reading received data
 * @param epkt ETCP instance
 * @return Pointer to output queue (ll_queue_t*)
 */
ll_queue_t* etcp_get_output_queue(epkt_t* epkt);

/**
 * @brief Set bandwidth limit
 * @param epkt ETCP instance
 * @param bandwidth Bytes per timebase (0.1us)
 */
void etcp_set_bandwidth(epkt_t* epkt, uint16_t bandwidth);

/**
 * @brief Update window size based on current RTT and bandwidth
 * @param epkt ETCP instance
 * Window size = RTT * bandwidth * 2 (bytes in flight)
 */
void etcp_update_window(epkt_t* epkt);

/**
 * @brief Get current RTT
 * @param epkt ETCP instance
 * @return RTT in timebase units
 */
uint16_t etcp_get_rtt(epkt_t* epkt);

/**
 * @brief Get current jitter
 * @param epkt ETCP instance
 * @return Jitter in timebase units
 */
uint16_t etcp_get_jitter(epkt_t* epkt);

#ifdef __cplusplus
}
#endif

#endif // ETCP_H