/**
 * @file ethernet.c
 * @brief Ethernet subsystem implementation.
 *
 * Provides a unified layer over individual Ethernet NIC drivers.
 * NIC drivers register through ethernet_register(), which creates the
 * `/dev/ethN` char device and adds the interface to an internal table.
 *
 * The subsystem also exposes network interface info via sysfs at
 * `/sys/net`, allowing userspace tools to query interface status.
 */

#include "ethernet.h"
#include "devicefs.h"
#include "sysfs.h"
#include <string.h>

/* Debug print helpers */
extern void offset_print(const char *str);
extern void print_hex(uint32_t val);

/* ================================================================
 * Global state
 * ================================================================ */

/** Interface table. */
static eth_iface_t ifaces[ETH_MAX_IFACES];

/** Number of registered interfaces. */
static uint32_t iface_count = 0;

/* ================================================================
 * Character device operations
 *
 * Maps devicefs char read/write to the NIC driver send/recv.
 * ================================================================ */

/**
 * Read from `/dev/ethN`: receive a raw Ethernet frame.
 */
static int32_t eth_char_read(void *dev_data, uint32_t size, void *buf) {
    eth_iface_t *iface = (eth_iface_t *)dev_data;
    if (!iface || !iface->active || !iface->recv) return -1;
    return (int32_t)iface->recv(iface->dev_data, buf, size);
}

/**
 * Write to `/dev/ethN`: send a raw Ethernet frame.
 */
static int32_t eth_char_write(void *dev_data, uint32_t size, const void *buf) {
    eth_iface_t *iface = (eth_iface_t *)dev_data;
    if (!iface || !iface->active || !iface->send) return -1;
    int ret = iface->send(iface->dev_data, buf, size);
    return (ret == 0) ? (int32_t)size : -1;
}

/** Devicefs char ops shared by all ethernet interfaces. */
static devicefs_char_ops_t eth_char_ops = {
    .read  = eth_char_read,
    .write = eth_char_write,
};

/* ================================================================
 * Sysfs operations for /sys/net
 *
 * Directory layout:
 *   /sys/net/
 *     eth1/
 *       mac          - MAC address as hex string
 *       ip           - IPv4 address
 *       netmask      - subnet mask
 *       gateway      - default gateway
 *       link         - "up" or "down"
 *     eth2/
 *       ...
 * ================================================================ */

/**
 * Format a MAC address as "XX:XX:XX:XX:XX:XX" into buf.
 */
static int format_mac(const uint8_t *mac, char *buf, uint32_t buf_size) {
    if (buf_size < 18) return -1;
    static const char hex[] = "0123456789ABCDEF";
    int pos = 0;
    for (int i = 0; i < 6; i++) {
        if (i > 0) buf[pos++] = ':';
        buf[pos++] = hex[(mac[i] >> 4) & 0xF];
        buf[pos++] = hex[mac[i] & 0xF];
    }
    buf[pos++] = '\n';
    buf[pos] = '\0';
    return pos;
}

/**
 * Format an IPv4 address as "A.B.C.D\n" into buf.
 */
static int format_ipv4(uint32_t ip, char *buf, uint32_t buf_size) {
    if (buf_size < 16) return -1;
    int pos = 0;
    for (int i = 0; i < 4; i++) {
        if (i > 0) buf[pos++] = '.';
        uint8_t octet = (uint8_t)((ip >> (24 - i * 8)) & 0xFF);
        if (octet >= 100) { buf[pos++] = (char)('0' + octet / 100); octet %= 100; buf[pos++] = (char)('0' + octet / 10); octet %= 10; }
        else if (octet >= 10) { buf[pos++] = (char)('0' + octet / 10); octet %= 10; }
        buf[pos++] = (char)('0' + octet);
    }
    buf[pos++] = '\n';
    buf[pos] = '\0';
    return pos;
}

/**
 * Parse interface name from the path prefix.
 * E.g., path "eth1/mac" → iface "eth1", subpath "mac".
 * Returns the iface, or NULL if not found.
 */
static eth_iface_t *parse_iface_path(const char *path, const char **subpath) {
    /* Find the first '/' */
    const char *slash = NULL;
    for (const char *p = path; *p; p++) {
        if (*p == '/') { slash = p; break; }
    }

    char iface_name[16];
    if (slash) {
        uint32_t len = (uint32_t)(slash - path);
        if (len >= sizeof(iface_name)) return NULL;
        memcpy(iface_name, path, len);
        iface_name[len] = '\0';
        *subpath = slash + 1;
    } else {
        /* No slash — path is just the interface name */
        uint32_t len = strlen(path);
        if (len >= sizeof(iface_name)) return NULL;
        memcpy(iface_name, path, len + 1);
        *subpath = "";
    }

    return ethernet_find_iface(iface_name);
}

/**
 * Sysfs list callback for /sys/net.
 */
static int net_sysfs_list(void *ctx, const char *path, uint32_t idx,
                          sysfs_entry_t *out) {
    (void)ctx;

    if (path[0] == '\0') {
        /* Root of /sys/net — list interfaces */
        uint32_t count = 0;
        for (uint32_t i = 0; i < ETH_MAX_IFACES; i++) {
            if (!ifaces[i].active) continue;
            if (count == idx) {
                memset(out, 0, sizeof(sysfs_entry_t));
                strncpy(out->name, ifaces[i].name, SYSFS_MAX_NAME - 1);
                out->is_dir = 1;
                return 0;
            }
            count++;
        }
        return -1;
    }

    /* Listing inside an interface directory */
    const char *subpath;
    eth_iface_t *iface = parse_iface_path(path, &subpath);
    if (!iface) return -1;

    /* Files: mac, ip, netmask, gateway, link */
    static const char *files[] = { "mac", "ip", "netmask", "gateway", "link" };
    if (idx >= 5) return -1;

    memset(out, 0, sizeof(sysfs_entry_t));
    strncpy(out->name, files[idx], SYSFS_MAX_NAME - 1);
    out->is_dir = 0;
    return 0;
}

/**
 * Sysfs read callback for /sys/net.
 */
static int net_sysfs_read(void *ctx, const char *path, char *buf,
                          uint32_t buf_size) {
    (void)ctx;

    const char *subpath;
    eth_iface_t *iface = parse_iface_path(path, &subpath);
    if (!iface) return -1;

    if (strcmp(subpath, "mac") == 0) {
        return format_mac(iface->mac, buf, buf_size);
    }
    if (strcmp(subpath, "ip") == 0) {
        return format_ipv4(iface->ip_addr, buf, buf_size);
    }
    if (strcmp(subpath, "netmask") == 0) {
        return format_ipv4(iface->netmask, buf, buf_size);
    }
    if (strcmp(subpath, "gateway") == 0) {
        return format_ipv4(iface->gateway, buf, buf_size);
    }
    if (strcmp(subpath, "link") == 0) {
        const char *s = iface->link_up ? "up\n" : "down\n";
        strncpy(buf, s, buf_size);
        return (int)strlen(s);
    }

    return -1;
}

/**
 * Sysfs write callback for /sys/net.
 * Allows setting IP address, netmask, gateway.
 */
static int net_sysfs_write(void *ctx, const char *path, const char *buf,
                           uint32_t size) {
    (void)ctx;
    (void)size;

    const char *subpath;
    eth_iface_t *iface = parse_iface_path(path, &subpath);
    if (!iface) return -1;

    /* Parse dotted-decimal IP from buf */
    if (strcmp(subpath, "ip") == 0 || strcmp(subpath, "netmask") == 0 ||
        strcmp(subpath, "gateway") == 0) {
        uint32_t octets[4] = {0};
        int octet_idx = 0;
        for (uint32_t i = 0; i < size && octet_idx < 4; i++) {
            if (buf[i] == '.' || buf[i] == '\n' || buf[i] == '\0') {
                octet_idx++;
            } else if (buf[i] >= '0' && buf[i] <= '9') {
                octets[octet_idx] = octets[octet_idx] * 10 + (uint32_t)(buf[i] - '0');
            }
        }
        uint32_t addr = (octets[0] << 24) | (octets[1] << 16) |
                        (octets[2] << 8)  | octets[3];

        if (strcmp(subpath, "ip") == 0)      iface->ip_addr = addr;
        if (strcmp(subpath, "netmask") == 0)  iface->netmask = addr;
        if (strcmp(subpath, "gateway") == 0)  iface->gateway = addr;

        return (int)size;
    }

    return -1;
}

/** Sysfs operations for /sys/net. */
static sysfs_ops_t net_sysfs_ops = {
    .list  = net_sysfs_list,
    .read  = net_sysfs_read,
    .write = net_sysfs_write,
};

/* ================================================================
 * Public API
 * ================================================================ */

void ethernet_init(void) {
    memset(ifaces, 0, sizeof(ifaces));
    iface_count = 0;

    sysfs_register("net", &net_sysfs_ops, NULL);
    offset_print("  ETHERNET: subsystem initialized\n");
}

eth_iface_t *ethernet_register(const uint8_t *mac,
                               eth_send_fn send,
                               eth_recv_fn recv,
                               void *dev_data) {
    if (iface_count >= ETH_MAX_IFACES) {
        offset_print("  ETHERNET: too many interfaces\n");
        return NULL;
    }

    /* Find free slot */
    eth_iface_t *iface = NULL;
    for (uint32_t i = 0; i < ETH_MAX_IFACES; i++) {
        if (!ifaces[i].active) {
            iface = &ifaces[i];
            break;
        }
    }
    if (!iface) return NULL;

    memset(iface, 0, sizeof(eth_iface_t));

    /* Copy MAC */
    memcpy(iface->mac, mac, ETH_ALEN);
    iface->send = send;
    iface->recv = recv;
    iface->dev_data = dev_data;
    iface->link_up = 1;  /* Assume link up after init */
    iface->active = 1;

    /* Register as /dev/ethN — devicefs assigns the number */
    devicefs_device_t *devfs_dev = devicefs_register_char("eth",
                                                          &eth_char_ops,
                                                          iface);
    if (devfs_dev) {
        /* Copy the assigned name back */
        strncpy(iface->name, devfs_dev->name, sizeof(iface->name) - 1);
    } else {
        /* Fallback name */
        iface->name[0] = 'e'; iface->name[1] = 't'; iface->name[2] = 'h';
        iface->name[3] = (char)('0' + iface_count + 1);
        iface->name[4] = '\0';
    }

    iface_count++;

    offset_print("  ETHERNET: registered ");
    offset_print(iface->name);
    offset_print(" MAC ");
    for (int i = 0; i < 6; i++) {
        if (i > 0) offset_print(":");
        print_hex(mac[i]);
    }
    offset_print("\n");

    return iface;
}

int ethernet_send(eth_iface_t *iface, const uint8_t *dst_mac,
                  uint16_t ethertype, const void *payload, uint32_t len) {
    if (!iface || !iface->active || !iface->send) return -1;
    if (len > ETH_MTU) return -1;

    /* Build complete Ethernet frame on stack */
    uint8_t frame[ETH_FRAME_LEN];
    eth_header_t *hdr = (eth_header_t *)frame;

    memcpy(hdr->dst, dst_mac, ETH_ALEN);
    memcpy(hdr->src, iface->mac, ETH_ALEN);
    hdr->ethertype = htons(ethertype);

    memcpy(frame + ETH_HLEN, payload, len);

    uint32_t frame_len = ETH_HLEN + len;
    if (frame_len < 60) frame_len = 60; /* Minimum Ethernet frame */

    return iface->send(iface->dev_data, frame, frame_len);
}

int ethernet_recv(eth_iface_t *iface, void *buf, uint32_t bufsize,
                  uint8_t *src_mac, uint16_t *ethertype) {
    if (!iface || !iface->active || !iface->recv) return -1;

    /* Receive into temporary buffer */
    uint8_t frame[ETH_FRAME_LEN];
    int ret = iface->recv(iface->dev_data, frame, sizeof(frame));
    if (ret <= 0) return ret;

    if ((uint32_t)ret < ETH_HLEN) return -1; /* Runt frame */

    eth_header_t *hdr = (eth_header_t *)frame;

    /* Copy out src MAC and ethertype if requested */
    if (src_mac) memcpy(src_mac, hdr->src, ETH_ALEN);
    if (ethertype) *ethertype = ntohs(hdr->ethertype);

    /* Copy payload */
    uint32_t payload_len = (uint32_t)ret - ETH_HLEN;
    if (payload_len > bufsize) payload_len = bufsize;
    memcpy(buf, frame + ETH_HLEN, payload_len);

    return (int)payload_len;
}

eth_iface_t *ethernet_get_iface(uint32_t index) {
    uint32_t count = 0;
    for (uint32_t i = 0; i < ETH_MAX_IFACES; i++) {
        if (!ifaces[i].active) continue;
        if (count == index) return &ifaces[i];
        count++;
    }
    return NULL;
}

uint32_t ethernet_get_iface_count(void) {
    return iface_count;
}

eth_iface_t *ethernet_find_iface(const char *name) {
    for (uint32_t i = 0; i < ETH_MAX_IFACES; i++) {
        if (!ifaces[i].active) continue;
        if (strcmp(ifaces[i].name, name) == 0) return &ifaces[i];
    }
    return NULL;
}