/**
 * slot.c — Framecache slot lifecycle: create, destroy, open.
 */
#include "slot.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <time.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <unistd.h>

#define SHM_DIR      "/dev/shm/framecache"
#define SEM_PREFIX   "/framecache-"
#define SEM_SUFFIX   "-write"

/* ── helpers ─────────────────────────────────────────────────────────── */

static void build_paths(const char *slot_id,
                        char *shm_path, size_t sp_len,
                        char *sem_name, size_t sn_len)
{
    snprintf(shm_path, sp_len, "%s/%s", SHM_DIR, slot_id);
    snprintf(sem_name, sn_len, "%s%s%s", SEM_PREFIX, slot_id, SEM_SUFFIX);
}

/* ── server-side: create / destroy ───────────────────────────────────── */

/**
 * Create a new slot. Allocates and initialises the shm region.
 * Returns handle on success, NULL on error (errno set).
 */
struct fc_slot *fc_slot_create(const char *slot_id,
                                uint32_t width, uint32_t height,
                                uint32_t fps_num, uint32_t fps_den,
                                uint32_t pixel_format,
                                const char *source_type)
{
    char shm_path[128], sem_name[128];
    build_paths(slot_id, shm_path, sizeof shm_path, sem_name, sizeof sem_name);

    uint32_t frame_size = width * height * 2;   /* UYVY422 */
    size_t   total      = fc_slot_shm_size(frame_size);

    /* Ensure directory exists */
    mkdir(SHM_DIR, 0755);

    /* Create shm file */
    int fd = open(shm_path, O_RDWR | O_CREAT | O_TRUNC, 0666);
    if (fd < 0) {
        perror("[framecache] open shm");
        return NULL;
    }
    if (ftruncate(fd, (off_t)total) < 0) {
        perror("[framecache] ftruncate");
        close(fd);
        unlink(shm_path);
        return NULL;
    }

    void *base = mmap(NULL, total, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    if (base == MAP_FAILED) {
        perror("[framecache] mmap");
        close(fd);
        unlink(shm_path);
        return NULL;
    }
    memset(base, 0, total);

    /* Initialise header */
    fc_header_t *hdr = (fc_header_t *)base;
    hdr->magic        = FC_MAGIC;
    hdr->version      = FC_VERSION;
    hdr->width        = width;
    hdr->height       = height;
    hdr->fps_num      = fps_num;
    hdr->fps_den      = fps_den;
    hdr->pixel_format = pixel_format;
    hdr->frame_size   = frame_size;
    hdr->ring_depth   = FC_RING_DEPTH;
    atomic_store(&hdr->write_cursor,   0);
    atomic_store(&hdr->dropped_frames, 0);
    strncpy(hdr->source_type, source_type ? source_type : "unknown",
            sizeof hdr->source_type - 1);
    strncpy(hdr->slot_id, slot_id, sizeof hdr->slot_id - 1);

    /* Create semaphore */
    sem_unlink(sem_name);   /* remove stale */
    sem_t *sem = sem_open(sem_name, O_CREAT | O_EXCL, 0666, 0);
    if (sem == SEM_FAILED) {
        perror("[framecache] sem_open");
        munmap(base, total);
        close(fd);
        unlink(shm_path);
        return NULL;
    }

    struct fc_slot *s = calloc(1, sizeof *s);
    if (!s) {
        sem_close(sem); sem_unlink(sem_name);
        munmap(base, total);
        close(fd);
        unlink(shm_path);
        return NULL;
    }
    s->shm_fd   = fd;
    s->base     = base;
    s->shm_size = total;
    s->sem      = sem;
    strncpy(s->slot_id,  slot_id,  sizeof s->slot_id  - 1);
    strncpy(s->shm_path, shm_path, sizeof s->shm_path - 1);
    strncpy(s->sem_name, sem_name, sizeof s->sem_name - 1);

    fprintf(stderr, "[framecache] slot created: %s (%ux%u %.2ffps %zuMB)\n",
            slot_id, width, height,
            fps_den ? (double)fps_num / fps_den : 0.0,
            total / 1024 / 1024);
    return s;
}

/**
 * Destroy a slot: unmap, close fd, delete files, free handle.
 */
void fc_slot_destroy(struct fc_slot *s)
{
    if (!s) return;
    sem_close(s->sem);
    sem_unlink(s->sem_name);
    munmap(s->base, s->shm_size);
    close(s->shm_fd);
    unlink(s->shm_path);
    fprintf(stderr, "[framecache] slot destroyed: %s\n", s->slot_id);
    free(s);
}

/* ── writer: called by ingest bridges ───────────────────────────────── */

/**
 * Write one frame into the ring. Never blocks — advances write_cursor
 * atomically and posts the semaphore. Slow consumers will be skipped.
 */
void fc_slot_write_frame(struct fc_slot *s,
                          const uint8_t *data, uint32_t size,
                          uint64_t pts_us)
{
    fc_header_t *hdr = (fc_header_t *)s->base;
    uint64_t cur = atomic_load_explicit(&hdr->write_cursor, memory_order_relaxed);
    fc_frame_t *frame = fc_frame_at(s->base, hdr->frame_size, cur);

    frame->pts_us  = pts_us;
    frame->wall_us = (uint64_t)({ struct timespec ts;
                                  clock_gettime(CLOCK_REALTIME, &ts);
                                  ts.tv_sec * 1000000ULL + ts.tv_nsec / 1000; });
    frame->size    = size < hdr->frame_size ? size : hdr->frame_size;
    memcpy(frame->data, data, frame->size);

    atomic_store_explicit(&hdr->write_cursor, cur + 1, memory_order_release);
    sem_post(s->sem);
}

/* ── client-side open / read / close (also used by capture-manager) ── */

/**
 * Open an existing slot for reading.
 * Returns NULL if slot not found or header magic mismatch.
 */
struct fc_slot *fc_slot_open(const char *slot_id)
{
    char shm_path[128], sem_name[128];
    build_paths(slot_id, shm_path, sizeof shm_path, sem_name, sizeof sem_name);

    int fd = open(shm_path, O_RDONLY);
    if (fd < 0) return NULL;

    /* Read header first to get frame_size */
    fc_header_t tmp_hdr;
    if (pread(fd, &tmp_hdr, sizeof tmp_hdr, 0) != sizeof tmp_hdr) {
        close(fd); return NULL;
    }
    if (tmp_hdr.magic != FC_MAGIC) {
        close(fd); return NULL;
    }
    size_t total = fc_slot_shm_size(tmp_hdr.frame_size);

    void *base = mmap(NULL, total, PROT_READ, MAP_SHARED, fd, 0);
    if (base == MAP_FAILED) { close(fd); return NULL; }

    sem_t *sem = sem_open(sem_name, 0);
    if (sem == SEM_FAILED) { munmap(base, total); close(fd); return NULL; }

    struct fc_slot *s = calloc(1, sizeof *s);
    if (!s) { sem_close(sem); munmap(base, total); close(fd); return NULL; }
    s->shm_fd   = fd;
    s->base     = base;
    s->shm_size = total;
    s->sem      = sem;
    strncpy(s->slot_id,  slot_id,  sizeof s->slot_id  - 1);
    strncpy(s->shm_path, shm_path, sizeof s->shm_path - 1);
    strncpy(s->sem_name, sem_name, sizeof s->sem_name - 1);
    return s;
}

/**
 * Close a client-side slot handle. Does not destroy the slot.
 */
void fc_slot_close(struct fc_slot *s)
{
    if (!s) return;
    sem_close(s->sem);
    munmap(s->base, s->shm_size);
    close(s->shm_fd);
    free(s);
}