#define _POSIX_C_SOURCE 200809L

#include <shmemq.h>

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

const char *shmemq_error_str(const ShmemqError error)
{
    switch (error) {
    case SHMEMQ_ERROR_NONE:
        return "NONE";
    case SHMEMQ_ERROR_INVALID_NAME:
        return "INVALID_NAME";
    case SHMEMQ_ERROR_BUG_POP_END_ON_EMPTY_QUEUE:
        return "BUG_POP_END_ON_EMPTY_QUEUE";
    case SHMEMQ_ERROR_BUG_PUSH_END_ON_FULL_QUEUE:
        return "BUG_PUSH_END_ON_FULL_QUEUE";
    case SHMEMQ_ERROR_BUG_PUSH_END_OVERFLOW:
        return "BUG_PUSH_END_OVERFLOW";
    case SHMEMQ_ERROR_FAILED_MALLOC:
        return "FAILED_MALLOC";
    case SHMEMQ_ERROR_FAILED_SHM_OPEN:
        return "FAILED_SHM_OPEN";
    case SHMEMQ_ERROR_FAILED_FTRUNCATE:
        return "FAILED_FTRUNCATE";
    case SHMEMQ_ERROR_FAILED_MMAP:
        return "FAILED_MMAP";
    case SHMEMQ_ERROR_FAILED_MUNMAP:
        return "FAILED_MUNMAP";
    case SHMEMQ_ERROR_FAILED_CLOSE:
        return "FAILED_CLOSE";
    case SHMEMQ_ERROR_FAILED_SHM_UNLINK:
        return "FAILED_SHM_UNLINK";
    case SHMEMQ_ERROR_FAILED_SEM_INIT:
        return "FAILED_SEM_INIT";
    default:
        return "UNKNOWN";
    }
}

void shmemq_delete(const Shmemq shmemq, ShmemqError *const error_ptr)
{
    shmemq_finish(shmemq, error_ptr);
    free(shmemq);
}

void shmemq_finish(const Shmemq shmemq, ShmemqError *const error_ptr)
{
    const size_t size =
        sizeof(struct ShmemqBufferHeader) +
        SHMEMQ_FRAME_SIZE * shmemq->buffer->header.frames_count;

    if (munmap(shmemq->buffer, size) != 0) {
        if (error_ptr) *error_ptr = SHMEMQ_ERROR_FAILED_MUNMAP;
        return;
    }

    shmemq->buffer = NULL;

    if (close(shmemq->shm_id) != 0) {
        if (error_ptr) *error_ptr = SHMEMQ_ERROR_FAILED_CLOSE;
        return;
    }

    shmemq->shm_id = -1;

    if (shmemq->is_consumer && shm_unlink(shmemq->name) != 0) {
        if (error_ptr) *error_ptr = SHMEMQ_ERROR_FAILED_SHM_UNLINK;
        return;
    }

    if (error_ptr) *error_ptr = SHMEMQ_ERROR_NONE;
}

Shmemq shmemq_new(
    const char *const name,
    const bool is_consumer,
    ShmemqError *const error_ptr
) {
    const Shmemq shmemq = malloc(sizeof(*shmemq));

    if (!shmemq) {
        if (error_ptr) *error_ptr = SHMEMQ_ERROR_FAILED_MALLOC;
        return NULL;
    }

    ShmemqError error;
    shmemq_init(shmemq, name, is_consumer, &error);

    if (error_ptr) *error_ptr = error;

    if (error) {
        free(shmemq);
        return NULL;
    }

    if (error_ptr) *error_ptr = SHMEMQ_ERROR_NONE;
    return shmemq;
}

void shmemq_init(
    const Shmemq shmemq,
    const char *const name,
    const bool is_consumer,
    ShmemqError *const error_ptr
) {
    if (strlen(name) > SHMEMQ_NAME_SLEN_MAX || name[0] != '/') {
        *error_ptr = SHMEMQ_ERROR_INVALID_NAME;
        return;
    }

    for (const char *chr = &name[1]; *chr; ++chr) {
        if (*chr == '/') {
            if (error_ptr) *error_ptr = SHMEMQ_ERROR_INVALID_NAME;
            return;
        }
    }

    strcpy(shmemq->name, name);

    shmemq->is_consumer = !!is_consumer;

    shmemq->shm_id = shm_open(
        shmemq->name,
        O_RDWR | (shmemq->is_consumer ? O_CREAT | O_EXCL : 0),
        S_IRUSR | S_IWUSR
    );

    if (shmemq->shm_id == -1) {
        if (error_ptr) *error_ptr = SHMEMQ_ERROR_FAILED_SHM_OPEN;
        return;
    }

    if (shmemq->is_consumer) {
        if (ftruncate(shmemq->shm_id, SHMEMQ_BUFFER_SIZE_MIN) != 0) {
            shm_unlink(shmemq->name);
            if (error_ptr) *error_ptr = SHMEMQ_ERROR_FAILED_FTRUNCATE;
            return;
        }
    }

    shmemq->buffer = mmap(
        NULL,
        SHMEMQ_BUFFER_SIZE_MIN,
        PROT_READ | PROT_WRITE,
        MAP_SHARED,
        shmemq->shm_id,
        0
    );

    if (shmemq->buffer == MAP_FAILED) {
        shm_unlink(shmemq->name);
        if (error_ptr) *error_ptr = SHMEMQ_ERROR_FAILED_MMAP;
        return;
    }

    if (sem_init(&shmemq->buffer->header.read_sem, 1, 0) != 0) {
        shm_unlink(shmemq->name);
        if (error_ptr) *error_ptr = SHMEMQ_ERROR_FAILED_SEM_INIT;
        return;
    }

    if (sem_init(&shmemq->buffer->header.write_sem, 1, 0) != 0) {
        shm_unlink(shmemq->name);
        if (error_ptr) *error_ptr = SHMEMQ_ERROR_FAILED_SEM_INIT;
        return;
    }

    // We don't really need this condition, but it is useful in tests
    // for platform sanity check and maybe we can use it to prevent race
    // condition.
    if (shmemq->is_consumer) {
        shmemq->buffer->header.is_ready = false;

        // TODO: Resize buffer dynamically.
        // shmemq->buffer->header.frames_count = 0;
        shmemq->buffer->header.frames_count = 100;

        shmemq->buffer->header.read_frame_index = 0;
        shmemq->buffer->header.write_frame_index = 0;
    }

    if (error_ptr) *error_ptr = SHMEMQ_ERROR_NONE;
}

ShmemqFrame shmemq_push_start(const Shmemq shmemq)
{
    if (
        shmemq->buffer->header.write_frame_index >=
        shmemq->buffer->header.frames_count
    ) {
        if (shmemq->buffer->header.read_frame_index > 0) {
            shmemq->buffer->header.write_frame_index = 0;
        }
        else {
            return NULL;
        }
    }

    const size_t half_frames_count = shmemq->buffer->header.frames_count / 2;

    if (
        shmemq->buffer->header.write_frame_index ==
        shmemq->buffer->header.read_frame_index &&
        shmemq->buffer->header.read_frame_index >
        half_frames_count
    ) {
        if (shmemq->buffer->header.read_frame_index > 0) {
            const ShmemqFrame high_frame = &shmemq->buffer->frames[
                shmemq->buffer->header.write_frame_index
            ];

            high_frame->header.message_frames_count = 0;
            shmemq->buffer->header.write_frame_index = 0;
        }
        else {
            return NULL;
        }
    }

    if (
        shmemq->buffer->header.write_frame_index ==
        shmemq->buffer->header.read_frame_index - 1
    ) {
        return NULL;
    }

    return &shmemq->buffer->frames[shmemq->buffer->header.write_frame_index];
}

void shmemq_push_end(
    const Shmemq shmemq,
    size_t data_size,
    ShmemqError *const error_ptr
) {
    if (error_ptr) *error_ptr = SHMEMQ_ERROR_NONE;

    if (
        shmemq->buffer->header.write_frame_index >=
        shmemq->buffer->header.frames_count
    ) {
        if (error_ptr) *error_ptr = SHMEMQ_ERROR_BUG_PUSH_END_ON_FULL_QUEUE;
        return;
    }

    if (
        shmemq->buffer->header.write_frame_index ==
        shmemq->buffer->header.read_frame_index - 1
    ) {
        if (error_ptr) *error_ptr = SHMEMQ_ERROR_BUG_PUSH_END_ON_FULL_QUEUE;
        return;
    }

    const ShmemqFrame frame =
        &shmemq->buffer->frames[shmemq->buffer->header.write_frame_index];

    const size_t header_and_data_size =
        data_size + sizeof(struct ShmemqFrameHeader);

    if (header_and_data_size % SHMEMQ_FRAME_SIZE == 0) {
        frame->header.message_frames_count =
            header_and_data_size / SHMEMQ_FRAME_SIZE;
    }
    else {
        frame->header.message_frames_count =
            header_and_data_size / SHMEMQ_FRAME_SIZE + 1;
    }

    const size_t new_write_frame_index =
        shmemq->buffer->header.write_frame_index +
        frame->header.message_frames_count;

    if (
        new_write_frame_index >
        shmemq->buffer->header.frames_count || (
            shmemq->buffer->header.write_frame_index <
            shmemq->buffer->header.read_frame_index &&
            new_write_frame_index >=
            shmemq->buffer->header.read_frame_index
        )
    ) {
        if (error_ptr) *error_ptr = SHMEMQ_ERROR_BUG_PUSH_END_OVERFLOW;
        return;
    }

    shmemq->buffer->header.write_frame_index = new_write_frame_index;
}

ShmemqFrame shmemq_pop_start(const Shmemq shmemq)
{
    if (
        shmemq->buffer->header.read_frame_index ==
        shmemq->buffer->header.write_frame_index
    ) return NULL;

    const ShmemqFrame low_frame  = &shmemq->buffer->frames[0];
    const ShmemqFrame high_frame = &shmemq->buffer->frames[
        shmemq->buffer->header.read_frame_index
    ];

    if (
        shmemq->buffer->header.read_frame_index <
        shmemq->buffer->header.write_frame_index ||
        high_frame->header.message_frames_count != 0
    ) {
        return high_frame;
    }

    shmemq->buffer->header.read_frame_index = 0;
    return low_frame;
}

void shmemq_pop_end(const Shmemq shmemq, ShmemqError *const error_ptr)
{
    if (error_ptr) *error_ptr = SHMEMQ_ERROR_NONE;

    if (
        shmemq->buffer->header.read_frame_index ==
        shmemq->buffer->header.write_frame_index
    ) {
        *error_ptr = SHMEMQ_ERROR_BUG_POP_END_ON_EMPTY_QUEUE;
        return;
    }

    const ShmemqFrame frame =
        &shmemq->buffer->frames[shmemq->buffer->header.read_frame_index];

    if (
        shmemq->buffer->header.read_frame_index <
        shmemq->buffer->header.write_frame_index ||
        frame->header.message_frames_count != 0
    ) {
        shmemq->buffer->header.read_frame_index +=
            frame->header.message_frames_count;

        return;
    }

    shmemq->buffer->header.read_frame_index = 0;
}