/*
 * Copyright (c) 2026, Chloe M.
 * Provided under the BSD-3 clause.
 */

#define _DEFAULT_SOURCE
#include <sys/stat.h>
#include <sys/mman.h>
#include <sys/queue.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdint.h>
#include <stddef.h>
#include <stdlib.h>
#include <stdbool.h>
#include <dirent.h>
#include <string.h>

/* Forward declarations */
struct idata_desc;

/* Data descriptor constants */
#define RDAR_MAX_PATHLEN 32
#define RDAR_MAGIC       ">RDAR!"
#define RDAR_MAGIC_LEN   6

/* Data descriptor file flags */
#define DATA_ROOT (1 << 0)    /* Is root data descriptor */
#define DATA_AVL  (1 << 1)    /* Available to consumer software; not touched by us */

/* Version conversion macros */
#define VERSION_U16(MAJOR, MINOR)   \
    (((MINOR) << 8) | (MAJOR))
#define VERSION_MAJOR(VERSION)      \
    ((VERSION) & 0xFF)
#define VERSION_MINOR(VERSION)      \
    (((VERSION) >> 8) & 0xFF)

/* Pushes idata descriptor to table */
#define IDATA_PUSH(IDATA_P)                             \
    ++d_desc_count;                                     \
    TAILQ_INSERT_TAIL(&d_desc_table, (IDATA_P), link);

/*
 * Software version
 *
 * XXX: We encode it as a U16 so that we may bundle it
 *      with the file data as binary.
 */
#define RDAR_VERSION VERSION_U16(1, 0)  /* v1.0 */

/* Fallback path if '-o' is not specified */
#define FALLBACK_OUTPUT_PATH "out.rdar"

/* Globals */
static const char *input_dir = NULL;
static const char *output_path = NULL;
static TAILQ_HEAD(, idata_desc) d_desc_table;
static size_t d_desc_count = 0;

/*
 * The root data region (RDR) contains information about the
 * entire archive.
 *
 * @desc_count:  Number of descriptors
 * @revision:    Format revision
 */
struct root_data_region {
    size_t desc_count;
    uint16_t revision;
};

/*
 * Represents a file that has been mapped into memory
 *
 * @data:     File data
 * @length:   Length of data
 */
struct file_view {
    char *data;
    size_t length;
};

/*
 * A data descriptor holds information about a specific
 * file along with an offset to which it is located at
 * in the offset.
 *
 * @magic:  Format magic
 * @path:   File path
 * @off:    File data offset
 * @flags:  File flags
 * @length: File length in bytes
 */
struct data_desc {
    char magic[RDAR_MAGIC_LEN];
    char path[RDAR_MAX_PATHLEN];
    off_t off;
    uint16_t flags;
    size_t length;
};

/*
 * Internal data descriptor, used to hold data
 * before being flushed to the archive
 *
 * @data:  Actual data descriptor
 * @file:  File view this descriptor references
 * @link:  TAILQ link
 */
struct idata_desc {
    struct data_desc data;
    struct file_view file;
    TAILQ_ENTRY(idata_desc) link;
};

static void
help(void)
{
    printf("usage: ./rdar <... flags>\n");
    printf("[-h]    Display this help menu\n");
    printf("[-v]    Display the program version\n");
    printf("[-i]    Input directory to pack\n");
    printf("[-o]    Output path for archive file\n");
}

static void
version(void)
{
    uint16_t Major, Minor;

    Major = VERSION_MAJOR(RDAR_VERSION);
    Minor = VERSION_MINOR(RDAR_VERSION);
    printf("Version v%d.%d\n", Major, Minor);
}

/*
 * Destroy a file view
 *
 * @view: View to destory
 */
static void
view_destroy(struct file_view *view)
{
    munmap(view->data, view->length);
    view->data = NULL;
    view->length = 0;
}

/*
 * Create a mapped file view from a file path
 */
static int
view_from_path(const char *path, struct file_view *result)
{
    struct stat sb;
    int fd;

    if (path == NULL || result == NULL) {
        return -1;
    }

    fd = open(path, O_RDONLY);
    if (fd < 0) {
        printf("fatal: failed to open '%s'\n", path);
        perror("open");
        return -1;
    }

    if (stat(path, &sb) < 0) {
        printf("fatal: failed to stat '%s'\n", path);
        perror("stat");
        close(fd);
        return -1;
    }

    result->data = mmap(
        NULL,
        sb.st_size,
        PROT_READ,
        MAP_SHARED,
        fd,
        0
    );

    if (result->data == NULL) {
        printf("fatal: failed to map '%s'\n", path);
        perror("mmap");
        close(fd);
        return -1;
    }

    result->length = sb.st_size;
    close(fd);
    return 0;
}

/*
 * Allocate an internal data descriptor
 *
 * @path:     Path of file
 * @is_root:  If set, don't create a view
 */
static struct idata_desc *
idata_from_file(const char *path, bool is_root)
{
    struct idata_desc *idata_desc;
    struct data_desc *data_desc;
    size_t path_len;
    const char *p;

    path_len = strlen(path);
    if (path_len >= RDAR_MAX_PATHLEN - 1) {
        printf("fatal: path '%s' is too long!\n", path);
        return NULL;
    }

    idata_desc = malloc(sizeof(*idata_desc));
    if (idata_desc == NULL) {
        printf("fatal: failed to allocate idata_desc\n");
        printf("* last file processed: %s\n", path);
        return NULL;
    }

    if (!is_root) {
        if (view_from_path(path, &idata_desc->file) < 0) {
            free(idata_desc);
            return NULL;
        }
    }

    p = path;

    /* Strip leading path stuff */
    while (*p == '.' && *p != '\0')
        ++p;
    while (*p == '/' && *p != '\0')
        ++p;

    /* Initialize the data descriptor */
    data_desc = &idata_desc->data;
    memcpy(data_desc->magic, RDAR_MAGIC, RDAR_MAGIC_LEN);
    memcpy(data_desc->path, p, strlen(p));
    data_desc->path[path_len] = '\0';
    data_desc->flags = 0;
    data_desc->off = 0;
    return idata_desc;
}

/*
 * Push the root descriptor to the table.
 *
 * The root descriptor is to contain an offset into a special
 * %root% file entry which contains data (e.g., version, file count)
 * encoded within.
 */
static int
idata_push_root(void)
{
    struct idata_desc *root;
    struct data_desc *desc;

    root = idata_from_file("%root%", true);
    if (root == NULL) {
        return -1;
    }

    desc = &root->data;
    desc->length = sizeof(struct root_data_region);
    IDATA_PUSH(root);
    return 0;
}

static void
idata_table_destroy(void)
{
    struct idata_desc *desc, *next;

    desc = TAILQ_FIRST(&d_desc_table);
    while (desc != NULL) {
        view_destroy(&desc->file);
        next = TAILQ_NEXT(desc, link);
        TAILQ_REMOVE(&d_desc_table, desc, link);
        desc = next;
    }
}

static void
flush_root_desc(struct data_desc *d_desc, int out_fd)
{
    struct root_data_region rdr = {
        .desc_count = d_desc_count,
        .revision = RDAR_VERSION
    };

    d_desc->off = lseek(out_fd, 0, SEEK_CUR);
    write(out_fd, &rdr, sizeof(rdr));
}

static void
idata_table_flush(void)
{
    const struct file_view *view;
    struct idata_desc *desc_iter;
    struct data_desc *d_desc;
    off_t new_off;
    int fd;

    fd = open(output_path, O_WRONLY | O_TRUNC | O_CREAT, 0666);
    if (fd < 0) {
        printf("fatal: failed to open output path\n");
        perror("open");
        return;
    }

    new_off = d_desc_count * sizeof(struct data_desc);
    lseek(fd, new_off, SEEK_SET);

    /* First pass write the file data */
    TAILQ_FOREACH(desc_iter, &d_desc_table, link) {
        view = &desc_iter->file;
        d_desc = &desc_iter->data;

        /*
         * Check if we need to flush the root descriptor, we ignore any files that start
         * with the '%' modifier.
         */
        if (d_desc->path[0] == '%') {
            if (strcmp(d_desc->path, "%root%") == 0)
                flush_root_desc(d_desc, fd);

            continue;
        }

        d_desc->off = lseek(fd, 0, SEEK_CUR);
        d_desc->length = view->length;
        write(fd, view->data, view->length);
    }

    /* Data descriptors go at the start */
    lseek(fd, 0, SEEK_SET);

    /* Second pass write the data descriptors */
    TAILQ_FOREACH(desc_iter, &d_desc_table, link) {
        view = &desc_iter->file;
        d_desc = &desc_iter->data;
        write(fd, d_desc, sizeof(*d_desc));
    }

    close(fd);
}

static void
recurse_dir(const char *dirpath)
{
    DIR *dir;
    struct dirent *dirent;
    struct idata_desc *idata_desc;
    char pathbuf[264];

    dir = opendir(dirpath);
    if (dir == NULL) {
        printf("fatal: failed to open '%s'\n", input_dir);
        perror("opendir");
        return;
    }

    while ((dirent = readdir(dir)) != NULL) {
        if (dirent->d_name[0] == '.') {
            continue;
        }

        switch (dirent->d_type) {
        case DT_REG:
            snprintf(pathbuf, sizeof(pathbuf), "%s/%s", dirpath, dirent->d_name);
            printf("[f] %s\n", pathbuf);

            idata_desc = idata_from_file(pathbuf, false);
            if (idata_desc == NULL) {
                printf("warn: ignoring '%s'\n", pathbuf);
                break;
            }

            IDATA_PUSH(idata_desc);
            break;
        case DT_DIR:
            snprintf(pathbuf, sizeof(pathbuf), "%s/%s", dirpath, dirent->d_name);
            printf("[d] %s\n", pathbuf);
            recurse_dir(pathbuf);
            break;
        }
    }

    closedir(dir);
}

int
main(int argc, char **argv)
{
    int opt;

    if (argc < 2) {
        printf("fatal: too few arguments\n");
        help();
        return -1;
    }

    while ((opt = getopt(argc, argv, "hvi:o:")) != -1) {
        switch (opt) {
        case 'h':
            help();
            return -1;
        case 'v':
            version();
            return -1;
        case 'i':
            input_dir = strdup(optarg);
            if (input_dir == NULL) {
                printf("fatal: failed to allocate input_dir\n");
                return -1;
            }

            break;
        case 'o':
            output_path = strdup(optarg);
            if (output_path == NULL) {
                printf("fatal: failed to allocate output dir\n");
                return -1;
            }

            break;
        }
    }

    if (input_dir == NULL) {
        printf("fatal: input path not specified\n");
        help();
        return -1;
    }

    if (output_path == NULL) {
        output_path = FALLBACK_OUTPUT_PATH;
    }

    TAILQ_INIT(&d_desc_table);
    idata_push_root();
    recurse_dir(input_dir);
    idata_table_flush();
    idata_table_destroy();
    return 0;
}