#include <stddef.h>
#include <memory.h>
#include "mount.h"
#include "../MassStorage.h"
#include "../mbr/mbr.h"
#include "../fs/fat32/fat32.h"

#define AUTOMOUNT_SECTOR_SIZE (512)

#define MIN(a,b) (((a) < (b)) ? (a) : (b))

static Mnt_MountTable mtab = { 0 };
static Mnt_FileTable ftab = { 0 };

/**
 * Attempts to mount a volume.
 * @param mstg pointer to Mass Storage object
 * @param part pointer to partition entry
 * @return 0 if concluded without error (even if partition of unknown type could not be mounted)
 */
static int mnt_mount_volume(MassStorage * mstg, const PartEntry * part) {
    // fetch common partition details
    Mnt_Volume * next_entry = mtab.vols + mtab.mounted_vols; // pointer to control block area
    uint8_t * cbk = next_entry->fs_control_block_area; // control block area to be written
    next_entry->mnt_name[MNT_MAX_MOUNT_NAME_LENGTH] = '\0'; // write terminating zero in advance
    int mount_success = -1;

    // attempt to mount partition
    switch (part->part_type) {
        case 0: // empty slot
            break;
        case FAT32_CHS_PART_ID: // FAT32
        case FAT32_LBA_PART_ID: {
            Fat32_CtrlBlock *ctrl = (Fat32_CtrlBlock *) cbk;
            mount_success = fat32_load(ctrl, part->lba_fa, mstg);
            if (mount_success == 0) {
                fat32_get_volume_label(ctrl, next_entry->mnt_name, MNT_MAX_MOUNT_NAME_LENGTH); // get volume name
                next_entry->driver = fat32_driver; // assign driver
            }
        }
            break;
        default: // unmountable file system's found on the disk
            MSG("Unknown file system type: %d, cannot mount!\n", part->part_type);
            break;
    }

    // if succeeded, then maintain mount table
    if (mount_success > -1) {
        next_entry->part_size = part->sector_count * AUTOMOUNT_SECTOR_SIZE; // save volume size
        mtab.mounted_vols++; // increase number of mounted partitions
    }

    return 0;
}

/**
 * Attempt to automount disk volumes.
 * @param mstg pointer to Mass Storage object
 * @return 0 if successful
 */
int mnt_automount_disk(MassStorage * mstg) {
    // load the first sector
    uint8_t buf[AUTOMOUNT_SECTOR_SIZE];
    mstg->read_sector(mstg, 0, buf);

    // fetch partitions from the disk
    const PartEntry * partList = mbr_get_partitions(buf);
    if (partList == NULL) { // not an MBR disk
        return 0;
    }

    // if it's an MBR disk, iterate over all four partition slots
    mtab.mounted_vols = 0;
    PartEntry parts[MBR_MAX_PARTITIONS];
    memcpy(parts, partList, sizeof(PartEntry) * MBR_MAX_PARTITIONS); // copy partition table
    for (uint8_t i = 0; (i < MBR_MAX_PARTITIONS) && (mtab.mounted_vols < MNT_MAX_MOUNTED_VOLUMES); i++) {
        const PartEntry * part = parts + i; // fetch a partition
        mnt_mount_volume(mstg, part); // attempt mounting a volume
    }

    return 0;
}

/**
 * Get volume by name.
 * @param name volume name
 * @return pointer to volume, if found OR NULL
 */
Mnt_Volume * mnt_get_volume_by_name(const char * name) {
    Mnt_Volume * vol = NULL;
    for (uint8_t i = 0; i < mtab.mounted_vols; i++) {
        if (!strncmp(mtab.vols[i].mnt_name, name, MNT_MAX_MOUNT_NAME_LENGTH)) {
            vol = mtab.vols + i;
            break;
        }
    }
    return vol;
}

#define MNT_DIRSEP '/'

/**
 * Separate volume name and the path relative to the volume's root.
 * @param volpath string of /volume/path
 * @param volname pointer to free area up to max_volname_len bytes
 * @param max_volname_len size of free area not including terminating zero
 * @return pointer to the relative path
 */
const char * mnt_separate_volume_path(const char * volpath, char * volname, uint16_t max_volname_len) {
    const char * iter = volpath;

    // strip first '/'
    if (*iter == MNT_DIRSEP) {
        iter++;
    }

    // search the end of volume name
    uint16_t i = 0;
    while ((*iter != MNT_DIRSEP) && (*iter != '\0')) {
        if (i < max_volname_len) { // copy only so many that we can store
            volname[i++] = *iter;
        }
        iter++;
    }
    volname[i] = '\0';

    // skip '/' at the end of the volume name
    if (*iter == MNT_DIRSEP) {
        iter++;
    }

    return iter;
}

/**
 * Get volume by name extracted from a file's path stored on the volume.
 * @param volpath path beginning with the /volume name/
 * @param path path of the file on the volume (relative to volume root)
 * @return pointer to a mounted volume OR NULL if not found
 */
Mnt_Volume * mnt_get_volume_by_path(const char * volpath, const char ** path) {
    const char * ret;
    char volname[MNT_MAX_MOUNT_NAME_LENGTH + 1];
    ret = mnt_separate_volume_path(volpath, volname, MNT_MAX_MOUNT_NAME_LENGTH);
    if (path != NULL) {
        *path = ret;
    }

    return mnt_get_volume_by_name(volname);
}

#define MNT_FTAB_BLOCK_FREE (0)
#define MNT_FTAB_BLOCK_OCCUPIED (1)

/**
 * Allocate space for a newly opened file's helper object.
 * @return allocated slot OR NULL is allocation was not possible
 */
Mnt_File * mnt_alloc_file_helper() {
    Mnt_File * slot = NULL;
    for (uint8_t i = 0; i < MNT_MAX_OPEN_FILES; i++) {
        if (ftab.files[i].ctrl_word == MNT_FTAB_BLOCK_FREE) {
            ftab.files[i].ctrl_word = MNT_FTAB_BLOCK_OCCUPIED;
            slot = ftab.files + i;
            break;
        }
    }
    return slot;
}

/**
 * Release file helper.
 * @param helper pointer to helper
 */
void mnt_free_file_helper(Mnt_File * file) {
    file->ctrl_word = MNT_FTAB_BLOCK_FREE;
}

// -----------------------

/**
 * List directory.
 * @param dir path to the directory
 */
void mnt_list(const char *dir) {
    // if
    if ((dir[0] == '\0') || ((dir[0] == MNT_DIRSEP) && (dir[1] == '\0'))) {
        for (uint8_t i = 0; i < mtab.mounted_vols; i++) {
            MSG("/%s     %.3f MB VOLUME\n", mtab.vols[i].mnt_name, mtab.vols[i].part_size * 1E-06);
        }
        return;
    }

    // if not empty path is specified
    const char * relpath;
    Mnt_Volume * vol = mnt_get_volume_by_path(dir, &relpath);
    if (vol != NULL) {
        (vol->driver).list((void *) vol->fs_control_block_area, relpath);
    }
}

/**
 * Open file.
 * @param path full path to file
 * @return pointer to file handle
 */
Mnt_File * mnt_open(const char * path) {
    Mnt_File * file = NULL;
    const char * relpath;
    Mnt_Volume * vol = mnt_get_volume_by_path(path, &relpath);
    if (vol != NULL) {
        file = mnt_alloc_file_helper();
        if (file != NULL) {
            file->vol = vol;
            (vol->driver).open(vol->fs_control_block_area, relpath, file->helper);
        }
    }
    return file;
}

/**
 * Read from the file.
 * @param file pointer to Mnt_File object
 * @param len (desired) read length
 * @param buf destination buffer
 * @return actual read length
 */
int mnt_read(Mnt_File * file, unsigned long len, void * buf) {
    Mnt_Volume * vol = file->vol;
    return vol->driver.read(vol->fs_control_block_area, (void *) file->helper, len, buf);
}

/**
 * Seek the file.
 * @param file pointer to Mnt_File object
 * @param pos position from the beginning
 * @return ???
 */
int mnt_seek(Mnt_File * file, unsigned long pos) {
    Mnt_Volume * vol = file->vol;
    return vol->driver.seek(vol->fs_control_block_area, (void *) file->helper, pos);
}

void mnt_close(Mnt_File *file) {
    mnt_free_file_helper(file);
}