#include "restore.h"

#include "file.h"
#include "print.h"

#include <errno.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static bool
is_reference_file_valid(resources_t *const res, uint32_t sector_size)
{
    const long ref_size = file_size(res->ref_file);

    if (ref_size < 0) {
        print_error("cannot get size of reference file: %s", strerror(errno));
        return false;
    } else if (ref_size == 0) {
        print_error("reference file is empty");
        return false;
    } else if ((ref_size % (sizeof(uint64_t) + sector_size)) != 0) {
        /* The reference file must hold equally sized sectors and the
         * offset of each of them
         */
        print_error(
            "reference file has size that cannot contain valid diff data");
        return false;
    }

    const long out_size = file_size(res->out_file);

    if (out_size < 0) {
        print_error("cannot get size of output file: %s", strerror(errno));
        return 1;
    }

    uint64_t ref_offset = 0;
    uint64_t prev_out_offset;

    /* Scan the reference file and check  */
    for (;;) {
        uint64_t out_offset;
        /* Read the next offset */
        const size_t ref_read =
            fread(&out_offset, sizeof(out_offset), 1U, res->ref_file);
        out_offset = le64toh(out_offset);

        if (feof(res->ref_file)) {
            break;
        } else if ((ref_read != 1U) || ferror(res->ref_file)) {
            print_error("cannot read from reference file: %s", strerror(errno));
            return false;
        } else if (((ref_offset != 0) && (out_offset <= prev_out_offset)) ||
                   ((out_offset + sector_size) > out_size)) {
            /* The offset must be higher than the previous one and it
             * must point into the file
             */
            print_error("reference file is not valid");
            return false;
        } else if (fseek(res->ref_file, sector_size, SEEK_CUR) != 0) {
            print_error("cannot seek in reference file: %s", strerror(errno));
            return false;
        }

        prev_out_offset = out_offset;
    }

    if (ftell(res->ref_file) != ref_size) {
        /* The reference file must be read completely */
        print_error("reference file is not valid");
        return false;
    } else if (fseek(res->ref_file, 0L, SEEK_SET) != 0) {
        /* The file must be prepared for the restoring */
        print_error("cannot seek in reference file: %s", strerror(errno));
        return false;
    }

    return true;
}

int
restore(const options_t *const opts, resources_t *const res)
{
    /* Check validity of the reference file */
    if (!is_reference_file_valid(res, opts->sector_size)) {
        return 1;
    }

    const long ref_size = file_size(res->ref_file);

    if (ref_size < 0) {
        print_error("cannot get size of reference file: %s", strerror(errno));
        return 1;
    }

    /* Allocate the buffer for data from the reference file */
    /* The reference buffer contains also the offsets */
    const size_t ref_buffer_size =
        ((opts->buffer_size / opts->sector_size) * sizeof(uint64_t)) +
        opts->buffer_size;

    if ((res->ref_buffer = (char *)malloc(ref_buffer_size)) == NULL) {
        print_error("cannot allocate buffer for reference file data");
        return 1;
    }

    /* Restore data from the differential image */
    uint64_t out_offset;

    for (;;) {
        /* Read data of the offset and the next sector */
        const size_t ref_read =
            fread(res->ref_buffer, ref_buffer_size, 1U, res->ref_file);

        if (feof(res->ref_file)) {
            break;
        } else if ((ref_read != 1U) || ferror(res->ref_file)) {
            print_error("cannot read from reference file: %s", strerror(errno));
            return 1;
        }

        /* Get offset */
        out_offset = le64toh(*((uint64_t *)res->ref_buffer));

        if (fseek(res->out_file, out_offset, SEEK_SET) != 0) {
            print_error("cannot seek in output file: %s", strerror(errno));
            return 1;
        }

        /* Write the sector data to the output file */
        const size_t out_written = fwrite(res->ref_buffer + sizeof(out_offset),
                                          opts->sector_size, 1U, res->out_file);

        if (out_written != 1U) {
            print_error("cannot write to output file: %s", strerror(errno));
            return 1;
        }
    }

    /* The reference file must be read completely */
    if (ftell(res->ref_file) != ref_size) {
        print_error("reference file is not valid");
        return 1;
    }

    return 0;
}