/* Copyright 2021 Ján Sučan <jan@jansucan.com>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 * 1. Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "backup.h"

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

#include <errno.h>
#include <inttypes.h>
#include <stdlib.h>
#include <string.h>

typedef struct {
    FILE *in_file;
    FILE *ref_file;
    FILE *out_file;

    char *in_buffer;
    char *ref_buffer;
    char *out_buffer;

    size_t out_buffer_size;
} resources_backup_t;

static int check_files(const OptionsBackup &opts,
                       const resources_backup_t *const res);
static int write_out_buffer(const char *const buffer, size_t size,
                            FILE *const file);

static int
resources_allocate_for_backup(const OptionsBackup &opts,
                              resources_backup_t *const res)
{
    if ((res->in_file = fopen(opts.getInFilePath().c_str(), "r")) == NULL) {
        print_error("cannot open input file: %s", strerror(errno));
        return 1;
    }

    if ((res->ref_file = fopen(opts.getRefFilePath().c_str(), "r")) == NULL) {
        print_error("cannot open reference file: %s", strerror(errno));
        return 1;
    }

    /* When backing up, the output file is truncated to hold the
     * new data
     */
    if ((res->out_file = fopen(opts.getOutFilePath().c_str(), "w+")) == NULL) {
        print_error("cannot open output file: %s", strerror(errno));
        return 1;
    }

    /* The output buffer contains also the offsets */
    res->out_buffer_size =
        ((opts.getBufferSize() / opts.getSectorSize()) * sizeof(uint64_t)) +
        opts.getBufferSize();

    // TODO: separate function
    if ((res->in_buffer = (char *)malloc(opts.getBufferSize())) == NULL) {
        print_error("cannot allocate buffer for input file data");
        return 1;
    } else if ((res->ref_buffer = (char *)malloc(opts.getBufferSize())) ==
               NULL) {
        print_error("cannot allocate buffer for reference file data");
        return 1;
    } else if ((res->out_buffer = (char *)malloc(res->out_buffer_size)) ==
               NULL) {
        print_error("cannot allocate buffer for output file data");
        return 1;
    }

    return 0;
}

static int
check_files(const OptionsBackup &opts, const resources_backup_t *const res)
{
    bool in_size_ok = false;
    const size_t in_size = file_size(res->in_file, &in_size_ok);

    if (!in_size_ok) {
        print_error("cannot get size of input file: %s", strerror(errno));
        return 1;
    }

    bool ref_size_ok = false;
    const size_t ref_size = file_size(res->ref_file, &ref_size_ok);

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

    /* Check sizes of the input file and the reference file */
    if (in_size != ref_size) {
        print_error("input file and reference file differ in size");
        return 1;
    } else if ((in_size % opts.getSectorSize()) != 0) {
        print_error(
            "size of input file and reference file is not multiple of %" PRIu32,
            opts.getSectorSize());
        return 1;
    }

    return 0;
}

static int
write_out_buffer(const char *const buffer, size_t size, FILE *const file)
{
    const size_t bytes_written = fwrite(buffer, 1U, size, file);

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

    return 0;
}

int
backup(const OptionsBackup &opts)
{
    resources_backup_t res;

    if (resources_allocate_for_backup(opts, &res) != 0) {
        return 1;
    }

    if (check_files(opts, &res) != 0) {
        return 1;
    }

    size_t out_buffer_index = 0;
    uint64_t input_file_offset = 0;

    for (;;) {
        /* Read the sectors from the input and reference files into the buffers
         */
        const size_t in_sectors_read =
            file_read_sectors(res.in_file, res.in_buffer, opts.getBufferSize(),
                              opts.getSectorSize());
        const size_t ref_sectors_read =
            file_read_sectors(res.ref_file, res.ref_buffer,
                              opts.getBufferSize(), opts.getSectorSize());

        if ((in_sectors_read == 0) || (ref_sectors_read == 0)) {
            break;
        } else if (in_sectors_read != ref_sectors_read) {
            print_error(
                "cannot read equal amount of sectors from the input files");
            return 1;
        }

        /* Process the sectors in the buffers */
        for (size_t sector = 0; sector < in_sectors_read; ++sector) {
            const size_t buffer_offset = sector * opts.getSectorSize();

            if (memcmp(res.in_buffer + buffer_offset,
                       res.ref_buffer + buffer_offset,
                       opts.getSectorSize()) != 0) {
                /* Backup the changed sector */
                if (out_buffer_index >= res.out_buffer_size) {
                    /* The output buffer is full. Write it to the output file */
                    if (write_out_buffer(res.out_buffer, out_buffer_index,
                                         res.out_file) != 0) {
                        return 1;
                    }
                    out_buffer_index = 0;
                }
                /* Write the next backup record */
                const uint64_t o = htole64(input_file_offset);
                memcpy(res.out_buffer + out_buffer_index, (void *)&o,
                       sizeof(o));
                out_buffer_index += sizeof(o);

                memcpy(res.out_buffer + out_buffer_index,
                       res.in_buffer + buffer_offset, opts.getSectorSize());
                out_buffer_index += opts.getSectorSize();
            }

            input_file_offset += opts.getSectorSize();
        }
    }

    /* Write out the output buffer */
    if (out_buffer_index > 0) {
        if (write_out_buffer(res.out_buffer, out_buffer_index, res.out_file) !=
            0) {
            return 1;
        }
    }

    return 0;
}