/* vi: set sw=4 ts=4: */
/*
 *  busybox patch applet to handle the unified diff format.
 *  Copyright (C) 2003 Glenn McGrath
 *
 *  Licensed under the GPL v2 or later, see the file LICENSE in this tarball.
 *
 *  This applet is written to work with patches generated by GNU diff,
 *  where there is equivalent functionality busybox patch shall behave
 *  as per GNU patch.
 *
 *  There is a SUSv3 specification for patch, however it looks to be
 *  incomplete, it doesnt even mention unified diff format.
 *  http://www.opengroup.org/onlinepubs/007904975/utilities/patch.html
 *
 *  Issues
 *   - Non-interactive
 *   - Patches must apply cleanly or patch (not just one hunk) will fail.
 *   - Reject file isnt saved
 */

#include "libbb.h"

static unsigned copy_lines(FILE *src_stream, FILE *dst_stream, unsigned lines_count)
{
        while (src_stream && lines_count) {
                char *line;
                line = xmalloc_fgets(src_stream);
                if (line == NULL) {
                        break;
                }
                if (fputs(line, dst_stream) == EOF) {
                        bb_perror_msg_and_die("error writing to new file");
                }
                free(line);
                lines_count--;
        }
        return lines_count;
}

/* If patch_level is -1 it will remove all directory names
 * char *line must be greater than 4 chars
 * returns NULL if the file doesnt exist or error
 * returns malloc'ed filename
 * NB: frees 1st argument!
 */
static char *extract_filename(char *line, int patch_level, const char *pat)
{
        char *temp = NULL, *filename_start_ptr = line + 4;

        if (strncmp(line, pat, 4) == 0) {
                /* Terminate string at end of source filename */
                line[strcspn(line, "\t\n\r")] = '\0';

                /* Skip over (patch_level) number of leading directories */
                while (patch_level--) {
                        temp = strchr(filename_start_ptr, '/');
                        if (!temp)
                                break;
                        filename_start_ptr = temp + 1;
                }
                temp = xstrdup(filename_start_ptr);
        }
        free(line);
        return temp;
}

int patch_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int patch_main(int argc UNUSED_PARAM, char **argv)
{
        struct stat saved_stat;
        char *patch_line;
        FILE *patch_file;
        int patch_level;
        int ret = 0;
        char plus = '+';

        xfunc_error_retval = 2;
        {
                const char *p = "-1";
                const char *i = "-"; /* compat */
                if (getopt32(argv, "p:i:R", &p, &i) & 4)
                        plus = '-';
                patch_level = xatoi(p); /* can be negative! */
                patch_file = xfopen_stdin(i);
        }

        patch_line = xmalloc_fgetline(patch_file);
        while (patch_line) {
                FILE *src_stream;
                FILE *dst_stream;
                //char *old_filename;
                char *new_filename;
                char *backup_filename;
                unsigned src_cur_line = 1;
                unsigned dst_cur_line = 0;
                unsigned dst_beg_line;
                unsigned bad_hunk_count = 0;
                unsigned hunk_count = 0;
                smallint copy_trailing_lines_flag = 0;

                /* Skip everything upto the "---" marker
                 * No need to parse the lines "Only in <dir>", and "diff <args>"
                 */
                do {
                        /* Extract the filename used before the patch was generated */
                        new_filename = extract_filename(patch_line, patch_level, "--- ");
                        // was old_filename above
                        patch_line = xmalloc_fgetline(patch_file);
                        if (!patch_line) goto quit;
                } while (!new_filename);
                free(new_filename); // "source" filename is irrelevant

                new_filename = extract_filename(patch_line, patch_level, "+++ ");
                if (!new_filename) {
                        bb_error_msg_and_die("invalid patch");
                }

                /* Get access rights from the file to be patched */
                if (stat(new_filename, &saved_stat) != 0) {
                        char *slash = strrchr(new_filename, '/');
                        if (slash) {
                                /* Create leading directories */
                                *slash = '\0';
                                bb_make_directory(new_filename, -1, FILEUTILS_RECUR);
                                *slash = '/';
                        }
                        backup_filename = NULL;
                        src_stream = NULL;
                        saved_stat.st_mode = 0644;
                } else {
                        backup_filename = xasprintf("%s.orig", new_filename);
                        xrename(new_filename, backup_filename);
                        src_stream = xfopen_for_read(backup_filename);
                }
                dst_stream = xfopen_for_write(new_filename);
                fchmod(fileno(dst_stream), saved_stat.st_mode);

                printf("patching file %s\n", new_filename);

                /* Handle all hunks for this file */
                patch_line = xmalloc_fgets(patch_file);
                while (patch_line) {
                        unsigned count;
                        unsigned src_beg_line;
                        unsigned hunk_offset_start;
                        unsigned src_last_line = 1;
                        unsigned dst_last_line = 1;

                        if ((sscanf(patch_line, "@@ -%d,%d +%d,%d", &src_beg_line, &src_last_line, &dst_beg_line, &dst_last_line) < 3)
                         && (sscanf(patch_line, "@@ -%d +%d,%d", &src_beg_line, &dst_beg_line, &dst_last_line) < 2)
                        ) {
                                /* No more hunks for this file */
                                break;
                        }
                        if (plus != '+') {
                                /* reverse patch */
                                unsigned tmp = src_last_line;
                                src_last_line = dst_last_line;
                                dst_last_line = tmp;
                                tmp = src_beg_line;
                                src_beg_line = dst_beg_line;
                                dst_beg_line = tmp;
                        }
                        hunk_count++;

                        if (src_beg_line && dst_beg_line) {
                                /* Copy unmodified lines upto start of hunk */
                                /* src_beg_line will be 0 if it's a new file */
                                count = src_beg_line - src_cur_line;
                                if (copy_lines(src_stream, dst_stream, count)) {
                                        bb_error_msg_and_die("bad src file");
                                }
                                src_cur_line += count;
                                dst_cur_line += count;
                                copy_trailing_lines_flag = 1;
                        }
                        src_last_line += hunk_offset_start = src_cur_line;
                        dst_last_line += dst_cur_line;

                        while (1) {
                                free(patch_line);
                                patch_line = xmalloc_fgets(patch_file);
                                if (patch_line == NULL)
                                        break; /* EOF */
                                if ((*patch_line != '-') && (*patch_line != '+')
                                 && (*patch_line != ' ')
                                ) {
                                        break; /* End of hunk */
                                }
                                if (*patch_line != plus) { /* '-' or ' ' */
                                        char *src_line = NULL;
                                        if (src_cur_line == src_last_line)
                                                break;
                                        if (src_stream) {
                                                src_line = xmalloc_fgets(src_stream);
                                                if (src_line) {
                                                        int diff = strcmp(src_line, patch_line + 1);
                                                        src_cur_line++;
                                                        free(src_line);
                                                        if (diff)
                                                                src_line = NULL;
                                                }
                                        }
                                        if (!src_line) {
                                                bb_error_msg("hunk #%u FAILED at %u", hunk_count, hunk_offset_start);
                                                bad_hunk_count++;
                                                break;
                                        }
                                        if (*patch_line != ' ') { /* '-' */
                                                continue;
                                        }
                                }
                                if (dst_cur_line == dst_last_line)
                                        break;
                                fputs(patch_line + 1, dst_stream);
                                dst_cur_line++;
                        } /* end of while loop handling one hunk */
                } /* end of while loop handling one file */

                /* Cleanup last patched file */
                if (copy_trailing_lines_flag) {
                        copy_lines(src_stream, dst_stream, (unsigned)(-1));
                }
                if (src_stream) {
                        fclose(src_stream);
                }
                fclose(dst_stream);
                if (bad_hunk_count) {
                        ret = 1;
                        bb_error_msg("%u out of %u hunk FAILED", bad_hunk_count, hunk_count);
                } else {
                        /* It worked, we can remove the backup */
                        if (backup_filename) {
                                unlink(backup_filename);
                        }
                        if ((dst_cur_line == 0) || (dst_beg_line == 0)) {
                                /* The new patched file is empty, remove it */
                                xunlink(new_filename);
                                // /* old_filename and new_filename may be the same file */
                                // unlink(old_filename);
                        }
                }
                free(backup_filename);
                //free(old_filename);
                free(new_filename);
        } /* end of "while there are patch lines" */
 quit:
        /* 0 = SUCCESS
         * 1 = Some hunks failed
         * 2 = More serious problems (exited earlier)
         */
        return ret;
}