#include <unistd.h>

#ifndef _POSIX_SOURCE
#define _POSIX_SOURCE
#endif

#include <stdio.h>
#include <stdlib.h>

#if !defined(__APPLE__)
#include <malloc.h>
#endif

#include <string.h>
#include <fcntl.h>
#include <sys/param.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <dirent.h>
#include <time.h>
#include <stddef.h>
#include <errno.h>

#ifndef S_ISLNK
#define S_ISLNK(mode) (((mode) & (_S_IFMT)) == (_S_IFLNK))
#endif

#ifndef PATH_MAX
#define PATH_MAX 1024
#endif

#define progver "%s: scan/change symbolic links - v1.4.3\n\n"

static char *progname;
static int verbose = 0,
           fix_links = 0,
           recurse = 0,
           delete = 0,
           shorten = 0,
           testing = 0,
           single_fs = 1;

/*
 * tidypath removes excess slashes and "." references from a path string
 */

static int substr(char *s, char *old, char *new) {
    char *tmp = NULL;
    unsigned long oldlen = strlen(old), newlen = 0;
    
    if (NULL == strstr(s, old)) {
        return 0;
    }
    
    if (new) {
        newlen = strlen(new);
    }
    
    if (newlen > oldlen) {
        if ((tmp = malloc(strlen(s))) == NULL) {
            fprintf(stderr, "no memory\n");
            exit(1);
        }
    }
    
    while (NULL != (s = strstr(s, old))) {
        char *p, *old_s = s;
        
        if (new) {
            if (newlen > oldlen) {
                old_s = strcpy(tmp, s);
            }
            
            p = new;
            
            while (*p) {
                *s++ = *p++;
            }
        }
        
        p = old_s + oldlen;
        
        while ((*s++ = *p++));
    }
    
    if (tmp) {
        free(tmp);
    }
    
    return 1;
}


static int tidy_path(char *path) {
    int tidied = 0;
    char *s, *p;
    s = path + strlen(path) - 1;
    
    if (s[0] != '/') {  /* tmp trailing slash simplifies things */
        s[1] = '/';
        s[2] = '\0';
    }
    
    while (substr(path, "/./", "/")) {
        tidied = 1;
    }
    
    while (substr(path, "//", "/")) {
        tidied = 1;
    }
    
    while ((p = strstr(path, "/../")) != NULL) {
        s = p + 3;
        
        for (p--; p != path; p--) {
            if (*p == '/') { break; }
        }
        
        if (*p != '/') { break; }
        
        while ((*p++ = *s++));
        
        tidied = 1;
    }
    
    if (*path == '\0') {
        strcpy(path, "/");
    }
    
    p = path + strlen(path) - 1;
    
    if (p != path && *p == '/') {
        *p-- = '\0';  /* remove tmp trailing slash */
    }
    
    while (p != path && *p == '/') {  /* remove any others */
        *p-- = '\0';
        tidied = 1;
    }
    
    while (!strncmp(path, "./", 2)) {
        for (p = path, s = path + 2; (*p++ = *s++););
        
        tidied = 1;
    }
    
    return tidied;
}


static int shorten_path(char *path, char *abspath) {
    static char dir[PATH_MAX];
    int shortened = 0;
    char *p;
    
    /* get rid of unnecessary "../dir" sequences */
    while (abspath && strlen(abspath) > 1 && (p = strstr(path, "../"))) {
        /* find innermost occurance of "../dir", and save "dir" */
        int slashes = 2;
        char *a, *s, *d = dir;
        
        while ((s = strstr(p + 3, "../"))) {
            ++slashes;
            p = s;
        }
        
        s = p + 3;
        *d++ = '/';
        
        while (*s && *s != '/') {
            *d++ = *s++;
        }
        
        *d++ = '/';
        *d = '\0';
        
        if (!strcmp(dir, "//")) {
            break;
        }
        
        /* note: p still points at ../dir */
        if (*s != '/' || !*++s) {
            break;
        }
        
        a = abspath + strlen(abspath) - 1;
        
        while (slashes-- > 0) {
            if (a <= abspath) {
                goto ughh;
            }
            
            while (*--a != '/') {
                if (a <= abspath) {
                    goto ughh;
                }
            }
        }
        
        if (strncmp(dir, a, strlen(dir))) {
            break;
        }
        
        while ((*p++ = *s++));  /* delete the ../dir */
        
        shortened = 1;
    }
    
ughh:
    return shortened;
}


static void fix_symlink(char *path, dev_t my_dev) {
    static char lpath[PATH_MAX], new[PATH_MAX], abspath[PATH_MAX];
    char *p, *np, *lp, *tail, *msg;
    struct stat stbuf, lstbuf;
    int fix_abs = 0, fix_messy = 0, fix_long = 0;
    size_t c;
    
    if ((c = readlink(path, lpath, sizeof(lpath))) == -1) {
        perror(path);
        return;
    }
    
    lpath[c] = '\0';  /* readlink does not null terminate it */
    /* construct the absolute address of the link */
    abspath[0] = '\0';
    
    if (lpath[0] != '/') {
        strcat(abspath, path);
        c = strlen(abspath);
        
        if ((c > 0) && (abspath[c - 1] == '/')) {
            abspath[c - 1] = '\0';    /* cut trailing / */
        }
        
        if ((p = strrchr(abspath, '/')) != NULL) {
            *p = '\0';    /* cut last component */
        }
        
        strcat(abspath, "/");
    }
    
    strcat(abspath, lpath);
    (void) tidy_path(abspath);
    
    /* check for various things */
    if (stat(abspath, &stbuf) == -1) {
        printf("dangling: %s -> %s\n", path, lpath);
        
        if (delete) {
            if (unlink(path)) {
                perror(path);
            } else {
                printf("deleted:  %s -> %s\n", path, lpath);
            }
        }
        
        return;
    }
    
    if (single_fs) {
        lstat(abspath, &lstbuf);  /* if the above didn't fail, then this shouldn't */
    }
    
    if (single_fs && lstbuf.st_dev != my_dev) {
        msg = "other_fs:";
    } else if (lpath[0] == '/') {
        msg = "absolute:";
        fix_abs = 1;
    } else if (verbose) {
        msg = "relative:";
    } else {
        msg = NULL;
    }
    
    fix_messy = tidy_path(strcpy(new, lpath));
    
    if (shorten) {
        fix_long = shorten_path(new, path);
    }
    
    if (!fix_abs) {
        if (fix_messy) {
            msg = "messy:   ";
        } else if (fix_long) {
            msg = "lengthy: ";
        }
    }
    
    if (msg != NULL) {
        printf("%s %s -> %s\n", msg, path, lpath);
    }
    
    if (!(fix_links || testing) || !(fix_messy || fix_abs || fix_long)) {
        return;
    }
    
    if (fix_abs) {
        /* convert an absolute link to relative: */
        /* point tail at first part of lpath that differs from path */
        /* point p    at first part of path  that differs from lpath */
        (void) tidy_path(lpath);
        tail = lp = lpath;
        p = path;
        
        while (*p && (*p == *lp)) {
            if (*lp++ == '/') {
                tail = lp;
                
                while (*++p == '/');
            }
        }
        
        /* now create new, with "../"s followed by tail */
        np = new;
        
        while (*p) {
            if (*p++ == '/') {
                *np++ = '.';
                *np++ = '.';
                *np++ = '/';
                
                while (*p == '/') {
                    ++p;
                }
            }
        }
        
        strcpy(np, tail);
        (void) tidy_path(new);
        
        if (shorten) {
            (void) shorten_path(new, path);
        }
    }
    
    shorten_path(new, path);
    
    if (!testing) {
        if (unlink(path)) {
            perror(path);
            return;
        }
        
        if (symlink(new, path)) {
            perror(path);
            return;
        }
    }
    
    printf("changed:  %s -> %s\n", path, new);
}

static void dirwalk(char *path, unsigned long pathlen, dev_t dev) {
    char *name;
    DIR *dfd;
    static struct stat st;
    static struct dirent *dp;
    
    if ((dfd = opendir(path)) == NULL) {
        perror(path);
        return;
    }
    
    name = path + pathlen;
    
    if (*(name - 1) != '/') {
        *name++ = '/';
    }
    
    while ((dp = readdir(dfd)) != NULL) {
        strcpy(name, dp->d_name);
        
        if (strcmp(name, ".") && strcmp(name, "..")) {
            if (lstat(path, &st) == -1) {
                perror(path);
            } else if (st.st_dev == dev) {
                if (S_ISLNK(st.st_mode)) {
                    fix_symlink(path, dev);
                } else if (recurse && S_ISDIR(st.st_mode)) {
                    dirwalk(path, strlen(path), dev);
                }
            }
        }
    }
    
    closedir(dfd);
    path[pathlen] = '\0';
}

static void usage_error(void) {
    fprintf(stderr, progver, progname);
    fprintf(stderr, "Usage:\t%s [-cdorstv] dirlist\n\n", progname);
    fprintf(stderr, "Flags:"
            "\t-c  change absolute/messy links to relative\n"
            "\t-d  delete dangling links\n"
            "\t-o  warn about links across file systems\n"
            "\t-r  recurse into subdirs\n"
            "\t-s  shorten lengthy links (displayed in output only when -c not specified)\n"
            "\t-t  show what would be done by -c\n"
            "\t-v  verbose (show all symlinks)\n\n");
    exit(1);
}

int main(int argc, char **argv) {
    static char path[PATH_MAX + 2], cwd[PATH_MAX + 2];
    int dircount = 0;
    char c, *p;
    
    if ((progname = (char *) strrchr(*argv, '/')) == NULL) {
        progname = *argv;
    } else {
        progname++;
    }
    
    if (NULL == getcwd(cwd, PATH_MAX)) {
        fprintf(stderr, "getcwd() failed\n");
        exit(1);
    }
    
    if (!*cwd || cwd[strlen(cwd) - 1] != '/') {
        strcat(cwd, "/");
    }
    
    while (--argc) {
        p = *++argv;
        
        if (*p == '-') {
            if (*++p == '\0') {
                usage_error();
            }
            
            while ((c = *p++)) {
                if (c == 'c') { fix_links = 1;
                } else if (c == 'd') { delete    = 1;
                } else if (c == 'o') { single_fs = 0;
                } else if (c == 'r') { recurse   = 1;
                } else if (c == 's') { shorten   = 1;
                } else if (c == 't') { testing   = 1;
                } else if (c == 'v') { verbose   = 1;
                } else {
                    usage_error();
                }
            }
        } else {
            struct stat st;
            
            if (*p == '/') {
                *path = '\0';
            } else {
                strcpy(path, cwd);
            }
            
            tidy_path(strcat(path, p));
            
            if (lstat(path, &st) == -1) {
                perror(path);
            } else {
                dirwalk(path, strlen(path), st.st_dev);
            }
            
            ++dircount;
        }
    }
    
    if (dircount == 0) {
        usage_error();
    }
    
    exit(0);
}