/* mini man implementation for busybox
 * Copyright (C) 2008 Denys Vlasenko <vda.linux@googlemail.com>
 * Licensed under GPLv2, see file LICENSE in this source tree.
 */
//config:config MAN
//config:       bool "man (26 kb)"
//config:       default y
//config:       help
//config:       Format and display manual pages.

//applet:IF_MAN(APPLET(man, BB_DIR_USR_BIN, BB_SUID_DROP))

//kbuild:lib-$(CONFIG_MAN) += man.o

//usage:#define man_trivial_usage
//usage:       "[-aw] [SECTION] MANPAGE[.SECTION]..."
//usage:#define man_full_usage "\n\n"
//usage:       "Display manual page\n"
//usage:     "\n        -a      Display all pages"
//usage:     "\n        -w      Show page locations"
//usage:     "\n"
//usage:     "\n$COLUMNS overrides output width"

#include "libbb.h"
#include "common_bufsiz.h"

enum {
        OPT_a = 1, /* all */
        OPT_w = 2, /* print path */
};

/* This is what I see on my desktop system being executed:
(
echo ".ll 12.4i"
echo ".nr LL 12.4i"
echo ".pl 1100i"
gunzip -c '/usr/man/man1/bzip2.1.gz'
echo ".\\\""
echo ".pl \n(nlu+10"
) | gtbl | nroff -Tlatin1 -mandoc | less

Some systems use -Tascii.

On another system I see this:

... | tbl | nroff -mandoc -rLL=<NNN>n -rLT=<NNN>n -Tutf8 | less

where <NNN> is screen width minus 5.
Replacing "DEFINE nroff nroff -mandoc" in /etc/man_db.conf
changes "nroff -mandoc" part; -rLL=<NNN>n, -rLT=<NNN>n and -Tutf8 parts are
appended to the user-specified command.

Redirecting to a pipe or file sets GROFF_NO_SGR=1 to prevent color escapes,
and uses "col -b -p -x" instead of pager, this filters out backspace
and underscore tricks.
*/

struct globals {
        const char *col;
        const char *tbl;
        const char *nroff;
        const char *pager;
} FIX_ALIASING;
#define G (*(struct globals*)bb_common_bufsiz1)
#define INIT_G() do { \
        setup_common_bufsiz(); \
        G.col = "col"; \
        G.tbl = "tbl"; \
        /* Removed -Tlatin1. Assuming system nroff has suitable default */ \
        G.nroff = "nroff -mandoc"; \
        G.pager = ENABLE_LESS ? "less" : "more"; \
} while (0)

static int show_manpage(char *man_filename, int man, int level);

static int run_pipe(char *man_filename, int man, int level)
{
        char *cmd;

        /* Prevent man page link loops */
        if (level > 10)
                return 0;

        if (access(man_filename, R_OK) != 0)
                return 0;

        if (option_mask32 & OPT_w) {
                puts(man_filename);
                return 1;
        }

        if (man) { /* man page, not cat page */
                /* Is this a link to another manpage? */
                /* The link has the following on the first line: */
                /* ".so another_man_page" */

                struct stat sb;
                char *line;
                char *linkname, *p;

                /* On my system:
                 * man1/genhostid.1.gz: 203 bytes - smallest real manpage
                 * man2/path_resolution.2.gz: 114 bytes - largest link
                 */
                xstat(man_filename, &sb);
                if (sb.st_size > 300) /* err on the safe side */
                        goto ordinary_manpage;

                line = xmalloc_open_zipped_read_close(man_filename, NULL);
                if (!line || !is_prefixed_with(line, ".so ")) {
                        free(line);
                        goto ordinary_manpage;
                }
                /* Example: man2/path_resolution.2.gz contains
                 * ".so man7/path_resolution.7\n<junk>"
                 */
                *strchrnul(line, '\n') = '\0';
                linkname = skip_whitespace(&line[4]);

                /* If link has no slashes, we just replace man page name.
                 * If link has slashes (however many), we go back *once*.
                 * ".so zzz/ggg/page.3" does NOT go back two levels. */
                p = strrchr(man_filename, '/');
                if (!p)
                        goto ordinary_manpage;
                *p = '\0';
                if (strchr(linkname, '/')) {
                        p = strrchr(man_filename, '/');
                        if (!p)
                                goto ordinary_manpage;
                        *p = '\0';
                }

                /* Links do not have .gz extensions, even if manpage
                 * is compressed */
                man_filename = xasprintf("%s/%s", man_filename, linkname);
                free(line);
                /* Note: we leak "new" man_filename string as well... */
                if (show_manpage(man_filename, man, level + 1))
                        return 1;
                /* else: show the link, it's better than nothing */
        }

 ordinary_manpage:
        close(STDIN_FILENO);
        open_zipped(man_filename, /*fail_if_not_compressed:*/ 0); /* guaranteed to use fd 0 (STDIN_FILENO) */
        if (man) {
                int w = get_terminal_width(-1);
                if (w > 10)
                        w -= 2;
                /* "2>&1" is added so that nroff errors are shown in pager too.
                 * Otherwise it may show just empty screen.
                 */
                cmd = xasprintf("%s | %s -rLL=%un -rLT=%un 2>&1 | %s",
                                G.tbl, G.nroff, w, w,
                                G.pager);
        } else {
                cmd = xstrdup(G.pager);
        }
        system(cmd);
        free(cmd);
        return 1;
}

/* man_filename is of the form "/dir/dir/dir/name.s" */
static int show_manpage(char *man_filename, int man, int level)
{
#if SEAMLESS_COMPRESSION
        /* We leak this allocation... */
        char *filename_with_zext = xasprintf("%s.lzma", man_filename);
        char *ext = strrchr(filename_with_zext, '.') + 1;
#endif

#if ENABLE_FEATURE_SEAMLESS_LZMA
        if (run_pipe(filename_with_zext, man, level))
                return 1;
#endif
#if ENABLE_FEATURE_SEAMLESS_XZ
        strcpy(ext, "xz");
        if (run_pipe(filename_with_zext, man, level))
                return 1;
#endif
#if ENABLE_FEATURE_SEAMLESS_BZ2
        strcpy(ext, "bz2");
        if (run_pipe(filename_with_zext, man, level))
                return 1;
#endif
#if ENABLE_FEATURE_SEAMLESS_GZ
        strcpy(ext, "gz");
        if (run_pipe(filename_with_zext, man, level))
                return 1;
#endif

        return run_pipe(man_filename, man, level);
}

static char **add_MANPATH(char **man_path_list, int *count_mp, char *path)
{
        if (path) while (*path) {
                char *next_path;
                char **path_element;

                next_path = strchr(path, ':');
                if (next_path) {
                        if (next_path == path) /* "::"? */
                                goto next;
                        *next_path = '\0';
                }
                /* Do we already have path? */
                path_element = man_path_list;
                if (path_element) while (*path_element) {
                        if (strcmp(*path_element, path) == 0) {
                                goto skip;
                        }
                        path_element++;
                }
                man_path_list = xrealloc_vector(man_path_list, 4, *count_mp);
                man_path_list[*count_mp] = xstrdup(path);
                (*count_mp)++;
                /* man_path_list is NULL terminated */
                /* man_path_list[*count_mp] = NULL; - xrealloc_vector did it */
 skip:
                if (!next_path)
                        break;
                /* "path" may be a result of getenv(), be nice and don't mangle it */
                *next_path = ':';
 next:
                path = next_path + 1;
        }
        return man_path_list;
}

static const char *if_redefined(const char *var, const char *key, const char *line)
{
        if (!is_prefixed_with(line, key))
                return var;
        line += strlen(key);
        if (!isspace(line[0]))
                return var;
        return xstrdup(skip_whitespace(line));
}

static int is_section_name(const char *sections, const char *str)
{
        const char *s = strstr(sections, str);
        if (s) {
                int l = strlen(str);
                return (s[l] == ':' || s[l] == '\0');
        }
        return 0;
}

int man_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int man_main(int argc UNUSED_PARAM, char **argv)
{
        parser_t *parser;
        char *conf_sec_list;
        char *sec_list;
        char **man_path_list;
        int count_mp;
        int opt, not_found;
        char *token[2];

        INIT_G();

        opt = getopt32(argv, "^+" "aw" "\0" "-1"/*at least one arg*/);
        argv += optind;

        conf_sec_list = xstrdup("0p:1:1p:2:3:3p:4:5:6:7:8:9");

        count_mp = 0;
        man_path_list = add_MANPATH(NULL, &count_mp,
                        getenv("MANDATORY_MANPATH"+10) /* "MANPATH" */
        );
        /* Parse man.conf[ig] or man_db.conf */
        /* man version 1.6f uses man.config */
        /* man-db implementation of man uses man_db.conf */
        parser = config_open2("/etc/man.config", fopen_for_read);
        if (!parser)
                parser = config_open2("/etc/man.conf", fopen_for_read);
        if (!parser)
                parser = config_open2("/etc/man_db.conf", fopen_for_read);

        while (config_read(parser, token, 2, 0, "# \t", PARSE_NORMAL)) {
                if (!token[1])
                        continue;
                if (strcmp("DEFINE", token[0]) == 0) {
                        G.col   = if_redefined(G.col  , "col",   token[1]);
                        G.tbl   = if_redefined(G.tbl  , "tbl",   token[1]);
                        G.nroff = if_redefined(G.nroff, "nroff", token[1]);
                        G.pager = if_redefined(G.pager, "pager", token[1]);
                } else
                if (strcmp("MANDATORY_MANPATH"+10, token[0]) == 0 /* "MANPATH"? */
                 || strcmp("MANDATORY_MANPATH", token[0]) == 0
                ) {
                        man_path_list = add_MANPATH(man_path_list, &count_mp, token[1]);
                }
                if (strcmp("MANSECT", token[0]) == 0) {
                        free(conf_sec_list);
                        conf_sec_list = xstrdup(token[1]);
                }
        }
        config_close(parser);

        if (!man_path_list) {
                static const char *const mpl[] = { "/usr/man", "/usr/share/man", NULL };
                man_path_list = (char**)mpl;
                /*count_mp = 2; - not used below anyway */
        }

        {
                /* environment overrides setting from man.config */
                char *env_pager = getenv("MANPAGER");
                if (!env_pager)
                        env_pager = getenv("PAGER");
                if (env_pager)
                        G.pager = env_pager;
        }

        if (!isatty(STDOUT_FILENO)) {
                putenv((char*)"GROFF_NO_SGR=1");
                G.pager = xasprintf("%s -b -p -x", G.col);
        }

        /* is 1st ARG a SECTION? */
        sec_list = conf_sec_list;
        if (is_section_name(conf_sec_list, *argv) && argv[1]) {
                /* yes */
                sec_list = *argv++;
        }

        not_found = 0;
        do { /* for each argv[] */
                const char *cur_path;
                int cur_mp;
                int found = 0;

                if (strchr(*argv, '/')) {
                        found = show_manpage(*argv, /*man:*/ 1, 0);
                        goto check_found;
                }

                /* for each MANPATH */
                cur_mp = 0;
                while ((cur_path = man_path_list[cur_mp++]) != NULL) {
                        const char *cur_sect = sec_list;

                        /* is MANPAGE of the form NAME.SECTION? */
                        char *sect_ext = strrchr(*argv, '.');
                        if (sect_ext && is_section_name(conf_sec_list, sect_ext + 1)) {
                                *sect_ext = '\0';
                                cur_sect = sect_ext + 1;
                        }

                        do { /* for each SECTION in cur_sect */
                                char *next_sect = strchrnul(cur_sect, ':');
                                int sect_len = next_sect - cur_sect;
                                char *man_filename;
                                int cat0man1 = 0;

                                /* Search for cat, then man page */
                                while (cat0man1 < 2) {
                                        int found_here;
                                        man_filename = xasprintf("%s/%s%.*s/%s.%.*s",
                                                        cur_path,
                                                        "cat\0man" + (cat0man1 * 4),
                                                        sect_len, cur_sect,
                                                        *argv,
                                                        sect_len, cur_sect);
                                        found_here = show_manpage(man_filename, cat0man1, 0);
                                        found |= found_here;
                                        cat0man1 += found_here + 1;
                                        free(man_filename);
                                }

                                if (found && !(opt & OPT_a))
                                        goto next_arg;
                                cur_sect = next_sect;
                                while (*cur_sect == ':')
                                        cur_sect++;
                        } while (*cur_sect);

                        if (sect_ext) *sect_ext = '.';
                }
 check_found:
                if (!found) {
                        bb_error_msg("no manual entry for '%s'", *argv);
                        not_found = 1;
                }
 next_arg:
                argv++;
        } while (*argv);

        return not_found;
}