#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <limits.h>
#include <stdarg.h>
#include <glob.h>

#ifndef PATH_MAX
# define PATH_MAX 4096
#endif

static const char git_usage[] =
        "Usage: git [--version] [--exec-path[=GIT_EXEC_PATH]] [--help] COMMAND [ ARGS ]";

struct string_list {
        size_t len;
        char *str;
        struct string_list *next;
};

/* most gui terms set COLUMNS (although some don't export it) */
static int term_columns(void)
{
        char *col_string = getenv("COLUMNS");
        int n_cols = 0;

        if (col_string && (n_cols = atoi(col_string)) > 0)
                return n_cols;

        return 80;
}

static inline void mput_char(char c, unsigned int num)
{
        while(num--)
                putchar(c);
}

static void pretty_print_string_list(struct string_list *list, int longest)
{
        int cols = 1;
        int space = longest + 1; /* min 1 SP between words */
        int max_cols = term_columns() - 1; /* don't print *on* the edge */

        if (space < max_cols)
                cols = max_cols / space;

        while (list) {
                int c;
                printf("  ");

                for (c = cols; c && list; list = list->next) {
                        printf("%s", list->str);

                        if (--c)
                                mput_char(' ', space - list->len);
                }
                putchar('\n');
        }
}

static void list_commands(const char *exec_path, const char *pattern)
{
        struct string_list *list = NULL, *tail = NULL;
        unsigned int longest = 0, i;
        glob_t gl;

        if (chdir(exec_path) < 0) {
                printf("git: '%s': %s\n", exec_path, strerror(errno));
                exit(1);
        }

        i = glob(pattern, 0, NULL, &gl);
        switch(i) {
        case GLOB_NOSPACE:
                puts("Out of memory when running glob()");
                exit(2);
        case GLOB_ABORTED:
                printf("'%s': Read error: %s\n", exec_path, strerror(errno));
                exit(2);
        case GLOB_NOMATCH:
                printf("No git commands available in '%s'.\n", exec_path);
                printf("Do you need to specify --exec-path or set GIT_EXEC_PATH?\n");
                exit(1);
        }

        for (i = 0; i < gl.gl_pathc; i++) {
                int len = strlen(gl.gl_pathv[i] + 4);

                if (access(gl.gl_pathv[i], X_OK))
                        continue;

                if (longest < len)
                        longest = len;

                if (!tail)
                        tail = list = malloc(sizeof(struct string_list));
                else {
                        tail->next = malloc(sizeof(struct string_list));
                        tail = tail->next;
                }
                tail->len = len;
                tail->str = gl.gl_pathv[i] + 4;
                tail->next = NULL;
        }

        printf("git commands available in '%s'\n", exec_path);
        printf("----------------------------");
        mput_char('-', strlen(exec_path));
        putchar('\n');
        pretty_print_string_list(list, longest);
        putchar('\n');
}

#ifdef __GNUC__
static void usage(const char *exec_path, const char *fmt, ...)
        __attribute__((__format__(__printf__, 2, 3), __noreturn__));
#endif
static void usage(const char *exec_path, const char *fmt, ...)
{
        if (fmt) {
                va_list ap;

                va_start(ap, fmt);
                printf("git: ");
                vprintf(fmt, ap);
                va_end(ap);
                putchar('\n');
        }
        else
                puts(git_usage);

        putchar('\n');

        if(exec_path)
                list_commands(exec_path, "git-*");

        exit(1);
}

static void prepend_to_path(const char *dir, int len)
{
        char *path, *old_path = getenv("PATH");
        int path_len = len;

        if (!old_path)
                old_path = "/bin:/usr/bin:.";

        path_len = len + strlen(old_path) + 1;

        path = malloc(path_len + 1);
        path[path_len + 1] = '\0';

        memcpy(path, dir, len);
        path[len] = ':';
        memcpy(path + len + 1, old_path, path_len - len);

        setenv("PATH", path, 1);
}

/* has anyone seen 'man' installed anywhere else than in /usr/bin? */
#define PATH_TO_MAN "/usr/bin/man"
static void show_man_page(char *git_cmd)
{
        char *page;

        if (!strncmp(git_cmd, "git", 3))
                page = git_cmd;
        else {
                int page_len = strlen(git_cmd) + 4;

                page = malloc(page_len + 1);
                strcpy(page, "git-");
                strcpy(page + 4, git_cmd);
                page[page_len] = 0;
        }

        execlp(PATH_TO_MAN, "man", page, NULL);
}

int main(int argc, char **argv, char **envp)
{
        char git_command[PATH_MAX + 1];
        char wd[PATH_MAX + 1];
        int i, len, show_help = 0;
        char *exec_path = getenv("GIT_EXEC_PATH");

        getcwd(wd, PATH_MAX);

        if (!exec_path)
                exec_path = GIT_EXEC_PATH;

        for (i = 1; i < argc; i++) {
                char *arg = argv[i];

                if (strncmp(arg, "--", 2))
                        break;

                arg += 2;

                if (!strncmp(arg, "exec-path", 9)) {
                        arg += 9;
                        if (*arg == '=')
                                exec_path = arg + 1;
                        else {
                                puts(exec_path);
                                exit(0);
                        }
                }
                else if (!strcmp(arg, "version")) {
                        printf("git version %s\n", GIT_VERSION);
                        exit(0);
                }
                else if (!strcmp(arg, "help"))
                        show_help = 1;
                else if (!show_help)
                        usage(NULL, NULL);
        }

        if (i >= argc || show_help) {
                if (i >= argc)
                        usage(exec_path, NULL);

                show_man_page(argv[i]);
        }

        /* allow relative paths, but run with exact */
        if (chdir(exec_path)) {
                printf("git: '%s': %s\n", exec_path, strerror(errno));
                exit (1);
        }

        getcwd(git_command, sizeof(git_command));
        chdir(wd);

        len = strlen(git_command);
        prepend_to_path(git_command, len);

        strncat(&git_command[len], "/git-", sizeof(git_command) - len);
        len += 5;
        strncat(&git_command[len], argv[i], sizeof(git_command) - len);

        if (access(git_command, X_OK))
                usage(exec_path, "'%s' is not a git-command", argv[i]);

        /* execve() can only ever return if it fails */
        execve(git_command, &argv[i], envp);
        printf("Failed to run command '%s': %s\n", git_command, strerror(errno));

        return 1;
}