#include <luna/StringBuilder.h>
#include <luna/Vector.h>

#include <errno.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <unistd.h>

static Result<Vector<char*>> split_command_into_argv(const char* cmd)
{
    char* str = strdup(cmd);

    Vector<char*> result;

    char* segment = strtok(str, " \n");
    TRY(result.try_append(segment));

    if (segment == NULL) return result;

    for (;;)
    {
        segment = strtok(NULL, " \n");
        TRY(result.try_append(segment));

        if (segment == NULL) return result;
    }

    return result;
}

static Result<String> join_path(const char* str1, const char* str2)
{
    StringBuilder sb;
    TRY(sb.add(StringView { str1 }));
    TRY(sb.add(StringView { str2 }));
    return sb.string();
}

static int execute_in_path(const char* dir, char** argv)
{
    String path;
    bool ok = join_path(dir, argv[0]).try_move_value_or_error(path, errno);
    if (!ok) return -1;

    int err = errno;

    int status = execv(path.chars(), argv);

    if (errno == ENOENT)
    {
        errno = err;
        return 0;
    }

    return status;
}

static int sh_execvp(char** argv)
{
    if (strchr(argv[0], '/'))
    {
        // Relative paths do not need path resolution.
        return execv(argv[0], argv);
    }

    if (execute_in_path("/bin/", argv) != 0) return -1;
    if (execute_in_path("/sbin/", argv) != 0) return -1;
    if (execute_in_path("/usr/bin/", argv) != 0) return -1;
    if (execute_in_path("/usr/local/bin/", argv) != 0) return -1;

    errno = ENOENT;
    return -1;
}

int main()
{
    while (1)
    {
        fputs("sh$ ", stdout);

        char command[4096];
        char* rc = fgets(command, sizeof(command), stdin);
        if (!rc) return 0;

        if (strspn(command, " \n") == strlen(command)) continue;

        pid_t child = fork();
        if (child < 0)
        {
            perror("fork");
            return 1;
        }

        if (child == 0)
        {
            Vector<char*> argv;
            bool ok = split_command_into_argv(command).try_move_value_or_error(argv, errno);
            if (!ok)
            {
                perror("failed to parse command");
                return 1;
            }

            if (argv[0] == NULL) return 0;
            sh_execvp(argv.data());
            perror(argv[0]);
            return 1;
        }

        if (waitpid(child, NULL, 0) < 0)
        {
            perror("waitpid");
            return 1;
        }
    }
}