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

// Removes new line from string
char *remove_nl(char *p) {
    char *nl = strchr( p, '\n' );
    if (nl)
        *nl = 0;
    memset(nl, 0, sizeof nl);
    return p;
}

// Checks for env variables in string and set them if found
int set_evar(char *evar) {
    char *end_evar;
    char *value;
    char *key;

    key = strtok_r(evar, "=", &end_evar);
    value = strtok_r(NULL, "=", &end_evar);

    setenv(key, value, 1);

    memset(evar, 0, sizeof evar);
    memset(end_evar, 0, sizeof end_evar);
    memset(key, 0, sizeof key);
    memset(value, 0, sizeof value);

    return 0;
}

// Displays basic shell prompt
int display_prompt() {
    char hostname[1024];
    char cwd[1024];
    char *username_p;

    gethostname(hostname, 1024);
    username_p = getenv("USER");
    getcwd(cwd, 1024);

    printf("[%s@%s %s] $ ", hostname, username_p, cwd);

    // Flush memory
    memset(hostname, 0, sizeof hostname);
    memset(cwd, 0, sizeof cwd);

    return 0;
}

// Commands
int my_exit(char *param_list[64]) {
    if (param_list[0] != NULL) {
        exit( (int)strtol(param_list[0], NULL, 0) );
    } else {
        exit(0);
    }
}

int my_cd(char *param_list[64]) {
    if (param_list[0] != NULL) {
        if (chdir(param_list[0]) == -1) {
            printf("cd: %s: %s\n", param_list[0], strerror(errno));
            return 1;
        }
    }

    return 0;
}

int my_kill(char *param_list[64]) {
    if (param_list[0] != NULL) {
        int process_pid = (int)strtol(param_list[0], NULL, 0);

        if (process_pid > 0) {
            if (kill(process_pid, SIGKILL) == -1) {
                printf("kill: %s\n", strerror(errno));
                memset(&process_pid, 0, sizeof process_pid);
                return 1;
            } else {
                printf("kill: Killing process %d", process_pid);
                memset(&process_pid, 0, sizeof process_pid);
                return 0;
            }
        } else {
            printf("kill: Invalid PID: %s\n" , param_list[0]);
            memset(&process_pid, 0, sizeof process_pid);
            return 1;
        }
    } else {
        printf("Please specify PID\n");
        return 1;
    }
}

// Allows you to run subshell
int my_myshell() {
    pid_t child_pid;
    child_pid = fork();

    if (child_pid != 0) {
        waitpid(child_pid, NULL, 0); //Wait for child
    }
}

int main() {
    char input[1024];
    char *input_p;
    char *param_p;
    char *command_p;
    char *param_list[64];
    char evar[256];
    pid_t child_pid;

    while (1) {
        evar[0] = '\0';
        display_prompt();

        fgets(input, 1024, stdin);

        input_p = input;
        input_p = remove_nl(input_p);

        command_p = strtok(input_p, " ");

        if (command_p != NULL) {
            if (strchr(command_p, '=') != NULL) {
                strcpy(evar, command_p);
                command_p = strtok(NULL, " ");
            }

            if (!command_p || !command_p[0]) {
                if (evar[0]  != '\0') {
                    set_evar(evar);
                }
            } else {
                param_p = strtok(NULL, " ");

                int i = 0;
                do {
                    param_list[i] = param_p;
                    param_p = strtok(NULL, " ");
                    i=i+1;
                } while(param_p != NULL);
                memset(&i, 0, sizeof i);

                if (strcmp(command_p, "exit") == 0) {
                    my_exit(param_list);
                } else if (strcmp(command_p, "cd") == 0) {
                    my_cd(param_list);
                } else if (strcmp(command_p, "kill") == 0)  {
                    my_kill(param_list);
                } else if (strcmp(command_p, "myshell") == 0) {
                    my_myshell();
                } else if (strcmp(command_p, "help") == 0) {
                    printf(" MyShell is Bash-like shell written in C\n");
                    printf(" Available commands: cd, kill, myshell, help, version, exit\n");
                } else if (strcmp(command_p, "version") == 0) {
                    printf(" Version: 0.0.1\n Author: Kamil Sowińśki\n");
                } else {
                    child_pid = fork();
                    if (child_pid == 0) {
                        char *args[66];
                        int i = 1;
                        int param_list_s = sizeof(param_list) / sizeof(param_list[0]);

                        if (evar[0]  != '\0') {
                            set_evar(evar);
                        }

                        args[0] = command_p;
                        while (i < param_list_s) {
                            args[i] = param_list[i - 1];
                            i++;
                        }
                        args[i] = NULL;
                        memset(&i, 0, sizeof i);

                        if (execvp(command_p, args) == -1) {
                            printf("%s: command not found\n", command_p);
                            exit(1);
                        }

                        memset(args, 0, sizeof args);
                    } else {
                        waitpid(child_pid, NULL, 0); //Wait for child
                    }
                    memset(command_p, 0, sizeof command_p);
                }
            }
        }

        // Fush memory
        memset(param_list, 0, sizeof param_list);
        memset(input, 0, sizeof input);
        memset(input_p, 0, sizeof input_p);
    }
}