// ============================================
// Final-Projekt: Todo-App in C
// Ein vollständiges CLI-Programm mit CRUD-Operationen
// ============================================

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <time.h>

#define MAX_TODOS 100
#define MAX_TITLE 100
#define MAX_DESC 500
#define DATA_FILE "todos.dat"

// Datenstruktur für ein Todo
typedef struct {
    int id;
    char title[MAX_TITLE];
    char description[MAX_DESC];
    bool completed;
    time_t created_at;
} Todo;

// Datenstruktur für die Todo-Liste
typedef struct {
    Todo items[MAX_TODOS];
    int count;
} TodoList;

// Funktionsprototypen
void todo_init(TodoList* list);
void todo_add(TodoList* list, const char* title, const char* description);
void todo_list(const TodoList* list);
void todo_complete(TodoList* list, int id);
void todo_delete(TodoList* list, int id);
void todo_save(const TodoList* list);
void todo_load(TodoList* list);
void print_menu(void);
void clear_input_buffer(void);

// ============================================
// IMPLEMENTATION
// ============================================

void todo_init(TodoList* list) {
    list->count = 0;
    for (int i = 0; i < MAX_TODOS; i++) {
        list->items[i].id = 0;
        list->items[i].title[0] = '\0';
        list->items[i].description[0] = '\0';
        list->items[i].completed = false;
        list->items[i].created_at = 0;
    }
}

void todo_add(TodoList* list, const char* title, const char* description) {
    if (list->count >= MAX_TODOS) {
        printf("Fehler: Maximale Anzahl erreicht!\n");
        return;
    }
    
    Todo* new_todo = &list->items[list->count];
    new_todo->id = list->count + 1;
    strncpy(new_todo->title, title, MAX_TITLE - 1);
    new_todo->title[MAX_TITLE - 1] = '\0';
    strncpy(new_todo->description, description, MAX_DESC - 1);
    new_todo->description[MAX_DESC - 1] = '\0';
    new_todo->completed = false;
    new_todo->created_at = time(NULL);
    
    list->count++;
    printf("Todo #%d hinzugefügt!\n", new_todo->id);
}

void todo_list(const TodoList* list) {
    if (list->count == 0) {
        printf("Keine Todos vorhanden.\n");
        return;
    }
    
    printf("\n=== DEINE TODOS ===\n");
    printf("%-4s | %-10s | %-30s | %-20s\n", "ID", "Status", "Titel", "Erstellt");
    printf("-----+------------+--------------------------------+--------------------\n");
    
    for (int i = 0; i < list->count; i++) {
        const Todo* todo = &list->items[i];
        char date_str[26];
        ctime_r(&todo->created_at, date_str);
        date_str[24] = '\0';  // Remove newline
        
        const char* status = todo->completed ? "[✓] Done   " : "[ ] Open   ";
        printf("%-4d | %s | %-30s | %.20s\n", 
               todo->id, status, todo->title, date_str);
        
        if (strlen(todo->description) > 0) {
            printf("     |            | %s\n", todo->description);
        }
    }
    printf("\n");
}

void todo_complete(TodoList* list, int id) {
    for (int i = 0; i < list->count; i++) {
        if (list->items[i].id == id) {
            list->items[i].completed = !list->items[i].completed;
            printf("Todo #%d %s!\n", id, 
                   list->items[i].completed ? "abgeschlossen" : "wieder geöffnet");
            return;
        }
    }
    printf("Fehler: Todo #%d nicht gefunden!\n", id);
}

void todo_delete(TodoList* list, int id) {
    int found_index = -1;
    
    for (int i = 0; i < list->count; i++) {
        if (list->items[i].id == id) {
            found_index = i;
            break;
        }
    }
    
    if (found_index == -1) {
        printf("Fehler: Todo #%d nicht gefunden!\n", id);
        return;
    }
    
    // Array komprimieren
    for (int i = found_index; i < list->count - 1; i++) {
        list->items[i] = list->items[i + 1];
        list->items[i].id = i + 1;  // ID neu zuweisen
    }
    
    list->count--;
    printf("Todo #%d gelöscht!\n", id);
}

void todo_save(const TodoList* list) {
    FILE* file = fopen(DATA_FILE, "wb");
    if (!file) {
        printf("Fehler: Konnte Datei nicht öffnen!\n");
        return;
    }
    
    fwrite(&list->count, sizeof(int), 1, file);
    fwrite(list->items, sizeof(Todo), list->count, file);
    
    fclose(file);
    printf("Todos gespeichert!\n");
}

void todo_load(TodoList* list) {
    FILE* file = fopen(DATA_FILE, "rb");
    if (!file) {
        printf("Keine gespeicherte Daten gefunden. Starte neu...\n");
        return;
    }
    
    fread(&list->count, sizeof(int), 1, file);
    fread(list->items, sizeof(Todo), list->count, file);
    
    fclose(file);
    printf("%d Todos geladen!\n", list->count);
}

void print_menu(void) {
    printf("\n=== TODO-APP ===\n");
    printf("1. Todo hinzufügen\n");
    printf("2. Todos anzeigen\n");
    printf("3. Todo abschließen/öffnen\n");
    printf("4. Todo löschen\n");
    printf("5. Speichern\n");
    printf("6. Beenden\n");
    printf("Wahl: ");
}

void clear_input_buffer(void) {
    int c;
    while ((c = getchar()) != '\n' && c != EOF);
}

// ============================================
// HAUPTPROGRAMM
// ============================================
int main(void) {
    TodoList list;
    todo_init(&list);
    todo_load(&list);
    
    int choice;
    char title[MAX_TITLE];
    char description[MAX_DESC];
    int id;
    
    printf("\n📝 Willkommen zur Todo-App!\n");
    
    while (true) {
        print_menu();
        
        if (scanf("%d", &choice) != 1) {
            clear_input_buffer();
            printf("Ungültige Eingabe!\n");
            continue;
        }
        clear_input_buffer();
        
        switch (choice) {
            case 1:
                printf("Titel: ");
                fgets(title, MAX_TITLE, stdin);
                title[strcspn(title, "\n")] = '\0';  // Remove newline
                
                printf("Beschreibung (optional): ");
                fgets(description, MAX_DESC, stdin);
                description[strcspn(description, "\n")] = '\0';
                
                todo_add(&list, title, description);
                break;
                
            case 2:
                todo_list(&list);
                break;
                
            case 3:
                printf("Todo-ID: ");
                if (scanf("%d", &id) == 1) {
                    todo_complete(&list, id);
                }
                clear_input_buffer();
                break;
                
            case 4:
                printf("Todo-ID: ");
                if (scanf("%d", &id) == 1) {
                    todo_delete(&list, id);
                }
                clear_input_buffer();
                break;
                
            case 5:
                todo_save(&list);
                break;
                
            case 6:
                printf("Speichern vor Beenden? (j/n): ");
                char save_choice;
                scanf(" %c", &save_choice);
                if (save_choice == 'j' || save_choice == 'J') {
                    todo_save(&list);
                }
                printf("Auf Wiedersehen!\n");
                return 0;
                
            default:
                printf("Ungültige Wahl!\n");
        }
    }
    
    return 0;
}