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/*
 * Two-Level Directory Implementation
 * Demonstrates Master File Directory (MFD) and User File Directories (UFDs).
 */
 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
 
#define MAX_USERS 32
#define MAX_FILES_PER_USER 64
#define MAX_NAME_LENGTH 32
#define PATH_SEPARATOR '/'
 
/*
 * File entry in a User File Directory (UFD)
 */
typedef struct {
    char name[MAX_NAME_LENGTH];
    uint32_t size;
    uint32_t first_block;
    bool in_use;
} FileEntry;
 
/*
 * User File Directory (UFD)
 * Each user has one of these - it's essentially a single-level directory.
 */
typedef struct {
    char username[MAX_NAME_LENGTH];
    FileEntry files[MAX_FILES_PER_USER];
    int file_count;
    bool active;
} UserDirectory;
 
/*
 * Master File Directory (MFD)
 * The top-level directory containing all user directories.
 */
typedef struct {
    UserDirectory users[MAX_USERS];
    int user_count;
    char current_user[MAX_NAME_LENGTH];  /* Logged-in user context */
} MasterDirectory;
 
/* Global file system state */
static MasterDirectory g_mfd;
 
/*
 * Initialize the two-level directory system
 */
void init_directory_system(void) {
    memset(&g_mfd, 0, sizeof(MasterDirectory));
    printf("Two-level directory system initialized.\n");
    printf("Capacity: %d users, %d files per user.\n\n", 
           MAX_USERS, MAX_FILES_PER_USER);
}
 
/*
 * Find a user directory in the MFD
 * Returns: pointer to UserDirectory, or NULL if not found
 */
UserDirectory* find_user(const char *username) {
    for (int i = 0; i < MAX_USERS; i++) {
        if (g_mfd.users[i].active &&
            strcmp(g_mfd.users[i].username, username) == 0) {
            return &g_mfd.users[i];
        }
    }
    return NULL;
}
 
/*
 * Create a new user (add entry to MFD)
 */
bool create_user(const char *username) {
    /* Check if user already exists */
    if (find_user(username) != NULL) {
        printf("ERROR: User '%s' already exists.\n", username);
        return false;
    }
    
    /* Find empty slot in MFD */
    for (int i = 0; i < MAX_USERS; i++) {
        if (!g_mfd.users[i].active) {
            strncpy(g_mfd.users[i].username, username, MAX_NAME_LENGTH - 1);
            g_mfd.users[i].active = true;
            g_mfd.users[i].file_count = 0;
            g_mfd.user_count++;
            printf("Created user '%s' with empty UFD.\n", username);
            return true;
        }
    }
    
    printf("ERROR: Maximum users reached.\n");
    return false;
}
 
/*
 * Set current user context (simulates login)
 */
void login_user(const char *username) {
    if (find_user(username) == NULL) {
        printf("ERROR: User '%s' does not exist.\n", username);
        return;
    }
    strncpy(g_mfd.current_user, username, MAX_NAME_LENGTH - 1);
    printf("Current user set to '%s'.\n", username);
}
 
/*
 * Parse a path into (user, filename) components.
 * If no user specified, uses current_user.
 * 
 * Examples:
 *   "budget.txt"      -> (current_user, "budget.txt")
 *   "alice/budget.txt" -> ("alice", "budget.txt")
 */
bool parse_path(const char *path, char *user_out, char *file_out) {
    const char *separator = strchr(path, PATH_SEPARATOR);
    
    if (separator == NULL) {
        /* No separator - use current user */
        if (strlen(g_mfd.current_user) == 0) {
            printf("ERROR: No current user context.\n");
            return false;
        }
        strncpy(user_out, g_mfd.current_user, MAX_NAME_LENGTH - 1);
        strncpy(file_out, path, MAX_NAME_LENGTH - 1);
    } else {
        /* Extract user and filename from path */
        size_t user_len = separator - path;
        if (user_len >= MAX_NAME_LENGTH) {
            printf("ERROR: Username too long.\n");
            return false;
        }
        strncpy(user_out, path, user_len);
        user_out[user_len] = '\0';
        strncpy(file_out, separator + 1, MAX_NAME_LENGTH - 1);
    }
    
    return true;
}
 
/*
 * Create a file in the two-level directory.
 * Path can be "filename" (uses current user) or "user/filename".
 */
bool create_file(const char *path, uint32_t size) {
    char username[MAX_NAME_LENGTH] = {0};
    char filename[MAX_NAME_LENGTH] = {0};
    
    if (!parse_path(path, username, filename)) {
        return false;
    }
    
    /* Find user's directory */
    UserDirectory *ufd = find_user(username);
    if (ufd == NULL) {
        printf("ERROR: User '%s' does not exist.\n", username);
        return false;
    }
    
    /* Check for duplicate filename within this user's directory */
    for (int i = 0; i < MAX_FILES_PER_USER; i++) {
        if (ufd->files[i].in_use &&
            strcmp(ufd->files[i].name, filename) == 0) {
            printf("ERROR: File '%s' already exists in %s's directory.\n",
                   filename, username);
            return false;
        }
    }
    
    /* Find empty slot in user's directory */
    for (int i = 0; i < MAX_FILES_PER_USER; i++) {
        if (!ufd->files[i].in_use) {
            strncpy(ufd->files[i].name, filename, MAX_NAME_LENGTH - 1);
            ufd->files[i].size = size;
            ufd->files[i].in_use = true;
            ufd->file_count++;
            
            printf("Created '%s/%s' (%u bytes).\n", 
                   username, filename, size);
            return true;
        }
    }
    
    printf("ERROR: User '%s' directory is full.\n", username);
    return false;
}
 
/*
 * List files - either for current user or all users
 */
void list_files(bool all_users) {
    printf("\n========== FILE LISTING ==========\n");
    
    if (all_users) {
        /* List all users and their files */
        for (int u = 0; u < MAX_USERS; u++) {
            if (!g_mfd.users[u].active) continue;
            
            UserDirectory *ufd = &g_mfd.users[u];
            printf("\n[%s/] (%d files)\n", ufd->username, ufd->file_count);
            
            for (int f = 0; f < MAX_FILES_PER_USER; f++) {
                if (ufd->files[f].in_use) {
                    printf("  ├── %s (%u bytes)\n", 
                           ufd->files[f].name, ufd->files[f].size);
                }
            }
        }
    } else {
        /* List only current user's files */
        UserDirectory *ufd = find_user(g_mfd.current_user);
        if (ufd == NULL) {
            printf("No current user context.\n");
            return;
        }
        
        printf("\nFiles for user '%s':\n", g_mfd.current_user);
        for (int f = 0; f < MAX_FILES_PER_USER; f++) {
            if (ufd->files[f].in_use) {
                printf("  %s (%u bytes)\n", 
                       ufd->files[f].name, ufd->files[f].size);
            }
        }
    }
    
    printf("\n===================================\n");
}
 
/*
 * Demonstrate the key benefit: multiple users can have same filename
 */
void demonstrate_namespace_isolation(void) {
    printf("\n=== Namespace Isolation Demo ===\n\n");
    
    /* Create users */
    create_user("alice");
    create_user("bob");
    create_user("carol");
    
    /* Each user creates their own budget.txt - NO CONFLICT! */
    login_user("alice");
    create_file("budget.txt", 1024);      /* Creates alice/budget.txt */
    create_file("report.doc", 2048);
    
    login_user("bob");
    create_file("budget.txt", 512);       /* Creates bob/budget.txt */
    create_file("notes.txt", 256);
    
    login_user("carol");
    create_file("budget.txt", 768);       /* Creates carol/budget.txt */
    
    printf("\nNotice: Three users all have 'budget.txt' - no conflict!\n");
    
    list_files(true);  /* Show all users */
}
 
/*
 * Demonstrate cross-user file access
 */
void demonstrate_cross_user_access(void) {
    printf("\n=== Cross-User Access Demo ===\n\n");
    
    login_user("alice");
    printf("Logged in as: alice\n\n");
    
    /* Accessing own files - implicit path */
    printf("Opening 'budget.txt' (implicit: alice/budget.txt)\n");
    
    /* Accessing another user's file - explicit path */
    printf("Opening 'bob/notes.txt' (explicit cross-user access)\n");
    
    /* The system allows this but could enforce permissions */
    printf("\nNote: Real systems would check permissions here.\n");
}
 
int main() {
    printf("=== Two-Level Directory System ===\n\n");
    
    init_directory_system();
    
    demonstrate_namespace_isolation();
    demonstrate_cross_user_access();
    
    return 0;
}

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/*
 * Sharing Mechanisms in Two-Level Directories
 * Demonstrates search paths and public directories.
 */
 
#include <stdio.h>
#include <string.h>
#include <stdbool.h>
 
#define MAX_PATH_DIRS 8
#define MAX_NAME 32
 
/*
 * Search path for file resolution
 * Checked in order when no explicit user is specified
 */
typedef struct {
    char directories[MAX_PATH_DIRS][MAX_NAME];
    int count;
} SearchPath;
 
/* Global search path */
static SearchPath g_search_path;
 
/*
 * Initialize default search path for a user
 * Order: user's directory, public, system
 */
void init_search_path(const char *username) {
    g_search_path.count = 0;
    
    /* User's own directory first */
    snprintf(g_search_path.directories[g_search_path.count++],
             MAX_NAME, "%s/", username);
    
    /* Public shared directory */
    strncpy(g_search_path.directories[g_search_path.count++],
            "public/", MAX_NAME);
    
    /* System directory last */
    strncpy(g_search_path.directories[g_search_path.count++],
            "system/", MAX_NAME);
    
    printf("Search path for %s:\n", username);
    for (int i = 0; i < g_search_path.count; i++) {
        printf("  %d. %s\n", i + 1, g_search_path.directories[i]);
    }
}
 
/*
 * Simulated file lookup (returns true if file exists at path)
 */
bool file_exists(const char *full_path) {
    /* Simulate: certain files exist */
    const char *existing[] = {
        "alice/budget.txt",
        "alice/report.doc",
        "bob/notes.txt",
        "public/shared_data.csv",
        "public/team_template.doc",
        "system/libc.so",
        "system/config.ini",
        NULL
    };
    
    for (int i = 0; existing[i] != NULL; i++) {
        if (strcmp(full_path, existing[i]) == 0) {
            return true;
        }
    }
    return false;
}
 
/*
 * Resolve a filename using the search path
 * Returns full path if found, NULL otherwise
 */
const char* resolve_file(const char *filename, char *result, size_t result_size) {
    printf("\nResolving '%s':\n", filename);
    
    for (int i = 0; i < g_search_path.count; i++) {
        char full_path[MAX_NAME * 2];
        snprintf(full_path, sizeof(full_path), "%s%s",
                 g_search_path.directories[i], filename);
        
        printf("  Checking %s... ", full_path);
        
        if (file_exists(full_path)) {
            printf("FOUND!\n");
            strncpy(result, full_path, result_size);
            return result;
        } else {
            printf("not found\n");
        }
    }
    
    printf("  File not found in any search path directory.\n");
    return NULL;
}
 
/*
 * Demonstrate search path in action
 */
void demonstrate_search_path(void) {
    char result[MAX_NAME * 2];
    
    printf("\n=== Search Path Demo ===\n\n");
    
    /* Alice's search path */
    init_search_path("alice");
    
    /* Try to find various files */
    printf("\n--- Finding files ---\n");
    
    /* Found in alice's directory */
    resolve_file("budget.txt", result, sizeof(result));
    
    /* Found in public directory */
    resolve_file("shared_data.csv", result, sizeof(result));
    
    /* Found in system directory */
    resolve_file("libc.so", result, sizeof(result));
    
    /* Not found anywhere */
    resolve_file("nonexistent.txt", result, sizeof(result));
    
    /* Now consider bob's perspective */
    printf("\n--- Bob's perspective ---\n");
    init_search_path("bob");
    
    /* Bob can find his notes */
    resolve_file("notes.txt", result, sizeof(result));
    
    /* Bob can also find shared files */
    resolve_file("shared_data.csv", result, sizeof(result));
    
    /* Bob CANNOT find alice's budget.txt with just filename */
    resolve_file("budget.txt", result, sizeof(result));
    /* (Alice's directory not in bob's search path) */
}
 
/*
 * Demonstrate public directory for sharing
 */
void demonstrate_public_sharing(void) {
    printf("\n\n=== Public Directory Sharing ===\n\n");
    
    printf("Alice wants to share a report with the team:\n\n");
    
    printf("1. Alice creates file in her directory:\n");
    printf("   CREATE alice/quarterly_report.doc\n\n");
    
    printf("2. Alice copies to public for sharing:\n");
    printf("   COPY alice/quarterly_report.doc -> public/q1_report.doc\n\n");
    
    printf("3. Bob can now access it:\n");
    printf("   OPEN public/q1_report.doc  (explicit path)\n");
    printf("   OPEN q1_report.doc         (via search path)\n\n");
    
    printf("Tradeoff: File is duplicated, changes need re-copying.\n");
}
 
int main() {
    demonstrate_search_path();
    demonstrate_public_sharing();
    
    return 0;
}