#include <stdio.h>
#include <assert.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#define MAX_DATA 512
#define MAX_ROWS 100
struct Address {
 int id;
 int set;
 char name[MAX_DATA];
 char email[MAX_DATA];
};
struct Database {
 struct Address rows[MAX_ROWS];
};
struct Connection {
 FILE *file;
 struct Database *db;
};
void die(const char *message)
{
 if(errno) {
 perror(message);
 } else {
 printf("ERROR: %s\n", message);
 }
 exit(1);
}
void Address_print(struct Address *addr)
{
 printf("%d %s %s\n",
 addr->id, addr->name, addr->email);
}
void Database_load(struct Connection *conn)
{
 int rc = fread(conn->db, sizeof(struct Database), 1, conn->file);
 if(rc != 1) die("Failed to load database.");
}
struct Connection *Database_open(const char *filename, char mode)
{
 struct Connection *conn = malloc(sizeof(struct Connection));
 if(!conn) die("Memory error");
 conn->db = malloc(sizeof(struct Database));
 if(!conn->db) die("Memory error");
 if(mode == 'c') {
 conn->file = fopen(filename, "w");
 } else {
 conn->file = fopen(filename, "r+");
 if(conn->file) {
 Database_load(conn);
 }
 }
 if(!conn->file) die("Failed to open the file");
 return conn;
}
void Database_close(struct Connection *conn)
{
 if(conn) {
 if(conn->file) fclose(conn->file);
 if(conn->db) free(conn->db);
 free(conn);
 }
}
void Database_write(struct Connection *conn)
{
 rewind(conn->file);
 int rc = fwrite(conn->db, sizeof(struct Database), 1, conn->file);
 if(rc != 1) die("Failed to write database.");
 rc = fflush(conn->file);
 if(rc == -1) die("Cannot flush database.");
}
void Database_create(struct Connection *conn)
{
 int i = 0;
 for(i = 0; i < MAX_ROWS; i++) {
 // make a prototype to initialize it
 struct Address addr = {.id = i, .set = 0};
 // then just assign it
 conn->db->rows[i] = addr;
 }
}
void Database_set(struct Connection *conn, int id, const char *name, const cha
r *email)
{
 struct Address *addr = &conn->db->rows[id];
 if(addr->set) die("Already set, delete it first");
 addr->set = 1;
 // WARNING: bug, read the "How To Break It" and fix this
 char *res = strncpy(addr->name, name, MAX_DATA);
 // demonstrate the strncpy bug
 if(!res) die("Name copy failed");
 res = strncpy(addr->email, email, MAX_DATA);
 if(!res) die("Email copy failed");
}
void Database_get(struct Connection *conn, int id)
{
 struct Address *addr = &conn->db->rows[id];
 if(addr->set) {
 Address_print(addr);
 } else {
 die("ID is not set");
 }
}
void Database_delete(struct Connection *conn, int id)
{
 struct Address addr = {.id = id, .set = 0};
 conn->db->rows[id] = addr;
}
void Database_list(struct Connection *conn)
{
 int i = 0;
 struct Database *db = conn->db;
 for(i = 0; i < MAX_ROWS; i++) {
 struct Address *cur = &db->rows[i];
 if(cur->set) {
 Address_print(cur);
 }
 }
}
int main(int argc, char *argv[])
{
 if(argc < 3) die("USAGE: ex17 <dbfile> <action> [action params]");
 char *filename = argv[1];
 char action = argv[2][0];
 struct Connection *conn = Database_open(filename, action);
 int id = 0;
 if(argc > 3) id = atoi(argv[3]);
 if(id >= MAX_ROWS) die("There's not that many records.");
 switch(action) {
 case 'c':
 Database_create(conn);
 Database_write(conn);
 break;
 case 'g':
 if(argc != 4) die("Need an id to get");
 Database_get(conn, id);
 break;
 case 's':
 if(argc != 6) die("Need id, name, email to set");
 Database_set(conn, id, argv[4], argv[5]);
 Database_write(conn);
 break;
 case 'd':
 if(argc != 4) die("Need id to delete");
 Database_delete(conn, id);
 Database_write(conn);
 break;
 case 'l':
 Database_list(conn);
 break;
 default:
 die("Invalid action, only: c=create, g=get, s=set, d=del, l=list")
;
 }
 Database_close(conn);
 return 0;
}