#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 within struct rows of Address.
};

struct Connection{
FILE *file;
struct Database *db;

};

void die (const char *message){


if(errno){

perror(message);
}else{
printf("ERROR:%s\n",message);

}
exit(1);// Check this out!

}

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);// important line,fread is new!

if(rc!=1)die("Failed to load database");
}

struct Connection* Database_open(const char *filename,char mode){// check if Connection* or Connection *Database
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);//New- word:rewind???
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 initialise 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 char *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);//new key!!
//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 ex 17<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]);// Convert String to number.
if(id>=MAX_ROWS)die("There aren't 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 '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;






}