#include <stdio.h>
#include <assert.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>

#define DEFAULT_MAX_DATA 512
#define DEFAULT_MAX_ROWS 100

struct Address {
    int id;
    int set;
    char *name;
    char *email;
};

struct Database {
    int max_data;
    int max_rows;
    struct Address rows[];
};

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

void Database_close(struct Connection *conn);

void die(const char *message, struct Connection *conn)
{
    if(errno) {
        perror(message);
    } else {
        printf("ERROR: %s\n", message);
    }

    Database_close(conn);

    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.", conn);
}

struct Connection* Database_open(const char *filename, char mode)
{
    struct Connection *conn = malloc(sizeof(struct Connection));
    if(!conn) die("Memory error", conn);

    conn->db = malloc(sizeof(struct Database));
    if(!conn->db) die("Memory error", conn);

    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", conn);

    return conn;
}

void Database_close(struct Connection *conn)
{
    if(conn != NULL) {
        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.", conn);

    rc = fflush(conn->file);
    if(rc == -1) die("Cannot flush database.", conn);
}

void Database_create(struct Connection *conn, int max_rows, int max_data)
{
    int i = 0;
    conn->db->max_rows = max_rows;
    conn->db->max_data = max_data;

    for(i = 0; i < conn->db->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 char *email)
{
    int max_data = conn->db->max_data;
    struct Address *addr = &conn->db->rows[id];
    if(addr->set) die("Already set, delete it first", conn);

    addr->set = 1;
    char *res = strncpy(addr->name, name, max_data);
    if(!res) die("Name copy failed", conn);
    addr->name[max_data - 1] = '\0';

    res = strncpy(addr->email, email, max_data);
    if(!res) die("Email copy failed", conn);
    addr->email[max_data - 1] = '\0';
}

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", conn);
    }
}

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 < conn->db->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>[:max_data,max_rows] [action params]", NULL);

    char *filename = argv[1];

    int max_data = DEFAULT_MAX_DATA;
    int max_rows = DEFAULT_MAX_ROWS;

    char action = argv[2][0];
    if(':' == argv[2][1]) {
        sscanf(argv[2], "%c:%d,%d", &action, &max_data, &max_rows);
    }

    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.", conn);

    switch(action) {
        case 'c':
            Database_create(conn, max_rows, max_data);
            Database_write(conn);
            break;

        case 'g':
            if(argc != 4) die("Need an id to get", conn);

            Database_get(conn, id);
            break;

        case 's':
            if(argc != 6) die("Need id, name, email to set", conn);

            Database_set(conn, id, argv[4], argv[5]);
            Database_write(conn);
            break;

        case 'd':
            if(argc != 4) die("Need id to delete", conn);

            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", conn);
    }

    Database_close(conn);

    return 0;
}