create table studenti (
    s_id serial,
    s_ime varchar(20) not null,
    s_prezime varchar(20) not null,
    s_korisnicko_ime varchar(50) not null,
    s_email varchar(100) not null,
    s_lozinka varchar(50) not null,
    s_index varchar(10) not null,
    constraint pk_studenti primary key (s_id)
);

create table administratori (
    a_id serial,
    a_ime varchar(20) not null,
    a_prezime varchar(20) not null,
    a_korisnicko_ime varchar(50) not null,
    a_email varchar(100) not null,
    a_lozinka varchar(50) not null,
    constraint pk_administratori primary key (a_id)
);

create table profesori (
    p_id serial,
    p_ime varchar(20) not null,
    p_prezime varchar(20) not null,
    p_korisnicko_ime varchar(50) not null,
    p_email varchar(100) not null,
    p_lozinka varchar(50) not null,
    constraint pk_profesori primary key (p_id)
);

create table predmeti (
	pr_id serial,
	pr_ime varchar(200) not null,
	a_id integer not null,
	constraint pk_predmeti primary key (pr_id),
	constraint fk_predmeti_administratori foreign key (a_id)
    references administratori (a_id)
);

create table kursevi(
	ku_id serial,
	ku_ime varchar(200) not null,
	ku_opis varchar(500),
	pr_id integer not null,
	constraint pk_kursevi primary key (ku_id),
	constraint fk_kursevi_predmeti foreign key (pr_id)
	references predmeti (pr_id)
);

create table kategorii(
	ka_id serial,
	ka_ime varchar(40) not null,
	ka_opis varchar(150),
	a_id integer not null,
	constraint pk_kategorii primary key (ka_id),
	constraint fk_kategorii_administratori foreign key (a_id)
    references administratori (a_id)
);

create table materijali(
	m_id serial,
    m_ime varchar(150) not null,
    p_id integer not null,
    ka_id integer,
    ku_id integer not null,
    constraint pk_materijali primary key (m_id),
    constraint fk_materijali_profesori foreign key (p_id)
    references profesori (p_id),
    constraint fk_materijali_kategorii foreign key (ka_id)
    references kategorii (ka_id),
    constraint fk_materijali_kursevi foreign key (ku_id)
    references kursevi (ku_id)
);

create table prasanja(
	pra_id serial,
	pra_naslov varchar(100) not null,
	pra_sodrzina text not null,
	pra_datum timestamp default now(),
	ku_id integer not null,
	s_id integer not null,
	constraint pk_prasanja primary key (pra_id),
	constraint fk_prasanja_kursevi foreign key (ku_id)
	references kursevi (ku_id),
	constraint fk_prasanja_studenti foreign key (s_id)
	references studenti (s_id)
);

create table odgovori(
	o_id serial,
	o_sodrzina text not null ,
	o_validen boolean default false,
	o_datum timestamp default now(),
	pra_id integer not null,
	s_id integer ,
	p_id integer,
	constraint pk_odgovori primary key (o_id),
	constraint fk_odgovori_prasanja foreign key (pra_id)
	references prasanja (pra_id),
	constraint fk_odgovori_studenti foreign key (s_id)
	references studenti (s_id),
	constraint fk_odgovori_profesori foreign key (p_id)
	references profesori (p_id),
	constraint chk_not_null_avtor check (s_id is not null or p_id is not null)
);

create table prof_term_za_kons(
	ptk_id serial primary key,
    termin timestamp not null,
    p_id integer not null,
    constraint fk_prof_term_za_kons_profesori foreign key (p_id) references profesori (p_id)
);

create table e_vo_vrska_so(
	vs_id serial primary key,
    pra_id integer not null,
    m_id integer not null,
    constraint fk_e_vp_vrska_so_prasanja foreign key (pra_id)
    references prasanja (pra_id),
    constraint fk_e_vp_vrska_so_materijali foreign key (m_id)
    references materijali (m_id)
);

create table moze_da_slusa(
	mds_id serial primary key,
    s_id integer not null,
    ku_id integer not null,
    constraint fk_moze_da_slusa_studenti foreign key (s_id)
    references studenti (s_id),
    constraint fk_moze_da_slusa_kursevi foreign key (ku_id)
    references kursevi (ku_id)
);

create table e_prof_na(
	pn_id serial primary key,
    p_id integer not null,
    ku_id integer not null,
    constraint fk_e_prof_na_profesori foreign key (p_id)
    references profesori (p_id),
    constraint fk_e_prof_na_kursevi foreign key (ku_id)
    references kursevi (ku_id)
);

create table e_oznaceno_so(
	os_id  serial primary key,
    pra_id integer not null,
    ka_id  integer not null,
    constraint fk_e_oznaceno_so_prasanja foreign key (pra_id)
    references prasanja (pra_id),
    constraint fk_e_oznaceno_so_kategorii foreign key (ka_id)
    references kategorii (ka_id)
);

create table dava_reakcija(
	dr_id serial primary key,
    p_id integer not null,
    o_id integer not null,
    reakcija boolean not null,
    constraint fk_dava_reakcija_profesori foreign key (p_id)
    references profesori (p_id),
    constraint fk_dava_reakcija_odgovori foreign key (o_id)
    references odgovori (o_id)
);

create table reagira_na(
	rn_id serial primary key,
    s_id integer not null,
    o_id integer not null,
    reakcija boolean not null,
    constraint fk_reagira_na_studenti foreign key (s_id)
    references studenti (s_id),
    constraint fk_reagira_na_odgovori foreign key (o_id)
    references odgovori (o_id)
);