create table users(
    id uuid primary key,
    name varchar(32) not null unique,
    password varchar(128)
);

create table accounts(
    id uuid primary key,
    "user" uuid not null references users(id),
    name varchar(32) not null,
    balance bigint not null default 0 constraint positive_balance check (balance >= 0),
    unique ("user", name)
);

create table transactions(
    id uuid primary key,
    "from" uuid references accounts(id),
    "to" uuid references accounts(id),
    interop_name text,
    system bool not null default false,
    amount bigint not null constraint positive_amount check (amount > 0),
    timestamp timestamp with time zone not null default now(),
    message text,
    constraint check_interop_name_from_to_null check (
        ((("from" is null and "to" is not null) or ("from" is not null and "to" is null)) and (interop_name is not null or system)) or
        ("from" is not null and "to" is not null and interop_name is null)
    )
);

create index transactions_from on transactions ("from");
create index transactions_to on transactions ("to");

create view transactions_with_user_info as select
    t.amount,
    t.message,
    t.timestamp,
    t.system,
    case
        when t."from" is null then t.interop_name
        when t."to" is null then t.interop_name
        else null
    end as interop_name,
    -- From Participant
    uf.id AS from_user_id,
    t."from" as from_account_id,
    uf.name AS from_user_name, 
    af.name AS from_account_name, 
    -- To Participant
    ut.id AS to_user_id, 
    t."to" as to_account_id,
    ut.name AS to_user_name, 
    at.name AS to_account_name
from transactions t
join accounts af ON t."from" = af.id
join users uf ON af."user" = uf.id
join accounts at ON t."to" = at.id
join users ut ON at."user" = ut.id;