-------------|
-- Cleanup --|
-------------|

drop table if exists input;
drop table if exists rolls;
drop function if exists part_2;

-----------|
-- Setup --|
-----------|

create unlogged table input (
    y serial primary key,
    value text
);
\copy input (value) from 'input/2025/4.txt';

create unlogged table rolls (
    x int not null,
    y int not null,
    primary key (x, y)
);


-----------------|
-- Parse input --|
-----------------|

insert into rolls (x, y)
select
    col.x,
    row.y
from input as row
cross join
    lateral
    unnest(string_to_array(row.value, null))
    with ordinality as col (char, x)
where col.char = '@';

------------|
-- Part 1 --|
------------|

select count(*) as part_1
from rolls as pos
where (
    select count(*) as count
    from rolls as neighbor
    where
        neighbor.x between pos.x - 1 and pos.x + 1
        and
        neighbor.y between pos.y - 1 and pos.y + 1
        and not
        (pos.x = neighbor.x and pos.y = neighbor.y)
) < 4;


------------|
-- Part 2 --|
------------|

-- Let's get procedural baybey
-- I tried for a long time to get this into a recursive CTE,
-- but couldn't find a way around the ban on outer joins
-- on the recursive table

create function part_2()
returns int
as $$
declare
    removed_total int = 0;
    removed_round int = 1;
begin
    while removed_round > 0 loop
        delete
        from rolls as pos
        where (
            select count(*) as count
            from rolls as neighbor
            where
                neighbor.x between pos.x - 1 and pos.x + 1
                and
                neighbor.y between pos.y - 1 and pos.y + 1
                and not
                (pos.x = neighbor.x and pos.y = neighbor.y)
        ) < 4;

        get diagnostics removed_round = row_count;
        removed_total = removed_total + removed_round;
    end loop;
    return removed_total;
end;
$$ language plpgsql;

select part_2();