include("utils.jl")

function parse_input(filename)
    line = collect(non_empty_lines(filename))[1]
    println(line)
    map(x->parse(Int, x.match), eachmatch(r"-?[0-9]+", line))
end

function inverse_gauss(x)
    sqrt(1/4 + 2 * x) - 1/2
end

function valid_x_velocities(left, right)
    Int64(ceil(inverse_gauss(left))):Int64(floor(inverse_gauss(right)))
end

function hitp(left, right, bottom, top, vel)
    pos = [0, 0]
    mpos = [0, 0]
    velocity = copy(vel)
    while pos[2] > bottom
        pos += velocity
        mpos = max(pos, mpos)
        velocity[1] = velocity[1] > 0 ? velocity[1] - 1 : 0
        velocity[2] -= 1

        if pos[1] >= left && pos[1] <= right && pos[2] >= bottom && pos[2] <= top
            return true, mpos[2], vel
        end
    end
    false, mpos[2], vel
end

function solution17_1()
    left, right, bottom, top = parse_input("17.data")
    for vx in valid_x_velocities(left, right)
        shots = map(v->hitp(left, right, bottom, top, v), [[vx, vy] for vy in 1:10000])
        hits = collect(Iterators.filter(x->x[1], shots))
        println(last(sort(hits, by=x->x[2])))
    end
end

function solution17_2()
    left, right, bottom, top = parse_input("17.data")
    sum = 0
    for vx in 1:right
        shots = map(v->hitp(left, right, bottom, top, v), [[vx, vy] for vy in bottom:1000])
        hits = collect(map(x->x[3], Iterators.filter(x->x[1], shots)))
        sum += length(hits)
    end
    sum
end

solution17_2()