#!/usr/bin/env julia

using DelimitedFiles

infile = size(ARGS, 1) > 0 ? ARGS[1] : "day6input.txt"
println("infile = ", infile)

fish = vec(readdlm(infile, ',', Int))

function simulate_lanternfish(fish, days)
    fish = copy(fish)
    for day in 1:days
        newfish = 0
        for i in 1:length(fish)
            fish[i] -= 1
            if fish[i] < 0
                fish[i] = 6
                newfish += 1
            end
        end
        append!(fish, repeat([8], newfish))
    end
    return fish
end

fish18 = simulate_lanternfish(fish, 18)
fish80 = simulate_lanternfish(fish18, 80-18)

println("18 : ", length(fish18))
println("80 : ", length(fish80))

using OffsetArrays

function simulate2(fish, days)
    fish_map = OffsetVector(zeros(Int, 9), 0:8)
    for i in 1:length(fish)
        fish_map[fish[i]] += 1
    end
    for day in 1:days
        add_next = 0
        for c in 8:-1:0
            tmp = fish_map[c]
            fish_map[c] = add_next
            add_next = tmp
        end
        fish_map[8] = add_next
        fish_map[6] += add_next
    end
    return sum(fish_map)
end

function simulate3(fish, days)
    fish_map = zeros(Int, 9)
    for i in 1:length(fish)
        fish_map[fish[i]+1] += 1
    end
    for day in 1:days
        fish_map = circshift(fish_map, -1)
        fish_map[7] += fish_map[9]
    end
    return sum(fish_map)
end


println("18 : ", simulate2(fish, 18))
println("80 : ", simulate2(fish, 80))
println("256: ", simulate2(fish, 256))

println("18 : ", simulate3(fish, 18))
println("80 : ", simulate3(fish, 80))
println("256: ", simulate3(fish, 256))

using BenchmarkTools

@btime simulate2(fish, 256)
@btime simulate3(fish, 256)