include("utils.jl")

function parse_input(filename)
    template, rawrules... = collect(non_empty_lines(filename))
    rules = Dict()
    for rule in rawrules
        front, back = split(rule, " -> ")
        first, second = split(front, "")
        rules[[first[1], second[1]]] = back[1]
    end
    pairs = Dict()
    for i in 1:length(template)-1
        get!(pairs, [template[i], template[i+1]], 0)
        pairs[[template[i], template[i+1]]] += 1
    end
    pairs, rules, [first(template), last(template)]
end

function countpoly(pairs, singles)
    result = Dict()
    for (key, value) in pairs
        get!(result, key[1], 0)
        result[key[1]] += value
        get!(result, key[2], 0)
        result[key[2]] += value
    end
    for single in singles
        result[single] += 1
    end
    for key in keys(result)
        result[key] = div(result[key], 2)
    end
    result
end

function solution14_2()
    pairs, rules, singles = parse_input("14.data")
    steps = 40
    for step in 1:steps
        new = Dict()
        for (key, value) in pairs
            insert = get!(rules, key, nothing)
            if typeof(insert) == Char
                get!(new, [key[1], insert], 0)
                new[[key[1], insert]] += value
                get!(new, [insert, key[2]], 0)
                new[[insert, key[2]]] += value
            else
                get!(new, key, 0)
                new[key] += value
            end
        end
        pairs = new
    end
    counts = sort(collect(values(countpoly(pairs, singles))))
    last(counts) - first(counts)
end

solution14_2()