using Mmap

mutable struct StationMeasurements
    min::Float64
    max::Float64
    sum::Float64
    count::Int64
end

function update(sm, temp::Float64)
    if temp < min
        sm.min = temp
    elseif temp > max
        sm.max = temp
    end
    sm.sum += temp
    sm.count += 1
end

function print_measurements(stations::Dict{String,StationMeasurements})
    sorted_keys = sort(collect(keys(stations)))
    print("{")
    sm_vec = []
    for city in sorted_keys
        sm = stations[city]
        min = round(sm.min; digits=1)
        max = round(sm.max; digits=1)
        avg = round((sm.sum / sm.count); digits=1)
        push!(sm_vec, "$city=$min/$avg/$max")
    end
    joined = join(sm_vec, ", ")
    print(joined)
    print("}")
end

function main()
    open("../../../measurements.txt", "r") do f
        println("Start")
        sz = Base.stat(f).size
        data = mmap(f, Vector{UInt8}, sz)
        idxs = findall(isequal(0x0a), data)
        stations = Dict{String,StationMeasurements}()
        iteration = 0
        last_idx = 1
        for i in eachindex(idxs)
            if iteration % 1000000 == 0 && iteration > 0
                print("\x1b[J\x1b[H")
                percent = round((iteration / 1000000000) * 100; digits=2)
                println("$(percent)%")
            end
            line = String(data[last_idx:idxs[i]-1])
            last_idx = idxs[i] + 1
            station, temp_str = rsplit(line, ";")
            temp = parse(Float32, temp_str)
            if haskey(stations, station)
                sm = stations[station]
                sm.min = ifelse(temp < sm.min, temp, sm.min)
                sm.max = ifelse(temp > sm.max, temp, sm.max)
                sm.sum += temp
                sm.count += 1
            else
                stations[station] = StationMeasurements(temp, temp, temp, 1)
            end
            iteration += 1
        end
        print_measurements(stations)
        println("End")
    end
end

main()