local internal = {
    waypoints = {},
    stats = {},
    sessions = 0,
    last = os.clock()
}

timer = {}

function timer.start()
    internal.waypoints = {}

    internal.now()

    internal.sessions = internal.sessions + 1
end

function timer.checkpoint(name)
    local now = os.clock()

    table.insert(internal.waypoints, { name, internal.last, now })

    internal.now()
end

function timer.stop()
    local name_len = 0

    for _, t in ipairs(internal.waypoints) do
        local name  = t[1]
        local start = t[2]
        local stop  = t[3]

        local stat = internal.stats[name]

        if stat then
            internal.stats[name] = stat + (stop - start)
        else
            internal.stats[name] = stop - start
        end

        name_len = math.max(name_len, string.len(name))
    end

    local h1 = "Task"
    local h2 = "Time"
    local h3 = "Time (avg)"
    
    internal.log(
        table.concat(
            { h1
            , string.rep(" ", name_len - string.len(h1))
            , " | "
            , h2
            , string.rep(" ", 8 - string.len(h2))
            , " | "
            , h3
            }
            , ""
        )
    )

    internal.log_hr(name_len)

    for _, t in ipairs(internal.waypoints) do
        local name = t[1]

        internal.log_time(
            name,
            internal.to_ms(t[3] - t[2]),
            internal.to_ms(internal.stats[name] / internal.sessions),
            name_len
        )
    end

    internal.log_hr(name_len)

    internal.log_time("Total", internal.sum(), internal.sum_avg(), name_len)
end

-- Log text to the Minetest chat
function internal.log(text)
    minetest.chat_send_all(os.time() .. " - " .. text)
end

function internal.log_hr(name_len)
    internal.log(string.rep("-", name_len + 3 + 8 + 3 + 8))
end

function internal.log_time(header, time, time_avg, header_max_len)
    local duration = tostring(time)
    local duration_avg = tostring(time_avg)

    internal.log(
        table.concat(
            { header
            , string.rep(" ", header_max_len - string.len(header))
            , " | "
            , string.rep(" ", 5 - string.len(duration))
            , duration
            , " ms | "
            , string.rep(" ", 5 - string.len(duration_avg))
            , duration_avg
            , " ms"
            }
            , ""
        )
    )
end

function internal.now()
    internal.last = os.clock()
end

function internal.sum()
    local s = 0

    for _, t in ipairs(internal.waypoints) do
        s = s + (t[3] - t[2])
    end

    return internal.to_ms(s)
end

function internal.sum_avg()
    local s = 0
    
    for _, t in pairs(internal.stats) do
        s = s + t
    end

    return internal.to_ms(s / internal.sessions)
end

function internal.to_ms(s)
    return math.round(s * 1e3)
end

internal.now()