local metrics = require("utils.metrics")

-- config
local flush_interval_ticks = 60 -- flush every n ticks

-- state
--- @type table<number, fun()>
local queue = {}

--- @type table<number, string>
local buffer = {}
local last_reset = 0

-- queue operations to perform for each round of metric processing
-- that way, avoid doing too much work in a single game tick and causing UPS inconsistencies
local function prepare_queue()
    queue = {}
    for _, surface in pairs(game.surfaces) do
        for _, force in pairs(game.forces) do
            table.insert(queue, metrics.calc_item_production_statistics(buffer, surface, force))
            table.insert(queue, metrics.calc_fluid_production_statistics(buffer, surface, force))
        end
        table.insert(queue, metrics.calc_power_statistics(buffer, surface))
    end
end

local function process_queue()
    local entry = table.remove(queue, 1)
    if entry then
        entry()
    end
end

local function tick()
    process_queue()

    if #queue == 0 and #buffer > 0 then
        helpers.write_file("metrics.prom", table.concat(buffer, "\n"), false)
        buffer = {}
    end

    if #queue == 0 and game.tick - last_reset >= flush_interval_ticks then
        prepare_queue()
        last_reset = game.tick
    end
end

-- main tick handler
script.on_event(defines.events.on_tick, tick)

-- startup
script.on_init(function()
    last_reset = game.tick
    prepare_queue()
end)