local misc = require("__flib__.misc")

local constants = require("constants")

-- Code based on "improved research queue" by sonaxaton
-- https://github.com/dbeckwith/factorio-research-queue/blob/af6404ab696502a86eec40a4baf7fe00d0c714c7/control.lua#L316
return function()
  local strings = {}

  for _, force in pairs(game.forces) do
    local tech = force.current_research
    if tech then
      -- Retrieve or create progress samples table
      local progress_samples = global.research_progress_samples[force.index]
      if not progress_samples then
        progress_samples = {}
        global.research_progress_samples[force.index] = progress_samples
      end
      progress_samples[#progress_samples + 1] = { tech = tech.name, progress = force.research_progress }
      if #progress_samples > constants.research_progress_samples_count then
        table.remove(progress_samples, 1)
      end

      local estimated_ticks = 0
      local num_samples = 0
      if #progress_samples > 1 then
        for i = 2, #progress_samples do
          local previous_sample = progress_samples[i - 1]
          local current_sample = progress_samples[i]
          if previous_sample.tech == current_sample.tech then
            -- How much the progress increased per tick
            local speed = (current_sample.progress - previous_sample.progress) / 60
            -- Don't add if the speed is negative for whatever reason
            if speed > 0 then
              -- How many ticks left until the research is finished
              estimated_ticks = estimated_ticks + ((1 - current_sample.progress) / speed)
              num_samples = num_samples + 1
            end
          end
        end
        -- Rolling average
        if num_samples > 0 then
          estimated_ticks = estimated_ticks / num_samples
        end
      end

      if num_samples > 0 then
        strings[force.index] = misc.ticks_to_timestring(estimated_ticks)
      else
        strings[force.index] = "∞"
      end
    end
  end

  global.research_progress_strings = strings
end