local gridElements = filteredSystem("gridElements", { gridPosition = T.XyPair, effectsToApply = T.AnyComponent })

filteredSystem("timers", { timerSec = T.number, callback = T.SelfFunction }, function(e, dt, system)
    e.timerSec = e.timerSec - dt
    if e.timerSec < 0 then
        e:callback()
        system.world:removeEntity(e)
    end
end)

function math.sign(n)
    return n > 0 and 1 or n < 0 and -1 or 0
end

RoundSystem = filteredSystem("rounds", { roundState = T.str }, function(e)
    -- print("roundState: " .. e.roundState)
end)

---@alias RoundState "active" | "animating" | "end"

---@param state RoundState
function RoundSystem:remove(state)
    for _, round in pairs(self.entities) do
        if round.roundState == state then
            self.world:removeEntity(round)
        end
    end
end

---@param state RoundState
function RoundSystem:hasState(state)
    for _, round in pairs(self.entities) do
        if round.roundState == state then
            return true
        end
    end
    return false
end

---@param n number
---@param nToSlowBy number
---@return number slowedValue
local function slowBy(n, nToSlowBy)
    if math.abs(n) < math.abs(nToSlowBy) then
        return 0
    end
    return n - (math.sign(n) * nToSlowBy)
end
---
---@param n number
---@param nToSlowTo number
---@return number slowedValue
local function slowTo(n, nToSlowTo)
    if math.abs(n) < math.abs(nToSlowTo) then
        return 0
    end
    return math.sign(n) * nToSlowTo
end

---@class BallEffects
---@field slowsTo nil | XyPair
---@field slowsBy nil | XyPair
---@field movement nil | XyPair
---@field fliesFor nil | number

---@type BallEffects
local BallEffects = {}

local activeBallEffects = filteredSystem(
    "activeBallEffects",
    { ballEffects = BallEffects, gridPosition = T.XyPair },
    function(e, _, system)
        local gridPosition, effects = e.gridPosition, e.ballEffects

        if effects.fliesFor == nil then
            -- Search for new effects from the current tile
            for _, gridElement in pairs(gridElements.entities) do
                if gridPosition.x == gridElement.gridPosition.x and gridPosition.y == gridElement.gridPosition.y then
                    -- More direct-mutation-y than I'd like,
                    -- but offers a simple way to overwrite existing effects.
                    -- We're "setting InRelations" :D
                    for key, value in pairs(gridElement.effectsToApply) do
                        effects[key] = value
                    end
                    if gridElement.spriteAfterEffect then
                        gridElement.drawAsSprite = gridElement.spriteAfterEffect
                        gridElement.spriteAfterEffect = nil
                    end
                    gridElement.effectsToApply = nil
                    system.world:addEntity(gridElement)
                end
            end
        else
            effects.fliesFor = effects.fliesFor - 1
            if effects.fliesFor == 0 then
                effects.fliesFor = nil
            end
        end

        --------------------------------------------------------
        -- Apply any effects currently connected to this ball --
        --------------------------------------------------------

        if effects.movement ~= nil then
            if effects.slowsBy ~= nil then
                effects.movement.x = slowBy(effects.movement.x, effects.slowsBy.x)
                effects.movement.y = slowBy(effects.movement.y, effects.slowsBy.y)
                effects.slowsBy = nil
            end
            if effects.slowsTo ~= nil then
                effects.movement.x = slowTo(effects.movement.x, effects.slowsTo.x)
                effects.movement.y = slowTo(effects.movement.y, effects.slowsTo.y)
                effects.slowsTo = nil
            end

            if effects.movement.x == 0 and effects.movement.y == 0 then
                effects.movement = nil
            else
                gridPosition.x = gridPosition.x + math.sign(effects.movement.x)
                gridPosition.y = gridPosition.y + math.sign(effects.movement.y)

                effects.movement.x = effects.movement.x - math.sign(effects.movement.x)
                effects.movement.y = effects.movement.y - math.sign(effects.movement.y)
            end
        end

        if effects.endOfRound ~= nil then
            effects.endOfRound = nil
            system.world:addEntity({ roundState = "end" })
            system.world:removeEntity(e)
            -- print("End of round")
            return
        end

        for _, _ in pairs(effects) do
            -- Return if there are any effects left
            -- print("Setting roundState to animating...")
            system.world:addEntity({ roundState = "animating" })
            -- system.world:removeEntity(e)
            return
        end

        -- print("End of round")
        system.world:addEntity({ roundState = "end" })
        system.world:removeEntity(e)
    end
)

function activeBallEffects:preProcess(dt)
    if RoundSystem:hasState("animating") then
        return tiny.SKIP_PROCESS
    end

    if RoundSystem:hasState("active") then
        return
    end

    return tiny.SKIP_PROCESS
end