-- Timing helpers for collab backgrounds ported from Lumen data. Lengths are multiples of
-- `unit` ms: a beat (60000 / bpm) for things that follow the song, 1 for plain ms.

-- Moves { length, distance, ease } run back to back (distance 0 is a hold); the offset
-- they describe is the sum of their attributes
local function chain_moves(moves, unit, scale)
    local out, at = {}, 0
    for _, m in ipairs(moves) do
        local length, distance, ease = m[1], m[2], m[3]
        if distance ~= 0 then
            local move = anim.move(length * unit, {
                total_distance = math.floor(distance * scale),
                delay = at,
                ease_in = ease == "in" and "quadratic" or nil,
                ease_out = ease == "out" and "quadratic" or nil,
            })
            move:start()
            table.insert(out, move)
        end
        at = at + length * unit
    end
    return out
end

-- Frames { index, length } shown back to back
local function frame_change(steps, unit, opts)
    local textures, t = {}, 0
    for _, step in ipairs(steps) do
        table.insert(textures, { t, t + step[2] * unit, step[1] })
        t = t + step[2] * unit
    end
    return anim.texture_change(t, textures, opts)
end

local function sum(moves)
    local total = 0
    for _, m in ipairs(moves) do total = total + m.attribute end
    return total
end

local function concat(...)
    local out = {}
    for _, t in ipairs({ ... }) do
        for _, v in ipairs(t) do table.insert(out, v) end
    end
    return out
end

-- Ambient loop: `build()` returns a table of one-shot anims (or lists of them) that is
-- rebuilt every `period` ms, so several anims stay in step without each looping alone
local Loop   = {}
Loop.__index = Loop

function Loop.new(period, build)
    return setmetatable({ period = period, build = build }, Loop)
end

function Loop:update(current_time_ms)
    if not self.t0 or current_time_ms - self.t0 >= self.period then
        self.t0 = current_time_ms
        self.anims = self.build()
    end
    for _, a in pairs(self.anims) do
        if a.update then
            a:update(current_time_ms)
        else
            for _, m in ipairs(a) do m:update(current_time_ms) end
        end
    end
end

return {
    chain_moves  = chain_moves,
    frame_change = frame_change,
    sum          = sum,
    concat       = concat,
    Loop         = Loop,
}