-- Generic replay of an exported cabinet backdrop movie (lower half of the screen).
--
-- Data: Scripts/background/bg_data/bg_anim/<name>.lua (generated by
-- scratchpad/lyric/movie_export.py): `shapes[c] = {w, h, ox, oy}` and `normal`, a
-- list of shape instances in depth order, each with the period of its own loop and
-- channels tx/ty/sx/sy/rot/a (one number when constant, else one value per frame;
-- a = 0 means not placed) plus an optional presence mask `on`/`on_period`.
-- `blend = 8` marks a leaf the cabinet draws with the add blend mode (lantern glows).
-- Textures: Graphics/background/bga_<name>/s<c>.png.  The stage is 1920x540 and is
-- drawn at screen y 540; the same schema as the donbg band player.
local BGAnim = {}
BGAnim.__index = BGAnim

local FRAME_MS = 1000.0 / 60.0
local STAGE_Y  = 540
local ONE = string.byte("1")

function BGAnim.available(name)
    local ok, data = pcall(require, "background/bg_data/bg_anim/" .. name)
    return ok and type(data) == "table" and data.normal ~= nil
end

function BGAnim.new(name, path)
    local ok, data = pcall(require, "background/bg_data/bg_anim/" .. name)
    if not ok or type(data) ~= "table" or not data.normal then return nil end
    local self = setmetatable({}, BGAnim)
    self.name = name
    self.subset = "bga_" .. name
    self.path = path or "background"
    tex.load_folder(self.path, self.subset)
    self.data = data
    self.ids = {}
    self.elapsed = 0
    self.last_ms = nil
    return self
end

function BGAnim:id_of(shape)
    local id = self.ids[shape]
    if id == nil then
        id = tex.get_id(self.subset, "s" .. shape) or false
        self.ids[shape] = id
    end
    return id or nil
end

function BGAnim:update(current_ms)
    if self.last_ms then
        local dt = current_ms - self.last_ms
        if dt > 0 and dt < 500 then self.elapsed = self.elapsed + dt end
    end
    self.last_ms = current_ms
end

local function ch(v, i)
    if type(v) == "number" then return v end
    return v[i]
end

function BGAnim:draw(fade)
    fade = fade or 1.0
    if fade <= 0.002 then return end
    local frame = math.floor(self.elapsed / FRAME_MS)
    local list = self.data.normal
    local shapes = self.data.shapes
    for k = 1, #list do
        local e = list[k]
        local i = (frame % e.period) + 1
        local a = ch(e.a, i)
        if a > 0.002 and e.on then
            if e.on:byte((frame % e.on_period) + 1) ~= ONE then a = 0 end
        end
        if a > 0.002 then
            local s = shapes[e.shape]
            local id = s and self:id_of(e.shape)
            if id then
                local sx, sy = ch(e.sx, i), ch(e.sy, i)
                tex.draw_texture(id, {
                    x        = ch(e.tx, i),
                    y        = STAGE_Y + ch(e.ty, i),
                    x2       = s[1] * (sx - 1),
                    y2       = s[2] * (sy - 1),
                    origin   = { s[3] * sx, s[4] * sy },
                    rotation = ch(e.rot, i),
                    fade     = a * fade,
                    blend    = (e.blend == 8) and "additive" or nil,   -- cabinet add-blended glows
                })
            end
        end
    end
end

function BGAnim:destroy()
    tex.unload_folder(self.path, self.subset)
end

return BGAnim