local Object = require "lib/classic"

---@class Frame
---@field sprite number The index of the sprite in the atlas.
---@field duration? number The duration (in seconds) of this frame.
---@field atlas? Atlas The sprite atlas this frame is drawn from.

---@class Animation
---A timed sequence of sprites.
local Animation = Object:extend()

---Creates a new animation.
---@param frames Frame[] A list of frames.
---@param duration? number The default duration to use for this animation. Defaults to 15 FPS.
---@param atlas? Atlas The default atlas to use for this animation.
function Animation:new(frames, duration, atlas)
  local default_duration = duration or (1.0 / 15.0)

  ---The list of frames.
  self.frames = {}

  local total_duration = 0

  for idx, frame in ipairs(frames) do
    total_duration = total_duration + (frame.duration or default_duration)

    self.frames[idx] = {
      sprite = frame.sprite,
      duration = frame.duration or duration,
      atlas = frame.atlas or atlas or error("Missing default atlas"),
    }
  end

  ---The total duration of this animation.
  self.duration = total_duration
end

---Creates a new animation from the sprites between start and end indices, plus an atlas.
---@param atlas Atlas The atlas that the sprites are from.
---@param start_idx number The first sprite index in the animation.
---@param end_idx number The last sprite index in the animation.
---@param duration? number The duration of each frame. Defaults to 15 FPS.
---@return Animation
function Animation:new_spanned(atlas, start_idx, end_idx, duration)
  local duration = duration or (1.0 / 15.0)
  local frames = {}

  for sprite = start_idx, end_idx do
    frames[#frames + 1] = { sprite = sprite, atlas = atlas, duration = duration }
  end

  return Animation(frames)
end

---Draws a frame of this animation.
---@param index number The index of the frame.
---@param x number The X position to draw at.
---@param y number The Y position to draw at.
function Animation:draw(index, x, y)
  local frame = self.frames[index]
  frame.atlas:draw(frame.sprite, x, y)
end

return Animation