local Object = require "lib/classic"

---@alias AnimationFinishBehavior
---| '"loop"' Loop the animation over from the beginning.
---| '"stop"' Freeze the animation on the last frame.
---| '"goto"' Go to another state.

---@class State
---@field animation Animation The animation frames for this state.
---@field on_finish? AnimationFinishBehavior What to do after this state's animation finishes. Defaults to "loop".
---@field next? string The next state to go to in the case of "goto" on_finish.

local Animator = Object:extend()

---Creates a new animator.
---@param states { [string]: State } A dictionary of all states in this animator.
---@param first_state string The first state of this animator.
function Animator:new(states, first_state)
  ---The states in this animator.
  self.states = states

  ---The current state.
  self.state = first_state

  ---The timestep of the current frame.
  self.step = 0

  ---The current frame in the current animation.
  self.frame = 1

  --- The next state to progress to.
  self.next_state = nil
end

function Animator:update(dt)
  local state = self.states[self.state]
  local frames = state.animation.frames

  --Step the current timestep and return if the frame hasn't changed.
  self.step = self.step + dt
  if self.step <= frames[self.frame].duration then
    return
  end

  --Step the current frame and return if there are more.
  self.step = 0
  self.frame = self.frame + 1
  if self.frame <= #frames then
    return
  end

  --We've reached the end of the current state.
  if self.next_state then
    self.state = self.next_state
    self.frame = 1
    self.next_state = nil
  elseif state.on_finish == "goto" then
    self.state = state.next
    self.frame = 1
  elseif state.on_finish == "stop" then
    self.frame = #frames
  elseif state.on_finish == "loop" or state.on_finish == nil then
    self.frame = 1
  else
    error("Invalid state on_finish " .. state.on_finish)
  end
end

function Animator:draw(x, y)
  local state = self.states[self.state]
  state.animation:draw(self.frame, x, y)
end

---Sets the state of this animator.
---@param state string The name of the state to set.
---@param queue? boolean If true, queues the state change for after the current state.
function Animator:setState(state, queue)
  if not self.states[state] then
    error("Invalid state " .. state)
  elseif queue then
    self.next_state = state
  else
    self.state = state
    self.step = 0
    self.frame = 1
  end
end

return Animator