local Math = require "math"
local Object = require "lib/classic"

---@class Atlas
---A spriteset laid out on a regular grid.
local Atlas = Object:extend()

---Creates a new atlas.
---@param image_path string The path to the source image for the atlas.
---@param sw integer The width of each sprite.
---@param sh integer The height of each sprite.
---@param ax integer? The anchor X coordinate of each sprite. Defaults to 0.
---@param ay integer? The anchor Y coordinate of each sprite. Defaults to 0.
function Atlas:new(image_path, sw, sh, ax, ay)
  local image = love.graphics.newImage(image_path)

  ---The source image of the atlas.
  self.image = image

  ---The width of each atlas's sprite.
  self.sw = sw

  ---The height of each atlas's sprite.
  self.sh = sh

  ---The anchor X coordinate of each sprite.
  self.ax = ax or 0

  ---The anchor Y coordinate of each sprite.
  self.ay = ay or 0

  ---The width of the atlas in texels.
  self.iw = image:getPixelWidth()

  ---The height of the atlas in texels.
  self.ih = image:getPixelHeight()

  ---The width of the atlas in sprites.
  self.w = Math.floor(self.iw / sw)

  ---The height of the atlas in sprites.
  self.h = Math.floor(self.ih / sh)

  ---The total number of sprites.
  self.num = self.w * self.h

  ---A drawable mesh for each sprite.
  self.meshes = {}

  for row = 1, self.h do
    for col = 1, self.w do
      --UV texture coordinates
      local l = (col - 1) * sw / self.iw
      local t = (row - 1) * sh / self.ih
      local r = col * sw / self.iw
      local b = row * sh / self.ih

      --Vertex data
      local vertices = {
        { 0,  0,  l, t },
        { sw, 0,  r, t },
        { 0,  sh, l, b },
        { sw, sh, r, b }
      }

      --Create and push the mesh
      local mesh = love.graphics.newMesh(vertices, "strip", "static")
      mesh:setTexture(self.image)
      self.meshes[#self.meshes + 1] = mesh
    end
  end
end

---Draws a sprite at a given location.
---@param sprite integer The index of the sprite to draw.
---@param x integer The X coordinate to draw at.
---@param y integer The Y coordinate to draw at.
function Atlas:draw(sprite, x, y)
  local mesh = self.meshes[sprite]
  love.graphics.draw(mesh, x - self.ax, y - self.ay)
end

return Atlas