-- A screen's own tile sheet, addressed the way the cart addresses it.
--
-- The Gen 2 menus that are not built out of text boxes -- the #DEX, the
-- POKeGEAR, the trainer card -- work by copying a sheet into VRAM at a known
-- tile id and then writing tile ids into the tilemap.  Transcribing one of
-- those screens means writing the same ids at the same hlcoords, so the only
-- primitive needed is "draw sheet tile $NN at (tx, ty)".
--
-- `firstTile` is the VRAM id the sheet's tile 0 was loaded at (vTiles2 tile
-- $31 for the dex, $00 for the town map), so a tile id maps to a sheet index
-- by subtracting it.  A sheet is `wide` tiles across, which is how the
-- extractor writes them.

local Assets = require("src.render.Assets")
local GbcPalette = require("src.render.GbcPalette")

local TileSheet = {}
TileSheet.__index = TileSheet

-- opts: path, wide, firstTile, palette (a 4-colour table) or palettes + a
-- paletteFor(tile, tx, ty) hook, transparent
function TileSheet.new(opts)
  local self = setmetatable({}, TileSheet)
  self.path = opts and opts.path
  self.wide = (opts and opts.wide) or 16
  self.firstTile = (opts and opts.firstTile) or 0
  self.palette = opts and opts.palette
  self.paletteFor = opts and opts.paletteFor
  self.quads = {}
  return self
end

function TileSheet:image()
  if self.loaded == nil then
    self.loaded = false
    if self.path then
      -- `and` would truncate pcall's second return, so this cannot fold into
      -- a one-liner.
      local ok, image = pcall(Assets.image, self.path)
      if ok and image then self.loaded = image end
    end
  end
  return self.loaded or nil
end

function TileSheet:available()
  return self:image() ~= nil
end

function TileSheet:quad(index)
  local quad = self.quads[index]
  if not quad then
    local image = self:image()
    if not image then return nil end
    local w, h = image:getDimensions()
    quad = love.graphics.newQuad(
      (index % self.wide) * 8, math.floor(index / self.wide) * 8, 8, 8, w, h)
    self.quads[index] = quad
  end
  return quad
end

-- Draws VRAM tile `tile` at tile coordinates (tx, ty).  A tile outside the
-- sheet is silently skipped, which is what lets a screen name a tile that
-- belongs to the font page instead.
function TileSheet:draw(tile, tx, ty)
  local image = self:image()
  if not image then return false end
  local index = tile - self.firstTile
  if index < 0 then return false end
  local quad = self:quad(index)
  if not quad then return false end
  local _, sy = quad:getViewport()
  local _, ih = image:getDimensions()
  if sy >= ih then return false end
  local G = love.graphics
  G.setColor(1, 1, 1, 1)
  local colors = self.palette
  if self.paletteFor then colors = self.paletteFor(tile, tx, ty) or colors end
  local function body() G.draw(image, quad, tx * 8, ty * 8) end
  if colors and GbcPalette.available() then
    GbcPalette.with(colors, body)
  else
    body()
  end
  return true
end

-- A run of consecutive ids, left to right: the shape most of these routines
-- use for a header strip or a caption.
function TileSheet:run(first, count, tx, ty)
  for i = 0, count - 1 do
    self:draw(first + i, tx + i, ty)
  end
end

-- A rectangle of consecutive ids, row-major.
function TileSheet:block(first, wide, high, tx, ty)
  for row = 0, high - 1 do
    for col = 0, wide - 1 do
      self:draw(first + row * wide + col, tx + col, ty + row)
    end
  end
end

return TileSheet