--Load and save the bmp formats used by DEFCON.
local t = {}
local love = assert( love )
local lfs = love.filesystem

--FFI bit-twiddling stuff.
local ffi = require 'ffi'
local bit = require 'bit'

local function getHeader( filename )
  local offset = love.data.unpack( "<I4", assert(love.filesystem.read( "data", filename, 14 )), 11 )
  local header, size = assert( love.filesystem.read( filename, offset ) )
  print( "BMP HEADER", filename, size, "\n", string.byte( header, 1, size ) )
  return header
end

local formats = {
  ["512rgb24"] = {
    header = getHeader( "data/earth/africa.bmp" ),
    encode = function( r ) return math.floor( r * 255 ) end,
    bytesPerPixel = 3,
    w = 512,
    h = 285,
  },
  ["512r4"]     = {
    header = getHeader( "data/earth/sailable.bmp" ),
    encode = function( r ) return math.floor( r * 255 / 16 )  end,
    bytesPerPixel = 0.5,
    w = 512,
    h = 285,
  },
  ["800r4"]     = {
    header = getHeader( "data/earth/travel_nodes.bmp" ),
    encode = function( r ) return math.floor( r * 255 / 16 ) end,
    bytesPerPixel = 0.5,
    w = 800,
    h = 400,
  }
}

function t.header( format )
  return formats[format] and formats[format].header
end

function t.load( filename )
  local imgd = love.image.newImageData( filename )
  print( "LOADING BITMAP: ", filename, imgd:getSize(), imgd:getFormat(), imgd:getDimensions() )
  local img = love.graphics.newImage( imgd )
  img:setFilter( "nearest", "nearest" )
  return img, imgd
end

--maps an array of 1-byte pixel values  (numbers 0 to 15 inclusive)
--to an array of half-byte pixel values (which can be concatenated into a string)
--BUT don't touch the first element (which is assumed to be a header or something)
local function foldByteArray( bytes )
  local nybbles = { bytes[1] }
  for j = 2, #bytes / 2 do
    local a, b = bytes[ 2 * j - 2 ], bytes[ 2 * j - 1 ]
    nybbles[j] = string.char( 16 * a + b )
  end
  return nybbles
end

local function packTwentyFour( bytes )
  local twentyFour = { bytes[1] }
  for j = 2, #bytes do
    twentyFour[j] = string.char( bytes[j], bytes[j], bytes[j] )
  end
  return twentyFour
end

function t.save( data, format )
  local w, h = data:getDimensions()
  format = assert( formats[format] )
  local bytes = { format.header }
  format.byte = 0
  local i = 2
  for y = h - 1, 0, -1 do
    for x = 0, w - 1 do
      bytes[i] = format.encode( data:getPixel(x, y) )
      i = i + 1
    end  
  end
  if format.bytesPerPixel < 1 then bytes = foldByteArray( bytes )
  else bytes = packTwentyFour( bytes ) end
  return table.concat( bytes )
end

--takes an array of world-space points in [-180, 180] x [-100, 100] 
--e.g { { x = 0.5, y = 0.5 }, { x = 0.4, y = 0.6 }, }, etc.
function t.savePoints( points, format )
  format = assert( formats[format] )

  --set up bitmap as an array of pixels
  local w, h = format.w, format.h
  local size = 2 + format.w * format.h
  local bitmap = { format.header }
  for j = 2, size do bitmap[j] = 0 end

  --this is black-and-white only. easy case
  if format.bytesPerPixel < 1 then
    for i, point in ipairs( points ) do
      local wx, wy = point.x, point.y
      -- get bitmap coordinates:
      -- N.B., y's divided by 190 rather than 200 because of an idiosyncracy in the travel node image
      local x, y = math.floor(format.w * (wx + 180) / 360), math.floor(format.h * (wy + 100) / 190)

      --get index into byte array
      local idx = 2 + y * format.w + x
      print( "SAVING POINT:", wx, wy, x, format.h - y - 1, idx )
      bitmap[idx] = 1 --white: this header uses an indexed palette
    end
    --now map pixels to 4-bit strings, slap on the header, and pass it back up
    return table.concat( foldByteArray( bitmap ) )
  end

  --cf. ai.lua: these points can be red or green
  for i, point in ipairs( points ) do
    local wx, wy = point.x, point.y
    --get bitmap coordinates
    local x, y = math.floor(format.w * (wx + 180) / 360), math.floor(format.h * (1.0 - (wy + 100) / 200))
    --get index into byte array
    local idx = 2 + x * format.h + y
    --in-editor we could have two points in the same place, possibly of the same or different types
    --in case we miss something upstream, don't corrupt these duplicate points,
    --just saturate the attack/defense value
    if bitmap[idx] == 0 then bitmap[idx] = { attack = point.attacking, place = not(point.attacking)}
    else 
      bitmap[idx].attack = bitmap[idx].attack or point.attacking
      bitmap[idx].place  = bitmap[idx].place  or not(point.attacking)
    end
  end

  --now map pixels to 3-byte strings
  for j = 2, size do
    if   bitmap[j] == 0
    then bitmap[j] = "\0\0\0"
    else bitmap[j] = string.char( 0, bitmap[j].place and 0xff or 0, bitmap[j].attack and 0xff or 0 ) --bgr24
    end
  end

  return table.concat( bitmap )
end
return t