-- This module assumes all objects and the player are 1x1 sprite in size.
-- Larger sprites will probably work for objects, but not for the player.
--
-- exported variables:
--   player_pos # integer tuple {x,y}. absolute position of the player on the
--              #   'world map'
--   camera_pos # integer tuple {x,y}. Represents top-left position of the
--              #   pico-8 camera on the pico-8 map
--   facing     # integer tuple {v,h}. Current facing of the player. Values of
--              #   each element can be -1 (up or left), 0 (neutral),
--              #   or 1 (down or right)
--
-- functions:
--   init_player({x,y}) # call this in _init(). Sets player starting position,
--                      #   assumes the top-left of the pico-8 map is currently
--                      #   world position 0,0
--   handle_input()     # call in _update() to handle movement key presses.
--                      #   Assumes any sprite with flag 0 set is an obstacle.
--   draw_player()      # call in _draw(). Draws the player sprite.

function init_player(start_pos)
   player_pos = start_pos
   camera_pos = {start_pos[1]-8, start_pos[2]-8}

   facing = {1, 0}

   -- this is a constant for looking up player sprites by facing
   player_lookup = {
      [0] = {
         [0] = -1, -- error state
         [-1] = 122, -- left
         [1] = 123, -- right
      },
      [-1] = {
         [0] = 120, -- up
         [-1] = 124, -- up-left
         [1] = 125, -- up-right
      },
      [1] = {
         [0] = 121, -- down
         [-1] = 126, -- down-left
         [1] = 127, -- down-right
      },
   }
end


function handle_input()
   local new_pos = {camera_pos[1], camera_pos[2]}
   local new_ppos = {player_pos[1], player_pos[2]}

   if btnp(0) or btnp(1) or btnp(2) or btnp(3) then
      if btnp(0) then
         new_pos[1] -= 1 -- move left
         new_ppos[1] -= 1
         facing[2] = -1
      end
      if btnp(1) then
         new_pos[1] += 1 -- move right
         new_ppos[1] += 1 -- move right
         facing[2] = 1
      end
      if not (btnp(0) or btnp(1)) then
         facing[2] = 0
      end

      if btnp(2) then
         new_pos[2] -= 1 -- move up
         new_ppos[2] -= 1 -- move up
         facing[1] = -1
      end
      if btnp(3) then
         new_pos[2] += 1 -- move down
         new_ppos[2] += 1 -- move down
         facing[1] = 1
      end
      if not (btnp(2) or btnp(3)) then
         facing[1] = 0
      end
   end

   if _legal_move(new_pos) then
      camera_pos = new_pos
      player_pos = new_ppos
   end
end

function draw_player()
   spr(player_lookup[facing[1]][facing[2]], 64, 64)
   -- todo: animate the character on move
end

-- pos is camera position, meaning the map-relative player
-- position is pos + {8, 8}.
function _legal_move(pos)
   return not fget(mget(pos[1]+8, pos[2]+8), 0)
end