-- idea 1
--? function find_path_for_crate(level, src, crate_to_move, dst)
--?   local done = {}
--?   local cands = {}
--?   table.insert(cands, {x=src.x, y=src.y})
--?   while #cands > 0 do
--?     local cand = table.remove(cands, 1)
--?     local x,y = cand.x, cand.y
--?     if x == dst.x and y == dst.y then return cand end
--?     if y >= 1 and y <= lh and x >= 1 and x <= lw and not done[y][x] then
--?       done[y][x] = true
--?       local curr = level[y][x]
--?       if curr ~= CELL_WALL and curr ~= CELL_CRATE and curr ~= CELL_CRATE_ON_TARGET then
--?         table.insert(cands, {x=x-1, y=y, dir='left', prev=cand})
--?         table.insert(cands, {x=x+1, y=y, dir='right', prev=cand})
--?         table.insert(cands, {x=x, y=y-1, dir='up', prev=cand})
--?         table.insert(cands, {x=x, y=y+1, dir='down', prev=cand})
--?       elseif curr == CELL_CRATE and crate_id[y][x] == cid then
--?         -- TODO: actually simulate a real move of a crate
--?         table.insert(cands, {x=x-1, y=y, dir='left', prev=cand})
--?         table.insert(cands, {x=x+1, y=y, dir='right', prev=cand})
--?         table.insert(cands, {x=x, y=y-1, dir='up', prev=cand})
--?         table.insert(cands, {x=x, y=y+1, dir='down', prev=cand})
--?       end end end end