require 'metalua.mlc'
require 'metalua.walk'

function weave_ast (src, ast, name)

   -------------------------------------------------------------------
   -- translation: associate an AST node to its recomposed source
   -- ast_children: associate an AST node to the list of its children
   -- ast_parent: associate an AST node to the list of its parent
   -- weavable: whether an AST node supports weaving of its children
   -- node: common walker config for exprs, stats & blocks
   -------------------------------------------------------------------
   local translation, ast_children, ast_parent, weaveable, node =
      { }, { }, { }, { }, { }

   -------------------------------------------------------------------
   -- Build up the parent/children relationships. This is not the same
   -- as inclusion between tables: the relation we're building only
   -- relates blocks, expressions and statements; in the AST, some
   -- tables don't represent any of these node kinds.
   -- For instance in `Local{ { `Id "x" }, { } }, `Id"x" is a child of
   -- the `Local{ } node, although it's not directly included in it.
   -------------------------------------------------------------------
   function node.down(ast, parent)
      ----------------------------------------------------
      -- `Do{ } blocks are processed twice:
      --  * once as a statement
      --  * once as a block, child of itself
      -- This prevents them from becoming their own child.
      ----------------------------------------------------
      if ast==parent then return end

      if not ast.lineinfo then 
         weaveable [ast] = false, false
         if parent then weaveable [parent] = false end
      else
         weaveable [ast] = true
         
         -- normalize lineinfo
         -- TODO: FIXME
         if ast.lineinfo.first[3] > ast.lineinfo.last[3] then
           ast.lineinfo.first, ast.lineinfo.last = ast.lineinfo.last, ast.lineinfo.first
         end
      end
      ast_children [ast] = { }
      ast_parent [ast] = parent
      if parent then table.insert (ast_children [parent], ast) end
   end

   -------------------------------------------------------------------
   -- Visit up, from leaves to upper-level nodes, and weave leaves
   -- back into the text of their parent node, recursively.  Since the
   -- visitor is imperative, we can't easily make it return a value
   -- (the resulting recomposed source, here). Therefore we
   -- imperatively store results in the association table
   -- `translation'.
   -------------------------------------------------------------------
   function node.up(ast)
      local _acc = { }
      local function acc(x) table.insert (_acc, x) end
      
      if not next(ast) then -- shadow node, remove from ast_children
         local x = ast_children[ast_parent[ast]]
         for i,a in ipairs (x) do if a==ast then table.remove (x, i); break end end
         return "" -- no need to continue, we know that the node is empty!
      end
      
      -- ast Can't be weaved normally, try something else --
      local function synthetize (ast)
         acc "-{expr: "
         acc (table.tostring (ast, 'nohash', 80, 8))
         acc " }"
      end

      -- regular weaving of chidren in the parent's sources --
      local function weave (ast)
         -- sort children in appearence order
         local comp = |a,b| a.lineinfo.first[3] < b.lineinfo.first[3]
         table.sort (ast_children [ast], comp)
 
         local li = ast.lineinfo
         if not li then return synthetize (ast) end
         local a, d = li.first[3], li.last[3]
         for child in ivalues (ast_children [ast]) do
            local li = child.lineinfo
            local b, c = li.first[3], li.last[3]
            acc (src:sub (a, b - 1))
            acc (translation [child])
            a = c + 1
         end
         acc (src:sub (a, d))
      end

      -- compute the translation from the children's ones --
      if not translation [ast] then
         if weaveable [ast] then weave (ast) else synthetize (ast) end
         translation [ast] = table.concat (_acc)
      end
   end

   local cfg = { expr=node; stat=node; block=node }
   walk.block (cfg, ast)

   return translation [ast]
end

-- Get the source. If none is given, use itself as an example. --
local filename = arg[2] or arg[1] or arg[0]
local f = assert (io.open (filename, 'r'))
local src = f:read '*a'
f:close()

local ast = mlc.luastring_to_ast (src, name)
if not next(ast) then
   io.write (src) -- Empty ast, probably empty file, or comments only
else
   local before = src:sub (1, ast.lineinfo.first[3]-1)
   local after  = src:sub (ast.lineinfo.last[3]+1, -1)
   io.write (before .. weave_ast (src, ast) .. after)
end