-------------------------------------------------------------------------------
-- Copyright (c) 2011-2012 Sierra Wireless and others.
-- All rights reserved. This program and the accompanying materials
-- are made available under the terms of the Eclipse Public License v1.0
-- which accompanies this distribution, and is available at
-- http://www.eclipse.org/legal/epl-v10.html
--
-- Contributors:
--     Sierra Wireless - initial API and implementation
-------------------------------------------------------------------------------
--  Context handling: allows to evaluate code snippets in the context of a function
-------------------------------------------------------------------------------

local M = { }

local dbgp = require "debugger.dbgp"
local util = require "debugger.util"

-- make unique object to access contexts
local LOCAL, UPVAL, GLOBAL, EVAL, STORE, HANDLE = {}, {}, {}, {}, {}, {}

local getglobals
if DBGP_CLIENT_LUA_VERSION == "Lua 5.1" then
  getglobals = function(f) return getfenv(f) end
elseif DBGP_CLIENT_LUA_VERSION == "Lua 5.2" then
  getglobals = function(f, cxt)
    -- 'global' environment: this is either the local _ENV or upvalue _ENV. A special case happen when a
    -- function does not reference any global variable: the upvalue _ENV may not exist at all. In this case,
    -- global environment is not relevant so it is fixed to an empty table. Another solution would be to set it
    -- to the environment from above stack level but it would require some overhead (especially if multiple
    -- levels must be instantiated)
    if     cxt[LOCAL][STORE]["_ENV"] then return cxt[LOCAL]["_ENV"]
    elseif cxt[UPVAL][STORE]["_ENV"] then return cxt[UPVAL]["_ENV"]
    else return { } end
  end
end

--- Captures variables for given stack level. The capture contains local, upvalues and global variables.
-- The capture can be seen as a proxy table to the stack level: any value can be queried or set no matter
-- it is a local or an upvalue.
-- The individual local and upvalues context are also available and can be queried and modified with indexed notation too.
-- These objects are NOT persistant and must not be used outside the debugger loop which instanciated them !
M.Context = {
  -- Context identifiers can be accessed by their DBGp context ID
  [0] = LOCAL,
  [1] = GLOBAL, -- DLTK internal ID for globals is 1
  [2] = UPVAL,
  -- EVAL is used to keep results from eval in cache in order to browse or modify them, results are stored as sequence
  [-1] = EVAL,
  STORE = STORE,

  -- gets a variable by name with correct handling of Lua scope chain
  -- the or chain does not work here beacause __index metamethod would raise an error instead of returning nil
  __index = function(self, k)
    if     self[LOCAL][STORE][k] then return self[LOCAL][k]
    elseif self[UPVAL][STORE][k] then return self[UPVAL][k]
    else return self[GLOBAL][k] end
  end,
  __newindex = function(self, k, v)
    if     self[LOCAL][STORE][k] then self[LOCAL][k] = v
    elseif self[UPVAL][STORE][k] then self[UPVAL][k] = v
    else self[GLOBAL][k] = v end
  end,

  -- debug only !!
  __tostring = function(self)
    local buf = { "Locals: \n" }
    for k,v in pairs(self[LOCAL][STORE]) do
      buf[#buf+1] = "\t"..tostring(k).."("..tostring(v)..")="..tostring(self[LOCAL][k]).."\n"
    end
    buf[#buf+1] = "Upvalues: \n"
    for k,v in pairs(self[UPVAL][STORE]) do
      buf[#buf+1] = "\t"..tostring(k).."("..tostring(v)..")="..tostring(self[UPVAL][k]).."\n"
    end
    return table.concat(buf)
  end,

  LocalContext = {
    __index = function(self, k)
      local index = self[STORE][k]
      if not index then error("The local "..tostring(k).." does not exists.") end
      local handle = self[HANDLE]
      return select(2, handle.coro:getlocal(handle.level, index))
    end,
    __newindex = function(self, k, v)
      local index = self[STORE][k]
      if index then
        local handle = self[HANDLE]
        handle.coro:setlocal(handle.level, index, v)
      else error("Cannot set local " .. k) end
    end,
    -- Lua 5.2 ready :)
    --__pairs = function(self) return getmetatable(self).iterator, self, nil end,
    iterator = function(self, prev)
      local key, index = next(self[STORE], prev)
      if key then return key, self[key] else return nil end
    end,
  },

  UpvalContext = {
    __index = function(self, k)
      local index = self[STORE][k]
      if not index then error("The local "..tostring(k).." does not exitsts.") end
      return select(2, debug.getupvalue(self[HANDLE], index))
    end,
    __newindex = function(self, k, v)
      local index = self[STORE][k]
      if index then debug.setupvalue(self[HANDLE], index, v)
      else error("Cannot set upvalue " .. k) end
    end,
    -- Lua 5.2 ready :)
    -- __pairs = function(self) return getmetatable(self).iterator, self, nil end,
    iterator = function(self, prev)
      local key, index = next(self[STORE], prev)
      if key then return key, self[key] else return nil end
    end,
  },

  --- Context constructor
  -- @param coro  (util.*Thread instance) coroutine to map to
  -- @param level (number) stack level do dump (script stack level)
  new = function(cls, coro, level)
    local locals, upvalues = {}, {}
    if level < 0 then dbgp.error(301, "No such stack level: "..tostring(level)) end
    local func = (coro:getinfo(level, "f") or dbgp.error(301, "No such stack level: "..tostring(level))).func

    -- local variables
    for i=1, math.huge do
      local name, val = coro:getlocal(level, i)
      if not name then break
      elseif name:sub(1,1) ~= "(" then -- skip internal values
        locals[name] = i
      end
    end

    -- upvalues
    for i=1, math.huge do
      local name, val = debug.getupvalue(func, i)
      if not name then break end
      upvalues[name] = i
    end

    locals = setmetatable({ [STORE] = locals, [HANDLE] = { level = level, coro = coro } }, cls.LocalContext)
    upvalues = setmetatable({ [STORE] = upvalues, [HANDLE] = func }, cls.UpvalContext)

    local result = setmetatable({ [LOCAL] = locals, [UPVAL] = upvalues, [EVAL] = {} }, cls)
    rawset(result, GLOBAL, getglobals(func, result))
    return result
  end,
}

--- Handle caching of all instantiated context.
-- Returns a function which takes 2 parameters: thread and stack level and returns the corresponding context. If this
-- context has been already queried there is no new instantiation. A ContextManager is valid only during the debug loop
-- on which it has been instantiated. References to a ContextManager must be lost after the end of debug loop (so
-- threads can be collected).
-- If a context cannot be instantiated, an 301 DBGP error is thrown.
function M.ContextManager()
  local cache = { }
  return function(thread, level)
    -- the real coroutine is used as key (not the wrapped instance as its unicity is not guaranteed)
    -- otherwise, true is used to identify current thread (as nil is not a valid table key)
    local key = thread[1] or true
    local thread_contexts = cache[key]
    if not thread_contexts then
      thread_contexts = { }
      cache[key] = thread_contexts
    end

    local context = thread_contexts[level]
    if not context then
      context = M.Context:new(thread, level)
      thread_contexts[level] = context
    end

    return context
  end
end

return M