--[[
Copyright (c) 2012-2013 Kaarle Ritvanen
See LICENSE file for license details
--]]

local M = {}

local err = require('acf.error')

-- TODO each transaction backend (i.e. persistence manager or
-- transaction proper) should be implemented as a thread or have its
-- internal state stored in shared storage (with appropriate locking)


local generation = 0
function M.gen_number()
   generation = generation + 1
   return generation
end


M.TransactionBackend = require('acf.object').class()

function M.TransactionBackend:init() self.mod_time = {} end

function M.TransactionBackend:get_if_older(path, timestamp)
   local value, ts = self:get(path)
   if ts > timestamp then err.raise('conflict', path) end
   return value, ts
end

function M.TransactionBackend:set(path, value)
   self:set_multiple{{path, value}}
end

function M.TransactionBackend:set_multiple(mods)
   -- TODO delegate to PM backends?
   local timestamp = M.gen_number()
   local effective = {}

   local function tostr(s) return s ~= nil and tostring(s) or nil end

   for _, mod in ipairs(mods) do
      local path, value = unpack(mod)

      if type(value) == 'table' or type(
	 self:get(path)
      ) == 'table' or self:get(path) ~= value then

	 table.insert(effective, mod)
	 self.mod_time[path] = timestamp
      end
   end

   self:_set_multiple(effective)
end

-- TODO should be atomic, mutex with set_multiple
function M.TransactionBackend:comp_and_setm(accessed, mods)
   local errors = err.ErrorDict()
   for path, timestamp in pairs(accessed) do
      errors:collect(self.get_if_older, self, path, timestamp)
   end
   errors:raise()

   self:set_multiple(mods)
end


return M