local export = {}

local base_location = "Module:data tables"
local metadata = mw.loadData(base_location.."/metadata")
--"Module:data tables/data"
local shard_location_base = metadata["shard_location_base"][1]
local shards = metadata["shards"][1]
local tables = metadata["tables"]
--[[
		{"grc_RLBG_lemma_to_index",
		"grc_RWoodhouse_lemma_to_headwords",
		"grc_RWoodhouse_lemma_to_infinitives",
		"la_RMA_index_to_phrases",
		"grc_RCunliffe_lemma_to_index",
		"la_RMA_lemmas_no_collision_to_ix_phrase" }
]]

function load_tables_unsharded()
	function maybe_mw_load(x)
		local success, val = pcall(function() return mw.loadData(x) end)
 		if success then return val else return nil end	end
	local unsharded, i = {}, 0
    while #unsharded == i do
    	---shard_location_base
      local val = maybe_mw_load(shard_location_base.."Unsharded"..tostring(i))
      if val ~= nil then 
      	unsharded[#unsharded+1] = val end
      i = i + 1
    end
    return unsharded
end

local unsharded = load_tables_unsharded()

function map(f, xs)
	local ys = {}	
	for i,x in pairs(xs) do ys[i]=f(x) end 
	return ys
end

function map_string(f, s)
	local ys = {}	
	for i = 1,#s do ys[i]=f(s:sub(i,i)) end 
	return ys
end

function fold(f, l, xs)
	for i,x in pairs(xs) do l = f(l, x) end
	return l
end

function hash(s)
	return fold(
		function(x,y) return x + y end,
		0,
		map_string(
			function(x) return x:byte() end, s
			)
		)%shards
end

function export.list_tables()
	return map(function (x) return x end, tables)
end

function export.load_table(n)
	local t = {}
	for i = 1,shards do 
		local curr = mw.loadData(shard_location_base..(i-1))
		if curr[n] ~= nil then
			for k,v in pairs(curr[n]) do
				t[k]=v end end end
	for i,curr in pairs(unsharded) do 
		if curr[n] ~= nil then
			for k,v in pairs(curr[n]) do
				t[k]=v end end end
	return t
end

--[[
eventually: 
   1 :	loop through all unsharded if multiple
   2 :	index k in unsharded and shard separately,
		returning from unsharded preferentially		]]
function export.index_table(t, k)
    local shard = mw.loadData(shard_location_base .. hash(k))				
    if unsharded[1] ~= nil
    	and unsharded[1][t] ~= nil
    	and unsharded[1][t][k] ~= nil
    		then
    	
    	return unsharded[1][t][k]
    else
    	if shard[t] ~= nil then
    		return shard[t][k]
    	else
    		return nil
    	end
    end
end

function export.index_table_all(t, ks)
    baskets, result = {}, {}
    for i,k in pairs(ks) do 
    	h = hash(k)
    	if baskets[h] == nil then 
    		baskets[h] = {k} 
    	else 
    		baskets[h][#(baskets[h])+1] = k
    	end
    end
    for h,b in pairs(baskets) do 
    	local shard = mw.loadData(shard_location_base..h)
    	for i,k in pairs(b) do
    		-- here, loop over all unsharded if multiple
    		if unsharded ~= nil
    			and unsharded[1] ~= nil
    			and unsharded[t] ~= nil
    				then
    			result[k] = unshared[t][k]
			else 
				if shard[t][k] ~= nil then 
					result[k] = shard[t][k]
    			end
			end
		end
	end
    return result
end

function export.select(t,p)
	return nil  --Not implemented.
end

return export