-- show a list of all trades

-- the player is accessing the trade list
yl_speak_up.input_trade_list = function(player, formname, fields)
        local pname = player:get_player_name()
	local d_id = yl_speak_up.speak_to[pname].d_id
	local n_id = yl_speak_up.speak_to[pname].n_id

        local dialog = yl_speak_up.speak_to[pname].dialog

	if(not(dialog.trades)) then
		dialog.trades = {}
	end

	-- the player wants to add a new trade
	if(fields.trade_list_add_trade) then
		-- show the trade config dialog for a new trade
		yl_speak_up.show_fs(player, "add_trade_simple", "new")
		return
	end

	-- toggle between view of dialog option trades and trade list trades
	if(fields.show_dialog_option_trades
	  or fields.show_trade_list) then
		yl_speak_up.show_fs(player, "trade_list", fields.show_dialog_option_trades)
		return
	end

	-- go back to the main dialog
	if(fields.finished_trading) then
		yl_speak_up.show_fs(player, "talk", {n_id = n_id, d_id = d_id})
		return
	end

	-- normal mode: the player wants to see a particular trade
	for k,v in pairs(dialog.trades) do
		if(fields[ k ]) then
			yl_speak_up.show_fs(player, "trade_simple", k)
			return
		end
	end

	-- show the inventory of the NPC
	if(fields.show_inventory) then
		yl_speak_up.show_fs(player, "inventory")
		return
	end
	-- TODO: and otherwise?
end


-- show a list of all trades the NPC has to offer
-- if show_dialog_option_trades is set: show only those trades that are attached to options of dialogs;
--   otherwise show only those trades attached to the trade list
yl_speak_up.get_fs_trade_list = function(player, show_dialog_option_trades)
	if(not(player)) then
		return ""
	end
	local pname = player:get_player_name()
	-- which NPC is the player talking to?
	local n_id = yl_speak_up.speak_to[pname].n_id
	local dialog = yl_speak_up.speak_to[pname].dialog
	-- do we have all the necessary data?
	if(not(n_id) or not(dialog.n_npc)) then
		return "size[6,2]"..
			"label[0.2,0.5;Ups! This NPC lacks ID or name.]"..
		                "button_exit[2,1.5;1,0.9;exit;Exit]"

	end

	-- make sure the NPC has that table defined
	if(not(dialog.trades)) then
		dialog.trades = {}
	end

	yl_speak_up.load_npc_inventory(n_id)
	local npc_inv = minetest.get_inventory({type="detached", name="yl_speak_up_npc_"..tostring(n_id)})

	local formspec = {}

	if(yl_speak_up.may_edit_npc(player, n_id)) then
		-- allow players with the right priv to switch view between dialog option trades
		-- and those normal ones in the trade list
		if(not(show_dialog_option_trades)) then
			table.insert(formspec, "button[3.0,-0.5;5.0,0.9;show_dialog_option_trades;"..
				"Show trades attached to dialog options]")
		else
			table.insert(formspec, "button[3.0,-0.5;5.0,0.9;show_trade_list;"..
				"Show trade list trades (player view)]")
		end
	else
		-- do not show trades attached to dialog options for players who cannot edit the NPC
		show_dialog_option_trades = false
	end

	-- arrange the offers in yl_speak_up.trade_max_cols columns horizontally
	-- and yl_speak_up.trade_max_rows row vertically
	local row = 0
	local col = 0
	local anz_trades = 0

	-- the order in which the trades appear shall not change each time;
	-- but lua cannot sort the keys of a table by itself...
	local sorted_trades = {}
	for k in pairs(dialog.trades) do
		table.insert(sorted_trades, k)
	end
	table.sort(sorted_trades)

	-- TODO: handle multiple pages?
	for i, k in ipairs(sorted_trades) do
		v = dialog.trades[ k ]
		if(col < yl_speak_up.trade_max_cols
		  -- needs both to be negated because show_dialog_option_trades will most of the time be nil
		  -- and the actual value of v.d_id isn't of intrest here either
		  and (not(show_dialog_option_trades) == not(v.d_id))
		  and v.pay and v.pay[1] and v.pay[1] ~= "" and v.buy and v.buy[1] and v.buy[1] ~= "") then
			local pay_stack = ItemStack(v.pay[1])
			local buy_stack = ItemStack(v.buy[1])
			-- do not show trades with nonexistant items
			if(  not(minetest.registered_items[ pay_stack:get_name() ])
			  or not(minetest.registered_items[ buy_stack:get_name() ])) then
				break
			end

			anz_trades = anz_trades + 1
			local kstr = tostring(minetest.formspec_escape(k))
			table.insert(formspec,
				"item_image_button["..tostring(1+(col*4))..","..tostring(1+row)..";1,1;"..
					tostring(v.pay[1])..";"..kstr..";]"..
				"image_button["..tostring(1.8+(col*4))..","..tostring(1+row)..";1,1;"..
					"gui_furnace_arrow_bg.png^[transformR270;"..kstr..";]"..
				"item_image_button["..tostring(2.6+(col*4))..","..tostring(1+row)..";1,1;"..
					tostring(v.buy[1])..";"..kstr..";]")
			if(not(npc_inv:contains_item("npc_main", buy_stack))) then
				table.insert(formspec,
					"label["..tostring(1.7+(col*4))..","..tostring(1.2+row)..";Sold out]")
			end
			row = row + 1
			if(row > yl_speak_up.trade_max_rows) then
				row = 0
				col = col + 1
			end
		end
	end

	-- if there are no trades, at least print a hint that there could be some here
	-- (a mostly empty formspec looks too boring and could irritate players)
	if(anz_trades == 0) then
		table.insert(formspec,
			"label[1,1;Sorry. There are currently no offers available.]")
	end

	-- button "add trade" for those who can edit the NPC (entering edit mode is not required)
	-- also add a quick way to access the inventory of the npc
	if(yl_speak_up.may_edit_npc(player, n_id)) then
		table.insert(formspec,
			"button["..tostring(yl_speak_up.trade_max_cols * 4 - 2.2)..
				",0.2;2.0,0.9;trade_list_add_trade;Add trade]"..
			"button["..tostring(yl_speak_up.trade_max_cols * 4 - 4.2)..
				",-0.5;4.0,0.9;show_inventory;Show inventory of NPC]")
	end

	return "size["..
		tostring(yl_speak_up.trade_max_cols * 4)..","..
		tostring(yl_speak_up.trade_max_rows + 2).."]"..
		"button[0.2,0.0;2.0,0.9;finished_trading;Back to talk]"..
		"label[3.0,0.2;"..tostring(dialog.n_npc).." offers you these trades:]"..
		table.concat(formspec, "")
end