-- store which player is monitoring the NPC (for preconditions and
-- effects)
yl_speak_up.debug_mode_set_by_player = {}

-- for sending debug information about preconditions and effects to
-- the player who is monitoring the NPC
-- (sometimes it is not easy/obvious to see why something failed)
yl_speak_up.debug_msg = function(player, n_id, o_id, text)
	local dname = yl_speak_up.debug_mode_set_by_player[ n_id ]
	-- nobody cares
	if(not(dname)) then
		return
	end
	local pname = player:get_player_name()
	local d_id = yl_speak_up.speak_to[pname].d_id
	minetest.chat_send_player(dname, "[NPC "..tostring(n_id)..": "..
		tostring(pname).."] <"..tostring(d_id).." "..tostring(o_id)..
		"> "..tostring(text))
end


-- a chat command for entering and leaving debug mode; needs to be a chat command
-- because the player may have wandered off from his NPC and get too many messages
-- without a quick way to get rid of them otherwise
minetest.register_chatcommand( 'npc_talk_debug', {
	description = "Sets you as debugger for the yl_speak_up-NPC with the ID <n_id>.\n"..
		"  <list> lists the NPC you are currently debugging.\n"..
		"  <off> turns debug mode off again.",
	privs = {npc_talk_owner},
	func = function(pname, param)
		if(param and param == "off") then
			local count = 0
			for k, v in pairs(yl_speak_up.debug_mode_set_by_player) do
				if(v and v == pname) then
					yl_speak_up.debug_mode_set_by_player[ k ] = nil
					count = count + 1
					minetest.chat_send_player(pname, "You are no longer "..
						"debugging the NPC with the ID "..tostring(k)..".")
				end
			end
			minetest.chat_send_player(pname, "Removed you as debugger of "..
				tostring(count).." NPCs.")
			return
		elseif(not(param) or param == "" or param == "list") then
			local count = 0
			local text = "You are currently debugging the NPCs with the following IDs:\n"
			for k, v in pairs(yl_speak_up.debug_mode_set_by_player) do
				if(v and v == pname) then
					count = count + 1
					text = text.."  "..tostring(k)
				end
			end
			if(count == 0) then
				text = text.." - none -"
			else
				text = text.."\nTo turn debugging off, call this command with the "..
					"parameter <off>."
			end
			minetest.chat_send_player(pname, text)
			return
		elseif(not(yl_speak_up.may_edit_npc(minetest.get_player_by_name(pname), n_id))) then
			minetest.chat_send_player(pname, "You do not have the necessary privs to "..
				"edit that NPC.")
			return
		else
			yl_speak_up.debug_mode_set_by_player[ param ] = pname
			minetest.chat_send_player(pname, "You are now receiving debug information "..
				"for NPC "..tostring(param)..".\nTo turn that off, type "..
				"\"/npc_talk_debug off\".")
		end
	end
});


-- evaluate those preconditions of type "function" (set by the staff)
-- and execute those effects/results of type "function" (set by the staff)
-- WARNING: This is extremly powerful!
--          The code is taken out of the function
--              calculate_displayable_options(..)
--          (written by AliasAlreadyTaken).
-- It requires the npc_master priv to add or edit this prereq.
-- The function is called by
--   * yl_speak_up.eval_precondition and
--   * yl_speak_up.eval_effect.
yl_speak_up.eval_and_execute_function = function(player, x_v, id_prefix)
	local pname = player:get_player_name()

        --minetest.chat_send_all("this is in a single prereq or effect: "..dump(x_v))
        local x_id = x_v[ id_prefix.. "id" ]
        if x_v[ id_prefix.."type" ] ~= "function" then
		return true
	end

        local code = x_v[ id_prefix.."value" ]
        if code:byte(1) == 27 then
            local obj = yl_speak_up.speak_to[pname].obj
            local n_id = yl_speak_up.speak_to[pname].n_id
            local npc = get_number_from_id(n_id)
            if obj:get_luaentity() and tonumber(npc) then
                minetest.log("error","[MOD] yl_speak_up: NPC with ID n_"..npc.." at position "..minetest.pos_to_string(obj:get_pos(),0).." could not compile the content of "..x_id.." :"..dump(code) .. " because of illegal bytecode for player "..pname)
            else
                minetest.log("error","[MOD] yl_speak_up: NPC with ID unknown could not compile the content of "..x_id.." :"..dump(code) .. " for player unknown because of illegal bytecode")
            end
        end

	local param = "playername"
	if( id_prefix == "r_") then
		param = "player"
	end
        local f, msg = loadstring("return function("..param..") " .. code .. " end")

        if not f then
            local obj = yl_speak_up.speak_to[pname].obj
            local n_id = yl_speak_up.speak_to[pname].n_id
            local npc = get_number_from_id(n_id)
            if obj:get_luaentity() and tonumber(npc) then
                minetest.log("error","[MOD] yl_speak_up: NPC with ID n_"..npc.." at position "..minetest.pos_to_string(obj:get_pos(),0).." could not compile the content of "..x_id.." :"..dump(code) .. " for player "..pname)
            else
                minetest.log("error","[MOD] yl_speak_up: NPC with ID unknown could not compile the content of "..x_id.." :"..dump(code) .. " for player unknown")
            end
        else
            local func = f()

            local ok, ret = pcall(func,pname)

            if not ok then
                local obj = yl_speak_up.speak_to[pname].obj
                local n_id = yl_speak_up.speak_to[pname].n_id
                local npc = get_number_from_id(n_id)
                if obj:get_luaentity() and tonumber(npc) then
                    minetest.log("error","[MOD] yl_speak_up: NPC with ID n_"..npc.." at position "..minetest.pos_to_string(obj:get_pos(),0).." could not execute the content of "..x_id.." :"..dump(code) .. " for player "..pname)
                else
                    minetest.log("error","[MOD] yl_speak_up: NPC with ID unknown could not execute the content of "..x_id.." :"..dump(code) .. " for player unknown")
                end
            end

            if type(ret) == "boolean" then
                return ret
            end
        end
	-- fallback
	return false
end


-- These two functions
--   * yl_speak_up.input_fs_edit_option_related and
--   * yl_speak_up.get_fs_edit_option_related
-- are very similar for preconditions and effects. Therefore they're called here
-- with a lot of parameters. fs_edit_preconditions.lua and fs_edit_effects.lua
-- contain only wrappers.

yl_speak_up.input_fs_edit_option_related = function(player, formname, fields,
		id_prefix, element_list_name, max_entries_allowed,
		element_desc, tmp_data_cache,
		text_ask_for_punching,
		values_what, values_operator, values_block, values_trade, values_inv,
		check_what, check_operator, check_block, check_trade, check_inv,
		get_sorted_player_var_list_function,
		formspec_input_to
		)
	if(not(player)) then
		return
	end
	local pname = player:get_player_name()
	-- what are we talking about?
	local n_id = yl_speak_up.speak_to[pname].n_id
	local d_id = yl_speak_up.speak_to[pname].d_id
	local o_id = yl_speak_up.speak_to[pname].o_id
	local x_id = yl_speak_up.speak_to[pname][ id_prefix.."id"]

	-- this only works in edit mode
	if(not(n_id) or yl_speak_up.edit_mode[pname] ~= n_id) then
		return
	end

	-- delete precondition
	if(fields.delete_element) then
		local dialog = yl_speak_up.speak_to[pname].dialog
		if(dialog and dialog.n_dialogs
		  and x_id
		  and dialog.n_dialogs[d_id]
		  and dialog.n_dialogs[d_id].d_options
		  and dialog.n_dialogs[d_id].d_options[o_id]) then
			-- actually delete the element
			dialog.n_dialogs[d_id].d_options[o_id][ element_list_name ][ x_id ] = nil
			-- record this as a change, but do not save do disk yet
			table.insert(yl_speak_up.npc_was_changed[ n_id ],
				"Dialog "..tostring(d_id)..": "..element_desc.." "..tostring( x_id )..
				" deleted for option "..tostring(o_id)..".")
			-- TODO: when trying to save: save to disk as well?
			-- show the new/changed element
			-- go back to the edit option dialog (after all we just deleted the prerequirement)
			yl_speak_up.show_fs(player, "msg", {
				input_to = "yl_speak_up:"..formspec_input_to,
				formspec = "size[6,2]"..
					"label[0.2,0.5;"..element_desc.." \""..
					minetest.formspec_escape(tostring( x_id ))..
					"\" has been deleted.]"..
					"button[1.5,1.5;2,0.9;back_from_delete_element;Back]"})
			return
		end
	end

	if(fields.select_block_pos) then
		minetest.chat_send_player(pname, text_ask_for_punching)
		-- this formspec expects the block punch:
		yl_speak_up.speak_to[pname].expect_block_punch = formspec_input_to
		return
	end

	-- field inputs: those do not trigger a sending of the formspec on their own

	-- are we talking about an inventory?
	-- (inventory only applies to preconditions; not effects)
	local data = yl_speak_up.speak_to[pname][ tmp_data_cache ]
	if(fields.inv_stack_name and fields.inv_stack_name ~= ""
	  and id_prefix == "p_"
	  and data and data.what and data.what >= 5 and data.what <= 6) then
		local parts = fields.inv_stack_name:split(" ")
		local size = 1
		if(parts and #parts > 1) then
			size = tonumber(parts[2])
			if(not(size) or size < 1) then
				size = 1
			end
		end
		-- does the item exist?
		if(minetest.registered_items[ parts[1] ]) then
			data.inv_stack_name = parts[1].." "..tostring(size)
		else
			-- show error message
			yl_speak_up.show_fs(player, "msg", {
				input_to = "yl_speak_up:"..formspec_input_to,
				formspec = "size[8,2]"..
					"label[0.2,0.5;Error: \""..
					minetest.formspec_escape(fields.inv_stack_name)..
					"\" is not a valid item(stack).]"..
					"button[1.5,1.5;2,0.9;back_from_error_msg;Back]"})
			return
		end

	-- comparison value for a variable (same for both preconditions and effects)
	elseif(fields.var_cmp_value
	  and data and data.what and data.what == 2) then
		data.var_cmp_value = fields.var_cmp_value

	-- text for a chat message
	elseif(fields.chat_msg_text
	  and data and data.what and data.what == 6 and id_prefix == "r_") then
		data.chat_msg_text = fields.chat_msg_text
	end

	-- the save button was pressed
	if(fields.save_element and data and data.what and values_what[ data.what ]) then
		-- for creating the new prerequirement; normal elements: p_type, p_value, p_id
		local v = {}
		-- determine p_type
		v[ id_prefix.."type" ] = values_what[ data.what ]

		local dialog = yl_speak_up.speak_to[pname].dialog
		if(not(dialog) or not(dialog.n_dialogs)
		  or not(dialog.n_dialogs[d_id])
		  or not(dialog.n_dialogs[d_id].d_options)
		  or not(dialog.n_dialogs[d_id].d_options[o_id])) then
			-- this really should not happen during the normal course of operation
			-- (only if the player sends forged formspec data or a bug occoured)
			minetest.chat_send_player(pname, "Dialog or option does not exist.")
			return
		end
		local elements = dialog.n_dialogs[d_id].d_options[o_id][ element_list_name ]
		if(not(elements)) then
			dialog.n_dialogs[d_id].d_options[o_id][ element_list_name ] = {}
			elements = dialog.n_dialogs[d_id].d_options[o_id][ element_list_name ]
			x_id = "new"
		end
		-- set x_id appropriately
		if(not(x_id) or x_id == "new") then
			x_id = id_prefix..yl_speak_up.find_next_id(elements)
		end
		v[ id_prefix.."id" ] = x_id

		local sorted_key_list = yl_speak_up.sort_keys(elements)
		if( x_id == "new" and #sorted_key_list >= max_entries_allowed) then
			-- this really should not happen during the normal course of operation
			-- (only if the player sends forged formspec data or a bug occoured)
			minetest.chat_send_player(pname, "Maximum number of allowed entries exceeded.")
			return
		end
		-- "an internal state (i.e. of a quest)", -- 2
		if(data.what == 2) then
			v[ id_prefix.."value" ] = "expression"
			v[ id_prefix.."operator" ] = values_operator[ data.operator ]
			v[ id_prefix.."var_cmp_value" ] = (data.var_cmp_value or "")
			v[ id_prefix.."variable" ] = data.variable_name

		-- "a block somewhere", -- 3
		elseif(data.what == 3) then
			v[ id_prefix.."value" ] = values_block[ data.block ]
			if(not(data.block_pos) or not(data.node_data) or not(data.node_data.name)) then
				yl_speak_up.show_fs(player, "msg", {
					input_to = "yl_speak_up:"..formspec_input_to,
					formspec = "size[8,2]"..
						"label[0.2,0.5;Error: Please select a block first!]"..
						"button[1.5,1.5;2,0.9;back_from_error_msg;Back]"})
				return
			end
			-- for "node_is_air", there is no need to store node name and parameter
			if(v[ id_prefix.."value" ]
			  and (v[ id_prefix.."value" ] == "node_is_like"
			    or v[ id_prefix.."value" ] == "node_is_diffrent_from")) then
				v[ id_prefix.."node" ]   = data.node_data.name
				v[ id_prefix.."param2" ] = data.node_data.param2
			end
			-- we also need to store the position of the node
			v[ id_prefix.."pos" ] = {x = data.block_pos.x, y = data.block_pos.y, z = data.block_pos.z }
			-- "I can't punch it. The block is as the block *above* the one I punched.",
			if(id_prefix == "p_" and data.block == 5) then
				v.p_pos.y = v.p_pos.y + 1
			end

		-- "a trade", -- 4
		-- (only for preconditions; not for effects)
		elseif(data.what == 4 and id_prefix == "p_") then
			-- this depends on the trade associated with that option; therefore,
			-- it does not need any more parameters (they come dynamicly from the
			-- trade)
			v.p_value = values_trade[ data.trade ]

		-- "the inventory of the player", -- 5
		-- "the inventory of the NPC", -- 6
		-- (only for preconditions; not for effects)
		elseif((data.what == 5 or data.what == 6) and id_prefix == "p_") then
			v.p_value = values_inv[ data.inv ]
			if(v.p_value and v.p_value ~= "inv_is_empty") then
				-- we have checked this value earlier on
				v[ "p_itemstack" ] = data.inv_stack_name
			end

		-- "NPC crafts soemthing", -- 4
		-- (only for effects; not for preconditions)
		elseif(data.what and id_prefix == "r_" and data.what == 4) then
			local player_inv = player:get_inventory()
			if(player_inv:get_stack("craftpreview", 1):is_empty()) then
				yl_speak_up.show_fs(player, "msg", {
					input_to = "yl_speak_up:"..formspec_input_to,
					formspec = "size[8,2]"..
						"label[0.2,0.5;Error: Please prepare your craft grid first!"..
							"\nYour NPC needs to know what to craft.]"..
						"button[1.5,1.5;2,0.9;back_from_error_msg;Back]"})
				return
			end
			-- store the craft result (Note: the craft result may change in the future
			-- if the server changes its craft result, making this craft invalid)
			v[ "r_value" ] = player_inv:get_stack("craftpreview", 1):to_string()
			v[ "r_craft_grid"] = {}
			for i = 1, 9 do
				-- store all the indigrents of the craft grid
				table.insert( v[ "r_craft_grid" ],
					player_inv:get_stack("craft", i):to_string())
			end

		-- "go to other dialog if the action (i.e. trade) failed", -- 5
		-- (only for effects; not for preconditions)
		elseif(data.what and id_prefix == "r_" and data.what == 5) then
			v[ "r_value" ] = data.on_failure

		-- "send a chat message to all players", -- 6
		-- (only for effects; not for preconditions)
		elseif(data.what and id_prefix == "r_" and data.what == 6) then
			data.chat_msg_text = fields.chat_msg_text
			-- allow saving only if the placeholders are all present
			-- (reason for requiring them: players and server owners ought to
			-- be able to see who is responsible for a message)
			if(not(string.find(data.chat_msg_text, "%$NPC_NAME%$"))
			  or not(string.find(data.chat_msg_text, "%$PLAYER_NAME%$"))
			  or not(string.find(data.chat_msg_text, "%$OWNER_NAME%$"))) then
				yl_speak_up.show_fs(player, "msg", {
					input_to = "yl_speak_up:"..formspec_input_to,
					formspec = "size[9,2.5]"..
						"label[0.2,0.5;Error: Your chat message needs to contain "..
							"the following\nplaceholders: $NPC_NAME$, "..
							"$PLAYER_NAME$ and $OWNER_NAME$.\nThat way, other "..
							"players will know who sent the message.]"..
						"button[1.5,2.0;2,0.9;back_from_error_msg;Back]"})
				return
			end
			v[ "r_value" ] = data.chat_msg_text
		end

		-- only save if something was actually selected
		if(v[ id_prefix.."value"]) then
			if(not(dialog.n_dialogs[d_id].d_options[o_id][ element_list_name ])) then
				dialog.n_dialogs[d_id].d_options[o_id][ element_list_name ] = {}
			end
			-- store the change in the dialog
			dialog.n_dialogs[d_id].d_options[o_id][ element_list_name ][ x_id ] = v
			-- clear up data
			yl_speak_up.speak_to[pname][ id_prefix.."id" ] = nil
			yl_speak_up.speak_to[pname][ tmp_data_cache ] = nil
			-- record this as a change, but do not save do disk yet
			table.insert(yl_speak_up.npc_was_changed[ n_id ],
				"Dialog "..tostring(d_id)..": "..element_desc.." "..tostring(x_id)..
				" added/changed for option "..tostring(o_id)..".")
			-- TODO: when trying to save: save to disk as well?
			-- show the new/changed precondition
			yl_speak_up.show_fs(player, formspec_input_to, x_id)
			return
		end
	end


	-- selections in a dropdown menu (they trigger sending the formspec)

	-- select a general direction/type first
	if(fields.select_what) then
		local nr = table.indexof(check_what, fields.select_what)
		yl_speak_up.speak_to[pname][ tmp_data_cache ] = { what = nr }

	-- select a subtype for the "a trade" selection
	elseif(fields.select_trade) then
		local nr = table.indexof(check_trade, fields.select_trade)
		yl_speak_up.speak_to[pname][ tmp_data_cache ].trade = nr

	-- select a subtype for the inventory selection (player or NPC)
	elseif(fields.select_inv) then
		local nr = table.indexof(check_inv, fields.select_inv)
		yl_speak_up.speak_to[pname][ tmp_data_cache ].inv = nr

	-- select data regarding a block
	elseif(fields.select_block) then
		local nr = table.indexof(check_block, fields.select_block)
		yl_speak_up.speak_to[pname][ tmp_data_cache ].block = nr

	-- select data regarding a variable
	elseif(fields.select_variable) then
		-- get the list of available variables (with the same elements
		-- and the same sort order as when the dropdown was displayed)
		local var_list = get_sorted_player_var_list_function(pname)
		local nr = table.indexof(var_list, fields.select_variable)
		if(nr) then
			yl_speak_up.speak_to[pname][ tmp_data_cache ].variable = nr
			yl_speak_up.speak_to[pname][ tmp_data_cache ].variable_name = var_list[ nr ]
		end

	-- select data regarding an operator
	elseif(fields.select_operator) then
		local nr = table.indexof(check_operator, fields.select_operator)
		yl_speak_up.speak_to[pname][ tmp_data_cache ].operator = nr

	elseif(fields.select_on_failure) then
		-- in this case we really want the name of the target dialog
		yl_speak_up.speak_to[pname][ tmp_data_cache ].on_failure = fields.select_on_failure
	end

	-- the player wants to change/edit a precondition
	if(not(fields.back)
	  and (fields.change_element or fields.select_what or fields.select_trade
	  or fields.select_inv or fields.select_block
	  or fields.select_variable or fields.select_operator
	  or fields.select_on_failure
	  or fields.back_from_error_msg)) then
		yl_speak_up.show_fs(player, formspec_input_to)
		return
	end

	-- go back to the edit option dialog
	yl_speak_up.show_fs(player, "edit_option_dialog",
		{n_id = n_id, d_id = d_id, o_id = o_id, caller= formspec_input_to})
end


yl_speak_up.get_fs_edit_option_related = function(player, table_click_result,
		id_prefix, element_list_name, max_entries_allowed,
		element_desc, tmp_data_cache,
		what_do_you_want_txt,
		check_what, check_operator, check_block, check_trade, check_inv,
		get_sorted_player_var_list_function,
		show_element_function,
		table_of_name,
		text_variable, text_select_operator, text_select_value,
		text_block_position)
	if(not(player)) then
		return ""
	end
	local pname = player:get_player_name()
	-- what are we talking about?
	local n_id = yl_speak_up.speak_to[pname].n_id
	local d_id = yl_speak_up.speak_to[pname].d_id
	local o_id = yl_speak_up.speak_to[pname].o_id
	local x_id = yl_speak_up.speak_to[pname][ id_prefix.."id" ]

	-- this only works in edit mode
	if(not(n_id) or yl_speak_up.edit_mode[pname] ~= n_id) then
		return "size[1,1]label[0,0;You cannot edit this NPC.]"
	end

	local dialog = yl_speak_up.speak_to[pname].dialog
	if(not(dialog) or not(dialog.n_dialogs)
	  or not(dialog.n_dialogs[d_id])
	  or not(dialog.n_dialogs[d_id].d_options)
	  or not(dialog.n_dialogs[d_id].d_options[o_id])) then
		return "size[4,1]label[0,0;Dialog option does not exist.]"
	end

	local elements = dialog.n_dialogs[d_id].d_options[o_id][ element_list_name ]
	if(not(elements)) then
		elements = {}
	end

	-- did we arrive here through clicking on an element in the dialog edit options menu?
	if(table_click_result or elements[ table_click_result ]) then
		if(not(elements[ table_click_result ])) then
			-- which element has the player selected?
			local sorted_key_list = yl_speak_up.sort_keys(elements)
			local selected = minetest.explode_table_event(table_click_result)
			-- use "new" if nothing fits
			x_id = "new"
			if((selected.type == "CHG" or selected.type == "DLC")
			  and selected.row <= #sorted_key_list) then
				x_id = sorted_key_list[ selected.row ]
			end

			if( x_id == "new" and #sorted_key_list >= max_entries_allowed) then
				return "size[9,1.5]"..
					"label[0.2,0.0;There are only up to "..
						minetest.formspec_escape(yl_speak_up.max_result_effects)..
						" "..element_desc.."s allowed per dialog option.]"..
						"button[2.0,0.8;1.0,0.9;back;Back]"
			end
		else
			-- allow to directly specify a x_id to show
			x_id = table_click_result
		end

		-- store which element we are talking about
		yl_speak_up.speak_to[pname][ id_prefix.."id" ] = x_id
		-- display the selected element
		if(x_id ~= "new") then
			return "formspec_version[3]"..
				"size[20,3]"..
				"bgcolor[#00000000;false]"..
				"label[0.2,0.5;Selected "..element_desc..":]"..
				"tablecolumns[text;color,span=1;text;text]"..
				"table[0.2,0.8;19.6,0.7;"..table_of_name..";"..
					minetest.formspec_escape(elements[ x_id ][ id_prefix.."id"])..
						",#FFFF00,"..
					minetest.formspec_escape(elements[ x_id ][ id_prefix.."type"])..
						","..
					minetest.formspec_escape(
						show_element_function(elements[ x_id ]))..";0]"..
				"button[2.0,1.8;1.5,0.9;delete_element;Delete]"..
				"button[4.0,1.8;1.5,0.9;change_element;Change]"..
				"button[6.0,1.8;1,0.9;back;Back]"
		end
	end

	-- did the player get here through punching a block in the meantime?
	local block_pos = yl_speak_up.speak_to[pname].block_punched
	yl_speak_up.speak_to[pname].block_punched = nil

	local data = yl_speak_up.speak_to[pname][ tmp_data_cache ]
	if(not(data) or not(data.what)) then
		data = { what = 1}
	end
	-- fallback
	if(not(x_id)) then
		x_id = "new"
	end
	local save_button = "button[5.0,9.3;1,0.7;save_element;Save]"
	local formspec =
		"formspec_version[3]"..
		"size[20,10]"..
		"label[5,0.5;Edit "..element_desc.." \""..minetest.formspec_escape(x_id).."\"]"..
		"label[0.2,1.5;"..what_do_you_want_txt.."]"..
		"label[0.2,2.0;Something regarding...]"..
		"dropdown[4.0,1.8;14.0,0.6;select_what;"..
			table.concat(check_what, ",")..";"..
			tostring(data.what)..";]"..
		"label[1,8.5;If you are unsure if your setup of pre(C)onditions and (Ef)fects "..
			"works as intended,\ntype \"/npc_talk_debug "..tostring(n_id).."\" "..
			"in chat in order to enter debug mode. You can leave it with "..
			"\"/npc_talk_debug off\".]"..
		"button[3.0,9.3;1,0.7;back;Abort]"

	-- "an internal state (i.e. of a quest)", -- 2
	-- (state is the second offered option in both preconditions and effects list)
	if(data.what and data.what == 2) then
		if(not(data.variable) or data.variable == 1) then
			data.variable = 1
			-- not enough selected yet for saving
			save_button = ""
		elseif(not(data.operator) or data.operator == 1) then
			data.operator = 1
			save_button = ""
		end
		local field_for_value = "field[11.2,4.8;7.0,0.6;var_cmp_value;;"..
			minetest.formspec_escape(data.var_cmp_value or "- enter value -").."]"
		-- do not show value input field for unary operators
		-- (unary operators are diffrent for prerequirements and effects)
		if(not(data.operator)
		  or (id_prefix == "p_" and (data.operator == 1 or data.operator >= 8))
		  or (id_prefix == "r_" and (data.operator == 3))) then
			field_for_value = "label[11.2,5.1;- not used for this operator -]"
		end
		-- the list of available variables needs to be extended with the ones
		-- the player has read access to, and the order has to be constant
		-- (because dropdown just returns an index)
		local var_list = get_sorted_player_var_list_function(pname)
		formspec = formspec..
			"label[0.2,3.3;"..text_variable.."]"..
			"label[0.2,4.3;Name of variable:]"..
			"dropdown[0.2,4.8;6.5,0.6;select_variable;"..
				table.concat(var_list, ",")..";"..
				tostring(data.variable)..";]"..
			"label[7.0,4.3;"..text_select_operator.."]"..
			"dropdown[7.0,4.8;4.0,0.6;select_operator;"..
				table.concat(check_operator, ",")..";"..
				tostring(data.operator)..";]"..
			"label[11.2,4.3;"..text_select_value.."]"..
			field_for_value

	-- "a block somewhere", -- 3
	-- (block is the third offered option in both preconditions and effects list)
	elseif(data.what and data.what == 3) then
		local block_pos_str = "- none set -"
		local node = {name = "- unknown -", param2 = "- unkown -"}
		if(not(block_pos) and data and data.block_pos) then
			block_pos = data.block_pos
		end
		local error_is_protected = ""
		if(block_pos) then
			-- store for later usage
			data.block_pos = block_pos
			local tmp_pos = {x=block_pos.x, y=block_pos.y, z=block_pos.z}
			-- "I can't punch it. The block is as the block *above* the one I punched.",
			-- (only valid for preconditions; not for effects - because the player and
			-- his NPC need to be able to build there)
			if(data.block and id_prefix == "p_" and data.block == 5) then
				tmp_pos.y = block_pos.y + 1
			end
			-- effects (and, likewise, preconditions): the player at least has to be able to
			-- build at that position - check that
			if(minetest.is_protected(tmp_pos, pname)) then
				error_is_protected = "label[0.2,7.8;Error: "..
					"The position you punched is protected. It cannot be used by "..
					"your NPC for checks or building. Please select a diffrent block!]"
				block_pos = nil
				data.block_pos = nil
			else
				block_pos_str = minetest.pos_to_string(tmp_pos)
				node = minetest.get_node_or_nil(tmp_pos)
				if(not(node)) then
					node = {name = "- unknown -", param2 = "- unkown -"}
				end
				-- "There shall be air instead of this block.",
				-- (only valid for preconditions)
				if(data.block and id_prefix == "p_" and data.block == 3) then
					node = {name = "air", param2 = 0}
				end
				-- cache that (in case a sapling grows or someone else changes it)
				data.node_data = node
			end
		end
		if(node.name == "- unknown -") then
			save_button = ""
		end
		if(not(data.block) or data.block == 1) then
			data.block = 1
			-- not enough selected yet for saving
			save_button = ""
		end
		formspec = formspec..
			"label[0.2,3.3;"..text_block_position.."]"..
			"dropdown[4.0,3.5;16.0,0.6;select_block;"..
				table.concat(check_block, ",")..";"..
				tostring(data.block)..";]"..
			"label[0.2,4.8;Position of the block:]"..
			"label[4.0,4.8;"..minetest.formspec_escape(block_pos_str).."]"..
			"label[0.2,5.8;Name of block:]"..
			"label[4.0,5.8;"..minetest.formspec_escape(node.name).."]"..
			"label[0.2,6.8;Orientation (param2):]"..
			"label[4.0,6.8;"..minetest.formspec_escape(node.param2).."]"..
			"button_exit[10.0,5.5;4.0,0.7;select_block_pos;Set position of block]"..
			"tooltip[select_block_pos;Click on this button to select a block.\n"..
				"This menu will close and you will be asked to punch\n"..
				"the block at the position you want to check or change.\n"..
				"After punching it, you will be returned to this menu.]"..
			error_is_protected

	-- "a trade", -- 4
	-- (trade - only for preconditions; effects have something else here)
	elseif(data.what and id_prefix == "p_" and data.what == 4) then
		if(not(data.trade) or data.trade == 1) then
			data.trade = 1
			-- not enough selected yet for saving
			save_button = ""
		end
		formspec = formspec..
			"label[0.2,3.3;If the action is a trade, the following shall be true:]"..
			"dropdown[4.0,3.5;16.0,0.6;select_trade;"..
				table.concat(check_trade, ",")..";"..
				tostring(data.trade)..";]"

	-- "the inventory of the player", -- 5
	-- "the inventory of the NPC", -- 6
	-- (inventory - only for preconditions; effects have something else here)
	elseif(data.what and id_prefix == "p_" and data.what >= 5 and data.what <= 6) then
		if(not(data.inv) or data.inv == 1) then
			data.inv = 1
			-- not enough selected yet for saving
			save_button = ""
		end
		formspec = formspec..
			"label[0.2,3.3;The following shall be true about the inventory:]"..
			"dropdown[4.0,3.5;16.0,0.6;select_inv;"..
				table.concat(check_inv, ",")..";"..
				tostring(data.inv)..";]"..
			"label[0.2,4.5;Name of the item(stack):]"..
			"field[4.0,4.3;16.0,0.6;inv_stack_name;;"..(data.inv_stack_name or "").."]"..
			"tooltip[inv_stack_name;Enter name of the block and amount.\n"..
				"Example: \"default:apple 3\" for three apples,\n"..
				"         \"farming:bread\" for a bread.]"

	-- "NPC crafts soemthing", -- 4
	-- (craft - only for effects - not for preconditions)
	elseif(data.what and id_prefix == "r_" and data.what == 4) then
		formspec = formspec..
			"label[8,2.6;Your invnetory:]"..
			"list[current_player;main;8,3;8,4;]"..
			"label[1,3.1;Your craft grid:]"..
			"list[current_player;craft;1,3.5;3,3;]"..
			"list[current_player;craftpreview;5.8,4.75;1,1;]"..
			"image[4.6,4.8;1,1;gui_furnace_arrow_bg.png^[transformR270]"..
			"label[1,8.0;Use your craft grid to show your NPC what to craft "..
				"and how. Click on \"Save\" to save.]"

	-- "go to other dialog if the action (i.e. trade) failed", -- 5
	-- (on_failure - only for effects - not for preconditions)
	elseif(data.what and id_prefix == "r_" and data.what == 5) then
		local dialog = yl_speak_up.speak_to[pname].dialog
		local sorted_dialog_list = yl_speak_up.sort_keys(dialog.n_dialogs)
		local nr = 1
		if(not(data) or not(data.on_failure)) then
			save_button = ""
		else
			nr = table.indexof(sorted_dialog_list, data.on_failure)
		end
		formspec = formspec..
			"label[0.2,3.3;If the action *failed* (i.e. the player didn't trade),]"..
			"label[0.2,3.8;switch to the following dialog:]"..
			"dropdown[5.0,3.5;6.5,0.6;select_on_failure;"..
				table.concat(sorted_dialog_list, ",")..";"..
				tostring(nr)..";]"

	-- "send a chat message to all players" -- 6
	elseif(data.what and id_prefix == "r_" and data.what == 6) then
		local text = "$NPC_NAME$ (owned by $OWNER_NAME$) announces: $PLAYER_NAME$ "..
			"- example; please enter the text -"
		if(data and data.chat_msg_text) then
			text = data.chat_msg_text
		end
		formspec = formspec..
			"label[0.2,3.3;Send the following chat message to *all* players:]"..
			"label[0.2,4.1;Message:]"..
			"field[2.0,3.8;16.0,0.6;chat_msg_text;;"..
				minetest.formspec_escape(tostring(text)).."]"..
			"label[0.2,5.3;Note: Your chat message needs to contain the following placeholders,"..
				" which will be replaced automaticly like in dialog texts:"..
				"\n$NPC_NAME$, $PLAYER_NAME$ and $OWNER_NAME$.]"
	end

	return formspec..save_button
end