====== LuaATC Programming Interface ======

LuaATC (Lua Advanced Train Control, also called LuaAutomation) utilises the Lua programming language to provide an immensely powerful automation system for Advtrains. Prior knowledge of Lua is highly reccommended.

===== Available Standard Lua functions =====

The standard Lua globals are available in the LuaATC environment:

  * ''string''
  * ''math''
  * ''table''
  * from ''os'':
    * ''os.clock()''
    * ''os.difftime()''
    * ''os.time()''
    * ''os.date()'' ((note that ''os.date()'' without parameters returns in table form ''("*t")''))

The standard Lua functions are available in the LuaATC environment:

  * ''assert''
  * ''error''
  * ''ipairs''
  * ''pairs''
  * ''next''
  * ''select''
  * ''tonumber''
  * ''tostring''
  * ''type''
  * ''unpack''

===== Important Helpers and Notes =====

Certain aspects of LuaAutomation can only be done at certain times, and others require specific conditions to be useful. These are noted under the section headings.

In the following functions, all parameters named ''pos'' designate a position. You can use either:

  * a default Minetest position vector (like ''{x=34, y=2, z=-18}'')
  * the ''[[#pos_x_y_z|POS(34,2,-18)]]'' shorthand
  * a string, the name of a [[usage:atlatc:passive#passive_component_naming|passive component]].

== POS(x, y, z) ==

A shorthand function to designate a Minetest position vector like ''{x=?, y=?, z=?}''.

===== Interacting with switches and other passive components =====

Switches (turnouts), simple signals and mesecon switches are so-called "[[usage:atlatc:passive]]". These functions are used to interact with them.

== getstate(pos) ==

Gets the state of a passive component at position ''pos''. The returned states are component-specific, see [[usage:atlatc:passive]].

== setstate(pos, new_state) ==

Sets the state of a passive component at position ''pos'' to the value ''new_state''. The states are component-specific, see [[usage:atlatc:passive]].

== is_passive(pos) ==

Checks whether there is a passive component at position ''pos''. If ''pos'' is a string, checks whether this passive component name exists.

===== Train Control =====

Train control is arguably the most important aspect of automating a rail system. The following functions can only be used from [[usage:nodes:atc_rail|ATC Tracks]].

To control a train, this train must be positioned on the ATC rail.((Exceptions: [[usage:atlatc:events#approach|event.type == "appraoch"]] and ''atc_send_to_train()'')) It does not matter which portion of the train is on the ATC rail, and whether the train is moving or not.

==== Fields ====

These fields are populated every time a train is occupying a LuaATC track.

== atc_id ==
The 6 digit ID of the train passing the rail as a string. ''nil'' if no there is no train.

== atc_speed ==
The current speed of the train passing the rail, in metres per second. ''nil'' if no there is no train.

== atc_arrow ==
Whether the train is driving in direction of the arrows on the ATC rail. ''nil'' if no there is no train.

**Note: this code does not indicate whether there is a train on the rail, as both ''false'' and ''nil'' evaluate to false:**
<code lua>
-- BAD
if not atc_arrow then
    -- ...do stuff
end

-- GOOD
if atc_arrow == false then
    -- ...do stuff
end
</code>

==== Functions ====
== atc_send(cmd) ==
Sends the specified [[usage:nodes:atc_controller#atc_command_syntax|ATC command]] to the train and returns ''true''. If there is no train, returns ''false'' and does nothing.

== atc_send_to_train(train_id, command) ==
//since version 2.3.0//

Sends the specified [[usage:nodes:atc_controller#atc_command_syntax|ATC command]] to the train specified by its 6 digit train ID and returns ''true''. If there is no train with such an ID, returns ''false'' and does nothing. Calling this function from an ATC rail is independent of any train that stands on the rail and does not affect it (except of course when train_id happens to be the ID of the train on the rail).

Note: ''train_id'' **MUST** be a string. Train IDs can begin with ''0'', which is ignored when the variable is of type ''number'', resulting in an invalid 5 digit ID.

== atc_reset() ==
Resets the train's current ATC command and returns ''true''. If there is no train, returns ''false'' and does nothing.

== atc_set_text_outside(text) ==
Sets the text shown on the outside of the train and returns ''true''. If there is no train, returns ''false'' and does nothing.

== atc_set_text_inside(text) ==
Sets the text shown inside the train and returns ''true''. If there is no train, returns ''false'' and does nothing.

== atc_get_text_outside() / atc_get_text_inside() ==
Gets the outside/inside text currently set on the train.

== get_line() ==
Returns the line property of the train, as a string. This string can be used to distinguish trains of different lines and route them properly.

This property is also used by the interlocking system for [[wiki:todo|Automatic Routesetting]].

If there is no train, the Lua program stored in the rail will exit immediately:

> 2019-01-01 15:00:00: WARNING[Server]: [advtrains]LuaAutomation ATC interface rail at (0,0,0) : LUA Error: .../mods/advtrains/advtrains_luaautomation/atc_rail.lua:93: attempt to index upvalue 'train' (a nil value)

This is a bug.

== set_line(line) ==
Sets the line property of the train, as a string.

On [[usage:trains:basic_trains:advtrains_subway|subway trains]], in the Basic Trains modpack, the line is automatically displayed on the outside of the trains, if the first character is a number between 0 and 9 (where 0 is displayed as "Line 10").

If there is no train, same behavior as [[#get_line()]] applies.

== get_rc() ==
Returns the routing code of the train, as a string. This property is used by the interlocking system for Automatic Routesetting.

If there is no train, same behavior as [[#get_line()]] applies.

== set_rc(rc) ==
Sets the routing code of the train, as a string. This property is used by the interlocking system for Automatic Routesetting.

If there is no train, same behavior as [[#get_line()]] applies.

== atc_set_ars_disable(value) ==

//since version 2.3.0//

Enables (''value == false'') or disables (''value == true'') interlocking for this train. The train will not trigger automatic route setting on signals based on ARS.

This function has essentially the same effect as the ATC command ''[[usage:nodes:atc_controller#a_enable_ARS|A<enable_ARS>]]''.

== atc_set_lzb_tsr(speed) ==

//since version 2.3.0//

Adds a Temporary Speed Restriction at the current rail, so that the train is passing the rail at the specified ''speed'', or at a lower speed.

Calling this function from an ''approach'' event has essentially the same effect as a [[usage:nodes:npr|Point Speed Restriction Rail]]. Note that due to internal implementation details, you must call this function again on any subsequent ''approach'' events received. (see [[usage:atlatc:events]])

  * This function is available only when the [[wiki:todo|approach callback mechanism]] is enabled.
  * This function is only accessible during ''approach'' events


==== Shunting-Specific Functions ====

Aside from basic train control, LuaAutomation enables automatic and complex shunting operations to be performed.

There are several functions available especially for shunting operations. Some of these functions make use of Freight Codes (FC) set in the Wagon Properties of each wagon.((For the purpose of this document, locomotives are also classed as wagons in this respect.))

FCs are composed of strings separated by ''!'', for instance ''foo!bar!baz''. Lists ending in ''?'' have a special function (see ''step_fc()'' below.) Each wagon has a current FC, indicating its next destination. By default this is an empty string.

== split_at_index(index, atc_command) ==

Splits the train at the specified index, into a train with ''index-1'' wagons and a second train starting with the ''index-th'' wagon. The ''atc_command'' specified is sent to the second train after decoupling. ''S0'' or ''B0'' is common to ensure any locomotives in the remaining train don't continue to move.

== get_fc() ==

//since version 2.4.3//

Returns a table with the entire FC list for each wagon in the train.

== set_fc(fc_list) ==

//since version 2.4.3//

Overwrites the FC list of the entire train according to a table ''fc_list''. A false or nil entry in the table will leave the wagon unaffecetd, however all others will be overwritten.

Useful for mass-programming freight trains that use FC shunting instead of walking to each wagon individually.

//**NOTE**: ''get_fc()'' and ''set_fc()'' currently only work when the wagon is in a loaded area. They will fail silently when not in a loaded area. This is a bug.//

== split_at_fc(atc_command, len) ==

Splits the train in such a way thay all wagons with non-empty current FC of the first part of the train have the same FC. ''atc_command'' is sent to the remainder of the train, as with ''split_at_index''. It returns the FC of the wagons of the first part.

The optional arguement ''len'' specifies a maximum train length to be split off.

== split_off_locomotive(atc_command, len) ==

Similar to ''split_at_fc'', this function will separate the first group of wagons with an empty FC, generally locomotives. ''atc_command'' and ''len'' area as above with ''split_at_fc''.

== step_fc() ==

Steps the FCs of all wagons forward, selecting the next code after the ''!''. If the end of the string is reached, then the code loops back and the first code is selected. If the string ends in a ''?'' however, the order of codes is reversed instead.

== train_length() == 

Returns the number of wagons in a train.

== set_autocouple() ==

Enables Autocouple mode. When the train hits another standing train, it couples to it and continues with its current ATC target speed in the same direction.

In contrast to the ''Cpl'' ATC command, the autocouple property does not reset after coupling. It needs to be explicitly disabled using ''unset_autocouple()''. Note that the ATC ''Cpl'' command and the LuaATC autocouple flag are independent and can be used at the same time.

//since version 2.4.0//

The train that is initiating the coupling (that is, the train that is driving and whose mode is set to autocouple) is guaranteed to retain its Train ID.

== unset_autocouple() ==

Disables the Autocouple mode.


== set_shunt() ==

//Deprecated//

Enables shunting mode for the currently passing train and returns ''true''. This mode permanently restricts the train speed to 6 m/s (or 21.6 km/h). When in shunt mode, the train will couple to trains it collides with, and will obey shunt signals.

Further details on the "Shunt Mode" are explained in the Interlocking section. ([[wiki:todo]])

If there is no train, returns ''false'' and does nothing.

== unset_shunt() ==

//Deprecated//

Disables shunting mode as set above

===== Interrupts =====

These functions allow to schedule interrupts, a.k.a events to be executed at a later time. They are not available in init code.

The time counter and queue handling these interrupts is synchronized to minetest's internal step time. It is written in a very simple fashion, and is NOT secured against "interrupt bombs". Be careful!
<code>
-- an example for an "interrupt bomb"
-- NEVER DO THIS!
if event.int then
  interrupt(1,"A")
  interrupt(1,"B")
-- run 1: {A,B}
-- run 2: {A,B,A,B}
-- run 3: {A,B,A,B,A,B,A,B}...
</code>
== interrupt(time, message) ==

Causes the LuaAutomation mod to trigger an ''int'' [[usage:atlatc:events|event]] (the Advtrains equivalent of [[usage:mods:mesecons|Mesecons]]' ''interrupt'') on this component after the given ''time'', in seconds, with the specified ''message''. ''message'' can be of any Lua data type.

Use of this function is discouraged, as "fork bombs" can easily be built. Please use ''interrupt_safe()'' or make sure to ''clear_interrupts()'' in appropriate places.

== interrupt_safe(time, message) ==

//since version 2.3.0//

Like ''interrupt()'', but returns false when an interrupt (of any type) is already present for this component and does not add an interrupt. Returns true when interrupt was successfully added.

== interrupt_pos(pos, message) ==

Triggers immediately an ''ext_int'' [[usage:atlatc:events|event]] on the active component at ''pos''. ''message'' can be of any Lua data type.

== clear_interrupts() ==

//since version 2.3.0//

Removes any pending interrupts (both of type 'int' and 'ext_int') set on this node.

===== Railway Time =====

When ''advtrains_line_automation'' is enabled, all Railway time functions are exposed as rwt.* and can safely be used in LuaATC code.

For the available functions, see [[dev:api:railway_time_api]].

<code>
--Example: print the time of the next full minute
local now = rwt.now()
local next_minute = rwt.next_rpt(now, "01;00", 0)
</code>

==== Railway Time Scheduler ====

This is a separate schedule queue. In contrast to the interrupt system, which is the original and established way to schedule interrupts, it relies on the Railway Time system and therefore is only accessible when ''advtrains_line_automation'' is enabled.

There are two important considerations to this:

  - While the interrupt system is always synchronized to minetest step time, the RWT scheduler follows the RWT time flow. In particular, this means that you must be able to handle "time jumps" that occur when RWT is set up to adapt to real time.
  - The RWT scheduler has a built-in protection against "interrupt bombs". There is a limit on how many interrupts can be enqueued from a single LuaATC component. At the time of this writing, this limit is set to ''1''.

Clicking "Save" on the code edit form clears all events currently scheduled in the RWT scheduler. It does NOT clear the interrupt scheduler events.

== schedule(rwtime, msg) ==

Triggers a ''schedule'' event AT the specified Railway Time.
The time value here is an absolute value.
msg can be any data type and is accessible in ''event.msg''.
<code>
  -- Example: schedule a "depart" event on the next full 5 minutes
  local now = rwt.now()
  local next_5minutes = rwt.next_rpt(now, "05;00", 0)
  schedule(next_5minutes, "depart")
</code>

== schedule_in(rwtime, msg) ==

Like schedule(), but the passed time is relative.
<code>
  -- Example: schedule a "depart" event in 1 minute
  schedule_in("01;00", "depart")
</code>

===== Digiline =====

== digiline_send(channel, message) ==

Sends a digiline message on the specified ''channel''. See the digilines [[https://content.minetest.net/packages/Jeija/digilines/|ContentDB]] page for more information.

This function is not available in init code.

===== Interlocking functions =====

Interlocking functions are available when the ''[[usage:mods#advtrains_interlocking|advtrains_interlocking]]'' mod is enabled.

== can_set_route(pos, route_name) ==

Checks whether it is possible to set the route designated by ''route_name'' from the signal at position ''pos''.

It emits a warning and halts execution of Lua code in the following cases:

  * the node at specified position is not a signal:

> LUA Error: ...: There's no signal at (0,0,0)

  * ''pos'' is a string, and the named passive component does not exist:

> LUA Error: ...: Invalid position supplied to ???: "..."

  * the specified route does not exist:

> LUA Error: ...: No route called B at (0,0,0)

== set_route(pos, route_name) ==

Requests the route designated by ''route_name'' from the signal at position ''pos''. Has the same effect as clicking the "Set Route" in the formspec from the designated signal.

Same warnings apply as for ''[[#can_set_route_pos_route_name|can_set_route]]''.

If the route can't be set, the signal remains red and waits for conflicting problems to be solved. Execution continues **immediately**.

There is currently no way to emit an event when the signal becomes green.

== cancel_route(pos) ==

Cancels the route that is set from the signal at position ''pos''. Has the same effect as clicking the "Cancel Route" in the formspec from the designated signal.

Same warnings apply as for ''[[#can_set_route_pos_route_name|can_set_route]]''.

If the route has already been canceled, nothing happens.

== get_aspect(pos) ==

Gets the aspect of the signal at ''pos''. The aspect format is described in the [[wiki:todo|Signal]] page.

Same warnings apply as for ''[[#can_set_route_pos_route_name|can_set_route]]''.