.. _modding-guide:

DFHack modding guide
====================

.. highlight:: lua

What is the difference between a script and a mod?
--------------------------------------------------

A script is a single file that can be run as a command in DFHack, like something
that modifies or displays game data on request. A mod is something you install
to get persistent behavioural changes in the game and/or add new content. Mods
can contain and use scripts in addition to (or instead of) modifications to the
DF game raws.

DFHack scripts are written in Lua. If you don't already know Lua, there's a
great primer at `lua.org <https://www.lua.org/pil/contents.html>`__.

Why not just mod the raws?
--------------------------

It depends on what you want to do. Some mods *are* better to do in just the
raws. You don't need DFHack to add a new race or modify attributes, for example.
However, DFHack scripts can do many things that you just can't do in the raws,
like make a creature that trails smoke. Some things *could* be done in the raws,
but writing a script is less hacky, easier to maintain, easier to extend, and is
not prone to side-effects. A great example is adding a syndrome when a reaction
is performed. If done in the raws, you have to create an exploding boulder to
apply the syndrome. DFHack scripts can add the syndrome directly and with much
more flexibility. In the end, complex mods will likely require a mix of raw
modding and DFHack scripting.

A mod-maker's development environment
-------------------------------------

While you're writing your mod, you need a place to store your in-development
scripts that will:

- be directly runnable by DFHack
- not get lost when you upgrade DFHack

The recommended approach is to create a directory somewhere outside of your DF
installation (let's call it "/path/to/own-scripts") and do all your script
development in there.

Inside your DF installation folder, there is a file named
:file:`dfhack-config/script-paths.txt`. If you add a line like this to that
file::

    +/path/to/own-scripts

Then that directory will be searched when you run DFHack commands from inside
the game. The ``+`` at the front of the path means to search that directory
first, before any other script directory (like :file:`hack/scripts` or
:file:`raw/scripts`). That way, your latest changes will always be used instead
of older copies that you may have installed in a DF directory.

For scripts with the same name, the `order of precedence <script-paths>` will
be:

1. ``own-scripts/``
2. ``data/save/*/raw/scripts/``
3. ``raw/scripts/``
4. ``hack/scripts/``

The structure of the game
-------------------------

"The game" is in the global variable `df <lua-df>`. The game's memory can be
found in ``df.global``, containing things like the list of all items, whether to
reindex pathfinding, et cetera. Also relevant to us in ``df`` are the various
types found in the game, e.g. ``df.pronoun_type`` which we will be using in this
guide. We'll explore more of the game structures below.

Your first script
-----------------

So! It's time to write your first script. This section will walk you through how
to make a script that will get the pronoun type of the currently selected unit.

First line, we get the unit::

    local unit = dfhack.gui.getSelectedUnit()

If no unit is selected, an error message will be printed (which can be silenced
by passing ``true`` to ``getSelectedUnit``) and ``unit`` will be ``nil``.

If ``unit`` is ``nil``, we don't want the script to run anymore::

    if not unit then
        return
    end

Now, the field ``sex`` in a unit is an integer, but each integer corresponds to
a string value ("it", "she", or "he"). We get this value by indexing the
bidirectional map ``df.pronoun_type``. Indexing the other way, incidentally,
with one of the strings, will yield its corresponding number. So::

    local pronounTypeString = df.pronoun_type[unit.sex]
    print(pronounTypeString)

Simple. Save this as a Lua file in your own scripts directory and run it as
shown before when a unit is selected in the Dwarf Fortress UI.

Exploring DF structures
-----------------------

So how could you have known about the field and type we just used? Well, there
are two main tools for discovering the various fields in the game's data
structures. The first is the ``df-structures``
`repository <https://github.com/DFHack/df-structures>`__ that contains XML files
describing the contents of the game's structures. These are complete, but
difficult to read (for a human). The second option is the `gui/gm-editor`
script, an interactive data explorer. You can run the script while objects like
units are selected to view the data within them. You can also run
``gui/gm-editor scr`` to view the data for the current screen. Press :kbd:`?`
while the script is active to view help.

Familiarising yourself with the many structs of the game will help with ideas
immensely, and you can always ask for help in the `right places <support>`.

Detecting triggers
------------------

The common method for injecting new behaviour into the game is to define a
callback function and get it called when something interesting happens. DFHack
provides two libraries for this, ``repeat-util`` and `eventful <eventful-api>`.
``repeat-util`` is used to run a function once per a configurable number of
frames (paused or unpaused), ticks (unpaused), in-game days, months, or years.
If you need to be aware the instant something happens, you'll need to run a
check once a tick. Be careful not to do this gratuitously, though, since
running that often can slow down the game!

``eventful``, on the other hand, is much more performance-friendly since it will
only call your callback when a relevant event happens, like a reaction or job
being completed or a projectile moving.

To get something to run once per tick, we can call
``repeat-util.scheduleEvery()``. First, we load the module::

    local repeatUtil = require('repeat-util')

Both ``repeat-util`` and ``eventful`` require keys for registered callbacks. You
should use something unique, like your mod name::

    local modId = "callback-example-mod"

Then, we pass the key, amount of time units between function calls, what the
time units are, and finally the callback function itself::

    repeatUtil.scheduleEvery(modId, 1, "ticks", function()
        -- Do something like iterating over all active units and
        -- check for something interesting
        for _, unit in ipairs(df.global.world.units.active) do
            ...
        end
    end)

``eventful`` is slightly more involved. First get the module::

    local eventful = require('plugins.eventful')

``eventful`` contains a table for each event which you populate with functions.
Each function in the table is then called with the appropriate arguments when
the event occurs. So, for example, to print the position of a moving (item)
projectile::

    eventful.onProjItemCheckMovement[modId] = function(projectile)
        print(projectile.cur_pos.x, projectile.cur_pos.y,
              projectile.cur_pos.z)
    end

Check out the `full list of supported events <eventful-api>` to see what else
you can react to with ``eventful``.

Now, you may have noticed that you won't be able to register multiple callbacks
with a single key named after your mod. You can, of course, call all the
functions you want from a single registered callback. Alternately, you can
create multiple callbacks using different keys, using your mod ID as a key name
prefix. If you do register multiple callbacks, though, there are no guarantees
about the call order.

Custom raw tokens
-----------------

.. highlight:: none

In this section, we are going to use `custom raw tokens <custom-raw-tokens>`
applied to a reaction to transfer the material of a reagent to a product as a
handle improvement (like on artifact buckets), and then we are going to see how
you could make boots that make units go faster when worn.

First, let's define a custom crossbow with its own custom reaction. The
crossbow::

    [ITEM_WEAPON:ITEM_WEAPON_CROSSBOW_SIEGE]
        [NAME:crossbow:crossbows]
        [SIZE:600]
        [SKILL:HAMMER]
        [RANGED:CROSSBOW:BOLT]
        [SHOOT_FORCE:4000]
        [SHOOT_MAXVEL:800]
        [TWO_HANDED:0]
        [MINIMUM_SIZE:17500]
        [MATERIAL_SIZE:4]
        [ATTACK:BLUNT:10000:4000:bash:bashes:NO_SUB:1250]
            [ATTACK_PREPARE_AND_RECOVER:3:3]
        [SIEGE_CROSSBOW_MOD_FIRE_RATE_MULTIPLIER:2] custom token (you'll see)

The reaction to make it (you would add the reaction and not the weapon to an
entity raw)::

    [REACTION:MAKE_SIEGE_CROSSBOW]
        [NAME:make siege crossbow]
        [BUILDING:BOWYER:NONE]
        [SKILL:BOWYER]
        [REAGENT:mechanism 1:2:TRAPPARTS:NONE:NONE:NONE]
        [REAGENT:bar:150:BAR:NONE:NONE:NONE]
            [METAL_ITEM_MATERIAL]
        [REAGENT:handle 1:1:BLOCKS:NONE:NONE:NONE] wooden handles
            [ANY_PLANT_MATERIAL]
        [REAGENT:handle 2:1:BLOCKS:NONE:NONE:NONE]
            [ANY_PLANT_MATERIAL]
        [SIEGE_CROSSBOW_MOD_TRANSFER_HANDLE_MATERIAL_TO_PRODUCT_IMPROVEMENT:1]
            another custom token
        [PRODUCT:100:1:WEAPON:ITEM_WEAPON_CROSSBOW_SIEGE:GET_MATERIAL_FROM_REAGENT:bar:NONE]

So, we are going to use the ``eventful`` module to make it so that (after the
script is run) when this crossbow is crafted, it will have two handles, each
with the material given by the block reagents.

.. highlight:: lua

First, require the modules we are going to use::

    local eventful = require("plugins.eventful")
    local customRawTokens = require("custom-raw-tokens")

Now, let's make a callback (we'll be defining the body of this function soon)::

    local modId = "siege-crossbow-mod"
    eventful.onReactionComplete[modId] = function(reaction,
            reactionProduct, unit, inputItems, inputReagents,
            outputItems)

First, we check to see if it the reaction that just happened is relevant to this
callback::

    if not customRawTokens.getToken(reaction,
        "SIEGE_CROSSBOW_MOD_TRANSFER_HANDLE_MATERIAL_TO_PRODUCT_IMPROVEMENT")
    then
        return
    end

Then, we get the product number listed. Next, for every reagent, if the reagent
name starts with "handle" then we get the corresponding item, and...

::

    for i, reagent in ipairs(inputReagents) do
        if reagent.code:startswith('handle') then
            -- Found handle reagent
            local item = inputItems[i]

...We then add a handle improvement to the listed product within our loop::

    local new = df.itemimprovement_itemspecificst:new()
    new.mat_type, new.mat_index = item.mat_type, item.mat_index
    new.type = df.itemimprovement_specific_type.HANDLE
    outputItems[productNumber - 1].improvements:insert('#', new)

This works well as long as you don't have multiple stacks filling up one
reagent.

Let's also make some code to modify the fire rate of our siege crossbow::

    eventful.onProjItemCheckMovement[modId] = function(projectile)
        if projectile.distance_flown > 0 then
            -- don't make this adjustment more than once
            return
        end

        local firer = projectile.firer
        if not firer then
            return
        end

        local weapon = df.item.find(projectile.bow_id)
        if not weapon then
            return
        end

        local multiplier = tonumber(customRawTokens.getToken(
                weapon.subtype,
                "SIEGE_CROSSBOW_MOD_FIRE_RATE_MULTIPLIER")) or 1
        firer.counters.think_counter = math.floor(
                firer.counters.think_counter * multiplier)
    end

.. highlight:: none

Now, let's see how we could make some "pegasus boots". First, let's define the
item in the raws::

    [ITEM_SHOES:ITEM_SHOES_BOOTS_PEGASUS]
        [NAME:pegasus boot:pegasus boots]
        [ARMORLEVEL:1]
        [UPSTEP:1]
        [METAL_ARMOR_LEVELS]
        [LAYER:OVER]
        [COVERAGE:100]
        [LAYER_SIZE:25]
        [LAYER_PERMIT:15]
        [MATERIAL_SIZE:2]
        [METAL]
        [LEATHER]
        [HARD]
        [PEGASUS_BOOTS_MOD_MOVEMENT_TIMER_REDUCTION_PER_TICK:5] custom raw token
            (you don't have to comment the custom token every time,
            but it does clarify what it is)

.. highlight:: lua

Then, let's make a ``repeat-util`` callback for once a tick::

    repeatUtil.scheduleEvery(modId, 1, "ticks", function()

Let's iterate over every active unit, and for every unit, iterate over their
worn items to calculate how much we are going to take from their movement
timer::

    for _, unit in ipairs(df.global.world.units.active) do
        local amount = 0
        for _, entry in ipairs(unit.inventory) do
            if entry.mode == df.unit_inventory_item.T_mode.Worn then
                local reduction = customRawTokens.getToken(
                        entry.item,
                        'PEGASUS_BOOTS_MOD_MOVEMENT_TIMER_REDUCTION_PER_TICK')
                amount = amount + (tonumber(reduction) or 0)
            end
        end
    end

    -- Subtract amount from movement timer if currently moving
    dfhack.units.addMoveTimer(-amount)

The structure of a full mod
---------------------------

For reference, `Tachy Guns <https://www.github.com/wolfboyft/tachy-guns>`__ is a
full mod that conforms to this guide.

Create a folder for mod projects somewhere outside your Dwarf Fortress
installation directory (e.g. ``/path/to/mymods/``) and use your mod IDs as the
names for the mod folders within it. In the example below, we'll use a mod ID of
``example-mod``. I'm sure your mods will have more creative names! The
``example-mod`` mod will be developed in the ``/path/to/mymods/example-mod/``
directory and has a basic structure that looks like this::

    raw/init.d/example-mod.lua
    raw/objects/...
    raw/scripts/example-mod.lua
    raw/scripts/example-mod/...
    README.md

Let's go through that line by line.

* A short (one-line) script in ``raw/init.d/`` to initialise your
  mod when a save is loaded.
* Modifications to the game raws (potentially with custom raw tokens) go in
  ``raw/objects/``.
* A control script in ``raw/scripts/`` that handles enabling and disabling your
  mod.
* A subfolder for your mod under ``raw/scripts/`` will contain all the internal
  scripts and/or modules used by your mod.

It is a good idea to use a version control system to organize changes to your
mod code. You can create a separate Git repository for each of your mods. The
``README.md`` file will be your mod help text when people browse to your online
repository.

Unless you want to install your ``raw/`` folder into your DF game folder every
time you make a change to your scripts, you should add your development scripts
directory to your script paths in ``dfhack-config/script-paths.txt``::

    +/path/to/mymods/example-mod/raw/scripts/

Ok, you're all set up! Now, let's take a look at an example
``raw/scripts/example-mod.lua`` file::

    -- main setup and teardown for example-mod
    -- this next line indicates that the script supports the "enable"
    -- API so you can start it by running "enable example-mod" and stop
    -- it by running "disable example-mod"
    --@ enable = true

    local usage = [[
    Usage
    -----

        enable example-mod
        disable example-mod
    ]]
    local repeatUtil = require('repeat-util')
    local eventful = require('plugins.eventful')

    -- you can reference global values or functions declared in any of
    -- your internal scripts
    local moduleA = reqscript('example-mod/module-a')
    local moduleB = reqscript('example-mod/module-b')
    local moduleC = reqscript('example-mod/module-c')
    local moduleD = reqscript('example-mod/module-d')

    enabled = enabled or false
    local modId = 'example-mod'

    if not dfhack_flags.enable then
        print(usage)
        print()
        print(('Example mod is currently '):format(
                enabled and 'enabled' or 'disabled'))
        return
    end

    if dfhack_flags.enable_state then
        -- do any initialization your internal scripts might require
        moduleA.onLoad()
        moduleB.onLoad()

        -- multiple functions in the same repeat callback
        repeatUtil.scheduleEvery(modId .. ' every tick', 1, 'ticks', function()
            moduleA.every1Tick()
            moduleB.every1Tick()
        end)

        -- one function per repeat callback (you can put them in the
        -- above format if you prefer)
        repeatUtil.scheduleEvery(modId .. ' 100 frames', 1, 'frames',
                                 moduleD.every100Frames)

        -- multiple functions in the same eventful callback
        eventful.onReactionComplete[modId] = function(reaction,
                reaction_product, unit, input_items, input_reagents,
                output_items)
            -- pass the event's parameters to the listeners
            moduleB.onReactionComplete(reaction, reaction_product,
                    unit, input_items, input_reagents, output_items)
            moduleC.onReactionComplete(reaction, reaction_product,
                    unit, input_items, input_reagents, output_items)
        end

        -- one function per eventful callback (you can put them in the
        -- above format if you prefer)
        eventful.onProjItemCheckMovement[modId] = moduleD.onProjItemCheckMovement
        eventful.onProjUnitCheckMovement[modId] = moduleD.onProjUnitCheckMovement

        print('Example mod enabled')
        enabled = true
    else
        -- call any shutdown functions your internal scripts might require
        moduleA.onUnload()

        repeatUtil.cancel(modId .. ' every ticks')
        repeatUtil.cancel(modId .. ' 100 frames')

        eventful.onReactionComplete[modId] = nil
        eventful.onProjItemCheckMovement[modId] = nil
        eventful.onProjUnitCheckMovement[modId] = nil

        print('Example mod disabled')
        enabled = false
    end

You can call ``enable example-mod`` and ``disable example-mod`` yourself while
developing, but for end users you can start your mod automatically from
``raw/init.d/example-mod.lua``::

    dfhack.run_command('enable example-mod')

Inside ``raw/scripts/example-mod/module-a.lua`` you could have code like this::

    --@ module = true
    -- The above line is required for reqscript to work

    function onLoad() -- global variables are exported
        -- do initialization here
    end

    -- this is an internal function: local functions/variables
    -- are not exported
    local function usedByOnTick(unit)
        -- ...
    end

    function onTick() -- exported
        for _,unit in ipairs(df.global.world.units.all) do
            usedByOnTick(unit)
        end
    end

The `reqscript <reqscript>` function reloads scripts that have changed, so you can modify
your scripts while DF is running and just disable/enable your mod to load the
changes into your ongoing game!
