# lightsd

`lightsd` is a small daemon to make the ambient light sensor on your
~~(actually, my)~~ laptop useful in Linux <sup>interjection</sup>
without using a full desktop environment (or `systemd`). It even works
in a tty!

This daemon watches the reading from the ambient light sensor and
controls the backlight of the screen and keyboard. It also creates a
fifo so that you can adjust relative brightness of the screen.

It only supports sensors using the industrial I/O bus. It has a generic
class for working with many types of iio devices though.

The project also demostrates how damn stupid a C++ program could look like
(not yet to its maximum extent).

Hopefully it does not yet hog the CPU.

# Warning
WIP. May segmentation fault at any time. The author uses Gentoo. _Very_
shitty code (I admit my code style is crap). The implementation is shitty
too (it works nevertheless).

As this daemon manipulates sysfs, IT ONLY RUNS AS ROOT!

# Dependencies
 - CMake
 - gcc 8.x or clang 6 with C++17 support  

# Building
Just `mkdir build && cd build && cmake .. && make`.

# Installing
`sudo make install`. If you are using `OpenRC`, an init script is also installed.
Sorry to `systemd` users but my only computer with iio sensors is not powered by
that.

# Documentation
None. The code documents itself (in a bad way).

## fifo usage
- `u [x=5,0<x<=100]`  
Makes lcd x% brighter. ([U]p)
- `d [x=5,0<x<=100]`  
Makes lcd x% darker. ([D]own)
- `s <x,-100<=x<=100>`  
[S]ets relative brightness of lcd.
- `r`  
[R]esets relative brightness of lcd, equivalent to `s 0`.
- `f`  
[F]orces an adjustment to be made. You may want to call this when the lid
is being opened in order to turn on the keyboard backlight.
- `m`  
Disables automatic brightness. ([M]anual)  
Some of the commands (`r`/`f`) does nothing in manual mode. 
Command `s` sets absolute brightness in manual mode.
- `a`  
Enables [a]utomatic brightness.
- `i`  
Print current status to stdout. ([I]nfo)  
Output is in the following format:
```
Mode: <Automatic|Manual>
ALS value: <%f|-->
Display brightness: %d%% [(+%d%%)]
Keyboard backlight brightness: %d%%
```

The fifo is owned by `root:video` and has permission `0220` so that
everyone in the video group could potentially mess with your brightness.
Surprise!

# Tested on
 - Lenovo ThinkPad X1 Yoga 1st gen.

# Integration
Take `acpid` as an example.

`/etc/acpi/events/brightness-down`:
```
event=video/brightnessdown
action=echo d 5 > /tmp/lightsd.cmd.fifo
```

`/etc/acpi/events/brightness-up`:
```
event=video/brightnessup
action=echo u 5 > /tmp/lightsd.cmd.fifo
```

If your laptop turns keyboard backlight off automatically when closing the
lid (which I believe is what most laptops do), you may also want the
following to turn it back on when you open the lid:

`/etc/acpi/events/lid-open`:
```
event=button/lid.*open
action=echo f > /tmp/lightsd.cmd.fifo
```

# To-do
 - Less segmentation faults (already eliminated in my daily usage)
 - Less data races (???)
 - Input sanitation (partially)
 - Actual, _real_ logging: not printf'ing to `stdout`. (probably done)
 - More commands: disabling auto adjustment, set absolute brightness etc. (done)
 - Change configuration format so that one can control something other than
   screen backlight and keyboard backlight? (does anybody actually use it?)
 - auto orientation using accelerometer? (otherwise my `Sensor` class is a waste)
 - hogging cpu and battery? (oh no)
 - triggers custom scripts? (detonate your computer once the reading reaches a
   certain value?)
 - ability to embed an email client and to order pizza? (not happening)