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https://github.com/propensive/profanity

A library for realtime interactive terminal software in Scala
https://github.com/propensive/profanity

console curses interactive ncurses scala terminal tty

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A library for realtime interactive terminal software in Scala

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# Profanity



__A library for realtime interactive terminal software__



_Profanity_ makes it possible to write real-time applications that interact through the terminal by

converting STDIN into an event stream of keypresses.



## Features



- capture a TTY terminal's individual keypresses

- interprets standard keys and control keys

- simple interactive line editor supporting standard keypresses

- simple interactive navigable menu



## Availability



## Getting Started



Java does not provide native support for direct access to keypress events. While Standard input (`STDIN`)

is accessible as an input stream, it is buffered until a newline is sent, which makes it impossible for a

Scala application to respond immediately to a keypress event, unless that keypress is the `Enter` key.



Profanity uses the Java Native Interface (JNI) to turn off buffering so that each keypress is received as

soon as it happens.



### Capturing the TTY



Before keypresses can be streamed as events, the TTY must be "captured". This is as simple as,

```scala

Tty.capture {

  // TTY operations are available here

}

```

but may not always succeed, for example if the JVM is not running inside a TTY, or if the TTY has already

been captured, or if the JNI calls fail for another reason. These exceptions are checked.



### Streaming keypresses



Within a `Tty.capture` block, a contextual `Tty` instance is made available, and `Tty.stream` can be

called which will, by default, return a `LazyList[Keypress]`, where `Keypress` is Profanity's standard

representation of a keypress event. `Keypress` is an enumeration providing the following cases:

- `Printable(c: Char)`, a keypress of a printable character, for example, `Shift+T` is `Printable('T')`

- `Function(i: Int)`, a function key keypress, where `i` is the function key number, for example `F2` is `Function(2)`

- `Ctrl(c: Char)`, a key combination of `Ctrl` and another character, for example, `Ctrl+C` is `Ctrl('c')`

- a keypress of one of the following keys: `Enter`, `Escape`, `Tab`, `Backspace`, `Delete`, `PageUp`,

  `PageDown`, `LeftArrow`, `RightArrow`, `UpArrow`, `DownArrow`, `CtrlLeftArrow`, `CtrlRightArrow`,

  `CtrlUpArrow`, `CtrlDownArrow`, `End`, `Home`, `Insert`

- `Escape(bytes: Byte*)`, any other escape sequence that hasn't been identified as one of the above



Additionally, the `Resize(rows: Int, cols: Int)` case represents the escape sequence that reports

the width and height of the console, and may be triggered by calling the `Tty.reportSize()`, or when a

`SIGWINCH` event occurs, i.e. when the terminal window's size changes. So a `Resize` event can be handled

just like a keypress event, where an action make be taken to ignore the event or redraw the screen, or

something else.



#### Alternative keyboards



`Tty.stream` takes an optional type parameter, `K`, which determines the type used to represent keypress events,

by resolving a contextual `Keyboard[K]` instance that interprets the bytes arriving in `STDIN` (either

individually, or as short sequences) as instances of `K`.



By default, only a single `Keyboard` given instance is defined, parameterized on the event type, `Keypress`,

which means that `Tty.stream` may be invoked without specifying its type parameter. Nevertheless, it is

possible to define alternative interpreters for the byte input to `STDIN`.



### Line Editor



Profanity provides a simple line editor that may be used inside a `Tty.capture` block, and will handle

common keypresses that may be used inside an editable field, including printable characters, arrow keys,

`Ctrl` key combinations such as `Ctrl+W` (delete word) and `Ctrl+U` (delete line).



This can be invoked inside a `Tty.capture` block with `LineEditor.ask()`, or pre-filled with an initial

value, `LineEditor.ask("initial")`.



#### Rendering



It is also possible to control how the line editor displays the text by overriding the default `render`

method of `LineEditor.ask`. This parameter is a `String => String` lambda, mapping from the current

value (i.e. the accumulation of several keypresses into a string) to the value that should be printed.



While `render` would normally use the identity function, it is possible to use the `LineEditor.concealed`

method to display each character as an `*` or even to include ANSI escape characters (e.g. from

[Escapade](https://github.com/propensive/escapade)) in the string. It is executed, and the line is

redrawn, for every keypress.



### Menus



A simple menu of two or more options is provided through the `SelectMenu` object. Its `ask` method,

which can only be called inside a `Tty.capture` block, will present a set of options to the user, of

which exactly one must be chosen using the arrow keys and the `Enter` key. In addition to the list of

choices being supplied as the first parameter of `SelectMenu.ask`, the initially-selected value may be

provided as the second.



Additionally, two lambdas, `renderOn` and `renderOff`, allow the rendering of each menu item (whether

_on_ or _off_) to be specified.



### Limitations



Profanity does not currently support Windows.



## Status



Profanity is classified as __fledgling__. For reference, Soundness projects are

categorized into one of the following five stability levels:



- _embryonic_: for experimental or demonstrative purposes only, without any guarantees of longevity

- _fledgling_: of proven utility, seeking contributions, but liable to significant redesigns

- _maturescent_: major design decisions broady settled, seeking probatory adoption and refinement

- _dependable_: production-ready, subject to controlled ongoing maintenance and enhancement; tagged as version `1.0.0` or later

- _adamantine_: proven, reliable and production-ready, with no further breaking changes ever anticipated



Projects at any stability level, even _embryonic_ projects, can still be used,

as long as caution is taken to avoid a mismatch between the project's stability

level and the required stability and maintainability of your own project.



Profanity is designed to be _small_. Its entire source code currently consists

of 428 lines of code.



## Building



Profanity will ultimately be built by Fury, when it is published. In the

meantime, two possibilities are offered, however they are acknowledged to be

fragile, inadequately tested, and unsuitable for anything more than

experimentation. They are provided only for the necessity of providing _some_

answer to the question, "how can I try Profanity?".



1. *Copy the sources into your own project*

   

   Read the `fury` file in the repository root to understand Profanity's build

   structure, dependencies and source location; the file format should be short

   and quite intuitive. Copy the sources into a source directory in your own

   project, then repeat (recursively) for each of the dependencies.



   The sources are compiled against the latest nightly release of Scala 3.

   There should be no problem to compile the project together with all of its

   dependencies in a single compilation.



2. *Build with [Wrath](https://github.com/propensive/wrath/)*



   Wrath is a bootstrapping script for building Profanity and other projects in

   the absence of a fully-featured build tool. It is designed to read the `fury`

   file in the project directory, and produce a collection of JAR files which can

   be added to a classpath, by compiling the project and all of its dependencies,

   including the Scala compiler itself.

   

   Download the latest version of

   [`wrath`](https://github.com/propensive/wrath/releases/latest), make it

   executable, and add it to your path, for example by copying it to

   `/usr/local/bin/`.



   Clone this repository inside an empty directory, so that the build can

   safely make clones of repositories it depends on as _peers_ of `profanity`.

   Run `wrath -F` in the repository root. This will download and compile the

   latest version of Scala, as well as all of Profanity's dependencies.



   If the build was successful, the compiled JAR files can be found in the

   `.wrath/dist` directory.



## Contributing



Contributors to Profanity are welcome and encouraged. New contributors may like

to look for issues marked

[beginner](https://github.com/propensive/profanity/labels/beginner).



We suggest that all contributors read the [Contributing

Guide](/contributing.md) to make the process of contributing to Profanity

easier.



Please __do not__ contact project maintainers privately with questions unless

there is a good reason to keep them private. While it can be tempting to

repsond to such questions, private answers cannot be shared with a wider

audience, and it can result in duplication of effort.



## Author



Profanity was designed and developed by Jon Pretty, and commercial support and

training on all aspects of Scala 3 is available from [Propensive

OÜ](https://propensive.com/).



## Name



A __profanity__ is an expletive or curse-word, and _Profanity_ imitates many of the features of the popular terminal library, Curses.



In general, Soundness project names are always chosen with some rationale,

however it is usually frivolous. Each name is chosen for more for its

_uniqueness_ and _intrigue_ than its concision or catchiness, and there is no

bias towards names with positive or "nice" meanings—since many of the libraries

perform some quite unpleasant tasks.



Names should be English words, though many are obscure or archaic, and it

should be noted how willingly English adopts foreign words. Names are generally

of Greek or Latin origin, and have often arrived in English via a romance

language.



## Logo



The logo shows the horns of a devil; the epitome of the profane.



## License



Profanity is copyright © 2024 Jon Pretty & Propensive OÜ, and

is made available under the [Apache 2.0 License](/license.md).