add calculator plugin (#104)

* feat: add calculator plugin

* add MIT license

* fix(calculator): typo

* fix(calculator): wrong PANEL_ID

* remove LICENSE

calculator/README.md

@@ -0,0 +1,99 @@
+# Calculator
+
+A calculator for the Noctalia bar. It evaluates whole expressions with operator
+precedence, offers both a keypad and a typed input line in its panel, and keeps
+the last result visible in the bar.
+
+## Plugin
+
+| Field | Value |
+| --- | --- |
+| ID | `yuuto/calculator` |
+| Entries | Bar widget: `bar`; panel: `panel` |
+
+The `panel` entry owns the calculator model and publishes it through Noctalia's
+per-plugin state channel. The `bar` widget is a thin client: it reads that state
+and opens the panel.
+
+## Usage
+
+Add the `bar` bar widget to your bar. It shows a calculator glyph, plus the last
+result once there is one. Left click opens the panel, right click clears the
+calculator. On a vertical bar only the glyph is shown, with the current
+expression as its tooltip.
+
+The panel evaluates as you type. The small line shows the expression, the large
+line the live result, and the copy button next to it puts the result on the
+clipboard.
+
+Enter expressions either with the keypad or by typing into the input line, where
+Enter evaluates. Pressing `=` keeps the result in the input, so the next
+operator continues from it. The keypad uses plain text labels (`AC`, `+/-`,
+`DEL`, `*`, `/`) rather than symbol glyphs, so it renders with any bar font.
+
+Open the panel over IPC:
+
+```sh
+noctalia msg panel-toggle yuuto/calculator:panel
+```
+
+### Expression syntax
+
+Operators are `+`, `-`, `*`, `/` and `^`, with parentheses and the usual
+precedence; `^` is right associative. A trailing `%` divides by 100, so
+`200*15%` is `30`. The typed input also accepts `×`, `÷` and `−`.
+
+Available constants: `pi`, `tau`, `e`.
+
+Available functions: `sin`, `cos`, `tan`, `asin`, `acos`, `atan`, `atan2`,
+`sinh`, `cosh`, `tanh`, `ln`, `log`, `log2`, `log10`, `exp`, `sqrt`, `cbrt`,
+`abs`, `floor`, `ceil`, `round`, `trunc`, `sign`, `mod`, `pow`, `hypot`, `min`,
+`max`.
+
+`log(x)` is base 10; `log(x, b)` is base `b`. `mod(a, b)` is the remainder, since
+`%` means percent here. The trigonometric functions follow the angle unit
+setting, shown in the panel header as `RAD` or `DEG`.
+
+## Settings
+
+### Plugin
+
+| Setting | Type | Default | Description |
+| --- | --- | --- | --- |
+| `precision` | `int` | `8` | Maximum decimals used when formatting results, 0 to 10. |
+| `angle_unit` | `select` | `rad` | Angle unit for the trigonometric functions. |
+
+### Bar Widget
+
+| Setting | Type | Default | Description |
+| --- | --- | --- | --- |
+| `show_bar_value` | `bool` | `true` | Shows the last result next to the calculator glyph. |
+| `max_bar_length` | `int` | `9` | Longer results are shortened with a trailing `~`. |
+
+## IPC
+
+Beyond opening the panel, the `panel` entry accepts three events. The `all`
+target addresses every live instance.
+
+```sh
+noctalia msg plugin yuuto/calculator:panel all eval "2+3*4"
+noctalia msg plugin yuuto/calculator:panel all insert "+8"
+noctalia msg plugin yuuto/calculator:panel all clear
+```
+
+`eval` replaces the expression and evaluates it, `insert` appends to the current
+expression, and `clear` resets the calculator.
+
+## Notes
+
+Expressions are tokenized and parsed by the plugin itself, so evaluating never
+runs a shell command and no external tool is required. Results reach the
+clipboard through `noctalia.copyToClipboard`.
+
+The panel keeps its model in the plugin state channel rather than in script
+locals, so clearing from the bar widget and reopening the panel stay in sync.
+
+## Credits
+
+Keypad layout and feature set are modelled on the v4 Quickshell calculator plugin
+by pir0c0pter0 (MIT).