feat(ui): shared colour selector used across all style editors (#94)

Add a reusable color_selector widget (ui/color_select.rs): a main-colour
dropdown plus a "more colours" button that expands the full 255-entry ACI
palette — the same design the properties panel uses. Replace the flat ACI
swatch rows added earlier in the dimension, multileader and table style
editors with it, wired through each editor's existing colour edit message
(the chosen colour is encoded as an ACI string) plus a per-field
palette-open toggle.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/ui/color_select.rs

@@ -0,0 +1,171 @@
+//! Shared colour selector: a main-colour dropdown plus a "more colours" button
+//! that expands the full ACI palette. Used by the properties panel and every
+//! style editor so colour selection looks and behaves the same everywhere.
+
+use crate::app::Message;
+use crate::ui::properties::acad_color_display;
+use acadrust::types::Color as AcadColor;
+use iced::widget::{button, column, container, pick_list, row, scrollable, text};
+use iced::{Background, Border, Color, Element, Theme};
+
+/// Which "logical" entries the main dropdown offers besides the standard ACI
+/// colours.
+#[derive(Clone, Copy, Default)]
+pub struct ColorExtras {
+    pub by_layer: bool,
+    pub by_block: bool,
+}
+
+/// Encode a colour as the ACI integer string the style editors store
+/// (ByBlock=0, ByLayer=256, indexed 1-255; RGB has no ACI slot → ByLayer).
+pub fn color_to_aci_string(c: AcadColor) -> String {
+    match c {
+        AcadColor::ByBlock => "0".to_string(),
+        AcadColor::ByLayer => "256".to_string(),
+        AcadColor::Index(i) => i.to_string(),
+        AcadColor::Rgb { .. } => "256".to_string(),
+    }
+}
+
+/// Decode an ACI integer string back into an `AcadColor`.
+pub fn aci_string_to_color(s: &str) -> AcadColor {
+    match s.trim().parse::<i16>().unwrap_or(256) {
+        0 => AcadColor::ByBlock,
+        256 => AcadColor::ByLayer,
+        n if (1..=255).contains(&n) => AcadColor::Index(n as u8),
+        _ => AcadColor::ByLayer,
+    }
+}
+
+/// A dropdown option wrapping an `AcadColor`, displayed by its colour name.
+#[derive(Clone, PartialEq)]
+struct ColorChoice(AcadColor);
+
+impl std::fmt::Display for ColorChoice {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let (_, name) = acad_color_display(self.0);
+        write!(f, "{name}")
+    }
+}
+
+const PICKER_BG: Color = Color {
+    r: 0.12,
+    g: 0.12,
+    b: 0.12,
+    a: 1.0,
+};
+const BORDER: Color = Color {
+    r: 0.35,
+    g: 0.35,
+    b: 0.35,
+    a: 1.0,
+};
+
+/// Build a colour selector.
+///
+/// * `current` — the currently selected colour (shown in the dropdown).
+/// * `palette_open` — whether the expanded 255-colour grid is shown.
+/// * `extras` — whether ByLayer / ByBlock appear in the dropdown.
+/// * `on_select` — called with the chosen colour (dropdown item or grid swatch).
+/// * `on_more` — toggles the expanded palette.
+pub fn color_selector<'a>(
+    current: AcadColor,
+    palette_open: bool,
+    extras: ColorExtras,
+    on_select: impl Fn(AcadColor) -> Message + 'a,
+    on_more: Message,
+) -> Element<'a, Message> {
+    // Standard ACI 1-7 plus the requested extras, and the current colour if it
+    // isn't already one of them (so a non-standard index still shows).
+    let mut opts: Vec<ColorChoice> = Vec::new();
+    if extras.by_layer {
+        opts.push(ColorChoice(AcadColor::ByLayer));
+    }
+    if extras.by_block {
+        opts.push(ColorChoice(AcadColor::ByBlock));
+    }
+    for i in 1u8..=7 {
+        opts.push(ColorChoice(AcadColor::Index(i)));
+    }
+    let cur_choice = ColorChoice(current);
+    if !opts.contains(&cur_choice) {
+        opts.push(cur_choice.clone());
+    }
+
+    // Expanded ACI palette. Built before the dropdown closure so it can borrow
+    // `on_select`; the dropdown then moves it.
+    let grid: Option<Element<'a, Message>> = if palette_open {
+        const COLS: u16 = 16;
+        let mut rows = column![].spacing(1);
+        let mut idx: u16 = 1;
+        while idx <= 255 {
+            let mut r = row![].spacing(1);
+            for _ in 0..COLS {
+                if idx > 255 {
+                    break;
+                }
+                let ci = idx as u8;
+                let (bg, _) = acad_color_display(AcadColor::Index(ci));
+                let msg = on_select(AcadColor::Index(ci));
+                r = r.push(
+                    button(text("").width(12).height(12))
+                        .on_press(msg)
+                        .style(move |_: &Theme, status| button::Style {
+                            background: Some(Background::Color(bg)),
+                            border: Border {
+                                color: if matches!(status, button::Status::Hovered) {
+                                    Color::WHITE
+                                } else {
+                                    Color {
+                                        r: 0.0,
+                                        g: 0.0,
+                                        b: 0.0,
+                                        a: 0.4,
+                                    }
+                                },
+                                width: if matches!(status, button::Status::Hovered) {
+                                    1.5
+                                } else {
+                                    1.0
+                                },
+                                radius: 1.0.into(),
+                            },
+                            ..Default::default()
+                        })
+                        .padding(0),
+                );
+                idx += 1;
+            }
+            rows = rows.push(r);
+        }
+        Some(
+            container(scrollable(rows).height(150))
+                .style(|_: &Theme| container::Style {
+                    background: Some(Background::Color(PICKER_BG)),
+                    border: Border {
+                        color: BORDER,
+                        width: 1.0,
+                        radius: 0.0.into(),
+                    },
+                    ..Default::default()
+                })
+                .padding(4)
+                .into(),
+        )
+    } else {
+        None
+    };
+
+    let dropdown = pick_list(opts, Some(cur_choice), move |c| on_select(c.0))
+        .text_size(11)
+        .width(150);
+    let more = button(text(if palette_open { "×" } else { "⋯" }).size(11))
+        .on_press(on_more)
+        .padding([2, 7]);
+    let top = row![dropdown, more].spacing(4).align_y(iced::Center);
+
+    match grid {
+        Some(g) => column![top, g].spacing(2).into(),
+        None => top.into(),
+    }
+}