import "package:flutter/gestures.dart";
import "package:flutter/widgets.dart";
import "package:flutter_lucide/flutter_lucide.dart";

import "context_menu.dart";
import "field_error.dart";
import "surface.dart";
import "semantics_scope.dart";
import "menu.dart";
import "theme/colour_scheme.dart";
import "theme/garage_theme.dart";

/// Where a [PropertyRow] splits label from control, as a fraction of the
/// row's width.
///
/// Blender doesnt give the label a fixed column - the split tracks the panel,
/// which is why the label/control pair always reads as centred no matter how
/// wide the editor gets. 0.4 is the split factor Blender itself defaults to
/// for `use_property_split` layouts.
const double kPropertySplitFactor = 0.4;

/// Gap between a property row's label column and its control.
const double kPropertyLabelGap = 10.0;

/// One property row: right-aligned label up to the split, control taking the
/// rest. Matches Blender's "Location X |" layout.
///
/// This is the app's form field - a labelled row that goes inside a
/// [PropertiesSection], with an optional right-click reset/copy/paste menu
/// via [PropertyActions].
class PropertyRow extends StatelessWidget {
  const PropertyRow({
    super.key,
    required this.label,
    required this.scheme,
    required this.child,
    this.subtitle,
    this.description,
    this.error,
    this.action,
    this.actions,
    this.split = kPropertySplitFactor,
    this.labelless = false,
  });

  final String label;
  final ColourScheme scheme;
  final Widget child;

  /// Second line under the label, INSIDE the label column - so it stays right
  /// aligned against the split the way the label is. For naming the value
  /// ("Used for account notifications"), not explaining it.
  final String? subtitle;

  /// Full width line under the whole row, spanning the label AND the control.
  /// For copy about the setting rather than about the field - consequences,
  /// caveats, what changes when you change it.
  final String? description;

  /// Why the value was refused. Reddens the control's outline and says why
  /// underneath it, in place of a toast that would float away from the field
  /// it was complaining about.
  final String? error;

  /// Beside the label, on its line - the same slot [SettingsRow] has, and the
  /// onboarding flow's ProductField before it. A muted "Required" or
  /// "Optional", usually.
  ///
  /// Styled here, at the subtitle's size and colour, so it reads as a tag on
  /// the label rather than a second label. A caller setting its own style
  /// still wins.
  ///
  /// Not to be confused with [actions], which is the right-click menu.
  final Widget? action;

  final PropertyActions? actions;

  /// fraction of the row width sitting left of the split. 0.5 would put the
  /// control's left edge dead centre.
  final double split;
  final bool labelless;

  @override
  Widget build(BuildContext context) {
    final theme = GarageTheme.of(context);
    final density = theme.density;
    final captionStyle = TextStyle(
      fontSize: density.textXxs,
      color: scheme.mutedForeground,
    );

    final row = Container(
      // a MINIMUM, not a fixed height. rows holding a single control already
      // measure controlHeight on their own; this is what stops a plain-Text
      // row (Type, Collection) collapsing to its ~11px line box and reading
      // as a different rhythm to the field rows above it. rows that are
      // legitimately taller - Size stacks two fields in a ButtonGroup - grow
      // past it untouched, which a fixed height would squash.
      //
      // It sits a step ABOVE controlHeight on purpose. The row's content is
      // not always the control: a label plus a subtitle is laid out on the
      // font's own metrics and comes out ~25 against a 23px compact control,
      // so at plain controlHeight the LABEL set the row height and the
      // control went along with it - backwards, and it moved with whatever
      // font resolved. With the minimum a little above both, neither one
      // drives it and the row is the same height either way.
      constraints: BoxConstraints(minHeight: density.propertyRowHeight),
      padding: density.buttonPadding.copyWith(top: 0, bottom: 0),
      // the content shrink-wraps and is centred in that minimum rather than
      // being stretched to fill it, so a taller row grows symmetrically
      // instead of hanging off the top.
      child: Align(
        alignment: Alignment.center,
        heightFactor: 1.0,
        child: Builder(
          builder: (context) {
            if (labelless) {
              return PropertySlotScope(
                child: FieldErrorScope(
                  invalid: error != null,
                  child: PropertyLabelScope(label: label, child: child),
                ),
              );
            }

            // A flex split, NOT a LayoutBuilder. LayoutBuilder builds its child
            // DURING layout, and an EditableText in that child marks itself
            // needing layout as it builds - which trips
            // _debugRelayoutBoundaryAlreadyMarkedNeedsLayout and takes the whole
            // subtree down with a focus-scope assert behind it. Only shows up
            // once a row holding a TextField is rebuilt mid-frame (a route swap
            // under it was enough), which is why the inspector never hit it.
            //
            // Geometry is unchanged: the gap comes out of the LABEL'S PADDING
            // rather than its width, so the label's text still ends at
            // `width * split - gap` and the control's left edge still lands
            // exactly on the split.
            return Row(
              crossAxisAlignment: CrossAxisAlignment.center,
              children: [
                Expanded(
                  flex: (split * 1000).round(),
                  child: Padding(
                    padding: const EdgeInsetsDirectional.only(
                      end: kPropertyLabelGap,
                    ),
                    child: Column(
                      crossAxisAlignment: CrossAxisAlignment.end,
                      mainAxisSize: MainAxisSize.min,
                      children: [
                        if (action == null)
                          Text(
                            label,
                            textAlign: TextAlign.right,
                            style: TextStyle(color: scheme.rowText),
                            overflow: TextOverflow.ellipsis,
                          )
                        else
                          Row(
                            mainAxisSize: MainAxisSize.min,
                            children: [
                              Flexible(
                                child: Text(
                                  label,
                                  textAlign: TextAlign.right,
                                  style: TextStyle(color: scheme.rowText),
                                  overflow: TextOverflow.ellipsis,
                                ),
                              ),
                              SizedBox(width: density.gapXs),
                              DefaultTextStyle.merge(
                                style: captionStyle,
                                child: action!,
                              ),
                            ],
                          ),
                        if (subtitle != null)
                          Text(
                            subtitle!,
                            textAlign: TextAlign.right,
                            style: captionStyle,
                          ),
                      ],
                    ),
                  ),
                ),
                // the row's label is the control's name as far as a screen
                // reader is concerned - publish it so the control can pick it
                // up instead of announcing itself as an anonymous checkbox.
                Expanded(
                  flex: ((1 - split) * 1000).round(),
                  child: PropertySlotScope(
                    child: FieldErrorScope(
                      invalid: error != null,
                      child: PropertyLabelScope(label: label, child: child),
                    ),
                  ),
                ),
              ],
            );
          },
        ),
      ),
    );

    final complaint = error;
    final description = this.description;

    // ALWAYS the column, even with nothing under the row - same as
    // settings_list.dart. A row that changes SHAPE when it gains a line
    // under it puts a different widget type at that position, so Flutter
    // throws the subtree away and builds a new one, and that takes the
    // CONTROL'S element with it. A control thats only just been built has
    // nothing to animate from, so the outline turned up already red.
    Widget content = Column(
      crossAxisAlignment: CrossAxisAlignment.stretch,
      mainAxisSize: MainAxisSize.min,
      children: [
        row,
        if (description != null)
          Padding(
            // horizontal inset matches the row's, so the box's edges line
            // up with the label column and the control above it rather
            // than floating inside them.
            padding: density.buttonPadding.copyWith(
              top: density.gapXs,
              bottom: 0,
            ),
            child: OutlinedContainer(
              // the outline field's own pair, not OutlinedContainer's
              // defaults - a description sits among outline controls and
              // should read as the same kind of surface. the default
              // borderColor is `muted`, which on most schemes is close
              // enough to the section fill to be invisible.
              backgroundColor: scheme.controlFill,
              borderColor: scheme.controlBorder,
              borderWidth: density.controlBorderWidth,
              // Md, matching the controls it sits under. the default is
              // Xl, which next to a section at Sm reads as a pill.
              borderRadius: theme.borderRadiusMd,
              padding: EdgeInsets.symmetric(
                horizontal: density.buttonPaddingX,
                vertical: density.gapXs,
              ),
              child: Text(
                description,
                textAlign: TextAlign.center,
                style: captionStyle,
              ),
            ),
          ),

        // under the control, where the control is - the outline says which
        // field, this says what about it.
        if (complaint != null)
          Padding(
            padding: density.buttonPadding.copyWith(
              top: density.gapXs,
              bottom: 0,
            ),
            child: Text(
              complaint,
              textAlign: TextAlign.center,
              style: captionStyle.copyWith(color: scheme.destructive),
            ),
          ),
      ],
    );

    // the row's height is what moves when a complaint arrives under it, so
    // it eases rather than jumping. Anchored top, or the rows above the
    // rejected one get shoved about by it.
    content = AnimatedSize(
      duration: kFieldErrorDuration,
      curve: kFieldErrorCurve,
      alignment: Alignment.topCenter,
      child: content,
    );

    final actions = this.actions;
    if (actions == null || !actions.hasAnyAction) return content;

    return GestureDetector(
      behavior: HitTestBehavior.opaque,
      onSecondaryTapDown: (details) {
        showContextMenu(
          context: context,
          globalPosition: details.globalPosition,
          onDismissed: () {},
          items: [
            MenuButton(
              enabled: actions.canReset,
              leading: const Icon(LucideIcons.rotate_ccw),
              onPressed: (_) => actions.reset(),
              child: const Text("Reset to Default"),
            ),
            MenuButton(
              enabled: actions.canCopy,
              leading: const Icon(LucideIcons.copy),
              onPressed: (_) => actions.copy(),
              child: const Text("Copy"),
            ),
            MenuButton(
              enabled: actions.canPaste,
              leading: const Icon(LucideIcons.clipboard_paste),
              onPressed: (_) => actions.paste(),
              child: const Text("Paste"),
            ),
          ],
        );
      },
      child: content,
    );
  }
}

/// Context-menu behaviour for a property row. It intentionally carries a typed
/// value instead of raw text, so a copied colour cannot be pasted into a width
/// field just because both can be displayed as strings.
class PropertyActions<T> {
  const PropertyActions({
    required this.value,
    required this.typeKey,
    this.defaultValue,
    this.onReset,
    this.onPaste,
  });

  final T value;
  final String typeKey;
  final T? defaultValue;
  final ValueChanged<T>? onReset;
  final ValueChanged<T>? onPaste;

  bool get canCopy => true;
  bool get canReset => defaultValue != null && onReset != null;
  bool get canPaste => onPaste != null && _PropertyClipboard.canPaste(typeKey);
  bool get hasAnyAction => canCopy || canReset || onPaste != null;

  void copy() {
    _PropertyClipboard.copy(typeKey: typeKey, value: value);
  }

  void reset() {
    final defaultValue = this.defaultValue;
    if (defaultValue == null) return;
    FocusManager.instance.primaryFocus?.unfocus();
    onReset?.call(defaultValue);
  }

  void paste() {
    final pasted = _PropertyClipboard.valueFor<T>(typeKey);
    if (pasted == null) return;
    FocusManager.instance.primaryFocus?.unfocus();
    onPaste?.call(pasted);
  }
}

class _PropertyClipboard {
  static String? _typeKey;
  static Object? _value;

  static void copy({required String typeKey, required Object? value}) {
    _typeKey = typeKey;
    _value = value;
  }

  static bool canPaste(String typeKey) => _typeKey == typeKey;

  static T? valueFor<T>(String typeKey) {
    if (!canPaste(typeKey)) return null;
    final value = _value;
    if (value is! T) return null;
    return value;
  }
}

/// icon + name bar that sits above a properties panel's sections - blender's
/// "[icon] Cube" row. Use this for panels whose subject is fixed (a settings
/// panel, a canvas panel) - a panel whose identity changes with a live
/// selection (an object inspector) usually wants its own header instead, tied
/// to that selection.
class PanelHeader extends StatelessWidget {
  const PanelHeader({
    super.key,
    required this.icon,
    required this.title,
    required this.scheme,
    this.trailing,
    this.bottomPadding = 8,
    this.titleWidget,
  });

  final IconData icon;
  final String title;
  final ColourScheme scheme;

  // optional row of action widgets (icon buttons, usually) after the title -
  // only the agent panel needs this so far (copy debug json / clear), every
  // other PanelHeader call site just leaves it null and gets the old layout.
  final Widget? trailing;

  // replaces the plain Text(title) in the middle slot when given - the agent
  // panel uses this for its thread switcher. [title] is still required even
  // then; its what a screen reader/tooltip falls back to and keeps every
  // other call site simple (they never pass this at all).
  final Widget? titleWidget;

  // a panel that fades its own content in under this header (ScrollEdgeFade)
  // wants that whitespace living INSIDE the fade zone instead of sitting
  // above it as dead space the fade never touches - pass 0 here and put the
  // same gap back as a SizedBox ahead of the faded child. Every other call
  // site just takes the default and looks exactly as before.
  final double bottomPadding;

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: EdgeInsets.fromLTRB(10, 10, 10, bottomPadding),
      child: Row(
        children: [
          // 18px slot round a 12px glyph - same icon column the explorer rows
          // use, so the panels all line up down the left edge.
          SizedBox(
            width: 18,
            child: Center(
              child: Icon(icon, size: 12, color: scheme.foreground),
            ),
          ),
          const SizedBox(width: 2),
          Expanded(
            // header:true so a screen reader can jump panel to panel by
            // heading instead of walking every control in between. The label
            // is [title] even when titleWidget replaces the text, which is
            // what that field's doc comment already promised.
            child: Semantics(
              header: true,
              label: title,
              child:
                  titleWidget ??
                  Text(
                    title,
                    style: GarageTheme.of(
                      context,
                    ).typography.medium.copyWith(color: scheme.foreground),
                    overflow: TextOverflow.ellipsis,
                  ),
            ),
          ),
          if (trailing != null) trailing!,
        ],
      ),
    );
  }
}

/// Shared collapsible section treatment for Blender-style properties panels -
/// the app's version of a form group. Holds a title bar (tap to collapse) and
/// a list of [PropertyRow]s (or any other rows).
class PropertiesSection extends StatelessWidget {
  const PropertiesSection({
    super.key,
    required this.title,
    required this.scheme,
    required this.collapsed,
    required this.onToggle,
    required this.rows,
    this.subtitle,
    this.trailing,
    this.actions = const [],
  });

  final String title;
  final ColourScheme scheme;
  final bool collapsed;
  final VoidCallback onToggle;
  final List<Widget> rows;

  /// Second line under the title, inside the header bar - the section's own
  /// version of [PropertyRow.subtitle]. Names what the section holds. Stays
  /// visible while collapsed, because it is part of the section's identity
  /// rather than part of its body.
  final String? subtitle;

  /// What the section can DO, as opposed to what it holds - a Save, a Reset, a
  /// Delete. Lives in a band at the bottom, separated from the rows and toned
  /// off them, so it reads as the section acting on itself rather than as one
  /// more property that happens to be a button.
  ///
  /// Toned between the section's own fill and `muted` rather than sat on
  /// `muted` itself. Straight muted is background - 7.4 while the section is
  /// background + 5.1, so the band was landing twelve points under the card it
  /// belongs to and within three of the editor's chrome - a hole cut through
  /// the pane rather than a floor under the rows. Mixed, it lands within about
  /// a point of whatever surface the section is sitting ON in every scheme we
  /// ship, which is what a footer reads as. Collapses with the rows - a
  /// collapsed section shows nothing but its title bar.
  /// Sits at the far end of the header bar, level with the title.
  ///
  /// For saying something ABOUT the section rather than doing something to it
  /// - a status, a badge, a count. Actions belong in [actions], which has its
  /// own band under the rows; this stays visible while the section is
  /// collapsed, because whatever it says is part of how you recognise the
  /// section in a list of them.
  final Widget? trailing;

  final List<Widget> actions;

  @override
  Widget build(BuildContext context) {
    final theme = GarageTheme.of(context);
    final density = theme.density;
    final radius = BorderRadius.circular(theme.radiusSm);
    // null unless a PropertiesList is above us. Sections work standalone and
    // always have; this is the only thing that changes when one isnt.
    final reorder = PropertiesReorderScope.maybeOf(context);
    final captionStyle = TextStyle(
      fontSize: density.textXxs,
      color: scheme.mutedForeground,
    );
    return Container(
      // bottom is gapLg, not gapXs: this margin is what separates one section
      // from the NEXT one, and gapXs is the step used between ROWS INSIDE a
      // section - so at gapXs a run of sections read as one striped block
      // rather than as separate subjects, which is the whole point of giving
      // each one its own. Three times the inner step, so the boundary between
      // two sections is unambiguously bigger than the boundary between two
      // rows. The sides stay gapXs; thats an inset from the pane edge, a
      // different job.
      margin: EdgeInsets.fromLTRB(
        density.gapXs,
        0,
        density.gapXs,
        density.gapLg,
      ),
      decoration: BoxDecoration(
        color: scheme.card,
        border: Border.all(color: scheme.propertiesSectionBorder),
        borderRadius: radius,
      ),
      child: ClipRRect(
        borderRadius: radius,
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            MergeSemantics(
              child: Semantics(
                container: true,
                button: true,
                header: true,
                expanded: !collapsed,
                onTap: onToggle,
                child: GestureDetector(
                  onTap: onToggle,
                  behavior: HitTestBehavior.opaque,
                  excludeFromSemantics: true,
                  child: Container(
                    padding: theme.density.buttonPadding,
                    child: Row(
                      children: [
                        AnimatedRotation(
                          turns: collapsed ? -0.25 : 0.0,
                          duration: const Duration(milliseconds: 120),
                          child: Icon(
                            LucideIcons.chevron_down,
                            size: theme.iconTheme.small.size,
                            color: scheme.mutedForeground,
                          ),
                        ),
                        SizedBox(width: density.gapSm),
                        Expanded(
                          child: Column(
                            crossAxisAlignment: CrossAxisAlignment.start,
                            mainAxisSize: MainAxisSize.min,
                            children: [
                              Text(
                                title,
                                style: theme.typography.semiBold.copyWith(
                                  color: scheme.rowText,
                                ),
                              ),
                              if (subtitle != null)
                                Text(subtitle!, style: captionStyle),
                            ],
                          ),
                        ),
                        if (trailing != null) ...[
                          SizedBox(width: density.gapSm),
                          trailing!,
                        ],
                        // The grab handle, when this section is inside a
                        // PropertiesList that lets it move. Last in the row,
                        // on the far edge - the left of the header belongs to
                        // the chevron, and two icons stacked there read as one
                        // control with two halves.
                        //
                        // Nothing at all when it cant move - not a disabled
                        // icon, not reserved space - so a page that never
                        // reorders looks exactly as it did before any of this
                        // existed.
                        if (reorder != null && reorder.draggable) ...[
                          SizedBox(width: density.gapSm),
                          _SectionDragHandle(
                            slot: reorder.slot,
                            child: MouseRegion(
                              cursor: SystemMouseCursors.grab,
                              // grip_horizontal: three across, two down. The
                              // list reorders VERTICALLY, and a grip whose
                              // rows run the same way as the travel is the one
                              // that reads as "drag me up and down".
                              //
                              // medium, not small - at the control icon size
                              // six dots turn into a smudge before they read
                              // as a texture you can grab.
                              //
                              // And well under mutedForeground, which is the
                              // colour of text you are meant to READ. A handle
                              // isnt read, its found - it only has to be there
                              // when you look for it, and at full muted it was
                              // competing with the section's own subtitle.
                              // Theres no token below muted, so this is muted
                              // taken down rather than a surface colour
                              // borrowed for a foreground job.
                              child: Icon(
                                LucideIcons.grip_horizontal,
                                size: theme.iconTheme.medium.size,
                                color: scheme.mutedForeground.withValues(
                                  alpha: 0.25,
                                ),
                              ),
                            ),
                          ),
                        ],
                      ],
                    ),
                  ),
                ),
              ),
            ),
            if (!collapsed) ...[
              for (var i = 0; i < rows.length; i++) ...[
                if (i > 0) SizedBox(height: density.gapXs),
                rows[i],
              ],
              // deliberately bigger than the between-rows step - the last row
              // was sitting right on the section's bottom edge.
              SizedBox(height: density.gapMd),
              if (actions.isNotEmpty) ...[
                Divider(color: scheme.propertiesSectionBorder),
                Container(
                  // most of the way to muted, not all of it - see [actions].
                  // Lerped off the section's own fill so it tracks whatever
                  // the section is filled with instead of being pinned to a
                  // token two surfaces below it.
                  color: Color.lerp(scheme.card, scheme.muted, 0.45),
                  padding: EdgeInsets.symmetric(
                    horizontal: density.buttonPaddingX,
                    vertical: density.gapSm,
                  ),
                  // the Row takes the full width, which is what makes the band
                  // span edge to edge rather than shrink to its buttons.
                  child: Row(
                    mainAxisAlignment: MainAxisAlignment.end,
                    children: [
                      for (var i = 0; i < actions.length; i++) ...[
                        if (i > 0) SizedBox(width: density.gapSm),
                        actions[i],
                      ],
                    ],
                  ),
                ),
              ],
            ],
          ],
        ),
      ),
    );
  }
}

// ─────────────────────────────────────────────────────────────────────────
//  reorderable lists of sections
// ─────────────────────────────────────────────────────────────────────────

/// One section in a [PropertiesList].
///
/// The flags live here rather than on [PropertiesSection] because a call site
/// almost never hands the list a bare section - it hands it a widget of its
/// own that renders one inside (`_GrantSection`, `_SubscriptionSection`). The
/// list cant read a field off somebody elses subtree, so what it needs to know
/// about an entry has to be said where the list can see it.
/// Which end of the list a pinned section is held at.
///
/// A roles list wants both: Owner at the top, Everyone at the bottom, and
/// neither of them anywhere else. A bool could only ever say "top", so the
/// section that belongs last ended up second from first.
enum PropertiesPin { top, bottom }

class PropertiesEntry {
  const PropertiesEntry({
    required this.id,
    required this.child,
    this.pin,
    this.movable = true,
  });

  /// Stable across rebuilds, and what [PropertiesList.onReorder] reports.
  ///
  /// NOT the position. The set changes under you - a grant revoked, a project
  /// added - and an order stored as indices quietly means something else the
  /// next time the list is a different length.
  final String id;

  final Widget child;

  /// Held at one end of the list, and never dragged.
  ///
  /// null - the default - means it moves with everything else. A pinned
  /// section is rendered outside the reorderable list entirely, which is what
  /// stops the list shifting it aside mid-drag and then correcting the drop.
  final PropertiesPin? pin;

  bool get pinned => pin != null;

  /// Can this one be picked up? Default true - everything moves unless said
  /// otherwise.
  ///
  /// This is about the HANDLE, not the slot: an unmovable section cant be
  /// dragged, but the ones around it can still move past it, so its index can
  /// change. If a section has to stay put, [pinned] is the flag for that.
  final bool movable;
}

/// A column of [PropertiesSection]s the user can drag into their own order.
///
/// It reports the order and stores nothing. Persisting it belongs to the
/// consumer - the kit has no business knowing where an app keeps preferences,
/// and one storage abstraction serving four call sites is exactly the thing it
/// shouldnt grow.
class PropertiesList extends StatefulWidget {
  const PropertiesList({
    super.key,
    required this.entries,
    required this.onReorder,
  });

  final List<PropertiesEntry> entries;

  /// The ids, in the order they now sit in, pinned ones included.
  ///
  /// The whole order rather than (oldIndex, newIndex): what a consumer stores
  /// IS an order, and turning a pair of indices back into one is the same
  /// dozen lines at every call site.
  final void Function(List<String> order) onReorder;

  @override
  State<PropertiesList> createState() => _PropertiesListState();
}

class _PropertiesListState extends State<PropertiesList> {
  /// One slot per entry id, kept for the life of the list.
  ///
  /// The point is the IDENTITY, not the contents. A slot's index is written
  /// in place as things move, so the scope handing it to a section never
  /// changes and the section never rebuilds - which is what makes a drag
  /// animate offsets instead of reconstructing every section's subtree, text
  /// fields and all, each time the gap shifts.
  final Map<String, PropertiesReorderSlot> _slots = {};

  PropertiesReorderSlot _slotFor(String id, int index) {
    final slot = _slots.putIfAbsent(id, () => PropertiesReorderSlot(index));
    slot.index = index;
    return slot;
  }

  @override
  Widget build(BuildContext context) {
    final entries = widget.entries;
    final onReorder = widget.onReorder;

    // Pinned sections are rendered OUTSIDE the reorderable list, not held at
    // index 0 inside it.
    //
    // Inside, the list owns them: it shifts them out of the way as you drag
    // past, and the only thing that can be done about it is to fix up the
    // result in onReorder - so the section you were dragging visibly took the
    // top slot and then snapped back one. A correction after the fact, and it
    // looked like one.
    //
    // Out here theres nothing to correct. The pinned block cant move because
    // it isnt in a list that moves things, nothing can be dropped above it
    // because there is no slot above it, and the top of the reorderable list
    // IS second place - so dragging to the top settles there instead of
    // bouncing.
    final top = entries.where((e) => e.pin == PropertiesPin.top).toList();
    final bottom = entries.where((e) => e.pin == PropertiesPin.bottom).toList();
    final movable = entries.where((e) => e.pin == null).toList();

    return Column(
      crossAxisAlignment: CrossAxisAlignment.stretch,
      mainAxisSize: MainAxisSize.min,
      children: [
        // no scope, so no handle - a pinned section renders exactly as it
        // would anywhere else.
        for (final entry in top) entry.child,
        if (movable.isNotEmpty) _reorderable(movable, top, bottom, onReorder),
        for (final entry in bottom) entry.child,
      ],
    );
  }

  Widget _reorderable(
    List<PropertiesEntry> movable,
    List<PropertiesEntry> top,
    List<PropertiesEntry> bottom,
    void Function(List<String> order) onReorder,
  ) {
    // ReorderableList, from flutter/widgets - NOT material's
    // ReorderableListView.
    //
    // The reordering machinery has allways lived in the widgets library;
    // ReorderableListView is only material's wrapper round it. Using the
    // wrapper meant a Material ancestor, and Material brings its own
    // DefaultTextStyle and IconTheme - which sit UNDER garage's and quietly
    // replaced the kit's typography and density derived sizes with flutter's
    // defaults for everything inside the list. The widgets version wants
    // WidgetsLocalizations and an Overlay, and GarageApp's WidgetsApp provides
    // both.
    return ReorderableList(
      // it sits inside the pane's scroll view, so it takes its height from its
      // children and doesnt scroll itself.
      shrinkWrap: true,
      physics: const NeverScrollableScrollPhysics(),
      itemCount: movable.length,
      // the section, unchanged, while its being dragged - a section is a flat
      // card on a flat pane and has nothing to lift off it.
      proxyDecorator: (child, index, animation) => child,
      itemBuilder: (context, i) {
        final entry = movable[i];
        return PropertiesReorderScope(
          key: ValueKey(entry.id),
          slot: _slotFor(entry.id, i),
          draggable: entry.movable,
          child: entry.child,
        );
      },
      onReorder: (oldIndex, newIndex) {
        // ReorderableList reports where the item would be INSERTED, which is
        // one past itself when its moving down.
        if (newIndex > oldIndex) newIndex -= 1;

        final next = [...movable];
        next.insert(newIndex, next.removeAt(oldIndex));
        // the whole order, ends included: theyre still part of what the
        // consumer stores, theyre just not part of the bit that moves.
        onReorder([
          for (final e in top) e.id,
          for (final e in next) e.id,
          for (final e in bottom) e.id,
        ]);
      },
    );
  }
}

/// Tells a [PropertiesSection] which slot of a [PropertiesList] it is in.
///
/// The handle has to be drawn by the SECTION - it belongs in the header beside
/// the chevron - but only the list knows the index a drag has to quote. So the
/// list puts the slot in scope and the section picks it up. Any depth of
/// wrapper in between is fine, which is the point: call sites wrap their
/// sections in widgets of their own everywhere.
class PropertiesReorderScope extends InheritedWidget {
  const PropertiesReorderScope({
    super.key,
    required this.slot,
    required this.draggable,
    required super.child,
  });

  final PropertiesReorderSlot slot;
  final bool draggable;

  static PropertiesReorderScope? maybeOf(BuildContext context) =>
      context.dependOnInheritedWidgetOfExactType<PropertiesReorderScope>();

  /// Deliberately NOT sensitive to the slot's index.
  ///
  /// The index changes constantly while something is being dragged, and
  /// notifying on it rebuilt every section in the list each time the gap
  /// moved - four subtrees of rows and text fields, mid-animation, which is
  /// what made the drag feel like it was catching. The slot is mutable so the
  /// handle can read the current index when a drag actually starts, and the
  /// only thing worth a rebuild is whether the section can be dragged at all.
  @override
  bool updateShouldNotify(PropertiesReorderScope old) =>
      draggable != old.draggable || !identical(slot, old.slot);
}

/// Where a section currently sits, as a thing rather than a number.
///
/// A widget field would have to be replaced to change, and replacing it is
/// what triggers the rebuilds this exists to avoid. So the object stays and
/// the number inside it moves.
class PropertiesReorderSlot {
  PropertiesReorderSlot(this.index);

  int index;
}

/// The grab handle: starts a reorder on pointer down, reading the section's
/// position AT THAT MOMENT.
///
/// This is [ReorderableDragStartListener] with one difference, and it is the
/// whole point: that one takes its index as a constructor argument, so it has
/// to be rebuilt every time the index changes. This one reads it off the slot
/// when the pointer actually goes down, so nothing above it needs rebuilding
/// while a drag is in flight.
class _SectionDragHandle extends StatelessWidget {
  const _SectionDragHandle({required this.slot, required this.child});

  final PropertiesReorderSlot slot;
  final Widget child;

  @override
  Widget build(BuildContext context) {
    return Listener(
      onPointerDown: (event) {
        final list = SliverReorderableList.maybeOf(context);
        list?.startItemDragReorder(
          index: slot.index,
          event: event,
          recognizer: ImmediateMultiDragGestureRecognizer(debugOwner: this)
            ..gestureSettings = MediaQuery.maybeGestureSettingsOf(context),
        );
      },
      child: child,
    );
  }
}