HexEditor: Store annotations in a Model

A model is necessary for displaying a list of them in the UI. We might
as well make that their home.

Userland/Applications/HexEditor/AnnotationsModel.cpp

@@ -0,0 +1,68 @@
+/*
+ * Copyright (c) 2024, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "AnnotationsModel.h"
+
+GUI::Variant AnnotationsModel::data(GUI::ModelIndex const& index, GUI::ModelRole role) const
+{
+    if (index.row() < 0 || index.row() >= row_count())
+        return {};
+
+    if (role == GUI::ModelRole::TextAlignment)
+        return Gfx::TextAlignment::CenterLeft;
+
+    auto& annotation = m_annotations.at(index.row());
+    if (role == GUI::ModelRole::Display) {
+        switch (index.column()) {
+        case Column::Start:
+            return MUST(String::formatted("{:#08X}", annotation.start_offset));
+        case Column::End:
+            return MUST(String::formatted("{:#08X}", annotation.end_offset));
+        case Column::Comments:
+            return annotation.comments;
+        }
+    }
+    switch (to_underlying(role)) {
+    case to_underlying(CustomRole::StartOffset):
+        return annotation.start_offset;
+    case to_underlying(CustomRole::EndOffset):
+        return annotation.end_offset;
+    case to_underlying(CustomRole::Comments):
+        return annotation.comments;
+    }
+
+    return {};
+}
+
+void AnnotationsModel::add_annotation(Annotation annotation)
+{
+    m_annotations.append(move(annotation));
+    invalidate();
+}
+
+void AnnotationsModel::delete_annotation(Annotation const& annotation)
+{
+    m_annotations.remove_first_matching([&](auto& other) {
+        return other == annotation;
+    });
+    invalidate();
+}
+
+Optional<Annotation&> AnnotationsModel::closest_annotation_at(size_t position)
+{
+    // FIXME: If we end up with a lot of annotations, we'll need to store them and query them in a smarter way.
+    Optional<Annotation&> result;
+    for (auto& annotation : m_annotations) {
+        if (annotation.start_offset <= position && position <= annotation.end_offset) {
+            // If multiple annotations cover this position, use whichever starts latest. This would be the innermost one
+            // if they overlap fully rather than partially.
+            if (!result.has_value() || result->start_offset < annotation.start_offset)
+                result = annotation;
+        }
+    }
+
+    return result;
+}