Extract canvas clear command planning

src/app_core/document_canvas.h

@@ -0,0 +1,58 @@
+#pragma once
+
+#include "foundation/result.h"
+
+#include <cmath>
+
+namespace pp::app {
+
+struct DocumentCanvasClearPlan {
+    float r = 0.0F;
+    float g = 0.0F;
+    float b = 0.0F;
+    float a = 0.0F;
+    bool clears_canvas = false;
+    bool records_undo = false;
+    bool marks_unsaved = false;
+    bool no_op = true;
+};
+
+[[nodiscard]] inline pp::foundation::Status validate_clear_color_channel(float value) noexcept
+{
+    if (!std::isfinite(value)) {
+        return pp::foundation::Status::invalid_argument("clear color channel must be finite");
+    }
+    if (value < 0.0F || value > 1.0F) {
+        return pp::foundation::Status::out_of_range("clear color channel must be within 0..1");
+    }
+    return pp::foundation::Status::success();
+}
+
+[[nodiscard]] inline pp::foundation::Result<DocumentCanvasClearPlan> plan_document_canvas_clear(
+    bool has_canvas,
+    float r = 0.0F,
+    float g = 0.0F,
+    float b = 0.0F,
+    float a = 0.0F) noexcept
+{
+    const float channels[] { r, g, b, a };
+    for (const float channel : channels) {
+        const auto status = validate_clear_color_channel(channel);
+        if (!status.ok()) {
+            return pp::foundation::Result<DocumentCanvasClearPlan>::failure(status);
+        }
+    }
+
+    DocumentCanvasClearPlan plan;
+    plan.r = r;
+    plan.g = g;
+    plan.b = b;
+    plan.a = a;
+    plan.clears_canvas = has_canvas;
+    plan.records_undo = has_canvas;
+    plan.marks_unsaved = has_canvas;
+    plan.no_op = !has_canvas;
+    return pp::foundation::Result<DocumentCanvasClearPlan>::success(plan);
+}
+
+} // namespace pp::app