Spreadsheet: Reorganise the sources a bit

This commit just moves some code around:
- Give Cell its own file
- Pull all forward-declared classes/structs into Forward.h
- Clean up the order of member functions a bit

Applications/Spreadsheet/Cell.cpp

@@ -0,0 +1,120 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "Cell.h"
+#include "Spreadsheet.h"
+#include <AK/StringBuilder.h>
+
+namespace Spreadsheet {
+
+void Cell::set_data(String new_data)
+{
+    if (data == new_data)
+        return;
+
+    if (new_data.starts_with("=")) {
+        new_data = new_data.substring(1, new_data.length() - 1);
+        kind = Formula;
+    } else {
+        kind = LiteralString;
+    }
+
+    data = move(new_data);
+    dirty = true;
+    evaluated_externally = false;
+}
+
+void Cell::set_data(JS::Value new_data)
+{
+    dirty = true;
+    evaluated_externally = true;
+
+    StringBuilder builder;
+
+    builder.append(new_data.to_string_without_side_effects());
+    data = builder.build();
+
+    evaluated_data = move(new_data);
+}
+
+void Cell::update_data()
+{
+    TemporaryChange cell_change { sheet->current_evaluated_cell(), this };
+    if (!dirty)
+        return;
+
+    dirty = false;
+    if (kind == Formula) {
+        if (!evaluated_externally)
+            evaluated_data = sheet->evaluate(data, this);
+    }
+
+    for (auto& ref : referencing_cells) {
+        if (ref) {
+            ref->dirty = true;
+            ref->update();
+        }
+    }
+}
+
+void Cell::update()
+{
+    sheet->update(*this);
+}
+
+JS::Value Cell::js_data()
+{
+    if (dirty)
+        update();
+
+    if (kind == Formula)
+        return evaluated_data;
+
+    return JS::js_string(sheet->interpreter(), data);
+}
+
+String Cell::source() const
+{
+    StringBuilder builder;
+    if (kind == Formula)
+        builder.append('=');
+    builder.append(data);
+    return builder.to_string();
+}
+
+// FIXME: Find a better way to figure out dependencies
+void Cell::reference_from(Cell* other)
+{
+    if (!other || other == this)
+        return;
+
+    if (!referencing_cells.find([other](auto& ptr) { return ptr.ptr() == other; }).is_end())
+        return;
+
+    referencing_cells.append(other->make_weak_ptr());
+}
+
+}