Source/core/html/imports/HTMLImport.h

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#ifndef HTMLImport_h
#define HTMLImport_h

#include "core/html/imports/HTMLImportState.h"
#include "platform/heap/Handle.h"
#include "wtf/TreeNode.h"
#include "wtf/Vector.h"

namespace WebCore {

class Document;
class LocalFrame;
class HTMLImportChild;
class HTMLImportLoader;
class HTMLImportsController;
class KURL;

//
// # Basic Data Structure and Algorithms of HTML Imports implemenation.
//
// ## The Import Tree
//
// HTML Imports form a tree:
//
// * The root of the tree is HTMLImportTreeRoot.
//
// * The HTMLImportTreeRoot is owned HTMLImportsController, which is owned by the master
//   document as a DocumentSupplement.
//
// * The non-root nodes are HTMLImportChild. They are all owned by HTMLImporTreeRoot.
//   LinkStyle is wired into HTMLImportChild by implementing HTMLImportChildClient interface
//
// * Both HTMLImportTreeRoot and HTMLImportChild are derived from HTMLImport superclass
//   that models the tree data structure using WTF::TreeNode and provides a set of
//   virtual functions.
//
// HTMLImportsController also owns all loaders in the tree and manages their lifetime through it.
// One assumption is that the tree is append-only and nodes are never inserted in the middle of the tree nor removed.
//
// Full diagram is here:
// https://docs.google.com/drawings/d/1jFQrO0IupWrlykTNzQ3Nv2SdiBiSz4UE9-V3-vDgBb0/
//
// # Import Sharing and HTMLImportLoader
//
// The HTML Imports spec calls for de-dup mechanism to share already loaded imports.
// To implement this, the actual loading machinery is split out from HTMLImportChild to
// HTMLImportLoader, and each loader shares HTMLImportLoader with other loader if the URL is same.
// Check around HTMLImportsController::findLink() for more detail.
//
// HTMLImportLoader can be shared by multiple imports.
//
//    HTMLImportChild (1)-->(*) HTMLImportLoader
//
//
// # Script Blocking
//
// - An import blocks the HTML parser of its own imported document from running <script>
//   until all of its children are loaded.
//   Note that dynamically added import won't block the parser.
//
// - An import under loading also blocks imported documents that follow from being created.
//   This is because an import can include another import that has same URLs of following ones.
//   In such case, the preceding import should be loaded and following ones should be de-duped.
//

// The superclass of HTMLImportTreeRoot and HTMLImportChild
// This represents the import tree data structure.
class HTMLImport : public NoBaseWillBeGarbageCollectedFinalized<HTMLImport>, public TreeNode<HTMLImport> {
public:
    enum SyncMode {
        Sync  = 0,
        Async = 1
    };

    virtual ~HTMLImport() { }

    // FIXME: Consider returning HTMLImportTreeRoot.
    HTMLImport* root();
    bool precedes(HTMLImport*);
    bool isRoot() const { return !parent(); }
    bool isSync() const { return SyncMode(m_sync) == Sync; }
    bool formsCycle() const;
    const HTMLImportState& state() const { return m_state; }

    void appendImport(HTMLImport*);

    virtual Document* document() const = 0;
    virtual bool isDone() const = 0; // FIXME: Should be renamed to haveFinishedLoading()
    virtual HTMLImportLoader* loader() const { return 0; }
    virtual void stateWillChange() { }
    virtual void stateDidChange();

    virtual void trace(Visitor*) { }

protected:
    // Stating from most conservative state.
    // It will be corrected through state update flow.
    explicit HTMLImport(SyncMode sync)
        : m_sync(sync)
    { }

    static void recalcTreeState(HTMLImport* root);

#if !defined(NDEBUG)
    void show();
    void showTree(HTMLImport* highlight, unsigned depth);
    virtual void showThis();
#endif

private:
    HTMLImportState m_state;
    unsigned m_sync : 1;
};

} // namespace WebCore

#endif // HTMLImport_h