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+// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// The main idea in Courgette is to do patching *under a tranformation*.  The
+// input is transformed into a new representation, patching occurs in the new
+// repesentation, and then the tranform is reversed to get the patched data.
+//
+// The idea is applied to pieces (or 'Elements') of the whole (or 'Ensemble').
+// Each of the elements has to go through the same set of steps in lock-step,
+// but there may be many different kinds of elements, which have different
+// transformation.
+//
+// This file declares all the main types involved in creating and applying a
+// patch with this structure.
+
+#ifndef COURGETTE_ENSEMBLE_H_
+#define COURGETTE_ENSEMBLE_H_
+
+#include <vector>
+#include <string>
+
+#include "base/basictypes.h"
+
+#include "courgette/courgette.h"
+#include "courgette/region.h"
+#include "courgette/streams.h"
+
+namespace courgette {
+
+// Forward declarations:
+class Ensemble;
+class PEInfo;
+
+// An Element is a region of an Ensemble with an identifyable kind.
+//
+class Element {
+ public:
+  enum Kind { WIN32_X86_WITH_CODE, WIN32_NOCODE };
+
+  virtual ~Element() {}
+
+  Kind kind() const { return kind_; }
+  const Region& region() const { return region_; }
+
+  // The name is used only for debugging and logging.
+  virtual std::string Name() const;
+
+  // Returns the byte position of this Element relative to the start of
+  // containing Ensemble.
+  size_t offset_in_ensemble() const;
+
+  // Some subclasses of Element might have a PEInfo.
+  virtual PEInfo* GetPEInfo() const { return NULL; }
+
+ protected:
+  Element(Kind kind, Ensemble* ensemble, const Region& region);
+
+ private:
+  Kind kind_;
+  Ensemble* ensemble_;
+  Region region_;
+
+  DISALLOW_COPY_AND_ASSIGN(Element);
+};
+
+
+class Ensemble {
+ public:
+  Ensemble(const Region& region, const char* name)
+      : region_(region), name_(name) {}
+  ~Ensemble();
+
+  const Region& region() const { return region_; }
+  const std::string& name() const { return name_; }
+
+  // Scans the region to find Elements within the region().
+  Status FindEmbeddedElements();
+
+  // Returns the elements found by 'FindEmbeddedElements'.
+  const std::vector<Element*>& elements() const { return elements_; }
+
+
+ private:
+  Region region_;       // The memory, owned by caller, containing the
+                        // Ensemble's data.
+  std::string name_;    // A debugging/logging name for the Ensemble.
+
+  std::vector<Element*> elements_;        // Embedded elements discovered.
+  std::vector<Element*> owned_elements_;  // For deallocation.
+
+  DISALLOW_COPY_AND_ASSIGN(Ensemble);
+};
+
+inline size_t Element::offset_in_ensemble() const {
+  return region().start() - ensemble_->region().start();
+}
+
+// The 'CourgettePatchFile' is class is a 'namespace' for the constants that
+// appear in a Courgette patch file.
+struct CourgettePatchFile {
+  //
+  // The Courgette patch format interleaves the data for N embedded Elements.
+  //
+  // Format of a patch file:
+  //  header:
+  //    magic
+  //    version
+  //    source-checksum
+  //    target-checksum
+  //  multiple-streams:
+  //    stream 0:
+  //      number-of-transformed-elements (N) - varint32
+  //      transformation-1-method-id
+  //      transformation-2-method-id
+  //      ...
+  //      transformation-1-initial-parameters
+  //      transformation-2-initial-parameters
+  //      ...
+  //    stream 1:
+  //      correction:
+  //        transformation-1-parameters
+  //        transformation-2-parameters
+  //        ...
+  //    stream 2:
+  //      correction:
+  //        transformed-element-1
+  //        transformed-element-2
+  //        ...
+  //    stream 3:
+  //      correction:
+  //        base-file
+  //        element-1
+  //        element-2
+  //        ...
+
+  static const uint32 kMagic = 'C' | ('o' << 8) | ('u' << 16);
+
+  static const uint32 kVersion = 20090320;
+
+  // Transformation method IDs.
+  enum TransformationMethodId {
+    T_COURGETTE_WIN32_X86 = 1,  // Windows 32 bit 'Portable Executable' x86.
+  };
+};
+
+// For any transform you would implement both a TransformationPatcher and a
+// TransformationPatchGenerator.
+//
+// TransformationPatcher is the interface which abstracts out the actual
+// transformation used on an Element.  The patching itself happens outside the
+// actions of a TransformationPatcher.  There are four steps.
+//
+// The first step is an Init step.  The parameters to the Init step identify the
+// element, for example, range of locations within the original ensemble that
+// correspond to the element.
+//
+// PredictTransformParameters, explained below.
+//
+// The two final steps are 'Transform' - to transform the element into a new
+// representation, and to 'Reform' - to transform from the new representation
+// back to the original form.
+//
+// The Transform step takes some parameters.  This allows the transform to be
+// customized to the particular element, or to receive some assistance in the
+// analysis required to perform the transform.  The transform parameters might
+// be extensive but mostly predicable, so preceeding Transform is a
+// PredictTransformParameters step.
+//
+class TransformationPatcher {
+ public:
+  virtual ~TransformationPatcher() {}
+
+  // First step: provides parameters for the patching.  This would at a minimum
+  // identify the element within the ensemble being patched.
+  virtual Status Init(SourceStream* parameter_stream) = 0;
+
+  // Second step: predicts transform parameters.
+  virtual Status PredictTransformParameters(
+      SinkStreamSet* predicted_parameters) = 0;
+
+  // Third step: transforms element from original representation into alternate
+  // representation.
+  virtual Status Transform(SourceStreamSet* corrected_parameters,
+                           SinkStreamSet* transformed_element) = 0;
+
+  // Final step: transforms element back from alternate representation into
+  // original representation.
+  virtual Status Reform(SourceStreamSet* transformed_element,
+                        SinkStream* reformed_element) = 0;
+};
+
+// TransformationPatchGenerator is the interface which abstracts out the actual
+// transformation used (and adjustment used) when differentially compressing one
+// Element from the |new_ensemble| against a corresponding element in the
+// |old_ensemble|.
+//
+// This is not a pure interface.  There is a small amount of inheritance
+// implementation for the fields and actions common to all
+// TransformationPatchGenerators.
+//
+// When TransformationPatchGenerator is subclassed, there will be a
+// corresponding subclass of TransformationPatcher.
+//
+class TransformationPatchGenerator {
+ public:
+  TransformationPatchGenerator(Element* old_element,
+                               Element* new_element,
+                               TransformationPatcher* patcher);
+
+  virtual ~TransformationPatchGenerator();
+
+  // Returns the TransformationMethodId that identies this transformation.
+  virtual CourgettePatchFile::TransformationMethodId Kind() = 0;
+
+  // Writes the parameters that will be passed to TransformationPatcher::Init.
+  virtual Status WriteInitialParameters(SinkStream* parameter_stream) = 0;
+
+  // Predicts the transform parameters for the |old_element|.  This must match
+  // exactly the output that will be produced by the PredictTransformParameters
+  // method of the corresponding subclass of TransformationPatcher.  This method
+  // is not pure. The default implementation delegates to the patcher to
+  // guarantee matching output.
+  virtual Status PredictTransformParameters(SinkStreamSet* prediction);
+
+  // Writes the desired parameters for the transform of the old element from the
+  // file representation to the alternate representation.
+  virtual Status CorrectedTransformParameters(SinkStreamSet* parameters) = 0;
+
+  // Writes both |old_element| and |new_element| in the new representation.
+  // |old_corrected_parameters| will match the |corrected_parameters| passed to
+  // the Transform method of the corresponding sublcass of
+  // TransformationPatcher.
+  //
+  // The output written to |old_transformed_element| must match exactly the
+  // output written by the Transform method of the corresponding subclass of
+  // TransformationPatcher.
+  virtual Status Transform(SourceStreamSet* old_corrected_parameters,
+                           SinkStreamSet* old_transformed_element,
+                           SinkStreamSet* new_transformed_element) = 0;
+
+  // Transforms the new transformed_element back from the alternate
+  // representation into the original file format.  This must match exactly the
+  // output that will be produced by the corresponding subclass of
+  // TransformationPatcher::Reform.  This method is not pure. The default
+  // implementation delegates to the patcher.
+  virtual Status Reform(SourceStreamSet* transformed_element,
+                        SinkStream* reformed_element);
+
+ protected:
+  Element* old_element_;
+  Element* new_element_;
+  TransformationPatcher* patcher_;
+};
+
+}  // namespace
+#endif  // COURGETTE_ENSEMBLE_H_