//===- Replacement.h - Framework for clang refactoring tools ----*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
//  Classes supporting refactorings that span multiple translation units.
//  While single translation unit refactorings are supported via the Rewriter,
//  when refactoring multiple translation units changes must be stored in a
//  SourceManager independent form, duplicate changes need to be removed, and
//  all changes must be applied at once at the end of the refactoring so that
//  the code is always parseable.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_TOOLING_CORE_REPLACEMENT_H
#define LLVM_CLANG_TOOLING_CORE_REPLACEMENT_H

#include "clang/Basic/LangOptions.h"
#include "clang/Basic/SourceLocation.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/raw_ostream.h"
#include <map>
#include <optional>
#include <set>
#include <string>
#include <system_error>
#include <utility>
#include <vector>

namespace clang {

class FileManager;
class Rewriter;
class SourceManager;

namespace tooling {

/// A source range independent of the \c SourceManager.
class Range {
public:
  Range() = default;
  Range(unsigned Offset, unsigned Length) : Offset(Offset), Length(Length) {}

  /// Accessors.
  /// @{
  unsigned getOffset() const { return Offset; }
  unsigned getLength() const { return Length; }
  /// @}

  /// \name Range Predicates
  /// @{
  /// Whether this range overlaps with \p RHS or not.
  bool overlapsWith(Range RHS) const {
    return Offset + Length > RHS.Offset && Offset < RHS.Offset + RHS.Length;
  }

  /// Whether this range contains \p RHS or not.
  bool contains(Range RHS) const {
    return RHS.Offset >= Offset &&
           (RHS.Offset + RHS.Length) <= (Offset + Length);
  }

  /// Whether this range equals to \p RHS or not.
  bool operator==(const Range &RHS) const {
    return Offset == RHS.getOffset() && Length == RHS.getLength();
  }
  /// @}

private:
  unsigned Offset = 0;
  unsigned Length = 0;
};

/// A text replacement.
///
/// Represents a SourceManager independent replacement of a range of text in a
/// specific file.
class Replacement {
public:
  /// Creates an invalid (not applicable) replacement.
  Replacement();

  /// Creates a replacement of the range [Offset, Offset+Length) in
  /// FilePath with ReplacementText.
  ///
  /// \param FilePath A source file accessible via a SourceManager.
  /// \param Offset The byte offset of the start of the range in the file.
  /// \param Length The length of the range in bytes.
  Replacement(StringRef FilePath, unsigned Offset, unsigned Length,
              StringRef ReplacementText);

  /// Creates a Replacement of the range [Start, Start+Length) with
  /// ReplacementText.
  Replacement(const SourceManager &Sources, SourceLocation Start,
              unsigned Length, StringRef ReplacementText);

  /// Creates a Replacement of the given range with ReplacementText.
  Replacement(const SourceManager &Sources, const CharSourceRange &Range,
              StringRef ReplacementText,
              const LangOptions &LangOpts = LangOptions());

  /// Creates a Replacement of the node with ReplacementText.
  template <typename Node>
  Replacement(const SourceManager &Sources, const Node &NodeToReplace,
              StringRef ReplacementText,
              const LangOptions &LangOpts = LangOptions());

  /// Returns whether this replacement can be applied to a file.
  ///
  /// Only replacements that are in a valid file can be applied.
  bool isApplicable() const;

  /// Accessors.
  /// @{
  StringRef getFilePath() const { return FilePath; }
  unsigned getOffset() const { return ReplacementRange.getOffset(); }
  unsigned getLength() const { return ReplacementRange.getLength(); }
  StringRef getReplacementText() const { return ReplacementText; }
  /// @}

  /// Applies the replacement on the Rewriter.
  bool apply(Rewriter &Rewrite) const;

  /// Returns a human readable string representation.
  std::string toString() const;

private:
  void setFromSourceLocation(const SourceManager &Sources, SourceLocation Start,
                             unsigned Length, StringRef ReplacementText);
  void setFromSourceRange(const SourceManager &Sources,
                          const CharSourceRange &Range,
                          StringRef ReplacementText,
                          const LangOptions &LangOpts);

  std::string FilePath;
  Range ReplacementRange;
  std::string ReplacementText;
};

enum class replacement_error {
  fail_to_apply = 0,
  wrong_file_path,
  overlap_conflict,
  insert_conflict,
};

/// Carries extra error information in replacement-related llvm::Error,
/// e.g. fail applying replacements and replacements conflict.
class ReplacementError : public llvm::ErrorInfo<ReplacementError> {
public:
  ReplacementError(replacement_error Err) : Err(Err) {}

  /// Constructs an error related to an existing replacement.
  ReplacementError(replacement_error Err, Replacement Existing)
      : Err(Err), ExistingReplacement(std::move(Existing)) {}

  /// Constructs an error related to a new replacement and an existing
  /// replacement in a set of replacements.
  ReplacementError(replacement_error Err, Replacement New, Replacement Existing)
      : Err(Err), NewReplacement(std::move(New)),
        ExistingReplacement(std::move(Existing)) {}

  std::string message() const override;

  void log(raw_ostream &OS) const override { OS << message(); }

  replacement_error get() const { return Err; }

  static char ID;

  const std::optional<Replacement> &getNewReplacement() const {
    return NewReplacement;
  }

  const std::optional<Replacement> &getExistingReplacement() const {
    return ExistingReplacement;
  }

private:
  // Users are not expected to use error_code.
  std::error_code convertToErrorCode() const override {
    return llvm::inconvertibleErrorCode();
  }

  replacement_error Err;

  // A new replacement, which is to expected be added into a set of
  // replacements, that is causing problem.
  std::optional<Replacement> NewReplacement;

  // An existing replacement in a replacements set that is causing problem.
  std::optional<Replacement> ExistingReplacement;
};

/// Less-than operator between two Replacements.
bool operator<(const Replacement &LHS, const Replacement &RHS);

/// Equal-to operator between two Replacements.
bool operator==(const Replacement &LHS, const Replacement &RHS);
inline bool operator!=(const Replacement &LHS, const Replacement &RHS) {
  return !(LHS == RHS);
}

/// Maintains a set of replacements that are conflict-free.
/// Two replacements are considered conflicts if they overlap or have the same
/// offset (i.e. order-dependent).
class Replacements {
private:
  using ReplacementsImpl = std::set<Replacement>;

public:
  using const_iterator = ReplacementsImpl::const_iterator;
  using const_reverse_iterator = ReplacementsImpl::const_reverse_iterator;

  Replacements() = default;

  explicit Replacements(const Replacement &R) { Replaces.insert(R); }

  /// Adds a new replacement \p R to the current set of replacements.
  /// \p R must have the same file path as all existing replacements.
  /// Returns `success` if the replacement is successfully inserted; otherwise,
  /// it returns an llvm::Error, i.e. there is a conflict between R and the
  /// existing replacements (i.e. they are order-dependent) or R's file path is
  /// different from the filepath of existing replacements. Callers must
  /// explicitly check the Error returned, and the returned error can be
  /// converted to a string message with `llvm::toString()`. This prevents users
  /// from adding order-dependent replacements. To control the order in which
  /// order-dependent replacements are applied, use merge({R}) with R referring
  /// to the changed code after applying all existing replacements.
  /// Two replacements A and B are considered order-independent if applying them
  /// in either order produces the same result. Note that the range of the
  /// replacement that is applied later still refers to the original code.
  /// These include (but not restricted to) replacements that:
  ///   - don't overlap (being directly adjacent is fine) and
  ///   - are overlapping deletions.
  ///   - are insertions at the same offset and applying them in either order
  ///     has the same effect, i.e. X + Y = Y + X when inserting X and Y
  ///     respectively.
  ///   - are identical replacements, i.e. applying the same replacement twice
  ///     is equivalent to applying it once.
  /// Examples:
  /// 1. Replacement A(0, 0, "a") and B(0, 0, "aa") are order-independent since
  ///    applying them in either order gives replacement (0, 0, "aaa").
  ///    However, A(0, 0, "a") and B(0, 0, "b") are order-dependent since
  ///    applying A first gives (0, 0, "ab") while applying B first gives (B, A,
  ///    "ba").
  /// 2. Replacement A(0, 2, "123") and B(0, 2, "123") are order-independent
  ///    since applying them in either order gives (0, 2, "123").
  /// 3. Replacement A(0, 3, "123") and B(2, 3, "321") are order-independent
  ///    since either order gives (0, 5, "12321").
  /// 4. Replacement A(0, 3, "ab") and B(0, 3, "ab") are order-independent since
  ///    applying the same replacement twice is equivalent to applying it once.
  /// Replacements with offset UINT_MAX are special - we do not detect conflicts
  /// for such replacements since users may add them intentionally as a special
  /// category of replacements.
  llvm::Error add(const Replacement &R);

  /// Merges \p Replaces into the current replacements. \p Replaces
  /// refers to code after applying the current replacements.
  [[nodiscard]] Replacements merge(const Replacements &Replaces) const;

  // Returns the affected ranges in the changed code.
  std::vector<Range> getAffectedRanges() const;

  // Returns the new offset in the code after replacements being applied.
  // Note that if there is an insertion at Offset in the current replacements,
  // \p Offset will be shifted to Offset + Length in inserted text.
  unsigned getShiftedCodePosition(unsigned Position) const;

  unsigned size() const { return Replaces.size(); }

  void clear() { Replaces.clear(); }

  bool empty() const { return Replaces.empty(); }

  const_iterator begin() const { return Replaces.begin(); }

  const_iterator end() const { return Replaces.end(); }

  const_reverse_iterator rbegin() const  { return Replaces.rbegin(); }

  const_reverse_iterator rend() const { return Replaces.rend(); }

  bool operator==(const Replacements &RHS) const {
    return Replaces == RHS.Replaces;
  }

private:
  Replacements(const_iterator Begin, const_iterator End)
      : Replaces(Begin, End) {}

  // Returns `R` with new range that refers to code after `Replaces` being
  // applied.
  Replacement getReplacementInChangedCode(const Replacement &R) const;

  // Returns a set of replacements that is equivalent to the current
  // replacements by merging all adjacent replacements. Two sets of replacements
  // are considered equivalent if they have the same effect when they are
  // applied.
  Replacements getCanonicalReplacements() const;

  // If `R` and all existing replacements are order-independent, then merge it
  // with `Replaces` and returns the merged replacements; otherwise, returns an
  // error.
  llvm::Expected<Replacements>
  mergeIfOrderIndependent(const Replacement &R) const;

  ReplacementsImpl Replaces;
};

/// Apply all replacements in \p Replaces to the Rewriter \p Rewrite.
///
/// Replacement applications happen independently of the success of
/// other applications.
///
/// \returns true if all replacements apply. false otherwise.
bool applyAllReplacements(const Replacements &Replaces, Rewriter &Rewrite);

/// Applies all replacements in \p Replaces to \p Code.
///
/// This completely ignores the path stored in each replacement. If all
/// replacements are applied successfully, this returns the code with
/// replacements applied; otherwise, an llvm::Error carrying llvm::StringError
/// is returned (the Error message can be converted to string using
/// `llvm::toString()` and 'std::error_code` in the `Error` should be ignored).
llvm::Expected<std::string> applyAllReplacements(StringRef Code,
                                                 const Replacements &Replaces);

/// Collection of Replacements generated from a single translation unit.
struct TranslationUnitReplacements {
  /// Name of the main source for the translation unit.
  std::string MainSourceFile;

  std::vector<Replacement> Replacements;
};

/// Calculates the new ranges after \p Replaces are applied. These
/// include both the original \p Ranges and the affected ranges of \p Replaces
/// in the new code.
///
/// \pre Replacements must be for the same file.
///
/// \return The new ranges after \p Replaces are applied. The new ranges will be
/// sorted and non-overlapping.
std::vector<Range>
calculateRangesAfterReplacements(const Replacements &Replaces,
                                 const std::vector<Range> &Ranges);

/// If there are multiple <File, Replacements> pairs with the same file
/// entry, we only keep one pair and discard the rest.
/// If a file does not exist, its corresponding replacements will be ignored.
std::map<std::string, Replacements> groupReplacementsByFile(
    FileManager &FileMgr,
    const std::map<std::string, Replacements> &FileToReplaces);

template <typename Node>
Replacement::Replacement(const SourceManager &Sources,
                         const Node &NodeToReplace, StringRef ReplacementText,
                         const LangOptions &LangOpts) {
  const CharSourceRange Range =
      CharSourceRange::getTokenRange(NodeToReplace->getSourceRange());
  setFromSourceRange(Sources, Range, ReplacementText, LangOpts);
}

} // namespace tooling

} // namespace clang

#endif // LLVM_CLANG_TOOLING_CORE_REPLACEMENT_H