//===--- Unicode.cpp - Unicode utilities ----------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

#include "swift/Basic/Unicode.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/ConvertUTF.h"

using namespace swift;

// HACK: Allow support for many newer emoji by overriding behavior of ZWJ and
// emoji modifiers. This does not make the breaks correct for any version of
// Unicode, but shifts the ways in which it is incorrect to be less harmful.
//
// TODO: Remove this hack and reevaluate whether we should have any static
// notion of what a grapheme is.
//
// Returns true if lhs and rhs shouldn't be considered as having a grapheme
// break between them. That is, whether we're overriding the behavior of the
// hard coded Unicode 8 rules surrounding ZWJ and emoji modifiers.
static inline bool graphemeBreakOverride(llvm::UTF32 lhs, llvm::UTF32 rhs) {
  // Assume ZWJ sequences produce new emoji
  if (lhs == 0x200D) {
    return true;
  }

  // Permit continuing regional indicators
  if (rhs >= 0x1F3FB && rhs <= 0x1F3FF) {
    return true;
  }

  // Permit emoji tag sequences
  if (rhs >= 0xE0020 && rhs <= 0xE007F) {
    return true;
  }

  return false;
}

StringRef swift::unicode::extractFirstExtendedGraphemeCluster(StringRef S) {
  // Extended grapheme cluster segmentation algorithm as described in Unicode
  // Standard Annex #29.
  if (S.empty())
    return StringRef();

  const llvm::UTF8 *SourceStart =
    reinterpret_cast<const llvm::UTF8 *>(S.data());

  const llvm::UTF8 *SourceNext = SourceStart;
  llvm::UTF32 C[2];
  llvm::UTF32 *TargetStart = C;

  ConvertUTF8toUTF32(&SourceNext, SourceStart + S.size(), &TargetStart, C + 1,
                     llvm::lenientConversion);
  if (TargetStart == C) {
    // The source string contains an ill-formed subsequence at the end.
    return S;
  }

  GraphemeClusterBreakProperty GCBForC0 = getGraphemeClusterBreakProperty(C[0]);
  while (true) {
    size_t C1Offset = SourceNext - SourceStart;
    ConvertUTF8toUTF32(&SourceNext, SourceStart + S.size(), &TargetStart, C + 2,
                       llvm::lenientConversion);

    if (TargetStart == C + 1) {
      // End of source string or the source string contains an ill-formed
      // subsequence at the end.
      return S.slice(0, C1Offset);
    }

    GraphemeClusterBreakProperty GCBForC1 =
        getGraphemeClusterBreakProperty(C[1]);
    if (isExtendedGraphemeClusterBoundary(GCBForC0, GCBForC1) &&
        !graphemeBreakOverride(C[0], C[1]))
      return S.slice(0, C1Offset);

    C[0] = C[1];
    TargetStart = C + 1;
    GCBForC0 = GCBForC1;
  }
}

static bool extractFirstUnicodeScalarImpl(StringRef S, unsigned &Scalar) {
  if (S.empty())
    return false;

  const llvm::UTF8 *SourceStart =
    reinterpret_cast<const llvm::UTF8 *>(S.data());

  const llvm::UTF8 *SourceNext = SourceStart;
  llvm::UTF32 C;
  llvm::UTF32 *TargetStart = &C;

  ConvertUTF8toUTF32(&SourceNext, SourceStart + S.size(), &TargetStart,
                     TargetStart + 1, llvm::lenientConversion);
  if (TargetStart == &C) {
    // The source string contains an ill-formed subsequence at the end.
    return false;
  }

  Scalar = C;
  return size_t(SourceNext - SourceStart) == S.size();
}

bool swift::unicode::isSingleUnicodeScalar(StringRef S) {
  unsigned Scalar;
  return extractFirstUnicodeScalarImpl(S, Scalar);
}

unsigned swift::unicode::extractFirstUnicodeScalar(StringRef S) {
  unsigned Scalar;
  bool Result = extractFirstUnicodeScalarImpl(S, Scalar);
  assert(Result && "string does not consist of one Unicode scalar");
  (void)Result;
  return Scalar;
}
