// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

#ifndef CARBON_TOOLCHAIN_DIAGNOSTICS_DIAGNOSTIC_EMITTER_H_
#define CARBON_TOOLCHAIN_DIAGNOSTICS_DIAGNOSTIC_EMITTER_H_

#include <functional>
#include <string>
#include <type_traits>
#include <utility>

#include "common/check.h"
#include "llvm/ADT/Any.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Support/FormatVariadic.h"
#include "llvm/Support/raw_ostream.h"
#include "toolchain/diagnostics/diagnostic_kind.h"

namespace Carbon {

enum class DiagnosticLevel : int8_t {
  // A note, not indicating an error on its own, but possibly providing context
  // for an error.
  Note,
  // A warning diagnostic, indicating a likely problem with the program.
  Warning,
  // An error diagnostic, indicating that the program is not valid.
  Error,
};

// Provides a definition of a diagnostic. For example:
//   CARBON_DIAGNOSTIC(MyDiagnostic, Error, "Invalid code!");
//   CARBON_DIAGNOSTIC(MyDiagnostic, Warning, "Found {0}, expected {1}.",
//              llvm::StringRef, llvm::StringRef);
//
// Arguments are passed to llvm::formatv; see:
// https://llvm.org/doxygen/FormatVariadic_8h_source.html
//
// See `DiagnosticEmitter::Emit` for comments about argument lifetimes.
#define CARBON_DIAGNOSTIC(DiagnosticName, Level, Format, ...) \
  static constexpr auto DiagnosticName =                      \
      Internal::DiagnosticBase<__VA_ARGS__>(                  \
          ::Carbon::DiagnosticKind::DiagnosticName,           \
          ::Carbon::DiagnosticLevel::Level, Format)

struct DiagnosticLocation {
  // Name of the file or buffer that this diagnostic refers to.
  // TODO: Move this out of DiagnosticLocation, as part of an expectation that
  // files will be compiled separately, so storing the file's path
  // per-diagnostic is wasteful.
  std::string file_name;
  // 1-based line number.
  int32_t line_number;
  // 1-based column number.
  int32_t column_number;
};

// A message composing a diagnostic. This may be the main message, but can also
// be notes providing more information.
struct DiagnosticMessage {
  explicit DiagnosticMessage(
      DiagnosticKind kind, DiagnosticLocation location,
      llvm::StringLiteral format, llvm::SmallVector<llvm::Any, 0> format_args,
      std::function<std::string(const DiagnosticMessage&)> format_fn)
      : kind(kind),
        location(std::move(location)),
        format(format),
        format_args(std::move(format_args)),
        format_fn(std::move(format_fn)) {}

  // The diagnostic's kind.
  DiagnosticKind kind;

  // The calculated location of the diagnostic.
  DiagnosticLocation location;

  // The diagnostic's format string. This, along with format_args, will be
  // passed to format_fn.
  llvm::StringLiteral format;

  // A list of format arguments.
  //
  // These may be used by non-standard consumers to inspect diagnostic details
  // without needing to parse the formatted string; however, it should be
  // understood that diagnostic formats are subject to change and the llvm::Any
  // offers limited compile-time type safety. Integration tests are required.
  llvm::SmallVector<llvm::Any, 0> format_args;

  // Returns the formatted string. By default, this uses llvm::formatv.
  std::function<std::string(const DiagnosticMessage&)> format_fn;
};

// An instance of a single error or warning.  Information about the diagnostic
// can be recorded into it for more complex consumers.
struct Diagnostic {
  // The diagnostic's level.
  DiagnosticLevel level;

  // The main error or warning.
  DiagnosticMessage message;

  // Notes that add context or supplemental information to the diagnostic.
  llvm::SmallVector<DiagnosticMessage> notes;
};

// Receives diagnostics as they are emitted.
class DiagnosticConsumer {
 public:
  virtual ~DiagnosticConsumer() = default;

  // Handle a diagnostic.
  //
  // This relies on moves of the Diagnostic. At present, diagnostics are
  // allocated on the stack, so their lifetime is that of HandleDiagnostic.
  // However, SortingDiagnosticConsumer needs a longer lifetime, until all
  // diagnostics have been produced. As a consequence, it needs to either copy
  // or move the Diagnostic, and right now we're moving due to the overhead of
  // notes.
  //
  // At present, there is no persistent storage of diagnostics because IDEs
  // would be fine with diagnostics being printed immediately and discarded,
  // without SortingDiagnosticConsumer. If this becomes a performance issue, we
  // may want to investigate alternative ownership models that address both IDE
  // and CLI user needs.
  virtual auto HandleDiagnostic(Diagnostic diagnostic) -> void = 0;

  // Flushes any buffered input.
  virtual auto Flush() -> void {}
};

// An interface that can translate some representation of a location into a
// diagnostic location.
//
// TODO: Revisit this once the diagnostics machinery is more complete and see
// if we can turn it into a `std::function`.
template <typename LocationT>
class DiagnosticLocationTranslator {
 public:
  virtual ~DiagnosticLocationTranslator() = default;

  [[nodiscard]] virtual auto GetLocation(LocationT loc)
      -> DiagnosticLocation = 0;
};

namespace Internal {

// Use the DIAGNOSTIC macro to instantiate this.
// This stores static information about a diagnostic category.
template <typename... Args>
struct DiagnosticBase {
  explicit constexpr DiagnosticBase(DiagnosticKind kind, DiagnosticLevel level,
                                    llvm::StringLiteral format)
      : Kind(kind), Level(level), Format(format) {}

  // Calls formatv with the diagnostic's arguments.
  auto FormatFn(const DiagnosticMessage& message) const -> std::string {
    return FormatFnImpl(message, std::make_index_sequence<sizeof...(Args)>());
  };

  // The diagnostic's kind.
  DiagnosticKind Kind;
  // The diagnostic's level.
  DiagnosticLevel Level;
  // The diagnostic's format for llvm::formatv.
  llvm::StringLiteral Format;

 private:
  // Handles the cast of llvm::Any to Args types for formatv.
  // TODO: Custom formatting can be provided with an format_provider, but that
  // affects all formatv calls. Consider replacing formatv with a custom call
  // that allows diagnostic-specific formatting.
  template <std::size_t... N>
  inline auto FormatFnImpl(const DiagnosticMessage& message,
                           std::index_sequence<N...> /*indices*/) const
      -> std::string {
    assert(message.format_args.size() == sizeof...(Args));
    return llvm::formatv(message.format.data(),
                         llvm::any_cast<Args>(message.format_args[N])...);
  }
};

// Disable type deduction based on `args`; the type of `diagnostic_base`
// determines the diagnostic's parameter types.
template <typename Arg>
using NoTypeDeduction = std::common_type_t<Arg>;

}  // namespace Internal

// Manages the creation of reports, the testing if diagnostics are enabled, and
// the collection of reports.
//
// This class is parameterized by a location type, allowing different
// diagnostic clients to provide location information in whatever form is most
// convenient for them, such as a position within a buffer when lexing, a token
// when parsing, or a parse tree node when type-checking, and to allow unit
// tests to be decoupled from any concrete location representation.
template <typename LocationT>
class DiagnosticEmitter {
 public:
  // A builder-pattern type to provide a fluent interface for constructing
  // a more complex diagnostic. See `DiagnosticEmitter::Build` for the
  // expected usage.
  class DiagnosticBuilder {
   public:
    // Adds a note diagnostic attached to the main diagnostic being built.
    // The API mirrors the main emission API: `DiagnosticEmitter::Emit`.
    // For the expected usage see the builder API: `DiagnosticEmitter::Build`.
    template <typename... Args>
    auto Note(LocationT location,
              const Internal::DiagnosticBase<Args...>& diagnostic_base,
              Internal::NoTypeDeduction<Args>... args) -> DiagnosticBuilder& {
      CARBON_CHECK(diagnostic_base.Level == DiagnosticLevel::Note)
          << static_cast<int>(diagnostic_base.Level);
      diagnostic_.notes.push_back(
          MakeMessage(location, diagnostic_base, std::move(args)...));
      return *this;
    }

    // Emits the built diagnostic and its attached notes.
    // For the expected usage see the builder API: `DiagnosticEmitter::Build`.
    template <typename... Args>
    auto Emit() -> void {
      emitter_->consumer_->HandleDiagnostic(std::move(diagnostic_));
    }

   private:
    friend class DiagnosticEmitter<LocationT>;

    template <typename... Args>
    explicit DiagnosticBuilder(
        DiagnosticEmitter<LocationT>* emitter, LocationT location,
        const Internal::DiagnosticBase<Args...>& diagnostic_base,
        Internal::NoTypeDeduction<Args>... args)
        : emitter_(emitter),
          diagnostic_({.level = diagnostic_base.Level,
                       .message = MakeMessage(location, diagnostic_base,
                                              std::move(args)...)}) {
      CARBON_CHECK(diagnostic_base.Level != DiagnosticLevel::Note);
    }

    template <typename... Args>
    auto MakeMessage(LocationT location,
                     const Internal::DiagnosticBase<Args...>& diagnostic_base,
                     Internal::NoTypeDeduction<Args>... args)
        -> DiagnosticMessage {
      return DiagnosticMessage(
          diagnostic_base.Kind, emitter_->translator_->GetLocation(location),
          diagnostic_base.Format, {std::move(args)...},
          [&diagnostic_base](const DiagnosticMessage& message) -> std::string {
            return diagnostic_base.FormatFn(message);
          });
    }

    DiagnosticEmitter<LocationT>* emitter_;
    Diagnostic diagnostic_;
  };

  // The `translator` and `consumer` are required to outlive the diagnostic
  // emitter.
  explicit DiagnosticEmitter(
      DiagnosticLocationTranslator<LocationT>& translator,
      DiagnosticConsumer& consumer)
      : translator_(&translator), consumer_(&consumer) {}
  ~DiagnosticEmitter() = default;

  // Emits an error.
  //
  // When passing arguments, they may be buffered. As a consequence, lifetimes
  // may outlive the `Emit` call.
  template <typename... Args>
  auto Emit(LocationT location,
            const Internal::DiagnosticBase<Args...>& diagnostic_base,
            Internal::NoTypeDeduction<Args>... args) -> void {
    DiagnosticBuilder(this, location, diagnostic_base, std::move(args)...)
        .Emit();
  }

  // A fluent interface for building a diagnostic and attaching notes for added
  // context or information. For example:
  //
  //   emitter_.Build(location1, MyDiagnostic)
  //     .Note(location2, MyDiagnosticNote)
  //     .Emit();
  template <typename... Args>
  auto Build(LocationT location,
             const Internal::DiagnosticBase<Args...>& diagnostic_base,
             Internal::NoTypeDeduction<Args>... args) -> DiagnosticBuilder {
    return DiagnosticBuilder(this, location, diagnostic_base,
                             std::move(args)...);
  }

 private:
  DiagnosticLocationTranslator<LocationT>* translator_;
  DiagnosticConsumer* consumer_;
};

inline auto ConsoleDiagnosticConsumer() -> DiagnosticConsumer& {
  class Consumer : public DiagnosticConsumer {
    auto HandleDiagnostic(Diagnostic diagnostic) -> void override {
      Print(diagnostic.message);
      for (const auto& note : diagnostic.notes) {
        Print(note);
      }
    }
    auto Print(const DiagnosticMessage& message) -> void {
      llvm::errs() << message.location.file_name << ":"
                   << message.location.line_number << ":"
                   << message.location.column_number << ": "
                   << message.format_fn(message) << "\n";
    }
  };
  static auto* consumer = new Consumer;
  return *consumer;
}

// Diagnostic consumer adaptor that tracks whether any errors have been
// produced.
class ErrorTrackingDiagnosticConsumer : public DiagnosticConsumer {
 public:
  explicit ErrorTrackingDiagnosticConsumer(DiagnosticConsumer& next_consumer)
      : next_consumer_(&next_consumer) {}

  auto HandleDiagnostic(Diagnostic diagnostic) -> void override {
    seen_error_ |= diagnostic.level == DiagnosticLevel::Error;
    next_consumer_->HandleDiagnostic(std::move(diagnostic));
  }

  // Reset whether we've seen an error.
  auto Reset() -> void { seen_error_ = false; }

  // Returns whether we've seen an error since the last reset.
  auto seen_error() const -> bool { return seen_error_; }

 private:
  DiagnosticConsumer* next_consumer_;
  bool seen_error_ = false;
};

}  // namespace Carbon

#endif  // CARBON_TOOLCHAIN_DIAGNOSTICS_DIAGNOSTIC_EMITTER_H_