// 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

#include "toolchain/base/shared_value_stores.h"
#include "toolchain/language_server/handle.h"
#include "toolchain/lex/lex.h"
#include "toolchain/parse/node_kind.h"
#include "toolchain/parse/parse.h"
#include "toolchain/parse/tree_and_subtrees.h"
#include "toolchain/source/source_buffer.h"

namespace Carbon::LanguageServer {

// Returns the token of first child of kind IdentifierNameBeforeParams or
// IdentifierNameNotBeforeParams.
static auto GetSymbolIdentifier(const Parse::TreeAndSubtrees& tree_and_subtrees,
                                Parse::NodeId node)
    -> std::optional<Lex::TokenIndex> {
  const auto& tokens = tree_and_subtrees.tree().tokens();
  for (auto child : tree_and_subtrees.children(node)) {
    switch (tree_and_subtrees.tree().node_kind(child)) {
      case Parse::NodeKind::IdentifierNameBeforeParams:
      case Parse::NodeKind::IdentifierNameNotBeforeParams: {
        auto token = tree_and_subtrees.tree().node_token(child);
        if (tokens.GetKind(token) == Lex::TokenKind::Identifier) {
          return token;
        }
        break;
      }
      default:
        break;
    }
  }
  return std::nullopt;
}

// Constructs a Range from a closed interval of tokens [start, end].
static auto GetTokenRange(const Lex::TokenizedBuffer& tokens,
                          Lex::TokenIndex start, Lex::TokenIndex end)
    -> clang::clangd::Range {
  auto start_line = tokens.GetLine(start);
  auto start_col = tokens.GetColumnNumber(start);
  auto [end_line, end_col] = tokens.GetEndLoc(end);

  return clang::clangd::Range{
      .start = {.line = start_line.index, .character = start_col - 1},
      .end = {.line = end_line.index, .character = end_col - 1},
  };
}

// Finds a spanning range for the provided definition / declaration ast node.
// In the case of a definition start, will include the body as well.
static auto GetSymbolRange(const Parse::TreeAndSubtrees& tree_and_subtrees,
                           const Parse::NodeId& ast_node)
    -> clang::clangd::Range {
  const auto& tokens = tree_and_subtrees.tree().tokens();

  // The left-most node will always be the first node in postorder traversal.
  auto start_node = *tree_and_subtrees.postorder(ast_node).begin();

  auto start_token = tree_and_subtrees.tree().node_token(start_node);
  auto end_token = tree_and_subtrees.tree().node_token(ast_node);
  if (tokens.GetKind(end_token).is_opening_symbol()) {
    // DefinitionStart nodes use an opening token, so find its closing token to
    // span the entire class/function body.
    return GetTokenRange(tokens, start_token,
                         tokens.GetMatchedClosingToken(end_token));
  } else {
    return GetTokenRange(tokens, start_token, end_token);
  }
}

auto HandleDocumentSymbol(
    Context& context, const clang::clangd::DocumentSymbolParams& params,
    llvm::function_ref<
        auto(llvm::Expected<std::vector<clang::clangd::DocumentSymbol>>)->void>
        on_done) -> void {
  auto* file = context.LookupFile(params.textDocument.uri.file());
  if (!file) {
    return;
  }

  const auto& tree_and_subtrees = file->tree_and_subtrees();
  const auto& tree = tree_and_subtrees.tree();
  const auto& tokens = tree.tokens();

  std::vector<clang::clangd::DocumentSymbol> result;
  for (const auto& node_id : tree.postorder()) {
    clang::clangd::SymbolKind symbol_kind;
    switch (tree.node_kind(node_id)) {
      case Parse::NodeKind::FunctionDecl:
      case Parse::NodeKind::FunctionDefinitionStart:
        symbol_kind = clang::clangd::SymbolKind::Function;
        break;
      case Parse::NodeKind::Namespace:
        symbol_kind = clang::clangd::SymbolKind::Namespace;
        break;
      case Parse::NodeKind::InterfaceDefinitionStart:
      case Parse::NodeKind::NamedConstraintDefinitionStart:
        symbol_kind = clang::clangd::SymbolKind::Interface;
        break;
      case Parse::NodeKind::ClassDefinitionStart:
        symbol_kind = clang::clangd::SymbolKind::Class;
        break;
      default:
        continue;
    }

    if (auto identifier = GetSymbolIdentifier(tree_and_subtrees, node_id)) {
      clang::clangd::DocumentSymbol symbol{
          .name = std::string(tokens.GetTokenText(*identifier)),
          .kind = symbol_kind,
          .range = GetSymbolRange(tree_and_subtrees, node_id),
          .selectionRange = GetTokenRange(tokens, *identifier, *identifier),
      };

      result.push_back(symbol);
    }
  }
  on_done(result);
}

}  // namespace Carbon::LanguageServer