// 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/parse/context.h"

namespace Carbon::Parse {

// Handles VarAs(Decl|For).
static auto HandleVar(Context& context, State finish_state,
                      Lex::TokenIndex returned_token = Lex::TokenIndex::Invalid)
    -> void {
  auto state = context.PopState();

  // The finished variable declaration will start at the `var` or `returned`.
  context.PushState(state, finish_state);

  context.PushState(state, State::VarAfterPattern);

  if (returned_token.is_valid()) {
    context.AddLeafNode(NodeKind::ReturnedModifier, returned_token);
  }

  context.PushState(State::Pattern);
}

auto HandleVarAsDecl(Context& context) -> void {
  HandleVar(context, State::VarFinishAsDecl);
}

auto HandleVarAsReturned(Context& context) -> void {
  auto returned_token = context.Consume();

  if (!context.PositionIs(Lex::TokenKind::Var)) {
    CARBON_DIAGNOSTIC(ExpectedVarAfterReturned, Error,
                      "Expected `var` after `returned`.");
    context.emitter().Emit(*context.position(), ExpectedVarAfterReturned);
    context.AddLeafNode(NodeKind::EmptyDecl,
                        context.SkipPastLikelyEnd(returned_token),
                        /*has_error=*/true);
    context.PopAndDiscardState();
    return;
  }

  context.AddLeafNode(NodeKind::VariableIntroducer, context.Consume());
  HandleVar(context, State::VarFinishAsDecl, returned_token);
}

auto HandleVarAsFor(Context& context) -> void {
  HandleVar(context, State::VarFinishAsFor);
}

auto HandleVarAfterPattern(Context& context) -> void {
  auto state = context.PopState();

  if (state.has_error) {
    if (auto after_pattern =
            context.FindNextOf({Lex::TokenKind::Equal, Lex::TokenKind::Semi})) {
      context.SkipTo(*after_pattern);
    }
  }

  if (auto equals = context.ConsumeIf(Lex::TokenKind::Equal)) {
    context.AddLeafNode(NodeKind::VariableInitializer, *equals);
    context.PushState(State::Expr);
  }
}

auto HandleVarFinishAsDecl(Context& context) -> void {
  auto state = context.PopState();

  auto end_token = state.token;
  if (context.PositionIs(Lex::TokenKind::Semi)) {
    end_token = context.Consume();
  } else {
    // TODO: Disambiguate between statement and member declaration.
    context.EmitExpectedDeclSemi(Lex::TokenKind::Var);
    state.has_error = true;
    end_token = context.SkipPastLikelyEnd(state.token);
  }
  context.AddNode(NodeKind::VariableDecl, end_token, state.subtree_start,
                  state.has_error);
}

auto HandleVarFinishAsFor(Context& context) -> void {
  auto state = context.PopState();

  auto end_token = state.token;
  if (context.PositionIs(Lex::TokenKind::In)) {
    end_token = context.Consume();
  } else if (context.PositionIs(Lex::TokenKind::Colon)) {
    CARBON_DIAGNOSTIC(ExpectedInNotColon, Error,
                      "`:` should be replaced by `in`.");
    context.emitter().Emit(*context.position(), ExpectedInNotColon);
    state.has_error = true;
    end_token = context.Consume();
  } else {
    CARBON_DIAGNOSTIC(ExpectedIn, Error,
                      "Expected `in` after loop `var` declaration.");
    context.emitter().Emit(*context.position(), ExpectedIn);
    state.has_error = true;
  }

  context.AddNode(NodeKind::ForIn, end_token, state.subtree_start,
                  state.has_error);
}

}  // namespace Carbon::Parse