/* Final validation after constant folding.
   Copyright (C) 2025 Free Software Foundation, Inc.

GCC is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.

GCC is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */

#include "elna/boot/validation.h"

#include <unordered_map>

namespace elna::boot
{
    validation_error::validation_error(const source_position position, payload_type payload)
        : error(position), payload(payload)
    {
    }

    std::string validation_error::what() const
    {
        return std::visit([](const auto& payload) -> std::string {
            using T = std::decay_t<decltype(payload)>;

            if constexpr (std::is_same_v<T, duplicate_case>)
            {
                return "Duplicate case label";
            }
        }, this->payload);
    }

    std::optional<std::pair<std::string, source_position>> validation_error::note() const
    {
        return std::visit([](const auto& payload) -> std::optional<std::pair<std::string, source_position>> {
            using T = std::decay_t<decltype(payload)>;

            if constexpr (std::is_same_v<T, duplicate_case>)
            {
                return std::make_pair("Previous label here", payload.first);
            }
        }, this->payload);
    }

    validation_visitor::validation_visitor(symbol_bag& bag, const target_info& target)
        : bag(bag), constant_evaluator(this->bag, target)
    {
    }

    void validation_visitor::visit(unit *unit)
    {
        for (procedure_declaration *procedure : unit->procedures)
        {
            procedure->accept(this);
        }
        for (auto *entry_statement : unit->entry_point)
        {
            entry_statement->accept(this);
        }
    }

    void validation_visitor::visit(procedure_declaration *declaration)
    {
        if (declaration->body.has_value())
        {
            auto procedure = this->bag.lookup(declaration->identifier.name())->is_procedure();
            this->bag.enter(procedure->scope);
        }
        walking_visitor::visit(declaration);
        if (declaration->body.has_value())
        {
            this->bag.leave();
        }
    }

    void validation_visitor::visit(case_statement *statement)
    {
        walking_visitor::visit(statement);
        std::unordered_map<constant_value, source_position, constant_value_hash> seen;
        for (const auto& case_block : statement->cases)
        {
            for (auto *label : case_block.labels)
            {
                auto value = this->constant_evaluator.evaluate(*label);
                if (!value.has_value())
                {
                    add_error<non_constant_expression_error>(label->position(),
                            non_constant_expression_error::case_label{});
                    continue;
                }
                auto [case_position, inserted] = seen.try_emplace(value.value(), label->position());
                if (!inserted)
                {
                    add_error<validation_error>(label->position(),
                            validation_error::duplicate_case{ case_position->second });
                }
            }
        }
    }
}