/* 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 <algorithm>
#include <numeric>
#include <unordered_map>

namespace elna::boot
{
    validation_error::validation_error(const source_position position, payload_type payload)
        : error(position), payload(std::move(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, non_constant_initializer>)
            {
                return "Variable initializers must be constant expressions";
            }
            else if constexpr (std::is_same_v<T, duplicate_case>)
            {
                return "Duplicate case label";
            }
            else if constexpr (std::is_same_v<T, non_constant_case_label>)
            {
                return "Case label must be a constant expression";
            }
        }, 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, non_constant_initializer>)
            {
                std::string identifier_list = std::accumulate(
                        std::next(payload.identifiers.begin()), payload.identifiers.end(),
                        payload.identifiers.front().name(),
                        [](const std::string& accumulator, const identifier& next) -> std::string {
                            return accumulator + ", " + next.name();
                        });
                auto position_span = source_position(payload.identifiers.front().position().start(),
                        payload.identifiers.back().position().end());
                return std::make_pair(std::move(identifier_list), position_span);
            }
            else if constexpr (std::is_same_v<T, duplicate_case>)
            {
                return std::make_pair("Previous label here", payload.first);
            }
            else if constexpr (std::is_same_v<T, non_constant_case_label>)
            {
                return std::nullopt;
            }
        }, this->payload);
    }

    validation_error validation_error::non_constant_initializer_error(const source_position position,
            const std::vector<identifier_definition>& identifiers)
    {
        non_constant_initializer payload;
        payload.identifiers.reserve(identifiers.size());

        std::ranges::transform(identifiers, std::back_inserter(payload.identifiers),
                [](const auto& identifier) { return identifier.id(); });

        return validation_error(position, std::move(payload));
    }

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

    void validation_visitor::visit(variable_declaration* declaration)
    {
        if (declaration->initializer == nullptr || has_errors())
        {
            return;
        }
        auto computed = this->constant_evaluator.evaluate(*declaration->initializer);
        if (!computed)
        {
            auto non_constant_initializer_error = validation_error::non_constant_initializer_error(
                    declaration->initializer->position(), declaration->identifiers);
            add_error<validation_error>(non_constant_initializer_error);
            return;
        }
        for (const auto& identifier : declaration->identifiers)
        {
            auto variable_symbol = this->bag.lookup(identifier.name())->is_variable();
            variable_symbol->value = computed;
        }
    }

    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<validation_error>(label->position(),
                            validation_error::non_constant_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 });
                }
            }
        }
    }
}