#include "typechecker.h"
#include "ast.h"
#include "errors.h"
#include "result.h"

namespace {
    enum class TypecheckResKind {
        Ok,
        Castable,
    };

    struct TypecheckRes {
        TypecheckResKind kind;
        std::shared_ptr<types::Type> result;
    };

    Result<TypecheckRes, std::string> check_type(
        typecheck::State& state,
        std::shared_ptr<types::Type> checked,
        std::shared_ptr<types::Type> target) {
        auto potential_cast = types::find_cast(state.casts, checked, target);


        if (types::types_equal(checked, target)) {
            return TypecheckRes{ TypecheckResKind::Ok, target };
        }
        else if (potential_cast.has_value()) {
            if (potential_cast->allow_implicit)
                return TypecheckRes{ TypecheckResKind::Castable, target };

            return std::string{ "Type " + checked->formatted() + " not implicitly castable to " + target->formatted() };
        }

        return std::string{ "Types " + checked->formatted() + " and " + target->formatted() + " incompatible" };
    }

    std::unique_ptr<AST::Expression> handle_res(
        std::unique_ptr<AST::Expression> expr,
        Result<TypecheckRes, std::string> res,
        typecheck::State& state) {
        if (res.ok()) {
            auto result = res.unwrap();
            if (result.kind == TypecheckResKind::Ok) {
                return expr;
            }
            else {
                return std::unique_ptr<AST::Expression> {
                    new AST::CastExpression{ expr->m_meta, result.result, std::move(expr) }
                };
            }
        }
        else {
            state.errors.push_back(CompileError(res.unwrap_err(), expr->m_meta));
            return expr;
        }
    }
}

namespace AST {
    std::shared_ptr<types::Type> IntLiteralExpression::typecheck(
        typecheck::State&,
        typecheck::Scope&,
        std::optional<std::shared_ptr<types::Type>> expected_ty
    ) {
        // Allow implicitly converting IntLiteralExpression to other types
        // representable by integers.
        if (expected_ty) {
            if ((*expected_ty)->m_kind == types::TypeKind::Fundamental) {
                auto ty = dynamic_cast<types::FundamentalType*>((*expected_ty).get());
                if (
                    ty->m_ty == types::FundamentalTypeKind::Bool
                    || ty->m_ty == types::FundamentalTypeKind::Char
                    || ty->m_ty == types::FundamentalTypeKind::Int
                    ) {
                    this->m_ty = *expected_ty;
                }
            }
        }

        return this->m_ty;
    }

    std::shared_ptr<types::Type> StringLiteralExpression::typecheck(
        typecheck::State&,
        typecheck::Scope&,
        std::optional<std::shared_ptr<types::Type>>
    ) {
        auto char_ty = std::shared_ptr<types::Type>{
            new types::FundamentalType{ types::FundamentalTypeKind::Char }
        };
        auto ptr_ty = new types::ArrayType{ char_ty, static_cast<uint32_t>(this->m_value.size()) + 1 };
        return std::shared_ptr<types::Type>{ptr_ty};
    }

    std::shared_ptr<types::Type> ValueReferenceExpression::typecheck(
        typecheck::State& state,
        typecheck::Scope& scope,
        std::optional<std::shared_ptr<types::Type>>
    ) {
        if (scope.symbols.find(this->m_name) != scope.symbols.end()) {
            return scope.symbols[this->m_name];
        }

        state.errors.push_back(CompileError("Value " + this->m_name + " not defined", this->m_meta));
        return std::shared_ptr<types::Type>{
            new types::FundamentalType{ types::FundamentalTypeKind::Void }
        };
    }

    std::shared_ptr<types::Type> BinaryOperationExpression::typecheck(
        typecheck::State& state,
        typecheck::Scope& scope,
        std::optional<std::shared_ptr<types::Type>> expected_ty
    ) {
        auto lhs_ty = this->m_lhs->typecheck(state, scope, {});
        auto rhs_ty = this->m_rhs->typecheck(state, scope, {});

        if (this->m_binop == types::BinOp::Assignment) {
            // Re-typecheck rhs to actually match lhs
            auto rhs_ty = this->m_rhs->typecheck(state, scope, lhs_ty);
            auto rhs_ty_res = check_type(state, rhs_ty, lhs_ty);
            this->m_rhs = handle_res(std::move(this->m_rhs), rhs_ty_res, state);
            return lhs_ty;
        }

        // Try to find a binop that matches exactly
        auto binop = types::find_binop(
            state.binops,
            lhs_ty,
            this->m_binop,
            rhs_ty
        );

        if (binop) {
            return binop->result(*binop, lhs_ty, rhs_ty);
        }

        // If that fails, try to find binop that matches on one side perfectly
        // and is castable on the other side, and would also be perfectly
        // assignable to the expected value.
        for (auto& binop : state.binops) {
            if (expected_ty) {
                // Skip any binops that would not be immediately assignable to
                // the expected type
                if (!types::types_equal(binop.result(binop, lhs_ty, rhs_ty), *expected_ty)) {
                    continue;
                }
            }
            if (types::types_equal(binop.lhs, lhs_ty)) {
                auto rhs_res = check_type(state, rhs_ty, binop.rhs);
                if (!rhs_res.ok())
                    // Skip if not implicitly castable to lhs
                    continue;
                this->m_rhs = handle_res(std::move(this->m_rhs), rhs_res, state);
                return binop.result(binop, lhs_ty, rhs_ty);
            }
            else if (types::types_equal(binop.rhs, rhs_ty)) {
                auto lhs_res = check_type(state, lhs_ty, binop.lhs);
                if (!lhs_res.ok())
                    // Skip if not implicitly castable to rhs
                    continue;
                this->m_lhs = handle_res(std::move(this->m_lhs), lhs_res, state);
                return binop.result(binop, lhs_ty, rhs_ty);
            }
        }

        // Finally check for any binop that allows the result to be implicitly
        // casted to the result
        for (auto& binop : state.binops) {
            if (expected_ty) {
                // Skip any binops that would not even be implicitly castable to
                // the expected result
                auto result_res = check_type(state, binop.result(binop, lhs_ty, rhs_ty), *expected_ty);
                if (!result_res.ok())
                    continue;
            }
            auto lhs_result = check_type(state, lhs_ty, binop.lhs);
            auto rhs_result = check_type(state, rhs_ty, binop.rhs);
            this->m_lhs = handle_res(std::move(this->m_lhs), lhs_result, state);
            this->m_rhs = handle_res(std::move(this->m_rhs), lhs_result, state);
            return binop.result(binop, lhs_ty, rhs_ty);
        }

        // No suitable binops found :(
        state.errors.push_back(CompileError(
            "No suitable binop between "
            + lhs_ty->formatted() + " "
            + types::format_operator(this->m_binop) + " "
            + rhs_ty->formatted(),
            this->m_meta));

        return std::shared_ptr<types::Type>{
            new types::FundamentalType{ types::FundamentalTypeKind::Void } };
    }

    std::shared_ptr<types::Type> FunctionCallExpression::typecheck(
        typecheck::State& state,
        typecheck::Scope& scope,
        std::optional<std::shared_ptr<types::Type>>
    ) {
        auto expr_ty = this->m_fn_expr->typecheck(state, scope, {});

        if (expr_ty->m_kind != types::TypeKind::Function) {
            state.errors.push_back(CompileError("Tried calling a non-function", this->m_meta));
            return std::shared_ptr<types::Type> {
                new types::FundamentalType{ types::FundamentalTypeKind::Void }
            };
        }

        auto fn_ty = dynamic_cast<types::FunctionType*>(expr_ty.get());

        if (this->m_args.size() < fn_ty->m_param_tys.size()) {
            state.errors.push_back(CompileError("too few arguments", this->m_meta));
        }
        else if (this->m_args.size() > fn_ty->m_param_tys.size() && !fn_ty->m_vararg) {
            state.errors.push_back(CompileError("too many arguments", this->m_meta));
        }
        else {
            for (int i = 0; i < static_cast<int>(this->m_args.size()); i++) {
                if (i < static_cast<int>(fn_ty->m_param_tys.size())) {
                    auto expected_param_ty = fn_ty->m_param_tys[i];
                    auto param_ty = this->m_args[i]->typecheck(state, scope, expected_param_ty);

                    auto check_res = check_type(state, param_ty, expected_param_ty);
                    this->m_args[i] = handle_res(std::move(this->m_args[i]), check_res, state);
                }
                else {
                    this->m_args[i]->typecheck(state, scope, {});
                }
            }
        }

        return fn_ty->m_ret_ty;
    }


    std::shared_ptr<types::Type> CastExpression::typecheck(
        typecheck::State& state,
        typecheck::Scope& scope,
        std::optional<std::shared_ptr<types::Type>>
    ) {
        auto expr_ty = this->m_expr->typecheck(state, scope, {});
        auto cast = types::find_cast(state.casts, expr_ty, this->m_ty);
        if (cast) {
            return cast->target_ty;
        }
        state.errors.push_back(CompileError("Cast from type "
            + expr_ty->formatted() + "to type " + this->m_ty->formatted()
            + " is not permitted", this->m_meta));
        return std::shared_ptr<types::Type> { new types::FundamentalType{
            types::FundamentalTypeKind::Void
        } };
    }

    std::shared_ptr<types::Type> RefExpression::typecheck(
        typecheck::State& state,
        typecheck::Scope& scope,
        std::optional<std::shared_ptr<types::Type>>
    ) {
        auto expr_ty = this->m_expr->typecheck(state, scope, {});
        return std::shared_ptr<types::Type> {
            new types::PointerType{ expr_ty }
        };
    }

    std::shared_ptr<types::Type> DerefExpression::typecheck(
        typecheck::State& state,
        typecheck::Scope& scope,
        std::optional<std::shared_ptr<types::Type>>
    ) {
        auto expr_ty = this->m_expr->typecheck(state, scope, {});
        if (expr_ty->m_kind != types::TypeKind::Pointer) {
            state.errors.push_back(
                CompileError("Tried to deref " + expr_ty->formatted(), this->m_meta));
            return std::shared_ptr<types::Type> {
                new types::FundamentalType{ types::FundamentalTypeKind::Void }
            };
        }
        auto ptr_ty = dynamic_cast<types::PointerType*>(expr_ty.get());
        return ptr_ty->m_inner;
    }

    std::shared_ptr<types::Type> IndexAccessExpression::typecheck(
        typecheck::State& state,
        typecheck::Scope& scope,
        std::optional<std::shared_ptr<types::Type>>
    ) {
        auto expr_ty = this->m_expr->typecheck(state, scope, {});
        if (expr_ty->m_kind != types::TypeKind::Pointer && expr_ty->m_kind != types::TypeKind::Array) {
            state.errors.push_back(
                CompileError("Tried to index " + expr_ty->formatted(), this->m_meta));
            return std::shared_ptr<types::Type> {
                new types::FundamentalType{ types::FundamentalTypeKind::Void }
            };
        }
        if (expr_ty->m_kind == types::TypeKind::Pointer) {
            auto ptr_ty = dynamic_cast<types::PointerType*>(expr_ty.get());
            return ptr_ty->m_inner;
        }
        else if (expr_ty->m_kind == types::TypeKind::Array) {
            auto ptr_ty = dynamic_cast<types::ArrayType*>(expr_ty.get());
            return ptr_ty->m_inner;
        }

        // Default return type
        return std::shared_ptr<types::Type> {
            new types::FundamentalType{ types::FundamentalTypeKind::Void }
        };
    }


    void ReturnStatement::typecheck(typecheck::State& state, typecheck::Scope& scope) {
        auto res_ty = this->m_expr->typecheck(state, scope, scope.return_ty);
        if (scope.return_ty) {
            auto check_res = check_type(state, res_ty, *scope.return_ty);
            this->m_expr = handle_res(std::move(this->m_expr), check_res, state);
        }
    }

    void InitializationStatement::typecheck(typecheck::State& state, typecheck::Scope& scope) {
        if (this->m_expr) {
            auto expr_ty = (*this->m_expr)->typecheck(state, scope, this->m_type);
            auto check_res = check_type(state, expr_ty, this->m_type);
            this->m_expr = handle_res(std::move(*this->m_expr), check_res, state);
        }
        scope.symbols[this->m_name] = this->m_type;
    }

    void ExpressionStatement::typecheck(typecheck::State& state, typecheck::Scope& scope) {
        this->m_expr->typecheck(state, scope, {});
    }

    void IfStatement::typecheck(typecheck::State& state, typecheck::Scope& scope) {
        auto bool_ty = std::shared_ptr<types::Type>{
            new types::FundamentalType{ types::FundamentalTypeKind::Bool } };
        auto expr_ty = this->m_condition->typecheck(state, scope, bool_ty);

        auto check_res = check_type(state, expr_ty, bool_ty);
        this->m_condition = handle_res(std::move(this->m_condition), check_res, state);

        this->m_then->typecheck(state, scope);
        if (this->m_else) {
            (*this->m_else)->typecheck(state, scope);
        }
    }

    void Function::typecheck(typecheck::State& state, typecheck::Scope& scope) {
        auto return_ty = this->m_return_ty;
        std::vector<std::shared_ptr<types::Type>> param_tys{};
        for (auto& param : this->m_params) {
            param_tys.push_back(param.second);
        }

        auto function_ty = new types::FunctionType{ return_ty, param_tys, this->m_is_vararg };
        scope.symbols[this->m_name] = std::shared_ptr<types::Type>{ function_ty };

        typecheck::Scope inner{ scope };
        inner.return_ty = return_ty;

        for (auto& param : this->m_params) {
            if (param.first) {
                inner.symbols[*param.first] = param.second;
            }
        }

        if (this->m_statements) {
            for (auto& statement : *this->m_statements) {
                statement->typecheck(state, inner);
            }
        }
    }
}