Crafter.DB/interfaces/Crafter.DB-Query.cppm

// SPDX-License-Identifier: LGPL-3.0-only
// SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®

// Queries are C++. A lambda over Row<T> is the general form; column tags
// give a readable expression form (iban == x && amount > 100) whose types
// the engine can look into: comparisons on the orderedBy column found in a
// top-level && chain become binary-search bounds instead of a scan, and
// string comparisons pre-encode their Key once instead of once per row.
export module Crafter.DB:Query;
import std;
import :Reflect;
import :Formatter;
import :Schema;
import :Storage;
import :Codec;
import :Row;

export namespace Crafter::DB {
    enum class CompareOp : std::uint8_t { Equal, NotEqual, Less, LessEqual, Greater, GreaterEqual };

    template<auto Ptr, CompareOp Op, class Operand>
    struct Compare {
        using Table = MemberClass<Ptr>;
        static constexpr auto pointer = Ptr;
        static constexpr CompareOp op = Op;
        Operand operand;

        bool operator()(Row<Table> row) const {
            const auto value = row.template Get<Ptr>();
            if constexpr (Op == CompareOp::Equal) return value == operand;
            else if constexpr (Op == CompareOp::NotEqual) return !(value == operand);
            else if constexpr (Op == CompareOp::Less) return value < operand;
            else if constexpr (Op == CompareOp::LessEqual) return value <= operand;
            else if constexpr (Op == CompareOp::Greater) return value > operand;
            else return value >= operand;
        }
    };

    template<class A, class B>
    struct And {
        A a;
        B b;
        template<class R> bool operator()(R row) const { return a(row) && b(row); }
    };

    template<class A, class B>
    struct Or {
        A a;
        B b;
        template<class R> bool operator()(R row) const { return a(row) || b(row); }
    };

    template<class A>
    struct Not {
        A a;
        template<class R> bool operator()(R row) const { return !a(row); }
    };

    template<class P> struct IsExpression : std::false_type {};
    template<auto Ptr, CompareOp Op, class V> struct IsExpression<Compare<Ptr, Op, V>> : std::true_type {};
    template<class A, class B> struct IsExpression<And<A, B>> : std::true_type {};
    template<class A, class B> struct IsExpression<Or<A, B>> : std::true_type {};
    template<class A> struct IsExpression<Not<A>> : std::true_type {};

    template<class P>
    concept Expression = IsExpression<std::remove_cvref_t<P>>::value;

    template<class M>
    concept StringColumn = std::is_same_v<M, std::string>;

    template<auto Ptr, CompareOp Op, class V>
    auto MakeCompare(V&& value) {
        using M = MemberTypeOf<Ptr>;
        if constexpr (StringColumn<M>) {
            if constexpr (Op == CompareOp::Equal || Op == CompareOp::NotEqual) return Compare<Ptr, Op, Key>{ Key(std::string_view(value)) };
            else return Compare<Ptr, Op, std::string>{ std::string(std::string_view(value)) };
        } else {
            return Compare<Ptr, Op, M>{ static_cast<M>(std::forward<V>(value)) };
        }
    }

    template<auto Ptr, class V> auto operator==(Column<Ptr>, V&& value) { return MakeCompare<Ptr, CompareOp::Equal>(std::forward<V>(value)); }
    template<auto Ptr, class V> auto operator!=(Column<Ptr>, V&& value) { return MakeCompare<Ptr, CompareOp::NotEqual>(std::forward<V>(value)); }
    template<auto Ptr, class V> auto operator<(Column<Ptr>, V&& value) { return MakeCompare<Ptr, CompareOp::Less>(std::forward<V>(value)); }
    template<auto Ptr, class V> auto operator<=(Column<Ptr>, V&& value) { return MakeCompare<Ptr, CompareOp::LessEqual>(std::forward<V>(value)); }
    template<auto Ptr, class V> auto operator>(Column<Ptr>, V&& value) { return MakeCompare<Ptr, CompareOp::Greater>(std::forward<V>(value)); }
    template<auto Ptr, class V> auto operator>=(Column<Ptr>, V&& value) { return MakeCompare<Ptr, CompareOp::GreaterEqual>(std::forward<V>(value)); }

    template<Expression A, Expression B> auto operator&&(A a, B b) { return And<A, B>{ std::move(a), std::move(b) }; }
    template<Expression A, Expression B> auto operator||(A a, B b) { return Or<A, B>{ std::move(a), std::move(b) }; }
    template<Expression A> auto operator!(A a) { return Not<A>{ std::move(a) }; }

    // Bounds on the ordered column harvested from a predicate's top-level
    // conjunction. Anything under || or ! contributes nothing (the whole
    // predicate still runs as the filter, so this is only ever a narrowing).
    template<class K>
    struct Bounds {
        std::optional<K> lower;
        bool lowerExclusive = false;
        std::optional<K> upper;
        bool upperExclusive = false;

        void Lower(const K& key, bool exclusive) {
            if (!lower || *lower < key || (*lower == key && exclusive)) {
                lower = key;
                lowerExclusive = exclusive;
            }
        }

        void Upper(const K& key, bool exclusive) {
            if (!upper || key < *upper || (*upper == key && exclusive)) {
                upper = key;
                upperExclusive = exclusive;
            }
        }
    };

    template<class P> struct IsAndType : std::false_type {};
    template<class A, class B> struct IsAndType<And<A, B>> : std::true_type {};
    template<class P> struct IsCompareType : std::false_type {};
    template<auto Ptr, CompareOp Op, class V> struct IsCompareType<Compare<Ptr, Op, V>> : std::true_type {};

    template<class T, class P> requires HasOrderedBy<T>
    void CollectBounds(const P& predicate, Bounds<OrderedKey<T>>& bounds) {
        if constexpr (IsAndType<P>::value) {
            CollectBounds<T>(predicate.a, bounds);
            CollectBounds<T>(predicate.b, bounds);
        } else if constexpr (IsCompareType<P>::value) {
            if constexpr (SameMemberPointer<P::pointer, T::orderedBy>()) {
                const OrderedKey<T> key = static_cast<OrderedKey<T>>(predicate.operand);
                switch (P::op) {
                    case CompareOp::Equal: bounds.Lower(key, false); bounds.Upper(key, false); break;
                    case CompareOp::Less: bounds.Upper(key, true); break;
                    case CompareOp::LessEqual: bounds.Upper(key, false); break;
                    case CompareOp::Greater: bounds.Lower(key, true); break;
                    case CompareOp::GreaterEqual: bounds.Lower(key, false); break;
                    case CompareOp::NotEqual: break;
                }
            }
        }
    }


    // A lazy range of Row<T> with the conveniences a result needs. Chainable:
    // table.Range<...>(a, b).Where(pred).Select<&T::amount>().
    template<TableType T, std::ranges::view R> requires std::is_same_v<std::ranges::range_value_t<R>, Row<T>>
    class Query : public std::ranges::view_interface<Query<T, R>> {
    public:
        Query() = default;
        explicit Query(R range) : range(std::move(range)) {}

        // A Query is iterable as a const object whenever its underlying view
        // is (LiveRange is; std::ranges::filter_view, by the standard's
        // design, is not).
        template<class Self> requires std::ranges::range<std::conditional_t<std::is_const_v<std::remove_reference_t<Self>>, const R, R>>
        auto begin(this Self&& self) { return std::ranges::begin(self.range); }

        template<class Self> requires std::ranges::range<std::conditional_t<std::is_const_v<std::remove_reference_t<Self>>, const R, R>>
        auto end(this Self&& self) { return std::ranges::end(self.range); }

        template<class Self> requires std::ranges::range<std::conditional_t<std::is_const_v<std::remove_reference_t<Self>>, const R, R>>
        std::vector<T> Materialize(this Self&& self) {
            std::vector<T> out;
            for (Row<T> row : self.range) out.push_back(row.Materialize());
            return out;
        }

        template<class Self> requires std::ranges::range<std::conditional_t<std::is_const_v<std::remove_reference_t<Self>>, const R, R>>
        std::uint64_t Count(this Self&& self) {
            std::uint64_t n = 0;
            for ([[maybe_unused]] Row<T> row : self.range) n++;
            return n;
        }

        template<class Self> requires std::ranges::range<std::conditional_t<std::is_const_v<std::remove_reference_t<Self>>, const R, R>>
        std::optional<Row<T>> First(this Self&& self) {
            for (Row<T> row : self.range) return row;
            return std::nullopt;
        }

        template<class Self> requires std::ranges::range<std::conditional_t<std::is_const_v<std::remove_reference_t<Self>>, const R, R>>
        bool Any(this Self&& self) { return self.First().has_value(); }

        template<class Pred>
        auto Where(Pred pred) && {
            return Query<T, std::ranges::filter_view<R, Pred>>(std::ranges::filter_view<R, Pred>(std::move(range), std::move(pred)));
        }

        template<class Pred>
        auto Where(Pred pred) const& {
            return Query<T, std::ranges::filter_view<R, Pred>>(std::ranges::filter_view<R, Pred>(range, std::move(pred)));
        }

        // Lazy view of one column's values (views for strings, values otherwise).
        template<auto Ptr> requires std::is_same_v<MemberClass<Ptr>, T>
        auto Select() && {
            return std::views::transform(std::move(range), [](Row<T> row) { return row.template Get<Ptr>(); });
        }

        const R& Range() const noexcept { return range; }

    private:
        R range;
    };
}