/*
 * Copyright (C) 2024 Samuel Weinig <sam@webkit.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#pragma once

#include "CSSCalcType.h"
#include "CSSUnits.h"
#include "CSSPrimitiveNumericTypes.h"
#include "CSSValueKeywords.h"
#include "CalculationTree.h"
#include <variant>
#include <wtf/StdLibExtras.h>
#include <wtf/TZoneMallocInlines.h>
#include <wtf/Vector.h>
#include <wtf/text/AtomString.h>

namespace WebCore {

enum class CSSUnitType : uint8_t;

namespace CSSCalc {

// Math Operators.
struct Sum;
struct Product;
struct Negate;
struct Invert;

// Math Functions.
struct Min;
struct Max;
struct Clamp;
struct RoundNearest;
struct RoundUp;
struct RoundDown;
struct RoundToZero;
struct Mod;
struct Rem;
struct Sin;
struct Cos;
struct Tan;
struct Asin;
struct Acos;
struct Atan;
struct Atan2;
struct Pow;
struct Sqrt;
struct Hypot;
struct Log;
struct Exp;
struct Abs;
struct Sign;
struct Progress;

// CSS Anchor Positioning functions.
struct Anchor;
struct AnchorSize;

template<typename Op>
concept Leaf = requires(Op) {
    Op::isLeaf == true;
};

template<typename Op>
concept Numeric = requires(Op) {
    Op::isNumeric == true;
};

// Leaf Values
struct Number {
    static constexpr bool isLeaf = true;
    static constexpr bool isNumeric = true;

    double value;

    bool operator==(const Number&) const = default;
};

struct Percentage {
    static constexpr bool isLeaf = true;
    static constexpr bool isNumeric = true;

    double value;
    Type::PercentHintValue hint;

    bool operator==(const Percentage&) const = default;
};

struct CanonicalDimension {
    static constexpr bool isLeaf = true;
    static constexpr bool isNumeric = true;

    enum class Dimension: uint8_t {
        Length,
        Angle,
        Time,
        Frequency,
        Resolution,
        Flex
    };

    double value;
    Dimension dimension;

    bool operator==(const CanonicalDimension&) const = default;
};

struct NonCanonicalDimension {
    static constexpr bool isLeaf = true;
    static constexpr bool isNumeric = true;

    double value;
    CSSUnitType unit;

    bool operator==(const NonCanonicalDimension&) const = default;
};

struct Symbol {
    static constexpr bool isLeaf = true;

    CSSValueID id;
    CSSUnitType unit;

    bool operator==(const Symbol&) const = default;
};

template<typename Op> struct IndirectNode {
    Type type;
    UniqueRef<Op> op;

    // Forward * and -> to the operation for convenience.
    const Op& operator*() const { return *op; }
    Op& operator*() { return *op; }
    const Op* operator->() const { return op.ptr(); }
    Op* operator->() { return op.ptr(); }
    operator const Op&() const { return *op; }
    operator Op&() { return *op; }

    bool operator==(const IndirectNode<Op>& other) const { return type == other.type && op.get() == other.op.get(); }
};

using Node = std::variant<
    Number,
    Percentage,
    CanonicalDimension,
    NonCanonicalDimension,
    Symbol,
    IndirectNode<Sum>,
    IndirectNode<Product>,
    IndirectNode<Negate>,
    IndirectNode<Invert>,
    IndirectNode<Min>,
    IndirectNode<Max>,
    IndirectNode<Clamp>,
    IndirectNode<RoundNearest>,
    IndirectNode<RoundUp>,
    IndirectNode<RoundDown>,
    IndirectNode<RoundToZero>,
    IndirectNode<Mod>,
    IndirectNode<Rem>,
    IndirectNode<Sin>,
    IndirectNode<Cos>,
    IndirectNode<Tan>,
    IndirectNode<Asin>,
    IndirectNode<Acos>,
    IndirectNode<Atan>,
    IndirectNode<Atan2>,
    IndirectNode<Pow>,
    IndirectNode<Sqrt>,
    IndirectNode<Hypot>,
    IndirectNode<Log>,
    IndirectNode<Exp>,
    IndirectNode<Abs>,
    IndirectNode<Sign>,
    IndirectNode<Progress>,
    IndirectNode<Anchor>,
    IndirectNode<AnchorSize>
>;

using Child = Node;
using ChildOrNone = std::variant<Child, CSS::NoneRaw>;
using Children = Vector<Child>;

enum class Stage : bool { Specified, Computed };

struct Tree {
    Child root;
    Type type;
    Calculation::Category category;
    Stage stage;
    ValueRange range;

    // `requiresConversionData` is used both to both indicate whether eager evaluation of the tree (at parse time) is possible or not and to trigger a warning in `CSSCalcValue::doubleValueDeprecated` that the evaluation results will be incorrect.
    bool requiresConversionData = false;

    bool operator==(const Tree&) const = default;
};

struct Sum {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Sum);
public:
    using Base = Calculation::Sum;

    Children children;

    bool operator==(const Sum&) const = default;
};

struct Product {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Product);
public:
    using Base = Calculation::Product;

    Children children;

    bool operator==(const Product&) const = default;
};

struct Negate {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Negate);
public:
    using Base = Calculation::Negate;

    Child a;

    bool operator==(const Negate&) const = default;
};

struct Invert {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Invert);
public:
    using Base = Calculation::Invert;

    Child a;

    bool operator==(const Invert&) const = default;
};

// Math Functions

// Comparison Functions - https://drafts.csswg.org/css-values-4/#comp-func
struct Min {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Min);
public:
    using Base = Calculation::Min;
    static constexpr auto id = CSSValueMin;

    // <min()>   = min( <calc-sum># )
    //     - INPUT: "consistent" <number>, <dimension>, or <percentage>
    //     - OUTPUT: consistent type
    static constexpr auto input = AllowedTypes::Any;
    static constexpr auto merge = MergePolicy::Consistent;
    static constexpr auto output = OutputTransform::None;

    Children children;

    bool operator==(const Min&) const = default;
};

struct Max {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Max);
public:
    using Base = Calculation::Max;
    static constexpr auto id = CSSValueMax;

    // <max()>   = max( <calc-sum># )
    //     - INPUT: "consistent" <number>, <dimension>, or <percentage>
    //     - OUTPUT: consistent type
    static constexpr auto input = AllowedTypes::Any;
    static constexpr auto merge = MergePolicy::Consistent;
    static constexpr auto output = OutputTransform::None;

    Children children;

    bool operator==(const Max&) const = default;
};

struct Clamp {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Clamp);
public:
    using Base = Calculation::Clamp;
    static constexpr auto id = CSSValueClamp;

    // <clamp()> = clamp( [ <calc-sum> | none ], <calc-sum>, [ <calc-sum> | none ] )
    //     - INPUT: "consistent" <number>, <dimension>, or <percentage>
    //     - OUTPUT: consistent type
    static constexpr auto input = AllowedTypes::Any;
    static constexpr auto merge = MergePolicy::Consistent;
    static constexpr auto output = OutputTransform::None;

    ChildOrNone min;
    Child val;
    ChildOrNone max;

    bool operator==(const Clamp&) const = default;
};

// Stepped Value Functions - https://drafts.csswg.org/css-values-4/#round-func
struct RoundNearest {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(RoundNearest);
public:
    using Base = Calculation::RoundNearest;
    static constexpr auto id = CSSValueNearest;

    // <round()> = round( <rounding-strategy>?, <calc-sum>, <calc-sum> )
    //     - INPUT: "consistent" <number>, <dimension>, or <percentage>
    //     - OUTPUT: consistent type
    static constexpr auto input = AllowedTypes::Any;
    static constexpr auto merge = MergePolicy::Consistent;
    static constexpr auto output = OutputTransform::None;

    //    -- and --

    // <round()> = round( <rounding-strategy>?, <calc-sum> )
    //     - INPUT: "consistent" <number>
    //     - OUTPUT: consistent type

    // NOTE: This is special cased in the code.

    Child a;
    std::optional<Child> b;

    bool operator==(const RoundNearest&) const = default;
};

struct RoundUp {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(RoundUp);
public:
    using Base = Calculation::RoundUp;
    static constexpr auto id = CSSValueUp;

    // <round()> = round( <rounding-strategy>?, <calc-sum>, <calc-sum> )
    //     - INPUT: "consistent" <number>, <dimension>, or <percentage>
    //     - OUTPUT: consistent type
    static constexpr auto input = AllowedTypes::Any;
    static constexpr auto merge = MergePolicy::Consistent;
    static constexpr auto output = OutputTransform::None;

    //    -- and --

    // <round()> = round( <rounding-strategy>?, <calc-sum> )
    //     - INPUT: "consistent" <number>
    //     - OUTPUT: consistent type

    // NOTE: This is special cased in the code.

    Child a;
    std::optional<Child> b;

    bool operator==(const RoundUp&) const = default;
};

struct RoundDown {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(RoundDown);
public:
    using Base = Calculation::RoundDown;
    static constexpr auto id = CSSValueDown;

    // <round()> = round( <rounding-strategy>?, <calc-sum>, <calc-sum> )
    //     - INPUT: "consistent" <number>, <dimension>, or <percentage>
    //     - OUTPUT: consistent type
    static constexpr auto input = AllowedTypes::Any;
    static constexpr auto merge = MergePolicy::Consistent;
    static constexpr auto output = OutputTransform::None;

    //    -- and --

    // <round()> = round( <rounding-strategy>?, <calc-sum> )
    //     - INPUT: "consistent" <number>
    //     - OUTPUT: consistent type

    // NOTE: This is special cased in the code.

    Child a;
    std::optional<Child> b;

    bool operator==(const RoundDown&) const = default;
};

struct RoundToZero {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(RoundToZero);
public:
    using Base = Calculation::RoundToZero;
    static constexpr auto id = CSSValueToZero;

    // <round()> = round( <rounding-strategy>?, <calc-sum>, <calc-sum> )
    //     - INPUT: "consistent" <number>, <dimension>, or <percentage>
    //     - OUTPUT: consistent type
    static constexpr auto input = AllowedTypes::Any;
    static constexpr auto merge = MergePolicy::Consistent;
    static constexpr auto output = OutputTransform::None;

    //    -- and --

    // <round()> = round( <rounding-strategy>?, <calc-sum> )
    //     - INPUT: "consistent" <number>
    //     - OUTPUT: consistent type

    // NOTE: This is special cased in the code.

    Child a;
    std::optional<Child> b;

    bool operator==(const RoundToZero&) const = default;
};

struct Mod {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Mod);
public:
    using Base = Calculation::Mod;
    static constexpr auto id = CSSValueMod;

    // <mod()>   = mod( <calc-sum>, <calc-sum> )
    //     - INPUT: "same" <number>, <dimension>, or <percentage>
    //     - OUTPUT: same type
    static constexpr auto input = AllowedTypes::Any;
    // FIXME: Spec says this should enforce same type, but tests indicate it should be consistent type.
    static constexpr auto merge = MergePolicy::Consistent;
    static constexpr auto output = OutputTransform::None;

    Child a;
    Child b;

    bool operator==(const Mod&) const = default;
};

struct Rem {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Rem);
public:
    using Base = Calculation::Rem;
    static constexpr auto id = CSSValueRem;

    // <rem()>   = rem( <calc-sum>, <calc-sum> )
    //     - INPUT: "same" <number>, <dimension>, or <percentage>
    //     - OUTPUT: same type
    static constexpr auto input = AllowedTypes::Any;
    // FIXME: Spec says this should enforce same type, but tests indicate it should be consistent type.
    static constexpr auto merge = MergePolicy::Consistent;
    static constexpr auto output = OutputTransform::None;

    Child a;
    Child b;

    bool operator==(const Rem&) const = default;
};

// Trigonometric Functions - https://drafts.csswg.org/css-values-4/#trig-funcs
struct Sin {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Sin);
public:
    using Base = Calculation::Sin;
    static constexpr auto id = CSSValueSin;

    // <sin()>   = sin( <calc-sum> )
    //     - INPUT: <number> or <angle>
    //     - OUTPUT: <number> "made consistent"
    static constexpr auto input = AllowedTypes::NumberOrAngle;
    static constexpr auto output = OutputTransform::NumberMadeConsistent;

    Child a;

    bool operator==(const Sin&) const = default;
};

struct Cos {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Cos);
public:
    using Base = Calculation::Cos;
    static constexpr auto id = CSSValueCos;

    // <cos()>   = cos( <calc-sum> )
    //     - INPUT: <number> or <angle>
    //     - OUTPUT: <number> "made consistent"
    static constexpr auto input = AllowedTypes::NumberOrAngle;
    static constexpr auto output = OutputTransform::NumberMadeConsistent;

    Child a;

    bool operator==(const Cos&) const = default;
};

struct Tan {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Tan);
public:
    using Base = Calculation::Tan;
    static constexpr auto id = CSSValueTan;

    // <tan()>   = tan( <calc-sum> )
    //     - INPUT: <number> or <angle>
    //     - OUTPUT: <number> "made consistent"
    static constexpr auto input = AllowedTypes::NumberOrAngle;
    static constexpr auto output = OutputTransform::NumberMadeConsistent;

    Child a;

    bool operator==(const Tan&) const = default;
};

struct Asin {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Asin);
public:
    using Base = Calculation::Asin;
    static constexpr auto id = CSSValueAsin;

    // <asin()>  = asin( <calc-sum> )
    //     - INPUT: <number>
    //     - OUTPUT: <angle> "made consistent"
    static constexpr auto input = AllowedTypes::Number;
    static constexpr auto output = OutputTransform::AngleMadeConsistent;

    Child a;

    bool operator==(const Asin&) const = default;
};

struct Acos {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Acos);
public:
    using Base = Calculation::Acos;
    static constexpr auto id = CSSValueAcos;

    // <acos()>  = acos( <calc-sum> )
    //     - INPUT: <number>
    //     - OUTPUT: <angle> "made consistent"
    static constexpr auto input = AllowedTypes::Number;
    static constexpr auto output = OutputTransform::AngleMadeConsistent;

    Child a;

    bool operator==(const Acos&) const = default;
};

struct Atan {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Atan);
public:
    using Base = Calculation::Atan;
    static constexpr auto id = CSSValueAtan;

    // <atan()>  = atan( <calc-sum> )
    //     - INPUT: <number>
    //     - OUTPUT: <angle> "made consistent"
    static constexpr auto input = AllowedTypes::Number;
    static constexpr auto output = OutputTransform::AngleMadeConsistent;

    Child a;

    bool operator==(const Atan&) const = default;
};

struct Atan2 {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Atan2);
public:
    using Base = Calculation::Atan2;
    static constexpr auto id = CSSValueAtan2;

    // <atan2()> = atan2( <calc-sum>, <calc-sum> )
    //     - INPUT: "consistent" <number>, <dimension>, or <percentage>
    //     - OUTPUT: <angle> "made consistent"
    static constexpr auto input = AllowedTypes::Any;
    static constexpr auto merge = MergePolicy::Consistent;
    static constexpr auto output = OutputTransform::AngleMadeConsistent;

    Child a;
    Child b;

    bool operator==(const Atan2&) const = default;
};

// Exponential Functions - https://drafts.csswg.org/css-values-4/#exponent-funcs
struct Pow {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Pow);
public:
    using Base = Calculation::Pow;
    static constexpr auto id = CSSValuePow;

    // <pow()>   = pow( <calc-sum>, <calc-sum> )
    //     - INPUT: "consistent" <number>
    //     - OUTPUT: consistent type
    static constexpr auto input = AllowedTypes::Number;
    static constexpr auto merge = MergePolicy::Consistent;
    static constexpr auto output = OutputTransform::None;

    Child a;
    Child b;

    bool operator==(const Pow&) const = default;
};

struct Sqrt {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Sqrt);
public:
    using Base = Calculation::Sqrt;
    static constexpr auto id = CSSValueSqrt;

    // <sqrt()>  = sqrt( <calc-sum> )
    //     - INPUT: <number>
    //     - OUTPUT: <number> "made consistent"
    static constexpr auto input = AllowedTypes::Number;
    static constexpr auto output = OutputTransform::NumberMadeConsistent;

    Child a;

    bool operator==(const Sqrt&) const = default;
};

struct Hypot {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Hypot);
public:
    using Base = Calculation::Hypot;
    static constexpr auto id = CSSValueHypot;

    // <hypot()> = hypot( <calc-sum># )
    //     - INPUT: "consistent" <number>, <dimension>, or <percentage>
    //     - OUTPUT: consistent type
    static constexpr auto input = AllowedTypes::Any;
    static constexpr auto merge = MergePolicy::Consistent;
    static constexpr auto output = OutputTransform::None;

    Children children;

    bool operator==(const Hypot&) const = default;
};

struct Log {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Log);
public:
    using Base = Calculation::Log;
    static constexpr auto id = CSSValueLog;

    // <log()>   = log( <calc-sum>, <calc-sum>? )
    //     - INPUT: <number>
    //     - OUTPUT: <number> "made consistent"
    static constexpr auto input = AllowedTypes::Number;
    static constexpr auto merge = MergePolicy::Consistent;
    static constexpr auto output = OutputTransform::NumberMadeConsistent;

    Child a;
    std::optional<Child> b;

    bool operator==(const Log&) const = default;
};

struct Exp {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Exp);
public:
    using Base = Calculation::Exp;
    static constexpr auto id = CSSValueExp;

    // <exp()>   = exp( <calc-sum> )
    //     - INPUT: <number>
    //     - OUTPUT: <number> "made consistent"
    static constexpr auto input = AllowedTypes::Number;
    static constexpr auto output = OutputTransform::NumberMadeConsistent;

    Child a;

    bool operator==(const Exp&) const = default;
};

// Sign-Related Functions - https://drafts.csswg.org/css-values-4/#sign-funcs
struct Abs {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Abs);
public:
    using Base = Calculation::Abs;
    static constexpr auto id = CSSValueAbs;

    // <abs()>   = abs( <calc-sum> )
    //     - INPUT: any
    //     - OUTPUT: input type
    static constexpr auto input = AllowedTypes::Any;
    static constexpr auto output = OutputTransform::None;

    Child a;

    bool operator==(const Abs&) const = default;
};

struct Sign {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Sign);
public:
    using Base = Calculation::Sign;
    static constexpr auto id = CSSValueSign;

    // <sign()>  = sign( <calc-sum> )
    //     - INPUT: any
    //     - OUTPUT: <number> "made consistent"
    static constexpr auto input = AllowedTypes::Any;
    static constexpr auto output = OutputTransform::NumberMadeConsistent;

    Child a;

    bool operator==(const Sign&) const = default;
};

// Progress-Related Functions - https://drafts.csswg.org/css-values-5/#progress
struct Progress {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Progress);
public:
    using Base = Calculation::Progress;
    static constexpr auto id = CSSValueProgress;

    // <progress()> = progress( <calc-sum> from <calc-sum> to <calc-sum> )
    //     - INPUT: "consistent" <number>, <dimension>, or <percentage>
    //     - OUTPUT: <number> "made consistent"
    static constexpr auto input = AllowedTypes::Any;
    static constexpr auto merge = MergePolicy::Consistent;
    static constexpr auto output = OutputTransform::NumberMadeConsistent;

    Child progress;
    Child from;
    Child to;

    bool operator==(const Progress&) const = default;
};

struct Anchor {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(Anchor);
public:
    static constexpr auto id = CSSValueAnchor;

    // <anchor()> = anchor( <anchor-element>? && <anchor-side>, <length-percentage>? )
    // <anchor-side> = inside | outside | top | left | right | bottom | start | end | self-start | self-end | <percentage> | center
    using Side = std::variant<CSSValueID, Child>;

    AtomString elementName;
    Side side;
    std::optional<Child> fallback;

    bool operator==(const Anchor&) const = default;
};

struct AnchorSize {
    WTF_MAKE_TZONE_ALLOCATED_INLINE(AnchorSize);
public:
    static constexpr auto id = CSSValueAnchorSize;

    // anchor-size() = anchor-size( [ <anchor-element> || <anchor-size> ]? , <length-percentage>? )
    // <anchor-element> = <dashed-ident>
    // <anchor-size> = width | height | block | inline | self-block | self-inline

    AtomString elementName;
    std::optional<CSSValueID> size;
    std::optional<Child> fallback;

    bool operator==(const AnchorSize&) const = default;
};

// MARK: Size assertions

static_assert(sizeof(Child) == 24);

// MARK: Reverse mappings

template<typename CalculationOp> struct ReverseMapping;
template<> struct ReverseMapping<Calculation::Sum> { using Op = Sum; };
template<> struct ReverseMapping<Calculation::Product> { using Op = Product; };
template<> struct ReverseMapping<Calculation::Negate> { using Op = Negate; };
template<> struct ReverseMapping<Calculation::Invert> { using Op = Invert; };
template<> struct ReverseMapping<Calculation::Min> { using Op = Min; };
template<> struct ReverseMapping<Calculation::Max> { using Op = Max; };
template<> struct ReverseMapping<Calculation::Clamp> { using Op = Clamp; };
template<> struct ReverseMapping<Calculation::RoundNearest> { using Op = RoundNearest; };
template<> struct ReverseMapping<Calculation::RoundUp> { using Op = RoundUp; };
template<> struct ReverseMapping<Calculation::RoundDown> { using Op = RoundDown; };
template<> struct ReverseMapping<Calculation::RoundToZero> { using Op = RoundToZero; };
template<> struct ReverseMapping<Calculation::Mod> { using Op = Mod; };
template<> struct ReverseMapping<Calculation::Rem> { using Op = Rem; };
template<> struct ReverseMapping<Calculation::Sin> { using Op = Sin; };
template<> struct ReverseMapping<Calculation::Cos> { using Op = Cos; };
template<> struct ReverseMapping<Calculation::Tan> { using Op = Tan; };
template<> struct ReverseMapping<Calculation::Asin> { using Op = Asin; };
template<> struct ReverseMapping<Calculation::Acos> { using Op = Acos; };
template<> struct ReverseMapping<Calculation::Atan> { using Op = Atan; };
template<> struct ReverseMapping<Calculation::Atan2> { using Op = Atan2; };
template<> struct ReverseMapping<Calculation::Pow> { using Op = Pow; };
template<> struct ReverseMapping<Calculation::Sqrt> { using Op = Sqrt; };
template<> struct ReverseMapping<Calculation::Hypot> { using Op = Hypot; };
template<> struct ReverseMapping<Calculation::Log> { using Op = Log; };
template<> struct ReverseMapping<Calculation::Exp> { using Op = Exp; };
template<> struct ReverseMapping<Calculation::Abs> { using Op = Abs; };
template<> struct ReverseMapping<Calculation::Sign> { using Op = Sign; };
template<> struct ReverseMapping<Calculation::Progress> { using Op = Progress; };

// MARK: TextStream

TextStream& operator<<(TextStream&, Tree);

// MARK: Construction

// Default implementation of ChildConstruction used for all indirect nodes.
template<typename Op> struct ChildConstruction {
    static Child make(Op&& op, Type type) { return Child { IndirectNode<Op> { type, makeUniqueRef<Op>(WTFMove(op)) } }; }
};

// Specialized implementation of ChildConstruction for Number, needed to avoid `makeUniqueRef`.
template<> struct ChildConstruction<Number> {
    static Child make(Number&& op, Type) { return Child { WTFMove(op) }; }
    static Child make(Number&& op) { return Child { WTFMove(op) }; }
};

// Specialized implementation of ChildConstruction for Percentage, needed to avoid `makeUniqueRef`.
template<> struct ChildConstruction<Percentage> {
    static Child make(Percentage&& op, Type) { return Child { WTFMove(op) }; }
    static Child make(Percentage&& op) { return Child { WTFMove(op) }; }
};

// Specialized implementation of ChildConstruction for CanonicalDimension, needed to avoid `makeUniqueRef`.
template<> struct ChildConstruction<CanonicalDimension> {
    static Child make(CanonicalDimension&& op, Type) { return Child { WTFMove(op) }; }
    static Child make(CanonicalDimension&& op) { return Child { WTFMove(op) }; }
};

// Specialized implementation of ChildConstruction for NonCanonicalDimension, needed to avoid `makeUniqueRef`.
template<> struct ChildConstruction<NonCanonicalDimension> {
    static Child make(NonCanonicalDimension&& op, Type) { return Child { WTFMove(op) }; }
    static Child make(NonCanonicalDimension&& op) { return Child { WTFMove(op) }; }
};

// Specialized implementation of ChildConstruction for Symbol, needed to avoid `makeUniqueRef`.
template<> struct ChildConstruction<Symbol> {
    static Child make(Symbol&& op, Type) { return Child { WTFMove(op) }; }
    static Child make(Symbol&& op) { return Child { WTFMove(op) }; }
};

template<typename Op> Child makeChild(Op op)
{
    return ChildConstruction<Op>::make(WTFMove(op));
}

template<typename Op> Child makeChild(Op op, Type type)
{
    return ChildConstruction<Op>::make(WTFMove(op), type);
}

// MARK: CSSCalc::Type Evaluation

// Gets the type stored in the IndirectNode.
template<typename T> inline Type getType(const IndirectNode<T>& root)
{
    return root.type;
}

// Gets the Type representing a CanonicalDimension::Dimension.
Type getType(CanonicalDimension::Dimension);

// Gets the Type of the leaf node.
Type getType(const Number&);
Type getType(const Percentage&);
Type getType(const NonCanonicalDimension&);
Type getType(const CanonicalDimension&);
Type getType(const Symbol&);

// Gets the Type of the child node.
Type getType(const Child&);

// Constructs the nodes's type from it the types of its arguments. Returns `std::nullopt` on failure.
std::optional<Type> toType(const Sum&);
std::optional<Type> toType(const Product&);
std::optional<Type> toType(const Negate&);
std::optional<Type> toType(const Invert&);
std::optional<Type> toType(const Min&);
std::optional<Type> toType(const Max&);
std::optional<Type> toType(const Clamp&);
std::optional<Type> toType(const RoundNearest&);
std::optional<Type> toType(const RoundUp&);
std::optional<Type> toType(const RoundDown&);
std::optional<Type> toType(const RoundToZero&);
std::optional<Type> toType(const Mod&);
std::optional<Type> toType(const Rem&);
std::optional<Type> toType(const Sin&);
std::optional<Type> toType(const Cos&);
std::optional<Type> toType(const Tan&);
std::optional<Type> toType(const Asin&);
std::optional<Type> toType(const Acos&);
std::optional<Type> toType(const Atan&);
std::optional<Type> toType(const Atan2&);
std::optional<Type> toType(const Pow&);
std::optional<Type> toType(const Sqrt&);
std::optional<Type> toType(const Hypot&);
std::optional<Type> toType(const Log&);
std::optional<Type> toType(const Exp&);
std::optional<Type> toType(const Abs&);
std::optional<Type> toType(const Sign&);
std::optional<Type> toType(const Progress&);

// MARK: CSSUnitType Evaluation

// Maps CanonicalDimension::Dimension to its CSSUnitType counterpart.
constexpr CSSUnitType toCSSUnit(const CanonicalDimension::Dimension& dimension)
{
    switch (dimension) {
    case CanonicalDimension::Dimension::Length:         return CSSUnitType::CSS_PX;
    case CanonicalDimension::Dimension::Angle:          return CSSUnitType::CSS_DEG;
    case CanonicalDimension::Dimension::Time:           return CSSUnitType::CSS_S;
    case CanonicalDimension::Dimension::Frequency:      return CSSUnitType::CSS_HZ;
    case CanonicalDimension::Dimension::Resolution:     return CSSUnitType::CSS_DPPX;
    case CanonicalDimension::Dimension::Flex:           return CSSUnitType::CSS_FR;
    }

    ASSERT_NOT_REACHED_UNDER_CONSTEXPR_CONTEXT();
    return CSSUnitType::CSS_PX;
}

// Maps Numeric type to its CSSUnitType counterpart.
constexpr CSSUnitType toCSSUnit(const Number&) { return CSSUnitType::CSS_NUMBER; }
constexpr CSSUnitType toCSSUnit(const Percentage&) { return CSSUnitType::CSS_PERCENTAGE; }
constexpr CSSUnitType toCSSUnit(const CanonicalDimension& dimension) { return toCSSUnit(dimension.dimension); }
constexpr CSSUnitType toCSSUnit(const NonCanonicalDimension& dimension) { return dimension.unit; }

// MARK: Predicates

inline bool isNumeric(const Child& root)
{
    return WTF::switchOn(root,
        []<Numeric T>(const T&) { return true; },
        [](const auto&) { return false; }
    );
}

// Convenience constructors

// Makes the appropriate child type (number, percentage, canonical-dimensions, non-canonical-dimension) based on the CSSUnitType.
Child makeNumeric(double, CSSUnitType);

inline Sum add(Child&& a, Child&& b)
{
    Vector<Child> sumChildren;
    sumChildren.append(WTFMove(a));
    sumChildren.append(WTFMove(b));
    return Sum { .children = WTFMove(sumChildren) };
}

inline Product multiply(Child&& a, Child&& b)
{
    Vector<Child> productChildren;
    productChildren.append(WTFMove(a));
    productChildren.append(WTFMove(b));
    return Product { .children = WTFMove(productChildren) };
}

inline Sum subtract(Child&& a, Child&& b)
{
    return add(WTFMove(a), makeChild(Negate { .a = WTFMove(b) }, getType(b)));
}

inline Child makeChildWithValueBasedOn(double value, const Number&)
{
    return makeChild(Number { .value = value });
}

inline Child makeChildWithValueBasedOn(double value, const Percentage& a)
{
    return makeChild(Percentage { .value = value, .hint = a.hint });
}

inline Child makeChildWithValueBasedOn(double value, const CanonicalDimension& a)
{
    return makeChild(CanonicalDimension { .value = value, .dimension = a.dimension });
}

inline Child makeChildWithValueBasedOn(double value, const NonCanonicalDimension& a)
{
    return makeChild(NonCanonicalDimension { .value = value, .unit = a.unit });
}

// MARK: Tuple Conformance

// get<> overload (along with std::tuple_size and std::tuple_element below) to support destructuring of operation nodes.

template<size_t I> const auto& get(const Sum& root)
{
    static_assert(!I);
    return root.children;
}

template<size_t I> const auto& get(const Product& root)
{
    static_assert(!I);
    return root.children;
}

template<size_t I> const auto& get(const Negate& root)
{
    static_assert(!I);
    return root.a;
}

template<size_t I> const auto& get(const Invert& root)
{
    static_assert(!I);
    return root.a;
}

template<size_t I> const auto& get(const Min& root)
{
    static_assert(!I);
    return root.children;
}

template<size_t I> const auto& get(const Max& root)
{
    static_assert(!I);
    return root.children;
}

template<size_t I> const auto& get(const Clamp& root)
{
    if constexpr (!I)
        return root.min;
    else if constexpr (I == 1)
        return root.val;
    else if constexpr (I == 2)
        return root.max;
}

template<size_t I> const auto& get(const RoundNearest& root)
{
    if constexpr (!I)
        return root.a;
    else if constexpr (I == 1)
        return root.b;
}

template<size_t I> const auto& get(const RoundUp& root)
{
    if constexpr (!I)
        return root.a;
    else if constexpr (I == 1)
        return root.b;
}

template<size_t I> const auto& get(const RoundDown& root)
{
    if constexpr (!I)
        return root.a;
    else if constexpr (I == 1)
        return root.b;
}

template<size_t I> const auto& get(const RoundToZero& root)
{
    if constexpr (!I)
        return root.a;
    else if constexpr (I == 1)
        return root.b;
}

template<size_t I> const auto& get(const Mod& root)
{
    if constexpr (!I)
        return root.a;
    else if constexpr (I == 1)
        return root.b;
}

template<size_t I> const auto& get(const Rem& root)
{
    if constexpr (!I)
        return root.a;
    else if constexpr (I == 1)
        return root.b;
}

template<size_t I> const auto& get(const Sin& root)
{
    static_assert(!I);
    return root.a;
}

template<size_t I> const auto& get(const Cos& root)
{
    static_assert(!I);
    return root.a;
}

template<size_t I> const auto& get(const Tan& root)
{
    static_assert(!I);
    return root.a;
}

template<size_t I> const auto& get(const Asin& root)
{
    static_assert(!I);
    return root.a;
}

template<size_t I> const auto& get(const Acos& root)
{
    static_assert(!I);
    return root.a;
}

template<size_t I> const auto& get(const Atan& root)
{
    static_assert(!I);
    return root.a;
}

template<size_t I> const auto& get(const Atan2& root)
{
    if constexpr (!I)
        return root.a;
    else if constexpr (I == 1)
        return root.b;
}

template<size_t I> const auto& get(const Pow& root)
{
    if constexpr (!I)
        return root.a;
    else if constexpr (I == 1)
        return root.b;
}

template<size_t I> const auto& get(const Sqrt& root)
{
    static_assert(!I);
    return root.a;
}

template<size_t I> const auto& get(const Hypot& root)
{
    static_assert(!I);
    return root.children;
}

template<size_t I> const auto& get(const Log& root)
{
    if constexpr (!I)
        return root.a;
    else if constexpr (I == 1)
        return root.b;
}

template<size_t I> const auto& get(const Exp& root)
{
    static_assert(!I);
    return root.a;
}

template<size_t I> const auto& get(const Abs& root)
{
    static_assert(!I);
    return root.a;
}

template<size_t I> const auto& get(const Sign& root)
{
    static_assert(!I);
    return root.a;
}

template<size_t I> const auto& get(const Progress& root)
{
    if constexpr (!I)
        return root.progress;
    else if constexpr (I == 1)
        return root.from;
    else if constexpr (I == 2)
        return root.to;
}

} // namespace CSSCalc
} // namespace WebCore

namespace std {

#define OP_TUPLE_LIKE_CONFORMANCE(op, numberOfArguments) \
    template<> class tuple_size<WebCore::CSSCalc::op> : public std::integral_constant<size_t, numberOfArguments> { }; \
    template<size_t I> class tuple_element<I, WebCore::CSSCalc::op> { \
    public: \
        using type = decltype(WebCore::CSSCalc::get<I>(std::declval<WebCore::CSSCalc::op>())); \
    } \
\

OP_TUPLE_LIKE_CONFORMANCE(Sum, 1);
OP_TUPLE_LIKE_CONFORMANCE(Product, 1);
OP_TUPLE_LIKE_CONFORMANCE(Negate, 1);
OP_TUPLE_LIKE_CONFORMANCE(Invert, 1);
OP_TUPLE_LIKE_CONFORMANCE(Min, 1);
OP_TUPLE_LIKE_CONFORMANCE(Max, 1);
OP_TUPLE_LIKE_CONFORMANCE(Clamp, 3);
OP_TUPLE_LIKE_CONFORMANCE(RoundNearest, 2);
OP_TUPLE_LIKE_CONFORMANCE(RoundUp, 2);
OP_TUPLE_LIKE_CONFORMANCE(RoundDown, 2);
OP_TUPLE_LIKE_CONFORMANCE(RoundToZero, 2);
OP_TUPLE_LIKE_CONFORMANCE(Mod, 2);
OP_TUPLE_LIKE_CONFORMANCE(Rem, 2);
OP_TUPLE_LIKE_CONFORMANCE(Sin, 1);
OP_TUPLE_LIKE_CONFORMANCE(Cos, 1);
OP_TUPLE_LIKE_CONFORMANCE(Tan, 1);
OP_TUPLE_LIKE_CONFORMANCE(Asin, 1);
OP_TUPLE_LIKE_CONFORMANCE(Acos, 1);
OP_TUPLE_LIKE_CONFORMANCE(Atan, 1);
OP_TUPLE_LIKE_CONFORMANCE(Atan2, 2);
OP_TUPLE_LIKE_CONFORMANCE(Pow, 2);
OP_TUPLE_LIKE_CONFORMANCE(Sqrt, 1);
OP_TUPLE_LIKE_CONFORMANCE(Hypot, 1);
OP_TUPLE_LIKE_CONFORMANCE(Log, 2);
OP_TUPLE_LIKE_CONFORMANCE(Exp, 1);
OP_TUPLE_LIKE_CONFORMANCE(Abs, 1);
OP_TUPLE_LIKE_CONFORMANCE(Sign, 1);
OP_TUPLE_LIKE_CONFORMANCE(Progress, 3);
// FIXME (webkit.org/b/280798): make Anchor and AnchorSize tuple-like
OP_TUPLE_LIKE_CONFORMANCE(Anchor, 0);
OP_TUPLE_LIKE_CONFORMANCE(AnchorSize, 0);

#undef OP_TUPLE_LIKE_CONFORMANCE

} // namespace std
