#pragma warning disable CA1859 // Use concrete types when possible for improved performance -- most of prototype methods return JsValue

using System.Text;
using System.Text.RegularExpressions;
using Jint.Native.Number;
using Jint.Native.Object;
using Jint.Native.String;
using Jint.Native.Symbol;
using Jint.Runtime;
using Jint.Runtime.Descriptors;
using Jint.Runtime.Interop;

namespace Jint.Native.RegExp;

internal sealed class RegExpPrototype : Prototype
{
    private static readonly JsString PropertyExec = new("exec");
    private static readonly JsString PropertyIndex = new("index");
    private static readonly JsString PropertyInput = new("input");
    private static readonly JsString PropertySticky = new("sticky");
    private static readonly JsString PropertyGlobal = new("global");
    internal static readonly JsString PropertySource = new("source");
    private static readonly JsString DefaultSource = new("(?:)");
    internal static readonly JsString PropertyFlags = new("flags");
    private static readonly JsString PropertyGroups = new("groups");
    private static readonly JsString PropertyIgnoreCase = new("ignoreCase");
    private static readonly JsString PropertyMultiline = new("multiline");
    private static readonly JsString PropertyDotAll = new("dotAll");
    private static readonly JsString PropertyUnicode = new("unicode");
    private static readonly JsString PropertyUnicodeSets = new("unicodeSets");

    private readonly RegExpConstructor _constructor;
    private readonly JsCallDelegate _defaultExec;

    internal RegExpPrototype(
        Engine engine,
        Realm realm,
        RegExpConstructor constructor,
        ObjectPrototype objectPrototype) : base(engine, realm)
    {
        _defaultExec = Exec;
        _constructor = constructor;
        _prototype = objectPrototype;
    }

    protected override void Initialize()
    {
        const PropertyFlag lengthFlags = PropertyFlag.Configurable;

        GetSetPropertyDescriptor CreateGetAccessorDescriptor(string name, Func<JsRegExp, JsValue> valueExtractor, JsValue? protoValue = null)
        {
            return new GetSetPropertyDescriptor(
                get: new ClrFunction(Engine, name, (thisObj, arguments) =>
                {
                    if (ReferenceEquals(thisObj, this))
                    {
                        return protoValue ?? Undefined;
                    }

                    var r = thisObj as JsRegExp;
                    if (r is null)
                    {
                        Throw.TypeError(_realm);
                    }

                    return valueExtractor(r);
                }, 0, lengthFlags),
                set: Undefined,
                flags: PropertyFlag.Configurable);
        }

        const PropertyFlag propertyFlags = PropertyFlag.Configurable | PropertyFlag.Writable;
        var properties = new PropertyDictionary(14, checkExistingKeys: false)
        {
            ["constructor"] = new PropertyDescriptor(_constructor, propertyFlags),
            ["toString"] = new PropertyDescriptor(new ClrFunction(Engine, "toString", ToRegExpString, 0, lengthFlags), propertyFlags),
            ["exec"] = new PropertyDescriptor(new ClrFunction(Engine, "exec", _defaultExec, 1, lengthFlags), propertyFlags),
            ["test"] = new PropertyDescriptor(new ClrFunction(Engine, "test", Test, 1, lengthFlags), propertyFlags),
            ["dotAll"] = CreateGetAccessorDescriptor("get dotAll", static r => r.DotAll),
            ["flags"] = new GetSetPropertyDescriptor(get: new ClrFunction(Engine, "get flags", Flags, 0, lengthFlags), set: Undefined, flags: PropertyFlag.Configurable),
            ["global"] = CreateGetAccessorDescriptor("get global", static r => r.Global),
            ["hasIndices"] = CreateGetAccessorDescriptor("get hasIndices", static r => r.Indices),
            ["ignoreCase"] = CreateGetAccessorDescriptor("get ignoreCase", static r => r.IgnoreCase),
            ["multiline"] = CreateGetAccessorDescriptor("get multiline", static r => r.Multiline),
            ["source"] = new GetSetPropertyDescriptor(get: new ClrFunction(Engine, "get source", Source, 0, lengthFlags), set: Undefined, flags: PropertyFlag.Configurable),
            ["sticky"] = CreateGetAccessorDescriptor("get sticky", static r => r.Sticky),
            ["unicode"] = CreateGetAccessorDescriptor("get unicode", static r => r.FullUnicode),
            ["unicodeSets"] = CreateGetAccessorDescriptor("get unicodeSets", static r => r.UnicodeSets)
        };
        SetProperties(properties);

        var symbols = new SymbolDictionary(5)
        {
            [GlobalSymbolRegistry.Match] = new PropertyDescriptor(new ClrFunction(Engine, "[Symbol.match]", Match, 1, lengthFlags), propertyFlags),
            [GlobalSymbolRegistry.MatchAll] = new PropertyDescriptor(new ClrFunction(Engine, "[Symbol.matchAll]", MatchAll, 1, lengthFlags), propertyFlags),
            [GlobalSymbolRegistry.Replace] = new PropertyDescriptor(new ClrFunction(Engine, "[Symbol.replace]", Replace, 2, lengthFlags), propertyFlags),
            [GlobalSymbolRegistry.Search] = new PropertyDescriptor(new ClrFunction(Engine, "[Symbol.search]", Search, 1, lengthFlags), propertyFlags),
            [GlobalSymbolRegistry.Split] = new PropertyDescriptor(new ClrFunction(Engine, "[Symbol.split]", Split, 2, lengthFlags), propertyFlags)
        };
        SetSymbols(symbols);
    }

    /// <summary>
    /// https://tc39.es/ecma262/#sec-get-regexp.prototype.source
    /// </summary>
    private JsValue Source(JsValue thisObject, JsCallArguments arguments)
    {
        if (ReferenceEquals(thisObject, this))
        {
            return DefaultSource;
        }

        var r = thisObject as JsRegExp;
        if (r is null)
        {
            Throw.TypeError(_realm);
        }

        if (string.IsNullOrEmpty(r.Source))
        {
            return JsRegExp.regExpForMatchingAllCharacters;
        }


        return r.Source
            .Replace("\\/", "/") // ensure forward-slashes
            .Replace("/", "\\/") // then escape again
            .Replace("\n", "\\n");
    }

    /// <summary>
    /// https://tc39.es/ecma262/#sec-regexp.prototype-@@replace
    /// </summary>
    private JsValue Replace(JsValue thisObject, JsCallArguments arguments)
    {
        var rx = AssertThisIsObjectInstance(thisObject, "RegExp.prototype.replace");
        var s = TypeConverter.ToString(arguments.At(0));
        var lengthS = s.Length;
        var replaceValue = arguments.At(1);
        var functionalReplace = replaceValue is ICallable;

        // we need heavier logic if we have named captures
        var mayHaveNamedCaptures = false;
        if (!functionalReplace)
        {
            var value = TypeConverter.ToString(replaceValue);
            replaceValue = value;
            mayHaveNamedCaptures = value.Contains('$');
        }

        var flags = TypeConverter.ToString(rx.Get(PropertyFlags));
        var global = flags.Contains('g');

        var fullUnicode = false;

        if (global)
        {
            fullUnicode = flags.Contains('u');
            rx.Set(JsRegExp.PropertyLastIndex, 0, true);
        }

        // check if we can access fast path
        if (!fullUnicode
            && !mayHaveNamedCaptures
            && !TypeConverter.ToBoolean(rx.Get(PropertySticky))
            && rx is JsRegExp rei && rei.HasDefaultRegExpExec)
        {
            var count = global ? int.MaxValue : 1;

            string result;
            if (functionalReplace)
            {
                string Evaluator(Match match)
                {
                    var actualGroupCount = GetActualRegexGroupCount(rei, match);
                    var replacerArgs = new List<JsValue>(actualGroupCount + 2);
                    replacerArgs.Add(match.Value);

                    ObjectInstance? groups = null;
                    for (var i = 1; i < actualGroupCount; i++)
                    {
                        var capture = match.Groups[i];
                        replacerArgs.Add(capture.Success ? capture.Value : Undefined);

                        var groupName = GetRegexGroupName(rei, i);
                        if (!string.IsNullOrWhiteSpace(groupName))
                        {
                            groups ??= OrdinaryObjectCreate(_engine, null);
                            groups.CreateDataPropertyOrThrow(groupName, capture.Success ? capture.Value : Undefined);
                        }
                    }

                    replacerArgs.Add(match.Index);
                    replacerArgs.Add(s);
                    if (groups is not null)
                    {
                        replacerArgs.Add(groups);
                    }

                    return CallFunctionalReplace(replaceValue, replacerArgs);
                }

                result = rei.Value.Replace(s, Evaluator, count);
            }
            else
            {
                result = rei.Value.Replace(s, TypeConverter.ToString(replaceValue), count);
            }

            rx.Set(JsRegExp.PropertyLastIndex, JsNumber.PositiveZero);
            return result;
        }

        var results = new List<ObjectInstance>();

        while (true)
        {
            var result = RegExpExec(rx, s);
            if (result.IsNull())
            {
                break;
            }

            results.Add((ObjectInstance) result);
            if (!global)
            {
                break;
            }

            var matchStr = TypeConverter.ToString(result.Get(0));
            if (matchStr == "")
            {
                var thisIndex = TypeConverter.ToLength(rx.Get(JsRegExp.PropertyLastIndex));
                var nextIndex = AdvanceStringIndex(s, thisIndex, fullUnicode);
                rx.Set(JsRegExp.PropertyLastIndex, nextIndex);
            }
        }

        var accumulatedResult = "";
        var nextSourcePosition = 0;

        var captures = new List<string>();
        for (var i = 0; i < results.Count; i++)
        {
            var result = results[i];
            var nCaptures = (int) result.GetLength();
            nCaptures = System.Math.Max(nCaptures - 1, 0);
            var matched = TypeConverter.ToString(result.Get(0));
            var matchLength = matched.Length;
            var position = (int) TypeConverter.ToInteger(result.Get(PropertyIndex));
            position = System.Math.Max(System.Math.Min(position, lengthS), 0);
            uint n = 1;

            captures.Clear();
            while (n <= nCaptures)
            {
                var capN = result.Get(n);
                var value = !capN.IsUndefined() ? TypeConverter.ToString(capN) : "";
                captures.Add(value);
                n++;
            }

            var namedCaptures = result.Get(PropertyGroups);
            string replacement;
            if (functionalReplace)
            {
                var replacerArgs = new List<JsValue>();
                replacerArgs.Add(matched);
                foreach (var capture in captures)
                {
                    replacerArgs.Add(capture);
                }

                replacerArgs.Add(position);
                replacerArgs.Add(s);
                if (!namedCaptures.IsUndefined())
                {
                    replacerArgs.Add(namedCaptures);
                }

                replacement = CallFunctionalReplace(replaceValue, replacerArgs);
            }
            else
            {
                if (!namedCaptures.IsUndefined())
                {
                    namedCaptures = TypeConverter.ToObject(_realm, namedCaptures);
                }

                replacement = GetSubstitution(matched, s, position, captures.ToArray(), namedCaptures, TypeConverter.ToString(replaceValue));
            }

            if (position >= nextSourcePosition)
            {
#pragma warning disable CA1845
                accumulatedResult = accumulatedResult +
                                    s.Substring(nextSourcePosition, position - nextSourcePosition) +
                                    replacement;
#pragma warning restore CA1845

                nextSourcePosition = position + matchLength;
            }
        }

        if (nextSourcePosition >= lengthS)
        {
            return accumulatedResult;
        }

#pragma warning disable CA1845
        return accumulatedResult + s.Substring(nextSourcePosition);
#pragma warning restore CA1845
    }

    private static string CallFunctionalReplace(JsValue replacer, List<JsValue> replacerArgs)
    {
        var result = ((ICallable) replacer).Call(Undefined, replacerArgs.ToArray());
        return TypeConverter.ToString(result);
    }

    /// <summary>
    /// https://tc39.es/ecma262/#sec-getsubstitution
    /// </summary>
    internal static string GetSubstitution(
        string matched,
        string str,
        int position,
        string[] captures,
        JsValue namedCaptures,
        string replacement)
    {
        // If there is no pattern, replace the pattern as is.
        if (!replacement.Contains('$'))
        {
            return replacement;
        }

        // Patterns
        // $$	Inserts a "$".
        // $&	Inserts the matched substring.
        // $`	Inserts the portion of the string that precedes the matched substring.
        // $'	Inserts the portion of the string that follows the matched substring.
        // $n or $nn	Where n or nn are decimal digits, inserts the nth parenthesized submatch string, provided the first argument was a RegExp object.
        using var sb = new ValueStringBuilder(stackalloc char[128]);
        for (var i = 0; i < replacement.Length; i++)
        {
            char c = replacement[i];
            if (c == '$' && i < replacement.Length - 1)
            {
                c = replacement[++i];
                switch (c)
                {
                    case '$':
                        sb.Append('$');
                        break;
                    case '&':
                        sb.Append(matched);
                        break;
                    case '`':
                        sb.Append(str.AsSpan(0, position));
                        break;
                    case '\'':
                        sb.Append(str.AsSpan(position + matched.Length));
                        break;
                    case '<':
                        var gtPos = replacement.IndexOf('>', i + 1);
                        if (gtPos == -1 || namedCaptures.IsUndefined())
                        {
                            sb.Append('$');
                            sb.Append(c);
                        }
                        else
                        {
                            var startIndex = i + 1;
                            var groupName = replacement.Substring(startIndex, gtPos - startIndex);
                            var capture = namedCaptures.Get(groupName);
                            if (!capture.IsUndefined())
                            {
                                sb.Append(TypeConverter.ToString(capture));
                            }

                            i = gtPos;
                        }
                        break;
                    default:
                        {
                            if (char.IsDigit(c))
                            {
                                int matchNumber1 = c - '0';

                                // The match number can be one or two digits long.
                                int matchNumber2 = 0;
                                if (i < replacement.Length - 1 && char.IsDigit(replacement[i + 1]))
                                {
                                    matchNumber2 = matchNumber1 * 10 + (replacement[i + 1] - '0');
                                }

                                // Try the two digit capture first.
                                if (matchNumber2 > 0 && matchNumber2 <= captures.Length)
                                {
                                    // Two digit capture replacement.
                                    sb.Append(TypeConverter.ToString(captures[matchNumber2 - 1]));
                                    i++;
                                }
                                else if (matchNumber1 > 0 && matchNumber1 <= captures.Length)
                                {
                                    // Single digit capture replacement.
                                    sb.Append(TypeConverter.ToString(captures[matchNumber1 - 1]));
                                }
                                else
                                {
                                    // Capture does not exist.
                                    sb.Append('$');
                                    i--;
                                }
                            }
                            else
                            {
                                // Unknown replacement pattern.
                                sb.Append('$');
                                sb.Append(c);
                            }

                            break;
                        }
                }
            }
            else
            {
                sb.Append(c);
            }
        }

        return sb.ToString();
    }

    /// <summary>
    /// https://tc39.es/ecma262/#sec-regexp.prototype-@@split
    /// </summary>
    private JsValue Split(JsValue thisObject, JsCallArguments arguments)
    {
        var rx = AssertThisIsObjectInstance(thisObject, "RegExp.prototype.split");
        var s = TypeConverter.ToString(arguments.At(0));
        var limit = arguments.At(1);
        var c = SpeciesConstructor(rx, _realm.Intrinsics.RegExp);
        var flags = TypeConverter.ToJsString(rx.Get(PropertyFlags));
        var unicodeMatching = flags.Contains('u');
        var newFlags = flags.Contains('y') ? flags : new JsString(flags.ToString() + 'y');
        var splitter = Construct(c, [
            rx,
            newFlags
        ]);
        uint lengthA = 0;
        var lim = limit.IsUndefined() ? NumberConstructor.MaxSafeInteger : TypeConverter.ToUint32(limit);

        if (lim == 0)
        {
            return _realm.Intrinsics.Array.ArrayCreate(0);
        }

        if (s.Length == 0)
        {
            var a = _realm.Intrinsics.Array.ArrayCreate(0);
            var z = RegExpExec(splitter, s);
            if (!z.IsNull())
            {
                return a;
            }

            a.SetIndexValue(0, s, updateLength: true);
            return a;
        }

        if (!unicodeMatching && rx is JsRegExp R && R.HasDefaultRegExpExec)
        {
            // we can take faster path

            if (string.Equals(R.Source, JsRegExp.regExpForMatchingAllCharacters, StringComparison.Ordinal))
            {
                // if empty string, just a string split
                return StringPrototype.SplitWithStringSeparator(_realm, "", s, (uint) s.Length);
            }

            var a = _realm.Intrinsics.Array.Construct(Arguments.Empty);

            int lastIndex = 0;
            uint index = 0;
            for (var match = R.Value.Match(s, 0); match.Success; match = match.NextMatch())
            {
                if (match.Length == 0 && (match.Index == 0 || match.Index == s.Length || match.Index == lastIndex))
                {
                    continue;
                }

                // Add the match results to the array.
                a.SetIndexValue(index++, s.Substring(lastIndex, match.Index - lastIndex), updateLength: true);

                if (index >= lim)
                {
                    return a;
                }

                lastIndex = match.Index + match.Length;
                var actualGroupCount = GetActualRegexGroupCount(R, match);
                for (int i = 1; i < actualGroupCount; i++)
                {
                    var group = match.Groups[i];
                    var item = Undefined;
                    if (group.Captures.Count > 0)
                    {
                        item = match.Groups[i].Value;
                    }

                    a.SetIndexValue(index++, item, updateLength: true);

                    if (index >= lim)
                    {
                        return a;
                    }
                }
            }

            // Add the last part of the split
            a.SetIndexValue(index, s.Substring(lastIndex), updateLength: true);

            return a;
        }

        return SplitSlow(s, splitter, unicodeMatching, lengthA, lim);
    }

    private JsArray SplitSlow(string s, ObjectInstance splitter, bool unicodeMatching, uint lengthA, long lim)
    {
        var a = _realm.Intrinsics.Array.ArrayCreate(0);
        ulong previousStringIndex = 0;
        ulong currentIndex = 0;
        while (currentIndex < (ulong) s.Length)
        {
            splitter.Set(JsRegExp.PropertyLastIndex, currentIndex, true);
            var z = RegExpExec(splitter, s);
            if (z.IsNull())
            {
                currentIndex = AdvanceStringIndex(s, currentIndex, unicodeMatching);
                continue;
            }

            var endIndex = TypeConverter.ToLength(splitter.Get(JsRegExp.PropertyLastIndex));
            endIndex = System.Math.Min(endIndex, (ulong) s.Length);
            if (endIndex == previousStringIndex)
            {
                currentIndex = AdvanceStringIndex(s, currentIndex, unicodeMatching);
                continue;
            }

            var t = s.Substring((int) previousStringIndex, (int) (currentIndex - previousStringIndex));
            a.SetIndexValue(lengthA, t, updateLength: true);
            lengthA++;
            if (lengthA == lim)
            {
                return a;
            }

            previousStringIndex = endIndex;
            var numberOfCaptures = (int) TypeConverter.ToLength(z.Get(CommonProperties.Length));
            numberOfCaptures = System.Math.Max(numberOfCaptures - 1, 0);
            var i = 1;
            while (i <= numberOfCaptures)
            {
                var nextCapture = z.Get(i);
                a.SetIndexValue(lengthA, nextCapture, updateLength: true);
                i++;
                lengthA++;
                if (lengthA == lim)
                {
                    return a;
                }
            }

            currentIndex = previousStringIndex;
        }

        a.SetIndexValue(lengthA, s.Substring((int) previousStringIndex, s.Length - (int) previousStringIndex), updateLength: true);
        return a;
    }

    private JsValue Flags(JsValue thisObject, JsCallArguments arguments)
    {
        var r = AssertThisIsObjectInstance(thisObject, "RegExp.prototype.flags");

        static string AddFlagIfPresent(JsValue o, JsValue p, char flag, string s)
        {
            return TypeConverter.ToBoolean(o.Get(p)) ? s + flag : s;
        }

        var result = AddFlagIfPresent(r, "hasIndices", 'd', "");
        result = AddFlagIfPresent(r, PropertyGlobal, 'g', result);
        result = AddFlagIfPresent(r, PropertyIgnoreCase, 'i', result);
        result = AddFlagIfPresent(r, PropertyMultiline, 'm', result);
        result = AddFlagIfPresent(r, PropertyDotAll, 's', result);
        result = AddFlagIfPresent(r, PropertyUnicode, 'u', result);
        result = AddFlagIfPresent(r, PropertyUnicodeSets, 'v', result);
        result = AddFlagIfPresent(r, PropertySticky, 'y', result);

        return result;
    }

    private JsValue ToRegExpString(JsValue thisObject, JsCallArguments arguments)
    {
        var r = AssertThisIsObjectInstance(thisObject, "RegExp.prototype.toString");

        var pattern = TypeConverter.ToString(r.Get(PropertySource));
        var flags = TypeConverter.ToString(r.Get(PropertyFlags));

        return "/" + pattern + "/" + flags;
    }

    private JsValue Test(JsValue thisObject, JsCallArguments arguments)
    {
        var r = AssertThisIsObjectInstance(thisObject, "RegExp.prototype.test");
        var s = TypeConverter.ToString(arguments.At(0));

        // check couple fast paths
        if (r is JsRegExp R && !R.FullUnicode)
        {
            if (!R.Sticky && !R.Global)
            {
                R.Set(JsRegExp.PropertyLastIndex, 0, throwOnError: true);
                return R.Value.IsMatch(s);
            }

            var lastIndex = (int) TypeConverter.ToLength(R.Get(JsRegExp.PropertyLastIndex));
            if (lastIndex >= s.Length && s.Length > 0)
            {
                return JsBoolean.False;
            }

            var m = R.Value.Match(s, lastIndex);
            if (!m.Success || (R.Sticky && m.Index != lastIndex))
            {
                R.Set(JsRegExp.PropertyLastIndex, 0, throwOnError: true);
                return JsBoolean.False;
            }
            R.Set(JsRegExp.PropertyLastIndex, m.Index + m.Length, throwOnError: true);
            return JsBoolean.True;
        }

        var match = RegExpExec(r, s);
        return !match.IsNull();
    }

    /// <summary>
    /// https://tc39.es/ecma262/#sec-regexp.prototype-@@search
    /// </summary>
    private JsValue Search(JsValue thisObject, JsCallArguments arguments)
    {
        var rx = AssertThisIsObjectInstance(thisObject, "RegExp.prototype.search");

        var s = TypeConverter.ToString(arguments.At(0));
        var previousLastIndex = rx.Get(JsRegExp.PropertyLastIndex);
        if (!SameValue(previousLastIndex, 0))
        {
            rx.Set(JsRegExp.PropertyLastIndex, 0, true);
        }

        var result = RegExpExec(rx, s);
        var currentLastIndex = rx.Get(JsRegExp.PropertyLastIndex);
        if (!SameValue(currentLastIndex, previousLastIndex))
        {
            rx.Set(JsRegExp.PropertyLastIndex, previousLastIndex, true);
        }

        if (result.IsNull())
        {
            return -1;
        }

        return result.Get(PropertyIndex);
    }

    /// <summary>
    /// https://tc39.es/ecma262/#sec-regexp.prototype-@@match
    /// </summary>
    private JsValue Match(JsValue thisObject, JsCallArguments arguments)
    {
        var rx = AssertThisIsObjectInstance(thisObject, "RegExp.prototype.match");

        var s = TypeConverter.ToString(arguments.At(0));
        var flags = TypeConverter.ToString(rx.Get(PropertyFlags));
        var global = flags.Contains('g');
        if (!global)
        {
            return RegExpExec(rx, s);
        }

        var fullUnicode = flags.Contains('u');
        rx.Set(JsRegExp.PropertyLastIndex, JsNumber.PositiveZero, true);

        if (!fullUnicode
            && rx is JsRegExp rei
            && rei.HasDefaultRegExpExec)
        {
            // fast path
            var a = _realm.Intrinsics.Array.ArrayCreate(0);

            if (rei.Sticky)
            {
                var match = rei.Value.Match(s);
                if (!match.Success || match.Index != 0)
                {
                    return Null;
                }

                a.SetIndexValue(0, match.Value, updateLength: false);
                uint li = 0;
                while (true)
                {
                    match = match.NextMatch();
                    if (!match.Success || match.Index != ++li)
                        break;
                    a.SetIndexValue(li, match.Value, updateLength: false);
                }
                a.SetLength(li);
                return a;
            }
            else
            {
                var matches = rei.Value.Matches(s);
                if (matches.Count == 0)
                {
                    return Null;
                }

                a.EnsureCapacity((uint) matches.Count);
                a.SetLength((uint) matches.Count);
                for (var i = 0; i < matches.Count; i++)
                {
                    a.SetIndexValue((uint) i, matches[i].Value, updateLength: false);
                }
                return a;
            }
        }

        return MatchSlow(rx, s, fullUnicode);
    }

    private JsValue MatchSlow(ObjectInstance rx, string s, bool fullUnicode)
    {
        var a = _realm.Intrinsics.Array.ArrayCreate(0);
        uint n = 0;
        while (true)
        {
            var result = RegExpExec(rx, s);
            if (result.IsNull())
            {
                a.SetLength(n);
                return n == 0 ? Null : a;
            }

            var matchStr = TypeConverter.ToString(result.Get(JsString.NumberZeroString));
            a.SetIndexValue(n, matchStr, updateLength: false);
            if (matchStr == "")
            {
                var thisIndex = TypeConverter.ToLength(rx.Get(JsRegExp.PropertyLastIndex));
                var nextIndex = AdvanceStringIndex(s, thisIndex, fullUnicode);
                rx.Set(JsRegExp.PropertyLastIndex, nextIndex, true);
            }

            n++;
        }
    }

    /// <summary>
    /// https://tc39.es/ecma262/#sec-regexp-prototype-matchall
    /// </summary>
    private JsValue MatchAll(JsValue thisObject, JsCallArguments arguments)
    {
        var r = AssertThisIsObjectInstance(thisObject, "RegExp.prototype.matchAll");

        var s = TypeConverter.ToString(arguments.At(0));
        var c = SpeciesConstructor(r, _realm.Intrinsics.RegExp);

        var flags = TypeConverter.ToJsString(r.Get(PropertyFlags));
        var matcher = Construct(c, [
            r,
            flags
        ]);

        var lastIndex = TypeConverter.ToLength(r.Get(JsRegExp.PropertyLastIndex));
        matcher.Set(JsRegExp.PropertyLastIndex, lastIndex, true);

        var global = flags.Contains('g');
        var fullUnicode = flags.Contains('u');

        return _realm.Intrinsics.RegExpStringIteratorPrototype.Construct(matcher, s, global, fullUnicode);
    }

    private static ulong AdvanceStringIndex(string s, ulong index, bool unicode)
    {
        if (!unicode || index + 1 >= (ulong) s.Length)
        {
            return index + 1;
        }

        var first = s[(int) index];
        if (first < 0xD800 || first > 0xDBFF)
        {
            return index + 1;
        }

        var second = s[(int) (index + 1)];
        if (second < 0xDC00 || second > 0xDFFF)
        {
            return index + 1;
        }

        return index + 2;
    }

    internal static JsValue RegExpExec(ObjectInstance r, string s)
    {
        var ri = r as JsRegExp;

        if ((ri is null || !ri.HasDefaultRegExpExec) && r.Get(PropertyExec) is ICallable callable)
        {
            var result = callable.Call(r, s);
            if (!result.IsNull() && !result.IsObject())
            {
                Throw.TypeError(r.Engine.Realm);
            }

            return result;
        }

        if (ri is null)
        {
            Throw.TypeError(r.Engine.Realm);
        }

        return RegExpBuiltinExec(ri, s);
    }

    internal bool HasDefaultExec => Get(PropertyExec) is ClrFunction functionInstance && functionInstance._func == _defaultExec;

    /// <summary>
    /// https://tc39.es/ecma262/#sec-regexpbuiltinexec
    /// </summary>
    private static JsValue RegExpBuiltinExec(JsRegExp R, string s)
    {
        var length = (ulong) s.Length;
        var lastIndex = TypeConverter.ToLength(R.Get(JsRegExp.PropertyLastIndex));

        var global = R.Global;
        var sticky = R.Sticky;
        if (!global && !sticky)
        {
            lastIndex = 0;
        }

        if (string.Equals(R.Source, JsRegExp.regExpForMatchingAllCharacters, StringComparison.Ordinal))  // Reg Exp is really ""
        {
            if (lastIndex > (ulong) s.Length)
            {
                return Null;
            }

            // "aaa".match() => [ '', index: 0, input: 'aaa' ]
            var array = R.Engine.Realm.Intrinsics.Array.ArrayCreate(1);
            array.FastSetDataProperty(PropertyIndex._value, lastIndex);
            array.FastSetDataProperty(PropertyInput._value, s);
            array.SetIndexValue(0, JsString.Empty, updateLength: false);
            return array;
        }

        var matcher = R.Value;
        var fullUnicode = R.FullUnicode;
        var hasIndices = R.Indices;

        if (!global && !sticky && !fullUnicode && !hasIndices)
        {
            // we can the non-stateful fast path which is the common case
            var m = matcher.Match(s, (int) lastIndex);
            if (!m.Success)
            {
                return Null;
            }

            return CreateReturnValueArray(R, m, s, fullUnicode: false, hasIndices: false);
        }

        // the stateful version
        Match match;

        if (lastIndex > length)
        {
            R.Set(JsRegExp.PropertyLastIndex, JsNumber.PositiveZero, true);
            return Null;
        }

        var startAt = (int) lastIndex;
        while (true)
        {
            match = R.Value.Match(s, startAt);

            // The conversion of Unicode regex patterns to .NET Regex has some flaws:
            // when the pattern may match empty strings, the adapted Regex will return empty string matches
            // in the middle of surrogate pairs. As a best effort solution, we remove these fake positive matches.
            // (See also: https://github.com/sebastienros/esprima-dotnet/pull/364#issuecomment-1606045259)

            if (match.Success
                && fullUnicode
                && match.Length == 0
                && 0 < match.Index && match.Index < s.Length
                && char.IsHighSurrogate(s[match.Index - 1]) && char.IsLowSurrogate(s[match.Index]))
            {
                startAt++;
                continue;
            }

            break;
        }

        var success = match.Success && (!sticky || match.Index == (int) lastIndex);
        if (!success)
        {
            R.Set(JsRegExp.PropertyLastIndex, JsNumber.PositiveZero, true);
            return Null;
        }

        var e = match.Index + match.Length;

        // NOTE: Even in Unicode mode, we don't need to translate indices as .NET regexes always return code unit indices.

        if (global || sticky)
        {
            R.Set(JsRegExp.PropertyLastIndex, e, true);
        }

        return CreateReturnValueArray(R, match, s, fullUnicode, hasIndices);
    }

    private static JsArray CreateReturnValueArray(
        JsRegExp rei,
        Match match,
        string s,
        bool fullUnicode,
        bool hasIndices)
    {
        var engine = rei.Engine;
        var actualGroupCount = GetActualRegexGroupCount(rei, match);
        var array = engine.Realm.Intrinsics.Array.ArrayCreate((ulong) actualGroupCount);
        array.CreateDataProperty(PropertyIndex, match.Index);
        array.CreateDataProperty(PropertyInput, s);

        ObjectInstance? groups = null;
        List<string>? groupNames = null;
        var indices = hasIndices ? new List<JsNumber[]?>(actualGroupCount) : null;
        for (uint i = 0; i < actualGroupCount; i++)
        {
            var capture = match.Groups[(int) i];
            var capturedValue = Undefined;
            if (capture?.Success == true)
            {
                capturedValue = capture.Value;
            }

            if (hasIndices)
            {
                if (capture?.Success == true)
                {
                    indices!.Add([JsNumber.Create(capture.Index), JsNumber.Create(capture.Index + capture.Length)]);
                }
                else
                {
                    indices!.Add(null);
                }
            }

            var groupName = GetRegexGroupName(rei, (int) i);
            if (!string.IsNullOrWhiteSpace(groupName))
            {
                groups ??= OrdinaryObjectCreate(engine, null);
                groups.CreateDataPropertyOrThrow(groupName, capturedValue);
                groupNames ??= [];
                groupNames.Add(groupName!);
            }

            array.SetIndexValue(i, capturedValue, updateLength: false);
        }

        array.CreateDataProperty(PropertyGroups, groups ?? Undefined);

        if (hasIndices)
        {
            var indicesArray = MakeMatchIndicesIndexPairArray(engine, s, indices!, groupNames, groupNames?.Count > 0);
            array.CreateDataPropertyOrThrow("indices", indicesArray);
        }

        return array;
    }

    /// <summary>
    /// https://tc39.es/ecma262/#sec-makematchindicesindexpairarray
    /// </summary>
    private static JsArray MakeMatchIndicesIndexPairArray(
        Engine engine,
        string s,
        List<JsNumber[]?> indices,
        List<string>? groupNames,
        bool hasGroups)
    {
        var n = indices.Count;
        var a = engine.Realm.Intrinsics.Array.Construct((uint) n);
        ObjectInstance? groups = null;
        if (hasGroups)
        {
            groups = OrdinaryObjectCreate(engine, null);
        }

        a.CreateDataPropertyOrThrow("groups", groups ?? Undefined);
        for (var i = 0; i < n; ++i)
        {
            var matchIndices = indices[i];

            var matchIndexPair = matchIndices is not null
                ? GetMatchIndexPair(engine, s, matchIndices)
                : Undefined;

            a.Push(matchIndexPair);
            if (i > 0 && !string.IsNullOrWhiteSpace(groupNames?[i - 1]))
            {
                groups!.CreateDataPropertyOrThrow(groupNames![i - 1], matchIndexPair);
            }
        }
        return a;
    }

    /// <summary>
    /// https://tc39.es/ecma262/#sec-getmatchindexpair
    /// </summary>
    private static JsValue GetMatchIndexPair(Engine engine, string s, JsNumber[] match)
    {
        return engine.Realm.Intrinsics.Array.CreateArrayFromList(match);
    }

    private static int GetActualRegexGroupCount(JsRegExp rei, Match match)
    {
        return rei.ParseResult.Success ? rei.ParseResult.ActualRegexGroupCount : match.Groups.Count;
    }

    private static string? GetRegexGroupName(JsRegExp rei, int index)
    {
        if (index == 0)
        {
            return null;
        }
        var regex = rei.Value;
        if (rei.ParseResult.Success)
        {
            return rei.ParseResult.GetRegexGroupName(index);
        }

        var groupNameFromNumber = regex.GroupNameFromNumber(index);
        if (groupNameFromNumber.Length == 1 && groupNameFromNumber[0] == 48 + index)
        {
            // regex defaults to index as group name when it's not a named group
            return null;
        }

        return groupNameFromNumber;
    }

    private JsValue Exec(JsValue thisObject, JsCallArguments arguments)
    {
        var r = thisObject as JsRegExp;
        if (r is null)
        {
            Throw.TypeError(_engine.Realm);
        }

        var s = TypeConverter.ToString(arguments.At(0));
        return RegExpBuiltinExec(r, s);
    }
}
