// ==========================================================================
//  Squidex Headless CMS
// ==========================================================================
//  Copyright (c) Squidex UG (haftungsbeschraenkt)
//  All rights reserved. Licensed under the MIT license.
// ==========================================================================

using System;

namespace Squidex.Infrastructure.Security
{
    public sealed partial class Permission
    {
        internal readonly struct Part
        {
            private const char SeparatorAlternative = '|';
            private const char SeparatorMain = '.';
            private const char CharAny = '*';
            private const char CharExclude = '^';

            public readonly ReadOnlyMemory<char>[]? Alternatives;

            public readonly bool Exclusion;

            public Part(ReadOnlyMemory<char>[]? alternatives, bool exclusion)
            {
                Alternatives = alternatives;

                Exclusion = exclusion;
            }

            public static Part[] ParsePath(string path)
            {
                if (string.IsNullOrWhiteSpace(path))
                {
                    return Array.Empty<Part>();
                }

                var current = path.AsMemory();
                var currentSpan = current.Span;

                var result = new Part[CountOf(currentSpan, SeparatorMain) + 1];

                if (result.Length == 1)
                {
                    result[0] = Parse(current);
                }
                else
                {
                    for (int i = 0, j = 0; i < currentSpan.Length; i++)
                    {
                        if (currentSpan[i] == SeparatorMain)
                        {
                            result[j] = Parse(current.Slice(0, i));

                            current = current.Slice(i + 1);
                            currentSpan = current.Span;

                            i = 0;
                            j++;
                        }
                        else if (i == currentSpan.Length - 1 || currentSpan[i] == SeparatorMain)
                        {
                            result[j] = Parse(current);
                        }
                    }
                }

                return result;
            }

            public static Part Parse(ReadOnlyMemory<char> current)
            {
                var currentSpan = current.Span;

                if (currentSpan.Length == 0)
                {
                    return new Part(Array.Empty<ReadOnlyMemory<char>>(), false);
                }

                var isExclusion = false;

                if (currentSpan[0] == CharExclude)
                {
                    isExclusion = true;

                    current = current.Slice(1);
                    currentSpan = current.Span;
                }

                if (currentSpan.Length == 0)
                {
                    return new Part(Array.Empty<ReadOnlyMemory<char>>(), isExclusion);
                }

                if (current.Length > 1 || currentSpan[0] != CharAny)
                {
                    var alternatives = new ReadOnlyMemory<char>[CountOf(currentSpan, SeparatorAlternative) + 1];

                    if (alternatives.Length == 1)
                    {
                        alternatives[0] = current;
                    }
                    else
                    {
                        for (int i = 0, j = 0; i < current.Length; i++)
                        {
                            if (currentSpan[i] == SeparatorAlternative)
                            {
                                alternatives[j] = current.Slice(0, i);

                                current = current.Slice(i + 1);
                                currentSpan = current.Span;

                                i = 0;
                                j++;
                            }
                            else if (i == current.Length - 1)
                            {
                                alternatives[j] = current;
                            }
                        }
                    }

                    return new Part(alternatives, isExclusion);
                }
                else
                {
                    return new Part(null, isExclusion);
                }
            }

            private static int CountOf(ReadOnlySpan<char> text, char character)
            {
                var count = 0;

                for (var i = 0; i < text.Length; i++)
                {
                    if (text[i] == character)
                    {
                        count++;
                    }
                }

                return count;
            }

            public static bool Intersects(ref Part lhs, ref Part rhs, bool allowNull)
            {
                if (lhs.Alternatives == null)
                {
                    return true;
                }

                if (rhs.Alternatives == null)
                {
                    return allowNull;
                }

                var shouldIntersect = !(lhs.Exclusion ^ rhs.Exclusion);

                var isIntersected = false;

                for (var i = 0; i < lhs.Alternatives.Length; i++)
                {
                    for (var j = 0; j < rhs.Alternatives.Length; j++)
                    {
                        if (lhs.Alternatives[i].Span.Equals(rhs.Alternatives[j].Span, StringComparison.OrdinalIgnoreCase))
                        {
                            isIntersected = true;
                            break;
                        }
                    }
                }

                return isIntersected == shouldIntersect;
            }
        }
    }
}