using System;
using System.Collections.Generic;
using System.IO;
using System.IO.Compression;
using System.Linq;
using System.Net;
using System.Text;
using System.Text.RegularExpressions;
using System.Xml;
using System.Xml.Linq;
using DocumentFormat.OpenXml;

namespace DCIT.Core.Utilities
{
    internal static class VmlTextMetadataUtility
    {
        private static readonly Regex Base64WhitespaceRegex = new Regex(@"\s+", RegexOptions.Compiled);

        public static bool IsVmlShapeElement(OpenXmlElement element)
        {
            return element != null
                && string.Equals(element.LocalName, "shape", StringComparison.OrdinalIgnoreCase)
                && string.Equals(element.NamespaceUri, "urn:schemas-microsoft-com:vml", StringComparison.OrdinalIgnoreCase);
        }

        public static IEnumerable<VmlTextBinding> CreateBindings(OpenXmlElement shape)
        {
            if (!IsVmlShapeElement(shape))
            {
                yield break;
            }

            foreach (var binding in CreateEquationBindings(shape))
            {
                yield return binding;
            }

            foreach (var binding in CreateChartBindings(shape))
            {
                yield return binding;
            }
        }

        private static IEnumerable<VmlTextBinding> CreateEquationBindings(OpenXmlElement shape)
        {
            var attribute = FindAttribute(shape, "equationxml");
            if (!attribute.HasValue || string.IsNullOrWhiteSpace(attribute.Value.Value))
            {
                yield break;
            }

            var actualAttribute = attribute.Value;

            XDocument document;
            try
            {
                var decoded = WebUtility.HtmlDecode(actualAttribute.Value);
                if (string.IsNullOrWhiteSpace(decoded))
                {
                    yield break;
                }

                document = XDocument.Parse(decoded, LoadOptions.PreserveWhitespace);
            }
            catch
            {
                yield break;
            }

            var textNodes = document
                .Descendants()
                .Where(item => string.Equals(item.Name.LocalName, "t", StringComparison.OrdinalIgnoreCase))
                .ToList();
            if (textNodes.Count == 0)
            {
                yield break;
            }

            foreach (var textNode in textNodes)
            {
                var initialText = textNode.Value ?? string.Empty;
                if (initialText.Length == 0)
                {
                    continue;
                }

                yield return new VmlTextBinding
                {
                    Text = initialText,
                    IsEquationText = true,
                    Apply = updatedText =>
                    {
                        textNode.Value = updatedText ?? string.Empty;
                        SetAttribute(shape, actualAttribute, SerializeXml(document));
                    },
                };
            }
        }

        private static IEnumerable<VmlTextBinding> CreateChartBindings(OpenXmlElement shape)
        {
            var attribute = FindAttribute(shape, "gfxdata");
            if (!attribute.HasValue || string.IsNullOrWhiteSpace(attribute.Value.Value))
            {
                yield break;
            }

            var actualAttribute = attribute.Value;

            ChartPackageContext context;
            try
            {
                context = ChartPackageContext.TryCreate(shape, actualAttribute);
            }
            catch
            {
                context = null;
            }

            if (context == null || context.XmlEntries.Count == 0)
            {
                yield break;
            }

            foreach (var entry in context.XmlEntries)
            {
                foreach (var textNode in entry.Document
                    .Descendants()
                    .Where(item => IsChartVisibleTextNode(item))
                    .ToList())
                {
                    var initialText = textNode.Value ?? string.Empty;
                    if (initialText.Length == 0)
                    {
                        continue;
                    }

                    yield return new VmlTextBinding
                    {
                        Text = initialText,
                        IsChartText = true,
                        Apply = updatedText =>
                        {
                            textNode.Value = updatedText ?? string.Empty;
                            context.Save();
                        },
                    };
                }
            }
        }

        private static bool IsChartVisibleTextNode(XElement element)
        {
            if (element == null)
            {
                return false;
            }

            var localName = element.Name.LocalName;
            return string.Equals(localName, "t", StringComparison.OrdinalIgnoreCase)
                || string.Equals(localName, "v", StringComparison.OrdinalIgnoreCase);
        }

        private static OpenXmlAttribute? FindAttribute(OpenXmlElement element, string localName)
        {
            if (element == null || string.IsNullOrWhiteSpace(localName))
            {
                return null;
            }

            foreach (var attribute in element.GetAttributes())
            {
                if (string.Equals(attribute.LocalName, localName, StringComparison.OrdinalIgnoreCase))
                {
                    return attribute;
                }
            }

            return null;
        }

        private static void SetAttribute(OpenXmlElement element, OpenXmlAttribute sourceAttribute, string value)
        {
            element.SetAttribute(new OpenXmlAttribute(
                sourceAttribute.Prefix,
                sourceAttribute.LocalName,
                sourceAttribute.NamespaceUri,
                value ?? string.Empty));
        }

        private static string SerializeXml(XDocument document)
        {
            using (var writer = new Utf8StringWriter())
            using (var xmlWriter = XmlWriter.Create(writer, new XmlWriterSettings
            {
                OmitXmlDeclaration = document.Declaration == null,
                Encoding = new UTF8Encoding(false),
                Indent = false,
                NewLineHandling = NewLineHandling.None,
            }))
            {
                document.Save(xmlWriter);
                xmlWriter.Flush();
                return writer.ToString();
            }
        }

        private sealed class ChartPackageContext
        {
            private readonly OpenXmlElement _shape;
            private readonly OpenXmlAttribute _attribute;
            private readonly List<EntryState> _allEntries;

            private ChartPackageContext(OpenXmlElement shape, OpenXmlAttribute attribute, List<EntryState> allEntries, List<EntryState> xmlEntries)
            {
                _shape = shape;
                _attribute = attribute;
                _allEntries = allEntries;
                XmlEntries = xmlEntries;
            }

            public List<EntryState> XmlEntries { get; private set; }

            public static ChartPackageContext TryCreate(OpenXmlElement shape, OpenXmlAttribute attribute)
            {
                var decoded = WebUtility.HtmlDecode(attribute.Value ?? string.Empty);
                if (string.IsNullOrWhiteSpace(decoded))
                {
                    return null;
                }

                var normalizedBase64 = Base64WhitespaceRegex.Replace(decoded, string.Empty);
                if (normalizedBase64.Length == 0)
                {
                    return null;
                }

                var bytes = Convert.FromBase64String(normalizedBase64);
                var allEntries = new List<EntryState>();
                var xmlEntries = new List<EntryState>();

                using (var input = new MemoryStream(bytes))
                using (var zip = new ZipArchive(input, ZipArchiveMode.Read, false))
                {
                    foreach (var entry in zip.Entries)
                    {
                        var state = new EntryState
                        {
                            FullName = entry.FullName,
                            LastWriteTime = entry.LastWriteTime,
                        };

                        using (var entryStream = entry.Open())
                        using (var memory = new MemoryStream())
                        {
                            entryStream.CopyTo(memory);
                            state.RawBytes = memory.ToArray();
                        }

                        if (entry.FullName.IndexOf("drs/charts/", StringComparison.OrdinalIgnoreCase) >= 0
                            && entry.FullName.EndsWith(".xml", StringComparison.OrdinalIgnoreCase))
                        {
                            try
                            {
                                state.Document = XDocument.Parse(
                                    Encoding.UTF8.GetString(state.RawBytes),
                                    LoadOptions.PreserveWhitespace);
                            }
                            catch
                            {
                                state.Document = null;
                            }

                            if (state.Document != null)
                            {
                                xmlEntries.Add(state);
                            }
                        }

                        allEntries.Add(state);
                    }
                }

                return new ChartPackageContext(shape, attribute, allEntries, xmlEntries);
            }

            public void Save()
            {
                using (var output = new MemoryStream())
                {
                    using (var zip = new ZipArchive(output, ZipArchiveMode.Create, true))
                    {
                        foreach (var entry in _allEntries)
                        {
                            var targetEntry = zip.CreateEntry(entry.FullName, CompressionLevel.Optimal);
                            targetEntry.LastWriteTime = entry.LastWriteTime;
                            using (var targetStream = targetEntry.Open())
                            {
                                var bytes = entry.Document == null
                                    ? (entry.RawBytes ?? Array.Empty<byte>())
                                    : Encoding.UTF8.GetBytes(SerializeXml(entry.Document));
                                targetStream.Write(bytes, 0, bytes.Length);
                            }
                        }
                    }

                    SetAttribute(_shape, _attribute, Convert.ToBase64String(output.ToArray()));
                }
            }
        }

        private sealed class Utf8StringWriter : StringWriter
        {
            public override Encoding Encoding
            {
                get { return new UTF8Encoding(false); }
            }
        }

        private sealed class EntryState
        {
            public string FullName { get; set; }

            public DateTimeOffset LastWriteTime { get; set; }

            public byte[] RawBytes { get; set; }

            public XDocument Document { get; set; }
        }
    }

    internal sealed class VmlTextBinding
    {
        public string Text { get; set; }

        public bool IsEquationText { get; set; }

        public bool IsChartText { get; set; }

        public Action<string> Apply { get; set; }
    }
}