// Copyright (c) Craftwork Games. All rights reserved.
// Licensed under the MIT license.
// See LICENSE file in the project root for full license information.

using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Runtime.InteropServices;
using System.Text;
using System.Xml;

namespace MonoGame.Extended.Content.BitmapFonts;

/// <summary>
/// A utility class for reading the contents of a font file in the AngleCode BMFont file spec.
/// </summary>
public static class BitmapFontFileReader
{
    /// <summary>
    /// Reads the content of the font file at the path specified.
    /// </summary>
    /// <param name="path">The path to the font file to read.</param>
    /// <returns>A <see cref="BitmapFontFileContent"/> instance containing the results of the read operation.</returns>
    /// <exception cref="InvalidOperationException">
    /// Thrown if the header for the file contents does not match a known header format.
    /// </exception>
    public static BitmapFontFileContent Read(string path)
    {
        using var stream = File.OpenRead(path);
        return Read(stream, path);
    }

    /// <summary>
    /// Reads the content of the font file at the path specified.
    /// </summary>
    /// <param name="stream">A <see cref="Stream"/> containing the font file contents to read.</param>
    /// <returns>A <see cref="BitmapFontFileContent"/> instance containing the results of the read operation.</returns>
    /// <exception cref="InvalidOperationException">
    /// Thrown if the header for the file contents does not match a known header format.
    /// </exception>
    [Obsolete("Use the overload that takes an explicit name parameter.")]
    public static BitmapFontFileContent Read(FileStream stream)
    {
        return Read(stream, stream.Name);
    }

    /// <summary>
    /// Reads the content of the font file at the path specified.
    /// </summary>
    /// <param name="stream">A <see cref="Stream"/> containing the font file contents to read.</param>
    /// <param name="name">The name or path that uniquely identifies this <see cref="BitmapFontFileContent"/>.</param>
    /// <returns>A <see cref="BitmapFontFileContent"/> instance containing the results of the read operation.</returns>
    /// <exception cref="InvalidOperationException">
    /// Thrown if the header for the file contents does not match a known header format.
    /// </exception>
    public static BitmapFontFileContent Read(Stream stream, string name)
    {
        long position = stream.Position;

        // Issue: MonoGame.Extended won't load XML format .fnt files if they begin with the byte order mark.
        // https://github.com/MonoGame-Extended/Monogame-Extended/issues/1073
        // It's possible that a consumer might edit the BMFont file using a different library such as SharpFNT.BitmapFont
        // which could save it with UTF-8 Byte Order Mark (BOM) preamble at the start of the file.
        // To get around this, we need to detect if the preamble is there and advance the stream past it if so.

        Span<byte> buffer = stackalloc byte[3];
        int bytesRead = stream.Read(buffer);
        if (bytesRead < 1)
        {
            throw new InvalidOperationException("Stream is empty or unreadable");
        }

        int sig;
        if (buffer.SequenceEqual(Encoding.UTF8.GetPreamble()))
        {
            sig = stream.ReadByte();
            stream.Seek(-1, SeekOrigin.Current);
        }
        else
        {
            sig = buffer[0];
            stream.Position = position;
        }

        var bmfFile = sig switch
        {
            //  Binary header begins with [66, 77, 70, 3]
            66 => ReadBinary(stream),

            //  XML format begins with [60, 63, 120, 109]
            60 => ReadXml(stream),

            //  Text format begins with [105, 110, 102, 111]
            105 => ReadText(stream),

            //  Unknown format
            _ => throw new InvalidOperationException("This does not appear to be a valid BMFont file!")
        };

        bmfFile.Path = name;

        return bmfFile;
    }



    #region ------------------------ Read BMFFont Binary Formatted File -----------------------------------------------

    private static BitmapFontFileContent ReadBinary(Stream stream)
    {
        using BinaryReader reader = new BinaryReader(stream);
        return ReadBinary(reader);
    }

    private static BitmapFontFileContent ReadBinary(BinaryReader reader)
    {
        BitmapFontFileContent bmfFile = new BitmapFontFileContent();
        bmfFile.Header = AsType<BitmapFontFileContent.HeaderBlock>(reader.ReadBytes(BitmapFontFileContent.HeaderBlock.StructSize));

        if (!bmfFile.Header.IsValid)
        {
            throw new InvalidOperationException($"The BMFFont file header is invalid, this does not appear to be a valid BMFont file");
        }


        while (reader.BaseStream.Position < reader.BaseStream.Length)
        {
            byte blockType = reader.ReadByte();
            int blockSize = reader.ReadInt32();

            switch (blockType)
            {
                case 1:
                    bmfFile.Info = AsType<BitmapFontFileContent.InfoBlock>(reader.ReadBytes(BitmapFontFileContent.InfoBlock.StructSize));
                    int stringLen = blockSize - BitmapFontFileContent.InfoBlock.StructSize;
                    bmfFile.FontName = Encoding.UTF8.GetString(reader.ReadBytes(stringLen)).Replace("\0", string.Empty);
                    break;
                case 2:
                    bmfFile.Common = AsType<BitmapFontFileContent.CommonBlock>(reader.ReadBytes(BitmapFontFileContent.CommonBlock.StructSize));
                    break;
                case 3:
                    string[] pages = Encoding.UTF8.GetString(reader.ReadBytes(blockSize)).Split('\0', StringSplitOptions.RemoveEmptyEntries);
                    bmfFile.Pages.AddRange(pages);
                    break;
                case 4:
                    int characterCount = blockSize / BitmapFontFileContent.CharacterBlock.StructSize;
                    for (int c = 0; c < characterCount; c++)
                    {
                        BitmapFontFileContent.CharacterBlock character = AsType<BitmapFontFileContent.CharacterBlock>(reader.ReadBytes(BitmapFontFileContent.CharacterBlock.StructSize));
                        bmfFile.Characters.Add(character);
                    }
                    break;
                case 5:
                    int kerningCount = blockSize / BitmapFontFileContent.KerningPairsBlock.StructSize;
                    for (int k = 0; k < kerningCount; k++)
                    {
                        BitmapFontFileContent.KerningPairsBlock kerning = AsType<BitmapFontFileContent.KerningPairsBlock>(reader.ReadBytes(BitmapFontFileContent.KerningPairsBlock.StructSize));
                        bmfFile.Kernings.Add(kerning);
                    }
                    break;
                default:
                    reader.BaseStream.Seek(blockSize, SeekOrigin.Current);
                    break;
            }
        }

        return bmfFile;
    }

    private static T AsType<T>(ReadOnlySpan<byte> buffer) where T : struct
    {
        T value;
        try
        {
            unsafe
            {
                fixed (byte* ptr = buffer)
                {
                    value = Marshal.PtrToStructure<T>((IntPtr)ptr);
                }
            }
            return value;
        }
        catch
        {
            return default;
        }

    }

    #endregion --------------------- Read BMFFont Binary Formatted File -----------------------------------------------

    #region ------------------------ Read BMFFont Xml Formatted File --------------------------------------------------


    private static BitmapFontFileContent ReadXml(Stream stream)
    {
        BitmapFontFileContent bmfFile = new BitmapFontFileContent();

        // XML does not contain the header like binary so we manually create it
        bmfFile.Header = new() { B = (byte)'B', M = (byte)'M', F = (byte)'F', Version = 3 };

        var document = new XmlDocument();
        document.Load(stream);
        var root = document.DocumentElement;

        ReadInfoNode(bmfFile, root);
        ReadCommonNode(bmfFile, root);
        ReadPageNodes(bmfFile, root);
        ReadCharacterNodes(bmfFile, root);
        ReadKerningNodes(bmfFile, root);

        return bmfFile;
    }

    private static void ReadInfoNode(BitmapFontFileContent bmfFile, XmlNode root)
    {
        var node = root.SelectSingleNode("info");
        bmfFile.FontName = node.GetStringAttribute("face");
        bmfFile.Info.FontSize = node.GetInt16Attribute("size");

        var smooth = node.GetByteAttribute("smooth");
        var unicode = node.GetByteAttribute("unicode");
        var italic = node.GetByteAttribute("italic");
        var bold = node.GetByteAttribute("bold");
        var fixedHeight = node.GetByteAttribute("fixedHeight");
        bmfFile.Info.BitField = (byte)(smooth << 7 | unicode << 6 | italic << 5 | bold << 4 | fixedHeight << 3);

        bmfFile.Info.CharSet = node.GetByteAttribute("charSet");
        bmfFile.Info.StretchH = node.GetUInt16Attribute("stretchH");
        bmfFile.Info.AA = node.GetByteAttribute("aa");

        var paddingValues = node.GetByteDelimitedAttribute("padding", 4);
        bmfFile.Info.PaddingUp = paddingValues[0];
        bmfFile.Info.PaddingRight = paddingValues[1];
        bmfFile.Info.PaddingDown = paddingValues[2];
        bmfFile.Info.PaddingLeft = paddingValues[3];

        var spacingValues = node.GetSignedByteDelimitedAttribute("spacing", 2);
        bmfFile.Info.SpacingHoriz = spacingValues[0];
        bmfFile.Info.SpacingVert = spacingValues[1];

        bmfFile.Info.Outline = node.GetByteAttribute("outline");
    }

    private static void ReadCommonNode(BitmapFontFileContent bmfFile, XmlNode root)
    {
        var node = root.SelectSingleNode("common");
        bmfFile.Common.LineHeight = node.GetUInt16Attribute("lineHeight");
        bmfFile.Common.Base = node.GetUInt16Attribute("base");
        bmfFile.Common.ScaleW = node.GetUInt16Attribute("scaleW");
        bmfFile.Common.ScaleH = node.GetUInt16Attribute("scaleH");
        bmfFile.Common.Pages = node.GetUInt16Attribute("pages");

        var packed = node.GetByteAttribute("packed");
        bmfFile.Common.BitField = (byte)(packed << 7);

        bmfFile.Common.AlphaChnl = node.GetByteAttribute("alphaChnl");
        bmfFile.Common.RedChnl = node.GetByteAttribute("redChnl");
        bmfFile.Common.GreenChnl = node.GetByteAttribute("greenChnl");
        bmfFile.Common.BlueChnl = node.GetByteAttribute("blueChnl");
    }

    private static void ReadPageNodes(BitmapFontFileContent bmfFile, XmlNode root)
    {
        var nodes = root.SelectNodes("pages/page");
        foreach (XmlNode node in nodes)
        {
            string file = node.GetStringAttribute("file");
            bmfFile.Pages.Add(file);
        }
    }

    private static void ReadCharacterNodes(BitmapFontFileContent bmfFile, XmlNode root)
    {
        var nodes = root.SelectNodes("chars/char");
        foreach (XmlNode node in nodes)
        {
            var character = new BitmapFontFileContent.CharacterBlock
            {
                ID = node.GetInt32Attribute("id"),
                X = node.GetUInt16Attribute("x"),
                Y = node.GetUInt16Attribute("y"),
                Width = node.GetUInt16Attribute("width"),
                Height = node.GetUInt16Attribute("height"),
                XOffset = node.GetInt16Attribute("xoffset"),
                YOffset = node.GetInt16Attribute("yoffset"),
                XAdvance = node.GetInt16Attribute("xadvance"),
                Page = node.GetByteAttribute("page"),
                Chnl = node.GetByteAttribute("chnl"),
            };

            bmfFile.Characters.Add(character);
        }
    }

    private static void ReadKerningNodes(BitmapFontFileContent bmfFile, XmlNode root)
    {
        var nodes = root.SelectNodes("kernings/kerning");
        foreach (XmlNode node in nodes)
        {
            var kerning = new BitmapFontFileContent.KerningPairsBlock
            {
                First = node.GetUInt32Attribute("first"),
                Second = node.GetUInt32Attribute("second"),
                Amount = node.GetInt16Attribute("amount"),
            };

            bmfFile.Kernings.Add(kerning);
        }
    }

    #endregion --------------------- Read BMFFont Xml Formatted File --------------------------------------------------

    #region ------------------------ Read BMFFont Text Formatted File -------------------------------------------------

    private static BitmapFontFileContent ReadText(Stream stream)
    {
        var bmfFile = new BitmapFontFileContent();

        // Text does not contain the header like binary so we manually create it
        bmfFile.Header = new() { B = (byte)'B', M = (byte)'M', F = (byte)'F', Version = 3 };

        using var reader = new StreamReader(stream);

        string line = default;
        while ((line = reader.ReadLine()) != null)
        {
            var tokens = GetTokens(line);
            if (tokens.Count == 0)
            {
                continue;
            }

            switch (tokens[0])
            {
                case "info":
                    ReadInfoTokens(bmfFile, CollectionsMarshal.AsSpan(tokens)[1..]);
                    break;
                case "common":
                    ReadCommonTokens(bmfFile, CollectionsMarshal.AsSpan(tokens)[1..]);
                    break;
                case "page":
                    ReadPageTokens(bmfFile, CollectionsMarshal.AsSpan(tokens)[1..]);
                    break;
                case "char":
                    ReadCharacterTokens(bmfFile, CollectionsMarshal.AsSpan(tokens)[1..]);
                    break;
                case "kerning":
                    ReadKerningTokens(bmfFile, CollectionsMarshal.AsSpan(tokens)[1..]);
                    break;
            }
        }

        return bmfFile;
    }

    private static void ReadInfoTokens(BitmapFontFileContent bmfFile, ReadOnlySpan<string> tokens)
    {
        for (int i = 0; i < tokens.Length; ++i)
        {
            var split = tokens[i].Split('=');

            if (split.Length != 2)
            {
                continue;
            }

            switch (split[0])
            {
                case "face":
                    bmfFile.FontName = split[1].Replace("\"", string.Empty);
                    break;
                case "size":
                    bmfFile.Info.FontSize = Convert.ToInt16(split[1], CultureInfo.InvariantCulture);
                    break;
                case "smooth":
                    var smooth = Convert.ToByte(split[1], CultureInfo.InvariantCulture);
                    bmfFile.Info.BitField |= (byte)(smooth << 7);
                    break;
                case "unicode":
                    var unicode = Convert.ToByte(split[1], CultureInfo.InvariantCulture);
                    bmfFile.Info.BitField |= (byte)(unicode << 6);
                    break;
                case "italic":
                    var italic = Convert.ToByte(split[1], CultureInfo.InvariantCulture);
                    bmfFile.Info.BitField |= (byte)(italic << 5);
                    break;
                case "bold":
                    var bold = Convert.ToByte(split[1], CultureInfo.InvariantCulture);
                    bmfFile.Info.BitField |= (byte)(bold << 4);
                    break;
                case "fixedHeight":
                    byte fixedHeight = Convert.ToByte(split[1], CultureInfo.InvariantCulture);
                    bmfFile.Info.BitField |= (byte)(fixedHeight << 3);
                    break;
                case "stretchH":
                    bmfFile.Info.StretchH = Convert.ToUInt16(split[1], CultureInfo.InvariantCulture);
                    break;
                case "aa":
                    bmfFile.Info.AA = Convert.ToByte(split[1], CultureInfo.InvariantCulture);
                    break;
                case "padding":
                    var paddingValues = split[1].Split(',');
                    if (paddingValues.Length == 4)
                    {
                        bmfFile.Info.PaddingUp = Convert.ToByte(paddingValues[0], CultureInfo.InvariantCulture);
                        bmfFile.Info.PaddingRight = Convert.ToByte(paddingValues[1], CultureInfo.InvariantCulture);
                        bmfFile.Info.PaddingDown = Convert.ToByte(paddingValues[2], CultureInfo.InvariantCulture);
                        bmfFile.Info.PaddingLeft = Convert.ToByte(paddingValues[3], CultureInfo.InvariantCulture);
                    }
                    break;
                case "spacing":
                    var spacingValues = split[1].Split(',');
                    if (spacingValues.Length == 2)
                    {
                        bmfFile.Info.SpacingHoriz = Convert.ToSByte(spacingValues[0], CultureInfo.InvariantCulture);
                        bmfFile.Info.SpacingVert = Convert.ToSByte(spacingValues[1], CultureInfo.InvariantCulture);
                    }
                    break;
                case "outline":
                    bmfFile.Info.Outline = Convert.ToByte(split[1], CultureInfo.InvariantCulture);
                    break;
            }
        }
    }

    private static void ReadCommonTokens(BitmapFontFileContent bmfFile, ReadOnlySpan<string> tokens)
    {
        for (int i = 0; i < tokens.Length; ++i)
        {
            var split = tokens[i].Split('=');

            if (split.Length != 2)
            {
                continue;
            }

            switch (split[0])
            {
                case "lineHeight":
                    bmfFile.Common.LineHeight = Convert.ToUInt16(split[1], CultureInfo.InvariantCulture);
                    break;
                case "base":
                    bmfFile.Common.Base = Convert.ToUInt16(split[1], CultureInfo.InvariantCulture);
                    break;
                case "scaleW":
                    bmfFile.Common.ScaleW = Convert.ToUInt16(split[1], CultureInfo.InvariantCulture);
                    break;
                case "scaleH":
                    bmfFile.Common.ScaleH = Convert.ToUInt16(split[1], CultureInfo.InvariantCulture);
                    break;
                case "pages":
                    bmfFile.Common.Pages = Convert.ToUInt16(split[1], CultureInfo.InvariantCulture);
                    break;
                case "packed":
                    var packed = Convert.ToByte(split[1], CultureInfo.InvariantCulture);
                    bmfFile.Common.BitField |= (byte)(packed << 7);
                    break;
                case "alphaChnl":
                    bmfFile.Common.AlphaChnl = Convert.ToByte(split[1], CultureInfo.InvariantCulture);
                    break;
                case "redChnl":
                    bmfFile.Common.RedChnl = Convert.ToByte(split[1], CultureInfo.InvariantCulture);
                    break;
                case "greenChnl":
                    bmfFile.Common.GreenChnl = Convert.ToByte(split[1], CultureInfo.InvariantCulture);
                    break;
                case "blueChnl":
                    bmfFile.Common.BlueChnl = Convert.ToByte(split[1], CultureInfo.InvariantCulture);
                    break;
            }
        }
    }

    private static void ReadPageTokens(BitmapFontFileContent bmfFile, ReadOnlySpan<string> tokens)
    {
        for (var i = 0; i < tokens.Length; ++i)
        {
            var split = tokens[i].Split('=');

            if (split.Length != 2)
            {
                continue;
            }

            if (split[0] == "file")
            {
                var page = split[1].Replace("\"", string.Empty);
                bmfFile.Pages.Add(page);
            }
        }
    }

    private static void ReadCharacterTokens(BitmapFontFileContent bmfFile, ReadOnlySpan<string> tokens)
    {
        var character = default(BitmapFontFileContent.CharacterBlock);

        for (var i = 0; i < tokens.Length; ++i)
        {
            var split = tokens[i].Split('=');

            if (split.Length != 2)
            {
                continue;
            }

            switch (split[0])
            {
                case "id":
                    character.ID = Convert.ToInt32(split[1], CultureInfo.InvariantCulture);
                    break;
                case "x":
                    character.X = Convert.ToUInt16(split[1], CultureInfo.InvariantCulture);
                    break;
                case "y":
                    character.Y = Convert.ToUInt16(split[1], CultureInfo.InvariantCulture);
                    break;
                case "width":
                    character.Width = Convert.ToUInt16(split[1], CultureInfo.InvariantCulture);
                    break;
                case "height":
                    character.Height = Convert.ToUInt16(split[1], CultureInfo.InvariantCulture);
                    break;
                case "xoffset":
                    character.XOffset = Convert.ToInt16(split[1], CultureInfo.InvariantCulture);
                    break;
                case "yoffset":
                    character.YOffset = Convert.ToInt16(split[1], CultureInfo.InvariantCulture);
                    break;
                case "xadvance":
                    character.XAdvance = Convert.ToInt16(split[1], CultureInfo.InvariantCulture);
                    break;
                case "page":
                    character.Page = Convert.ToByte(split[1], CultureInfo.InvariantCulture);
                    break;
                case "chnl":
                    character.Chnl = Convert.ToByte(split[1], CultureInfo.InvariantCulture);
                    break;
            }
        }

        bmfFile.Characters.Add(character);
    }

    private static void ReadKerningTokens(BitmapFontFileContent bmfFile, ReadOnlySpan<string> tokens)
    {
        var kerning = default(BitmapFontFileContent.KerningPairsBlock);

        for (var i = 0; i < tokens.Length; ++i)
        {
            var split = tokens[i].Split('=');

            if (split.Length != 2)
            {
                continue;
            }

            switch (split[0])
            {
                case "first":
                    kerning.First = Convert.ToUInt32(split[1], CultureInfo.InvariantCulture);
                    break;
                case "second":
                    kerning.Second = Convert.ToUInt32(split[1], CultureInfo.InvariantCulture);
                    break;
                case "amount":
                    kerning.Amount = Convert.ToInt16(split[1], CultureInfo.InvariantCulture);
                    break;
            }
        }

        bmfFile.Kernings.Add(kerning);
    }

    private static List<string> GetTokens(ReadOnlySpan<char> line)
    {
        var tokens = new List<string>();
        var currentToken = new StringBuilder();
        var inQuotes = false;

        for (int i = 0; i < line.Length; i++)
        {
            var c = line[i];

            if (c == ' ' && !inQuotes)
            {
                if (currentToken.Length > 0)
                {
                    tokens.Add(currentToken.ToString());
                    currentToken.Clear();
                }
            }
            else if (c == '"')
            {
                inQuotes = !inQuotes;
            }
            else
            {
                currentToken.Append(c);
            }
        }

        if (currentToken.Length > 0)
        {
            tokens.Add(currentToken.ToString());
        }

        return tokens;
    }

    #endregion --------------------- Read BMFFont Text Formatted File -------------------------------------------------


}