namespace SimpleAdmin.Application;

/// <summary>
/// 负责从 DOCX 中识别占位符并在不依赖 Word 进程的情况下替换文本节点。
/// </summary>
public static class DocxTemplateProcessor
{
    private static readonly global::System.Text.RegularExpressions.Regex PlaceholderRegex = new(
        @"\{\{\s*(?<code>[A-Za-z][A-Za-z0-9_.-]*)\s*\}\}",
        global::System.Text.RegularExpressions.RegexOptions.Compiled);

    private static readonly global::System.Xml.Linq.XNamespace WordNamespace =
        "http://schemas.openxmlformats.org/wordprocessingml/2006/main";

    /// <summary>
    /// 扫描正文、表格、页眉和页脚，返回去重后的变量编码。
    /// </summary>
    public static List<string> ExtractVariableCodes(byte[] docx)
    {
        ValidateDocxHeader(docx);
        try
        {
            using var input = new MemoryStream(docx);
            using var archive = new global::System.IO.Compression.ZipArchive(
                input,
                global::System.IO.Compression.ZipArchiveMode.Read);
            if (archive.GetEntry("word/document.xml") == null)
                throw Oops.Bah("上传文件不是有效的 DOCX 文档，请使用 Word 或 WPS 另存为“Word 文档（*.docx）”后重新上传");

            var codes = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
            foreach (var entry in archive.Entries.Where(entry => IsWordTextXml(entry.FullName)))
            {
                using var stream = entry.Open();
                var document = global::System.Xml.Linq.XDocument.Load(stream);
                foreach (var paragraph in document.Descendants(WordNamespace + "p"))
                {
                    var text = string.Concat(paragraph.Descendants(WordNamespace + "t").Select(node => node.Value));
                    ValidatePlaceholderSyntax(text);
                    foreach (global::System.Text.RegularExpressions.Match match in PlaceholderRegex.Matches(text))
                        codes.Add(match.Groups["code"].Value.Trim());
                }
            }

            return codes.OrderBy(code => code).ToList();
        }
        catch (global::System.IO.InvalidDataException)
        {
            throw Oops.Bah("DOCX 文件结构已经损坏或上传不完整，请重新另存为 DOCX 后上传");
        }
        catch (global::System.Xml.XmlException)
        {
            throw Oops.Bah("DOCX 文件内部内容损坏，Word 可以尝试修复该文件；请修复并重新另存为 DOCX 后上传");
        }
    }

    /// <summary>
    /// 占位符提取正则只会匹配正确格式，因此必须先主动检查错误格式，
    /// 避免缺少花括号或变量编码写错时被静默忽略并继续创建版本。
    /// </summary>
    private static void ValidatePlaceholderSyntax(string text)
    {
        if (string.IsNullOrEmpty(text))
            return;

        if (text.Contains("｛｛", StringComparison.Ordinal)
            || text.Contains("｝｝", StringComparison.Ordinal))
        {
            throw Oops.Bah(
                "DOCX 占位符格式错误：检测到中文全角花括号。请使用英文半角双花括号，例如 {{employee.EmployeeName}}。");
        }

        if (text.Contains("{{{", StringComparison.Ordinal)
            || text.Contains("}}}", StringComparison.Ordinal))
        {
            throw Oops.Bah(
                "DOCX 占位符格式错误：检测到多余的花括号。占位符必须使用成对的英文半角双花括号，例如 {{employee.EmployeeName}}。");
        }

        var searchStart = 0;
        while (searchStart < text.Length)
        {
            var openIndex = text.IndexOf("{{", searchStart, StringComparison.Ordinal);
            var closeIndex = text.IndexOf("}}", searchStart, StringComparison.Ordinal);

            if (closeIndex >= 0 && (openIndex < 0 || closeIndex < openIndex))
            {
                throw Oops.Bah(
                    $"DOCX 占位符格式错误：{BuildPlaceholderPreview(text, closeIndex)} 缺少对应的起始符“{{{{”。正确格式示例：{{{{employee.EmployeeName}}}}。");
            }

            if (openIndex < 0)
                return;

            closeIndex = text.IndexOf("}}", openIndex + 2, StringComparison.Ordinal);
            if (closeIndex < 0)
            {
                throw Oops.Bah(
                    $"DOCX 占位符格式错误：{BuildPlaceholderPreview(text, openIndex)} 缺少结束符“}}}}”。正确格式示例：{{{{employee.EmployeeName}}}}。");
            }

            var placeholder = text.Substring(openIndex, closeIndex + 2 - openIndex);
            var match = PlaceholderRegex.Match(placeholder);
            if (!match.Success || match.Length != placeholder.Length)
            {
                throw Oops.Bah(
                    $"DOCX 占位符格式错误：“{placeholder}”。变量编码只能包含英文字母、数字、下划线、点和短横线，并且必须使用成对的英文半角双花括号。");
            }

            searchStart = closeIndex + 2;
        }
    }

    private static string BuildPlaceholderPreview(string text, int markerIndex)
    {
        const int maxLength = 60;
        var preview = text[markerIndex..].Trim();
        if (preview.Length > maxLength)
            preview = preview[..maxLength] + "…";
        return $"“{preview}”";
    }

    /// <summary>
    /// 使用任务变量快照替换 DOCX 中的占位符，支持占位符跨多个 Word 文本节点。
    /// </summary>
    public static byte[] Render(byte[] docx, IReadOnlyDictionary<string, string> values)
    {
        ValidateDocxHeader(docx);
        using var input = new MemoryStream(docx);
        using var archive = new global::System.IO.Compression.ZipArchive(
            input,
            global::System.IO.Compression.ZipArchiveMode.Read);
        using var output = new MemoryStream();
        using var target = new global::System.IO.Compression.ZipArchive(
            output,
            global::System.IO.Compression.ZipArchiveMode.Create,
            true);

        foreach (var entry in archive.Entries)
        {
            var next = target.CreateEntry(
                entry.FullName,
                global::System.IO.Compression.CompressionLevel.Optimal);
            using var sourceStream = entry.Open();
            using var targetStream = next.Open();
            if (!IsWordTextXml(entry.FullName))
            {
                sourceStream.CopyTo(targetStream);
                continue;
            }

            var document = global::System.Xml.Linq.XDocument.Load(sourceStream);
            foreach (var paragraph in document.Descendants(WordNamespace + "p"))
                ReplaceParagraphVariables(paragraph, values);
            document.Save(targetStream, global::System.Xml.Linq.SaveOptions.DisableFormatting);
        }

        target.Dispose();
        return output.ToArray();
    }

    private static void ReplaceParagraphVariables(
        global::System.Xml.Linq.XElement paragraph,
        IReadOnlyDictionary<string, string> values)
    {
        var replacements = 0;
        while (replacements < 1000)
        {
            var nodes = paragraph.Descendants(WordNamespace + "t").ToList();
            var text = string.Concat(nodes.Select(node => node.Value));
            var match = PlaceholderRegex.Matches(text)
                .Cast<global::System.Text.RegularExpressions.Match>()
                .LastOrDefault(item => values.ContainsKey(item.Groups["code"].Value.Trim()));
            if (match == null)
                return;

            var code = match.Groups["code"].Value.Trim();
            ReplaceRange(nodes, match.Index, match.Length, values[code] ?? string.Empty);
            replacements++;
        }

        throw Oops.Bah("合同模板单个段落中的变量数量异常");
    }

    private static void ReplaceRange(
        List<global::System.Xml.Linq.XElement> nodes,
        int start,
        int length,
        string replacement)
    {
        var end = start + length;
        var offset = 0;
        global::System.Xml.Linq.XElement startNode = null;
        global::System.Xml.Linq.XElement endNode = null;
        var startIndex = 0;
        var endIndex = 0;

        foreach (var node in nodes)
        {
            var nextOffset = offset + node.Value.Length;
            if (startNode == null && start >= offset && start < nextOffset)
            {
                startNode = node;
                startIndex = start - offset;
            }

            if (end > offset && end <= nextOffset)
            {
                endNode = node;
                endIndex = end - offset;
                break;
            }

            offset = nextOffset;
        }

        if (startNode == null || endNode == null)
            return;

        if (ReferenceEquals(startNode, endNode))
        {
            startNode.Value = startNode.Value[..startIndex]
                              + replacement
                              + startNode.Value[endIndex..];
            return;
        }

        var startNodePosition = nodes.IndexOf(startNode);
        var endNodePosition = nodes.IndexOf(endNode);
        startNode.Value = startNode.Value[..startIndex] + replacement;
        for (var index = startNodePosition + 1; index < endNodePosition; index++)
            nodes[index].Value = string.Empty;
        endNode.Value = endNode.Value[endIndex..];
    }

    private static bool IsWordTextXml(string entryName)
    {
        return entryName == "word/document.xml"
               || ((entryName.StartsWith("word/header", StringComparison.OrdinalIgnoreCase)
                    || entryName.StartsWith("word/footer", StringComparison.OrdinalIgnoreCase))
                   && entryName.EndsWith(".xml", StringComparison.OrdinalIgnoreCase));
    }

    /// <summary>
    /// 根据文件头识别真实格式，避免只修改扩展名的旧版 DOC 在解压时变成系统异常。
    /// </summary>
    private static void ValidateDocxHeader(byte[] docx)
    {
        if (docx == null || docx.Length < 4)
            throw Oops.Bah("上传的 DOCX 文件为空或上传不完整，请重新选择文件上传");

        // 旧版 Word 97-2003 二进制 DOC 使用 OLE Compound File 文件头：D0 CF 11 E0。
        if (docx[0] == 0xD0
            && docx[1] == 0xCF
            && docx[2] == 0x11
            && docx[3] == 0xE0)
        {
            throw Oops.Bah("上传文件实际是旧版 DOC 格式，不能直接修改后缀名；请使用 Word 或 WPS 另存为“Word 文档（*.docx）”后重新上传");
        }

        // DOCX 是 Open XML ZIP 包，正常文件以 PK 开头。
        if (docx[0] != 0x50 || docx[1] != 0x4B)
            throw Oops.Bah("上传文件的真实格式不是 DOCX，请使用 Word 或 WPS 另存为“Word 文档（*.docx）”后重新上传");
    }
}