using DevExpress.Pdf;
using DocumentOperator.Application.Common.Interfaces;
using DocumentOperator.Domain.Common.Exceptions;

namespace DocumentOperator.Infrastructure.Services.PdfProcessing;

/// <summary>
/// PDF processor implementation using DevExpress.Pdf library.
/// Handles PDF validation and metadata extraction.
/// </summary>
public class DevExpressPdfProcessor : IPdfProcessor
{
    /// <summary>
    /// Validates a PDF document and returns metadata.
    /// </summary>
    /// <param name="pdfBytes">PDF content as byte array</param>
    /// <returns>PDF metadata (page count, file size, version, etc.)</returns>
    /// <exception cref="PdfProcessingException">Thrown when PDF is invalid or null</exception>
    public async Task<DocumentOperator.Domain.Models.ValueObjects.PdfMetadata> ValidateAsync(byte[] pdfBytes)
    {
        // 1. Input Validation (Defensive Programming)
        if (pdfBytes == null)
        {
            throw new PdfProcessingException("PDF bytes cannot be null");
        }

        if (pdfBytes.Length == 0)
        {
            throw new PdfProcessingException("PDF bytes cannot be empty");
        }

        try
        {
            // 2. Load PDF with DevExpress Document API (PdfDocumentProcessor)
            using var processor = new PdfDocumentProcessor();
            processor.LoadDocument(new MemoryStream(pdfBytes));

            // 3. Extract metadata
            var document = processor.Document;

            int pageCount = document.Pages.Count;
            string pdfVersion = document.Version.ToString(); // z.B. "1.4", "1.7"

            // Attachments (embedded files)
            // DevExpress PdfDocument API doesn't expose EmbeddedFiles directly.
            // We use a simple PDF raw data scan for "/EmbeddedFiles" keyword.
            // This is a pragmatic approach until Feature 2 (ExtractAttachments) is implemented.
            bool hasAttachments = DetectEmbeddedFiles(pdfBytes);
            int attachmentCount = hasAttachments ? -1 : 0; // -1 = "has attachments, count unknown"

            // 4. Create and return PdfMetadata Value Object (fully qualified name!)
            return new DocumentOperator.Domain.Models.ValueObjects.PdfMetadata(
                pageCount: pageCount,
                fileSizeBytes: pdfBytes.Length,
                pdfVersion: pdfVersion,
                hasAttachments: hasAttachments,
                attachmentCount: attachmentCount
            );
        }
        catch (Exception ex) when (ex is not PdfProcessingException)
        {
            // Wrap DevExpress exceptions in our domain exception
            throw new PdfProcessingException(
                $"Failed to validate PDF: {ex.Message}",
                ex);
        }
    }

    /// <summary>
    /// Detects embedded files in PDF by scanning raw PDF data for /EmbeddedFiles keyword.
    /// This is a pragmatic approach as DevExpress PdfDocument API doesn't expose EmbeddedFiles directly.
    /// </summary>
    /// <param name="pdfBytes">PDF raw bytes</param>
    /// <returns>True if PDF contains /EmbeddedFiles keyword in proper context, false otherwise</returns>
    private static bool DetectEmbeddedFiles(byte[] pdfBytes)
    {
        // PDF embedded files are declared in the document catalog:
        // /Names << /EmbeddedFiles << /Names [...] >> >>
        // We search for the pattern "/Names" followed by "/EmbeddedFiles"

        string pdfText = System.Text.Encoding.ASCII.GetString(pdfBytes);

        // Look for the specific PDF dictionary pattern: /Names and /EmbeddedFiles
        // This is more precise than just searching for /EmbeddedFiles alone
        int namesIndex = pdfText.IndexOf("/Names", StringComparison.Ordinal);
        if (namesIndex == -1)
            return false;

        // Check if /EmbeddedFiles appears after /Names within reasonable distance (< 1000 chars)
        int embeddedFilesIndex = pdfText.IndexOf("/EmbeddedFiles", namesIndex, Math.Min(1000, pdfText.Length - namesIndex), StringComparison.Ordinal);
        return embeddedFilesIndex > namesIndex;
    }
}