DocumentService/DocumentService.Application/Common/DTOs/AttachmentInfo.cs

namespace DocumentService.Application.Common.DTOs;

/// <summary>
/// Represents complete attachment information for a PDF document.
/// Immutable value object containing attachment presence flag, count, and detailed metadata.
/// </summary>
public sealed class AttachmentInfo
{
    /// <summary>
    /// Gets a value indicating whether the PDF contains any attachments
    /// </summary>
    public bool HasAttachments { get; }

    /// <summary>
    /// Gets the total number of attachments in the PDF
    /// </summary>
    public int AttachmentCount { get; }

    /// <summary>
    /// Gets the collection of attachment metadata (file details)
    /// </summary>
    public IReadOnlyList<AttachmentMetadata> Attachments { get; }

    /// <summary>
    /// Initializes a new instance of the AttachmentInfo class.
    /// </summary>
    /// <param name="hasAttachments">Whether PDF has attachments</param>
    /// <param name="attachmentCount">Total number of attachments</param>
    /// <param name="attachments">List of attachment metadata (can be empty)</param>
    public AttachmentInfo(bool hasAttachments, int attachmentCount, IReadOnlyList<AttachmentMetadata> attachments)
    {
        HasAttachments = hasAttachments;
        AttachmentCount = attachmentCount;
        Attachments = attachments ?? [];

        // Defensive Programming: Ensure count matches list length
        if (Attachments.Count != attachmentCount)
        {
            throw new ArgumentException(
                $"Attachment count mismatch: expected {attachmentCount}, got {Attachments.Count}",
                nameof(attachments));
        }
    }

    /// <summary>
    /// Creates an AttachmentInfo instance for a PDF with no attachments.
    /// </summary>
    public static AttachmentInfo Empty =>
        new(
            hasAttachments: false,
            attachmentCount: 0,
            attachments: []);

    public override string ToString()
    {
        return HasAttachments
            ? $"PDF has {AttachmentCount} attachment(s): {string.Join(", ", Attachments.Select(a => a.FileName))}"
            : "PDF has no attachments";
    }
}