namespace GB5Shared.DocumentMerge;

/// <summary>
/// Result of a document merge — the merged file's bytes plus enough metadata for a caller to
/// save it (e.g. via the ECM/TATTACHMENT pattern) or stream it back in an HTTP response.
/// </summary>
public class DocumentMergeResultDTO
{
    public byte[] Content     { get; set; } = System.Array.Empty<byte>();
    public string ContentType { get; set; } = string.Empty;
    public string FileName    { get; set; } = string.Empty;
}

/// <summary>
/// Shared, module-independent Word/Excel template merge engine (plan: "Document Generation
/// Engine — shared foundation, not Correspondence-specific"). Consumers (Correspondence today;
/// a future Sales/CRM quotation generator later) own their own template storage and data
/// assembly — this service only knows how to merge bytes + field values into a finished
/// document. It never touches TATTACHMENT/ECM or any DB table directly (GB5Shared must not
/// depend on FrameworkDAL/FrameworkBLL) — callers load template bytes and pass them in.
/// </summary>
public interface IDocumentMergeService
{
    /// <summary>
    /// Merges a .docx or .xlsx template (detected from <paramref name="templateFileName"/>'s
    /// extension) against <paramref name="fields"/> (flat placeholder values, ##FieldName##) and
    /// <paramref name="tables"/> (named repeating-row datasets — each key is the repeat-region
    /// name used in the template via a ##REPEAT:Name## marker row/table-row, each value is the
    /// list of per-row field dictionaries). Conditional blocks (##IF:Field##...##ENDIF##) and
    /// image fields (##IMG:Field## with a <c>byte[]</c> value in <paramref name="fields"/>) are
    /// resolved automatically by whichever engine handles the file type.
    /// </summary>
    Task<DocumentMergeResultDTO> MergeAsync(
        byte[] templateBytes,
        string templateFileName,
        IReadOnlyDictionary<string, object?> fields,
        IReadOnlyDictionary<string, IReadOnlyList<IReadOnlyDictionary<string, object?>>>? tables = null,
        CancellationToken ct = default);
}

/// <summary>
/// Facade that dispatches to <see cref="IWordMergeEngine"/> or <see cref="IExcelMergeEngine"/>
/// based on the template's file extension.
/// </summary>
public sealed class DocumentMergeService(
    IWordMergeEngine  _wordEngine,
    IExcelMergeEngine _excelEngine
) : IDocumentMergeService
{
    public async Task<DocumentMergeResultDTO> MergeAsync(
        byte[] templateBytes,
        string templateFileName,
        IReadOnlyDictionary<string, object?> fields,
        IReadOnlyDictionary<string, IReadOnlyList<IReadOnlyDictionary<string, object?>>>? tables = null,
        CancellationToken ct = default)
    {
        if (templateBytes is null || templateBytes.Length == 0)
            throw new ArgumentException("Template bytes cannot be empty.", nameof(templateBytes));

        var ext = Path.GetExtension(templateFileName).ToLowerInvariant();

        return ext switch
        {
            ".docx" => await _wordEngine.MergeAsync(templateBytes, fields, tables, ct).ConfigureAwait(false),
            ".xlsx" => await _excelEngine.MergeAsync(templateBytes, fields, tables, ct).ConfigureAwait(false),
            _ => throw new NotSupportedException(
                $"Unsupported template file type '{ext}'. Only .docx and .xlsx templates are supported.")
        };
    }
}