using System;
using System.IO;
using System.Printing;

namespace Elwig.Helpers.Printing {
    public class PdfPrinter {

        public string PrinterName { get; init; }

        public PdfPrinter(string? printerName = null) {
            PrinterName = printerName ?? GetDefaultPrinterName() ?? throw new InvalidOperationException("No default Windows printer is configured.");
        }

        public void Print(string pdfPath, int copies = 1, bool doublePaged = false) {
            if (!File.Exists(pdfPath)) throw new FileNotFoundException("PDF file not found.", pdfPath);

            IntPtr document = PdfiumNative.FPDF_LoadDocument(pdfPath, null);
            if (document == IntPtr.Zero) throw new InvalidOperationException("PDFium could not open the PDF.");

            try {
                int pageCount = PdfiumNative.FPDF_GetPageCount(document);
                if (pageCount <= 0)
                    return;

                using var printer = new Win32Printer.Printer(PrinterName);
                printer.TrySetDuplex(doublePaged ? Duplexing.TwoSidedLongEdge : Duplexing.OneSided);
                for (int i = 0; i < copies; i++) {
                    printer.StartDocument(Path.GetFileName(pdfPath));
                    bool documentStarted = true;
                    try {
                        for (int j = 0; j < pageCount; j++) {
                            PrintPage(document, printer, j);
                        }
                        printer.EndDocument();
                        documentStarted = false;
                    } finally {
                        if (documentStarted) printer.AbortDocument();
                    }
                }
            } finally {
                PdfiumNative.FPDF_CloseDocument(document);
            }
        }

        private static void PrintPage(IntPtr document, Win32Printer.Printer printer, int pageIndex) {
            if (!PdfiumNative.FPDF_GetPageSizeByIndex(document, pageIndex, out double pageWidthPt, out double pageHeightPt)) {
                throw new InvalidOperationException($"Unable to obtain PDF page {pageIndex} size.");
            }

            IntPtr page = PdfiumNative.FPDF_LoadPage(document, pageIndex);
            if (page == IntPtr.Zero)
                throw new InvalidOperationException($"Unable to load PDF page {pageIndex}.");

            try {
                // PDF coordinates are points (1/72 inch).
                //
                // HORZRES/VERTRES are the printable area in
                // device pixels for the current printer DC.
                int widthPx = printer.PixelWidth;
                int heightPx = printer.PixelHeight;

                // Preserve aspect ratio.
                double scaleX = widthPx / pageWidthPt;
                double scaleY = heightPx / pageHeightPt;
                double scale = Math.Min(scaleX, scaleY);
                int renderWidth = Math.Max(1, (int)Math.Round(pageWidthPt * scale));
                int renderHeight = Math.Max(1, (int)Math.Round(pageHeightPt * scale));
                int offsetX = (widthPx - renderWidth) / 2;
                int offsetY = (heightPx - renderHeight) / 2;

                printer.StartPage();
                try {
                    PdfiumNative.FPDF_RenderPage(printer.Hdc, page, offsetX, offsetY, renderWidth, renderHeight, 0, PdfiumNative.FPDF_PRINTING | PdfiumNative.FPDF_ANNOT);
                } finally {
                    printer.EndPage();
                }
            } finally {
                PdfiumNative.FPDF_ClosePage(page);
            }
        }

        private static string? GetDefaultPrinterName() {
            using var key = Microsoft.Win32.Registry.CurrentUser.OpenSubKey(@"Software\Microsoft\Windows NT\CurrentVersion\Windows");
            string? printer = key?.GetValue("Device") as string;
            if (string.IsNullOrWhiteSpace(printer))
                return null;

            // Device has the form:
            // Printer Name,winspool,PORT
            int comma = printer.IndexOf(',');
            return comma >= 0 ? printer[..comma] : printer;
        }
    }
}