1 files changed, 260 insertions, 3 deletions
diff --git a/internal/comic/pdf.go b/internal/comic/pdf.go
index 23a7e11..15288dc 100644
--- a/internal/comic/pdf.go
+++ b/internal/comic/pdf.go
@@ -2,13 +2,69 @@ package comic
 
 import (
 	"fmt"
+	"image"
+	_ "image/png"
+	"math"
+	"os"
 	"os/exec"
 	"path/filepath"
 	"strings"
 )
 
+// PDFAssembleOptions configures ImageMagick conversion when building the comic PDF.
+type PDFAssembleOptions struct {
+	// Density is passed to ImageMagick -density (DPI for the vector/page coordinate system).
+	Density int
+	// JPEGQuality is 0 for default lossless-style output, or 1–100 for JPEG compression
+	// inside the PDF (smaller files, similar to a "compressed" comic PDF).
+	JPEGQuality int
+	// Presentation is one of:
+	//   none  — full bleed
+	//   print — light matte border, then each page is fitted to ISO A4 portrait at pdf.density
+	//   book  — aged newsprint, tilt, shadow, thick page-edge strip, then ISO A4 portrait pages
+	Presentation string
+}
+
+// BookPageAspectRatio is the Gemini image aspect ratio for pdf.presentation print or book.
+// API-supported ratio closest to ISO 216 A4 portrait (210×297 mm, 1:√2).
+const BookPageAspectRatio = "3:4"
+
+const (
+	pdfPresentationNone  = "none"
+	pdfPresentationPrint = "print"
+	pdfPresentationBook  = "book"
+
+	printMatteColor = "#f4efe6"
+	bookDeskColor   = "#ebe6dc"
+	// bookEdgeGradient is drawn on the outer vertical edge after tilt (paper → block shadow).
+	bookEdgeGradient = "gradient:#ddd7cd-#2c2926"
+
+	// bookAged* tune the “yellowed / shelf-worn” pass (ImageMagick) before tilt/shadow.
+	bookAgedModulate      = "100,86,100" // brightness,saturation,hue
+	bookAgedSepiaPercent  = "16%"
+	bookAgedNoiseAtten    = "0.4"
+	bookAgedVignetteBlur  = "0x22"
+	bookAgedVignetteLevel = "50x100%" // edge darkening strength
+)
+
+// IsBookPDFPresentation reports whether p selects the book (aged / tilt / shadow) PDF pipeline.
+func IsBookPDFPresentation(p string) bool {
+	return strings.ToLower(strings.TrimSpace(p)) == pdfPresentationBook
+}
+
+// IsDINA4ClassPDFPresentation reports whether p assembles each PDF page at ISO A4 portrait
+// (210×297 mm at the configured density): print or book.
+func IsDINA4ClassPDFPresentation(p string) bool {
+	switch strings.ToLower(strings.TrimSpace(p)) {
+	case pdfPresentationPrint, pdfPresentationBook:
+		return true
+	default:
+		return false
+	}
+}
+
 // AssembleComicPDF combines comic pages into a PDF using ImageMagick.
-func AssembleComicPDF(outputDir, titleSlug string, imagePaths []string) (string, error) {
+func AssembleComicPDF(outputDir, titleSlug string, imagePaths []string, opts PDFAssembleOptions) (string, error) {
 	if len(imagePaths) == 0 {
 		return "", fmt.Errorf("no comic images to assemble into PDF")
 	}
@@ -16,9 +72,53 @@ func AssembleComicPDF(outputDir, titleSlug string, imagePaths []string) (string,
 		return "", fmt.Errorf("ImageMagick 'convert' not found — install ImageMagick to generate the PDF")
 	}
 
+	opts = normalizePDFAssembleOptions(opts)
 	pdfPath := filepath.Join(outputDir, titleSlug+".pdf")
-	args := []string{"-density", "150"}
-	args = append(args, imagePaths...)
+
+	inputs := imagePaths
+	if opts.Presentation == pdfPresentationPrint || opts.Presentation == pdfPresentationBook {
+		tmpDir, err := os.MkdirTemp("", "comicforge-pdf-*")
+		if err != nil {
+			return "", fmt.Errorf("temp dir for pdf frames: %w", err)
+		}
+		defer func() { _ = os.RemoveAll(tmpDir) }()
+
+		inputs = make([]string, len(imagePaths))
+		for i, src := range imagePaths {
+			dst := filepath.Join(tmpDir, fmt.Sprintf("frame_%04d.png", i))
+			var ferr error
+			switch opts.Presentation {
+			case pdfPresentationPrint:
+				ferr = renderPrintFrame(src, dst)
+			case pdfPresentationBook:
+				ferr = renderBookFrame(src, dst, tmpDir, i)
+			}
+			if ferr != nil {
+				return "", ferr
+			}
+			inputs[i] = dst
+		}
+
+		fitBG := printMatteColor
+		if opts.Presentation == pdfPresentationBook {
+			fitBG = bookDeskColor
+		}
+		fitted := make([]string, len(inputs))
+		for i, p := range inputs {
+			out := filepath.Join(tmpDir, fmt.Sprintf("din_a4_%04d.png", i))
+			if err := fitRasterPageToDINA4(p, out, opts.Density, fitBG); err != nil {
+				return "", err
+			}
+			fitted[i] = out
+		}
+		inputs = fitted
+	}
+
+	args := []string{"-density", fmt.Sprintf("%d", opts.Density)}
+	args = append(args, inputs...)
+	if opts.JPEGQuality > 0 {
+		args = append(args, "-compress", "JPEG", "-quality", fmt.Sprintf("%d", opts.JPEGQuality))
+	}
 	args = append(args, pdfPath)
 
 	cmd := exec.Command("convert", args...)
@@ -28,3 +128,160 @@ func AssembleComicPDF(outputDir, titleSlug string, imagePaths []string) (string,
 	}
 	return pdfPath, nil
 }
+
+func renderPrintFrame(src, dst string) error {
+	args := []string{
+		src,
+		"-background", printMatteColor,
+		"-gravity", "center",
+		"-extent", "108%x108%",
+		dst,
+	}
+	cmd := exec.Command("convert", args...)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		return fmt.Errorf("convert matte frame: %w\n%s", err, strings.TrimSpace(string(out)))
+	}
+	return nil
+}
+
+func renderBookAgedPage(src, dst string) error {
+	// Sepia + desaturation + fine grain + vignette ≈ old newsprint / stored comic.
+	args := []string{
+		src,
+		"-modulate", bookAgedModulate,
+		"-sepia-tone", bookAgedSepiaPercent,
+		"-attenuate", bookAgedNoiseAtten,
+		"+noise", "Gaussian",
+		"(", "+clone", "-colorspace", "gray", "-blur", bookAgedVignetteBlur, "+level", bookAgedVignetteLevel, ")",
+		"-compose", "multiply",
+		"-composite",
+		dst,
+	}
+	cmd := exec.Command("convert", args...)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		return fmt.Errorf("convert book aged page: %w\n%s", err, strings.TrimSpace(string(out)))
+	}
+	return nil
+}
+
+func renderBookFrame(src, dst, tmpDir string, pageIndex int) error {
+	aged := filepath.Join(tmpDir, fmt.Sprintf("book_aged_%04d.png", pageIndex))
+	if err := renderBookAgedPage(src, aged); err != nil {
+		return err
+	}
+
+	step1 := filepath.Join(tmpDir, fmt.Sprintf("book_step1_%04d.png", pageIndex))
+	angle := 2.1
+	if pageIndex%2 == 1 {
+		angle = -2.1
+	}
+	// Room for shadow after rotation; cream fill for empty corners.
+	args := []string{
+		aged,
+		"-background", printMatteColor,
+		"-gravity", "center",
+		"-extent", "125%x125%",
+		"-background", printMatteColor,
+		"-rotate", fmt.Sprintf("%.1f", angle),
+		"(", "+clone", "-background", "black", "-shadow", "78x5+14+22", ")",
+		"+swap",
+		"-background", bookDeskColor,
+		"-layers", "merge",
+		"+repage",
+		step1,
+	}
+	cmd := exec.Command("convert", args...)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		return fmt.Errorf("convert book frame (tilt/shadow): %w\n%s", err, strings.TrimSpace(string(out)))
+	}
+
+	h, err := imageHeight(step1)
+	if err != nil {
+		return fmt.Errorf("book frame dimensions: %w", err)
+	}
+	if h < 1 {
+		h = 1
+	}
+	grad := filepath.Join(tmpDir, fmt.Sprintf("book_grad_%04d.png", pageIndex))
+	cmd = exec.Command("convert", "-size", fmt.Sprintf("12x%d", h), bookEdgeGradient, grad)
+	out, err = cmd.CombinedOutput()
+	if err != nil {
+		return fmt.Errorf("convert book edge gradient: %w\n%s", err, strings.TrimSpace(string(out)))
+	}
+
+	cmd = exec.Command("convert", step1, grad, "-gravity", "east", "-compose", "over", "-composite", dst)
+	out, err = cmd.CombinedOutput()
+	if err != nil {
+		return fmt.Errorf("convert book frame (edge): %w\n%s", err, strings.TrimSpace(string(out)))
+	}
+	return nil
+}
+
+func dinAPortraitPixels(dpi int) (w, h int) {
+	const mmW, mmH = 210.0, 297.0
+	w = int(math.Round(float64(dpi) * mmW / 25.4))
+	h = int(math.Round(float64(dpi) * mmH / 25.4))
+	if w < 1 {
+		w = 1
+	}
+	if h < 1 {
+		h = 1
+	}
+	return w, h
+}
+
+// fitRasterPageToDINA4 letterboxes or fits raster art into exact ISO A4 portrait pixels at the given DPI.
+// background is the letterbox / pad color (print matte vs book desk).
+func fitRasterPageToDINA4(src, dst string, density int, background string) error {
+	w, h := dinAPortraitPixels(density)
+	if strings.TrimSpace(background) == "" {
+		background = printMatteColor
+	}
+	args := []string{
+		src,
+		"-resize", fmt.Sprintf("%dx%d", w, h),
+		"-background", background,
+		"-gravity", "center",
+		"-extent", fmt.Sprintf("%dx%d", w, h),
+		dst,
+	}
+	cmd := exec.Command("convert", args...)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		return fmt.Errorf("convert DIN A4 page: %w\n%s", err, strings.TrimSpace(string(out)))
+	}
+	return nil
+}
+
+func imageHeight(path string) (int, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return 0, err
+	}
+	defer func() { _ = f.Close() }()
+	cfg, _, err := image.DecodeConfig(f)
+	if err != nil {
+		return 0, err
+	}
+	return cfg.Height, nil
+}
+
+func normalizePDFAssembleOptions(o PDFAssembleOptions) PDFAssembleOptions {
+	if o.Density <= 0 {
+		o.Density = 150
+	}
+	if o.JPEGQuality < 0 {
+		o.JPEGQuality = 0
+	}
+	if o.JPEGQuality > 100 {
+		o.JPEGQuality = 100
+	}
+	o.Presentation = strings.ToLower(strings.TrimSpace(o.Presentation))
+	if o.Presentation == "" {
+		o.Presentation = pdfPresentationNone
+	}
+	return o
+}