From f3868f9d7be48f24a1505cd596f5b73ae733e916 Mon Sep 17 00:00:00 2001
From: Ekaitz Zarraga <ekaitz@elenq.tech>
Date: Tue, 16 Jul 2024 17:13:02 +0200
Subject: Add PDF cover creation system

---
 Makefile.scm          | 29 +++++++++++++++++++++++++++--
 utils/cover/cover.scm | 28 +++++++++++++++++++++++-----
 2 files changed, 50 insertions(+), 7 deletions(-)

diff --git a/Makefile.scm b/Makefile.scm
index 6a40e43..72565b4 100644
--- a/Makefile.scm
+++ b/Makefile.scm
@@ -4,6 +4,7 @@ exec chibi-scheme -A utils/ $0 $@
 |#
 (import (chibi)
         (chibi json)
+        (chibi string)
         (only (chibi filesystem)
               directory-files
               create-directory*
@@ -11,7 +12,6 @@ exec chibi-scheme -A utils/ $0 $@
         (chibi process)
         (only (chibi pathname) path-strip-directory path-extension make-path)
         ;(chibi app)
-        (only (chibi string) string-prefix? string-trim-right string-join)
         (prefix (chibi io) io:)
         (utils cover cover)
         (srfi 1)
@@ -180,6 +180,20 @@ exec chibi-scheme -A utils/ $0 $@
         files)
       "Error in ebook creation")))
 
+(define (get-print-box svg-file)
+  "SVG covers have a rectangle `meta-content-box` prepared to serve as the
+  printing bounding box. Its position is the (x0,y0) and (width,height) is
+  (x1,y1). This function extracts that information."
+  (string-join
+    (string-split
+      (process->string-or-fail
+        `("inkscape"
+          ,svg-file
+          "-I" "meta-content-box"
+          "-XYWH")
+        "Error: impossible to extract cover printing bounding box")
+      #\newline)
+    ":"))
 (define (make-cover lang output input)
   (let* ((outpath  (make-path output lang))
          (files    (directory-sources lang input))
@@ -197,7 +211,18 @@ exec chibi-scheme -A utils/ $0 $@
           "--export-filename" ,(make-path outpath "cover.pdf")
           "--export-type=pdf"
           ,svg-file))
-      "Error in cover creation")))
+      "Error in PDF cover creation")
+
+    (process->string-or-fail
+      (append
+        `("inkscape"
+          ,svg-file
+          "--export-filename" ,(make-path outpath "cover.png")
+          "--export-type=png"
+          "--export-background=white"
+          "--export-background-opacity=1.0"
+          "--export-area" ,(get-print-box svg-file)))
+      "Error in PNG cover creation")))
 
 (define (build-lang lang output input)
   (pandoc-web         lang output input)
diff --git a/utils/cover/cover.scm b/utils/cover/cover.scm
index 915f42a..65769a5 100644
--- a/utils/cover/cover.scm
+++ b/utils/cover/cover.scm
@@ -140,8 +140,12 @@
          (style
            (string-append
              "
+             #meta-content-box{
+             stroke: none;
+             fill:   none;
+             }
              .margin-mark {
-             stroke-width: 0.1;
+             stroke-width: 0.1mm;
              stroke-linecap: butt;
              stroke: red;
              }
@@ -245,6 +249,8 @@
         ;; CUTTING MARKS
         ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
         ,(map (lambda (posx posy rot)
+                (let* ((margin (- margin 0.1))
+                       (len    (* 0.6 margin)))
                 `(g (@ (id ,(string-append "marks-"
                                            (num posx)
                                            "-"
@@ -253,15 +259,15 @@
                     (line (@
                             (x1 ,(+ posx))
                             (y1 ,(+ posy margin))
-                            (x2 ,(+ posx (* 0.6 margin)))
+                            (x2 ,(+ posx len))
                             (y2 ,(+ posy margin))
                             (class "margin-mark")))
                     (line (@
                             (x1 ,(+ posx margin))
                             (y1 ,(+ posy))
                             (x2 ,(+ posx margin))
-                            (y2 ,(+ posy (* 0.6 margin)))
-                            (class "margin-mark")))))
+                            (y2 ,(+ posy len))
+                            (class "margin-mark"))))))
 
               (list 0 0      width width)
               (list 0 height 0     height)
@@ -272,7 +278,19 @@
                                                   (num height) ")")))
 
 
-        ;; BACK SIDE 
+         ; NOTE:
+         ; This element simulates the offset and size of the full page inside
+         ; the svg file.
+         ; inkscape cover.svg -I meta-content-box -XYWH
+         ; will return the bounding box of the printable part of the file in
+         ; X0\nY0\nX1\nY1 format
+         (rect (@ (id "meta-content-box")
+                  (x ,margin)
+                  (y ,margin)
+                  (width  ,(- width margin))
+                  (height ,(- height margin))))
+
+        ;; BACK SIDE
         ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
         ; TITLE + BOOK SUMMARY
-- 
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