nix: add derivation to build docs site

using pandoc, tailwindcss, our standard fonts and lucide, we can build a
simple docs site with a single pandoc command.

Signed-off-by: oppiliappan <[e-mail]>

flake.nix

···
           inherit htmx-src htmx-ws-src lucide-src inter-fonts-src ibm-plex-mono-src actor-typeahead-src;
         };
         appview = self.callPackage ./nix/pkgs/appview.nix {};
+        docs = self.callPackage ./nix/pkgs/docs.nix {
+          inherit inter-fonts-src ibm-plex-mono-src lucide-src;
+        };
         spindle = self.callPackage ./nix/pkgs/spindle.nix {};
         knot-unwrapped = self.callPackage ./nix/pkgs/knot-unwrapped.nix {};
         knot = self.callPackage ./nix/pkgs/knot.nix {};
       });
   in {
     overlays.default = final: prev: {
-      inherit (mkPackageSet final) lexgen goat sqlite-lib spindle knot-unwrapped knot appview;
+      inherit (mkPackageSet final) lexgen goat sqlite-lib spindle knot-unwrapped knot appview docs;
     };
 
     packages = forAllSystems (system: let
···
       staticPackages = mkPackageSet pkgs.pkgsStatic;
       crossPackages = mkPackageSet pkgs.pkgsCross.gnu64.pkgsStatic;
     in {
-      inherit (packages) appview appview-static-files lexgen goat spindle knot knot-unwrapped sqlite-lib;
+      inherit (packages) appview appview-static-files lexgen goat spindle knot knot-unwrapped sqlite-lib docs;
 
       pkgsStatic-appview = staticPackages.appview;
       pkgsStatic-knot = staticPackages.knot;

nix/pkgs/docs.nix

···
+{
+  pandoc,
+  tailwindcss,
+  runCommandLocal,
+  inter-fonts-src,
+  ibm-plex-mono-src,
+  lucide-src,
+  src,
+}:
+runCommandLocal "docs" {} ''
+  mkdir -p working
+
+  # copy templates, themes, styles, filters to working directory
+  cp ${src}/docs/*.html working/
+  cp ${src}/docs/*.theme working/
+  cp ${src}/docs/*.css working/
+
+  # icons
+  cp -rf ${lucide-src}/*.svg working/
+
+  # content
+  ${pandoc}/bin/pandoc ${src}/docs/DOCS.md \
+    -o $out/ \
+    -t chunkedhtml \
+    --variable toc \
+    --toc-depth=2 \
+    --css=stylesheet.css \
+    --chunk-template="%i.html" \
+    --highlight-style=working/highlight.theme \
+    --template=working/template.html
+
+  # fonts
+  mkdir -p $out/static/fonts
+  cp -f ${inter-fonts-src}/web/InterVariable*.woff2 $out/static/fonts/
+  cp -f ${inter-fonts-src}/web/InterDisplay*.woff2 $out/static/fonts/
+  cp -f ${inter-fonts-src}/InterVariable*.ttf $out/static/fonts/
+  cp -f ${ibm-plex-mono-src}/fonts/complete/woff2/IBMPlexMono*.woff2 $out/static/fonts/
+
+  # styles
+  cd ${src} && ${tailwindcss}/bin/tailwindcss -i input.css -o $out/stylesheet.css
+''