From 9be73a459c989cb312c780096014f97af0822166 Mon Sep 17 00:00:00 2001
From: Igor Melo <igoracmelo@protonmail.com>
Date: Wed, 10 Jun 2026 00:36:15 -0300
Subject: [PATCH] libretro.melondsds: custom updateScript

---
 .../emulators/libretro/cores/melondsds.nix    | 89 ++++++++++++++++++-
 1 file changed, 85 insertions(+), 4 deletions(-)

diff --git a/pkgs/applications/emulators/libretro/cores/melondsds.nix b/pkgs/applications/emulators/libretro/cores/melondsds.nix
index aad929747265..cfcddf3a523a 100644
--- a/pkgs/applications/emulators/libretro/cores/melondsds.nix
+++ b/pkgs/applications/emulators/libretro/cores/melondsds.nix
@@ -1,16 +1,24 @@
 {
   lib,
   applyPatches,
+  coreutils,
   fetchFromGitHub,
-  glm,
-  libslirp,
   fmt_11,
-  span-lite,
+  glm,
+  gnugrep,
+  gnused,
   howard-hinnant-date,
+  jq,
   libGL,
   libGLU,
-  cmake,
+  libslirp,
   mkLibretroCore,
+  nix,
+  nix-prefetch-git,
+  cmake,
+  span-lite,
+  unstableGitUpdater,
+  writeShellApplication,
 }:
 let
   # https://github.com/JesseTG/melonds-ds/blob/33c48260402865ef77667487528efd5ca7ce1233/cmake/FetchDependencies.cmake#L44
@@ -99,6 +107,79 @@ mkLibretroCore rec {
 
   postBuild = "cd src/libretro";
 
+  passthru.updateScript = [
+    (lib.getExe (writeShellApplication {
+      name = "update-libretro-melondsds";
+      runtimeInputs = [
+        coreutils
+        gnugrep
+        gnused
+        jq
+        nix
+        nix-prefetch-git
+      ];
+      text = ''
+        ${lib.escapeShellArgs (unstableGitUpdater {
+          hardcodeZeroVersion = true;
+        })}
+
+        src=$(nix-build --no-out-link -A "$UPDATE_NIX_ATTR_PATH.src")
+        core_file="pkgs/applications/emulators/libretro/cores/melondsds.nix"
+
+        # find lines in the format:
+        #   fetch_dependency(name url rev)
+        # and extracts name, url and rev
+        grep "^fetch_dependency" "''${src}/cmake/FetchDependencies.cmake" |
+          sed 's/"//g' |
+          sed 's/fetch_dependency(\(.*\))/\1/' |
+          while read -r name url rev
+          do
+            echo >&2
+
+            # example: if there is fetch_dependency(melonDS ...) and no melonDS-src
+            if ! fetch_block=$(grep -A10 "''${name}-src =" "$core_file")
+            then
+
+              # if the dependency comes from nix, we just skip it
+              if grep -q "FETCHCONTENT_SOURCE_DIR_''${name^^}" "$core_file"
+              then
+                echo "> skipped: ''${name} is provided by nixpkgs" >&2
+                continue
+              fi
+
+              # otherwise, its a new dependency not specified on the config, and the updater can't continue
+              echo "> ERROR: dependency missing: ''${name}" >&2
+              exit 1
+            fi
+
+            echo "> ''${name}: ''${url} (''${rev})" >&2
+
+            prefetch=$(nix-prefetch-git --url "''${url}" --rev "''${rev}" --quiet)
+            rev=$(echo "$prefetch" | jq -r ".rev")
+            hash=$(echo "$prefetch" | jq -r ".hash")
+
+            old_rev=$(echo "$fetch_block" | grep -m1 "rev =" | sed 's/\s*rev = "\(.*\)".*/\1/')
+            old_hash=$(echo "$fetch_block" | grep -m1 "hash =" | sed 's/\s*hash = "\(.*\)".*/\1/')
+
+            if [[ "$old_hash" == "$hash" ]]
+            then
+              echo "> skipped: same hash" >&2
+              continue
+            fi
+
+            echo "rev - old: $old_rev" >&2
+            echo "rev - new: $rev" >&2
+            echo "hash - old: $old_hash" >&2
+            echo "hash - new: $hash" >&2
+
+            # finally replace old revision and old hash by the new one
+            sed -i "s|$old_hash|$hash|" "$core_file"
+            sed -i "s/$old_rev/$rev/" "$core_file"
+          done
+      '';
+    }))
+  ];
+
   meta = {
     description = "A remake of the libretro MelonDS core";
     homepage = "https://github.com/JesseTG/melonds-ds";