From b01a2a8a57b0854be4bb6c87b3de76fc43d7b211 Mon Sep 17 00:00:00 2001
From: Tobias Happ <tobias.happ@gmx.de>
Date: Thu, 27 Oct 2022 12:33:17 +0200
Subject: [PATCH] bootstrap: use env vars to set custom channel urls

---
 README.md        |  4 +++-
 pkgs/default.nix | 16 ++++++++++++----
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/README.md b/README.md
index 921f31c..9ebe633 100644
--- a/README.md
+++ b/README.md
@@ -137,7 +137,9 @@ To re-trigger the installation, you can use
 
 If you want to change the nix-on-droid channel to your custom one,
 you can do that either with `nix-channel` after the installation,
-or by using `--argstr nixOnDroidChannelURL <URL>`.
+or by setting the environment variable `NIX_ON_DROID_CHANNEL_URL`.
+Other environment variables are `NIXPKGS_CHANNEL_URL` an
+`NIX_ON_DROID_FLAKE_URL`.
 
 **Note**: The `proot` binary is not built on the android device
 (NDK is required for building it, and it's not available on mobile platforms).
diff --git a/pkgs/default.nix b/pkgs/default.nix
index ef88518..ed965b6 100644
--- a/pkgs/default.nix
+++ b/pkgs/default.nix
@@ -14,6 +14,14 @@ let
 
   pkgs = import nixpkgs { inherit system; };
 
+  urlOptionValue = url: envVar:
+    let
+      envValue = builtins.getEnv envVar;
+    in
+    pkgs.lib.mkIf
+      (envValue != "" || url != null)
+      (if url == null then envValue else url);
+
   modules = import ../modules {
     inherit pkgs;
 
@@ -29,15 +37,15 @@ let
       # Fix invoking bash after initial build.
       user.shell = "${initialPackageInfo.bash}/bin/bash";
 
-      build = with pkgs.lib; {
+      build = {
         inherit arch;
 
         channel = {
-          nixpkgs = mkIf (nixpkgsChannelURL != null) nixpkgsChannelURL;
-          nix-on-droid = mkIf (nixOnDroidChannelURL != null) nixOnDroidChannelURL;
+          nixpkgs = urlOptionValue nixpkgsChannelURL "NIXPKGS_CHANNEL_URL";
+          nix-on-droid = urlOptionValue nixOnDroidChannelURL "NIX_ON_DROID_CHANNEL_URL";
         };
 
-        flake.nix-on-droid = mkIf (nixOnDroidFlakeURL != null) nixOnDroidFlakeURL;
+        flake.nix-on-droid = urlOptionValue nixOnDroidFlakeURL "NIX_ON_DROID_FLAKE_URL";
       };
     };
   };