Use makefile for a reusable docker image

Dockerfile

@@ -1,6 +1,4 @@
-FROM zmkfirmware/zmk-build-arm:2.4
-
-RUN mkdir -p /app/firmware
+FROM zmkfirmware/zmk-build-arm:stable
 
 WORKDIR /app
 

Makefile

@@ -0,0 +1,21 @@
+.PHONY: clean timestamp setup
+
+all: setup build
+
+build: timestamp firmware/$$(TIMESTAMP)-left.uf2 firmware/$$(TIMESTAMP)-right.uf2
+
+clean:
+	rm ./firmware/*.uf2
+
+firmware/%-left.uf2 firmware/%-right.uf2: config/adv360.keymap timestamp
+	docker run --rm -it --name zmk \
+		-v $(PWD)/firmware:/app/firmware \
+		-v $(PWD)/config:/app/config:ro \
+		-e TIMESTAMP=$(TIMESTAMP) \
+		zmk
+
+setup:
+	docker build --tag zmk .
+
+timestamp:
+	$(eval TIMESTAMP:=$(shell date -u +"%Y%m%d%H%M%S"))

bin/build.sh

@@ -1,9 +1,9 @@
 #!/usr/bin/env bash
 
-set -e
+set -eu
 
 PWD=$(pwd)
-TIMESTAMP=$(date -u +"%Y%m%d%H%M%S")
+TIMESTAMP="${TIMESTAMP:-$(date -u +"%Y%m%d%H%M%S")}"
 
 # West Build (left)
 west build -s zmk/app -d build/left -b adv360_left -- -DZMK_CONFIG="${PWD}/config"