FROM alpine:3.13

RUN apk add --no-cache ca-certificates

# set up nsswitch.conf for Go's "netgo" implementation
# - https://github.com/golang/go/blob/go1.9.1/src/net/conf.go#L194-L275
# - docker run --rm debian grep '^hosts:' /etc/nsswitch.conf
RUN [ ! -e /etc/nsswitch.conf ] && echo 'hosts: files dns' > /etc/nsswitch.conf

ENV PATH /usr/local/go/bin:$PATH

ENV GOLANG_VERSION 1.18.4

RUN set -eux; \
	apk add --no-cache --virtual .fetch-deps gnupg; \
	arch="$(apk --print-arch)"; \
	url=; \
	case "$arch" in \
		'x86_64') \
			export GOAMD64='v1' GOARCH='amd64' GOOS='linux'; \
			;; \
		'armhf') \
			export GOARCH='arm' GOARM='6' GOOS='linux'; \
			;; \
		'armv7') \
			export GOARCH='arm' GOARM='7' GOOS='linux'; \
			;; \
		'aarch64') \
			export GOARCH='arm64' GOOS='linux'; \
			;; \
		'x86') \
			export GO386='softfloat' GOARCH='386' GOOS='linux'; \
			;; \
		'ppc64le') \
			export GOARCH='ppc64le' GOOS='linux'; \
			;; \
		's390x') \
			export GOARCH='s390x' GOOS='linux'; \
			;; \
		*) echo >&2 "error: unsupported architecture '$arch' (likely packaging update needed)"; exit 1 ;; \
	esac; \
	build=; \
	if [ -z "$url" ]; then \
# https://github.com/golang/go/issues/38536#issuecomment-616897960
		build=1; \
		url='https://dl.google.com/go/go1.18.4.src.tar.gz'; \
		sha256='4525aa6b0e3cecb57845f4060a7075aafc9ab752bb7b6b4cf8a212d43078e1e4'; \
# the precompiled binaries published by Go upstream are not compatible with Alpine, so we always build from source here 😅
	fi; \
	\
	wget -O go.tgz.asc "$url.asc"; \
	wget -O go.tgz "$url"; \
	echo "$sha256 *go.tgz" | sha256sum -c -; \
	\
# https://github.com/golang/go/issues/14739#issuecomment-324767697
	GNUPGHOME="$(mktemp -d)"; export GNUPGHOME; \
# https://www.google.com/linuxrepositories/
	gpg --batch --keyserver keyserver.ubuntu.com --recv-keys 'EB4C 1BFD 4F04 2F6D DDCC  EC91 7721 F63B D38B 4796'; \
# let's also fetch the specific subkey of that key explicitly that we expect "go.tgz.asc" to be signed by, just to make sure we definitely have it
	gpg --batch --keyserver keyserver.ubuntu.com --recv-keys '2F52 8D36 D67B 69ED F998  D857 78BD 6547 3CB3 BD13'; \
	gpg --batch --verify go.tgz.asc go.tgz; \
	gpgconf --kill all; \
	rm -rf "$GNUPGHOME" go.tgz.asc; \
	\
	tar -C /usr/local -xzf go.tgz; \
	rm go.tgz; \
	\
	if [ -n "$build" ]; then \
		apk add --no-cache --virtual .build-deps \
			bash \
			gcc \
			go \
			musl-dev \
		; \
		\
		export GOCACHE='/tmp/gocache'; \
		\
		( \
			cd /usr/local/go/src; \
# set GOROOT_BOOTSTRAP + GOHOST* such that we can build Go successfully
			export GOROOT_BOOTSTRAP="$(go env GOROOT)" GOHOSTOS="$GOOS" GOHOSTARCH="$GOARCH"; \
			./make.bash; \
		); \
		\
		apk del --no-network .build-deps; \
		\
# remove a few intermediate / bootstrapping files the official binary release tarballs do not contain
		rm -rf \
			/usr/local/go/pkg/*/cmd \
			/usr/local/go/pkg/bootstrap \
			/usr/local/go/pkg/obj \
			/usr/local/go/pkg/tool/*/api \
			/usr/local/go/pkg/tool/*/go_bootstrap \
			/usr/local/go/src/cmd/dist/dist \
			"$GOCACHE" \
		; \
	fi; \
	\
	apk del --no-network .fetch-deps; \
	\
	go version

ENV GOPATH /go
ENV PATH $GOPATH/bin:$PATH
RUN mkdir -p "$GOPATH/src" "$GOPATH/bin" && chmod -R 777 "$GOPATH"
WORKDIR $GOPATH

RUN apk add --no-cache bash make git gcc libc-dev jq curl dumb-init
RUN cd /tmp && \
    git clone https://github.com/go-delve/delve && \
    cd delve && \
    go install github.com/go-delve/delve/cmd/dlv && \
    cd .. && \
    curl -sSfL https://raw.githubusercontent.com/cosmtrek/air/master/install.sh | sh -s -- -b $(go env GOPATH)/bin && \
    rm -rf delve && \
    chmod -R 777 /go
ENTRYPOINT ["/usr/bin/dumb-init", "--"]