# Lint stage — fast feedback on formatting and lint issues
# golangci/golangci-lint:v2.12.2 (Debian-based), 2026-08-07
FROM golangci/golangci-lint:v2.12.2@sha256:5cceeef04e53efe1470638d4b4b4f5ceefd574955ab3941b2d9a68a8c9ad5240 AS lint
WORKDIR /src
COPY go.mod go.sum ./
RUN go mod download
COPY . .

# Cache-buster for the gate layers, and only for them. Docker
# invalidates COPY only when the copied content changes, so on an
# unchanged tree the gates below would be served from cache and the
# build would exit 0 having run nothing. script/cibuild and
# script/docker pass a fresh CHECK_EPOCH on every invocation.
#
# Two properties this depends on. ARG is per-stage, so the build stage
# below declares it again; one declaration here would leave that
# stage's gate cacheable. And each gate RUN must reference the value,
# because BuildKit hashes the expanded command: a declared but
# unreferenced ARG invalidates nothing.
#
# It sits below the dependency layers deliberately. Everything above it
# (the pinned base image, go mod download) keeps its cache; only the
# gates go cold.
ARG CHECK_EPOCH
RUN echo "gate fmt-check, epoch ${CHECK_EPOCH}" && make fmt-check
RUN echo "gate lint, epoch ${CHECK_EPOCH}" && make lint

# Build stage
# golang:1.25-alpine, 2026-07-23
FROM golang@sha256:56961d79ea8129efddcc0b8643fd8a5416b4e6228cfd477e3fd61deb2672c587 AS builder

RUN apk add --no-cache make

# We never build or run as root. Create an unprivileged user and point
# HOME and the Go caches at its home so go build/test and golangci-lint
# can write their caches when we drop to it below.
RUN adduser -D -u 1000 builder
ENV HOME=/home/builder
ENV GOPATH=/home/builder/go
ENV GOCACHE=/home/builder/.cache/go-build

WORKDIR /src

# Reuse the linter binary from the lint stage; the copy also forces
# BuildKit to complete linting before this stage proceeds.
COPY --from=lint /usr/bin/golangci-lint /usr/local/bin/golangci-lint

COPY go.mod go.sum ./
RUN go mod download
COPY . .

# Hand the sources and caches to the unprivileged user, then drop root
# before running any checks or builds.
RUN chown -R builder:builder /src /home/builder
USER builder

# Fail the build unless the branch is green. Runs as non-root so the
# permission-denied test paths are exercised legitimately (root would
# bypass the chmod(0) the tests rely on).
#
# Second per-stage declaration of the gate cache-buster; see the lint
# stage above for why one is not enough. It is placed after USER so the
# drop to the unprivileged user still happens before the checks run.
ARG CHECK_EPOCH
RUN echo "gate check, epoch ${CHECK_EPOCH}" && make check

RUN make build

# Runtime stage
# alpine:3.22, 2026-07-23
FROM alpine@sha256:14358309a308569c32bdc37e2e0e9694be33a9d99e68afb0f5ff33cc1f695dce

COPY --from=builder /src/sfdupes /usr/local/bin/sfdupes

ENTRYPOINT ["sfdupes"]