#!/usr/bin/env sh
#
# Does this artifact need building, or is the channel already serving this exact
# source? Prints `true` or `false`.
#
#   should-build.sh <desktop|android> <dev|stable>
#
# Skip-if-exists, keyed on what the channel serves rather than on a registry tag:
# there are no `:<version>` tags to ask about. Both clients' channels publish the
# version they serve, so if the channel already serves what this source derives,
# the artifact would be byte-identical and there is nothing to build.
#
# This is also why the workflows carry no `paths:` filters: a second, hand-kept
# statement of each artifact's file set beside the one in `version.sh` drifts from
# it, and a lane whose filter misses a file never runs on the commit that changed
# it. One definition with one reader; the cost saving is a bonus.
#
# THE SERVER IS NOT LISTED HERE, DELIBERATELY. Its image build is ~15 seconds against
# 6 and 9 minutes for the clients, so there is little to save — and always building
# it is strictly better for a server that can face the internet, because it picks up
# `python:3.12-slim` base updates on every push. The clients' bases are CI runner
# images, pinned deliberately.
set -eu

ROOT="$(cd "$(dirname "$0")/.." && pwd)"

artifact="${1:?usage: should-build.sh <desktop|android> <dev|stable>}"
channel="${2:?usage: should-build.sh <desktop|android> <dev|stable>}"

case "$artifact" in desktop|android) : ;; *)
  echo "should-build.sh: unknown artifact '$artifact'" >&2; exit 2 ;;
esac
case "$channel" in dev|stable) : ;; *)
  echo "should-build.sh: unknown channel '$channel'" >&2; exit 2 ;;
esac

# The value that answers "is this the same code?" — which is not the same as the one
# the guard compares.
#
#   desktop  the ordering key IS the identity; one value, one clock.
#   android  the NAME. Its versionCode is build-time and moves every run, so
#            comparing that would report a change on every push and never skip.
case "$artifact" in
  desktop) derived="$(sh "$ROOT/packaging/version.sh" key desktop)" ;;
  android) derived="$(sh "$ROOT/packaging/version.sh" display android)" ;;
esac

published="$(sh "$ROOT/packaging/guard-forward.sh" published "$artifact" "$channel")"

if [ -z "$published" ]; then
  echo "should-build: $channel serves no $artifact yet — building." >&2
  echo true
  exit 0
fi

if [ "$derived" = "$published" ]; then
  # UNCHANGED. The channel is already serving this exact source, so a build would
  # produce the same artifact under the same name and republish it for nothing.
  #
  # Skipping is safe here in a way it would not be if anything pinned: there is no
  # version tag to re-push with different bytes, so this stands on cost alone.
  echo "should-build: $channel already serves $artifact $derived — skipping." >&2
  echo false
  exit 0
fi

echo "should-build: $artifact moved $published -> $derived — building." >&2
echo true