#!/bin/sh

set -eu

# Feature-finish front door. Run as `npm run create:finish`.
#
# Mirror image of `create:branch`: asserts the merge-side preconditions, merges
# the current `feature/`/`fix/`/`chore/` branch into `main` with `--no-ff`,
# proves the result with `npm run verify`, and only then deletes the branch. The
# push is owned by `create:release`, so the merge stays local and reviewable.
# On a conflict it aborts and returns to the feature branch.
#
# Rationale and the rejected alternatives: development/workflow.md § Branching
# model.

BASE="main"
PREFIXES="feature fix chore"

git rev-parse --is-inside-work-tree >/dev/null 2>&1 || {
    echo "error: not inside a git work tree." >&2
    exit 1
}

STATE_ROOT=$(git rev-parse --absolute-git-dir)
for state in MERGE_HEAD rebase-merge rebase-apply CHERRY_PICK_HEAD BISECT_LOG; do
    [ -e "${STATE_ROOT}/${state}" ] && {
        echo "error: a '${state}' operation is in progress; finish or abort it first." >&2
        exit 1
    }
done

# `--porcelain` is deliberately stricter than `git diff --quiet`: it also
# reports untracked files, which would otherwise not be part of the merge and
# silently outlive the branch deletion.
DIRTY=$(git status --porcelain)
if [ -n "${DIRTY}" ]; then
    echo "error: working tree is not clean:" >&2
    echo "${DIRTY}" | sed 's/^/         /' >&2
    exit 1
fi

START_REF=$(git symbolic-ref --quiet --short HEAD || true)
if [ -z "${START_REF}" ]; then
    echo "error: detached HEAD; switch to the branch you want to finish." >&2
    exit 1
fi

if [ "${START_REF}" = "${BASE}" ]; then
    echo "error: already on '${BASE}'; switch to the branch to finish." >&2
    exit 1
fi

MATCH=0
for p in ${PREFIXES}; do
    case "${START_REF}" in
    "${p}/"*) MATCH=1 ;;
    esac
done
if [ "${MATCH}" -ne 1 ]; then
    echo "error: '${START_REF}' must start with one of: ${PREFIXES}." >&2
    echo "       refusing to merge a branch that is not a unit of work." >&2
    exit 1
fi

git show-ref --verify --quiet "refs/heads/${BASE}" || {
    echo "error: no local '${BASE}' to merge into." >&2
    exit 1
}

# Derive the remote rather than hardcoding it: this repo has `origin` (ssh) and
# `origin_https`, and `main` tracks the latter — `git fetch origin main` would
# check currency against a ref that is never updated here.
# `--quiet` echoes the unresolved `main@{upstream}` literal to stdout on
# failure, so it cannot be paired with a `$(...) || fallback`; the non-quiet
# form prints nothing on failure and the fallback runs.
UPSTREAM=$(git rev-parse --abbrev-ref --symbolic-full-name "${BASE}@{upstream}" 2>/dev/null) || UPSTREAM=""
BEHIND=0
if [ -n "${UPSTREAM}" ]; then
    git fetch --quiet "${UPSTREAM%/*}" "${UPSTREAM#*/}" || {
        echo "error: '${UPSTREAM}' check failed: could not reach '${UPSTREAM%/*}'." >&2
        echo "       refusing to merge onto a possibly stale '${BASE}'." >&2
        exit 1
    }
    BEHIND=$(git rev-list --count "${BASE}..${UPSTREAM}")
    AHEAD=$(git rev-list --count "${UPSTREAM}..${BASE}")
    if [ "${AHEAD}" -ne 0 ] && [ "${BEHIND}" -ne 0 ]; then
        echo "error: '${BASE}' has diverged from '${UPSTREAM}' (ahead ${AHEAD}, behind ${BEHIND})." >&2
        echo "       reconcile '${BASE}' with '${UPSTREAM}' before finishing." >&2
        exit 1
    fi
else
    echo "warning: '${BASE}' has no upstream; freshness against the remote is unchecked." >&2
fi

echo "Finishing into ${BASE}:"
git --no-pager log --oneline --no-decorate "${BASE}..${START_REF}" | sed 's/^/  /'

git switch --quiet "${BASE}"
if [ "${BEHIND}" -ne 0 ]; then
    echo "Fast-forwarding ${BASE} to ${UPSTREAM} (${BEHIND} commit(s))."
    git merge --quiet --ff-only "${UPSTREAM}"
fi

if ! git merge --quiet --no-ff -m ":twisted_rightwards_arrows: Merge ${START_REF} into ${BASE}" "${START_REF}"; then
    echo "error: merge of '${START_REF}' failed; aborting and returning to it." >&2
    git merge --abort 2>/dev/null || true
    git switch --quiet "${START_REF}"
    exit 1
fi

echo "Verify: npm run verify"
if ! npm run --silent verify; then
    echo "error: 'npm run verify' is red after the merge." >&2
    echo "       the merge is local and not yet pushed; fix it on '${BASE}' and commit," >&2
    echo "       then drop the now-merged branch with 'git branch -d ${START_REF}'." >&2
    exit 1
fi

git branch --delete "${START_REF}" >/dev/null
echo "Merged ${START_REF} into ${BASE} and deleted the branch."
echo "Next: npm run create:release (or git push, for a merge with no release)."