#!/usr/bin/env bash
# {{PROJECT_NAME}} — fast-forward the local default branch to its origin from anywhere.
# The default branch (main/master/trunk) is resolved from origin/HEAD, never hardcoded.
#
# Usage: scripts/main-sync.sh   (or: make main-sync)
#
# - Fetches origin, then fast-forwards the default branch wherever it is checked out.
# - If the default branch is checked out nowhere (invariant temporarily violated — e.g. the
#   primary checkout is detached), restores it into the primary checkout when clean.
# - Refuses (non-zero) if the default branch has diverged (any commit ahead of its origin).
set -euo pipefail

log()  { printf "→ %s\n" "$*"; }
warn() { printf "! %s\n" "$*" >&2; }

git rev-parse --is-inside-work-tree >/dev/null 2>&1 || { warn "not in a git repository"; exit 1; }

# Resolve the remote's default branch NAME (bare, e.g. "main"), falling back to
# "main" when origin/HEAD is unset. Same helper as setup-agent-worktree.sh — a
# repo whose default is `master`/`trunk` must not have `main` hardcoded here.
resolve_default_branch() {
  local d
  d="$(git symbolic-ref refs/remotes/origin/HEAD --short 2>/dev/null | sed 's@^origin/@@')"
  printf '%s' "${d:-main}"
}
DEFAULT="$(resolve_default_branch)"

log "Fetching origin..."
git fetch --quiet origin || { warn "fetch failed"; exit 1; }
git rev-parse --verify --quiet "origin/$DEFAULT" >/dev/null || { warn "origin/$DEFAULT not found"; exit 1; }

# Where is the default branch checked out (if anywhere)?
main_wt="$(git worktree list --porcelain | awk -v def="refs/heads/$DEFAULT" '
  /^worktree /{ wt = substr($0, 10) }
  $0 == "branch " def { print wt }')"

if [[ -z "$main_wt" ]]; then
  # The default branch is checked out nowhere: restore it into the PRIMARY checkout (the first
  # worktree — it belongs there), NOT wherever main-sync happens to be run from.
  primary="$(git worktree list --porcelain | awk 'NR==1 && /^worktree /{ print substr($0, 10) }')"
  if [[ -z "$primary" ]]; then
    warn "$DEFAULT is checked out nowhere and the primary checkout could not be located."
    exit 1
  fi
  # Only restore when the primary is detached — never silently switch it off a feature branch.
  primary_branch="$(git -C "$primary" symbolic-ref --quiet --short HEAD 2>/dev/null || true)"
  if [[ -n "$primary_branch" && "$primary_branch" != "$DEFAULT" ]]; then
    warn "$DEFAULT is checked out nowhere and the primary checkout ($primary) is on branch '$primary_branch'."
    warn "Refusing to switch it away. Restore $DEFAULT yourself: git -C \"$primary\" switch $DEFAULT"
    exit 1
  fi
  if [[ -n "$(git -C "$primary" status --porcelain --untracked-files=no)" ]]; then
    warn "$DEFAULT is checked out nowhere and the primary checkout ($primary) has uncommitted changes to tracked files — cannot restore."
    warn "Expected $DEFAULT in the primary checkout."
    exit 1
  fi
  log "$DEFAULT checked out nowhere — restoring it into the primary checkout: $primary"
  if git -C "$primary" rev-parse --verify --quiet "refs/heads/$DEFAULT" >/dev/null; then
    git -C "$primary" checkout "$DEFAULT" >/dev/null 2>&1
  else
    git -C "$primary" checkout -b "$DEFAULT" --track "origin/$DEFAULT" >/dev/null 2>&1
  fi
  main_wt="$primary"
fi

# Best-effort, DETECT-ONLY: report (never modify) stray timestamp-only regenerated
# artifacts a generator left in the checkout that holds the default branch, so they
# don't silently block the ff-only merge below — a person decides whether to discard
# or regenerate in a worktree. A hiccup here must never fail the sync (|| true).
check="$(dirname "$0")/check-regen-artifacts.sh"
[[ -x "$check" ]] && "$check" "$main_wt" || true

ahead="$(git -C "$main_wt" rev-list --count "origin/$DEFAULT..$DEFAULT")"
if [[ "$ahead" != "0" ]]; then
  warn "$DEFAULT has diverged from origin/$DEFAULT ($ahead commit(s) ahead) — refusing to fast-forward."
  warn "Investigate: 'git -C \"$main_wt\" log --oneline origin/$DEFAULT..$DEFAULT'."
  exit 1
fi

git -C "$main_wt" merge --ff-only "origin/$DEFAULT" >/dev/null
log "$DEFAULT is in sync at $(git -C "$main_wt" rev-parse --short "$DEFAULT") (worktree: $main_wt)."