#!/usr/bin/env bash
# lib/adopt.sh — Non-destructive adoption merge primitive
#
# Provides:
#   adopt_branch() — Create one adoption merge commit and push it fast-forward
#
# The orchestration (state machine, import → wait → finalize) lives in
# lib/onboard.sh under strategy="adopt". `josh-sync adopt` is now a CLI alias
# for `josh-sync onboard --mode=adopt`; see ADR-013 for design rationale.
#
# Requires: lib/core.sh, lib/config.sh, lib/auth.sh sourced

# ─── Adopt Branch ────────────────────────────────────────────────
# Establishes shared ancestry without rewriting the existing subrepo branch.
#
# Preconditions:
# - The subrepo branch and josh-filtered monorepo branch must have identical trees.
#
# Resulting commit:
# - parent 1: josh-filtered HEAD, so josh can follow first-parent history
# - parent 2: existing subrepo HEAD, so old subrepo history stays reachable
# - tree:     josh-filtered tree
#
# Returns: adopted | already-adopted | tree-mismatch | push-rejected | missing-branch

adopt_branch() (
  # Subshell function: contains the function-level EXIT trap, the internal cd,
  # and any set -e propagation so it cannot pollute the caller's shell. Without
  # this, the trap below would clobber callers' EXIT handlers (bats's own test
  # reporting in particular silently disappears).
  local mono_branch="$SYNC_BRANCH_MONO"
  local subrepo_branch="$SYNC_BRANCH_SUBREPO"
  local work_dir
  work_dir=$(mktemp -d)
  # shellcheck disable=SC2064  # Intentional early expansion — work_dir is local
  trap "rm -rf '$work_dir'" EXIT

  log "INFO" "=== Adopt: subrepo/${subrepo_branch} ↔ mono/${mono_branch} ==="

  local remote_subrepo_sha
  remote_subrepo_sha=$(git ls-remote "$(subrepo_auth_url)" "refs/heads/${subrepo_branch}" | awk '{print $1}') \
    || die "Failed to reach subrepo (check SSH key / auth)"
  if [ -z "$remote_subrepo_sha" ]; then
    log "ERROR" "Subrepo branch ${subrepo_branch} does not exist"
    echo "missing-branch"
    return
  fi

  git clone "$(subrepo_auth_url)" \
    --branch "$subrepo_branch" --single-branch \
    "${work_dir}/subrepo" || die "Failed to clone subrepo"

  cd "${work_dir}/subrepo" || exit
  git config user.name "$BOT_NAME"
  git config user.email "$BOT_EMAIL"

  local subrepo_head subrepo_tree
  subrepo_head=$(git rev-parse HEAD)
  # shellcheck disable=SC1083  # {tree} is git syntax, not shell brace expansion
  subrepo_tree=$(git rev-parse "HEAD^{tree}")
  log "INFO" "Subrepo HEAD: ${subrepo_head:0:12}"

  git remote add josh-filtered "$(josh_auth_url)"
  git fetch josh-filtered "$mono_branch" || die "Failed to fetch from josh-proxy"

  local josh_head josh_tree
  josh_head=$(git rev-parse "josh-filtered/${mono_branch}")
  # shellcheck disable=SC1083
  josh_tree=$(git rev-parse "josh-filtered/${mono_branch}^{tree}")
  log "INFO" "Josh-filtered HEAD: ${josh_head:0:12}"

  if [ "$subrepo_tree" != "$josh_tree" ]; then
    log "ERROR" "Tree mismatch: merge the import PR and ensure subrepo/${subrepo_branch} matches mono/${mono_branch} before adopting"
    echo "tree-mismatch"
    return
  fi

  if git merge-base --is-ancestor "$josh_head" "$subrepo_head" \
    && git merge-base --is-ancestor "$subrepo_head" "$josh_head"; then
    log "INFO" "Subrepo and josh-filtered histories already point to the same commit"
    echo "already-adopted"
    return
  fi

  if git merge-base --is-ancestor "$josh_head" "$subrepo_head"; then
    log "INFO" "Josh-filtered HEAD is already an ancestor of subrepo HEAD"
    echo "already-adopted"
    return
  fi

  local merge_commit
  merge_commit=$(git commit-tree "$josh_tree" \
    -p "$josh_head" \
    -p "$subrepo_head" \
    -m "Adopt ${JOSH_SYNC_TARGET_NAME} for josh-sync

${BOT_TRAILER}: adopt/${mono_branch}/$(date -u +%Y-%m-%dT%H:%M:%SZ)")

  git reset --hard "$merge_commit" >&2
  log "INFO" "Created adoption merge: ${merge_commit:0:12}"

  if git push "$(subrepo_auth_url)" "HEAD:refs/heads/${subrepo_branch}"; then
    log "INFO" "Adoption complete: pushed fast-forward merge to subrepo/${subrepo_branch}"
    echo "adopted"
  else
    log "WARN" "Fast-forward push rejected — subrepo changed during adoption"
    echo "push-rejected"
  fi
)