#!/usr/bin/env bash
# Compare this fork against upstream and optionally write UPSTREAM_STATUS.md.
set -euo pipefail

UPSTREAM_REMOTE="${UPSTREAM_REMOTE:-upstream}"
UPSTREAM_URL="${UPSTREAM_URL:-https://github.com/komikku-app/komikku.git}"
UPSTREAM_BRANCH="${UPSTREAM_BRANCH:-master}"
FORK_BRANCH="${FORK_BRANCH:-main}"
BEHIND_WARN="${BEHIND_WARN:-10}"
OUTPUT_MD="${OUTPUT_MD:-UPSTREAM_STATUS.md}"
OUTPUT_JSON="${OUTPUT_JSON:-docs/upstream-status.json}"
FETCH="${FETCH:-1}"
WRITE="${WRITE:-0}"

usage() {
  cat <<'EOF'
Usage: scripts/check-upstream.sh [options]

Options:
  --no-fetch     Skip git fetch upstream
  --write        Write UPSTREAM_STATUS.md and docs/upstream-status.json
  --json         Print JSON status to stdout
  -h, --help     Show this help

Environment:
  UPSTREAM_REMOTE   Git remote name (default: upstream)
  UPSTREAM_BRANCH   Upstream branch (default: master)
  FORK_BRANCH       Local fork branch (default: main)
  BEHIND_WARN       Warn when behind by this many commits (default: 10)
EOF
}

print_json=0
while [[ $# -gt 0 ]]; do
  case "$1" in
    --no-fetch) FETCH=0 ;;
    --write) WRITE=1 ;;
    --json) print_json=1 ;;
    -h|--help) usage; exit 0 ;;
    *) echo "Unknown option: $1" >&2; usage >&2; exit 2 ;;
  esac
  shift
done

repo_root="$(git rev-parse --show-toplevel)"
cd "$repo_root"

if ! git rev-parse --verify "$FORK_BRANCH" >/dev/null 2>&1; then
  echo "Fork branch not found: $FORK_BRANCH" >&2
  exit 1
fi

if ! git remote get-url "$UPSTREAM_REMOTE" >/dev/null 2>&1; then
  echo "Adding upstream remote: $UPSTREAM_REMOTE -> $UPSTREAM_URL" >&2
  git remote add "$UPSTREAM_REMOTE" "$UPSTREAM_URL"
fi

if [[ "$FETCH" == "1" ]]; then
  git fetch "$UPSTREAM_REMOTE" "$UPSTREAM_BRANCH" --prune
fi

upstream_ref="$UPSTREAM_REMOTE/$UPSTREAM_BRANCH"
if ! git rev-parse --verify "$upstream_ref" >/dev/null 2>&1; then
  echo "Upstream ref not found: $upstream_ref" >&2
  exit 1
fi

merge_base="$(git merge-base "$FORK_BRANCH" "$upstream_ref")"
behind="$(git rev-list --count "$FORK_BRANCH".."$upstream_ref")"
ahead="$(git rev-list --count "$upstream_ref".."$FORK_BRANCH")"
fork_head="$(git rev-parse --short "$FORK_BRANCH")"
upstream_head="$(git rev-parse --short "$upstream_ref")"
checked_at="$(date -u +"%Y-%m-%d %H:%M UTC")"

if [[ "$behind" -eq 0 ]]; then
  status="up_to_date"
  status_label="Up to date"
  status_emoji="✅"
elif [[ "$behind" -le "$BEHIND_WARN" ]]; then
  status="slightly_behind"
  status_label="Slightly behind"
  status_emoji="🟡"
else
  status="behind"
  status_label="Behind upstream"
  status_emoji="🔴"
fi

upstream_sample="$(git log --oneline "$FORK_BRANCH".."$upstream_ref" -10)"
fork_sample="$(git log --oneline "$upstream_ref".."$FORK_BRANCH" -10)"

if [[ "$print_json" == "1" ]]; then
  python3 - <<PY
import json
print(json.dumps({
    "checked_at": "$checked_at",
    "status": "$status",
    "status_label": "$status_label",
    "behind": $behind,
    "ahead": $ahead,
    "fork_branch": "$FORK_BRANCH",
    "upstream_remote": "$UPSTREAM_REMOTE",
    "upstream_branch": "$UPSTREAM_BRANCH",
    "upstream_url": "$UPSTREAM_URL",
    "merge_base": "$(git rev-parse --short "$merge_base")",
    "fork_head": "$fork_head",
    "upstream_head": "$upstream_head",
    "behind_warn": $BEHIND_WARN,
}, indent=2))
PY
fi

echo "Upstream: $UPSTREAM_REMOTE ($UPSTREAM_URL) @ $UPSTREAM_BRANCH"
echo "Fork:     $FORK_BRANCH @ $fork_head"
echo "Merge base: $(git rev-parse --short "$merge_base")"
echo "Behind upstream: $behind commits"
echo "Ahead of upstream: $ahead commits"
echo "Status: $status_emoji $status_label"

if [[ "$WRITE" != "1" ]]; then
  exit 0
fi

mkdir -p "$(dirname "$OUTPUT_JSON")"

python3 - <<PY
import json
from pathlib import Path
Path("$(dirname "$OUTPUT_JSON")").mkdir(parents=True, exist_ok=True)
json.dump({
    "schemaVersion": 1,
    "checked_at": "$checked_at",
    "status": "$status",
    "status_label": "$status_label",
    "behind": $behind,
    "ahead": $ahead,
    "fork_branch": "$FORK_BRANCH",
    "upstream_remote": "$UPSTREAM_REMOTE",
    "upstream_branch": "$UPSTREAM_BRANCH",
    "upstream_url": "$UPSTREAM_URL",
    "merge_base": "$(git rev-parse "$merge_base")",
    "fork_head": "$(git rev-parse "$FORK_BRANCH")",
    "upstream_head": "$(git rev-parse "$upstream_ref")",
    "behind_warn": $BEHIND_WARN,
}, open("$OUTPUT_JSON", "w"), indent=2)
PY

{
  cat <<EOF
# Upstream sync status

> Auto-generated by [\`scripts/check-upstream.sh\`](scripts/check-upstream.sh). Last check: **$checked_at**.

| | |
|---|---|
| Status | $status_emoji **$status_label** |
| Behind upstream | **$behind** commits on [\`$UPSTREAM_REMOTE/$UPSTREAM_BRANCH\`]($UPSTREAM_URL) |
| Ahead of upstream | **$ahead** fork-only commits on \`$FORK_BRANCH\` |
| Merge base | \`$(git rev-parse --short "$merge_base")\` |
| Fork HEAD | \`$fork_head\` |
| Upstream HEAD | \`$upstream_head\` |

EOF

  if [[ "$behind" -gt 0 ]]; then
    cat <<EOF
## Action recommended

This fork is **$behind commits behind** [komikku-app/komikku]($UPSTREAM_URL). Consider merging upstream soon.

See [docs/upstream-sync.md](docs/upstream-sync.md) for the manual sync procedure.

EOF
  else
    echo "## No merge needed"
    echo
    echo "The fork includes all commits from upstream \`$UPSTREAM_BRANCH\`."
    echo
  fi

  cat <<EOF
## Recent upstream commits not in fork

\`\`\`
$(printf '%s\n' "$upstream_sample")
\`\`\`

## Recent fork-only commits

\`\`\`
$(printf '%s\n' "$fork_sample")
\`\`\`
EOF
} >"$OUTPUT_MD"

echo "Wrote $OUTPUT_MD and $OUTPUT_JSON"