#!/usr/bin/env bash
set -euo pipefail

# CASAN Level 5 drift detector.
# Usage:
#   drift-detect.sh <golden-file> <candidate-file> <report-json>

GOLDEN="${1:-}"
CANDIDATE="${2:-}"
REPORT="${3:-}"

if [[ -z "$GOLDEN" || -z "$CANDIDATE" || -z "$REPORT" ]]; then
  echo "Usage: drift-detect.sh <golden-file> <candidate-file> <report-json>" >&2
  exit 64
fi

SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
PROJECT_ROOT="$(cd "$SCRIPT_DIR/../../.." && pwd)"
mkdir -p "$(dirname "$REPORT")" "$PROJECT_ROOT/.specify/logs/level5"

python3 - "$GOLDEN" "$CANDIDATE" "$REPORT" <<'PY'
import difflib
import hashlib
import json
import pathlib
import sys
from datetime import datetime, timezone

golden_path = pathlib.Path(sys.argv[1])
candidate_path = pathlib.Path(sys.argv[2])
report_path = pathlib.Path(sys.argv[3])

golden = golden_path.read_text(encoding="utf-8")
candidate = candidate_path.read_text(encoding="utf-8")

similarity = difflib.SequenceMatcher(None, golden, candidate).ratio()
length_delta = abs(len(candidate) - len(golden)) / max(len(golden), 1)

status = "pass"
action = "allow"
if similarity < 0.70 or length_delta > 0.50:
    status = "fail"
    action = "block_or_fallback"
elif similarity < 0.85 or length_delta > 0.30:
    status = "warn"
    action = "require_review"

report = {
    "timestamp": datetime.now(timezone.utc).strftime("%Y-%m-%dT%H:%M:%SZ"),
    "harness": "L5-drift-detection",
    "status": status,
    "action": action,
    "similarity_ratio": round(similarity, 4),
    "length_delta_ratio": round(length_delta, 4),
    "golden_hash": hashlib.sha256(golden.encode()).hexdigest(),
    "candidate_hash": hashlib.sha256(candidate.encode()).hexdigest(),
    "golden_file": str(golden_path),
    "candidate_file": str(candidate_path),
}

report_path.write_text(json.dumps(report, indent=2) + "\n", encoding="utf-8")
print(f"DRIFT_{status.upper()} similarity={report['similarity_ratio']} length_delta={report['length_delta_ratio']} report={report_path}")

if status == "fail":
    raise SystemExit(2)
PY