#!/usr/bin/env bash
# backup-memory.sh — PreToolUse hook for memory write tools.
# Snapshots the memory graph FILE before a write. Debounced so one apply-run
# produces a single backup. Never blocks the tool call (always exits 0).
#
# Config (env, all optional):
#   KG_MEMORY_FILE     explicit path to the MCP memory server's JSON store
#                      (falls back to MEMORY_FILE_PATH, the official server's var)
#   KG_BACKUP_DIR      where backups land            (default: ~/.claude/kg-backups)
#   KG_BACKUP_DEBOUNCE seconds; skip if a newer backup exists (default: 120)
#   KG_BACKUP_KEEP     how many backups to retain    (default: 20)
#
# Tip: set KG_MEMORY_FILE in your shell / Claude Code env so the hook knows
# which file to copy. Without it the hook logs a notice and exits cleanly.

set -uo pipefail

# Drain stdin (hook receives JSON; we don't need it) so the pipe never blocks.
cat >/dev/null 2>&1 || true

MEM="${KG_MEMORY_FILE:-${MEMORY_FILE_PATH:-}}"
BACKUP_DIR="${KG_BACKUP_DIR:-$HOME/.claude/kg-backups}"
DEBOUNCE="${KG_BACKUP_DEBOUNCE:-120}"
KEEP="${KG_BACKUP_KEEP:-20}"
LOG="$BACKUP_DIR/backup.log"

note() { mkdir -p "$BACKUP_DIR" 2>/dev/null || true; echo "[$(date -Iseconds)] $*" >>"$LOG" 2>/dev/null || true; }

# No file configured or file missing -> notice + clean exit (never block writes).
if [ -z "$MEM" ]; then
  note "no KG_MEMORY_FILE/MEMORY_FILE_PATH set; skipping file backup"
  exit 0
fi
if [ ! -f "$MEM" ]; then
  note "memory file not found at '$MEM'; skipping"
  exit 0
fi

mkdir -p "$BACKUP_DIR" 2>/dev/null || { note "cannot create $BACKUP_DIR"; exit 0; }

# Debounce: if the newest existing backup is younger than DEBOUNCE seconds, skip.
newest="$(ls -t "$BACKUP_DIR"/kg-backup-*.json 2>/dev/null | head -n1 || true)"
if [ -n "$newest" ]; then
  age=$(( $(date +%s) - $(stat -c %Y "$newest" 2>/dev/null || echo 0) ))
  if [ "$age" -lt "$DEBOUNCE" ]; then
    note "debounced (last backup ${age}s ago < ${DEBOUNCE}s)"
    exit 0
  fi
fi

ts="$(date +%Y%m%dT%H%M%S)"
dest="$BACKUP_DIR/kg-backup-$ts.json"
if cp "$MEM" "$dest" 2>/dev/null; then
  note "backup ok -> $dest"
else
  note "backup FAILED copying $MEM"
  exit 0
fi

# Prune: keep only the most recent $KEEP backups.
mapfile -t old < <(ls -t "$BACKUP_DIR"/kg-backup-*.json 2>/dev/null | tail -n +"$((KEEP+1))")
for f in "${old[@]:-}"; do [ -n "$f" ] && rm -f "$f" 2>/dev/null || true; done

exit 0