import { createHash } from "node:crypto";
import { query } from "../pool.js";

export interface AuditEventInput {
  actorType: "user" | "system" | "service";
  actorId?: string | null;
  action: string;
  resourceType: string;
  resourceId?: string | null;
  metadata?: Record<string, unknown>;
  ipAddress?: string | null;
}

function canonicalJson(value: unknown): string {
  if (value === null || typeof value !== "object") return JSON.stringify(value);
  if (Array.isArray(value)) return `[${value.map(canonicalJson).join(",")}]`;
  const obj = value as Record<string, unknown>;
  const keys = Object.keys(obj).sort();
  return `{${keys.map((k) => `${JSON.stringify(k)}:${canonicalJson(obj[k])}`).join(",")}}`;
}

/**
 * Appends one event to the audit_log hash chain (see baseline-schema
 * migration and .claude/skills/eden-security/references/audit.md). Never
 * call this inside a larger transaction that might roll back for
 * unrelated reasons without considering that the chain must stay
 * contiguous — a rolled-back event never happened (fine, nothing was
 * recorded), but a *committed* event must never be skipped when
 * computing previous_event_hash for the next one.
 */
export async function appendAuditEvent(input: AuditEventInput): Promise<void> {
  const { rows } = await query<{ event_hash: string }>(
    "SELECT event_hash FROM audit_log ORDER BY seq DESC LIMIT 1",
  );
  const previousEventHash = rows[0]?.event_hash ?? "";

  const fields = {
    actorType: input.actorType,
    actorId: input.actorId ?? null,
    action: input.action,
    resourceType: input.resourceType,
    resourceId: input.resourceId ?? null,
    metadata: input.metadata ?? {},
    ipAddress: input.ipAddress ?? null,
  };
  const eventHash = createHash("sha256")
    .update(previousEventHash + canonicalJson(fields))
    .digest("hex");

  await query(
    `INSERT INTO audit_log
       (actor_type, actor_id, action, resource_type, resource_id, metadata, ip_address, previous_event_hash, event_hash)
     VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9)`,
    [
      input.actorType,
      input.actorId ?? null,
      input.action,
      input.resourceType,
      input.resourceId ?? null,
      JSON.stringify(input.metadata ?? {}),
      input.ipAddress ?? null,
      previousEventHash || null,
      eventHash,
    ],
  );
}