import { randomUUID } from "node:crypto";
import { and, appLogs, desc, eq, sql, type Db } from "@parking/db";
import {
  LOG_LEVEL_ORDER,
  type AppLogRecord,
  type ClientLogInput,
  type LogLevel,
  type LogSource,
} from "@parking/shared";

// Application/diagnostic LOG SINK — the host-side store behind the third log stream
// (app_logs), distinct from the signed ledger and device telemetry. It persists:
//   - BACKEND warn/error/fatal, fed by a pino stream (see pinoDbStream) so any
//     app.log.warn/error lands in the DB without changing call sites.
//   - FRONTEND errors POSTed to /api/logs (failed requests, uncaught errors).
// Everything here is UNSIGNED + prunable. Pruned by age AND a row cap so an offline
// appliance with finite disk can't be filled by a log storm. See
// wiki/concepts/app-logs.md, decisions/event-streams-split.md.

/** Only warn and above are persisted from the backend (info/debug stay stdout-only). */
const BACKEND_PERSIST_MIN: LogLevel = "warn";

/** Defensive caps so one runaway log can't bloat a row (chars). */
const MAX_MESSAGE = 4_000;
const MAX_STACK = 16_000;
const MAX_CONTEXT_JSON = 16_000;

export interface LogRetention {
  /** Delete logs older than this many days. */
  readonly maxAgeDays: number;
  /** Hard cap on total rows — the oldest beyond this are pruned. */
  readonly maxRows: number;
}

export const DEFAULT_RETENTION: LogRetention = {
  // 60 days (~2 months) — the operator's chosen diagnostic window (2026-07-04),
  // matched by the container-log rotation caps in docker-compose.prod.yml. The row
  // cap below still bounds a burst regardless of age.
  maxAgeDays: Number(process.env.LOG_RETENTION_DAYS ?? 60),
  maxRows: Number(process.env.LOG_RETENTION_MAX_ROWS ?? 50_000),
};

function clamp(s: string | null | undefined, max: number): string | null {
  if (s == null) return null;
  return s.length > max ? s.slice(0, max) : s;
}

/** Serialize context to JSON, bounded — never throw on a circular/huge object. */
function safeContext(ctx: Record<string, unknown> | null | undefined): Record<string, unknown> | null {
  if (ctx == null) return null;
  try {
    const json = JSON.stringify(ctx);
    if (json.length <= MAX_CONTEXT_JSON) return ctx;
    return { _truncated: true, preview: json.slice(0, MAX_CONTEXT_JSON) };
  } catch {
    return { _unserializable: true };
  }
}

export class LogService {
  readonly #db: Db;
  readonly #retention: LogRetention;
  /** Reentrancy guard: never let persisting a log itself emit a persisted log. */
  #writing = false;

  constructor(db: Db, retention: LogRetention = DEFAULT_RETENTION) {
    this.#db = db;
    this.#retention = retention;
  }

  /** Low-level insert. Best-effort: a logging failure must never break a request or
   *  recurse (a DB error here would otherwise log → insert → error → log …). */
  #insert(row: {
    level: LogLevel;
    source: LogSource;
    message: string;
    context?: Record<string, unknown> | null;
    httpStatus?: number | null;
    path?: string | null;
    stack?: string | null;
    userId?: string | null;
    userAgent?: string | null;
    createdAt?: string;
  }): void {
    if (this.#writing) return;
    this.#writing = true;
    try {
      this.#db
        .insert(appLogs)
        .values({
          id: randomUUID(),
          level: row.level,
          source: row.source,
          message: clamp(row.message, MAX_MESSAGE) ?? "",
          context: safeContext(row.context),
          httpStatus: row.httpStatus ?? null,
          path: clamp(row.path, 512),
          stack: clamp(row.stack, MAX_STACK),
          userId: row.userId ?? null,
          userAgent: clamp(row.userAgent, 512),
          createdAt: row.createdAt ?? new Date().toISOString(),
        })
        .run();
    } catch {
      // Swallow — diagnostics must never take down the path they observe. (Can't log
      // it; that's the recursion we're guarding against.)
    } finally {
      this.#writing = false;
    }
  }

  /** Persist a BACKEND log line (called by the pino stream). Below warn is dropped. */
  recordBackend(level: LogLevel, message: string, context?: Record<string, unknown> | null): void {
    if (LOG_LEVEL_ORDER[level] < LOG_LEVEL_ORDER[BACKEND_PERSIST_MIN]) return;
    this.#insert({ level, source: "backend", message, context });
  }

  /** Persist a FRONTEND-reported log (from POST /api/logs). The server stamps the
   *  user + receive time; the client supplies level/message/context. */
  recordClient(
    input: ClientLogInput,
    meta: { userId?: string | null; userAgent?: string | null },
  ): void {
    this.#insert({
      level: input.level,
      source: "frontend",
      message: input.message,
      context: input.context ?? null,
      httpStatus: input.httpStatus ?? null,
      path: input.path ?? null,
      stack: input.stack ?? null,
      userId: meta.userId ?? null,
      userAgent: meta.userAgent ?? null,
      // Keep the client's capture time in context for ordering; createdAt is server time.
      createdAt: new Date().toISOString(),
    });
  }

  /** Read recent logs, newest first, with optional level/source/since filters. */
  query(opts: {
    limit: number;
    level?: LogLevel;
    source?: LogSource;
    since?: string;
  }): AppLogRecord[] {
    const conds = [];
    if (opts.level) conds.push(eq(appLogs.level, opts.level));
    if (opts.source) conds.push(eq(appLogs.source, opts.source));
    if (opts.since) conds.push(sql`${appLogs.createdAt} >= ${opts.since}`);
    const rows = this.#db
      .select()
      .from(appLogs)
      .where(conds.length ? and(...conds) : undefined)
      .orderBy(desc(appLogs.createdAt))
      .limit(opts.limit)
      .all();
    return rows as unknown as AppLogRecord[];
  }

  /** Prune by age then by row cap. Returns how many rows were deleted. Safe to call
   *  on a timer; cheap (indexed on created_at). */
  prune(): number {
    let deleted = 0;
    try {
      const cutoff = new Date(Date.now() - this.#retention.maxAgeDays * 86_400_000).toISOString();
      const byAge = this.#db.delete(appLogs).where(sql`${appLogs.createdAt} < ${cutoff}`).run();
      deleted += byAge.changes ?? 0;

      // Row cap: keep the newest maxRows, delete the rest. One subquery — find the
      // created_at boundary of the keep-window, delete older.
      const total = this.#db.select({ c: sql<number>`count(*)` }).from(appLogs).get();
      const count = total?.c ?? 0;
      if (count > this.#retention.maxRows) {
        const boundary = this.#db
          .select({ createdAt: appLogs.createdAt })
          .from(appLogs)
          .orderBy(desc(appLogs.createdAt))
          .limit(1)
          .offset(this.#retention.maxRows - 1)
          .get();
        if (boundary) {
          const byCap = this.#db
            .delete(appLogs)
            .where(sql`${appLogs.createdAt} < ${boundary.createdAt}`)
            .run();
          deleted += byCap.changes ?? 0;
        }
      }
    } catch {
      // best-effort
    }
    return deleted;
  }
}

/**
 * A pino-compatible write stream that forwards BACKEND warn+ lines into the LogService.
 * Pino writes one JSON object per line to this stream; we parse, resolve the level
 * (name or numeric encoding), and persist. Returned as `{ write }` so it can be passed
 * as pino's stream. stdout still receives the same line (we tee), so console logging is
 * unchanged.
 */
export function pinoDbStream(
  service: LogService,
  tee: NodeJS.WritableStream,
): { write: (line: string) => void } {
  const NUM_TO_LEVEL: Record<number, LogLevel> = {
    10: "trace",
    20: "debug",
    30: "info",
    40: "warn",
    50: "error",
    60: "fatal",
  };
  return {
    write(line: string): void {
      // Always tee to the original destination first (don't lose stdout logging).
      try {
        tee.write(line);
      } catch {
        /* ignore */
      }
      try {
        const obj = JSON.parse(line) as {
          level?: number | string;
          msg?: string;
          err?: { stack?: string; message?: string };
          [k: string]: unknown;
        };
        // The logger emits level NAMES (formatters.level in server.ts, for human-
        // readable container logs); a default pino config emits numbers. Accept both.
        const level: LogLevel =
          typeof obj.level === "string" && obj.level in LOG_LEVEL_ORDER
            ? (obj.level as LogLevel)
            : NUM_TO_LEVEL[typeof obj.level === "number" ? obj.level : 30] ?? "info";
        if (LOG_LEVEL_ORDER[level] < LOG_LEVEL_ORDER[BACKEND_PERSIST_MIN]) return;
        // Strip pino's noisy standard fields from the persisted context.
        const { level: _l, time: _t, pid: _p, hostname: _h, msg, ...rest } = obj;
        service.recordBackend(level, typeof msg === "string" ? msg : "", rest);
      } catch {
        // A non-JSON line (shouldn't happen with pino) — ignore for persistence.
      }
    },
  };
}