import { InjectionToken } from './di';
/** Log severity, low to high. */
export type LogLevel = 'debug' | 'info' | 'warn' | 'error';
/** A structured log record: level, message, time, request id, and any fields. */
export interface LogRecord {
    /** Severity of the record. */
    level: LogLevel;
    /** Human-readable event message; keep it stable and put variable data in the free-form fields below. */
    msg: string;
    /** ISO-8601 timestamp of when the record was emitted. */
    time: string;
    /** Correlation id of the request that produced it, when inside one. */
    requestId?: string;
    /** Arbitrary structured fields merged into the record. */
    [key: string]: unknown;
}
/** Consumes each emitted record (already past the level filter); called synchronously, once per record. */
export type LogSink = (record: LogRecord) => void;
/** Override where log records go (default: JSON to stdout, warn/error to stderr). */
export declare const LOG_SINK: InjectionToken<LogSink>;
/** Override the minimum level (default: `LOG_LEVEL` env, else `"info"`). */
export declare const LOG_LEVEL: InjectionToken<LogLevel>;
/**
 * Structured, injectable logger. Quiet by default — only records at or above the
 * minimum level (`info` unless `LOG_LEVEL` says otherwise) are emitted — and,
 * when the {@link requestId} plugin is active, each record emitted inside a
 * request is stamped with its id, so logs correlate to requests with no per-call
 * plumbing.
 *
 * ```ts
 * class Orders {
 *   private log = inject(Logger)
 *   place() { this.log.info('order placed', { total: 42 }) }
 * }
 * ```
 *
 * Records are JSON to stdout (warnings/errors to stderr) by default; bind a
 * `LOG_SINK` provider to route them elsewhere (a file, a collector, a test spy).
 */
export declare class Logger {
    private readonly sink;
    private readonly min;
    private write;
    /**
     * Log at `debug` — the lowest level, dropped unless the minimum is `debug`.
     *
     * @param msg - Event message; becomes the record's `msg` field.
     * @param fields - Structured fields; merged last, so keys `level`/`msg`/`time`/`requestId` here override the built-ins.
     */
    debug(msg: string, fields?: Record<string, unknown>): void;
    /**
     * Log at `info` — the default minimum level; goes to stdout via the default sink.
     *
     * @param msg - Event message; becomes the record's `msg` field.
     * @param fields - Structured fields; merged last, so keys `level`/`msg`/`time`/`requestId` here override the built-ins.
     */
    info(msg: string, fields?: Record<string, unknown>): void;
    /**
     * Log at `warn` — routed to stderr (not stdout) by the default sink.
     *
     * @param msg - Event message; becomes the record's `msg` field.
     * @param fields - Structured fields; merged last, so keys `level`/`msg`/`time`/`requestId` here override the built-ins.
     */
    warn(msg: string, fields?: Record<string, unknown>): void;
    /**
     * Log at `error` — the highest level; routed to stderr by the default sink.
     *
     * @param msg - Event message; becomes the record's `msg` field.
     * @param fields - Structured fields; merged last, so keys `level`/`msg`/`time`/`requestId` here override the built-ins. Pass a caught error under a field (e.g. `{ err }`) rather than as `msg`.
     */
    error(msg: string, fields?: Record<string, unknown>): void;
}
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