/**
 * Client Hints header parsing for edge-side device capability detection.
 *
 * Converts HTTP Client Hints headers into the same `ExtendedDeviceCapabilities`
 * structure that `@czap/detect` uses, enabling reuse of the pure tier mapping
 * functions at the edge without browser APIs.
 *
 * @module
 */
import type { ExtendedDeviceCapabilities } from '@czap/detect';
import type { ResponsiveMediaCapabilities } from '@czap/core';
/**
 * Plain-object header bag accepted by {@link ClientHints.parseClientHints}.
 *
 * All names are lowercased because Client Hints headers are always lowercase
 * in spec. Values that are missing simply fall back to conservative
 * defaults during parsing.
 */
export interface ClientHintsHeaders {
    /** `Sec-CH-UA-Platform` (e.g. `"macOS"`, `"Windows"`). */
    readonly 'sec-ch-ua-platform'?: string;
    /** `Sec-CH-Device-Memory` in GiB (one of the standard buckets). */
    readonly 'sec-ch-device-memory'?: string;
    /** `Sec-CH-DPR` — devicePixelRatio as a decimal string. */
    readonly 'sec-ch-dpr'?: string;
    /** `Sec-CH-Viewport-Width` in CSS pixels. */
    readonly 'sec-ch-viewport-width'?: string;
    /** `Sec-CH-Viewport-Height` in CSS pixels. */
    readonly 'sec-ch-viewport-height'?: string;
    /** `Sec-CH-Prefers-Reduced-Motion` (`reduce` / `no-preference`). */
    readonly 'sec-ch-prefers-reduced-motion'?: string;
    /** `Sec-CH-Prefers-Color-Scheme` (`light` / `dark`). */
    readonly 'sec-ch-prefers-color-scheme'?: string;
    /** `Sec-CH-UA-Mobile` as a structured boolean (`?1` / `?0`). */
    readonly 'sec-ch-ua-mobile'?: string;
    /** `Sec-CH-UA` — full user-agent brand list. */
    readonly 'sec-ch-ua'?: string;
    /** `Save-Data` (`on`). */
    readonly 'save-data'?: string;
    /** `Downlink` estimate in Mb/s. */
    readonly downlink?: string;
    /** `ECT` effective connection type. */
    readonly ect?: string;
    /** `RTT` round-trip-time estimate in ms. */
    readonly rtt?: string;
    /** `User-Agent` fallback for GPU-tier heuristics. */
    readonly 'user-agent'?: string;
}
/**
 * Parse Client Hints headers into an {@link ExtendedDeviceCapabilities} structure.
 *
 * For properties that cannot be determined from headers (GPU tier, WebGPU
 * support, CPU cores), conservative defaults are used.
 *
 * @example
 * ```ts
 * import { ClientHints } from '@czap/edge';
 *
 * const caps = ClientHints.parseClientHints({
 *   'sec-ch-device-memory': '8',
 *   'sec-ch-dpr': '2',
 *   'sec-ch-viewport-width': '1440',
 *   'sec-ch-prefers-color-scheme': 'dark',
 *   'sec-ch-ua-mobile': '?0',
 * });
 * console.log(caps.memory);             // 8
 * console.log(caps.devicePixelRatio);    // 2
 * console.log(caps.prefersColorScheme);  // 'dark'
 * ```
 *
 * @param headers - Client Hints headers (plain object or Web API Headers)
 * @returns An {@link ExtendedDeviceCapabilities} structure
 */
declare function parseClientHints(headers: ClientHintsHeaders | Headers): ExtendedDeviceCapabilities;
/**
 * Generate the `Accept-CH` header value for requesting all useful Client Hints
 * on subsequent requests.
 *
 * @example
 * ```ts
 * import { ClientHints } from '@czap/edge';
 *
 * const response = new Response('OK', {
 *   headers: { 'Accept-CH': ClientHints.acceptCHHeader() },
 * });
 * ```
 *
 * @returns A comma-separated list of Client Hint header names
 */
declare function acceptCHHeader(): string;
/**
 * Generate the `Critical-CH` header value for hints needed on the very first
 * request (triggers a browser retry if missing).
 *
 * @example
 * ```ts
 * import { ClientHints } from '@czap/edge';
 *
 * const response = new Response('OK', {
 *   headers: {
 *     'Accept-CH': ClientHints.acceptCHHeader(),
 *     'Critical-CH': ClientHints.criticalCHHeader(),
 *   },
 * });
 * ```
 *
 * @returns A comma-separated list of critical Client Hint header names
 */
declare function criticalCHHeader(): string;
/**
 * Produce the `Vary` response header value listing every Client Hint (and
 * network hint) that shapes tier-specific HTML. CDN caches must vary on these
 * inputs or they can serve the wrong tier's representation (#122).
 */
declare function varyCHHeader(): string;
/**
 * Derive Save-Data / DPR capabilities for responsive-media projection (#125).
 * Hosts that already parsed caps can also call this with the result of
 * {@link parseClientHints}.
 */
declare function responsiveMediaCapabilities(headersOrCaps: Headers | ClientHintsHeaders | ExtendedDeviceCapabilities): ResponsiveMediaCapabilities;
/**
 * `Vary` inputs that shape responsive-media projection (DPR + Save-Data).
 * CDN caches must vary on these or they can serve the wrong srcset (#125).
 */
declare function responsiveMediaVaryHeader(): string;
/**
 * Client Hints namespace.
 *
 * Parses HTTP Client Hints headers into the same
 * {@link ExtendedDeviceCapabilities} structure used by `@czap/detect`,
 * enabling server-side / edge-side tier mapping without browser APIs.
 * Also generates the `Accept-CH` and `Critical-CH` response headers needed
 * to request hints from the browser.
 *
 * @example
 * ```ts
 * import { ClientHints } from '@czap/edge';
 *
 * // In an edge handler:
 * const caps = ClientHints.parseClientHints(request.headers);
 * const response = new Response(body, {
 *   headers: {
 *     'Accept-CH': ClientHints.acceptCHHeader(),
 *     'Critical-CH': ClientHints.criticalCHHeader(),
 *   },
 * });
 * ```
 */
export declare const ClientHints: {
    /** Parse Client Hints headers into {@link ExtendedDeviceCapabilities}. */
    readonly parseClientHints: typeof parseClientHints;
    /** Produce the `Accept-CH` response header value listing all useful hints. */
    readonly acceptCHHeader: typeof acceptCHHeader;
    /** Produce the `Critical-CH` response header value listing boot-required hints. */
    readonly criticalCHHeader: typeof criticalCHHeader;
    /** Produce the `Vary` response header value for tier-varying HTML (#122). */
    readonly varyCHHeader: typeof varyCHHeader;
    /** Derive Save-Data/DPR capabilities for responsive-media projection (#125). */
    readonly responsiveMediaCapabilities: typeof responsiveMediaCapabilities;
    /** Produce the `Vary` value for responsive-media representations (#125). */
    readonly responsiveMediaVaryHeader: typeof responsiveMediaVaryHeader;
};
export declare namespace ClientHints {
    /** Alias for {@link ClientHintsHeaders} — plain-object header bag shape. */
    type Headers = ClientHintsHeaders;
}
export {};
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