import type { TokenCounter } from './types.js';
/**
 * The prefix length below which unifying buys nothing, and `Infinity` when there
 * is no answer.
 *
 * Lives here rather than in the CLI because it is the gate on this whole report
 * and a gate with no test is decoration. It was a private function in the CLI
 * first; a mutation run deleting the `unknown` branch survived, which is what a
 * function nothing can reach looks like from the outside.
 *
 * `unknown` and a missing minimum both yield `Infinity`, so nothing is reported.
 * That is the direction to fail: telling somebody to unify a preamble across
 * twelve files to enable caching their provider may not offer spends their
 * afternoon, and unlike a wrong number on a report nothing later corrects it.
 */
export declare function cacheableMinimum(model: {
    caching?: string | null;
    cacheMinTokens?: number | null;
} | undefined): number;
export interface PrefixCandidate {
    /** How the report names it. A path, or a path with a marked prompt's id. */
    path: string;
    text: string;
}
export interface SharedPrefix {
    /** Every prompt in the group, in the order they were given. */
    paths: string[];
    /** Blocks the group has in common, counted from the start. */
    blocks: number;
    /** Estimated tokens in that prefix, as the first prompt writes it. */
    tokens: number;
    /**
     * What stops the prefixes being byte-identical today.
     *
     * `whitespace` — collapsing runs of whitespace makes them equal, so a
     * formatter fixes it and no wording decision is needed.
     * `wording` — something else differs: capitalisation, punctuation, word order,
     * or genuinely different words. Someone has to choose.
     */
    drift: 'whitespace' | 'wording';
    /** The shared prefix as the first prompt in the group writes it. */
    sample: string;
}
export interface SharedPrefixOptions {
    /**
     * The model's cacheable minimum. A shared prefix below it buys nothing, so it
     * is not reported — the same refusal `reorder.ts` makes, for the same reason:
     * a change that recovers nothing is a diff for its own sake.
     */
    minTokens?: number;
    countTokens?: TokenCounter;
}
/**
 * Groups of prompts that could share a cache prefix and do not.
 *
 * Grouped by their **first** block, which is not a shortcut. Caching matches from
 * the beginning of the request, so two prompts whose opening paragraphs differ
 * share nothing no matter how identical the rest is — a group keyed on anything
 * later would name prompts that cannot be made to share a prefix without
 * reordering them, which is a different and far more dangerous change.
 */
export declare function sharedPrefixes(prompts: readonly PrefixCandidate[], options?: SharedPrefixOptions): SharedPrefix[];
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