import type { MemoryIdentity } from '../identity/index.js';
/**
 * MemoryEntry — a single stored item with decay-, version-, and source-aware
 * metadata.
 *
 * Entry shape is generic over `T` so stores can hold messages, facts,
 * narrative traces, or anything else JSON-serializable. The metadata fields
 * around `value` are what make entries first-class objects instead of raw
 * blobs:
 *
 *   - `version`       — optimistic concurrency (`putIfVersion`) + migration
 *   - `tier`          — MemGPT-style hot/warm/cold classification
 *   - `source`        — provenance — "where did this memory come from?"
 *   - `lastAccessedAt` / `accessCount` — decay signals
 *   - `ttl`           — absolute expiry at the storage layer
 *   - `embeddingModel`— compatibility check for semantic search
 *
 * Entries are **immutable in spirit** — a "mutation" is a new entry with the
 * same `id` and an incremented `version`. Storage adapters may implement
 * this as an in-place update or an append-only log, but the library treats
 * entries as values.
 *
 * NOTE: `readonly` modifiers are a TypeScript compile-time hint only. At
 * runtime, nothing prevents a consumer from mutating an entry they received.
 * The library's internal code never mutates entries; adapters that wish to
 * enforce this at runtime may `Object.freeze(entry)` before returning.
 */
export interface MemoryEntry<T = unknown> {
    /** Stable id within the identity namespace. */
    readonly id: string;
    /** The actual stored payload. JSON-serializable. */
    readonly value: T;
    /**
     * Free-form metadata — tags, labels, user-supplied annotations. Kept
     * separate from the decay / version fields so those stay typed.
     */
    readonly metadata?: Record<string, unknown>;
    /**
     * Monotonic version number. Stores use this for `putIfVersion` optimistic
     * concurrency — write only if the entry is still at the version the
     * writer expected. Defaults to 1 on first write; callers increment.
     */
    readonly version: number;
    /** Unix ms. */
    readonly createdAt: number;
    /** Unix ms. Equal to createdAt on first write. */
    readonly updatedAt: number;
    /** Unix ms. Updated by `store.get` / retrieval stages. Decay input. */
    readonly lastAccessedAt: number;
    /** Number of times this entry has been read. Decay input. */
    readonly accessCount: number;
    /**
     * Optional absolute expiry (unix ms). Storage adapters MUST refuse to
     * return entries past their ttl. Implementations: InMemory filters on
     * read, Redis uses native EXPIRE, DynamoDB uses TTL attribute.
     */
    readonly ttl?: number;
    /**
     * Optional decay policy applied at retrieval time. When present, stages
     * that rank entries (picker, reranker) decrease relevance for entries
     * whose `lastAccessedAt` is far in the past. See `decay.ts`.
     */
    readonly decayPolicy?: DecayPolicy;
    /**
     * Tier classification — enables MemGPT-style page-in/page-out policies.
     * Stages can filter by tier (e.g. "load hot entries first, consult cold
     * only under pressure"). Omitting the field means "untiered."
     */
    readonly tier?: 'hot' | 'warm' | 'cold';
    /**
     * Provenance — which turn / runtime stage / message produced this entry.
     * Lets retrieval cite sources ("remembered from turn 5") and lets
     * `causalChain` cross session boundaries.
     */
    readonly source?: MemorySource;
    /**
     * Optional dense vector embedding of this entry's value. Populated
     * by semantic-memory pipelines (see `embedMessages` / `embedBeats`
     * stages) when an `Embedder` is configured. Stores that support
     * vector search index on this field; stores that don't ignore it.
     *
     * Vector length MUST match the configured embedder's `dimensions`.
     * Mixing embedders of different sizes within the same identity
     * namespace will break cosine similarity — `store.search()` uses
     * `cosineSimilarity()` which throws on length mismatch.
     */
    readonly embedding?: readonly number[];
    /**
     * Identifier of the embedder that produced `embedding`. Search
     * stages compare this against the active embedder's id before
     * trusting distance scores — prevents silent retrieval corruption
     * when an embedding model is swapped but old entries are still
     * indexed with the previous vector space.
     */
    readonly embeddingModel?: string;
}
/**
 * Where a memory entry came from. The library populates this automatically
 * when entries are written from inside a memory stage (writeMessages,
 * extractFacts, etc.); consumers can populate it when writing programmatically.
 *
 * When searching across sessions ("did we learn this in a previous session?"),
 * `identity` + `turn` + `runtimeStageId` form a globally-unique causal coordinate
 * — you can replay exactly what the agent was doing when the entry was born.
 */
export interface MemorySource {
    /** Run-local turn counter. */
    readonly turn?: number;
    /** footprintjs runtime stage id (`stageId#executionIndex`). */
    readonly runtimeStageId?: string;
    /** Originating message id, if the entry came from a conversation turn. */
    readonly messageId?: string;
    /**
     * Cross-session provenance — the `MemoryIdentity` that produced this entry.
     * Lets retrieval stages show "remembered from session X, user Y, turn 5"
     * instead of anonymous citation. Storage adapters MUST preserve this field
     * verbatim on every read/write.
     */
    readonly identity?: MemoryIdentity;
}
/**
 * Natural-forgetting policy. Decay applies at retrieval time: the entry's
 * stored value is never mutated; only its computed "relevance" is adjusted.
 *
 * Consumers choose half-life + access boost to match their domain:
 *   - Fast-moving (news, tickets) — halfLifeMs ≈ 1 day, accessBoost ≈ 1.5
 *   - Stable (user profile, facts)— halfLifeMs ≈ 30 days, accessBoost ≈ 1.1
 */
export interface DecayPolicy {
    /**
     * How long for relevance to halve when never accessed. Milliseconds.
     */
    readonly halfLifeMs: number;
    /**
     * Multiplier applied per access (clamped to a reasonable ceiling inside
     * `applyDecay`). Values > 1.0 boost frequently-used entries; values in
     * (0, 1.0) would *reduce* relevance with use (rarely desired).
     */
    readonly accessBoost: number;
}
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