/**
 * ============================================================
 * Embeddings — local hybrid (sparse + dense) retrieval support
 *
 * TF-IDF is fast and zero-cost but misses synonyms / paraphrase. A small local
 * embedding model (BGE-small, multilingual-e5-small, nomic-embed-text, …)
 * loaded in LM Studio or Ollama bridges that gap without sending anything
 * off the machine.
 *
 * Design choices:
 *   - Opt-in via g1nation.embeddingModel (empty = disabled). We don't auto-
 *     pick a model because the user has to load it in LM Studio/Ollama first.
 *   - Calls are best-effort: a missing model / network blip falls back to
 *     pure TF-IDF without breaking the query.
 *   - We never block retrieval on embedding work. Missing-file embeddings are
 *     populated by a separate fire-and-forget pass after the TF-IDF answer
 *     ships, so the *next* query benefits.
 *
 * Numerical format:
 *   - Vectors are `number[]` (not Float32Array) so they JSON-serialize for
 *     the brain-index cache without per-element conversion. The hot loop
 *     (cosine) is small enough that the extra precision is irrelevant to
 *     throughput on typical brain sizes.
 * ============================================================
 */

import { resolveEngine, buildApiUrl, logError, logInfo } from '../utils';

/** Maximum characters of a single text chunk fed to the embedding model. */
const EMBED_INPUT_CAP = 4000;
/** Maximum texts per embedding API call. */
const BATCH_SIZE = 16;
/** Request timeout for one embedding batch. */
const REQ_TIMEOUT_MS = 30000;

export interface EmbeddingCallOptions {
    /** OpenAI-compatible base URL (e.g. http://127.0.0.1:1234 for LM Studio). */
    baseUrl: string;
    /** Embedding model name as registered in LM Studio / Ollama. Empty disables. */
    model: string;
    /** AbortSignal for cancellation propagation. */
    signal?: AbortSignal;
    /**
     * Task kind for asymmetric embedding models. nomic-embed v1.5 / e5 계열은
     * 질의·문서에 서로 다른 prefix 를 *반드시* 붙여야 본래 품질이 나온다.
     * embedTexts 기본 'document', embedQuery 는 항상 'query'.
     */
    kind?: 'query' | 'document';
}

/**
 * 모델별 task prefix. prefix 미적용 시 nomic/e5 는 의미 매칭 품질이 크게 떨어진다
 * (모델 카드 명시 요구사항). 알 수 없는 모델은 prefix 없음.
 */
export function taskPrefix(model: string, kind: 'query' | 'document'): string {
    if (/nomic/i.test(model)) return kind === 'query' ? 'search_query: ' : 'search_document: ';
    if (/(^|[^a-z0-9])e5([^a-z0-9]|$)/i.test(model)) return kind === 'query' ? 'query: ' : 'passage: ';
    return '';
}

/**
 * Embed a batch of texts. Returns one vector per input. Throws if the call
 * fails — callers wrap with try/catch and fall back to TF-IDF.
 *
 * Engine selection mirrors the chat path: LM Studio takes precedence when the
 * URL points at port 1234 or includes the /v1/ prefix, otherwise Ollama.
 */
export async function embedTexts(texts: string[], opts: EmbeddingCallOptions): Promise<number[][]> {
    if (!opts.model.trim()) throw new Error('Embedding model not configured.');
    if (!texts || texts.length === 0) return [];
    const engine = resolveEngine(opts.baseUrl);
    const url = buildApiUrl(opts.baseUrl, engine, 'embeddings');
    const prefix = taskPrefix(opts.model, opts.kind ?? 'document');
    const out: number[][] = [];
    for (let i = 0; i < texts.length; i += BATCH_SIZE) {
        const batch = texts.slice(i, i + BATCH_SIZE).map((t) => prefix + clipForEmbedding(t));
        const body = engine === 'lmstudio'
            ? { model: opts.model, input: batch }
            : { model: opts.model, input: batch };  // Ollama 0.1.30+ also accepts array input
        const controller = opts.signal ? undefined : new AbortController();
        const timer = controller ? setTimeout(() => controller.abort(), REQ_TIMEOUT_MS) : undefined;
        try {
            const response = await fetch(url, {
                method: 'POST',
                headers: { 'Content-Type': 'application/json' },
                body: JSON.stringify(body),
                signal: opts.signal ?? controller?.signal,
            });
            if (!response.ok) {
                const errText = await response.text().catch(() => '');
                throw new Error(`Embedding endpoint returned ${response.status}: ${errText.slice(0, 200)}`);
            }
            const json = await response.json() as any;
            // OpenAI-compatible: { data: [{ embedding: [...] }, ...] }
            // Ollama: { embedding: [...] } (single) or { embeddings: [[...], ...] } (newer)
            if (Array.isArray(json?.data)) {
                for (const row of json.data) {
                    if (Array.isArray(row?.embedding)) out.push(row.embedding as number[]);
                }
            } else if (Array.isArray(json?.embeddings)) {
                for (const v of json.embeddings) {
                    if (Array.isArray(v)) out.push(v as number[]);
                }
            } else if (Array.isArray(json?.embedding)) {
                out.push(json.embedding as number[]);
            }
        } finally {
            if (timer) clearTimeout(timer);
        }
    }
    return out;
}

/** Cosine similarity for equal-length vectors. Returns 0 when either vector is empty / zero. */
export function cosineSimilarity(a: number[], b: number[]): number {
    if (!a || !b || a.length === 0 || b.length === 0) return 0;
    const n = Math.min(a.length, b.length);
    let dot = 0, na = 0, nb = 0;
    for (let i = 0; i < n; i++) {
        const va = a[i], vb = b[i];
        dot += va * vb;
        na += va * va;
        nb += vb * vb;
    }
    if (na === 0 || nb === 0) return 0;
    return dot / (Math.sqrt(na) * Math.sqrt(nb));
}

/** Clip a text to a length the embedding model will accept without truncation surprises. */
function clipForEmbedding(text: string): string {
    if (!text) return '';
    return text.length <= EMBED_INPUT_CAP ? text : text.slice(0, EMBED_INPUT_CAP);
}

/**
 * Tiny LRU for query embeddings: typing the same query twice (or retrying)
 * shouldn't re-hit the embedding endpoint. Keyed on `model + text`.
 *
 * Capped at QUERY_CACHE_MAX entries; oldest evicted. Strictly process-local
 * (no disk persistence) because the query strings are short and the gains
 * across restarts are marginal.
 */
const QUERY_CACHE_MAX = 32;
const _queryCache = new Map<string, number[]>();
function queryCacheKey(model: string, text: string): string { return `${model}|${text}`; }
export function getCachedQueryEmbedding(model: string, text: string): number[] | undefined {
    const k = queryCacheKey(model, text);
    const v = _queryCache.get(k);
    if (!v) return undefined;
    // refresh recency
    _queryCache.delete(k);
    _queryCache.set(k, v);
    return v;
}
export function setCachedQueryEmbedding(model: string, text: string, vec: number[]): void {
    const k = queryCacheKey(model, text);
    _queryCache.set(k, vec);
    if (_queryCache.size > QUERY_CACHE_MAX) {
        const oldest = _queryCache.keys().next().value;
        if (oldest !== undefined) _queryCache.delete(oldest);
    }
}

/**
 * Embed a single query string, using the in-process LRU. Returns `undefined`
 * if the embedding endpoint fails — callers treat that as "semantic
 * scoring unavailable for this turn, fall back to TF-IDF".
 */
export async function embedQuery(text: string, opts: EmbeddingCallOptions): Promise<number[] | undefined> {
    if (!opts.model.trim() || !text.trim()) return undefined;
    const cached = getCachedQueryEmbedding(opts.model, text);
    if (cached) return cached;
    try {
        const [vec] = await embedTexts([text], { ...opts, kind: 'query' });
        if (vec && vec.length > 0) {
            setCachedQueryEmbedding(opts.model, text, vec);
            logInfo('Query embedding computed.', { model: opts.model, dim: vec.length });
            return vec;
        }
    } catch (e: any) {
        logError('Query embedding failed.', { model: opts.model, error: e?.message ?? String(e) });
    }
    return undefined;
}