/* The Swan engine interface, and the runtime choice between backends.
 *
 * Event Horizon asks Swan two things: "run this PyRel" and "turn this question
 * into PyRel and run it". Where that happens is a deployment detail:
 *
 *   wasm    Pyodide + DuckDB + swan.duckdb_extension, in the tab. Swan itself
 *           loads and runs (verified: tools/verify_pyrel_wasm.mjs), but PyRel
 *           compilation is Python, so this backend serves SQL only for now.
 *           Staged by tools/vendor_swan_wasm.mjs.
 *   server  tools/swan_sidecar.py behind server.js's /api proxy, running the
 *           native extension from the rai-swan wheel. Works today.
 *
 * Both satisfy the same interface, so nothing above this module knows which one
 * answered:
 *
 *   await engine.ready()            -> { engine, swan, duckdb, model, nl }
 *   await engine.schema()           -> { schema, model }
 *   await engine.pyrel(code)        -> { code, rows }
 *   await engine.ask(question)      -> { question, code, rows, attempts, examples }
 *   await engine.chat(q, history)   -> the same, with prior turns as context
 *
 * `auto` prefers wasm and falls back to server, reporting *why* it fell back
 * rather than silently degrading — a browser-only Swan and a proxied one have
 * very different privacy and latency characteristics, and which one you got is
 * something the page shows the user.
 */
import { createServerEngine } from './server_engine.js';
import { createWasmEngine } from './wasm_engine.js';

const BACKENDS = { wasm: createWasmEngine, server: createServerEngine };

/** Engine order for `auto`. wasm first: it needs no server and no proxy hop. */
const AUTO_ORDER = ['wasm', 'server'];

export function engineModeFromLocation(search = (typeof location !== 'undefined' ? location.search : '')) {
  const mode = new URLSearchParams(search).get('engine');
  return mode && mode in BACKENDS ? mode : (mode === 'auto' ? 'auto' : 'auto');
}

/* The project's own hosted generator, used when a page says nothing else.
 *
 * A default is a decision about where a visitor's question travels, so it is a
 * named public endpoint this project runs rather than a guess at localhost — and
 * the page says where questions go, in `note` below, rather than leaving it to
 * be discovered. `?nlq=off` opts out and `?nlq=<url>` points elsewhere.
 *
 * Everything except producing text already runs in the browser: schema
 * rendering, few-shot selection, the sandbox, error translation and retries are
 * all in the compiled `pyrel_duckdb.nlq`. Only the prompt leaves. */
export const DEFAULT_NLQ = [
  /* Unquantized weights on a shared GPU, ~2s a question — reached through a
   * proxy rather than directly, and the indirection is the whole point.
   *
   * ZeroGPU bills GPU time to a Hugging Face account, and the daily allowance
   * depends on which one: 2 minutes for an unauthenticated caller, 40 for PRO,
   * with the highest queue priority. A request from a visitor's tab names no
   * account, so it draws on that 2 minutes — which a public page exhausts almost
   * immediately, and every call after that is refused in ~0.4s with
   * `event: error` and a null body. No status code, no message, and nothing in
   * the Space's own log, so an exhausted quota and a hard block look exactly
   * alike from here. black-swan-proxy holds a token and lends the account.
   *
   * Pointing at the GPU Space directly instead would spend that 2 minutes and
   * then be a guaranteed half-second of nothing before every question. */
  'https://maxdemarzi-black-swan-proxy.hf.space/v1/chat/completions',
  /* The same model quantized, on CPU, unmetered. The proxy spends a finite
   * daily quota; when it runs out this is what answers, which is why the chain
   * outlived the problem that created it. Slower — though 14s on a pruned
   * schema, not the ~110s a full one costs. */
  'https://maxdemarzi-black-swan-pyrel.hf.space/v1/chat/completions',
];
export const DEFAULT_NLQ_MODEL = 'maxdemarzi/black-swan-lora';

/**
 * Where the browser engine sends a prompt.
 *
 *   (nothing)                 the hosted generator above
 *   ?nlq=off                  no generation; PyRel still works, `nl: false`
 *   ?nlq=http://host/...      somewhere else
 */
export function nlqEndpointFromLocation(search = (typeof location !== 'undefined' ? location.search : '')) {
  const raw = new URLSearchParams(search).get('nlq');
  if (raw === null) return DEFAULT_NLQ;
  if (/^(off|none|0|false)$/i.test(raw)) return null;
  // Comma-separated, so a caller can supply their own chain rather than being
  // stuck with one host.
  const urls = raw.split(',').map((u) => u.trim()).filter(Boolean).map((u) => {
    try {
      // Reject anything that is not an absolute http(s) URL rather than letting
      // a typo become a request to this origin's own 404 page, parsed as a model.
      const parsed = new URL(u, typeof location !== 'undefined' ? location.href : undefined);
      return /^https?:$/.test(parsed.protocol) ? parsed.href : null;
    } catch {
      return null;
    }
  }).filter(Boolean);
  return urls.length ? urls : null;
}

/**
 * Whether to send only the concepts a question needs. `?prune=0` turns it off.
 *
 * On by default because the alternative is measurably broken: TPC-DS renders to
 * 8,203 prompt tokens whole, against the 317-640 the adapter was trained on, and
 * the attention that costs peaks at 11 GiB on a 12 GiB card — which then spills
 * to system memory and takes ~150s instead of ~4s. Pruning brings it to ~1,850.
 * A retry escalates to the full schema, so a question the pruner misjudges costs
 * an extra attempt rather than an answer, which is what makes a default safe.
 */
export function nlqPruneFromLocation(search = (typeof location !== 'undefined' ? location.search : '')) {
  const v = new URLSearchParams(search).get('prune');
  return !(v === '0' || v === 'false' || v === 'off');
}

/**
 * Which model to name in the request. `?nlqModel=black-swan-sft15-q4:1.5b`
 *
 * Not optional for every server, which is why it is here rather than assumed: a
 * host serving one fine-tune usually ignores the field, but ollama's
 * OpenAI-compatible endpoint rejects a request without it. Named `nlqModel`
 * rather than `model` because this page already has a *data* model and a `graph`
 * parameter, and one of those confusions is enough.
 */
export function nlqModelFromLocation(search = (typeof location !== 'undefined' ? location.search : '')) {
  const params = new URLSearchParams(search);
  const named = params.get('nlqModel');
  if (named) return named;
  // Only default the model name alongside the default endpoint. Sending our
  // model's name to someone else's server is at best ignored and at worst a 404
  // naming a model they have never heard of.
  return params.get('nlq') === null ? DEFAULT_NLQ_MODEL : null;
}

/**
 * @param {object} opts
 * @param {'auto'|'wasm'|'server'} opts.mode
 * @param {(msg: string) => void} [opts.onProgress] surfaced in the UI while a
 *        backend boots — the wasm one downloads tens of megabytes, so silence
 *        for that long reads as a hang.
 */
export function createEngine({ mode = 'auto', onProgress = () => {}, nlq = null, nlqPrune = true, nlqModel = null } = {}) {
  const attempts = [];
  let chosen = null;
  let readyPromise = null;

  async function boot() {
    const order = mode === 'auto' ? AUTO_ORDER : [mode];
    /* An engine that booted but cannot compile PyRel *yet*. Held back in case a
     * later one can answer immediately, and selected if none can — see the end
     * of this function for why "none can" is the normal case, not the odd one. */
    let deferred = null;
    for (const name of order) {
      onProgress(`starting ${name} engine…`);
      // `nlq` means something only to the wasm backend; the sidecar holds its
      // own generator. Passed to both rather than special-cased, so adding a
      // third backend does not need this line changed.
      const candidate = BACKENDS[name]({ onProgress, nlq, nlqPrune, nlqModel });
      try {
        const info = await candidate.ready();
        /* Booting is not the same as being able to answer. The wasm engine loads
         * Swan and runs SQL, but has no PyRel front-end — compiling PyRel needs
         * pyrel_duckdb, which is Python. `auto` exists to find an engine that can
         * serve this page, so an engine that cannot compile PyRel is passed over
         * with a reason rather than selected and then failing on first use.
         * `?engine=wasm` still reaches it, for SQL. */
        if (mode === 'auto' && info.pyrel === false && info.pyrelAvailable) {
          const note = {
            engine: name,
            error: 'loaded, but has no PyRel front-end yet (needs Pyodide + pyrel_duckdb)',
          };
          attempts.push(note);
          deferred ||= { candidate, info: { ...info, engine: name }, note };
          onProgress(`${name} engine cannot compile PyRel — trying the next`);
          continue;
        }
        chosen = candidate;
        return { ...info, engine: name, attempts };
      } catch (err) {
        attempts.push({ engine: name, error: String(err && err.message || err) });
        // An explicitly requested backend that fails is an error, not a cue to
        // try something else — the caller asked for that one specifically.
        if (mode !== 'auto') throw err;
        onProgress(`${name} engine unavailable — ${attempts[attempts.length - 1].error}`);
      }
    }
    /* Nothing could answer straight away, so take the one that can answer once
     * it is asked to. This is the ordinary case wherever there is no sidecar —
     * a static host, or anyone who cloned the repo and opened a page without
     * starting a second process — and reporting "no Swan engine available" for
     * it was wrong: the engine is right there, it just wanted a hundred
     * megabytes of Python first, which is a question for the user rather than
     * grounds for refusing to run.
     *
     * Its own passed-over note is dropped on the way out. It is what the page
     * ends up running, and listing it under "engine unavailable" would describe
     * the thing that is working. A genuinely failed backend keeps its note. */
    if (deferred) {
      const i = attempts.indexOf(deferred.note);
      if (i >= 0) attempts.splice(i, 1);
      chosen = deferred.candidate;
      return { ...deferred.info, attempts };
    }

    const why = attempts.map((a) => `${a.engine}: ${a.error}`).join('; ');
    throw new Error(`no Swan engine available (${why})`);
  }

  function require() {
    if (!chosen) throw new Error('engine not ready — await ready() first');
    return chosen;
  }

  return {
    /** Idempotent: repeated calls share one boot, so two callers can't race two backends. */
    ready() { return (readyPromise ||= boot()); },
    get name() { return chosen ? chosen.name : null; },
    attempts,
    schema() { return require().schema(); },
    pyrel(code) { return require().pyrel(code); },
    ask(question) { return require().ask(question); },
    chat(question, history) {
      const backend = require();
      if (!backend.chat) throw new Error(`the ${backend.name} engine has no conversational endpoint`);
      return backend.chat(question, history);
    },

    /* Backend-specific capabilities, forwarded rather than assumed.
     *
     * These exist only on the wasm engine. Leaving them off the façade meant
     * `engine.sql(...)` was `undefined` even when the backend implemented it —
     * invisible to every static check, because the façade is an object literal
     * and nothing cross-references it against the backends. A browser session
     * calling sql() is what surfaced it. */
    sql(text) {
      const backend = require();
      if (!backend.sql) throw new Error(`the ${backend.name} engine does not execute raw SQL`);
      return backend.sql(text);
    },
    startPyrel(opts) {
      const backend = require();
      if (!backend.startPyrel) {
        throw new Error(`the ${backend.name} engine has no separate PyRel front-end to start`);
      }
      return backend.startPyrel(opts);
    },
    loadModel(source) {
      const backend = require();
      if (!backend.loadModel) throw new Error(`the ${backend.name} engine cannot load a model in-process`);
      return backend.loadModel(source);
    },
    loadDataset() {
      const backend = require();
      if (!backend.loadDataset) {
        throw new Error(`the ${backend.name} engine already has its data — loadDataset is for the browser`);
      }
      return backend.loadDataset();
    },

    /* Templates, forwarded for exactly the reason the comment above sql() gives
     * — and it caught me anyway. Both were implemented on the wasm backend and
     * verified there, the worker contract check passed, and the page still met
     * `engine.prepareTemplate is not a function`, because the façade is an
     * object literal that nothing cross-references against the backends. */
    prepareTemplate(spec) {
      const backend = require();
      if (!backend.prepareTemplate) {
        throw new Error(`the ${backend.name} engine cannot run templates — they need the browser engine`);
      }
      return backend.prepareTemplate(spec);
    },
    runTemplateCell(source) {
      const backend = require();
      if (!backend.runTemplateCell) {
        throw new Error(`the ${backend.name} engine cannot run templates — they need the browser engine`);
      }
      return backend.runTemplateCell(source);
    },
    templateGraph() {
      const backend = require();
      if (!backend.templateGraph) {
        throw new Error(`the ${backend.name} engine cannot read a template's model — that needs the browser engine`);
      }
      return backend.templateGraph();
    },
    /* Best-effort and fire-and-forget: this runs while the page is going away,
     * so an engine that cannot do it is not worth an error nobody will see. */
    closeTemplate() {
      const backend = require();
      return backend.closeTemplate ? backend.closeTemplate() : Promise.resolve(null);
    },

    /* The rules tier lands well after the dataset does — see the comment on
     * loadDataset in pyrel-worker.js. Engines that have no separate rules phase
     * (the sidecar evaluated them at startup) report so immediately, so a caller
     * can await this unconditionally. */
    rulesReady() {
      const backend = require();
      return backend.rulesReady ? backend.rulesReady() : Promise.resolve(null);
    },

    /* The two escape hatches from the cache, forwarded for the same reason as
     * sql() above: a capability the façade does not name is a capability no
     * caller can reach, and nothing static would notice. Both are browser-only —
     * the sidecar has no cache to be stale. */
    reloadModel() {
      const backend = require();
      if (!backend.reloadModel) {
        throw new Error(`the ${backend.name} engine evaluates its rules at startup — there is nothing cached to rebuild`);
      }
      return backend.reloadModel();
    },
    reloadData() {
      const backend = require();
      if (!backend.reloadData) {
        throw new Error(`the ${backend.name} engine reads its data directly — there is no cached copy to discard`);
      }
      return backend.reloadData();
    },
  };
}