/**
 * backendDelegationBlock.ts — S496: extracted from agentLoop.ts
 *
 * Tenta di delegare il task al backend smolagents (HuggingFace Spaces) tramite
 * SSE streaming. Viene attivato solo per task ad alta complessità quando il
 * backend è sano e disponibile.
 *
 * Comportamento:
 * - Se il backend risponde con successo → streama chunks e restituisce true
 *   (il chiamante deve fare `return` dal loop agente).
 * - Se il backend non è eleggibile (non healthy / task non adatto) → { handled: false, failed: false }
 * - Se il backend risponde con successo → { handled: true, failed: false }
 * - Se il backend viene tentato ma fallisce (SSE error / risposta vuota) → { handled: false, failed: true }
 *   (S638: il chiamante può usare failed:true per attivare graph orchestration come fallback)
 *
 * @module backendDelegationBlock
 */

import type { PlanLike } from "../agent/GraphOrchestrator";
import { vfsAsync } from "@/lib/vfsDb"; // GAP-2: vfsAsync per notifica Safari

export interface BackendDelegationCtx {
  BACKEND_BASE:        string | undefined;
  BACKEND_TOKEN:       string | undefined;
  isBackendHealthy:    () => boolean;
  taskPlan:            PlanLike | null;
  signal?:             AbortSignal;
  lastUserMsg:         string;
  initialMessages:     Array<{ role: string; content: string }>;
  onStatus:            (msg: string) => void;
  onChunk:             (c: string) => void;
  getProjectContext:   () => string;
  getLearnHints:       () => string[];
  recordBackendResult: (success: boolean) => void;
}

export interface BackendDelegationResult {
  handled:      boolean;                               // true → backend ha gestito il task, caller deve fare return
  failed:       boolean;                               // true → backend tentato ma fallito (S638: attiva graph fallback)
  updatedFiles: Array<{ path: string; content: string }>;  // GAP-1: file scritti dal backend per VFS sync
  // GAP-4: stato parziale catturato prima del timeout — seed GraphOrchestrator con tool gia' completati
  partialToolOutputs: Array<{ tool: string; result: string; path?: string }>;
}

// S638: return type cambiato da boolean a BackendDelegationResult per distinguere
// "non eleggibile" (failed:false) da "tentato e fallito" (failed:true).
export async function runBackendDelegation(ctx: BackendDelegationCtx): Promise<BackendDelegationResult> {
  const {
    BACKEND_BASE, BACKEND_TOKEN, isBackendHealthy, taskPlan, signal,
    lastUserMsg, initialMessages, onStatus, onChunk,
    getProjectContext, getLearnHints, recordBackendResult,
  } = ctx;

  // Gate: backend presente, sano, task complesso, non abortito
  if (
    !BACKEND_BASE ||
    !isBackendHealthy() ||
    !taskPlan ||
    !(
      taskPlan.complexity === "high" ||
      (taskPlan.complexity === "medium" && (taskPlan.subtasks?.length ?? 0) >= 3)
    ) ||
    (taskPlan.subtasks?.length ?? 0) < 2 ||
    signal?.aborted
  ) {
    return { handled: false, failed: false, updatedFiles: [], partialToolOutputs: [] };  // S638: non eleggibile, non tentato
  }

  // T009: SSE consumer — mostra step progress in tempo reale + result streaming
  onStatus("Delegazione al backend (smolagents — task ad alta complessità)…");
  let _sseResultText = "";
  let _sseSuccess    = false;
  const _vfsUpdates: Array<{ path: string; content: string }> = [];  // GAP-1: file scritti dal backend
  const _toolOutputs: Array<{ tool: string; result: string; path?: string }> = [];  // GAP-4: partial tool outputs per graph seed
  let _bgTaskId: string | null = null;

  try {
    const _sseCtrl = new AbortController();
    const _sseTid  = setTimeout(() => _sseCtrl.abort(), 120_000);

    const _projCtx    = getProjectContext();
    const _learnHints = getLearnHints();

    // S-PERSIST step 1: crea task persistente con UUID stabile — sopravvive alla chiusura del browser
    const _taskPayload = JSON.stringify({
      goal:            lastUserMsg,
      context:         initialMessages.slice(-20).map(m => ({
        role:    m.role,
        content: String(m.content).slice(0, 400),
      })),
      max_steps:       8,
      project_context: _projCtx,
      learning_hints:  _learnHints,
    });
    const _taskCreateRes = await fetch(BACKEND_BASE + "/api/agent/tasks", {
      method: "POST",
      headers: {
        "Content-Type": "application/json",
        ...(BACKEND_TOKEN ? { "X-Internal-Token": BACKEND_TOKEN } : {}),
      },
      body: _taskPayload,
    }).catch(() => null);

    if (_taskCreateRes?.ok) {
      try {
        const _td = await _taskCreateRes.json() as { taskId?: string };
        _bgTaskId = _td.taskId ?? null;
      } catch { /* non-fatal */ }
    }

    // S-PERSIST step 2: salva task_id in localStorage — recovery al boot se il telefono si spegne
    if (_bgTaskId) {
      try {
        const _pending: Array<{ taskId: string; goal: string; timestamp: number }> =
          JSON.parse(localStorage.getItem("agente:pending_bg_tasks") ?? "[]");
        _pending.push({ taskId: _bgTaskId, goal: lastUserMsg.slice(0, 200), timestamp: Date.now() });
        localStorage.setItem("agente:pending_bg_tasks", JSON.stringify(_pending.slice(-5)));
      } catch { /* non-fatal — Safari Private Mode */ }
    }

    // S-PERSIST step 3: apre SSE stream del task creato (fallback a run-stream se tasks API non disponibile)
    const _streamUrl    = _bgTaskId
      ? `${BACKEND_BASE}/api/agent/tasks/${_bgTaskId}/stream`
      : BACKEND_BASE + "/api/agent/run-stream";
    const _streamMethod = _bgTaskId ? "GET" : "POST";
    const _streamBody   = _bgTaskId ? undefined : _taskPayload;

    const _sseRes = await fetch(_streamUrl, {
      method: _streamMethod,
      headers: {
        ...(_streamBody ? { "Content-Type": "application/json" } : {}),
        ...(BACKEND_TOKEN ? { "X-Internal-Token": BACKEND_TOKEN } : {}),
      },
      body: _streamBody,
      signal: _sseCtrl.signal,
    }).catch(() => null);

    if (_sseRes?.ok && _sseRes.body) {
      const _sseReader = _sseRes.body.getReader();
      const _sseDec    = new TextDecoder();
      let _sseBuf      = "";

      const _stepLabels: Record<string, string> = {
        llm:        "Ragionamento AI in corso…",
        fallback:   "Generazione risposta…",
        smolagents: "Agente multi-step…",
        tool:       "Uso tool…",
        search:     "Ricerca…",
        code:       "Esecuzione codice…",
      };

      outer: while (true) {
        const { done, value } = await _sseReader.read();
        if (done || signal?.aborted) break;
        _sseBuf += _sseDec.decode(value, { stream: true });
        const _sseLines = _sseBuf.split("\n");
        _sseBuf = _sseLines.pop() ?? "";

        for (const _sseLine of _sseLines) {
          const _sseData = _sseLine.startsWith("data: ")
            ? _sseLine.slice(6).trim()
            : "";
          if (!_sseData || _sseData === "[DONE]") continue;

          try {
            const _sseEvt = JSON.parse(_sseData) as Record<string, unknown>;
            const _evType = _sseEvt.type as string;

            if (_evType === "step_done") {
              const _step   = _sseEvt.step as Record<string, unknown> | undefined;
              const _action = String(_step?.action ?? "");
              // GAP-1: file scritto dal backend → sync VFS locale
              if (_action === "file_written" && _step?.path && _step?.content !== undefined) {
                const _fPath = String(_step.path);
                const _fContent = String(_step.content);
                _vfsUpdates.push({ path: _fPath, content: _fContent });
                // GAP-4: cattura come tool output per seed del grafo
                _toolOutputs.push({ tool: "write_file", result: `✅ File scritto: ${_fPath}`, path: _fPath });
                // GAP-2: usa vfsAsync.write che chiama _notifyVfsChanged → aggiorna FileExplorer su Safari iOS
                // vfsDb.files.put() bypassava il listener del file tree su tab in background
                vfsAsync.write(_fPath, _fContent)
                  .catch(() => { /* non-blocking — VFS sync best-effort */ });
              } else {
                // GAP-4: cattura output strutturati se presenti nel step event (backend tool_name + result)
                const _backendToolName = String(_step?.tool_name ?? "");
                const _backendResult   = String(_step?.result ?? _step?.output ?? "");
                if (_backendToolName && _backendResult) {
                  _toolOutputs.push({ tool: _backendToolName, result: _backendResult.slice(0, 600) });
                }
                const _label  = _stepLabels[_action] ?? `Step ${_step?.loop ?? ""}…`;
                onStatus(_label);
              }
            } else if (_evType === "task_done") {
              const _res = _sseEvt.result;
              const _txt: string =
                typeof _res === "string" ? _res :
                ((_res as Record<string, unknown>)?.output as string ?? JSON.stringify(_res ?? ""));
              if (_txt && _txt.length > 10 && _sseEvt.success) {
                _sseResultText = _txt;
                _sseSuccess    = true;
              }
              break outer;
            } else if (_evType === "task_error") {
              break outer;
            } else if (_evType === "plan_update") {
              // GAP-1: plan_update SSE → StreamingPlanBubble in real-time (Replit-style)
              // Prima: entrambi frontend e backend credevano che l'altro gestisse il piano — nessuno lo faceva.
              // Ora: dispatcha custom events che StreamingPlanBubble ascolta per il piano live.
              const _su = _sseEvt.subtasks as Array<{id: number|string, description: string, tool: string}> | undefined;
              if (_su?.length) {
                window.dispatchEvent(new CustomEvent("agente-ai:plan-clear", {}));
                _su.forEach((_item, _i) => {
                  window.dispatchEvent(new CustomEvent("agente-ai:plan-reveal", {
                    detail: { id: _i, total: _su.length, item: { title: _item.description, tool: _item.tool } }
                  }));
                });
                // P22-NE: emetti agent:plan-update nativo (completa migrazione P21-F2)
                window.dispatchEvent(new CustomEvent("agent:plan-update", {
                  detail: {
                    taskId:   undefined,
                    goal:     "",
                    subtasks: _su.map((_s, _i) => ({ id: _i, description: _s.description, tool: _s.tool })),
                  },
                }));
              }
            }
            // S367/GAP-1: plan_update events now wired — prima dead-end, ora dispatched
          } catch { /* malformed SSE line — skip */ }
        }
      }
      try { _sseReader.cancel(); } catch { /* non-blocking */ }
    }

    clearTimeout(_sseTid);
    recordBackendResult(_sseSuccess);
  } catch {
    /* SSE failed — fall through to browser loop */
    recordBackendResult(false);
  }

  if (
    _sseSuccess &&
    _sseResultText &&
    !_sseResultText.includes("non disponibile") &&
    !_sseResultText.includes("Backend reasoning")
  ) {
    onStatus("");
    for (let i = 0; i < _sseResultText.length; i += 12) {
      if (signal?.aborted) break;
      onChunk(_sseResultText.slice(i, i + 12));
    }
    // S-PERSIST: task completato → rimuovi dal pending (recovery non più necessaria)
    if (_bgTaskId) {
      try {
        const _p: Array<{ taskId: string }> = JSON.parse(localStorage.getItem("agente:pending_bg_tasks") ?? "[]");
        localStorage.setItem("agente:pending_bg_tasks", JSON.stringify(_p.filter(t => t.taskId !== _bgTaskId)));
      } catch { /* non-fatal */ }
    }
    return { handled: true, failed: false, updatedFiles: _vfsUpdates, partialToolOutputs: [] };  // S638: successo
  }

  onStatus("");
  return { handled: false, failed: true, updatedFiles: _vfsUpdates, partialToolOutputs: _toolOutputs };  // S638+GAP-4: tentato ma fallito → graph fallback con stato parziale
}