/**
 * OpenAI WebSocket StreamFn Integration
 *
 * Wraps `OpenAIWebSocketManager` in a `StreamFn` that can be plugged into the
 * pi-embedded-runner agent in place of the default `streamSimple` HTTP function.
 *
 * Key behaviours:
 *  - Per-session `OpenAIWebSocketManager` (keyed by sessionId)
 *  - Tracks `previous_response_id` to send only incremental tool-result inputs
 *  - Falls back to `streamSimple` (HTTP) if the WebSocket connection fails
 *  - Cleanup helpers for releasing sessions after the run completes
 *
 * Complexity budget & risk mitigation:
 *  - **Transport aware**: respects `transport` (`auto` | `websocket` | `sse`)
 *  - **Transparent fallback in `auto` mode**: connect/send failures fall back to
 *    the existing HTTP `streamSimple`; forced `websocket` mode surfaces WS errors
 *  - **Zero shared state**: per-session registry; session cleanup on dispose prevents leaks
 *  - **Full parity**: all generation options (temperature, top_p, max_output_tokens,
 *    tool_choice, reasoning) forwarded identically to the HTTP path
 *
 * @see src/agents/openai-ws-connection.ts for the connection manager
 */

import type { StreamFn } from "@mariozechner/pi-agent-core";
import * as piAi from "@mariozechner/pi-ai";
import type {
  AssistantMessage,
  AssistantMessageEvent,
  AssistantMessageEventStream,
  StopReason,
} from "@mariozechner/pi-ai";
import {
  OpenAIWebSocketManager,
  type FunctionToolDefinition,
  type OpenAIWebSocketManagerOptions,
} from "./openai-ws-connection.js";
import {
  buildAssistantMessageFromResponse,
  convertMessagesToInputItems,
  convertTools,
  planTurnInput,
} from "./openai-ws-message-conversion.js";
import { log } from "./pi-embedded-runner/logger.js";
import {
  buildAssistantMessageWithZeroUsage,
  buildStreamErrorAssistantMessage,
} from "./stream-message-shared.js";

// ─────────────────────────────────────────────────────────────────────────────
// Per-session state
// ─────────────────────────────────────────────────────────────────────────────

interface WsSession {
  manager: OpenAIWebSocketManager;
  /** Number of messages that were in context.messages at the END of the last streamFn call. */
  lastContextLength: number;
  /** True if the connection has been established at least once. */
  everConnected: boolean;
  /** True once a best-effort warm-up attempt has run for this session. */
  warmUpAttempted: boolean;
  /** True if the session is permanently broken (no more reconnect). */
  broken: boolean;
}

/** Module-level registry: sessionId → WsSession */
const wsRegistry = new Map<string, WsSession>();

type OpenAIWsStreamDeps = {
  createManager: (options?: OpenAIWebSocketManagerOptions) => OpenAIWebSocketManager;
  streamSimple: typeof piAi.streamSimple;
};

const defaultOpenAIWsStreamDeps: OpenAIWsStreamDeps = {
  createManager: (options) => new OpenAIWebSocketManager(options),
  streamSimple: (...args) => piAi.streamSimple(...args),
};

let openAIWsStreamDeps: OpenAIWsStreamDeps = defaultOpenAIWsStreamDeps;

type AssistantMessageEventStreamLike = {
  push(event: AssistantMessageEvent): void;
  end(result?: AssistantMessage): void;
  result(): Promise<AssistantMessage>;
  [Symbol.asyncIterator](): AsyncIterator<AssistantMessageEvent>;
};

class LocalAssistantMessageEventStream implements AssistantMessageEventStreamLike {
  private readonly queue: AssistantMessageEvent[] = [];
  private readonly waiting: Array<(value: IteratorResult<AssistantMessageEvent>) => void> = [];
  private done = false;
  private readonly finalResultPromise: Promise<AssistantMessage>;
  private resolveFinalResult!: (result: AssistantMessage) => void;

  constructor() {
    this.finalResultPromise = new Promise((resolve) => {
      this.resolveFinalResult = resolve;
    });
  }

  push(event: AssistantMessageEvent): void {
    if (this.done) {
      return;
    }
    if (event.type === "done") {
      this.done = true;
      this.resolveFinalResult(event.message);
    } else if (event.type === "error") {
      this.done = true;
      this.resolveFinalResult(event.error);
    }
    const waiter = this.waiting.shift();
    if (waiter) {
      waiter({ value: event, done: false });
      return;
    }
    this.queue.push(event);
  }

  end(result?: AssistantMessage): void {
    this.done = true;
    if (result) {
      this.resolveFinalResult(result);
    }
    while (this.waiting.length > 0) {
      const waiter = this.waiting.shift();
      waiter?.({ value: undefined as unknown as AssistantMessageEvent, done: true });
    }
  }

  async *[Symbol.asyncIterator](): AsyncIterator<AssistantMessageEvent> {
    while (true) {
      if (this.queue.length > 0) {
        yield this.queue.shift()!;
        continue;
      }
      if (this.done) {
        return;
      }
      const result = await new Promise<IteratorResult<AssistantMessageEvent>>((resolve) => {
        this.waiting.push(resolve);
      });
      if (result.done) {
        return;
      }
      yield result.value;
    }
  }

  result(): Promise<AssistantMessage> {
    return this.finalResultPromise;
  }
}

function createEventStream(): AssistantMessageEventStream {
  return typeof piAi.createAssistantMessageEventStream === "function"
    ? piAi.createAssistantMessageEventStream()
    : (new LocalAssistantMessageEventStream() as unknown as AssistantMessageEventStream);
}

// ─────────────────────────────────────────────────────────────────────────────
// Public registry helpers
// ─────────────────────────────────────────────────────────────────────────────

/**
 * Release and close the WebSocket session for the given sessionId.
 * Call this after the agent run completes to free the connection.
 */
export function releaseWsSession(sessionId: string): void {
  const session = wsRegistry.get(sessionId);
  if (session) {
    try {
      session.manager.close();
    } catch {
      // Ignore close errors — connection may already be gone.
    }
    wsRegistry.delete(sessionId);
  }
}

/**
 * Returns true if a live WebSocket session exists for the given sessionId.
 */
export function hasWsSession(sessionId: string): boolean {
  const s = wsRegistry.get(sessionId);
  return !!(s && !s.broken && s.manager.isConnected());
}

export {
  buildAssistantMessageFromResponse,
  convertMessagesToInputItems,
  convertTools,
  planTurnInput,
} from "./openai-ws-message-conversion.js";

// ─────────────────────────────────────────────────────────────────────────────
// StreamFn factory
// ─────────────────────────────────────────────────────────────────────────────

export interface OpenAIWebSocketStreamOptions {
  /** Manager options (url override, retry counts, etc.) */
  managerOptions?: OpenAIWebSocketManagerOptions;
  /** Abort signal forwarded from the run. */
  signal?: AbortSignal;
}

type WsTransport = "sse" | "websocket" | "auto";
const WARM_UP_TIMEOUT_MS = 8_000;

function resolveWsTransport(options: Parameters<StreamFn>[2]): WsTransport {
  const transport = (options as { transport?: unknown } | undefined)?.transport;
  return transport === "sse" || transport === "websocket" || transport === "auto"
    ? transport
    : "auto";
}

type WsOptions = Parameters<StreamFn>[2] & { openaiWsWarmup?: unknown; signal?: AbortSignal };

function resolveWsWarmup(options: Parameters<StreamFn>[2]): boolean {
  const warmup = (options as WsOptions | undefined)?.openaiWsWarmup;
  return warmup === true;
}

async function runWarmUp(params: {
  manager: OpenAIWebSocketManager;
  modelId: string;
  tools: FunctionToolDefinition[];
  instructions?: string;
  signal?: AbortSignal;
}): Promise<void> {
  if (params.signal?.aborted) {
    throw new Error("aborted");
  }
  await new Promise<void>((resolve, reject) => {
    const timeout = setTimeout(() => {
      cleanup();
      reject(new Error(`warm-up timed out after ${WARM_UP_TIMEOUT_MS}ms`));
    }, WARM_UP_TIMEOUT_MS);

    const abortHandler = () => {
      cleanup();
      reject(new Error("aborted"));
    };
    const closeHandler = (code: number, reason: string) => {
      cleanup();
      reject(new Error(`warm-up closed (code=${code}, reason=${reason || "unknown"})`));
    };
    const unsubscribe = params.manager.onMessage((event) => {
      if (event.type === "response.completed") {
        cleanup();
        resolve();
      } else if (event.type === "response.failed") {
        cleanup();
        const errMsg = event.response?.error?.message ?? "Response failed";
        reject(new Error(`warm-up failed: ${errMsg}`));
      } else if (event.type === "error") {
        cleanup();
        reject(new Error(`warm-up error: ${event.message} (code=${event.code})`));
      }
    });

    const cleanup = () => {
      clearTimeout(timeout);
      params.signal?.removeEventListener("abort", abortHandler);
      params.manager.off("close", closeHandler);
      unsubscribe();
    };

    params.signal?.addEventListener("abort", abortHandler, { once: true });
    params.manager.on("close", closeHandler);
    params.manager.warmUp({
      model: params.modelId,
      tools: params.tools.length > 0 ? params.tools : undefined,
      instructions: params.instructions,
    });
  });
}

/**
 * Creates a `StreamFn` backed by a persistent WebSocket connection to the
 * OpenAI Responses API.  The first call for a given `sessionId` opens the
 * connection; subsequent calls reuse it, sending only incremental tool-result
 * inputs with `previous_response_id`.
 *
 * If the WebSocket connection is unavailable, the function falls back to the
 * standard `streamSimple` HTTP path and logs a warning.
 *
 * @param apiKey     OpenAI API key
 * @param sessionId  Agent session ID (used as the registry key)
 * @param opts       Optional manager + abort signal overrides
 */
export function createOpenAIWebSocketStreamFn(
  apiKey: string,
  sessionId: string,
  opts: OpenAIWebSocketStreamOptions = {},
): StreamFn {
  return (model, context, options) => {
    const eventStream = createEventStream();

    const run = async () => {
      const transport = resolveWsTransport(options);
      if (transport === "sse") {
        return fallbackToHttp(model, context, options, apiKey, eventStream, opts.signal);
      }

      // ── 1. Get or create session state ──────────────────────────────────
      let session = wsRegistry.get(sessionId);

      if (!session) {
        const manager = openAIWsStreamDeps.createManager(opts.managerOptions);
        session = {
          manager,
          lastContextLength: 0,
          everConnected: false,
          warmUpAttempted: false,
          broken: false,
        };
        wsRegistry.set(sessionId, session);
      }

      // ── 2. Ensure connection is open ─────────────────────────────────────
      if (!session.manager.isConnected() && !session.broken) {
        try {
          await session.manager.connect(apiKey);
          session.everConnected = true;
          log.debug(`[ws-stream] connected for session=${sessionId}`);
        } catch (connErr) {
          // Cancel any background reconnect attempts before marking as broken.
          try {
            session.manager.close();
          } catch {
            /* ignore */
          }
          session.broken = true;
          wsRegistry.delete(sessionId);
          if (transport === "websocket") {
            throw connErr instanceof Error ? connErr : new Error(String(connErr));
          }
          log.warn(
            `[ws-stream] WebSocket connect failed for session=${sessionId}; falling back to HTTP. error=${String(connErr)}`,
          );
          // Fall back to HTTP immediately
          return fallbackToHttp(model, context, options, apiKey, eventStream, opts.signal);
        }
      }

      if (session.broken || !session.manager.isConnected()) {
        if (transport === "websocket") {
          throw new Error("WebSocket session disconnected");
        }
        log.warn(`[ws-stream] session=${sessionId} broken/disconnected; falling back to HTTP`);
        // Clean up stale session to prevent next turn from using stale
        // previousResponseId / lastContextLength after a mid-request drop.
        try {
          session.manager.close();
        } catch {
          /* ignore */
        }
        wsRegistry.delete(sessionId);
        return fallbackToHttp(model, context, options, apiKey, eventStream, opts.signal);
      }

      const signal = opts.signal ?? (options as WsOptions | undefined)?.signal;

      if (resolveWsWarmup(options) && !session.warmUpAttempted) {
        session.warmUpAttempted = true;
        let warmupFailed = false;
        try {
          await runWarmUp({
            manager: session.manager,
            modelId: model.id,
            tools: convertTools(context.tools),
            instructions: context.systemPrompt ?? undefined,
            signal,
          });
          log.debug(`[ws-stream] warm-up completed for session=${sessionId}`);
        } catch (warmErr) {
          if (signal?.aborted) {
            throw warmErr instanceof Error ? warmErr : new Error(String(warmErr));
          }
          warmupFailed = true;
          log.warn(
            `[ws-stream] warm-up failed for session=${sessionId}; continuing without warm-up. error=${String(warmErr)}`,
          );
        }
        if (warmupFailed && !session.manager.isConnected()) {
          try {
            session.manager.close();
          } catch {
            /* ignore */
          }
          try {
            await session.manager.connect(apiKey);
            session.everConnected = true;
            log.debug(`[ws-stream] reconnected after warm-up failure for session=${sessionId}`);
          } catch (reconnectErr) {
            session.broken = true;
            wsRegistry.delete(sessionId);
            if (transport === "websocket") {
              throw reconnectErr instanceof Error ? reconnectErr : new Error(String(reconnectErr));
            }
            log.warn(
              `[ws-stream] reconnect after warm-up failed for session=${sessionId}; falling back to HTTP. error=${String(reconnectErr)}`,
            );
            return fallbackToHttp(model, context, options, apiKey, eventStream, opts.signal);
          }
        }
      }

      // ── 3. Compute incremental vs full input ─────────────────────────────
      const turnInput = planTurnInput({
        context,
        model,
        previousResponseId: session.manager.previousResponseId,
        lastContextLength: session.lastContextLength,
      });

      if (turnInput.mode === "incremental_tool_results") {
        log.debug(
          `[ws-stream] session=${sessionId}: incremental send (${turnInput.inputItems.length} tool results) previous_response_id=${turnInput.previousResponseId}`,
        );
      } else if (turnInput.mode === "full_context_restart") {
        // The WebSocket guide requires a fresh full-context turn here: when we
        // cannot continue the incremental chain, omit previous_response_id.
        log.debug(
          `[ws-stream] session=${sessionId}: no new tool results found; sending full context without previous_response_id`,
        );
      } else {
        log.debug(
          `[ws-stream] session=${sessionId}: full context send (${turnInput.inputItems.length} items)`,
        );
      }

      // ── 4. Build & send response.create ──────────────────────────────────
      const tools = convertTools(context.tools);

      // Forward generation options that the HTTP path (openai-responses provider) also uses.
      // Cast to record since SimpleStreamOptions carries openai-specific fields as unknown.
      const streamOpts = options as
        | (Record<string, unknown> & {
            temperature?: number;
            maxTokens?: number;
            topP?: number;
            toolChoice?: unknown;
          })
        | undefined;
      const extraParams: Record<string, unknown> = {};
      if (streamOpts?.temperature !== undefined) {
        extraParams.temperature = streamOpts.temperature;
      }
      if (streamOpts?.maxTokens !== undefined) {
        extraParams.max_output_tokens = streamOpts.maxTokens;
      }
      if (streamOpts?.topP !== undefined) {
        extraParams.top_p = streamOpts.topP;
      }
      if (streamOpts?.toolChoice !== undefined) {
        extraParams.tool_choice = streamOpts.toolChoice;
      }
      if (streamOpts?.reasoningEffort || streamOpts?.reasoningSummary) {
        const reasoning: { effort?: string; summary?: string } = {};
        if (streamOpts.reasoningEffort !== undefined) {
          reasoning.effort = streamOpts.reasoningEffort as string;
        }
        if (streamOpts.reasoningSummary !== undefined) {
          reasoning.summary = streamOpts.reasoningSummary as string;
        }
        extraParams.reasoning = reasoning;
      }

      // Respect compat.supportsStore — providers like Gemini reject unknown
      // fields such as `store` with a 400 error.  Fixes #39086.
      const supportsStore = (model as { compat?: { supportsStore?: boolean } }).compat
        ?.supportsStore;

      const payload: Record<string, unknown> = {
        type: "response.create",
        model: model.id,
        ...(supportsStore !== false ? { store: false } : {}),
        input: turnInput.inputItems,
        instructions: context.systemPrompt ?? undefined,
        tools: tools.length > 0 ? tools : undefined,
        ...(turnInput.previousResponseId
          ? { previous_response_id: turnInput.previousResponseId }
          : {}),
        ...extraParams,
      };
      const nextPayload = options?.onPayload?.(payload, model);
      const requestPayload = (nextPayload ?? payload) as Parameters<
        OpenAIWebSocketManager["send"]
      >[0];

      try {
        session.manager.send(requestPayload);
      } catch (sendErr) {
        if (transport === "websocket") {
          throw sendErr instanceof Error ? sendErr : new Error(String(sendErr));
        }
        log.warn(
          `[ws-stream] send failed for session=${sessionId}; falling back to HTTP. error=${String(sendErr)}`,
        );
        // Fully reset session state so the next WS turn doesn't use stale
        // previous_response_id or lastContextLength from before the failure.
        try {
          session.manager.close();
        } catch {
          /* ignore */
        }
        wsRegistry.delete(sessionId);
        return fallbackToHttp(model, context, options, apiKey, eventStream, opts.signal);
      }

      eventStream.push({
        type: "start",
        partial: buildAssistantMessageWithZeroUsage({
          model,
          content: [],
          stopReason: "stop",
        }),
      });

      // ── 5. Wait for response.completed ───────────────────────────────────
      const capturedContextLength = context.messages.length;

      await new Promise<void>((resolve, reject) => {
        // Honour abort signal
        const abortHandler = () => {
          cleanup();
          reject(new Error("aborted"));
        };
        if (signal?.aborted) {
          reject(new Error("aborted"));
          return;
        }
        signal?.addEventListener("abort", abortHandler, { once: true });

        // If the WebSocket drops mid-request, reject so we don't hang forever.
        const closeHandler = (code: number, reason: string) => {
          cleanup();
          reject(
            new Error(`WebSocket closed mid-request (code=${code}, reason=${reason || "unknown"})`),
          );
        };
        session.manager.on("close", closeHandler);

        const cleanup = () => {
          signal?.removeEventListener("abort", abortHandler);
          session.manager.off("close", closeHandler);
          unsubscribe();
        };

        const unsubscribe = session.manager.onMessage((event) => {
          if (event.type === "response.completed") {
            cleanup();
            // Update session state
            session.lastContextLength = capturedContextLength;
            // Build and emit the assistant message
            const assistantMsg = buildAssistantMessageFromResponse(event.response, {
              api: model.api,
              provider: model.provider,
              id: model.id,
            });
            const reason: Extract<StopReason, "stop" | "length" | "toolUse"> =
              assistantMsg.stopReason === "toolUse" ? "toolUse" : "stop";
            eventStream.push({ type: "done", reason, message: assistantMsg });
            resolve();
          } else if (event.type === "response.failed") {
            cleanup();
            const errMsg = event.response?.error?.message ?? "Response failed";
            reject(new Error(`OpenAI WebSocket response failed: ${errMsg}`));
          } else if (event.type === "error") {
            cleanup();
            reject(new Error(`OpenAI WebSocket error: ${event.message} (code=${event.code})`));
          } else if (event.type === "response.output_text.delta") {
            // Stream partial text updates for responsive UI
            const partialMsg: AssistantMessage = buildAssistantMessageWithZeroUsage({
              model,
              content: [{ type: "text", text: event.delta }],
              stopReason: "stop",
            });
            eventStream.push({
              type: "text_delta",
              contentIndex: 0,
              delta: event.delta,
              partial: partialMsg,
            });
          }
        });
      });
    };

    queueMicrotask(() =>
      run().catch((err) => {
        const errorMessage = err instanceof Error ? err.message : String(err);
        log.warn(`[ws-stream] session=${sessionId} run error: ${errorMessage}`);
        eventStream.push({
          type: "error",
          reason: "error",
          error: buildStreamErrorAssistantMessage({
            model,
            errorMessage,
          }),
        });
        eventStream.end();
      }),
    );

    return eventStream;
  };
}

/**
 * Fall back to HTTP (`streamSimple`) and pipe events into the existing stream.
 * This is called when the WebSocket is broken or unavailable.
 */
async function fallbackToHttp(
  model: Parameters<StreamFn>[0],
  context: Parameters<StreamFn>[1],
  options: Parameters<StreamFn>[2],
  apiKey: string,
  eventStream: AssistantMessageEventStreamLike,
  signal?: AbortSignal,
): Promise<void> {
  const mergedOptions = {
    ...options,
    apiKey,
    ...(signal ? { signal } : {}),
  };
  const httpStream = openAIWsStreamDeps.streamSimple(model, context, mergedOptions);
  for await (const event of httpStream) {
    eventStream.push(event);
  }
}

export const __testing = {
  setDepsForTest(overrides?: Partial<OpenAIWsStreamDeps>) {
    openAIWsStreamDeps = overrides
      ? {
          ...defaultOpenAIWsStreamDeps,
          ...overrides,
        }
      : defaultOpenAIWsStreamDeps;
  },
};