import type { GatewayConfig, ChatCompletionResponse } from "./types";

/**
 * HTTP client for the Hermes Gateway's OpenAI-compatible REST API.
 * Handles Bearer auth, SSE streaming, session header continuity,
 * and model/capabilities discovery.
 *
 * Uses the standard fetch() API available in Obsidian's Electron runtime.
 */
export class ApiClient {
  private baseUrl: string;
  private apiKey: string;
  private model: string;
  private currentSessionId: string | null;

  constructor(config: GatewayConfig) {
    this.baseUrl = config.baseUrl.replace(/\/+$/, ""); // strip trailing slashes
    this.apiKey = config.apiKey;
    this.model = config.model;
    this.currentSessionId = null;
  }

  /** Update configuration without recreating the client. Preserves session. */
  updateConfig(config: Partial<GatewayConfig>): void {
    if (config.baseUrl !== undefined) {
      this.baseUrl = config.baseUrl.replace(/\/+$/, "");
    }
    if (config.apiKey !== undefined) {
      this.apiKey = config.apiKey;
    }
    if (config.model !== undefined) {
      this.model = config.model;
    }
    // Do NOT reset currentSessionId — preserve conversation continuity
  }

  /** Get the current session ID, if one has been established. */
  getSessionId(): string | null {
    return this.currentSessionId;
  }

  /** Restore a previously-saved session ID (from plugin data). */
  setSessionId(id: string): void {
    this.currentSessionId = id || null;
  }

  /** The root URL without the /v1 suffix, e.g. http://192.168.1.12:8642 */
  private get rootUrl(): string {
    // baseUrl ends with /v1; strip it to reach the server root
    if (this.baseUrl.endsWith("/v1")) {
      return this.baseUrl.slice(0, -3);
    }
    return new URL("/", this.baseUrl).href.replace(/\/+$/, "");
  }

  /**
   * Fetch with a configurable timeout. Aborts the request if it takes
   * longer than `timeoutMs` milliseconds.
   */
  private async fetchWithTimeout(
    url: string,
    options: RequestInit,
    timeoutMs: number = 60000
  ): Promise<Response> {
    const controller = new AbortController();
    const timeout = setTimeout(() => controller.abort(), timeoutMs);
    try {
      const response = await fetch(url, {
        ...options,
        signal: controller.signal,
      });
      return response;
    } finally {
      clearTimeout(timeout);
    }
  }

  /**
   * Extract a useful error message from a non-OK response.
   * Tries JSON first, falls back to plain text (truncated), and finally
   * to the HTTP status line.
   */
  private async extractErrorBody(response: Response): Promise<string> {
    let detail = "";
    const contentType = response.headers.get("content-type") ?? "";

    // Only attempt JSON if the server says it sent JSON
    if (contentType.includes("application/json")) {
      try {
        const errBody = await response.json();
        if (errBody.error?.message) {
          detail = errBody.error.message;
        } else if (typeof errBody.message === "string") {
          detail = errBody.message;
        } else if (typeof errBody.error === "string") {
          detail = errBody.error;
        }
        if (detail) return detail;
      } catch {
        // JSON parsing failed — fall through to text
      }
    }

    // Try reading as plain text (e.g. HTML error page, gateway nginx page)
    try {
      const text = await response.text();
      if (text.trim()) {
        // Truncate to avoid dumping huge HTML pages into error messages
        detail = text.trim().substring(0, 300);
        return detail;
      }
    } catch {
      // Body isn't readable at all
    }

    // Ultimate fallback
    return response.statusText || `HTTP ${response.status}`;
  }

  /**
   * Send a chat completion request (non-streaming).
   * Returns the assistant's response with session and usage metadata.
   */
  async chat(
    messages: { role: string; content: string }[],
    stream: boolean = false
  ): Promise<ChatCompletionResponse> {
    const headers: Record<string, string> = {
      Authorization: `Bearer ${this.apiKey}`,
      "Content-Type": "application/json",
    };

    if (this.currentSessionId) {
      headers["X-Hermes-Session-Id"] = this.currentSessionId;
    }

    const response = await this.fetchWithTimeout(
      `${this.baseUrl}/chat/completions`,
      {
        method: "POST",
        headers,
        body: JSON.stringify({
          model: this.model,
          messages,
          stream,
        }),
      }
    );

    if (!response.ok) {
      const detail = await this.extractErrorBody(response);
      throw new Error(`API error ${response.status}: ${detail}`);
    }

    // Capture session ID from response headers for continuity
    const sessionId = response.headers.get("X-Hermes-Session-Id");
    if (sessionId) {
      this.currentSessionId = sessionId;
    }

    const data = await response.json();

    if (data.error) {
      throw new Error(data.error.message || "Unknown API error");
    }

    const choice = data.choices?.[0];
    const content: string = choice?.message?.content ?? "";

    return {
      content,
      sessionId: this.currentSessionId ?? "",
      model: data.model ?? this.model,
      usage: data.usage,
    };
  }

  /**
   * Send a streaming chat completion request.
   * Calls `onDelta` with each text chunk as it arrives via SSE.
   * Returns the final ChatCompletionResponse after the stream concludes.
   */
  async streamChat(
    messages: { role: string; content: string }[],
    onDelta: (text: string) => void
  ): Promise<ChatCompletionResponse> {
    const headers: Record<string, string> = {
      Authorization: `Bearer ${this.apiKey}`,
      "Content-Type": "application/json",
    };

    if (this.currentSessionId) {
      headers["X-Hermes-Session-Id"] = this.currentSessionId;
    }

    const response = await this.fetchWithTimeout(
      `${this.baseUrl}/chat/completions`,
      {
        method: "POST",
        headers,
        body: JSON.stringify({
          model: this.model,
          messages,
          stream: true,
        }),
      }
    );

    if (!response.ok) {
      const detail = await this.extractErrorBody(response);
      throw new Error(`API error ${response.status}: ${detail}`);
    }

    // Capture session ID from response headers
    const sessionId = response.headers.get("X-Hermes-Session-Id");
    if (sessionId) {
      this.currentSessionId = sessionId;
    }

    // Read the SSE stream
    const reader = response.body?.getReader();
    if (!reader) {
      throw new Error("Response body is not readable");
    }

    const decoder = new TextDecoder("utf-8");
    let buffer = "";
    let fullContent = "";
    let model = this.model;
    let usage: ChatCompletionResponse["usage"];

    while (true) {
      const { done, value } = await reader.read();
      if (done) break;

      buffer += decoder.decode(value, { stream: true });

      // SSE events are separated by double newlines
      const parts = buffer.split("\n\n");
      // The last part may be incomplete; keep it in the buffer
      buffer = parts.pop() ?? "";

      for (const part of parts) {
        const lines = part.split("\n");
        for (const line of lines) {
          if (!line.startsWith("data: ")) continue;
          const jsonStr = line.slice(6).trim();

          if (jsonStr === "[DONE]") {
            // Stream finished signal — continue processing any remaining data
            continue;
          }

          try {
            const event = JSON.parse(jsonStr);

            if (event.error) {
              throw new Error(event.error.message || "Stream error");
            }

            const delta = event.choices?.[0]?.delta?.content;
            if (delta) {
              fullContent += delta;
              onDelta(delta);
            }

            // Capture model and usage from the final event
            if (event.model) {
              model = event.model;
            }
            if (event.usage) {
              usage = event.usage;
            }
          } catch (e) {
            // If it's our own thrown error, rethrow
            if (
              e instanceof Error &&
              e.message !== "Unexpected token" &&
              !e.message.includes("JSON")
            ) {
              throw e;
            }
            // Otherwise skip malformed SSE lines
          }
        }
      }
    }

    // Flush any remaining data in the buffer
    if (buffer.trim()) {
      const lines = buffer.split("\n");
      for (const line of lines) {
        if (!line.startsWith("data: ")) continue;
        const jsonStr = line.slice(6).trim();
        if (jsonStr === "[DONE]") continue;
        try {
          const event = JSON.parse(jsonStr);
          const delta = event.choices?.[0]?.delta?.content;
          if (delta) {
            fullContent += delta;
            onDelta(delta);
          }
        } catch {
          // ignore
        }
      }
    }

    return {
      content: fullContent,
      sessionId: this.currentSessionId ?? "",
      model,
      usage,
    };
  }

  /**
   * List available models from the gateway.
   * GET /v1/models
   */
  async getModels(): Promise<{ id: string }[]> {
    const response = await this.fetchWithTimeout(
      `${this.baseUrl}/models`,
      {
        headers: {
          Authorization: `Bearer ${this.apiKey}`,
        },
      }
    );

    if (!response.ok) {
      const detail = await this.extractErrorBody(response);
      throw new Error(`Failed to fetch models: ${response.status} — ${detail}`);
    }

    const data = await response.json();
    return data.data ?? [];
  }

  /**
   * Fetch gateway capabilities.
   * GET /v1/capabilities
   */
  async getCapabilities(): Promise<any> {
    const response = await this.fetchWithTimeout(
      `${this.baseUrl}/capabilities`,
      {
        headers: {
          Authorization: `Bearer ${this.apiKey}`,
        },
      }
    );

    if (!response.ok) {
      const detail = await this.extractErrorBody(response);
      throw new Error(
        `Failed to fetch capabilities: ${response.status} — ${detail}`
      );
    }

    return response.json();
  }

  /**
   * Health check against the gateway root.
   * GET /health → returns true if status === "ok"
   * Uses a shorter 10-second timeout since this is a liveness probe.
   */
  async healthCheck(): Promise<boolean> {
    try {
      const response = await this.fetchWithTimeout(
        `${this.rootUrl}/health`,
        {},
        10000 // 10-second timeout for health checks
      );
      if (!response.ok) return false;
      const data = await response.json();
      return data.status === "ok";
    } catch {
      return false;
    }
  }
}