import type {
  ChatMessage,
  ChatCompletionResponse,
  ChatCompletionChunk,
  Platform,
} from '@freellmapi/shared/types.js';
import { BaseProvider, type CompletionOptions } from './base.js';

/**
 * Generic provider for platforms that use an OpenAI-compatible API.
 * Covers: Groq, Cerebras, SambaNova, NVIDIA NIM, Mistral, OpenRouter,
 * GitHub Models, Fireworks AI.
 */
export class OpenAICompatProvider extends BaseProvider {
  readonly platform: Platform;
  readonly name: string;
  private readonly baseUrl: string;
  private readonly extraHeaders: Record<string, string>;
  private readonly validateUrl?: string;

  constructor(opts: {
    platform: Platform;
    name: string;
    baseUrl: string;
    extraHeaders?: Record<string, string>;
    validateUrl?: string;
  }) {
    super();
    this.platform = opts.platform;
    this.name = opts.name;
    this.baseUrl = opts.baseUrl;
    this.extraHeaders = opts.extraHeaders ?? {};
    this.validateUrl = opts.validateUrl;
  }

  async chatCompletion(
    apiKey: string,
    messages: ChatMessage[],
    modelId: string,
    options?: CompletionOptions,
  ): Promise<ChatCompletionResponse> {
    const res = await this.fetchWithTimeout(`${this.baseUrl}/chat/completions`, {
      method: 'POST',
      headers: {
        'Authorization': `Bearer ${apiKey}`,
        'Content-Type': 'application/json',
        ...this.extraHeaders,
      },
      body: JSON.stringify({
        model: modelId,
        messages,
        temperature: options?.temperature,
        max_tokens: options?.max_tokens,
        top_p: options?.top_p,
      }),
    });

    if (!res.ok) {
      const err = await res.json().catch(() => ({}));
      throw new Error(`${this.name} API error ${res.status}: ${(err as any).error?.message ?? res.statusText}`);
    }

    const data = await res.json() as ChatCompletionResponse;
    data._routed_via = { platform: this.platform, model: modelId };
    return data;
  }

  async *streamChatCompletion(
    apiKey: string,
    messages: ChatMessage[],
    modelId: string,
    options?: CompletionOptions,
  ): AsyncGenerator<ChatCompletionChunk> {
    const res = await this.fetchWithTimeout(`${this.baseUrl}/chat/completions`, {
      method: 'POST',
      headers: {
        'Authorization': `Bearer ${apiKey}`,
        'Content-Type': 'application/json',
        ...this.extraHeaders,
      },
      body: JSON.stringify({
        model: modelId,
        messages,
        temperature: options?.temperature,
        max_tokens: options?.max_tokens,
        top_p: options?.top_p,
        stream: true,
      }),
    });

    if (!res.ok) {
      const err = await res.json().catch(() => ({}));
      throw new Error(`${this.name} API error ${res.status}: ${(err as any).error?.message ?? res.statusText}`);
    }

    const reader = res.body?.getReader();
    if (!reader) throw new Error('No response body');

    const decoder = new TextDecoder();
    let buffer = '';

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

      buffer += decoder.decode(value, { stream: true });
      const lines = buffer.split('\n');
      buffer = lines.pop() ?? '';

      for (const line of lines) {
        const trimmed = line.trim();
        if (!trimmed || !trimmed.startsWith('data: ')) continue;
        const data = trimmed.slice(6);
        if (data === '[DONE]') return;
        try {
          yield JSON.parse(data) as ChatCompletionChunk;
        } catch {
          // Skip malformed chunks
        }
      }
    }
  }

  async validateKey(apiKey: string): Promise<boolean> {
    try {
      const url = this.validateUrl ?? `${this.baseUrl}/models`;
      const res = await this.fetchWithTimeout(url, {
        method: 'GET',
        headers: {
          'Authorization': `Bearer ${apiKey}`,
          ...this.extraHeaders,
        },
      }, 10000);
      // 401/403 = bad key, anything else (200, 404, etc) = key is valid
      return res.status !== 401 && res.status !== 403;
    } catch {
      return false;
    }
  }
}
