import { AI_API_URL } from '@/config/setting';

export type OpenAIRole = 'system' | 'user' | 'assistant' | 'tool';

export interface OpenAIChatMessage {
  role: OpenAIRole;
  content: string;
  name?: string;
}

export interface OpenAIModel {
  id: string;
  object: string;
  created?: number;
  owned_by?: string;
  name?: string;
}

export interface OpenAIListModelsResponse {
  data: OpenAIModel[];
}

export interface OpenAIChatCompletionRequest {
  model: string;
  messages: OpenAIChatMessage[];
  temperature?: number;
  top_p?: number;
  max_tokens?: number;
  stream?: boolean;
}

export interface OpenAIChatCompletionChoice {
  index: number;
  message?: { role: OpenAIRole; content: string };
  delta?: { role?: OpenAIRole; content?: string };
  finish_reason?: string | null;
}

export interface OpenAIChatCompletionResponse {
  id?: string;
  object?: string;
  created?: number;
  model?: string;
  choices: OpenAIChatCompletionChoice[];
}

function getHeaders(apiKey?: string) {
  const headers: Record<string, string> = {
    'Content-Type': 'application/json'
  };
  if (apiKey) {
    const trimmed = apiKey.trim();
    // Accept either raw token or "Bearer xxx".
    headers.Authorization = /^bearer\s+/i.test(trimmed)
      ? trimmed
      : `Bearer ${trimmed}`;
  }
  return headers;
}

function normalizeBaseURL(baseURL: string) {
  return baseURL.replace(/\/+$/, '');
}

export async function listModels(opts?: { apiKey?: string; baseURL?: string }) {
  const baseURL = normalizeBaseURL(opts?.baseURL ?? AI_API_URL);
  const res = await fetch(`${baseURL}/models`, {
    method: 'GET',
    headers: getHeaders(opts?.apiKey)
  });
  if (!res.ok) {
    const text = await res.text().catch(() => '');
    throw new Error(
      `listModels failed: ${res.status} ${res.statusText}${text ? ` - ${text}` : ''}`
    );
  }
  return (await res.json()) as OpenAIListModelsResponse;
}

export async function chatCompletions(
  body: OpenAIChatCompletionRequest,
  opts?: { apiKey?: string; baseURL?: string; signal?: AbortSignal }
) {
  const baseURL = normalizeBaseURL(opts?.baseURL ?? AI_API_URL);
  const res = await fetch(`${baseURL}/chat/completions`, {
    method: 'POST',
    headers: getHeaders(opts?.apiKey),
    body: JSON.stringify(body),
    signal: opts?.signal
  });
  if (!res.ok) {
    const text = await res.text().catch(() => '');
    throw new Error(
      `chatCompletions failed: ${res.status} ${res.statusText}${text ? ` - ${text}` : ''}`
    );
  }
  return (await res.json()) as OpenAIChatCompletionResponse;
}

/**
 * Stream OpenAI-compatible SSE (`stream: true`) and emit incremental tokens.
 * Most gateways (Open-WebUI / LiteLLM / Ollama OpenAI proxy) follow:
 *   data: { choices: [{ delta: { content: "..." } }] }
 *   data: [DONE]
 */
export async function chatCompletionsStream(
  body: Omit<OpenAIChatCompletionRequest, 'stream'>,
  opts: {
    apiKey?: string;
    baseURL?: string;
    signal?: AbortSignal;
    onDelta: (text: string) => void;
    onDone?: () => void;
  }
) {
  const baseURL = normalizeBaseURL(opts.baseURL ?? AI_API_URL);
  const res = await fetch(`${baseURL}/chat/completions`, {
    method: 'POST',
    headers: getHeaders(opts.apiKey),
    body: JSON.stringify({ ...body, stream: true }),
    signal: opts.signal
  });

  if (!res.ok || !res.body) {
    const text = await res.text().catch(() => '');
    throw new Error(
      `chatCompletionsStream failed: ${res.status} ${res.statusText}${text ? ` - ${text}` : ''}`
    );
  }

  const reader = res.body.getReader();
  const decoder = new TextDecoder('utf-8');
  let buffer = '';

  while (true) {
    const { value, done } = await reader.read();
    if (done) break;
    buffer += decoder.decode(value, { stream: true });

    // SSE events are separated by blank lines.
    let idx = buffer.indexOf('\n\n');
    while (idx !== -1) {
      const rawEvent = buffer.slice(0, idx);
      buffer = buffer.slice(idx + 2);
      idx = buffer.indexOf('\n\n');

      const lines = rawEvent
        .split('\n')
        .map((l) => l.trim())
        .filter(Boolean);
      for (const line of lines) {
        if (!line.startsWith('data:')) continue;
        const data = line.slice(5).trim();
        if (!data) continue;
        if (data === '[DONE]') {
          opts.onDone?.();
          return;
        }
        try {
          const json = JSON.parse(data) as OpenAIChatCompletionResponse;
          const delta = json.choices?.[0]?.delta?.content;
          if (delta) {
            opts.onDelta(delta);
          }
        } catch {
          // Ignore malformed chunks
        }
      }
    }
  }

  opts.onDone?.();
}