gods-eye-view/server/providers/gemini/chat.js

import { createTextChatHandler } from '../common/textChat.js';
import { invalidCalls } from '../common/textTools.js';
import { textInstructions } from '../common/textInstructions.js';
import { GEV_REALTIME_TOOLS } from '../openai/tools.js';
import { normalizeGeminiModel } from './config.js';

const object = (value) =>
  value && typeof value === 'object' && !Array.isArray(value);
const keys = (value, allowed) =>
  Object.keys(value).every((key) => allowed.includes(key));

// Only text and function exchanges may cross this route, never media or config.
export function validChatContents(contents, names) {
  return (
    Array.isArray(contents) &&
    contents.length > 0 &&
    contents.length <= 96 &&
    contents.every(
      (content) =>
        object(content) &&
        keys(content, ['role', 'parts']) &&
        ['user', 'model'].includes(content.role) &&
        Array.isArray(content.parts) &&
        content.parts.length > 0 &&
        content.parts.length <= 32 &&
        content.parts.every((part) => {
          if (
            !object(part) ||
            !keys(part, [
              'text',
              'functionCall',
              'functionResponse',
              'thoughtSignature',
            ])
          )
            return false;
          if (
            part.thoughtSignature !== undefined &&
            (typeof part.thoughtSignature !== 'string' ||
              part.thoughtSignature.length > 32000 ||
              content.role !== 'model')
          )
            return false;
          if (Object.hasOwn(part, 'text'))
            return (
              keys(part, ['text', 'thoughtSignature']) &&
              typeof part.text === 'string'
            );
          const call = part.functionCall ?? part.functionResponse;
          if (
            !object(call) ||
            typeof call.name !== 'string' ||
            call.name.length > 128 ||
            (names && !names.has(call.name)) ||
            (call.id !== undefined &&
              (typeof call.id !== 'string' || call.id.length > 1024))
          )
            return false;
          if (part.functionCall)
            return (
              content.role === 'model' &&
              keys(part, ['functionCall', 'thoughtSignature']) &&
              keys(call, ['name', 'args', 'id']) &&
              (call.args === null || object(call.args ?? {}))
            );
          return (
            content.role === 'user' &&
            keys(part, ['functionResponse']) &&
            keys(call, ['name', 'response', 'id']) &&
            object(call.response)
          );
        }),
    )
  );
}

export function createGeminiChatHandler({
  annotationGuidance,
  tools = GEV_REALTIME_TOOLS,
  resolveChatModel = () =>
    process.env.GEMINI_CHAT_MODEL || 'gemini-3.5-flash-lite',
  resolveApiKey = () => process.env.GEMINI_API_KEY,
  ...options
} = {}) {
  return createTextChatHandler({
    ...options,
    provider: 'gemini',
    resolveApiKey,
    prepare(input) {
      const model = normalizeGeminiModel(resolveChatModel());
      if (!model || /live|audio|tts/i.test(model)) return { errorStatus: 503 };
      if (
        !object(input) ||
        !keys(input, ['contents']) ||
        !validChatContents(input.contents, null)
      )
        return null;
      if (!pairedContents(input.contents)) return null;
      return {
        endpoint: `https://generativelanguage.googleapis.com/v1beta/models/${model}:generateContent`,
        headers: (key) => ({ 'x-goog-api-key': key }),
        body: {
          contents: input.contents,
          systemInstruction: {
            parts: [{ text: textInstructions(annotationGuidance) }],
          },
          tools: [
            {
              functionDeclarations: tools.map(
                ({ name, description, parameters }) => ({
                  name,
                  description,
                  parametersJsonSchema: parameters,
                }),
              ),
            },
          ],
          generationConfig: {
            responseModalities: ['TEXT'],
            maxOutputTokens: 4096,
            thinkingConfig: { thinkingLevel: 'LOW' },
          },
        },
      };
    },
    parse(data) {
      const candidate = data?.candidates?.[0];
      const content = candidate?.content;
      if (
        !content ||
        !validChatContents([content], null) ||
        content.role !== 'model'
      )
        return null;
      const calls = content.parts
        .filter((part) => part.functionCall)
        .map((part) => part.functionCall);
      return {
        content,
        finishReason: candidate.finishReason,
        invalidCalls: invalidCalls(calls, tools),
      };
    },
  });
}

// Never forward an orphan result or an unfinished batch in browser history.
function pairedContents(contents) {
  let pending = [];
  for (const content of contents) {
    const calls = content.parts
      .filter((part) => part.functionCall)
      .map((part) => part.functionCall);
    const results = content.parts
      .filter((part) => part.functionResponse)
      .map((part) => part.functionResponse);
    if (pending.length) {
      if (
        calls.length ||
        results.length !== pending.length ||
        results.some(
          (result, i) =>
            result.name !== pending[i].name || result.id !== pending[i].id,
        )
      )
        return false;
      pending = [];
    } else if (results.length) return false;
    if (calls.length) pending = calls;
  }
  return !pending.length;
}