Generative AI – Cosplay Camera App

function doPost(e) {
  // Main handler for POST requests from App Inventor.
  // Returns a JSON string with: { status, message, prompt, imageData }

  let response = {
    status: 'error',
    message: 'An unknown error occurred.',
    imageData: null
  };

  try {
    // Validate and parse incoming JSON payload
    if (!e || !e.postData || !e.postData.contents) {
      throw new Error('Invalid request: No data received.');
    }
    const jsonData = JSON.parse(e.postData.contents);

    // Expecting base64 image data and optional character/prompt fields
    const base64Data = jsonData.imageData;
    const character = jsonData.character; 
    const prompt =
      jsonData.prompt ||
      `Convert this into a full-body photo, do not modify the face at all, and apply cosplay as ${character}. No textual reply is needed.`;

    // Basic input validation
    if (!base64Data || typeof base64Data !== 'string') {
      throw new Error('Invalid request: imageData is missing or not a string.');
    }

    // Remove data URL header (e.g., "data:image/png;base64,")
    const cleanedBase64 = cleanBase64String(base64Data);

    // Read API key from Script Properties
    const apiKey = PropertiesService.getScriptProperties().getProperty('GEMINI_API_KEY');
    if (!apiKey) {
      throw new Error('Configuration error: API key is not set in Script Properties.');
    }

    // Call Gemini image-generation endpoint
    const generatedBase64 = callGeminiApi(apiKey, cleanedBase64, prompt);

    // Success response
    response = {
      status: 'success',
      message: 'Image generated successfully.',
      prompt: prompt,
      imageData: generatedBase64
    };

  } catch (error) {
    // Failure response
    console.error(error.toString());
    response.message = error.message;
  }

  // Return JSON output
  return ContentService.createTextOutput(JSON.stringify(response))
    .setMimeType(ContentService.MimeType.JSON);
}

function cleanBase64String(base64String) {
  // Strip a leading data URL header like "data:image/png;base64,"
  return base64String.replace(/^data:image\/[a-z]+;base64,/, '');
}

function callGeminiApi(apiKey, base64Image, prompt) {
  // Invoke the Gemini image-generation model with an image + instruction text
  const model = 'gemini-2.5-flash-image-preview';
  const url = `https://generativelanguage.googleapis.com/v1beta/models/${model}:generateContent?key=${apiKey}`;

  const payload = {
    contents: [{
      parts: [
        { text: prompt },
        {
          inlineData: {
            mimeType: 'image/png', // App Inventor Canvas exports PNG
            data: base64Image
          }
        }
      ]
    }],
    generationConfig: {
      // Request both image and text modalities in the response
      responseModalities: ['IMAGE', 'TEXT']
    }
  };

  const options = {
    method: 'post',
    contentType: 'application/json',
    payload: JSON.stringify(payload),
    muteHttpExceptions: true // Capture non-2xx responses instead of throwing
  };

  const response = UrlFetchApp.fetch(url, options);
  const responseCode = response.getResponseCode();
  const responseBody = response.getContentText();

  if (responseCode === 200) {
    const jsonResponse = JSON.parse(responseBody);

    // Find the image part in the response
    const imagePart = jsonResponse?.candidates?.[0]?.content?.parts?.find(p => p.inlineData);

    if (imagePart && imagePart.inlineData.data) {
      // Return base64 image data
      return imagePart.inlineData.data;
    } else {
      // If no image, surface any returned text as the error message
      console.error('API response did not contain image data. Response: ' + responseBody);
      const textPart = jsonResponse?.candidates?.[0]?.content?.parts?.find(p => p.text);
      const errorMessage = textPart ? textPart.text : 'No image data in response.';
      throw new Error(`API Error: ${errorMessage}`);
    }
  } else {
    // Non-2xx HTTP response
    console.error('API Error. Code: ' + responseCode + '. Body: ' + responseBody);
    throw new Error(`API request failed with status code ${responseCode}. Details: ${responseBody}`);
  }
}