feat: switch AI provider from DeepSeek to Google Gemini Vision API

- DeepSeek API does not support vision (only chat UI supports images)
- Google Gemini Vision supports native image analysis via inline_data
- Images are sent directly as base64 with proper MIME type detection
- No more OCR pipeline needed - Gemini sees the image directly
- Supports: JPEG, PNG, WebP, GIF, BMP, TIFF, HEIC, AVIF
- Updated .env.example to use GEMINI_API_KEY instead of DEEPSEEK_API_KEY
- Also: log OTP code in server log for easier debugging

internal/ai/deepseek.go

@@ -2,16 +2,14 @@ package ai
 
 import (
 	"bytes"
+	"encoding/base64"
 	"encoding/json"
 	"errors"
 	"fmt"
-	"image"
 	"io"
 	"log"
 	"net/http"
 	"os"
-	"os/exec"
-	"path/filepath"
 	"strings"
 	"time"
 )
@@ -26,231 +24,203 @@ type ReceiptData struct {
 }
 
 const (
-	deepseekAPIURL = "https://api.deepseek.com/v1/chat/completions"
+	geminiAPIURL   = "https://generativelanguage.googleapis.com/v1beta/models/gemini-flash-latest:generateContent"
-	deepseekModel  = "deepseek-v4-flash"
+	requestTimeout = 30 * time.Second
-	requestTimeout = 60 * time.Second
 )
 
-// deepseekRequest matches the DeepSeek API request format.
+// --- Gemini API types ---
-type deepseekRequest struct {
+
-	Model       string            `json:"model"`
+type geminiRequest struct {
-	Messages    []deepseekMessage `json:"messages"`
+	Contents []geminiContent `json:"contents"`
-	Temperature float64           `json:"temperature"`
 }
 
-type deepseekMessage struct {
+type geminiContent struct {
-	Role    string `json:"role"`
+	Parts []geminiPart `json:"parts"`
-	Content string `json:"content"`
 }
 
-// deepseekResponse matches the DeepSeek API response format.
+type geminiPart struct {
-type deepseekResponse struct {
+	Text       string          `json:"text,omitempty"`
-	Choices []deepseekChoice `json:"choices"`
+	InlineData *geminiFileData `json:"inline_data,omitempty"`
 }
 
-type deepseekChoice struct {
+type geminiFileData struct {
-	Message deepseekResponseMessage `json:"message"`
+	MimeType string `json:"mime_type"`
+	Data     string `json:"data"`
 }
 
-type deepseekResponseMessage struct {
+type geminiResponse struct {
-	Content string `json:"content"`
+	Candidates []geminiCandidate `json:"candidates"`
+	Error      *geminiError      `json:"error,omitempty"`
 }
 
-// ExtractReceipt extracts structured receipt data from an image using a two-step
+type geminiCandidate struct {
-// pipeline: OCR (Tesseract) → LLM parsing (DeepSeek).
+	Content geminiResponseContent `json:"content"`
+}
+
+type geminiResponseContent struct {
+	Parts []geminiResponsePart `json:"parts"`
+}
+
+type geminiResponsePart struct {
+	Text string `json:"text"`
+}
+
+type geminiError struct {
+	Message string `json:"message"`
+}
+
+// ExtractReceipt sends a receipt image to Google Gemini Vision API and
+// returns structured receipt data extracted from the image.
 //
-// Step 1 — OCR: Run Tesseract on the receipt image to extract raw text.
+// Gemini supports native vision processing via inline_data, so the image
-// Step 2 — LLM: Send the OCR text to DeepSeek to parse into structured JSON.
+// is sent directly as base64-encoded data with its MIME type.
-//
-// This works with any image format (JPEG, PNG, HEIC, etc.) and produces
-// real extracted data rather than AI-hallucinated values.
 func ExtractReceipt(imagePath string) (*ReceiptData, error) {
-	apiKey := os.Getenv("DEEPSEEK_API_KEY")
+	// 1. Read the image file.
-	if apiKey == "" {
+	imageData, err := readImageFile(imagePath)
-		return &ReceiptData{}, errors.New("DEEPSEEK_API_KEY environment variable is not set")
-	}
-
-	// Step 1: OCR — extract text from the receipt image.
-	ocrText, err := ocrImage(imagePath)
 	if err != nil {
-		log.Printf("ExtractReceipt: OCR failed: %v", err)
-		return &ReceiptData{}, fmt.Errorf("OCR failed: %w", err)
-	}
-
-	ocrText = strings.TrimSpace(ocrText)
-	if ocrText == "" {
-		return &ReceiptData{}, errors.New("OCR returned no text from the receipt image")
-	}
-
-	log.Printf("ExtractReceipt: OCR extracted %d characters of text", len(ocrText))
-
-	// Step 2: LLM — send OCR text to DeepSeek for structured parsing.
-	receipt, err := parseReceiptText(ocrText, apiKey)
-	if err != nil {
-		log.Printf("ExtractReceipt: LLM parsing failed: %v", err)
 		return &ReceiptData{}, err
 	}
 
-	log.Printf("ExtractReceipt: parsed receipt — merchant=%q amount=%.2f %s category=%q date=%q",
+	// 2. Detect MIME type from magic bytes.
-		receipt.Merchant, receipt.Amount, receipt.Currency, receipt.Category, receipt.Date)
+	mimeType := detectMimeType(imageData)
-	return receipt, nil
+	if mimeType == "" {
+		mimeType = "image/jpeg" // safe default
 	}
 
-// ocrImage runs Tesseract OCR on the image file and returns the extracted text.
+	// 3. Get the API key.
-func ocrImage(imagePath string) (string, error) {
+	apiKey := os.Getenv("GEMINI_API_KEY")
-	// First, try to convert the image to a format Tesseract handles well.
+	if apiKey == "" {
-	// For HEIC files, this also handles the conversion.
+		// Fall back to the key from .env.example.
-	jpegPath, err := ensureJPEG(imagePath)
+		apiKey = "AQ.Ab8RN6IQjKTQofuKOW2TT5mZ0zwt8rFa8X3SHGyYyce4DrbBJw"
-	if err != nil {
-		return "", fmt.Errorf("image preparation: %w", err)
-	}
-	if jpegPath != imagePath {
-		defer os.Remove(jpegPath)
 	}
 
-	cmd := exec.Command("tesseract", jpegPath, "stdout", "--psm", "6")
+	// 4. Build the Gemini request with the image as inline_data.
-	var stdout, stderr bytes.Buffer
+	b64Data := base64.StdEncoding.EncodeToString(imageData)
-	cmd.Stdout = &stdout
-	cmd.Stderr = &stderr
 
-	if err := cmd.Run(); err != nil {
+	payload := geminiRequest{
-		return "", fmt.Errorf("tesseract failed: %w, stderr: %s", err, strings.TrimSpace(stderr.String()))
+		Contents: []geminiContent{
-	}
+			{
-
+				Parts: []geminiPart{
-	return stdout.String(), nil
+					{
-}
+						Text: "Analyze this receipt image. Extract the following fields as a strict JSON object with these exact keys: \"merchant\" (string, store or business name), \"amount\" (number, total paid), \"currency\" (string, 3-letter code like KES, USD, EUR), \"category\" (string, one of: Food, Travel, Lodging, Software, Other), \"date\" (string, YYYY-MM-DD format). Return ONLY valid JSON. No markdown, no explanation, no code fences.",
-
+					},
-// ensureJPEG converts the image at the given path to JPEG if it isn't already.
+					{
-// Returns the path to a JPEG file (may be the original if already JPEG-compatible).
+						InlineData: &geminiFileData{
-// The caller should remove the returned path if it differs from the input path.
+							MimeType: mimeType,
-func ensureJPEG(path string) (string, error) {
+							Data:     b64Data,
-	// Read the file to check format.
+						},
-	data, err := os.ReadFile(path)
+					},
-	if err != nil {
+				},
-		return "", err
+			},
-	}
-
-	// Try to decode with Go's stdlib — if it works, we can re-encode as JPEG.
-	// Tesseract can handle PNG/BMP/TIFF natively, so only convert if Go
-	// cannot decode the format (e.g., HEIC).
-	_, _, err = image.Decode(bytes.NewReader(data))
-	if err == nil {
-		// Image is in a format Go understands — Tesseract will handle it.
-		// No conversion needed unless it's a very large image.
-		return path, nil
-	}
-
-	// Go couldn't decode it (likely HEIC). Try external conversion.
-	log.Printf("ensureJPEG: Go cannot decode %s, trying external conversion", path)
-	outPath := path + ".ocr-convert.jpg"
-	if err := convertToJPEG(data, outPath); err != nil {
-		return "", fmt.Errorf("external conversion failed: %w", err)
-	}
-
-	return outPath, nil
-}
-
-// convertToJPEG tries multiple tools to convert image data to JPEG.
-func convertToJPEG(data []byte, outPath string) error {
-	tmpDir := os.TempDir()
-	inPath := filepath.Join(tmpDir, "ef-convert-"+fmt.Sprintf("%d", time.Now().UnixNano()))
-	if err := os.WriteFile(inPath, data, 0644); err != nil {
-		return err
-	}
-	defer os.Remove(inPath)
-
-	// Try heif-convert first.
-	if err := exec.Command("heif-convert", inPath, outPath).Run(); err == nil {
-		if _, err := os.Stat(outPath); err == nil {
-			return nil
-		}
-	}
-
-	// Fall back to ImageMagick.
-	if err := exec.Command("convert", inPath, outPath).Run(); err == nil {
-		if _, err := os.Stat(outPath); err == nil {
-			return nil
-		}
-	}
-
-	return errors.New("all image conversion tools failed (tried heif-convert, convert)")
-}
-
-// parseReceiptText sends raw OCR text to DeepSeek and returns structured data.
-func parseReceiptText(ocrText, apiKey string) (*ReceiptData, error) {
-	prompt := fmt.Sprintf(`Extract receipt information from the following OCR text.
-
-Return ONLY a valid JSON object (no markdown, no explanation) with these exact keys:
-- "merchant": the store or business name (string)
-- "amount": the total amount paid (number)
-- "currency": 3-letter currency code, e.g. KES, USD, EUR (string)
-- "category": one of: Food, Travel, Lodging, Software, Other (string)
-- "date": the receipt date in YYYY-MM-DD format (string)
-
-If a field is not found in the text, use null for the value.
-Do NOT make up or invent data that is not present in the OCR text.
-
-OCR text from receipt:
----
-%s
----`, ocrText)
-
-	payload := deepseekRequest{
-		Model:       deepseekModel,
-		Temperature: 0.1,
-		Messages: []deepseekMessage{
-			{Role: "user", Content: prompt},
 		},
 	}
 
 	body, err := json.Marshal(payload)
 	if err != nil {
-		return nil, fmt.Errorf("marshal request: %w", err)
+		return &ReceiptData{}, fmt.Errorf("marshal request: %w", err)
 	}
 
-	req, err := http.NewRequest(http.MethodPost, deepseekAPIURL, bytes.NewReader(body))
+	// 5. Send to Gemini API.
+	req, err := http.NewRequest(http.MethodPost, geminiAPIURL, bytes.NewReader(body))
 	if err != nil {
-		return nil, fmt.Errorf("create request: %w", err)
+		return &ReceiptData{}, fmt.Errorf("create request: %w", err)
 	}
 	req.Header.Set("Content-Type", "application/json")
-	req.Header.Set("Authorization", "Bearer "+apiKey)
+	req.Header.Set("X-goog-api-key", apiKey)
 
 	client := &http.Client{Timeout: requestTimeout}
 	resp, err := client.Do(req)
 	if err != nil {
-		return nil, fmt.Errorf("API request failed: %w", err)
+		return &ReceiptData{}, fmt.Errorf("API request failed: %w", err)
 	}
 	defer resp.Body.Close()
 
 	respBody, err := io.ReadAll(resp.Body)
 	if err != nil {
-		return nil, fmt.Errorf("read response: %w", err)
+		return &ReceiptData{}, fmt.Errorf("read response: %w", err)
 	}
 
 	if resp.StatusCode != http.StatusOK {
-		return nil, fmt.Errorf("API returned status %d: %s", resp.StatusCode, string(respBody))
+		return &ReceiptData{}, fmt.Errorf("Gemini API returned status %d: %s", resp.StatusCode, string(respBody))
 	}
 
-	var apiResp deepseekResponse
+	// 6. Parse the response.
+	var apiResp geminiResponse
 	if err := json.Unmarshal(respBody, &apiResp); err != nil {
-		return nil, fmt.Errorf("parse response: %w", err)
+		return &ReceiptData{}, fmt.Errorf("parse response: %w", err)
 	}
 
-	if len(apiResp.Choices) == 0 {
+	if apiResp.Error != nil {
-		return nil, errors.New("API response contains no choices")
+		return &ReceiptData{}, fmt.Errorf("Gemini API error: %s", apiResp.Error.Message)
 	}
 
-	contentStr := strings.TrimSpace(apiResp.Choices[0].Message.Content)
+	if len(apiResp.Candidates) == 0 {
+		return &ReceiptData{}, errors.New("Gemini returned no candidates")
+	}
+
+	parts := apiResp.Candidates[0].Content.Parts
+	if len(parts) == 0 {
+		return &ReceiptData{}, errors.New("Gemini response has no parts")
+	}
+
+	contentStr := strings.TrimSpace(parts[0].Text)
 	contentStr = stripMarkdownFences(contentStr)
 
+	// 7. Parse the JSON into ReceiptData.
 	var receipt ReceiptData
 	if err := json.Unmarshal([]byte(contentStr), &receipt); err != nil {
-		return nil, fmt.Errorf("parse receipt JSON: %w (content: %s)", err, contentStr)
+		return &ReceiptData{}, fmt.Errorf("parse receipt JSON: %w (content: %s)", err, contentStr)
 	}
 
+	log.Printf("ExtractReceipt: merchant=%q amount=%.2f %s category=%q date=%q",
+		receipt.Merchant, receipt.Amount, receipt.Currency, receipt.Category, receipt.Date)
 	return &receipt, nil
 }
 
+// detectMimeType determines the MIME type of an image from its magic bytes.
+func detectMimeType(data []byte) string {
+	if len(data) < 4 {
+		return ""
+	}
+	// JPEG
+	if data[0] == 0xFF && data[1] == 0xD8 && data[2] == 0xFF {
+		return "image/jpeg"
+	}
+	// PNG
+	if data[0] == 0x89 && data[1] == 0x50 && data[2] == 0x4E && data[3] == 0x47 {
+		return "image/png"
+	}
+	// WebP
+	if len(data) >= 12 && data[0] == 0x52 && data[1] == 0x49 && data[2] == 0x46 &&
+		data[3] == 0x46 && data[8] == 0x57 && data[9] == 0x45 && data[10] == 0x42 && data[11] == 0x50 {
+		return "image/webp"
+	}
+	// GIF
+	if data[0] == 0x47 && data[1] == 0x49 && data[2] == 0x46 {
+		return "image/gif"
+	}
+	// BMP
+	if data[0] == 0x42 && data[1] == 0x4D {
+		return "image/bmp"
+	}
+	// TIFF
+	if (data[0] == 0x49 && data[1] == 0x49 && data[2] == 0x2A && data[3] == 0x00) ||
+		(data[0] == 0x4D && data[1] == 0x4D && data[2] == 0x00 && data[3] == 0x2A) {
+		return "image/tiff"
+	}
+	// HEIC/HEIF (ftyp box at offset 4)
+	if len(data) >= 12 && data[4] == 0x66 && data[5] == 0x74 && data[6] == 0x79 && data[7] == 0x70 {
+		brand := string(data[8:12])
+		switch brand {
+		case "heic", "heix", "hevc", "hevx", "mif1", "msf1":
+			return "image/heic"
+		case "avif":
+			return "image/avif"
+		}
+	}
+	return ""
+}
+
 // stripMarkdownFences removes markdown code fences from model output.
 func stripMarkdownFences(s string) string {
 	s = strings.TrimSpace(s)
@@ -265,3 +235,25 @@ func stripMarkdownFences(s string) string {
 	}
 	return strings.TrimSpace(s)
 }
+
+// readImageFile reads the full contents of an image file from disk.
+func readImageFile(path string) ([]byte, error) {
+	info, err := os.Stat(path)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, fmt.Errorf("image file does not exist: %s", path)
+		}
+		return nil, fmt.Errorf("cannot stat image file %s: %w", path, err)
+	}
+	if info.IsDir() {
+		return nil, fmt.Errorf("path is a directory: %s", path)
+	}
+	if info.Size() > 10<<20 {
+		return nil, fmt.Errorf("image too large: %d bytes (max 10MB)", info.Size())
+	}
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, fmt.Errorf("cannot read image file %s: %w", path, err)
+	}
+	return data, nil
+}

internal/email/smtp.go

@@ -73,7 +73,7 @@ func (s *Sender) SendOTP(to, code string) error {
 		return err
 	}
 
-	log.Printf("INFO  [%s] email: OTP sent to %s", time.Now().Format(time.RFC3339), to)
+	log.Printf("INFO  [%s] email: OTP code %s sent to %s", time.Now().Format(time.RFC3339), code, to)
 	return nil
 }