fix: support HEIC/HEIF photos from iPhone + broaden accepted image formats

- detectImageExtension now handles: JPEG, PNG, WebP, GIF, BMP, TIFF, HEIC, AVIF
- Added heif-convert + ImageMagick fallback for decoding unsupported formats
- AI extraction properly converts HEIC to JPEG before analysis
- Model: deepseek-v4-flash (confirmed working)

internal/ai/deepseek.go

@@ -12,6 +12,8 @@ import (
 	"log"
 	"net/http"
 	"os"
+	"os/exec"
+	"path/filepath"
 	"strings"
 	"time"
 )
@@ -180,11 +182,24 @@ Image data: %s`, b64)
 
 // compressImage decodes the image, downscales it (preserving aspect ratio)
 // to fit within maxImageSize, and re-encodes as JPEG with the configured quality.
+// If Go's built-in decoders cannot handle the format (e.g. HEIC from iPhones),
+// it attempts to convert via external tools (heif-convert or ImageMagick).
 func compressImage(data []byte) ([]byte, error) {
-	// Detect format and decode.
+	// Try Go's built-in image decoders first (covers JPEG, PNG, GIF, BMP, TIFF, WebP).
 	img, format, err := image.Decode(bytes.NewReader(data))
 	if err != nil {
-		return nil, fmt.Errorf("image decode: %w", err)
+		// Built-in decoder failed — try external tools for HEIC and other formats.
+		log.Printf("compressImage: Go decoder failed (%v), trying external conversion", err)
+		converted, err := convertWithExternalTool(data)
+		if err != nil {
+			return nil, fmt.Errorf("image decode and external conversion both failed: %w", err)
+		}
+		// Try decoding the converted data.
+		img, format, err = image.Decode(bytes.NewReader(converted))
+		if err != nil {
+			return nil, fmt.Errorf("decoding converted image also failed: %w", err)
+		}
+		data = converted
 	}
 
 	bounds := img.Bounds()
@@ -261,6 +276,63 @@ func stripMarkdownFences(s string) string {
 	return strings.TrimSpace(s)
 }
 
+// convertWithExternalTool tries to convert an unsupported image format (e.g. HEIC)
+// to JPEG using heif-convert or ImageMagick's convert command.
+func convertWithExternalTool(data []byte) ([]byte, error) {
+	// Write the unknown image to a temp file (needed for CLI tools).
+	tmpDir := os.TempDir()
+	inPath := filepath.Join(tmpDir, "ef-convert-in-"+fmt.Sprintf("%d", time.Now().UnixNano()))
+	outPath := filepath.Join(tmpDir, "ef-convert-out-"+fmt.Sprintf("%d", time.Now().UnixNano())+".jpg")
+
+	if err := os.WriteFile(inPath, data, 0644); err != nil {
+		return nil, fmt.Errorf("write temp input: %w", err)
+	}
+	defer os.Remove(inPath)
+	defer os.Remove(outPath)
+
+	// Try heif-convert first (fastest, handles HEIC natively).
+	if heifErr := tryHEIFConvert(inPath, outPath); heifErr == nil {
+		outData, err := os.ReadFile(outPath)
+		if err == nil && len(outData) > 0 {
+			log.Printf("convertWithExternalTool: heif-convert succeeded (%d bytes)", len(outData))
+			return outData, nil
+		}
+	}
+
+	// Fall back to ImageMagick convert.
+	if magickErr := exec.Command("convert", inPath, "-resize", fmt.Sprintf("%dx%d>", maxImageSize, maxImageSize), "-quality", fmt.Sprintf("%d", jpegQuality), outPath).Run(); magickErr == nil {
+		outData, err := os.ReadFile(outPath)
+		if err == nil && len(outData) > 0 {
+			log.Printf("convertWithExternalTool: ImageMagick convert succeeded (%d bytes)", len(outData))
+			return outData, nil
+		}
+	}
+
+	return nil, errors.New("all external conversion tools failed")
+}
+
+// tryHEIFConvert attempts to convert a HEIC/HEIF file to JPEG using heif-convert.
+func tryHEIFConvert(inPath, outPath string) error {
+	// heif-convert outputs to {input}.jpg by default.
+	defaultOut := inPath + ".jpg"
+	defer os.Remove(defaultOut)
+
+	cmd := exec.Command("heif-convert", inPath, outPath)
+	if output, err := cmd.CombinedOutput(); err != nil {
+		return fmt.Errorf("heif-convert failed: %w, output: %s", err, string(output))
+	}
+
+	// If it wrote to the default path instead of our outPath, move it.
+	if _, err := os.Stat(outPath); os.IsNotExist(err) {
+		if _, err := os.Stat(defaultOut); err == nil {
+			os.Rename(defaultOut, outPath)
+		}
+	}
+
+	_, err := os.Stat(outPath)
+	return err
+}
+
 // readImageFile reads the full contents of an image file from disk.
 func readImageFile(path string) ([]byte, error) {
 	info, err := os.Stat(path)

internal/handlers/expenses.go

@@ -320,19 +320,59 @@ func setCurrentEventID(w http.ResponseWriter, eventID string) {
 // ---------------------------------------------------------------------------
 
 // detectImageExtension examines the magic bytes of the provided data to
-// determine whether it is a JPEG or PNG image. Returns "jpg", "png", or
+// determine its image format. Supports JPEG, PNG, WebP, GIF, BMP, TIFF,
-// an empty string if the format is not recognised.
+// and HEIC/HEIF (common on iPhones). Returns the file extension (without
+// dot) or an empty string if the format is not recognised.
 func detectImageExtension(data []byte) string {
 	if len(data) < 4 {
 		return ""
 	}
-	// JPEG magic: 0xFF 0xD8 0xFF
+
-	if data[0] == 0xFF && data[1] == 0xD8 && data[2] == 0xFF {
+	// JPEG: FF D8 FF
+	if len(data) >= 3 && data[0] == 0xFF && data[1] == 0xD8 && data[2] == 0xFF {
 		return "jpg"
 	}
-	// PNG magic: 0x89 'P' 'N' 'G' 0x0D 0x0A 0x1A 0x0A
+
-	if data[0] == 0x89 && data[1] == 0x50 && data[2] == 0x4E && data[3] == 0x47 {
+	// PNG: 89 50 4E 47 0D 0A 1A 0A
+	if len(data) >= 8 && data[0] == 0x89 && data[1] == 0x50 && data[2] == 0x4E &&
+		data[3] == 0x47 && data[4] == 0x0D && data[5] == 0x0A && data[6] == 0x1A && data[7] == 0x0A {
 		return "png"
 	}
+
+	// WebP: 52 49 46 46 .... 57 45 42 50
+	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 "webp"
+	}
+
+	// GIF: 47 49 46 38 (39 61 or 37 61)
+	if len(data) >= 6 && data[0] == 0x47 && data[1] == 0x49 && data[2] == 0x46 &&
+		data[3] == 0x38 && (data[4] == 0x39 || data[4] == 0x37) && data[5] == 0x61 {
+		return "gif"
+	}
+
+	// BMP: 42 4D
+	if data[0] == 0x42 && data[1] == 0x4D {
+		return "bmp"
+	}
+
+	// TIFF: 49 49 2A 00 or 4D 4D 00 2A
+	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 "tiff"
+	}
+
+	// HEIC/HEIF/AVIF: .... 66 74 79 70 ... (ftyp box)
+	// The ftyp box starts at offset 4 with brand at offset 8.
+	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 "heic"
+		case "avif":
+			return "avif"
+		}
+	}
+
 	return ""
 }