feat: image metadata reading - width, height, format, file_size with fixture test

crates/zx_document_core/Cargo.toml

@@ -10,3 +10,4 @@ infer = "0.16"
 mime_guess = "2"
 comrak = "0.29"
 uuid = { version = "1", features = ["v4"] }
+image = { version = "0.25", default-features = false, features = ["png", "jpeg", "webp", "gif"] }

crates/zx_document_core/src/image_meta.rs

@@ -0,0 +1,77 @@
+use std::path::Path;
+
+use image::GenericImageView;
+use serde::{Deserialize, Serialize};
+
+use crate::error::DocumentError;
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct ImageMeta {
+    pub width: u32,
+    pub height: u32,
+    pub format: String,
+    pub file_size: u64,
+}
+
+/// Read image metadata from a file path.
+pub fn read_image_meta(file_path: &str) -> Result<ImageMeta, DocumentError> {
+    let path = Path::new(file_path);
+
+    let file_size = std::fs::metadata(file_path)
+        .map(|m| m.len())?;
+
+    let format = path
+        .extension()
+        .and_then(|e| e.to_str())
+        .unwrap_or("unknown")
+        .to_lowercase();
+
+    let img = image::open(file_path).map_err(|e| {
+        DocumentError::ParseError(format!("image decode failed: {e}"))
+    })?;
+
+    let (width, height) = img.dimensions();
+
+    Ok(ImageMeta {
+        width,
+        height,
+        format,
+        file_size,
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_read_image_meta_not_found() {
+        let result = read_image_meta("/nonexistent/img.png");
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn test_read_fixture_png() {
+        let path = concat!(env!("CARGO_MANIFEST_DIR"), "/../../fixtures/images/test-red.png");
+        let meta = read_image_meta(path).unwrap();
+        assert_eq!(meta.width, 1);
+        assert_eq!(meta.height, 1);
+        assert_eq!(meta.format, "png");
+        assert!(meta.file_size > 0);
+    }
+
+    #[test]
+    fn test_image_meta_serde() {
+        let meta = ImageMeta {
+            width: 800,
+            height: 600,
+            format: "png".to_string(),
+            file_size: 12345,
+        };
+        let json = serde_json::to_string(&meta).unwrap();
+        let parsed: ImageMeta = serde_json::from_str(&json).unwrap();
+        assert_eq!(parsed.width, 800);
+        assert_eq!(parsed.height, 600);
+        assert_eq!(parsed.format, "png");
+    }
+}