Add documentation for internal code where needed

Related to #3

src/model.rs

@@ -10,7 +10,9 @@ pub struct ImageThumbs<T> {
 
 #[derive(Deserialize, Debug, Clone)]
 pub(crate) struct Params {
+    /// this name will be added to the thumbnail with an underscore (_)
     pub(crate) name: String,
+    /// PNG ignores this variable as it is always lossless
     pub(crate) quality: u8,
     pub(crate) size: (u32, u32),
     pub(crate) mode: Mode,
@@ -19,12 +21,18 @@ pub(crate) struct Params {
 #[derive(Deserialize, Debug, Clone)]
 #[serde(rename_all = "snake_case")]
 pub(crate) enum Mode {
+    /// The image's aspect ratio is preserved. The image is scaled to the maximum possible size that
+    /// fits within the bounds.
     Fit,
+    /// The image's aspect ratio is preserved. The image is scaled to the maximum possible size that
+    /// fits within the larger (relative to aspect ratio) of the bounds, then cropped to fit within
+    /// the other bound.
     Crop,
 }
 
 #[derive(Debug)]
 pub(crate) struct ImageDetails {
+    /// image filename without path and extension
     pub(crate) stem: String,
     pub(crate) format: ImageFormat,
     pub(crate) path: Path,

src/storage.rs

@@ -7,6 +7,10 @@ use crate::Error::NotSupported;
 use crate::{ImageThumbs, ThumbsResult};
 
 impl<T: ObjectStore> ImageThumbs<T> {
+    /// returns options for an [`object_store`] client that maps the file extensions `.jpeg`,
+    /// `.jpg`, and `.png` to its MIME types.
+    ///
+    /// Allows `http` connections in case of tests
     pub(crate) fn client_options() -> ClientOptions {
         #[allow(unused_mut)]
         let mut client_options = ClientOptions::new()
@@ -60,7 +64,7 @@ impl<T: ObjectStore> ImageThumbs<T> {
         })
     }
 
-    pub(crate) fn extract_stem(path: &Path) -> ThumbsResult<&str> {
+    fn extract_stem(path: &Path) -> ThumbsResult<&str> {
         let (stem, _) = path
             .filename()
             .ok_or(NotSupported)?