Add crop operation implementation

src/arg_parsers/filename.rs

@@ -11,14 +11,15 @@ use super::{Geometry, ResizeGeometry};
 pub struct InputFileArg {
     path: PathBuf,
     //format: Option<String>, // TODO: turn into an enum and enable
-    read_mod: ReadModifier,
+    read_mod: Option<ReadModifier>,
 }
 
 /// The action to be taken upon loading the image.
 /// `convert` accepts any single one of: frame selection, resize, or crop.
 ///
 /// See <https://imagemagick.org/Usage/files/#read_mods> for details.
 /// I've also verified it behaves according to the documentation.
+#[derive(Debug, Clone, Copy, PartialEq)]
 pub enum ReadModifier {
     Resize(ResizeGeometry),
     Crop(LoadCropGeometry),

src/operations/crop.rs

@@ -0,0 +1,10 @@
+use crate::{arg_parsers::LoadCropGeometry, wm_try};
+
+pub fn crop_on_load(
+    image: &mut image::DynamicImage,
+    geom: &LoadCropGeometry,
+) -> Result<(), crate::error::MagickError> {
+    let cropped = wm_try!(image.crop_imm(geom.xoffset, geom.yoffset, geom.width, geom.height));
+    *image = cropped;
+    Ok(())
+}

src/operations/mod.rs

@@ -1,15 +1,20 @@
+mod crop;
 mod resize;
 
 use image::DynamicImage;
 
-use crate::{arg_parsers::ResizeGeometry, error::MagickError};
+use crate::{
+    arg_parsers::{LoadCropGeometry, ResizeGeometry},
+    error::MagickError,
+};
 
 #[derive(Debug, Copy, Clone, PartialEq)]
 pub enum Operation {
     Resize(ResizeGeometry),
     Thumbnail(ResizeGeometry),
     Scale(ResizeGeometry),
     Sample(ResizeGeometry),
+    CropOnLoad(LoadCropGeometry),
 }
 
 impl Operation {
@@ -19,6 +24,7 @@ impl Operation {
             Operation::Thumbnail(geom) => resize::thumbnail(image, geom),
             Operation::Scale(geom) => resize::scale(image, geom),
             Operation::Sample(geom) => resize::sample(image, geom),
+            Operation::CropOnLoad(geom) => crop::crop_on_load(image, geom),
         }
     }
 }