From 18123a6511c5cdfd884b7417747f54b2bd54c290 Mon Sep 17 00:00:00 2001
From: Chris Price <price.c@gmail.com>
Date: Tue, 17 May 2022 21:14:50 +0100
Subject: [PATCH] Refactor to use thiserror

---
 Cargo.lock                  |  2 +-
 crates/fj-export/Cargo.toml |  2 +-
 crates/fj-export/src/lib.rs | 51 +++++++++++++++++++++++++++++--------
 3 files changed, 43 insertions(+), 12 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index f9e38d25b..58320c68d 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -733,10 +733,10 @@ dependencies = [
 name = "fj-export"
 version = "0.6.0"
 dependencies = [
- "anyhow",
  "fj-interop",
  "fj-math",
  "stl",
+ "thiserror",
  "threemf",
 ]
 
diff --git a/crates/fj-export/Cargo.toml b/crates/fj-export/Cargo.toml
index dd85e88c9..66202bfe4 100644
--- a/crates/fj-export/Cargo.toml
+++ b/crates/fj-export/Cargo.toml
@@ -13,7 +13,7 @@ categories = ["encoding", "mathematics", "rendering"]
 
 
 [dependencies]
-anyhow = "1.0.57"
+thiserror = "1.0.31"
 threemf = "0.3.0"
 stl = "0.2.1"
 
diff --git a/crates/fj-export/src/lib.rs b/crates/fj-export/src/lib.rs
index 130fb0a2a..642fee7ab 100644
--- a/crates/fj-export/src/lib.rs
+++ b/crates/fj-export/src/lib.rs
@@ -16,7 +16,7 @@
 
 use std::{fs::File, path::Path};
 
-use anyhow::{anyhow, Result};
+use thiserror::Error;
 
 use fj_interop::mesh::Mesh;
 use fj_math::{Point, Triangle, Vector};
@@ -27,7 +27,7 @@ use fj_math::{Point, Triangle, Vector};
 ///
 /// Currently 3MF & STL file types are supported. The case insensitive file extension of
 /// the provided path is used to switch between supported types.
-pub fn export(mesh: &Mesh<Point<3>>, path: &Path) -> Result<()> {
+pub fn export(mesh: &Mesh<Point<3>>, path: &Path) -> Result<(), Error> {
     match path.extension() {
         Some(extension) if extension.to_ascii_uppercase() == "3MF" => {
             export_3mf(mesh, path)
@@ -35,14 +35,14 @@ pub fn export(mesh: &Mesh<Point<3>>, path: &Path) -> Result<()> {
         Some(extension) if extension.to_ascii_uppercase() == "STL" => {
             export_stl(mesh, path)
         }
-        Some(extension) => {
-            Err(anyhow!("Extension not recognised, got {:?}", extension))
-        }
-        None => Err(anyhow!("No extension specified")),
+        Some(extension) => Err(Error::InvalidExtension(
+            extension.to_str().map(|s| s.to_string()),
+        )),
+        None => Err(Error::NoExtension),
     }
 }
 
-fn export_3mf(mesh: &Mesh<Point<3>>, path: &Path) -> Result<()> {
+fn export_3mf(mesh: &Mesh<Point<3>>, path: &Path) -> Result<(), Error> {
     let vertices = mesh.vertices().map(|vertex| vertex.into()).collect();
 
     let indices: Vec<_> = mesh.indices().collect();
@@ -67,7 +67,7 @@ fn export_3mf(mesh: &Mesh<Point<3>>, path: &Path) -> Result<()> {
     Ok(())
 }
 
-fn export_stl(mesh: &Mesh<Point<3>>, path: &Path) -> Result<()> {
+fn export_stl(mesh: &Mesh<Point<3>>, path: &Path) -> Result<(), Error> {
     let points = mesh
         .triangles()
         .map(|triangle| triangle.points)
@@ -84,7 +84,7 @@ fn export_stl(mesh: &Mesh<Point<3>>, path: &Path) -> Result<()> {
         .map(|&points| points.into())
         .map(|triangle: Triangle<3>| triangle.to_parry().normal())
         .collect::<Option<Vec<_>>>()
-        .ok_or_else(|| anyhow!("Unable to compute normal"))?;
+        .ok_or(ExportError::InvalidTriangle)?;
 
     let normals = normals.iter().map(|vector| vector.into_inner().into()).map(
         |vector: Vector<3>| {
@@ -112,7 +112,10 @@ fn export_stl(mesh: &Mesh<Point<3>>, path: &Path) -> Result<()> {
     let binary_stl_file = stl::BinaryStlFile {
         header: stl::BinaryStlHeader {
             header: [0u8; 80],
-            num_triangles: triangles.len().try_into()?,
+            num_triangles: triangles
+                .len()
+                .try_into()
+                .map_err(|_| Error::InvalidTriangleCount)?,
         },
         triangles,
     };
@@ -121,3 +124,31 @@ fn export_stl(mesh: &Mesh<Point<3>>, path: &Path) -> Result<()> {
 
     Ok(())
 }
+
+/// An error that can occur while exporting
+#[derive(Debug, Error)]
+pub enum Error {
+    /// No extension specified
+    #[error("no extension specified")]
+    NoExtension,
+
+    /// Unrecognised extension found `{0:?}`
+    #[error("unrecognised extension found `{0:?}`")]
+    InvalidExtension(Option<String>),
+
+    /// Invalid triangle found when trying to compute normal
+    #[error("invalid triangle found when trying to compute normal")]
+    InvalidTriangle,
+
+    /// I/O error whilst exporting to file
+    #[error("I/O error whilst exporting to file")]
+    Io(#[from] std::io::Error),
+
+    /// Maximum triangle count exceeded
+    #[error("maximum triangle count exceeded")]
+    InvalidTriangleCount,
+
+    /// Threemf error whilst exporting to 3MF file
+    #[error("threemf error whilst exporting to 3MF file")]
+    ThreeMF(#[from] threemf::Error),
+}