From 9ce344220ec7d03ec2902907aa41f126faf84df0 Mon Sep 17 00:00:00 2001
From: HampusM <hampus@hampusmat.com>
Date: Sat, 18 May 2024 15:11:38 +0200
Subject: feat(engine): add Obj method to read & parse it's material libs

---
 engine/src/file_format/wavefront/obj.rs | 67 +++++++++++++++++++++++++++++++++
 1 file changed, 67 insertions(+)

(limited to 'engine/src/file_format/wavefront')

diff --git a/engine/src/file_format/wavefront/obj.rs b/engine/src/file_format/wavefront/obj.rs
index 4df5fe5..6367ead 100644
--- a/engine/src/file_format/wavefront/obj.rs
+++ b/engine/src/file_format/wavefront/obj.rs
@@ -2,6 +2,7 @@
 //!
 //! File format documentation: <https://paulbourke.net/dataformats/obj>
 
+use std::fs::read_to_string;
 use std::path::PathBuf;
 
 use crate::file_format::wavefront::common::{
@@ -244,6 +245,35 @@ impl Obj
             ),
         ))
     }
+
+    /// Reads and parses the material libraries of this `Obj`.
+    ///
+    /// # Errors
+    /// Returns `Err` if:
+    /// - Reading the contents of a material library fails
+    /// - Parsing a material library fails
+    pub fn read_and_parse_material_libs<ParsedMaterial, ParseError>(
+        &self,
+        parse_material_lib: impl Fn(&str) -> Result<Vec<ParsedMaterial>, ParseError>,
+    ) -> Result<Vec<ParsedMaterial>, MaterialLibsError<ParseError>>
+    {
+        self.mtl_libs
+            .iter()
+            .flatten()
+            .map(|mtl_lib| {
+                Ok(parse_material_lib(&read_to_string(mtl_lib).map_err(
+                    |err| MaterialLibsError::ReadingMaterialLibFailed {
+                        source: err,
+                        material_lib: mtl_lib.clone(),
+                    },
+                )?)?)
+            })
+            .flat_map(|res| match res {
+                Ok(inner) => Either::A(inner.into_iter().map(Ok)),
+                Err(err) => Either::B(vec![Err(err)].into_iter()),
+            })
+            .collect::<Result<Vec<_>, _>>()
+    }
 }
 
 #[derive(Debug)]
@@ -365,6 +395,21 @@ pub enum Error
     },
 }
 
+#[derive(Debug, thiserror::Error)]
+pub enum MaterialLibsError<MaterialLibParseError>
+{
+    #[error("Parsing material library failed")]
+    ParsingFailed(#[from] MaterialLibParseError),
+
+    #[error("Failed to read material library {}", material_lib.display())]
+    ReadingMaterialLibFailed
+    {
+        #[source]
+        source: std::io::Error,
+        material_lib: PathBuf,
+    },
+}
+
 keyword! {
     #[derive(Debug, PartialEq, Eq, Clone, Copy)]
     enum Keyword {
@@ -412,6 +457,28 @@ fn find_material_specifier_for_line_no(
         .find(|material_specifier| material_specifier.line_no < line_no)
 }
 
+enum Either<ValA, ValB>
+{
+    A(ValA),
+    B(ValB),
+}
+
+impl<ValA, ValB, Item> Iterator for Either<ValA, ValB>
+where
+    ValA: Iterator<Item = Item>,
+    ValB: Iterator<Item = Item>,
+{
+    type Item = Item;
+
+    fn next(&mut self) -> Option<Self::Item>
+    {
+        match self {
+            Self::A(iter_a) => iter_a.next(),
+            Self::B(iter_b) => iter_b.next(),
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests
 {
-- 
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