Introduce a file access interface for reading additional files.

src/context/file_access_interface.rs

@@ -0,0 +1,13 @@
+use std::path::Path;
+
+pub trait FileAccessInterface {
+    fn read_file<P: AsRef<Path>>(&self, path: P) -> Result<String, Box<dyn std::error::Error>>;
+}
+
+pub struct LocalFileAccessInterface;
+
+impl FileAccessInterface for LocalFileAccessInterface {
+    fn read_file<P: AsRef<Path>>(&self, path: P) -> Result<String, Box<dyn std::error::Error>> {
+        Ok(std::fs::read_to_string(path)?)
+    }
+}

src/context/global_settings.rs

@@ -1,16 +1,20 @@
+use super::FileAccessInterface;
+use super::LocalFileAccessInterface;
 use crate::types::Object;
 
 // TODO: Ultimately, I think we'll need most of this: https://orgmode.org/manual/In_002dbuffer-Settings.html
 
 #[derive(Debug, Clone)]
-pub struct GlobalSettings<'g, 's> {
+pub struct GlobalSettings<'g, 's, F: FileAccessInterface> {
     pub radio_targets: Vec<&'g Vec<Object<'s>>>,
+    pub file_access: F,
 }
 
 impl<'g, 's> GlobalSettings<'g, 's> {
     pub fn new() -> Self {
         GlobalSettings {
             radio_targets: Vec::new(),
+            file_access: LocalFileAccessInterface,
         }
     }
 }

src/context/mod.rs

@@ -2,6 +2,7 @@ use crate::error::Res;
 use crate::parser::OrgSource;
 
 mod exiting;
+mod file_access_interface;
 mod global_settings;
 mod list;
 mod parser_context;
@@ -18,6 +19,8 @@ pub trait Matcher = for<'s> Fn(OrgSource<'s>) -> Res<OrgSource<'s>, OrgSource<'s
 pub type DynMatcher<'c> = dyn Matcher + 'c;
 
 pub use exiting::ExitClass;
+pub use file_access_interface::FileAccessInterface;
+pub use file_access_interface::LocalFileAccessInterface;
 pub use global_settings::GlobalSettings;
 pub use list::List;
 pub use parser_context::Context;