3 files changed, 99 insertions, 1 deletions

diff --git a/Cargo.toml b/Cargo.toml
index adfe5d6..7303bc8 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -3,6 +3,7 @@
 members = [
     "bin",
     "lib",
-    "macros"
+    "macros",
+    "vfs"
 ]
 
diff --git a/vfs/Cargo.toml b/vfs/Cargo.toml
new file mode 100644
index 0000000..56a2c61
--- /dev/null
+++ b/vfs/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "vfs"
+version = "0.1.0"
+edition = "2018"
+
+[dependencies]
+indexmap = "1.6.2"
+
diff --git a/vfs/src/lib.rs b/vfs/src/lib.rs
new file mode 100644
index 0000000..f620ab9
--- /dev/null
+++ b/vfs/src/lib.rs
@@ -0,0 +1,89 @@
+use std::{
+    collections::HashMap,
+    default::Default,
+    path::{Path, PathBuf},
+};
+
+use indexmap::IndexSet;
+
+#[derive(Copy, Clone, Debug, PartialEq, PartialOrd, Eq, Ord, Hash)]
+pub struct FileId(u32);
+
+#[derive(Debug, Default)]
+pub struct Interner {
+    map: IndexSet<PathBuf>,
+}
+
+impl Interner {
+    pub fn get<P: AsRef<Path>>(&self, path: P) -> Option<FileId> {
+        self.map
+            .get_index_of(path.as_ref())
+            .map(|i| FileId(i as u32))
+    }
+    pub fn intern(&mut self, path: PathBuf) -> FileId {
+        let (id, _) = self.map.insert_full(path);
+        FileId(id as u32)
+    }
+    pub fn lookup(&self, file: FileId) -> Option<&Path> {
+        self.map.get_index(file.0 as usize).map(|p| p.as_path())
+    }
+}
+
+#[derive(Default)]
+pub struct ReadOnlyVfs {
+    interner: Interner,
+    data: HashMap<FileId, Vec<u8>>,
+}
+
+impl ReadOnlyVfs {
+    pub fn alloc_file_id<P: AsRef<Path>>(&mut self, path: P) -> FileId {
+        self.interner.intern(path.as_ref().to_owned())
+    }
+    pub fn len(&self) -> usize {
+        self.data.len()
+    }
+    pub fn file_path(&self, file_id: FileId) -> &Path {
+        self.interner.lookup(file_id).unwrap()
+    }
+    pub fn get(&self, file_id: FileId) -> &Vec<u8> {
+        self.data.get(&file_id).unwrap()
+    }
+    pub fn get_str(&self, file_id: FileId) -> &str {
+        std::str::from_utf8(self.get(file_id)).unwrap()
+    }
+    pub fn get_mut(&mut self, file_id: FileId) -> &mut Vec<u8> {
+        self.data.get_mut(&file_id).unwrap()
+    }
+    pub fn set_file_contents<P: AsRef<Path>>(&mut self, path: P, contents: &[u8]) {
+        let file_id = self.alloc_file_id(path);
+        self.data.insert(file_id, contents.to_owned());
+    }
+    pub fn iter<'ρ>(&'ρ self) -> impl Iterator<Item = VfsEntry<'ρ>> {
+        self.data.iter().map(move |(file_id, _)| VfsEntry {
+            file_id: *file_id,
+            file_path: self.file_path(*file_id),
+            contents: self.get_str(*file_id),
+        })
+    }
+}
+
+pub struct VfsEntry<'ρ> {
+    pub file_id: FileId,
+    pub file_path: &'ρ Path,
+    pub contents: &'ρ str,
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn trivial() {
+        let mut vfs = ReadOnlyVfs::default();
+        let f1 = "a/b/c";
+        let id1 = vfs.alloc_file_id(f1);
+        let data = "hello".as_bytes().to_vec();
+        vfs.set_file_contents(f1, &data);
+        assert_eq!(vfs.get(id1), &data);
+    }
+}