1 files changed, 94 insertions, 0 deletions
diff --git a/src/repo/profile/useflags/mod.rs b/src/repo/profile/useflags/mod.rs
new file mode 100644
index 0000000..d7fb96c
--- /dev/null
+++ b/src/repo/profile/useflags/mod.rs
@@ -0,0 +1,94 @@
+use std::{
+    io,
+    path::{Path, PathBuf},
+};
+
+use mon::{Parser, ParserIter, ascii_whitespace1, input::InputIter};
+
+use crate::{
+    Parseable,
+    repo::profile::{FlagOperation, LineBasedFileExpr, Profile, read_config_files},
+    useflag::UseFlag,
+};
+
+#[derive(Debug, thiserror::Error)]
+pub enum Error {
+    #[error("{0}: io error: {1}")]
+    Io(PathBuf, io::Error),
+    #[error("parser error: {0}")]
+    Parser(String),
+}
+
+#[derive(Debug, Clone, Copy)]
+pub(super) enum Kind {
+    Force,
+    Mask,
+    StableForce,
+    StableMask,
+}
+
+#[allow(clippy::unnecessary_wraps)]
+pub(super) fn evaluate<P: AsRef<Path>>(
+    parents: &[Profile],
+    kind: Kind,
+    path: P,
+) -> Result<Vec<UseFlag>, Error> {
+    let file_path = match kind {
+        Kind::Force => "use.force",
+        Kind::Mask => "use.mask",
+        Kind::StableForce => "use.stable.force",
+        Kind::StableMask => "use.stable.mask",
+    };
+
+    let parsed = match read_config_files(path.as_ref().join(file_path)) {
+        Ok(contents) => parse(&contents)?,
+        Err(e) if matches!(e.kind(), io::ErrorKind::NotFound) => Vec::new(),
+        Err(e) => return Err(Error::Io(path.as_ref().to_path_buf(), e)),
+    };
+
+    Ok(inherit(parents, kind, parsed))
+}
+
+fn inherit(parents: &[Profile], kind: Kind, operations: Vec<FlagOperation>) -> Vec<UseFlag> {
+    let mut accumulated = Vec::new();
+
+    for parent in parents {
+        let source = match kind {
+            Kind::Force => parent.use_force(),
+            Kind::Mask => parent.use_mask(),
+            Kind::StableForce => parent.use_stable_force(),
+            Kind::StableMask => parent.use_stable_mask(),
+        };
+
+        for flag in source {
+            accumulated.push(flag.clone());
+        }
+    }
+
+    for operation in operations {
+        match operation {
+            FlagOperation::Add(flag) => {
+                accumulated.push(flag);
+            }
+            FlagOperation::Remove(flag) => {
+                accumulated.retain(|v| *v != flag);
+            }
+        }
+    }
+
+    accumulated
+}
+
+fn parse(contents: &str) -> Result<Vec<FlagOperation>, Error> {
+    Ok(LineBasedFileExpr::<FlagOperation>::parser()
+        .separated_by_with_opt_trailing(ascii_whitespace1())
+        .many()
+        .parse_finished(InputIter::new(contents))
+        .map_err(|e| Error::Parser(e.rest().to_string()))?
+        .into_iter()
+        .filter_map(|expr| match expr {
+            LineBasedFileExpr::Comment => None,
+            LineBasedFileExpr::Expr(flag_operation) => Some(flag_operation),
+        })
+        .collect())
+}