2 files changed, 161 insertions, 0 deletions
diff --git a/src/repo/profile/package_use/mod.rs b/src/repo/profile/package_use/mod.rs
new file mode 100644
index 0000000..ddad8b3
--- /dev/null
+++ b/src/repo/profile/package_use/mod.rs
@@ -0,0 +1,125 @@
+use std::{
+    collections::HashMap,
+    io,
+    path::{Path, PathBuf},
+};
+
+use mon::{Parser, ParserIter, ascii_whitespace1, input::InputIter};
+
+use crate::{
+    Parseable,
+    atom::Atom,
+    repo::profile::{FlagOperation, LineBasedFileExpr, Profile, read_config_files},
+    useflag::UseFlag,
+};
+
+mod parsers;
+
+#[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)]
+struct Expr(Atom, Vec<FlagOperation>);
+
+#[derive(Debug, Clone, Copy)]
+pub(super) enum Kind {
+    Use,
+    Force,
+    Mask,
+    StableForce,
+    StableMask,
+}
+
+pub(super) fn evaluate<P: AsRef<Path>>(
+    parents: &[Profile],
+    kind: Kind,
+    path: P,
+) -> Result<HashMap<Atom, Vec<UseFlag>>, Error> {
+    let file_path = match kind {
+        Kind::Use => "package.use",
+        Kind::Force => "package.use.force",
+        Kind::Mask => "package.use.mask",
+        Kind::StableForce => "package.use.stable.force",
+        Kind::StableMask => "package.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) => HashMap::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,
+    vars: HashMap<Atom, Vec<FlagOperation>>,
+) -> HashMap<Atom, Vec<UseFlag>> {
+    let mut accumulated: HashMap<Atom, Vec<UseFlag>> = HashMap::new();
+
+    for parent in parents {
+        let source = match kind {
+            Kind::Use => parent.package_use(),
+            Kind::Force => parent.package_use_force(),
+            Kind::Mask => parent.package_use_mask(),
+            Kind::StableForce => parent.package_use_stable_force(),
+            Kind::StableMask => parent.package_use_stable_mask(),
+        };
+
+        for (atom, flags) in source {
+            accumulated
+                .entry(atom.clone())
+                .and_modify(|f| f.extend(flags.iter().cloned()))
+                .or_insert(flags.clone());
+        }
+    }
+
+    for (atom, flags) in vars {
+        match accumulated.get_mut(&atom) {
+            Some(accumulated) => {
+                for flag in flags {
+                    match flag {
+                        FlagOperation::Add(flag) => accumulated.push(flag),
+                        FlagOperation::Remove(flag) => accumulated.retain(|v| *v != flag),
+                    }
+                }
+            }
+            None => {
+                accumulated.insert(
+                    atom.clone(),
+                    flags
+                        .iter()
+                        .filter_map(|flag| match flag {
+                            FlagOperation::Add(flag) => Some(flag),
+                            FlagOperation::Remove(_) => None,
+                        })
+                        .cloned()
+                        .collect(),
+                );
+            }
+        }
+    }
+
+    accumulated
+}
+
+fn parse(contents: &str) -> Result<HashMap<Atom, Vec<FlagOperation>>, Error> {
+    Ok(LineBasedFileExpr::<Expr>::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(Expr(atom, operations)) => Some((atom, operations)),
+        })
+        .collect())
+}
diff --git a/src/repo/profile/package_use/parsers.rs b/src/repo/profile/package_use/parsers.rs
new file mode 100644
index 0000000..f7bc801
--- /dev/null
+++ b/src/repo/profile/package_use/parsers.rs
@@ -0,0 +1,36 @@
+use mon::{Parser, ParserIter, ascii_whitespace, ascii_whitespace1, tag};
+
+use crate::{
+    Parseable,
+    atom::Atom,
+    repo::profile::{FlagOperation, package_use::Expr},
+};
+
+impl<'a> Parseable<'a, &'a str> for Expr {
+    type Parser = impl Parser<&'a str, Output = Self>;
+
+    fn parser() -> Self::Parser {
+        Atom::parser()
+            .followed_by(ascii_whitespace1())
+            .and(
+                FlagOperation::parser()
+                    .separated_by(ascii_whitespace().and_not(tag("\n")).repeated().at_least(1))
+                    .at_least(1),
+            )
+            .map(|(atom, operations)| Expr(atom, operations))
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use mon::input::InputIter;
+
+    use super::*;
+
+    #[test]
+    fn test_parse_expr() {
+        let it = InputIter::new("foo/bar a -b");
+
+        Expr::parser().check_finished(it).unwrap();
+    }
+}