1 files changed, 107 insertions, 0 deletions
diff --git a/src/imap/search.rs b/src/imap/search.rs
new file mode 100644
index 0000000..bf1d30e
--- /dev/null
+++ b/src/imap/search.rs
@@ -0,0 +1,107 @@
+use imap_codec::imap_types::core::NonEmptyVec;
+use imap_codec::imap_types::search::SearchKey;
+use imap_codec::imap_types::sequence::{SeqOrUid, Sequence, SequenceSet};
+use std::num::NonZeroU32;
+
+pub enum SeqType {
+    Undefined,
+    NonUid,
+    Uid,
+}
+impl SeqType {
+    pub fn is_uid(&self) -> bool {
+        matches!(self, Self::Uid)
+    }
+}
+
+pub struct Criteria<'a>(pub &'a SearchKey<'a>);
+impl<'a> Criteria<'a> {
+    /// Returns a set of email identifiers that is greater or equal
+    /// to the set of emails to return
+    pub fn to_sequence_set(&self) -> (SequenceSet, SeqType) {
+        match self.0 {
+            SearchKey::All => (sequence_set_all(), SeqType::Undefined),
+            SearchKey::SequenceSet(seq_set) => (seq_set.clone(), SeqType::NonUid),
+            SearchKey::Uid(seq_set) => (seq_set.clone(), SeqType::Uid),
+            SearchKey::Not(_inner) => {
+                tracing::debug!(
+                    "using NOT in a search request is slow: it selects all identifiers"
+                );
+                (sequence_set_all(), SeqType::Undefined)
+            }
+            SearchKey::Or(left, right) => {
+                tracing::debug!("using OR in a search request is slow: no deduplication is done");
+                let (base, base_seqtype) = Self(&left).to_sequence_set();
+                let (ext, ext_seqtype) = Self(&right).to_sequence_set();
+
+                // Check if we have a UID/ID conflict in fetching: now we don't know how to handle them
+                match (base_seqtype, ext_seqtype) {
+                    (SeqType::Uid, SeqType::NonUid) | (SeqType::NonUid, SeqType::Uid) => {
+                        (sequence_set_all(), SeqType::Undefined)
+                    }
+                    (SeqType::Undefined, x) | (x, _) => {
+                        let mut new_vec = base.0.into_inner();
+                        new_vec.extend_from_slice(ext.0.as_ref());
+                        let seq = SequenceSet(
+                            NonEmptyVec::try_from(new_vec)
+                                .expect("merging non empty vec lead to non empty vec"),
+                        );
+                        (seq, x)
+                    }
+                }
+            }
+            SearchKey::And(search_list) => {
+                tracing::debug!(
+                    "using AND in a search request is slow: no intersection is performed"
+                );
+                search_list
+                    .as_ref()
+                    .iter()
+                    .map(|crit| Self(&crit).to_sequence_set())
+                    .min_by(|(x, _), (y, _)| {
+                        let x_size = approx_sequence_set_size(x);
+                        let y_size = approx_sequence_set_size(y);
+                        x_size.cmp(&y_size)
+                    })
+                    .unwrap_or((sequence_set_all(), SeqType::Undefined))
+            }
+            _ => (sequence_set_all(), SeqType::Undefined),
+        }
+    }
+
+    fn need_meta(&self) {
+        unimplemented!();
+    }
+
+    fn need_body(&self) {
+        unimplemented!();
+    }
+}
+
+fn sequence_set_all() -> SequenceSet {
+    SequenceSet::from(Sequence::Range(
+        SeqOrUid::Value(NonZeroU32::MIN),
+        SeqOrUid::Asterisk,
+    ))
+}
+
+// This is wrong as sequences can overlap
+fn approx_sequence_set_size(seq_set: &SequenceSet) -> u64 {
+    seq_set.0.as_ref().iter().fold(0u64, |acc, seq| {
+        acc.saturating_add(approx_sequence_size(seq))
+    })
+}
+
+// This is wrong as sequence UID can have holes,
+// as we don't know the number of messages in the mailbox also
+fn approx_sequence_size(seq: &Sequence) -> u64 {
+    match seq {
+        Sequence::Single(_) => 1,
+        Sequence::Range(SeqOrUid::Asterisk, _) | Sequence::Range(_, SeqOrUid::Asterisk) => u64::MAX,
+        Sequence::Range(SeqOrUid::Value(x1), SeqOrUid::Value(x2)) => {
+            let x2 = x2.get() as i64;
+            let x1 = x1.get() as i64;
+            (x2 - x1).abs().try_into().unwrap_or(1)
+        }
+    }
+}