From f623f19b3d4bfffed9da76850eb644a79e103cc7 Mon Sep 17 00:00:00 2001
From: Damien Elmes <gpg@ankiweb.net>
Date: Sun, 15 Mar 2020 19:11:45 +1000
Subject: [PATCH] basic search parsing

---
 rslib/src/lib.rs           |   1 +
 rslib/src/search/mod.rs    |   1 +
 rslib/src/search/parser.rs | 132 +++++++++++++++++++++++++++++++++++++
 3 files changed, 134 insertions(+)
 create mode 100644 rslib/src/search/mod.rs
 create mode 100644 rslib/src/search/parser.rs

diff --git a/rslib/src/lib.rs b/rslib/src/lib.rs
index 8f815dce8..f66dd1bd6 100644
--- a/rslib/src/lib.rs
+++ b/rslib/src/lib.rs
@@ -19,6 +19,7 @@ pub mod log;
 pub mod media;
 pub mod notes;
 pub mod sched;
+pub mod search;
 pub mod storage;
 pub mod template;
 pub mod template_filters;
diff --git a/rslib/src/search/mod.rs b/rslib/src/search/mod.rs
new file mode 100644
index 000000000..b93e263bb
--- /dev/null
+++ b/rslib/src/search/mod.rs
@@ -0,0 +1 @@
+mod parser;
diff --git a/rslib/src/search/parser.rs b/rslib/src/search/parser.rs
new file mode 100644
index 000000000..3517fa817
--- /dev/null
+++ b/rslib/src/search/parser.rs
@@ -0,0 +1,132 @@
+// Copyright: Ankitects Pty Ltd and contributors
+// License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
+
+use nom::branch::alt;
+use nom::bytes::complete::{escaped, is_not, take_while1};
+use nom::character::complete::{char, one_of};
+use nom::combinator::{all_consuming, map};
+use nom::sequence::{delimited, preceded};
+use nom::{multi::many0, IResult};
+
+#[derive(Debug, PartialEq)]
+pub(super) enum Node<'a> {
+    And,
+    Or,
+    Not(Box<Node<'a>>),
+    Group(Vec<Node<'a>>),
+    Text(&'a str),
+}
+
+/// Parse the input string into a list of nodes.
+#[allow(dead_code)]
+pub(super) fn parse(input: &str) -> std::result::Result<Vec<Node>, String> {
+    let (_, nodes) = all_consuming(group_inner)(input).map_err(|e| format!("{:?}", e))?;
+    Ok(nodes)
+}
+
+/// One or more nodes surrounded by brackets, eg (one OR two)
+fn group(s: &str) -> IResult<&str, Node> {
+    map(delimited(char('('), group_inner, char(')')), |nodes| {
+        Node::Group(nodes)
+    })(s)
+}
+
+/// One or more nodes inside brackets, er 'one OR two -three'
+fn group_inner(input: &str) -> IResult<&str, Vec<Node>> {
+    let mut remaining = input;
+    let mut nodes = vec![];
+
+    loop {
+        match node(remaining) {
+            Ok((rem, node)) => {
+                remaining = rem;
+
+                if nodes.len() % 2 == 0 {
+                    // before adding the node, if the length is even then the node
+                    // must not be a boolean
+                    if matches!(node, Node::And | Node::Or) {
+                        return Err(nom::Err::Failure(("", nom::error::ErrorKind::NoneOf)));
+                    }
+                } else {
+                    // if the length is odd, the next item must be a boolean. if it's
+                    // not, add an implicit and
+                    if !matches!(node, Node::And | Node::Or) {
+                        nodes.push(Node::And);
+                    }
+                }
+                nodes.push(node);
+            }
+            Err(e) => match e {
+                nom::Err::Error(_) => break,
+                _ => return Err(e),
+            },
+        };
+    }
+
+    Ok((remaining, nodes))
+}
+
+/// Optional leading space, then a (negated) group or text
+fn node(s: &str) -> IResult<&str, Node> {
+    let whitespace0 = many0(one_of(" \u{3000}"));
+    preceded(whitespace0, alt((negated_node, group, text)))(s)
+}
+
+fn negated_node(s: &str) -> IResult<&str, Node> {
+    map(preceded(char('-'), alt((group, text))), |node| {
+        Node::Not(Box::new(node))
+    })(s)
+}
+
+/// Either quoted or unquoted text
+fn text(s: &str) -> IResult<&str, Node> {
+    alt((quoted_term, unquoted_term))(s)
+}
+
+/// Unquoted text, terminated by a space or )
+fn unquoted_term(s: &str) -> IResult<&str, Node> {
+    map(take_while1(|c| c != ' ' && c != ')'), |text: &str| {
+        if text.len() == 2 && text.to_ascii_lowercase() == "or" {
+            Node::Or
+        } else if text.len() == 3 && text.to_ascii_lowercase() == "and" {
+            Node::And
+        } else {
+            Node::Text(text)
+        }
+    })(s)
+}
+
+// Quoted text, including the outer double quotes.
+fn quoted_term(s: &str) -> IResult<&str, Node> {
+    delimited(char('"'), quoted_term_inner, char('"'))(s)
+}
+
+/// Quoted text, terminated by a non-escaped double quote
+/// Can escape :, " and \
+fn quoted_term_inner(s: &str) -> IResult<&str, Node> {
+    map(escaped(is_not(r#""\"#), '\\', one_of(r#"":\"#)), |o| {
+        Node::Text(o)
+    })(s)
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn parsing() -> Result<(), String> {
+        use Node::*;
+        assert_eq!(
+            parse(r#"hello  -(world and "foo bar") OR test"#)?,
+            vec![
+                Text("hello"),
+                And,
+                Not(Box::new(Group(vec![Text("world"), And, Text("foo bar")]))),
+                Or,
+                Text("test")
+            ]
+        );
+
+        Ok(())
+    }
+}