1 files changed, 156 insertions, 0 deletions
diff --git a/src/util/slice.rs b/src/util/slice.rs
new file mode 100644
index 0000000..2134069
--- /dev/null
+++ b/src/util/slice.rs
@@ -0,0 +1,156 @@
+//! Utilities to deal with characters.
+
+use crate::constant::TAB_SIZE;
+use crate::tokenizer::{Event, EventType, Point};
+
+/// A range between two places.
+#[derive(Debug)]
+pub struct Position<'a> {
+    pub start: &'a Point,
+    pub end: &'a Point,
+}
+
+impl<'a> Position<'a> {
+    /// Get a position from an exit event.
+    ///
+    /// Looks backwards for the corresponding `enter` event.
+    /// This does not support nested events (such as lists in lists).
+    ///
+    /// ## Panics
+    ///
+    /// This function panics if an enter event is given.
+    /// When `micromark` is used, this function never panics.
+    pub fn from_exit_event(events: &'a [Event], index: usize) -> Position<'a> {
+        let exit = &events[index];
+        assert_eq!(
+            exit.event_type,
+            EventType::Exit,
+            "expected `from_exit_event` to be called on `exit` event"
+        );
+        let mut enter_index = index - 1;
+
+        loop {
+            let enter = &events[enter_index];
+            if enter.event_type == EventType::Enter && enter.token_type == exit.token_type {
+                return Position {
+                    start: &enter.point,
+                    end: &exit.point,
+                };
+            }
+
+            enter_index -= 1;
+        }
+    }
+}
+
+/// Chars belonging to a range.
+///
+/// Includes information on virtual spaces before and after the chars.
+#[derive(Debug)]
+pub struct Slice<'a> {
+    pub chars: &'a [char],
+    pub before: usize,
+    pub after: usize,
+}
+
+impl<'a> Slice<'a> {
+    /// Get the slice belonging to a position.
+    pub fn from_point(list: &'a [char], point: &Point) -> Slice<'a> {
+        let mut before = point.vs;
+        let mut start = point.index;
+        let end = if start < list.len() { start + 1 } else { start };
+
+        // If we have virtual spaces before, it means we are past the actual
+        // character at that index, and those virtual spaces.
+        if before > 0 {
+            before = TAB_SIZE - before;
+            start += 1;
+        };
+
+        Slice {
+            chars: if start < end { &list[start..end] } else { &[] },
+            before,
+            after: 0,
+        }
+    }
+
+    /// Get the slice belonging to a position.
+    pub fn from_position(list: &'a [char], position: &Position) -> Slice<'a> {
+        let mut before = position.start.vs;
+        let mut after = position.end.vs;
+        let mut start = position.start.index;
+        let mut end = position.end.index;
+
+        // If we have virtual spaces before, it means we are past the actual
+        // character at that index, and those virtual spaces.
+        if before > 0 {
+            before = TAB_SIZE - before;
+            start += 1;
+        };
+
+        // If we have virtual spaces after, it means that character is included,
+        // and one less virtual space.
+        if after > 0 {
+            after -= 1;
+            end += 1;
+        }
+
+        Slice {
+            chars: &list[start..end],
+            before,
+            after,
+        }
+    }
+
+    /// To do.
+    pub fn size(&self) -> usize {
+        self.chars.len() + self.before + self.after
+    }
+
+    // To do:
+    // When we have u8s, we could use: <https://doc.rust-lang.org/std/str/fn.from_utf8.html>
+    // to implement an `as_str`.
+
+    /// To do.
+    pub fn head(&self) -> Option<char> {
+        if self.before > 0 {
+            Some(' ')
+        } else if self.chars.is_empty() {
+            None
+        } else {
+            Some(self.chars[0])
+        }
+    }
+
+    /// To do.
+    pub fn tail(&self) -> Option<char> {
+        if self.after > 0 {
+            Some(' ')
+        } else {
+            let index = self.chars.len();
+            if index > 0 {
+                Some(self.chars[index - 1])
+            } else {
+                None
+            }
+        }
+    }
+
+    /// To do.
+    pub fn serialize(&self) -> String {
+        let mut string = String::with_capacity(self.size());
+        let mut index = self.before;
+        while index > 0 {
+            string.push(' ');
+            index -= 1;
+        }
+        string.push_str(&self.chars.iter().collect::<String>());
+        index = self.after;
+        while index > 0 {
+            string.push(' ');
+            index -= 1;
+        }
+
+        string
+    }
+}