From 8a525f753b801f551e8012340e106c7084570806 Mon Sep 17 00:00:00 2001
From: Noah Hellman <noah@hllmn.net>
Date: Tue, 6 Dec 2022 21:55:46 +0100
Subject: [PATCH] wip

---
 src/block.rs |  9 +++------
 src/span.rs  | 48 ++++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 49 insertions(+), 8 deletions(-)

diff --git a/src/block.rs b/src/block.rs
index a0f20fd..3d3272d 100644
--- a/src/block.rs
+++ b/src/block.rs
@@ -95,10 +95,7 @@ impl<'s> Parser<'s> {
                         let first = &mut lines[0];
                         *first = first.with_start(span.end());
                         // trim starting whitespace of block
-                        *first = Span::new(
-                            first.end() - first.of(self.src).trim_start().len(),
-                            first.end(),
-                        );
+                        *first = first.trim_start(self.src);
                         let line_count = match l {
                             CodeBlock { .. } => line_count - 1,
                             _ => line_count,
@@ -106,7 +103,7 @@ impl<'s> Parser<'s> {
                         if !matches!(l, Leaf::CodeBlock { .. }) {
                             // trim ending whitespace of block
                             let last = &mut lines[line_count - 1];
-                            *last = last.with_len(last.of(self.src).trim_end().len());
+                            *last = last.trim_end(self.src);
                         }
                         for line in &lines[0..line_count] {
                             self.tree.elem(Atom::Inline, *line);
@@ -134,7 +131,7 @@ impl<'s> Parser<'s> {
                                     .count()
                                     + usize::from(skip_chars))
                                 .min(sp.len());
-                                *sp = sp.trim_start(skip);
+                                *sp = sp.skip(skip);
                             });
 
                         self.tree.enter(kind, span);
diff --git a/src/span.rs b/src/span.rs
index e81a364..6d2f49a 100644
--- a/src/span.rs
+++ b/src/span.rs
@@ -28,8 +28,8 @@ impl Span {
         Self::by_len(self.start(), len)
     }
 
-    pub fn trim_start(self, n: usize) -> Self {
-        Self::new(self.start().checked_add(n).unwrap(), self.end())
+    pub fn skip(self, n: usize) -> Self {
+        Self::new(self.start() + n, self.end())
     }
 
     pub fn translate(self, n: usize) -> Self {
@@ -66,4 +66,48 @@ impl Span {
     pub fn of(self, s: &str) -> &str {
         &s[self.start()..self.end()]
     }
+
+    pub fn from_slice(s: &str, slice: &str) -> Self {
+        Self::by_len(slice.as_ptr() as usize - s.as_ptr() as usize, slice.len())
+    }
+
+    pub fn trim_start(self, s: &str) -> Self {
+        Self::from_slice(s, self.of(s).trim_start())
+    }
+
+    pub fn trim_end(self, s: &str) -> Self {
+        Self::from_slice(s, self.of(s).trim_end())
+    }
+
+    pub fn trim(self, s: &str) -> Self {
+        Self::from_slice(s, self.of(s).trim_start().trim_end())
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::Span;
+
+    #[test]
+    fn from_slice() {
+        let src = "0123456789";
+        assert_eq!(Span::from_slice(src, &src[0..0]), Span::new(0, 0));
+        assert_eq!(Span::from_slice(src, &src[0..5]), Span::new(0, 5));
+        assert_eq!(Span::from_slice(src, &src[5..5]), Span::new(5, 5));
+        assert_eq!(Span::from_slice(src, &src[5..8]), Span::new(5, 8));
+        assert_eq!(Span::from_slice(src, &src[5..10]), Span::new(5, 10));
+        assert_eq!(Span::from_slice(src, &src[5..]), Span::new(5, 10));
+    }
+
+    #[test]
+    fn trim() {
+        let src = "  23456   ";
+        assert_eq!(Span::by_len(0, src.len()).trim_start(src), Span::new(2, 10));
+        assert_eq!(Span::by_len(0, src.len()).trim_end(src), Span::new(0, 7));
+        assert_eq!(Span::by_len(0, src.len()).trim(src), Span::new(2, 7));
+        assert_eq!(
+            Span::by_len(0, src.len()).trim_start(src).trim_end(src),
+            Span::new(2, 7)
+        );
+    }
 }