1 files changed, 157 insertions, 0 deletions
diff --git a/helix-core/src/movement.rs b/helix-core/src/movement.rs
new file mode 100644
index 00000000..57abc498
--- /dev/null
+++ b/helix-core/src/movement.rs
@@ -0,0 +1,157 @@
+use crate::graphemes::{nth_next_grapheme_boundary, nth_prev_grapheme_boundary, RopeGraphemes};
+use crate::{coords_at_pos, pos_at_coords, ChangeSet, Position, Range, Rope, RopeSlice, Selection};
+
+pub fn move_next_word_start(slice: RopeSlice, mut pos: usize, count: usize) -> usize {
+    for _ in 0..count {
+        if pos + 1 == slice.len_chars() {
+            return pos;
+        }
+
+        let mut ch = slice.char(pos);
+        let next = slice.char(pos + 1);
+
+        // if we're at the end of a word, or on whitespce right before new one
+        if categorize(ch) != categorize(next) {
+            pos += 1;
+            ch = next;
+        }
+
+        if is_word(ch) {
+            skip_over_next(slice, &mut pos, is_word);
+        } else if ch.is_ascii_punctuation() {
+            skip_over_next(slice, &mut pos, |ch| ch.is_ascii_punctuation());
+        }
+
+        // TODO: don't include newline?
+        skip_over_next(slice, &mut pos, |ch| ch.is_ascii_whitespace());
+    }
+
+    pos
+}
+
+pub fn move_prev_word_start(slice: RopeSlice, mut pos: usize, count: usize) -> usize {
+    for _ in 0..count {
+        if pos == 0 {
+            return pos;
+        }
+
+        let ch = slice.char(pos);
+        let prev = slice.char(pos - 1);
+
+        if categorize(ch) != categorize(prev) {
+            pos -= 1;
+        }
+
+        // match (category c1, category c2) => {
+        //  if c1 != c2 {
+        //  }
+        // }
+
+        // TODO: skip while eol
+
+        // TODO: don't include newline?
+        skip_over_prev(slice, &mut pos, |ch| ch.is_ascii_whitespace());
+
+        // refetch
+        let ch = slice.char(pos);
+
+        if is_word(ch) {
+            skip_over_prev(slice, &mut pos, is_word);
+        } else if ch.is_ascii_punctuation() {
+            skip_over_prev(slice, &mut pos, |ch| ch.is_ascii_punctuation());
+        }
+        pos = pos.saturating_add(1)
+    }
+
+    pos
+}
+
+pub fn move_next_word_end(slice: RopeSlice, mut pos: usize, count: usize) -> usize {
+    for _ in 0..count {
+        if pos + 1 == slice.len_chars() {
+            return pos;
+        }
+
+        let ch = slice.char(pos);
+        let next = slice.char(pos + 1);
+
+        if categorize(ch) != categorize(next) {
+            pos += 1;
+        }
+
+        // TODO: don't include newline?
+        skip_over_next(slice, &mut pos, |ch| ch.is_ascii_whitespace());
+
+        // refetch
+        let ch = slice.char(pos);
+
+        if is_word(ch) {
+            skip_over_next(slice, &mut pos, is_word);
+        } else if ch.is_ascii_punctuation() {
+            skip_over_next(slice, &mut pos, |ch| ch.is_ascii_punctuation());
+        }
+        pos -= 1
+    }
+
+    pos
+}
+
+// ---- util ------------
+
+// used for by-word movement
+
+fn is_word(ch: char) -> bool {
+    ch.is_alphanumeric() || ch == '_'
+}
+
+#[derive(Debug, Eq, PartialEq)]
+enum Category {
+    Whitespace,
+    Eol,
+    Word,
+    Punctuation,
+}
+fn categorize(ch: char) -> Category {
+    if ch == '\n' {
+        Category::Eol
+    } else if ch.is_ascii_whitespace() {
+        Category::Whitespace
+    } else if ch.is_ascii_punctuation() {
+        Category::Punctuation
+    } else if ch.is_ascii_alphanumeric() {
+        Category::Word
+    } else {
+        unreachable!()
+    }
+}
+
+#[inline]
+pub fn skip_over_next<F>(slice: RopeSlice, pos: &mut usize, fun: F)
+where
+    F: Fn(char) -> bool,
+{
+    let mut chars = slice.chars_at(*pos);
+
+    for ch in chars {
+        if !fun(ch) {
+            break;
+        }
+        *pos += 1;
+    }
+}
+
+#[inline]
+pub fn skip_over_prev<F>(slice: RopeSlice, pos: &mut usize, fun: F)
+where
+    F: Fn(char) -> bool,
+{
+    // need to +1 so that prev() includes current char
+    let mut chars = slice.chars_at(*pos + 1);
+
+    while let Some(ch) = chars.prev() {
+        if !fun(ch) {
+            break;
+        }
+        *pos = pos.saturating_sub(1);
+    }
+}