malvim mostly working, ish

src/utils.rs

@@ -1,10 +1,39 @@
 
+pub trait Substring {
+  fn substring(&self, start: usize, end: usize) -> &str;
+  fn remove(&self, index: usize, len: usize) -> String;
+}
+
+impl Substring for String {
+  fn substring(&self, start: usize, end: usize) -> &str {
+    let mut byte_start = 0;
+    let mut byte_end = 0;
+    let mut chars = self.chars();
+    for i in 0..end {
+      let char_length = chars.next().unwrap().len_utf8();
+      if i < start {
+        byte_start += char_length;
+      }
+      if i == end {
+        break;
+      }
+      byte_end += char_length;
+      
+    }
+    &self[byte_start..byte_end]
+  }
+
+  fn remove(&self, index: usize, len: usize) -> String {
+    self.substring(0, index).to_string() + self.substring(index + len, self.len())
+  }
+}
+
 //the tuple is first, line #, actual line
-pub fn calc_actual_lines<'a>(lines: impl Iterator<Item = &'a String>, max_chars_per_line: usize) -> Vec<(bool, usize, String)> {
+pub fn calc_actual_lines<'a>(lines: impl Iterator<Item = &'a String>, max_chars_per_line: usize, one_extra: bool) -> Vec<(bool, usize, String)> {
   let mut actual_lines = Vec::new();
   let mut line_num = 0;
   for real_line in lines {
-    let mut line = real_line.to_string();
+    let mut line = real_line.to_string() + if one_extra { " " } else { "" };
     let mut first = true;
     loop {
       if line.chars().count() <= max_chars_per_line {
@@ -26,3 +55,16 @@ pub fn calc_actual_lines<'a>(lines: impl Iterator<Item = &'a String>, max_chars_
   actual_lines
 }
 
+pub fn calc_new_cursor_pos(cursor_pos: usize, new_length: usize) -> usize {
+  if cursor_pos >= new_length {
+    if new_length == 0 {
+      0
+    } else {
+      new_length - 1
+    }
+  } else {
+    cursor_pos
+  }
+}
+
+