feat: whitespace stripping (#3)

* feat: whitespace stripping

* fix: bool negation

* chore: cargo fmt

* Update wdl_util.rs

* Update wdl_util.rs

* Update wdl_util.rs

src/lib.rs

@@ -1,6 +1,7 @@
 //! Crankshaft.
 
 pub mod engine;
+pub mod wdl_util;
 
 /// A boxed [`std::error::Error`].
 pub type BoxedError = Box<dyn std::error::Error>;

src/wdl_util.rs

@@ -0,0 +1,122 @@
+//! Module for utility functions.
+//!
+//! Currently that is whitespace stripping.
+
+/// Removes line continuations from a string.
+fn remove_line_continuations(s: &str) -> String {
+    let mut result = String::new();
+    let mut chars = s.chars();
+    while let Some(c) = chars.next() {
+        if c == '\\' {
+            if let Some(next) = chars.next() {
+                if next == '\n' {
+                    for ws in chars.by_ref() {
+                        if ws == ' ' || ws == '\t' {
+                            continue;
+                        } else {
+                            result.push(ws);
+                            break;
+                        }
+                    }
+                }
+            }
+        }
+        result.push(c);
+    }
+    result
+}
+
+/// Calculates the leading whitespace of a string.
+fn calculate_leading_whitespace(s: &str) -> usize {
+    let mut min_leading_whitespace = usize::MAX;
+    let mut parsing_leading_whitespace = true;
+    let mut cur_char_index = 0;
+    let mut cur_line_index = 0;
+    s.chars().for_each(|c| match c {
+        ' ' | '\t' if parsing_leading_whitespace => cur_char_index += 1,
+        '\n' => {
+            parsing_leading_whitespace = true;
+            cur_line_index += 1;
+            cur_char_index = 0;
+        }
+        _ => {
+            parsing_leading_whitespace = false;
+            if cur_char_index < min_leading_whitespace {
+                min_leading_whitespace = cur_char_index;
+            }
+            cur_char_index += 1;
+        }
+    });
+    if min_leading_whitespace == usize::MAX {
+        0
+    } else {
+        min_leading_whitespace
+    }
+}
+
+/// Strips leading whitespace from a string.
+pub fn strip_leading_whitespace(s: &str, command: bool) -> String {
+    let s_owned = if command {
+        s.to_string()
+    } else {
+        remove_line_continuations(s)
+    };
+    let leading_whitespace = calculate_leading_whitespace(&s_owned);
+    let result = s_owned
+        .lines()
+        .map(|line| {
+            if line.len() >= leading_whitespace {
+                &line[leading_whitespace..]
+            } else {
+                ""
+            }
+        })
+        .collect::<Vec<&str>>()
+        .join("\n");
+    result
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_remove_line_continuations() {
+        let input = "first line \
+                     still first line
+second line";
+        let expected = "first line still first line\nsecond line";
+        assert_eq!(remove_line_continuations(input), expected);
+    }
+
+    #[test]
+    fn test_calculate_leading_whitespace() {
+        let input = "    first line is indented 4 spaces
+        second line is indented 8 spaces
+    third line is indented 4 spaces";
+        assert_eq!(calculate_leading_whitespace(input), 4);
+        let input = "    first line is indented 4 spaces
+ \t \t    second line is indented with a mix of 8 spaces and tabs
+\t\t\t\tfourth line is indented 4 tabs";
+        assert_eq!(calculate_leading_whitespace(input), 4);
+    }
+
+    #[test]
+    fn test_strip_leading_whitespace_not_in_command() {
+        let input = "    first line is indented 4 spaces \
+                     still first line
+        second line is indented 8 spaces
+    third line is indented 4 spaces";
+        let expected = "first line is indented 4 spaces still first line\n    second line is indented 8 spaces\nthird line is indented 4 spaces";
+        assert_eq!(strip_leading_whitespace(input, false), expected);
+    }
+
+    #[test]
+    fn test_strip_leading_whitespace_in_command() {
+        let input = "    first line is indented 4 spaces and trails a backslash \\
+        second line is indented 8 spaces
+    third line is indented 4 spaces";
+        let expected = "first line is indented 4 spaces and trails a backslash \\\n    second line is indented 8 spaces\nthird line is indented 4 spaces";
+        assert_eq!(strip_leading_whitespace(input, true), expected);
+    }
+}