Parse StyleSheet into Css struct and pretty print it

Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "grass"
+version = "0.1.0"
+authors = ["ConnorSkees <39542938+ConnorSkees@users.noreply.github.com>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

src/main.rs

@@ -211,6 +211,104 @@ impl StyleSheet {
     pub fn pretty_print<W: std::io::Write>(&self, buf: W) -> io::Result<()> {
         PrettyPrinter::new(buf).pretty_print(self)
     }
+
+    pub fn pretty_print_selectors<W: std::io::Write>(&self, buf: W) -> io::Result<()> {
+        PrettyPrinter::new(buf).pretty_print_preserve_super_selectors(self)
+    }
+
+    pub fn print_as_css<W: std::io::Write>(self, buf: &mut W) -> io::Result<()> {
+        Css::from_stylesheet(self).pretty_print(buf)
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct Block {
+    selector: Selector,
+    styles: Vec<Style>,
+}
+
+impl Block {
+    fn new(selector: Selector) -> Self {
+        Block {
+            selector,
+            styles: Vec::new(),
+        }
+    }
+
+    fn push(&mut self, s: Style) {
+        self.styles.push(s);
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct Css {
+    blocks: Vec<Block>,
+    idx: usize,
+}
+
+impl Css {
+    pub fn new() -> Self {
+        Css {
+            blocks: Vec::new(),
+            idx: 0,
+        }
+    }
+
+    pub fn from_stylesheet(s: StyleSheet) -> Self {
+        Css {
+            blocks: Vec::new(),
+            idx: 0,
+        }
+        .parse_stylesheet(s)
+    }
+
+    fn parse_stmt(&mut self, stmt: Stmt) {
+        match stmt {
+            Stmt::Style(s) => self.blocks[self.idx - 1].push(s),
+            Stmt::RuleSet(RuleSet {
+                selector,
+                super_selector,
+                rules,
+            }) => {
+                if self.idx == 0 {
+                    self.idx = self.blocks.len() + 1;
+                    self.blocks.push(Block::new(super_selector.zip(selector)));
+                    for rule in rules {
+                        self.parse_stmt(rule);
+                    }
+                    self.idx = 0;
+                } else {
+                    self.idx += 1;
+                    self.blocks.push(Block::new(super_selector.zip(selector)));
+                    for rule in rules {
+                        self.parse_stmt(rule);
+                    }
+                    self.idx -= 1;
+                }
+            }
+        }
+    }
+
+    fn parse_stylesheet(mut self, s: StyleSheet) -> Css {
+        for stmt in s.rules {
+            self.parse_stmt(stmt);
+        }
+        self
+    }
+
+    pub fn pretty_print<W: std::io::Write>(self, buf: &mut W) -> io::Result<()> {
+        for block in self.blocks {
+            if block.styles.is_empty() {
+                continue;
+            }
+            writeln!(buf, "{} {{", block.selector)?;
+            for style in block.styles {
+                writeln!(buf, "  {}", style)?;
+            }
+            writeln!(buf, "}}")?;
+        }
+        Ok(())
+    }
 }
 
 #[derive(Debug, Clone)]