added Swift code generator

Author: nesium

README.md

@@ -72,4 +72,48 @@ into this…
 
 ![Xcode Screenshot](./.github/Xcode.png)
 
+and also this…
+
+```swift
+import UIKit
+
+extension UIColor {
+  enum Custom {}
+}
+
+extension UIColor.Custom {
+  static let applicationBackgroundLight = UIColor(named: "ApplicationBackgroundLight")!
+  static let applicationBackgroundDark = UIColor(named: "ApplicationBackgroundDark")!
+  static let iconActive = UIColor(named: "IconActive")!
+  static let iconInactive = UIColor(named: "IconInactive")!
+  static let textPrimary = UIColor(named: "TextPrimary")!
+  static let textSecondary = UIColor(named: "TextSecondary")!
+  static let lightContentSeparator = UIColor(named: "LightContentSeparator")!
+  static let numericInputActionKeyBackground = UIColor(named: "NumericInputActionKeyBackground")!
+  static let numericInputActionKeyHighlight = UIColor(named: "NumericInputActionKeyHighlight")!
+  static let numericInputActionKeyShadow = UIColor(named: "NumericInputActionKeyShadow")!
+  static let numericInputActionKeyText = UIColor(named: "NumericInputActionKeyText")!
+  static let numericInputDoneKeyBackground = UIColor(named: "NumericInputDoneKeyBackground")!
+  static let numericInputDoneKeyHighlight = UIColor(named: "NumericInputDoneKeyHighlight")!
+  static let numericInputDoneKeyShadow = UIColor(named: "NumericInputDoneKeyShadow")!
+  static let numericInputDoneKeyText = UIColor(named: "NumericInputDoneKeyText")!
+  static let numericInputFunctionKeyBackground = UIColor(named: "NumericInputFunctionKeyBackground")!
+  static let numericInputFunctionKeyHighlight = UIColor(named: "NumericInputFunctionKeyHighlight")!
+  static let numericInputFunctionKeyShadow = UIColor(named: "NumericInputFunctionKeyShadow")!
+  static let numericInputFunctionKeyText = UIColor(named: "NumericInputFunctionKeyText")!
+  static let numericInputNumericKeyBackground = UIColor(named: "NumericInputNumericKeyBackground")!
+  static let numericInputNumericKeyHighlight = UIColor(named: "NumericInputNumericKeyHighlight")!
+  static let numericInputNumericKeyShadow = UIColor(named: "NumericInputNumericKeyShadow")!
+  static let numericInputNumericKeyText = UIColor(named: "NumericInputNumericKeyText")!
+  static let numericInputBackground = UIColor(named: "NumericInputBackground")!
+}
+```
+
+Usage:
+
+```
+$ ./xcode-color-assets gen-assets colors.assetstyles -o Colors.xcassets
+$ ./xcode-color-assets gen-swift colors.assetstyles -o Colors.swift
+```
+
 > Caveat: This project is in the "works for me" state. There is basically no error handling at this point.

src/gen_swift.rs

@@ -0,0 +1,70 @@
+use super::ast::{Document, DocumentItem, RuleSet, RuleSetItem};
+use std::fs;
+
+pub fn gen_swift(doc: &Document, path: &str) -> std::io::Result<()> {
+  let mut identifiers: Vec<String> = vec![];
+
+  for item in doc.items.iter() {
+    match item {
+      DocumentItem::RuleSet(r) => {
+        append_identifiers_from_ruleset(r, "", &mut identifiers);
+      }
+      _ => {}
+    }
+  }
+
+  let prefix = r#"
+import UIKit
+
+extension UIColor {
+  enum Custom {}
+}
+
+extension UIColor.Custom {
+"#;
+
+  let suffix = r#"
+}
+"#;
+
+  let mapped_idents: Vec<String> = identifiers
+    .iter()
+    .map(|ident| {
+      format!(
+        "  static let {} = UIColor(named: \"{}\")!",
+        lowercase_first_letter(ident),
+        ident
+      )
+    })
+    .collect();
+
+  let result = format!("{}{}{}", prefix, mapped_idents.join("\n"), suffix);
+
+  fs::write(path, result.as_bytes())
+}
+
+fn append_identifiers_from_ruleset(
+  ruleset: &RuleSet,
+  identifier: &str,
+  identifiers_bucket: &mut Vec<String>,
+) {
+  for item in ruleset.items.iter() {
+    match item {
+      RuleSetItem::RuleSet(r) => {
+        let identifier = format!("{}{}", identifier, r.identifier);
+        append_identifiers_from_ruleset(r, &identifier, identifiers_bucket);
+      }
+      RuleSetItem::Declaration(d) => {
+        identifiers_bucket.push(format!("{}{}", identifier, d.identifier));
+      }
+    }
+  }
+}
+
+fn lowercase_first_letter(s: &str) -> String {
+  let mut c = s.chars();
+  match c.next() {
+    None => String::new(),
+    Some(f) => f.to_lowercase().collect::<String>() + c.as_str(),
+  }
+}

src/main.rs

@@ -1,36 +1,70 @@
 mod asset_catalog;
 mod ast;
+mod gen_swift;
 mod parser;
 
 use crate::asset_catalog::write_asset_catalog;
+use crate::gen_swift::gen_swift;
 use crate::parser::parse_document_from_file;
-use clap::{App, Arg};
+use clap::{App, Arg, SubCommand};
 
 fn main() {
   let matches = App::new("color-assets")
     .version("1.0")
     .about("Create Xcode Asset Catalog with colors for light & dark mode.")
-    .arg(
-      Arg::with_name("output")
-        .short("o")
-        .help("Sets the output filename")
-        .value_name("OUTPUT_FILE")
-        .required(true),
+    .subcommand(
+      SubCommand::with_name("gen-assets")
+        .about("generates the Asset Catalog")
+        .arg(
+          Arg::with_name("output")
+            .short("o")
+            .help("Sets the output filename (e.g. Colors.xcassets)")
+            .value_name("OUTPUT_FILE")
+            .required(true),
+        )
+        .arg(
+          Arg::with_name("input")
+            .help("Sets the input file")
+            .value_name("INPUT_FILE")
+            .required(true)
+            .index(1),
+        ),
     )
-    .arg(
-      Arg::with_name("input")
-        .help("Sets the input file")
-        .value_name("INPUT_FILE")
-        .required(true)
-        .index(1),
+    .subcommand(
+      SubCommand::with_name("gen-swift")
+        .about("generates Swift code")
+        .arg(
+          Arg::with_name("output")
+            .short("o")
+            .help("Sets the output filename (e.g. Colors.swift)")
+            .value_name("OUTPUT_FILE")
+            .required(true),
+        )
+        .arg(
+          Arg::with_name("input")
+            .help("Sets the input file")
+            .value_name("INPUT_FILE")
+            .required(true)
+            .index(1),
+        ),
     )
     .get_matches();
 
-  let input_file = matches.value_of("input").unwrap();
-  let output_path = matches.value_of("output").unwrap();
-
-  let doc = parse_document_from_file(&input_file).expect("Could not parse input file.");
-  write_asset_catalog(&doc, &output_path).expect("Could not write asset catalog.");
+  match matches.subcommand() {
+    ("gen-assets", Some(m)) => {
+      let input_file = m.value_of("input").unwrap();
+      let output_path = m.value_of("output").unwrap();
+      let doc = parse_document_from_file(&input_file).expect("Could not parse input file.");
+      write_asset_catalog(&doc, &output_path).expect("Could not write asset catalog.");
+    }
+    ("gen-swift", Some(m)) => {
+      let input_file = m.value_of("input").unwrap();
+      let output_path = m.value_of("output").unwrap();
+      let doc = parse_document_from_file(&input_file).expect("Could not parse input file.");
+      gen_swift(&doc, &output_path).expect("Could not generate Swift code.");
+    }
+    (&_, _) => {}
+  }
 }
 
 #[cfg(test)]