1 files changed, 82 insertions, 0 deletions
diff --git a/core/module_specifier.rs b/core/module_specifier.rs
new file mode 100644
index 000000000..1bdd5beee
--- /dev/null
+++ b/core/module_specifier.rs
@@ -0,0 +1,82 @@
+use std::fmt;
+use url::Url;
+
+#[derive(Debug, Clone, PartialEq)]
+/// Resolved module specifier
+pub struct ModuleSpecifier(Url);
+
+impl ModuleSpecifier {
+  pub fn to_url(&self) -> Url {
+    self.0.clone()
+  }
+
+  /// Resolves module using this algorithm:
+  /// https://html.spec.whatwg.org/multipage/webappapis.html#resolve-a-module-specifier
+  pub fn resolve(
+    specifier: &str,
+    base: &str,
+  ) -> Result<ModuleSpecifier, url::ParseError> {
+    // 1. Apply the URL parser to specifier. If the result is not failure, return
+    //    the result.
+    // let specifier = parse_local_or_remote(specifier)?.to_string();
+    if let Ok(url) = Url::parse(specifier) {
+      return Ok(ModuleSpecifier(url));
+    }
+
+    // 2. If specifier does not start with the character U+002F SOLIDUS (/), the
+    //    two-character sequence U+002E FULL STOP, U+002F SOLIDUS (./), or the
+    //    three-character sequence U+002E FULL STOP, U+002E FULL STOP, U+002F
+    //    SOLIDUS (../), return failure.
+    if !specifier.starts_with('/')
+      && !specifier.starts_with("./")
+      && !specifier.starts_with("../")
+    {
+      // TODO This is (probably) not the correct error to return here.
+      // TODO: This error is very not-user-friendly
+      return Err(url::ParseError::RelativeUrlWithCannotBeABaseBase);
+    }
+
+    // 3. Return the result of applying the URL parser to specifier with base URL
+    //    as the base URL.
+    let base_url = Url::parse(base)?;
+    let u = base_url.join(&specifier)?;
+    Ok(ModuleSpecifier(u))
+  }
+
+  /// Takes a string representing a path or URL to a module, but of the type
+  /// passed through the command-line interface for the main module. This is
+  /// slightly different than specifiers used in import statements: "foo.js" for
+  /// example is allowed here, whereas in import statements a leading "./" is
+  /// required ("./foo.js"). This function is aware of the current working
+  /// directory and returns an absolute URL.
+  pub fn resolve_root(
+    root_specifier: &str,
+  ) -> Result<ModuleSpecifier, url::ParseError> {
+    if let Ok(url) = Url::parse(root_specifier) {
+      Ok(ModuleSpecifier(url))
+    } else {
+      let cwd = std::env::current_dir().unwrap();
+      let base = Url::from_directory_path(cwd).unwrap();
+      let url = base.join(root_specifier)?;
+      Ok(ModuleSpecifier(url))
+    }
+  }
+}
+
+impl fmt::Display for ModuleSpecifier {
+  fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+    self.0.fmt(f)
+  }
+}
+
+impl From<Url> for ModuleSpecifier {
+  fn from(url: Url) -> Self {
+    ModuleSpecifier(url)
+  }
+}
+
+impl PartialEq<String> for ModuleSpecifier {
+  fn eq(&self, other: &String) -> bool {
+    &self.to_string() == other
+  }
+}