Extract and adjust relative URL handling

The code for generating relative URLs is extracted into a public method,
making it easier to reuse. In addition, the last component of the
current URL is now treated as a file instead of a directory, meaning
that linking to ../foo.css from /foo/bar/baz results in /foo/foo.css,
instead of /foo/bar/foo.css.

Changelog: changed

src/wobsite.inko

@@ -15,7 +15,7 @@ import std.sys.(exit)
 import std.time.DateTime
 import wobsite.fnmatch
 import wobsite.time.(parse_date)
-import wobsite.url.(file_url)
+import wobsite.url.(file_url, relative_to_absolute)
 
 let INDEX_FILE = 'index.md'
 
@@ -371,19 +371,7 @@ class UpdateAssetLinks {
 
   fn hashed_url(url: String) -> String {
     let key = if url.starts_with?('..') {
-      let steps = url.split('/').take_while fn (v) { v == '..' }.count
-      let mut pending = steps
-      let chunks = @url.split('/').to_array
-
-      while pending > 0 {
-        chunks.pop
-        pending -= 1
-      }
-
-      let base = String.join(chunks.into_iter, '/')
-      let rel = String.join(url.split('/').skip(steps), '/')
-
-      "{base}/{rel}"
+      relative_to_absolute(@url, url)
     } else {
       url
     }

src/wobsite/url.inko

@@ -78,3 +78,24 @@ fn pub file_url(directory: ref Path, path: ref Path) -> String {
     "/{rel.with_extension('')}/"
   }
 }
+
+fn pub relative_to_absolute(current: String, url: String) -> String {
+  let steps = url.split('/').take_while fn (v) { v == '..' }.count
+
+  # We add 1 here such that if the current URL is /foo/bar and we link to
+  # foo.css, the returned URL is /foo/foo.css, not /foo/bar/foo.css. In other
+  # words, the final component is treated as if it were a file instead of a
+  # directory.
+  let mut pending = steps + 1
+  let chunks = current.split('/').to_array
+
+  while pending > 0 {
+    chunks.pop
+    pending -= 1
+  }
+
+  let base = String.join(chunks.into_iter, '/')
+  let rel = String.join(url.split('/').skip(steps), '/')
+
+  "{base}/{rel}"
+}

test/test_wobsite.inko

@@ -333,11 +333,16 @@ fn pub tests(t: mut Tests) {
 
     assets.url = '/foo/bar'
     t.equal(assets.hashed_url('/style.css'), '/style.css?hash=123')
-    t.equal(assets.hashed_url('../style.css'), '../style.css')
+    t.equal(assets.hashed_url('../style.css'), '../style.css?hash=123')
     t.equal(assets.hashed_url('../../style.css'), '../../style.css?hash=123')
 
     assets.url = '/foo/bar/'
     t.equal(assets.hashed_url('/style.css'), '/style.css?hash=123')
+    t.equal(assets.hashed_url('../style.css'), '../style.css?hash=123')
+    t.equal(assets.hashed_url('../../style.css'), '../../style.css?hash=123')
+
+    assets.url = '/foo/bar/baz'
+    t.equal(assets.hashed_url('/style.css'), '/style.css?hash=123')
     t.equal(assets.hashed_url('../style.css'), '../style.css')
     t.equal(assets.hashed_url('../../style.css'), '../../style.css?hash=123')
   }

test/wobsite/test_url.inko

@@ -33,4 +33,18 @@ fn pub tests(t: mut Tests) {
       '/foo/'
     )
   }
+
+  t.test('url.relative_to_absolute') fn (t) {
+    t.equal(url.relative_to_absolute('/', '../style.css'), '/style.css')
+    t.equal(url.relative_to_absolute('/foo/', '../style.css'), '/style.css')
+    t.equal(url.relative_to_absolute('/foo/', 'style.css'), '/style.css')
+    t.equal(
+      url.relative_to_absolute('/foo/bar', '../style.css'),
+      '/style.css'
+    )
+    t.equal(
+      url.relative_to_absolute('/foo/bar/baz', '../style.css'),
+      '/foo/style.css'
+    )
+  }
 }