From e81e059e39603a6c01cd157bc8fb6f1ffbfa7cf5 Mon Sep 17 00:00:00 2001
From: John Sundell <john@sundell.co>
Date: Thu, 5 Mar 2020 11:17:24 +0100
Subject: [PATCH] Add support for the HTML <picture> element (#32)

This change adds support for `<picture>`, and its associated `srcset`
and `media` attributes. This is done by creating a new `HTMLSourceListContext`
protocol which `<picture>` shares with `<audio>` and `<video>`, enabling
maximum code reuse while still preserving type safety. Since an `<img>`
element can also appear inside of `<picture>`, image tags are now constrained
to a new `HTMLImageContainerContext`, which `HTML.BodyContext` also adopts.
---
 Sources/Plot/API/HTML.swift           | 21 +++++++++++----
 Sources/Plot/API/HTMLAttributes.swift | 14 ++++++++++
 Sources/Plot/API/HTMLElements.swift   | 38 +++++++++++++++++----------
 Tests/PlotTests/HTMLTests.swift       | 20 +++++++++++++-
 4 files changed, 73 insertions(+), 20 deletions(-)
diff --git a/Sources/Plot/API/HTML.swift b/Sources/Plot/API/HTML.swift
index 7ac2c5f..86561d0 100644
--- a/Sources/Plot/API/HTML.swift
+++ b/Sources/Plot/API/HTML.swift
@@ -42,7 +42,7 @@ public extension HTML {
     /// The context within an HTML document's `<head>` element.
     enum HeadContext: HTMLContext, HTMLScriptableContext {}
     /// The context within an HTML document's `<body>` element.
-    class BodyContext: HTMLStylableContext, HTMLScriptableContext {}
+    class BodyContext: HTMLStylableContext, HTMLScriptableContext, HTMLImageContainerContext {}
     /// The context within an HTML `<abbr>` element.
     final class AbbreviationContext: BodyContext {}
     /// The context within an HTML `<a>` element.
@@ -85,6 +85,12 @@ public extension HTML {
     enum MetaContext: HTMLNamableContext {}
     /// The context within an HTML `<option>` element.
     enum OptionContext: HTMLValueContext {}
+    /// The context within an HTML `<picture>` element.
+    enum PictureContext: HTMLSourceListContext, HTMLImageContainerContext {
+        public typealias SourceContext = PictureSourceContext
+    }
+    /// The context within a picture `<source>` element.
+    enum PictureSourceContext {}
     /// The context within an HTML `<script>` element.
     enum ScriptContext: HTMLSourceContext, HTMLIntegrityContext {}
     /// The context within an HTML `<select>` element.
@@ -106,15 +112,14 @@ public protocol HTMLContext {}
 /// Context shared among all HTML elements that can have their dimensions
 /// (width and height) specified through attributes, such as `<video>`.
 public protocol HTMLDimensionContext: HTMLContext {}
+/// Context shared among all HTML elements that can contain an `<img>` element.
+public protocol HTMLImageContainerContext: HTMLContext {}
 /// Context shared among all HTML elements that act as some form
 /// of link to an external resource, such as `<link>` or `<a>`.
 public protocol HTMLLinkableContext: HTMLContext {}
 /// Context shared among all HTML elements that enable media playback,
 /// such as `<audio>` and `<video>`.
-public protocol HTMLMediaContext: HTMLContext {
-    /// The context within the media element's `<source>` element.
-    associatedtype SourceContext: HTMLSourceContext
-}
+public protocol HTMLMediaContext: HTMLSourceListContext {}
 /// Context shared among all HTML elements that support the `integrity`
 /// attribute, such as `<link>` and `<script>`
 public protocol HTMLIntegrityContext: HTMLContext {}
@@ -130,6 +135,12 @@ public protocol HTMLScriptableContext: HTMLContext {}
 /// Context shared among all HTML elements that support the `src`
 /// attribute, for example `<img>` and `<iframe>`.
 public protocol HTMLSourceContext: HTMLContext {}
+/// Context shared among all HTML elements that can act as containers
+/// for a list of `<source>` elements.
+public protocol HTMLSourceListContext: HTMLContext {
+    /// The context within the element's `<source>` child elements.
+    associatedtype SourceContext
+}
 /// Context shared among all HTML elements that can be styled using
 /// inline CSS through the `style` attribute.
 public protocol HTMLStylableContext: HTMLContext {}
diff --git a/Sources/Plot/API/HTMLAttributes.swift b/Sources/Plot/API/HTMLAttributes.swift
index 1bfa5ea..8da0397 100644
--- a/Sources/Plot/API/HTMLAttributes.swift
+++ b/Sources/Plot/API/HTMLAttributes.swift
@@ -203,6 +203,20 @@ public extension Attribute where Context == HTML.VideoSourceContext {
     }
 }
 
+public extension Attribute where Context == HTML.PictureSourceContext {
+    /// Assign a string describing a set of sources, using the `srcset` attribute.
+    /// - parameter set: The set of sources that this element should point to.
+    static func srcset(_ set: String) -> Attribute {
+        Attribute(name: "srcset", value: set)
+    }
+
+    /// Assign a media query that determines whether this source should be used.
+    /// - parameter query: The media query that the browser should evaluate.
+    static func media(_ query: String) -> Attribute {
+        Attribute(name: "media", value: query)
+    }
+}
+
 // MARK: - Forms, input and options
 
 public extension Node where Context == HTML.FormContext {
diff --git a/Sources/Plot/API/HTMLElements.swift b/Sources/Plot/API/HTMLElements.swift
index cd11f5d..f4e600e 100644
--- a/Sources/Plot/API/HTMLElements.swift
+++ b/Sources/Plot/API/HTMLElements.swift
@@ -253,12 +253,6 @@ public extension Node where Context: HTML.BodyContext {
         .element(named: "iframe", attributes: attributes)
     }
 
-    /// Add an `<img/>` HTML element within the current context.
-    /// - parameter attributes: The element's attributes.
-    static func img(_ attributes: Attribute<HTML.ImageContext>...) -> Node {
-        .selfClosedElement(named: "img", attributes: attributes)
-    }
-
     /// Add an `<ins>` HTML element within the current context.
     /// - parameter nodes: The element's attributes and child elements.
     static func ins(_ nodes: Node<HTML.BodyContext>...) -> Node {
@@ -301,6 +295,12 @@ public extension Node where Context: HTML.BodyContext {
         .element(named: "p", nodes: nodes)
     }
 
+    /// Add a `<picture>` HTML element within the current context.
+    /// - parameter nodes: The element's attributes and child elements.
+    static func picture(_ nodes: Node<HTML.PictureContext>...) -> Node {
+        .element(named: "picture", nodes: nodes)
+    }
+
     /// Add a `<pre>` HTML element within the current context.
     /// - parameter nodes: The element's attributes and child elements.
     static func pre(_ nodes: Node<HTML.BodyContext>...) -> Node {
@@ -424,6 +424,24 @@ public extension Node where Context == HTML.TableRowContext {
     }
 }
 
+// MARK: - Media
+
+public extension Node where Context: HTMLImageContainerContext {
+    /// Add an `<img/>` HTML element within the current context.
+    /// - parameter attributes: The element's attributes.
+    static func img(_ attributes: Attribute<HTML.ImageContext>...) -> Node {
+        .selfClosedElement(named: "img", attributes: attributes)
+    }
+}
+
+public extension Node where Context: HTMLSourceListContext {
+    /// Add a `<source/>` HTML element within the current context.
+    /// - parameter attributes: The element's attributes.
+    static func source(_ attributes: Attribute<Context.SourceContext>...) -> Node {
+        .selfClosedElement(named: "source", attributes: attributes)
+    }
+}
+
 // MARK: - Forms
 
 public extension Node where Context == HTML.FormContext {
@@ -448,14 +466,6 @@ public extension Node where Context == HTML.FormContext {
 
 // MARK: - Other
 
-public extension Node where Context: HTMLMediaContext {
-    /// Add a `<source/>` HTML element within the current context.
-    /// - parameter attributes: The element's attributes.
-    static func source(_ attributes: Attribute<Context.SourceContext>...) -> Node {
-        .selfClosedElement(named: "source", attributes: attributes)
-    }
-}
-
 public extension Node where Context == HTML.DetailsContext {
     /// Add a `<summary>` HTML element within the current context.
     /// - parameter nodes: The element's attributes and child elements.
diff --git a/Tests/PlotTests/HTMLTests.swift b/Tests/PlotTests/HTMLTests.swift
index d4a09ee..cac9831 100644
--- a/Tests/PlotTests/HTMLTests.swift
+++ b/Tests/PlotTests/HTMLTests.swift
@@ -632,6 +632,23 @@ final class HTMLTests: XCTestCase {
         let html = HTML(.comment("Hello"), .body(.comment("World")))
         assertEqualHTMLContent(html, "<!--Hello--><body><!--World--></body>")
     }
+
+    func testPicture() {
+        let html = HTML(.body(.picture(
+            .source(
+                .srcset("dark.jpg"),
+                .media("(prefers-color-scheme: dark)")
+            ),
+            .img(.src("default.jpg"))
+        )))
+
+        assertEqualHTMLContent(html, """
+        <body><picture>\
+        <source srcset="dark.jpg" media="(prefers-color-scheme: dark)"/>\
+        <img src="default.jpg"/>\
+        </picture></body>
+        """)
+    }
 }
 
 extension HTMLTests {
@@ -695,7 +712,8 @@ extension HTMLTests {
             ("testAccessibilityExpanded", testAccessibilityExpanded),
             ("testDataAttributes", testDataAttributes),
             ("testSubresourceIntegrity", testSubresourceIntegrity),
-            ("testComments", testComments)
+            ("testComments", testComments),
+            ("testPicture", testPicture)
         ]
     }
 }
