From 9fdbbc99e90c781bd14428d44876559641d7f923 Mon Sep 17 00:00:00 2001
From: Kyle Fuller <kyle@fuller.li>
Date: Sun, 27 Nov 2016 19:47:50 +0000
Subject: [PATCH] feat(filters): Add a join filter

---
 CHANGELOG.md                        |  6 ++++++
 Sources/Filters.swift               | 16 ++++++++++++++++
 Sources/Namespace.swift             |  1 +
 Tests/StencilTests/FilterSpec.swift |  9 +++++++++
 docs/builtins.rst                   | 11 +++++++++++
 5 files changed, 43 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index ed1d734..4ba0080 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -18,6 +18,12 @@
     Hello {{ name|default:"World" }}
     ```
 
+- There is now a `join` filter.
+
+    ```html+django
+    {{ value|join:", " }}
+    ```
+
 ### Bug Fixes
 
 - Variables (`{{ variable.5 }}`) that reference an array index at an unknown
diff --git a/Sources/Filters.swift b/Sources/Filters.swift
index 1574a58..0bac235 100644
--- a/Sources/Filters.swift
+++ b/Sources/Filters.swift
@@ -35,3 +35,19 @@ func lowercase(_ value: Any?) -> Any? {
 func defaultFilter(value: Any?, arguments: [Any?]) -> Any? {
   return value ?? arguments.first as Any
 }
+
+func joinFilter(value: Any?, arguments: [Any?]) throws -> Any? {
+  guard arguments.count == 1 else {
+    throw TemplateSyntaxError("'join' filter takes a single argument")
+  }
+
+  guard let separator = arguments.first as? String else {
+    throw TemplateSyntaxError("'join' filter takes a separator as string")
+  }
+
+  if let value = value as? [String] {
+    return value.joined(separator: separator)
+  }
+
+  return nil
+}
diff --git a/Sources/Namespace.swift b/Sources/Namespace.swift
index 2b1d41e..fd62d99 100644
--- a/Sources/Namespace.swift
+++ b/Sources/Namespace.swift
@@ -49,6 +49,7 @@ public class Namespace {
     registerFilter("capitalize", filter: capitalise)
     registerFilter("uppercase", filter: uppercase)
     registerFilter("lowercase", filter: lowercase)
+    registerFilter("join", filter: joinFilter)
   }
 
   /// Registers a new template tag
diff --git a/Tests/StencilTests/FilterSpec.swift b/Tests/StencilTests/FilterSpec.swift
index 824ba80..60d6c39 100644
--- a/Tests/StencilTests/FilterSpec.swift
+++ b/Tests/StencilTests/FilterSpec.swift
@@ -103,4 +103,13 @@ func testFilter() {
       try expect(result) == "Hello World"
     }
   }
+
+  describe("join filter") {
+    let template = Template(templateString: "{{ value|join:\", \" }}")
+
+    $0.it("transforms a string to be lowercase") {
+      let result = try template.render(Context(dictionary: ["value": ["One", "Two"]]))
+      try expect(result) == "One, Two"
+    }
+  }
 }
diff --git a/docs/builtins.rst b/docs/builtins.rst
index 6b3bcbe..dab8a41 100644
--- a/docs/builtins.rst
+++ b/docs/builtins.rst
@@ -130,3 +130,14 @@ value of the variable. For example:
 .. code-block:: html+django
 
     Hello {{ name|default:"World" }}
+
+``join``
+~~~~~~~~
+
+Join an array with a string.
+
+.. code-block:: html+django
+
+    {{ value|join:", " }}
+
+.. note:: The value MUST be an array of Strngs and the separator must be a string.