From c63916df3aff04b2c56621deafabf11587c45af3 Mon Sep 17 00:00:00 2001
From: Alex Deem <alexdeem@gmail.com>
Date: Sun, 9 Jun 2024 22:32:36 +1000
Subject: [PATCH] Add SequenceVariableProvider

---
 .../ScreamURITemplate/VariableProvider.swift    | 17 +++++++++++++++++
 Tests/ScreamURITemplateTests/Tests.swift        | 16 +++++++++++++++-
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/Sources/ScreamURITemplate/VariableProvider.swift b/Sources/ScreamURITemplate/VariableProvider.swift
index 739d94b..2467e9c 100644
--- a/Sources/ScreamURITemplate/VariableProvider.swift
+++ b/Sources/ScreamURITemplate/VariableProvider.swift
@@ -20,3 +20,20 @@ public protocol VariableProvider {
 public typealias VariableDictionary = [String: VariableValue]
 
 extension VariableDictionary: VariableProvider {}
+
+public struct SequenceVariableProvider: VariableProvider, ExpressibleByArrayLiteral {
+    let sequence: any Sequence<VariableProvider>
+
+    public init(arrayLiteral elements: VariableProvider...) {
+        sequence = elements
+    }
+
+    public subscript(_ key: String) -> VariableValue? {
+        for provider in sequence {
+            if let value = provider[key] {
+                return value
+            }
+        }
+        return nil
+    }
+}
diff --git a/Tests/ScreamURITemplateTests/Tests.swift b/Tests/ScreamURITemplateTests/Tests.swift
index 681c762..630a4ad 100644
--- a/Tests/ScreamURITemplateTests/Tests.swift
+++ b/Tests/ScreamURITemplateTests/Tests.swift
@@ -17,7 +17,12 @@ import XCTest
 
 struct TestVariableProvider: VariableProvider {
     subscript(_ key: String) -> VariableValue? {
-        return "_\(key)_"
+        switch key {
+        case "missing":
+            return nil
+        default:
+            return "_\(key)_"
+        }
     }
 }
 
@@ -28,6 +33,15 @@ class Tests: XCTestCase {
         XCTAssertEqual(urlString, "https://api.github.com/repos/_owner_/_repo_/collaborators/_username_")
     }
 
+    func testSequenceVariableProvider() throws {
+        let template: URITemplate = "https://api.github.com/repos/{owner}/{repo}/collaborators/{username}{missing}"
+        let urlString = try template.process(variables: [
+            ["owner": "SwiftScream"],
+            TestVariableProvider(),
+        ] as SequenceVariableProvider)
+        XCTAssertEqual(urlString, "https://api.github.com/repos/SwiftScream/_repo_/collaborators/_username_")
+    }
+
     func testStringStringDictionary() throws {
         let template: URITemplate = "https://api.github.com/repos/{owner}/{repo}/collaborators/{username}"
         let variables = ["owner": "SwiftScream",