From d062fdaba2328d073011edbf5f1ab22d1e0942d6 Mon Sep 17 00:00:00 2001
From: Paul Kraft <pauljohanneskraft@users.noreply.github.com>
Date: Tue, 4 May 2021 16:15:26 +0200
Subject: [PATCH] Introduce Publish resultBuilder

---
 Sources/XUI/Combine/CancellableBuilder.swift |  2 +-
 Sources/XUI/Combine/Publish.swift            | 80 ++++++++++++++++++++
 Sources/XUI/Combine/PublishModifier.swift    | 33 ++++++++
 3 files changed, 114 insertions(+), 1 deletion(-)
 create mode 100644 Sources/XUI/Combine/Publish.swift
 create mode 100644 Sources/XUI/Combine/PublishModifier.swift

diff --git a/Sources/XUI/Combine/CancellableBuilder.swift b/Sources/XUI/Combine/CancellableBuilder.swift
index e23a310..eba5cd9 100644
--- a/Sources/XUI/Combine/CancellableBuilder.swift
+++ b/Sources/XUI/Combine/CancellableBuilder.swift
@@ -11,7 +11,7 @@
 ///
 /// Possible use case: Storing multiple cancellables in a collection
 /// without writing `.store(in:)` for each subscription separately.
-@_functionBuilder
+@resultBuilder
 public struct CancellableBuilder {
 
     public static func buildBlock(_ components: [Cancellable]...) -> [Cancellable] {
diff --git a/Sources/XUI/Combine/Publish.swift b/Sources/XUI/Combine/Publish.swift
new file mode 100644
index 0000000..3a7ec56
--- /dev/null
+++ b/Sources/XUI/Combine/Publish.swift
@@ -0,0 +1,80 @@
+//
+//  File.swift
+//  
+//
+//  Created by Paul Kraft on 04.05.21.
+//
+
+public typealias Pipeline<T> = AnyPublisher<T, Error>
+public typealias Observable<T> = AnyPublisher<T, Never>
+
+@resultBuilder
+public struct Publish<Modifier: PublishModifier> {
+
+    // MARK: Build
+
+    public static func build<P: Publisher>(
+        @Publish<Modifier> from build: () -> P
+    ) -> P {
+        build()
+    }
+
+    public static func build<Output>(
+        @Publish<Modifier> from build: () throws -> AnyPublisher<Output, Error>
+    ) -> AnyPublisher<Output, Error> {
+        do {
+            return try build()
+        } catch {
+            return Modifier.modify(Fail<Output, Error>(error: error))
+        }
+    }
+
+    // MARK: Build Block
+
+    public static func buildBlock<Output>(
+        _ component: Output
+    ) -> AnyPublisher<Output, Never> {
+        Modifier.modify(Just(component))
+    }
+
+    public static func buildBlock<Output>(
+        _ component: Output
+    ) -> AnyPublisher<Output, Error> {
+        Modifier.modify(Just(component).setFailureType(to: Error.self))
+    }
+
+    public static func buildBlock<P: Publisher>(
+        _ component: P
+    ) -> AnyPublisher<P.Output, Never> where P.Failure == Never {
+        Modifier.modify(component)
+    }
+
+    public static func buildBlock<P: Publisher>(
+        _ component: P
+    ) -> AnyPublisher<P.Output, Error> where P.Failure == Never {
+        Modifier.modify(component.setFailureType(to: Error.self))
+    }
+
+    public static func buildBlock<P: Publisher>(
+        _ component: P
+    ) -> AnyPublisher<P.Output, Error> {
+        Modifier.modify(component.mapError { $0 as Error })
+    }
+
+    // MARK: Build Either
+
+    public static func buildEither<P: Publisher>(first component: P) -> P {
+        component
+    }
+
+    public static func buildEither<P: Publisher>(second component: P) -> P {
+        component
+    }
+
+    // MARK: Build Limited Availability
+
+    public static func buildLimitedAvailability<P: Publisher>(_ component: P) -> P {
+        component
+    }
+
+}
diff --git a/Sources/XUI/Combine/PublishModifier.swift b/Sources/XUI/Combine/PublishModifier.swift
new file mode 100644
index 0000000..222f71c
--- /dev/null
+++ b/Sources/XUI/Combine/PublishModifier.swift
@@ -0,0 +1,33 @@
+//
+//  File.swift
+//  
+//
+//  Created by Paul Kraft on 04.05.21.
+//
+
+public protocol PublishModifier {
+    static func modify<P: Publisher>(_ publisher: P) -> AnyPublisher<P.Output, P.Failure>
+}
+
+public struct MainQueue: PublishModifier {
+
+    public static func modify<P: Publisher>(
+        _ publisher: P
+    ) -> AnyPublisher<P.Output, P.Failure> {
+        publisher
+            .receive(on: DispatchQueue.main)
+            .eraseToAnyPublisher()
+    }
+
+}
+
+extension Never: PublishModifier {
+
+    public static func modify<P: Publisher>(
+        _ publisher: P
+    ) -> AnyPublisher<P.Output, P.Failure> {
+        publisher
+            .eraseToAnyPublisher()
+    }
+
+}