Expose adding plugins as a public API on SiteGenerator

SiteGenerator/Sources/SiteGenerator/Generator/AnyPlugin.swift

@@ -0,0 +1,30 @@
+//
+//  AnyPlugin.swift
+//  SiteGenerator
+//
+//  Created by Sami Samhuri on 2019-12-14.
+//
+
+import Foundation
+
+struct AnyPlugin: Plugin {
+    private let _setUp: (Site, URL) throws -> Void
+    private let _render: (Site, URL, TemplateRenderer) throws -> Void
+
+    init<PluginType: Plugin>(_ plugin: PluginType) {
+        self._setUp = { site, sourceURL in
+            try plugin.setUp(site: site, sourceURL: sourceURL)
+        }
+        self._render = { site, targetURL, templateRenderer in
+            try plugin.render(site: site, targetURL: targetURL, templateRenderer: templateRenderer)
+        }
+    }
+
+    func setUp(site: Site, sourceURL: URL) throws {
+        try _setUp(site, sourceURL)
+    }
+
+    func render(site: Site, targetURL: URL, templateRenderer: TemplateRenderer) throws {
+        try _render(site, targetURL, templateRenderer)
+    }
+}

SiteGenerator/Sources/SiteGenerator/Generator/Plugin.swift

@@ -8,8 +8,6 @@
 import Foundation
 
 public protocol Plugin {
-    init(options: [String: Any])
-
     func setUp(site: Site, sourceURL: URL) throws
 
     func render(site: Site, targetURL: URL, templateRenderer: TemplateRenderer) throws

SiteGenerator/Sources/SiteGenerator/Generator/SitePlugin.swift

@@ -10,4 +10,16 @@ import Foundation
 public enum SitePlugin: String, Codable {
     case posts
     case projects
+
+    func construct(options: [String: Any]) -> AnyPlugin {
+        switch self {
+        case .posts:
+            let plugin = PostsPlugin(options: options)
+            return AnyPlugin(plugin)
+
+        case .projects:
+            let plugin = ProjectsPlugin(options: options)
+            return AnyPlugin(plugin)
+        }
+    }
 }

SiteGenerator/Sources/SiteGenerator/SiteGenerator.swift

@@ -13,10 +13,10 @@ public final class SiteGenerator {
     let templateRenderer: TemplateRenderer
 
     // Site properties
-    let site: Site
-    let sourceURL: URL
-    var plugins: [Plugin] = []
-    let renderers: [Renderer]
+    public let site: Site
+    public let sourceURL: URL
+    public private(set) var plugins: [Plugin] = []
+    public let renderers: [Renderer]
 
     let ignoredFilenames = [".DS_Store", ".gitkeep"]
 
@@ -39,17 +39,16 @@ public final class SiteGenerator {
     }
 
     private func initializePlugins() throws {
-        plugins = site.plugins.map { (sitePlugin, options) in
-            switch sitePlugin {
-            case .projects:
-                return ProjectsPlugin(options: options)
-            case .posts:
-                return PostsPlugin(options: options)
-            }
-        }
-        for plugin in plugins {
-            try plugin.setUp(site: site, sourceURL: sourceURL)
+        plugins = site.plugins.map { pair in
+            let (sitePlugin, options) = pair
+            return sitePlugin.construct(options: options)
         }
+        try plugins.forEach(addPlugin)
+    }
+
+    public func addPlugin(_ plugin: Plugin) throws {
+        try plugin.setUp(site: site, sourceURL: sourceURL)
+        plugins.append(plugin)
     }
 
     public func generate(targetURL: URL) throws {