GeminiRenderer: Add Markdown renderer

GeminiRenderer/GeminiHTMLRenderer.swift

@@ -73,7 +73,7 @@ public class GeminiHTMLRenderer {
     
 }
 
-fileprivate extension Document.Line {
+extension Document.Line {
     var isListItem: Bool {
         switch self {
         case .unorderedListItem(_):

GeminiRenderer/GeminiMarkdownRenderer.swift

@@ -0,0 +1,82 @@
+//
+//  GeminiMarkdownRenderer.swift
+//  GeminiRenderer
+//
+//  Created by Shadowfacts on 10/1/21.
+//
+
+import Foundation
+import GeminiFormat
+import HTMLEntities
+
+public class GeminiMarkdownRenderer {
+    
+    public init() {
+    }
+    
+    public func renderDocumentToMarkdown(_ doc: Document) -> String {
+        var str = ""
+        
+        var inPreformatting = false
+        var inList = false
+        
+        for line in doc.lines {
+            if inList && !line.isListItem {
+                str += "\n"
+                inList = false
+            }
+            
+            switch line {
+            case let .text(text):
+                if !text.trimmingCharacters(in: .whitespaces).isEmpty {
+                    str += text.htmlEscape()
+                    str += "\n\n"
+                }
+                
+            case let .link(url, text: maybeText):
+                let text = maybeText ?? url.absoluteString
+                // todo: do ] in the text need to be escaped?
+                str += "[\(text.htmlEscape())](\(url))"
+                str += "\n\n"
+                
+            case let .preformattedToggle(alt: alt):
+                inPreformatting = !inPreformatting
+                if inPreformatting {
+                    str += "```"
+                    if let alt = alt {
+                        str += alt
+                    }
+                    str += "\n"
+                } else {
+                    str += "```"
+                    str += "\n\n"
+                }
+                
+            case let .preformattedText(text):
+                str += text
+                str += "\n"
+                
+            case let .heading(text, level: level):
+                str += String(repeating: "#", count: level.rawValue)
+                str += " "
+                str += text.htmlEscape()
+                str += "\n\n"
+                
+            case let .unorderedListItem(text):
+                if !inList {
+                    inList = true
+                }
+                str += "* \(text.htmlEscape())"
+                str += "\n"
+                
+            case let .quote(text):
+                str += "> "
+                str += text.htmlEscape()
+                str += "\n\n"
+            }
+        }
+        
+        return str
+    }
+    
+}

GeminiRendererTests/GeminiMarkdownRendererTests.swift

@@ -0,0 +1,103 @@
+//
+//  GeminiMarkdownRendererTests.swift
+//  GeminiRendererTests
+//
+//  Created by Shadowfacts on 10/1/21.
+//
+
+import XCTest
+import GeminiFormat
+@testable import GeminiRenderer
+
+class GeminiMarkdownRendererTests: XCTestCase {
+    
+    private var doc: Document!
+
+    override func setUp() {
+        doc = Document(url: URL(string: "gemini://example.com/")!)
+    }
+    
+    func testEscapeToEntities() {
+        doc.lines = [.text("<b>hello</b>")]
+        let markdown = GeminiMarkdownRenderer().renderDocumentToMarkdown(doc)
+        XCTAssertEqual(markdown, "&#x3C;b&#x3E;hello&#x3C;/b&#x3E;\n\n")
+    }
+
+    func testParagraph() {
+        doc.lines = [.text("Hello, world!")]
+        let markdown = GeminiMarkdownRenderer().renderDocumentToMarkdown(doc)
+        XCTAssertEqual(markdown, "Hello, world!\n\n")
+    }
+    
+    func testLink() {
+        doc.lines = [.link(URL(string: "gemini://example.com/")!, text: "text")]
+        let markdown = GeminiMarkdownRenderer().renderDocumentToMarkdown(doc)
+        XCTAssertEqual(markdown, "[text](gemini://example.com/)\n\n")
+        
+        doc.lines = [.link(URL(string: "gemini://example.com/")!, text: nil)]
+        let noText = GeminiMarkdownRenderer().renderDocumentToMarkdown(doc)
+        XCTAssertEqual(noText, "[gemini://example.com/](gemini://example.com/)\n\n")
+    }
+    
+    func testLinksAfterList() {
+        doc.lines = [
+            .unorderedListItem("a"),
+            .unorderedListItem("b"),
+            .link(URL(string: "gemini://example.com")!, text: "one"),
+            .link(URL(string: "gemini://example.com")!, text: "two"),
+        ]
+        let markdown = GeminiMarkdownRenderer().renderDocumentToMarkdown(doc)
+        XCTAssertEqual(markdown, "* a\n* b\n\n[one](gemini://example.com)\n\n[two](gemini://example.com)\n\n")
+    }
+    
+    func testPreformatting() {
+        doc.lines = [
+            .preformattedToggle(alt: nil),
+            .preformattedText("foo"),
+            .preformattedText("* bar"),
+            .preformattedToggle(alt: nil),
+        ]
+        let markdown = GeminiMarkdownRenderer().renderDocumentToMarkdown(doc)
+        XCTAssertEqual(markdown, "```\nfoo\n* bar\n```\n\n")
+    }
+    
+    func testHeading() {
+        doc.lines = [
+            .heading("One", level: .h1),
+            .heading("Two", level: .h2),
+        ]
+        let markdown = GeminiMarkdownRenderer().renderDocumentToMarkdown(doc)
+        XCTAssertEqual(markdown, "# One\n\n## Two\n\n")
+    }
+    
+    func testUnorderedList() {
+        doc.lines = [
+            .text("before"),
+            .unorderedListItem("a"),
+            .unorderedListItem("b"),
+            .unorderedListItem("c"),
+            .text("after"),
+        ]
+        let markdown = GeminiMarkdownRenderer().renderDocumentToMarkdown(doc)
+        XCTAssertEqual(markdown, "before\n\n* a\n* b\n* c\n\nafter\n\n")
+    }
+    
+    func testQuote() {
+        doc.lines = [
+            .quote("quoted")
+        ]
+        let markdown = GeminiMarkdownRenderer().renderDocumentToMarkdown(doc)
+        XCTAssertEqual(markdown, "> quoted\n\n")
+    }
+    
+    func testSkipBlankLines() {
+        doc.lines = [
+            .heading("Hello", level: .h1),
+            .text(""),
+            .text("World"),
+        ]
+        let markdown = GeminiMarkdownRenderer().renderDocumentToMarkdown(doc)
+        XCTAssertEqual(markdown, "# Hello\n\nWorld\n\n")
+    }
+
+}