Support for starting from a progression in the HTML content iterator (#597)

Author: mickael-menu

CHANGELOG.md

@@ -11,6 +11,7 @@ All notable changes to this project will be documented in this file. Take a look
 #### Shared
 
 * Implementation of the [W3C Accessibility Metadata Display Guide](https://w3c.github.io/publ-a11y/a11y-meta-display-guide/2.0/guidelines/) specification to facilitate displaying accessibility metadata to users. [See the dedicated user guide](docs/Guides/Accessibility.md).
+* Support for starting from a progression in the HTML content iterator.
 
 #### Navigator
 

Sources/Shared/Publication/Services/Content/Iterators/HTMLResourceContentIterator.swift

@@ -94,17 +94,16 @@ public class HTMLResourceContentIterator: ContentIterator {
     private var currentIndex: Int?
 
     private func elements() async throws -> ParsedElements {
-        try await elementsTask.value
+        try await elementsTask.value.get()
     }
 
     private lazy var elementsTask = Task {
-        let result = await resource
+        await resource
             .readAsString()
             .eraseToAnyError()
             .tryMap { try SwiftSoup.parse($0) }
             .tryMap { try parse(document: $0, locator: locator, beforeMaxLength: beforeMaxLength) }
             .asyncMap { await adjustProgressions(of: $0) }
-        return try result.get()
     }
 
     private func parse(document: Document, locator: Locator, beforeMaxLength: Int) throws -> ParsedElements {
@@ -141,6 +140,20 @@ public class HTMLResourceContentIterator: ContentIterator {
                 }
             )
         }
+
+        // Update the `startIndex` if a particular progression was requested.
+        if
+            elements.startIndex == 0,
+            locator.locations.cssSelector == nil,
+            let progression = locator.locations.progression,
+            progression > 0, progression < 1
+        {
+            elements.startIndex = elements.elements.lastIndex { element in
+                let elementProgression = element.locator.locations.progression ?? 0
+                return elementProgression < progression
+            } ?? 0
+        }
+
         return elements
     }
 

Tests/SharedTests/Publication/Services/Content/Iterators/HTMLResourceContentIteratorTests.swift

@@ -229,6 +229,21 @@ class HTMLResourceContentIteratorTest: XCTestCase {
         XCTAssertEqual(elements[0], result)
     }
 
+    func testStartingFromProgression() async throws {
+        func next(from progression: Double) async throws -> AnyEquatableContentElement? {
+            try await iterator(html, start: locator(progression: progression)).next()?.equatable()
+        }
+
+        var result = try await next(from: 0.5)
+        XCTAssertEqual(result, elements[2])
+
+        result = try await next(from: 0.21)
+        XCTAssertEqual(result, elements[1])
+
+        result = try await next(from: 0.81)
+        XCTAssertEqual(result, elements[4])
+    }
+
     func testStartingFromCSSSelector() async throws {
         let iter = iterator(html, start: locator(selector: "#pgepubid00498 > p:nth-child(3)"))