Add paginated panel loading

ios/Sources/DetailScreens.swift

@@ -5,12 +5,18 @@ import SwiftUI
 import UIKit
 
 @MainActor
-class MarkdownPageViewController: UIViewController {
+class MarkdownPageViewController: UIViewController, UIScrollViewDelegate {
     let context: AppContext
     let scrollView = UIScrollView()
     let stack = UIStackView()
     private let spinner = UIActivityIndicatorView(style: .medium)
     var loadingTask: Task<Void, Never>?
+    private lazy var moreButton = UIButton(
+        configuration: .plain(),
+        primaryAction: UIAction { [weak self] _ in self?.requestMoreContent() }
+    )
+    private var hasMoreContent = false
+    private var loadingMore = false
 
     init(context: AppContext) {
         self.context = context
@@ -25,6 +31,7 @@ class MarkdownPageViewController: UIViewController {
         view.backgroundColor = .systemGroupedBackground
         scrollView.translatesAutoresizingMaskIntoConstraints = false
         scrollView.alwaysBounceVertical = true
+        scrollView.delegate = self
         scrollView.refreshControl = UIRefreshControl()
         scrollView.refreshControl?.addTarget(self, action: #selector(refreshRequested), for: .valueChanged)
         view.addSubview(scrollView)
@@ -49,6 +56,8 @@ class MarkdownPageViewController: UIViewController {
 
     func loadContent(refreshing: Bool) {}
 
+    func loadMoreContent() {}
+
     func beginLoading(refreshing: Bool) {
         if !refreshing { beginNavigationLoading(spinner) }
     }
@@ -63,6 +72,54 @@ class MarkdownPageViewController: UIViewController {
         views.forEach(stack.addArrangedSubview)
     }
 
+    func resetPagination() {
+        hasMoreContent = false
+        loadingMore = false
+        stack.removeArrangedSubview(moreButton)
+        moreButton.removeFromSuperview()
+    }
+
+    func finishPagination(hasMore: Bool) {
+        hasMoreContent = hasMore
+        loadingMore = false
+        guard hasMore else { return }
+        var configuration = moreButton.configuration
+        configuration?.title = "Pull up or tap to load more"
+        configuration?.showsActivityIndicator = false
+        moreButton.configuration = configuration
+        moreButton.accessibilityLabel = "Load more results"
+        if moreButton.superview !== stack { stack.addArrangedSubview(moreButton) }
+        if moreButton.constraints.isEmpty {
+            moreButton.heightAnchor.constraint(equalToConstant: 50).isActive = true
+        }
+    }
+
+    func failPagination() {
+        loadingMore = false
+        finishPagination(hasMore: hasMoreContent)
+    }
+
+    func scrollViewDidScroll(_ scrollView: UIScrollView) {
+        guard scrollView.isDragging, hasMoreContent, !loadingMore else { return }
+        let bottom = max(
+            -scrollView.adjustedContentInset.top,
+            scrollView.contentSize.height
+                + scrollView.adjustedContentInset.bottom
+                - scrollView.bounds.height
+        )
+        if scrollView.contentOffset.y > bottom + 60 { requestMoreContent() }
+    }
+
+    private func requestMoreContent() {
+        guard hasMoreContent, !loadingMore else { return }
+        loadingMore = true
+        var configuration = moreButton.configuration
+        configuration?.title = "Loading more…"
+        configuration?.showsActivityIndicator = true
+        moreButton.configuration = configuration
+        loadMoreContent()
+    }
+
     @objc private func refreshRequested() {
         loadContent(refreshing: true)
     }
@@ -73,6 +130,8 @@ final class IssueViewController: MarkdownPageViewController {
     private let owner: String
     private let repository: String
     private let number: Int64
+    private var page: IssuePage?
+    private var currentPage: UInt32 = 0
 
     init(context: AppContext, owner: String, repository: String, number: Int64) {
         self.owner = owner
@@ -110,27 +169,52 @@ final class IssueViewController: MarkdownPageViewController {
     }
 
     override func loadContent(refreshing: Bool) {
-        beginLoading(refreshing: refreshing)
+        loadPage(1, refreshing: refreshing)
+    }
+
+    override func loadMoreContent() {
+        loadPage(currentPage + 1, refreshing: false)
+    }
+
+    private func loadPage(_ requestedPage: UInt32, refreshing: Bool) {
+        if requestedPage == 1 {
+            resetPagination()
+            beginLoading(refreshing: refreshing)
+        }
         loadingTask?.cancel()
         loadingTask = Task {
             do {
-                let page = try await context.core.issue(
+                let result = try await context.core.issue(
                     owner: owner,
                     repository: repository,
-                    number: number
+                    number: number,
+                    page: requestedPage
                 )
-                replaceContent(detailViews(
-                    title: page.title,
-                    issueState: page.state,
-                    meta: page.meta,
-                    body: page.body,
-                    comments: page.comments,
-                    milestone: page.milestone
-                ))
+                if requestedPage == 1 {
+                    page = result
+                } else {
+                    page?.comments.append(contentsOf: result.comments)
+                    page?.hasMore = result.hasMore
+                }
+                currentPage = requestedPage
+                if let page {
+                    replaceContent(detailViews(
+                        title: page.title,
+                        issueState: page.state,
+                        meta: page.meta,
+                        body: page.body,
+                        comments: page.comments,
+                        milestone: page.milestone
+                    ))
+                    finishPagination(hasMore: page.hasMore)
+                }
             } catch {
-                if !Task.isCancelled { show(error: error) }
+                if !Task.isCancelled {
+                    show(error: error)
+                    failPagination()
+                }
             }
-            endLoading()
+            if requestedPage == 1 { endLoading() }
         }
     }
 }
@@ -140,6 +224,8 @@ final class PullViewController: MarkdownPageViewController {
     private let owner: String
     private let repository: String
     private let number: Int64
+    private var page: PullPage?
+    private var currentPage: UInt32 = 0
 
     init(context: AppContext, owner: String, repository: String, number: Int64) {
         self.owner = owner
@@ -158,24 +244,45 @@ final class PullViewController: MarkdownPageViewController {
     }
 
     override func loadContent(refreshing: Bool) {
-        beginLoading(refreshing: refreshing)
+        loadPage(1, refreshing: refreshing)
+    }
+
+    override func loadMoreContent() {
+        loadPage(currentPage + 1, refreshing: false)
+    }
+
+    private func loadPage(_ requestedPage: UInt32, refreshing: Bool) {
+        if requestedPage == 1 {
+            resetPagination()
+            beginLoading(refreshing: refreshing)
+        }
         loadingTask?.cancel()
         loadingTask = Task {
             do {
-                let page = try await context.core.pull(
+                let result = try await context.core.pull(
                     owner: owner,
                     repository: repository,
-                    number: number
+                    number: number,
+                    page: requestedPage
                 )
-                var views = detailViews(
-                    title: page.title,
-                    meta: page.meta,
-                    body: page.body,
-                    comments: []
-                )
-                if !page.files.isEmpty {
-                    views.append(sectionLabel(page.filesRef))
-                    views.append(contentsOf: page.files.map { file in
+                if requestedPage == 1 {
+                    page = result
+                } else {
+                    page?.files.append(contentsOf: result.files)
+                    page?.comments.append(contentsOf: result.comments)
+                    page?.hasMore = result.hasMore
+                }
+                currentPage = requestedPage
+                if let page {
+                    var views = detailViews(
+                        title: page.title,
+                        meta: page.meta,
+                        body: page.body,
+                        comments: []
+                    )
+                    if !page.files.isEmpty {
+                        views.append(sectionLabel(page.filesRef))
+                        views.append(contentsOf: page.files.map { file in
                         detailButton(title: file.path, detail: file.status) { [weak self] in
                             guard let self else { return }
                             self.navigationController?.pushViewController(
@@ -191,14 +298,19 @@ final class PullViewController: MarkdownPageViewController {
                                 animated: true
                             )
                         }
-                    })
+                        })
+                    }
+                    views.append(contentsOf: commentViews(page.comments))
+                    replaceContent(views)
+                    finishPagination(hasMore: page.hasMore)
                 }
-                views.append(contentsOf: commentViews(page.comments))
-                replaceContent(views)
             } catch {
-                if !Task.isCancelled { show(error: error) }
+                if !Task.isCancelled {
+                    show(error: error)
+                    failPagination()
+                }
             }
-            endLoading()
+            if requestedPage == 1 { endLoading() }
         }
     }
 }