import AppKit
import SwiftUI

// MARK: - A rendered comment body

/// One comment's Markdown, rendered — **the card-body subset, through the card body's own renderer**
/// (05-card-window.md ▸ The comments column: "the rendered Markdown body (the card-body subset)").
///
/// ### Why the same renderer and not a `Text(AttributedString(markdown:))`
///
/// Because "the card-body subset" is a promise about *this* app's subset: fenced code, nested quotes,
/// GFM tables with per-column alignment, task markers, images resolved against the card's own folder,
/// HTML shown verbatim as literal code-styled text. `BodyMarkupRenderer` is where every one of those
/// is decided, and a second renderer here would be a second answer to each — a comment quoting a code
/// block would look like a different app from the card that carries it.
///
/// ### Why it is not `CardBodySurface`
///
/// That surface is a hosted **scroll** view, because ⌘F's find bar lives in one and because a card
/// body is a document. A thread is a *list* of bodies inside one scroller, and a scroll view per row
/// would be a scroll view that fights its parent — the same reasoning that put the card's title above
/// the body's scroller rather than inside it. So this is the same TextKit 1 stack with the scroller
/// taken off and an intrinsic height instead: it lays out at the width it is proposed and reports
/// exactly the height its text needs.
///
/// The pane's find-in-text over the whole rendered thread is phase 3's (05 ▸ Preview scopes ⌘F to
/// "the comments pane, where it searches the whole rendered thread"); nothing here forecloses it.
struct CommentBodyView: NSViewRepresentable {

    let body: String
    /// The **card**'s folder, not the comment's — relative images and links in a comment resolve the
    /// same way a card body's do, which is what makes `![](attachments/shot.png)` mean one thing in
    /// this window (05 ▸ Preview).
    let cardFolder: URL?

    /// The height a measurement pass lays out into — tall enough that no comment reaches it, finite
    /// so the arithmetic stays well-defined.
    private static let layoutCeiling: CGFloat = 100_000

    func makeCoordinator() -> Coordinator {
        Coordinator()
    }

    func makeNSView(context: Context) -> NSTextView {
        // TextKit 1, explicitly, for `CardBodySurface`'s reason: `NSTextTable` — the browser sizing
        // rule GFM tables are laid out by — does not lay out in TextKit 2.
        let storage = NSTextStorage()
        let layoutManager = NSLayoutManager()
        storage.addLayoutManager(layoutManager)
        let container = NSTextContainer(size: CGSize(width: 0, height: CGFloat.greatestFiniteMagnitude))
        container.widthTracksTextView = true
        container.lineFragmentPadding = 0
        layoutManager.addTextContainer(container)

        let textView = NSTextView(frame: .zero, textContainer: container)
        textView.delegate = context.coordinator
        textView.isEditable = false
        // Selectable and copyable, the whole thread — Preview's own posture, and the reason a comment
        // can be quoted without a mode flip.
        textView.isSelectable = true
        textView.isRichText = true
        textView.drawsBackground = false
        textView.isVerticallyResizable = true
        textView.isHorizontallyResizable = false
        textView.textContainerInset = .zero
        textView.linkTextAttributes = [.cursor: NSCursor.pointingHand]
        textView.displaysLinkToolTips = true
        return textView
    }

    func updateNSView(_ textView: NSTextView, context: Context) {
        let key = Coordinator.RenderKey(
            body: body,
            cardFolder: cardFolder,
            pointSize: CardWindowMetrics.bodyPointSize
        )
        guard context.coordinator.rendered != key else { return }
        context.coordinator.rendered = key
        textView.textStorage?.setAttributedString(BodyMarkupRenderer.attributedString(
            for: BodyMarkup.parse(body),
            context: BodyMarkupRenderer.Context(pointSize: key.pointSize, cardFolder: cardFolder)
        ))
    }

    /// **The intrinsic height** — the whole reason this is not a scroll view.
    ///
    /// The container is laid out at the proposed width and asked what it used. `ensureLayout` is not
    /// optional: `usedRect` is only meaningful once the glyphs have been laid, and an unlaid container
    /// answers a zero-height rect, which would collapse every comment in the thread to nothing.
    func sizeThatFits(_ proposal: ProposedViewSize, nsView: NSTextView, context: Context) -> CGSize? {
        guard let container = nsView.textContainer, let layoutManager = nsView.layoutManager else {
            return nil
        }
        guard let width = proposal.width, width > 0, width.isFinite else { return nil }

        // A large finite height rather than `.greatestFiniteMagnitude`: the container tracks the
        // view's width, so the frame is how the width is proposed at all, and an infinite frame
        // height propagates into the layout arithmetic as a value nothing can subtract from.
        nsView.frame = NSRect(x: 0, y: 0, width: width, height: Self.layoutCeiling)
        layoutManager.ensureLayout(for: container)
        return CGSize(width: width, height: layoutManager.usedRect(for: container).height.rounded(.up))
    }

    // MARK: - Coordinator

    @MainActor
    final class Coordinator: NSObject, NSTextViewDelegate {

        struct RenderKey: Equatable {
            let body: String
            let cardFolder: URL?
            let pointSize: CGFloat
        }

        var rendered: RenderKey?

        /// Links behave exactly as they do in a card body: external URLs go to the browser, relative
        /// ones — already resolved to file URLs by the renderer — go to their default app.
        ///
        /// **A task marker in a comment is inert.** 05 makes live checkboxes a rule about *Preview*,
        /// the card body's one interactive exception, and gives a comment no toggle write path at all
        /// — the way to change a comment is Edit it. Swallowing the click (rather than letting it fall
        /// through to `NSWorkspace.open`, which would try to open a `kanban-task:` URL) is what keeps
        /// the checkbox drawn-but-dead rather than drawn-and-broken.
        func textView(_ textView: NSTextView, clickedOnLink link: Any, at charIndex: Int) -> Bool {
            guard let url = Self.url(from: link) else { return false }
            guard CardBodyLink.parseTask(url) == nil else { return true }
            NSWorkspace.shared.open(url)
            return true
        }

        private static func url(from link: Any) -> URL? {
            switch link {
            case let url as URL: url
            case let string as String: URL(string: string)
            default: nil
            }
        }
    }
}