import SwiftUI
import AppKit
import VorleserKit

/// A custom NSView subclass that accepts keyboard events and forwards them to the coordinator.
private class PagedContainerView: NSView {
	weak var coordinator: PagedBookView.Coordinator?

	override var acceptsFirstResponder: Bool { true }

	override func keyDown(with event: NSEvent) {
		switch event.keyCode {
		case 123: // left arrow
			coordinator?.navigatePage(delta: -1)
		case 124: // right arrow
			coordinator?.navigatePage(delta: 1)
		default:
			super.keyDown(with: event)
		}
	}
}

struct PagedBookView: NSViewRepresentable {
	let attributedText: NSAttributedString
	let highlightRange: Range<Int>?
	let onClickCharacter: (CharacterOffset) -> Void
	var scrollToOffset: CharacterOffset?

	func makeNSView(context: Context) -> NSView {
		let container = PagedContainerView()
		container.coordinator = context.coordinator

		let textView = NSTextView()
		textView.isEditable = false
		textView.isSelectable = false
		textView.textContainerInset = NSSize(width: 16, height: 16)
		textView.translatesAutoresizingMaskIntoConstraints = false
		container.addSubview(textView)
		NSLayoutConstraint.activate([
			textView.topAnchor.constraint(equalTo: container.topAnchor),
			textView.bottomAnchor.constraint(equalTo: container.bottomAnchor),
			textView.leadingAnchor.constraint(equalTo: container.leadingAnchor),
			textView.trailingAnchor.constraint(equalTo: container.trailingAnchor),
		])

		let click = NSClickGestureRecognizer(target: context.coordinator, action: #selector(Coordinator.handleClick(_:)))
		textView.addGestureRecognizer(click)
		context.coordinator.textView = textView

		DispatchQueue.main.async {
			container.window?.makeFirstResponder(container)
		}

		return container
	}

	func updateNSView(_ container: NSView, context: Context) {
		guard let textView = context.coordinator.textView else { return }

		context.coordinator.parent = self
		context.coordinator.recomputePages(for: container.bounds.size)

		if let offset = scrollToOffset {
			context.coordinator.currentPageIndex = context.coordinator.pageIndex(containing: offset)
		} else if let range = highlightRange {
			let pageIndex = context.coordinator.pageIndex(containing: range.lowerBound)
			if pageIndex != context.coordinator.currentPageIndex {
				context.coordinator.currentPageIndex = pageIndex
			}
		}

		context.coordinator.displayCurrentPage()
	}

	func makeCoordinator() -> Coordinator {
		Coordinator(parent: self)
	}

	class Coordinator: NSObject {
		var parent: PagedBookView
		weak var textView: NSTextView?
		var currentPageIndex = 0
		var pageBreaks: [Int] = [0]

		init(parent: PagedBookView) {
			self.parent = parent
		}

		func recomputePages(for size: CGSize) {
			guard parent.attributedText.length > 0 else {
				pageBreaks = [0]
				return
			}

			let insets = NSSize(width: 16, height: 16)
			let pageWidth = size.width - insets.width * 2
			let pageHeight = size.height - insets.height * 2
			guard pageWidth > 0, pageHeight > 0 else {
				pageBreaks = [0]
				return
			}

			let textStorage = NSTextStorage(attributedString: parent.attributedText)
			let layoutManager = NSLayoutManager()
			textStorage.addLayoutManager(layoutManager)

			var breaks: [Int] = [0]
			var offset = 0

			while offset < parent.attributedText.length {
				let container = NSTextContainer(size: NSSize(width: pageWidth, height: pageHeight))
				container.lineFragmentPadding = 0
				layoutManager.addTextContainer(container)

				let glyphRange = layoutManager.glyphRange(for: container)
				let charRange = layoutManager.characterRange(forGlyphRange: glyphRange, actualGlyphRange: nil)

				if charRange.length == 0 { break }

				offset = charRange.location + charRange.length
				if offset < parent.attributedText.length {
					breaks.append(offset)
				}
			}

			pageBreaks = breaks
		}

		func pageIndex(containing characterOffset: Int) -> Int {
			for (i, breakOffset) in pageBreaks.enumerated().reversed() {
				if characterOffset >= breakOffset {
					return i
				}
			}
			return 0
		}

		func displayCurrentPage() {
			guard let textView else { return }
			let index = min(currentPageIndex, pageBreaks.count - 1)
			let start = pageBreaks[index]
			let end = index + 1 < pageBreaks.count ? pageBreaks[index + 1] : parent.attributedText.length
			let range = NSRange(location: start, length: end - start)

			let pageText = NSMutableAttributedString(attributedString: parent.attributedText.attributedSubstring(from: range))

			if let highlightRange = parent.highlightRange {
				let hlStart = max(highlightRange.lowerBound - start, 0)
				let hlEnd = min(highlightRange.upperBound - start, pageText.length)
				if hlStart < hlEnd {
					let nsRange = NSRange(location: hlStart, length: hlEnd - hlStart)
					pageText.addAttribute(.backgroundColor, value: NSColor.systemYellow.withAlphaComponent(0.3), range: nsRange)
				}
			}

			textView.textStorage?.setAttributedString(pageText)
		}

		func navigatePage(delta: Int) {
			let newIndex = currentPageIndex + delta
			guard newIndex >= 0, newIndex < pageBreaks.count else { return }
			currentPageIndex = newIndex
			displayCurrentPage()
		}

		@objc func handleClick(_ gesture: NSClickGestureRecognizer) {
			guard let textView else { return }
			let point = gesture.location(in: textView)
			let localIndex = textView.characterIndexForInsertion(at: point)
			let pageStart = pageBreaks[min(currentPageIndex, pageBreaks.count - 1)]
			let globalIndex = pageStart + localIndex
			if globalIndex < parent.attributedText.length {
				parent.onClickCharacter(globalIndex)
			}
		}
	}
}