import UIKit

#if canImport(DTCoreText)
import DTCoreText

/// 基于 DTCoreText 的 Core Text 直接绘制视图
/// 将 DTCoreText 的排版结果直接绘制到 UIView 上，跳过 UITextView 的间接渲染。
/// 对齐 WXRead 的 WRPageView：在同一 drawRect 中绘制高亮背景、文字和选区。
final class RDEPUBTextPageRenderView: UIView {
    var layoutFrame: DTCoreTextLayoutFrame? {
        didSet {
            setNeedsDisplay()
        }
    }

    var drawOptions: DTCoreTextLayoutFrameDrawingOptions = DTCoreTextLayoutFrameDrawingOptions(rawValue: 1)! {
        didSet {
            setNeedsDisplay()
        }
    }

    /// 用于高亮绘制的 attributed string（包含 com.rdreader.highlight 等自定义属性）
    var attributedDisplayContent: NSAttributedString? {
        didSet {
            setNeedsDisplay()
        }
    }

    // MARK: - 选区绘制（对齐 WXRead 的 _drawSelectionInContext:）

    /// 选区矩形数组，由 RDEPUBTextSelectionController 设置
    var selectionRects: [CGRect] = [] {
        didSet {
            setNeedsDisplay()
        }
    }

    /// 选区颜色（蓝色半透明，对齐 WXRead）
    var selectionColor: UIColor = UIColor(red: 70 / 255, green: 140 / 255, blue: 1, alpha: 0.24)

    // MARK: - Init

    override init(frame: CGRect) {
        super.init(frame: frame)
        backgroundColor = .clear
        isOpaque = false
        contentMode = .redraw
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    // MARK: - Draw

    override func draw(_ rect: CGRect) {
        guard let context = UIGraphicsGetCurrentContext(),
              let layoutFrame else { return }

        context.saveGState()

        // 1. 绘制高亮背景（在文字下方，对齐 WXRead 的 drawHighlightsInContext:）
        if let attributedDisplayContent {
            drawHighlights(in: context, attributedString: attributedDisplayContent, layoutFrame: layoutFrame)
        }

        // 2. 绘制文字
        layoutFrame.draw(in: context, options: drawOptions)

        // 3. 绘制选区（在文字上方）
        drawSelection(in: context)

        context.restoreGState()
    }

    // MARK: - 高亮绘制（对齐 WXRead 的 WRCoreTextLayoutFrame.drawHighlightsInContext:）

    private func drawHighlights(
        in context: CGContext,
        attributedString: NSAttributedString,
        layoutFrame: DTCoreTextLayoutFrame
    ) {
        let fullRange = NSRange(location: 0, length: attributedString.length)

        // 绘制高亮背景
        attributedString.enumerateAttribute(kRDEPUBHighlightAttributeName, in: fullRange) { value, range, _ in
            guard let color = value as? UIColor else { return }
            let rects = computeHighlightRects(for: range, layoutFrame: layoutFrame)
            color.setFill()
            for rect in rects {
                context.fill(rect)
            }
        }

        // 绘制下划线
        attributedString.enumerateAttribute(kRDEPUBUnderlineAttributeName, in: fullRange) { value, range, _ in
            guard let color = value as? UIColor else { return }
            let rects = computeHighlightRects(for: range, layoutFrame: layoutFrame)
            color.setStroke()
            context.setLineWidth(2)
            for rect in rects {
                let y = rect.maxY - 1
                context.move(to: CGPoint(x: rect.minX, y: y))
                context.addLine(to: CGPoint(x: rect.maxX, y: y))
                context.strokePath()
            }
        }
    }

    /// 计算指定字符范围的视觉矩形（对齐 WXRead 的 rectsForRange: 算法）
    private func computeHighlightRects(for range: NSRange, layoutFrame: DTCoreTextLayoutFrame) -> [CGRect] {
        var rects: [CGRect] = []
        guard let lines = layoutFrame.lines as? [DTCoreTextLayoutLine] else { return rects }

        for line in lines {
            let lineRange = line.stringRange()
            let overlap = NSIntersectionRange(range, lineRange)
            guard overlap.length > 0 else { continue }

            let startX = line.offset(forStringIndex: overlap.location)
            let endX = line.offset(forStringIndex: overlap.location + overlap.length)
            let rect = CGRect(
                x: line.baselineOrigin.x + startX,
                y: line.baselineOrigin.y - line.ascent,
                width: endX - startX,
                height: line.ascent + line.descent
            )
            rects.append(rect)
        }

        return rects
    }

    // MARK: - 选区绘制

    private func drawSelection(in context: CGContext) {
        guard !selectionRects.isEmpty else { return }
        selectionColor.setFill()
        for rect in selectionRects {
            context.fill(rect)
        }
    }
}
#endif