import UIKit

#if canImport(DTCoreText)
import DTCoreText
#endif

// MARK: - 页面交互控制器

/// 页面交互控制器，负责文本层面的坐标映射与选择逻辑
/// 在 DTCoreText 排版结果和用户交互之间充当桥梁
/// 提供字符索引查找、选择范围计算、选择矩形计算等功能
final class RDEPUBPageInteractionController {

    var snapshot: RDEPUBPageLayoutSnapshot?
    private var dtLayoutFrame: DTCoreTextLayoutFrame?

#if canImport(DTCoreText)
    func configure(layoutFrame: DTCoreTextLayoutFrame?, page: RDEPUBTextPage?) {
        dtLayoutFrame = layoutFrame
        if let layoutFrame, let page {
            snapshot = RDEPUBPageLayoutSnapshot.build(from: layoutFrame, page: page)
        } else {
            snapshot = nil
        }
    }
#endif

    // MARK: - Hit Testing

    func characterIndex(at point: CGPoint) -> Int? {
        guard let snapshot else { return nil }

        // Attachment rect priority (6pt inset for easier tapping)
        for attachment in snapshot.attachments {
            if attachment.frame.insetBy(dx: -6, dy: -6).contains(point) {
                return attachment.stringRange.location
            }
        }

        guard let line = nearestLine(to: point, in: snapshot.lines) else { return nil }

#if canImport(DTCoreText)
        guard let dtLine = dtLineContaining(range: line.stringRange) else { return nil }
        let relativePoint = CGPoint(
            x: point.x - line.baselineOrigin.x,
            y: point.y - line.baselineOrigin.y
        )
        let idx = dtLine.stringIndex(forPosition: relativePoint)
        guard idx != NSNotFound, idx >= 0 else { return nil }
        return normalizedIndex(idx, lineRange: line.stringRange, pageRange: snapshot.pageContentRange)
#else
        return nil
#endif
    }

    // MARK: - Selection Range

    func selectionRange(from startPoint: CGPoint, to endPoint: CGPoint) -> NSRange? {
        guard let start = characterIndex(at: startPoint),
              let end = characterIndex(at: endPoint) else { return nil }
        let lower = min(start, end)
        let upper = max(start, end)
        return NSRange(location: lower, length: max(upper - lower, 1))
    }

    // MARK: - Selection Rects

    func selectionRects(for absoluteRange: NSRange) -> [CGRect] {
        guard let snapshot else { return [] }
        var rects: [CGRect] = []

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

#if canImport(DTCoreText)
            guard let dtLine = dtLineContaining(range: line.stringRange) else { continue }
            let startX = dtLine.offset(forStringIndex: overlap.location)
            let endIdx = overlap.location + overlap.length
            let endX = dtLine.offset(forStringIndex: endIdx)
#else
            let startX: CGFloat = 0
            let endX: CGFloat = line.frame.width
#endif

            let rect = CGRect(
                x: line.baselineOrigin.x + startX,
                y: line.baselineOrigin.y - line.ascent,
                width: max(endX - startX, 2),
                height: line.ascent + line.descent
            )
            rects.append(rect)
        }

        return mergeAdjacentRects(rects)
    }

    func firstRect(for absoluteRange: NSRange) -> CGRect? {
        selectionRects(for: absoluteRange).first
    }

    func lastRect(for absoluteRange: NSRange) -> CGRect? {
        selectionRects(for: absoluteRange).last
    }

    func boundingRect(for absoluteRange: NSRange) -> CGRect? {
        let rects = selectionRects(for: absoluteRange)
        guard var rect = rects.first else { return nil }
        for next in rects.dropFirst() {
            rect = rect.union(next)
        }
        return rect
    }

    func menuAnchorRect(for absoluteRange: NSRange) -> CGRect? {
        guard let first = firstRect(for: absoluteRange),
              let last = lastRect(for: absoluteRange) else {
            return boundingRect(for: absoluteRange)
        }

        let minX = min(first.minX, last.minX)
        let maxX = max(first.maxX, last.maxX)
        let minY = min(first.minY, last.minY)
        let maxY = max(first.maxY, last.maxY)
        return CGRect(x: minX, y: minY, width: max(maxX - minX, 2), height: max(maxY - minY, 2))
    }

    // MARK: - Caret Rect

    func caretRect(at index: Int) -> CGRect? {
        guard let snapshot else { return nil }
        guard let line = snapshot.lines.first(where: { NSLocationInRange(index, $0.stringRange) }) else {
            return nil
        }

#if canImport(DTCoreText)
        guard let dtLine = dtLineContaining(range: line.stringRange) else { return nil }
        let offsetX = dtLine.offset(forStringIndex: index)
#else
        let offsetX: CGFloat = 0
#endif

        return CGRect(
            x: line.baselineOrigin.x + offsetX - 1,
            y: line.baselineOrigin.y - line.ascent,
            width: 2,
            height: line.ascent + line.descent
        )
    }

    // MARK: - Private Helpers

    private func nearestLine(to point: CGPoint, in lines: [RDEPUBPageLine]) -> RDEPUBPageLine? {
        var bestLine: RDEPUBPageLine?
        var bestDistance: CGFloat = .greatestFiniteMagnitude

        for line in lines {
            let lineBottom = line.baselineOrigin.y + line.descent
            let lineTop = line.baselineOrigin.y - line.ascent
            if point.y >= lineTop && point.y <= lineBottom {
                return line
            }
            let lineMidY = (lineTop + lineBottom) / 2
            let distance = abs(point.y - lineMidY)

            if distance < bestDistance {
                bestDistance = distance
                bestLine = line
            }
        }

        return bestLine
    }

    private func normalizedIndex(_ idx: Int, lineRange: NSRange, pageRange: NSRange) -> Int {
        var result = idx
        if result < lineRange.location {
            result = lineRange.location
        }
        let lineEnd = lineRange.location + lineRange.length
        if result >= lineEnd {
            result = max(lineEnd - 1, lineRange.location)
        }
        return result
    }

#if canImport(DTCoreText)
    private func dtLineContaining(range: NSRange) -> DTCoreTextLayoutLine? {
        guard let dtLayoutFrame else { return nil }
        return dtLayoutFrame.lineContaining(UInt(range.location))
    }
#endif

    private func mergeAdjacentRects(_ rects: [CGRect]) -> [CGRect] {
        guard rects.count > 1 else { return rects }

        let sorted = rects.sorted { a, b in
            if abs(a.origin.y - b.origin.y) < 1 {
                return a.origin.x < b.origin.x
            }
            return a.origin.y < b.origin.y
        }

        var merged: [CGRect] = [sorted[0]]
        for rect in sorted.dropFirst() {
            let last = merged[merged.count - 1]
            if abs(rect.origin.y - last.origin.y) < 1,
               rect.origin.x <= last.maxX + 2 {
                merged[merged.count - 1] = last.union(rect)
            } else {
                merged.append(rect)
            }
        }

        return merged
    }
}