import UIKit

/// 原生文本渲染路径的批注覆盖层，负责绘制用户高亮、搜索命中高亮和当前选区装饰。
final class RDEPUBTextAnnotationOverlay: RDEPUBSelectionOverlayView {
    private let normalSearchColor = UIColor(red: 0.21, green: 0.48, blue: 0.95, alpha: 0.16)
    private let activeSearchColor = UIColor(red: 0.14, green: 0.42, blue: 0.95, alpha: 0.34)

    /// 将用户高亮批注以富文本属性形式应用到页面内容上
    /// - Parameters:
    ///   - highlights: 高亮批注数组
    ///   - content: 待修改的富文本
    ///   - page: 目标文本页
    ///   - contentBaseOffset: 内容在全局偏移中的起始位置
    func applyHighlights(
        _ highlights: [RDEPUBHighlight],
        to content: NSMutableAttributedString,
        page: RDEPUBTextPage,
        contentBaseOffset: Int
    ) {
        let pageRange = absoluteOffsetRange(for: page)
        let pageStart = pageRange.lowerBound
        let pageEndExclusive = pageRange.upperBound

        for highlight in highlights where highlight.location.href == page.href {
            guard let range = RDEPUBTextOffsetRangeInfo.decode(from: highlight.rangeInfo)?.nsRange else { continue }
            let overlapStart = max(range.location, pageStart)
            let overlapEnd = min(range.location + range.length, pageEndExclusive)
            guard overlapStart < overlapEnd else { continue }

            let relativeRange = NSRange(
                location: overlapStart - contentBaseOffset,
                length: overlapEnd - overlapStart
            )
            switch highlight.style {
            case .highlight:
                content.addAttribute(
                    .backgroundColor,
                    value: UIColor(rdHexString: highlight.color, alpha: 0.35) ?? UIColor(red: 248 / 255, green: 225 / 255, blue: 108 / 255, alpha: 0.35),
                    range: relativeRange
                )
            case .underline:
                content.addAttribute(.underlineStyle, value: NSUnderlineStyle.single.rawValue, range: relativeRange)
                if let color = UIColor(rdHexString: highlight.color, alpha: 1) {
                    content.addAttribute(.underlineColor, value: color, range: relativeRange)
                }
            }
        }
    }

    /// 将搜索命中高亮以富文本背景色形式应用到页面内容上
    /// - Parameters:
    ///   - content: 待修改的富文本
    ///   - page: 目标文本页
    ///   - searchState: 当前搜索状态
    ///   - contentBaseOffset: 内容在全局偏移中的起始位置
    func applySearchHighlights(
        to content: NSMutableAttributedString,
        page: RDEPUBTextPage,
        searchState: RDEPUBSearchState?,
        contentBaseOffset: Int
    ) {
        guard let searchState else { return }

        let pageRange = absoluteOffsetRange(for: page)
        let pageStart = pageRange.lowerBound
        let pageEndExclusive = pageRange.upperBound

        for match in searchState.matches {
            guard let matchStart = match.rangeLocation else { continue }
            let matchEnd = matchStart + match.rangeLength
            let overlapStart = max(matchStart, pageStart)
            let overlapEnd = min(matchEnd, pageEndExclusive)
            guard overlapStart < overlapEnd else { continue }

            let relativeRange = NSRange(location: Int(overlapStart - contentBaseOffset), length: Int(overlapEnd - overlapStart))
            let color = match == searchState.currentMatch ? activeSearchColor : normalSearchColor
            content.addAttribute(.backgroundColor, value: color, range: relativeRange)
        }
    }

    /// 构建页面的背景和前景装饰数组（搜索高亮为背景，下划线批注为前景）
    /// - Parameters:
    ///   - page: 目标文本页
    ///   - highlights: 高亮批注数组
    ///   - searchState: 当前搜索状态
    ///   - interactionController: 用于计算选区矩形的交互控制器
    /// - Returns: 分离的背景和前景装饰数组
    func buildDecorations(
        page: RDEPUBTextPage,
        highlights: [RDEPUBHighlight],
        searchState: RDEPUBSearchState?,
        interactionController: RDEPUBPageInteractionController
    ) -> (background: [RDEPUBTextOverlayDecoration], foreground: [RDEPUBTextOverlayDecoration]) {
        var background: [RDEPUBTextOverlayDecoration] = []
        var foreground: [RDEPUBTextOverlayDecoration] = []
        let pageRange = absoluteOffsetRange(for: page)
        let pageStart = pageRange.lowerBound
        let pageEndExclusive = pageRange.upperBound

        if let searchState {
            for match in searchState.matches {
                guard let matchStart = match.rangeLocation else { continue }
                let matchEnd = matchStart + match.rangeLength
                let overlapStart = max(matchStart, pageStart)
                let overlapEnd = min(matchEnd, pageEndExclusive)
                guard overlapStart < overlapEnd else { continue }

                let absoluteRange = NSRange(location: overlapStart, length: overlapEnd - overlapStart)
                let rects = interactionController.selectionRects(for: absoluteRange)
                guard !rects.isEmpty else { continue }

                let isActive = match == searchState.currentMatch
                let kind: RDEPUBTextOverlayDecoration.Kind = isActive ? .activeSearch : .search
                let color = isActive ? activeSearchColor : normalSearchColor
                background.append(RDEPUBTextOverlayDecoration(kind: kind, absoluteRange: absoluteRange, rects: rects, color: color))
            }
        }

        for highlight in highlights where highlight.location.href == page.href {
            guard let range = RDEPUBTextOffsetRangeInfo.decode(from: highlight.rangeInfo)?.nsRange else { continue }
            let overlapStart = max(range.location, pageStart)
            let overlapEnd = min(range.location + range.length, pageEndExclusive)
            guard overlapStart < overlapEnd else { continue }

            let absoluteRange = NSRange(location: overlapStart, length: overlapEnd - overlapStart)
            let rects = interactionController.selectionRects(for: absoluteRange)
            guard !rects.isEmpty else { continue }

            let color = UIColor(rdHexString: highlight.color, alpha: 0.35)
                ?? UIColor(red: 248 / 255, green: 225 / 255, blue: 108 / 255, alpha: 0.35)
            let decoration = RDEPUBTextOverlayDecoration(
                kind: highlight.style == .underline ? .underline : .highlight,
                absoluteRange: absoluteRange,
                rects: rects,
                color: color
            )

            if decoration.kind == .underline {
                foreground.append(decoration)
            } else {
                background.append(decoration)
            }
        }

        return (background, foreground)
    }

    private func absoluteOffsetRange(for page: RDEPUBTextPage) -> Range<Int> {
        let lowerBound = page.pageStartOffset
        let upperBound = page.pageEndOffset + 1
        return lowerBound..<max(upperBound, lowerBound)
    }
}