import UIKit

#if canImport(DTCoreText)
import DTCoreText
#endif

struct RDEPUBPageLine {

    let stringRange: NSRange

    let frame: CGRect

    let baselineOrigin: CGPoint

    let ascent: CGFloat

    let descent: CGFloat

    let leading: CGFloat
}

struct RDEPUBPageRun {

    let stringRange: NSRange

    let frame: CGRect

    let isAttachment: Bool
}

struct RDEPUBPageAttachment {

    let stringRange: NSRange

    let frame: CGRect

    let displaySize: CGSize

    let placement: RDEPUBTextAttachmentPlacement?

    let kind: RDEPUBTextAttachmentKind?
}

struct RDEPUBPageLayoutSnapshot {

    let page: RDEPUBTextPage

    let lines: [RDEPUBPageLine]

    let runs: [RDEPUBPageRun]

    let attachments: [RDEPUBPageAttachment]

    let pageContentRange: NSRange
#if canImport(DTCoreText)

    let layoutFrame: DTCoreTextLayoutFrame
#endif

    var contentBounds: CGRect {
        let rects = lines.map(\.frame) + attachments.map(\.frame)
        guard var bounds = rects.first else { return .zero }
        for rect in rects.dropFirst() {
            bounds = bounds.union(rect)
        }
        return bounds
    }

    func line(containing absoluteIndex: Int) -> RDEPUBPageLine? {
        lines.first { NSLocationInRange(absoluteIndex, $0.stringRange) }
    }

    func run(containing absoluteIndex: Int) -> RDEPUBPageRun? {
        runs.first { NSLocationInRange(absoluteIndex, $0.stringRange) }
    }

    func runs(intersecting range: NSRange) -> [RDEPUBPageRun] {
        runs.filter { NSIntersectionRange($0.stringRange, range).length > 0 }
    }

    func attachment(at point: CGPoint, hitSlop: CGFloat = 6) -> RDEPUBPageAttachment? {
        attachments.first { $0.frame.insetBy(dx: -hitSlop, dy: -hitSlop).contains(point) }
    }

    func line(at point: CGPoint, hitSlop: CGFloat = 4) -> RDEPUBPageLine? {
        lines.first { line in
            let lineRect = CGRect(
                x: line.frame.minX,
                y: line.baselineOrigin.y - line.ascent,
                width: max(line.frame.width, 1),
                height: line.ascent + line.descent + line.leading
            )
            return lineRect.insetBy(dx: -hitSlop, dy: -hitSlop).contains(point)
        }
    }

    func run(at point: CGPoint, hitSlop: CGFloat = 4) -> RDEPUBPageRun? {
        runs.first { $0.frame.insetBy(dx: -hitSlop, dy: -hitSlop).contains(point) }
    }

    func rects(containing point: CGPoint, in decorations: [RDEPUBTextOverlayDecoration]) -> [RDEPUBTextOverlayDecoration] {
        decorations.filter { decoration in
            decoration.rects.contains { $0.insetBy(dx: -4, dy: -4).contains(point) }
        }
    }

    func absoluteRange(at point: CGPoint, in decorations: [RDEPUBTextOverlayDecoration]) -> NSRange? {
        if let attachment = attachment(at: point) {
            return attachment.stringRange
        }
        if let run = run(at: point) {
            return run.stringRange
        }
        let hitDecorations = rects(containing: point, in: decorations)
        if let mostSpecific = hitDecorations.min(by: { lhs, rhs in
            lhs.absoluteRange.length < rhs.absoluteRange.length
        }) {
            return mostSpecific.absoluteRange
        }
        return line(at: point)?.stringRange
    }

#if canImport(DTCoreText)

    static func build(
        from layoutFrame: DTCoreTextLayoutFrame,
        page: RDEPUBTextPage
    ) -> RDEPUBPageLayoutSnapshot? {
        guard let dtLines = layoutFrame.lines as? [DTCoreTextLayoutLine], !dtLines.isEmpty else {
            return nil
        }

        var lines: [RDEPUBPageLine] = []
        var runs: [RDEPUBPageRun] = []
        var attachments: [RDEPUBPageAttachment] = []
        let pageOffset = page.pageStartOffset

        for dtLine in dtLines {
            let lineRange = offset(dtLine.stringRange(), by: pageOffset)
            let line = RDEPUBPageLine(
                stringRange: lineRange,
                frame: dtLine.frame,
                baselineOrigin: dtLine.baselineOrigin,
                ascent: dtLine.ascent,
                descent: dtLine.descent,
                leading: dtLine.leading
            )
            lines.append(line)

            if let glyphRuns = dtLine.glyphRuns as? [DTCoreTextGlyphRun] {
                for run in glyphRuns {
                    let runRange = offset(run.stringRange(), by: pageOffset)
                    let isAttachment = run.attachment != nil
                    runs.append(
                        RDEPUBPageRun(
                            stringRange: runRange,
                            frame: run.frame,
                            isAttachment: isAttachment
                        )
                    )

                    guard isAttachment else { continue }
                    let metadata = attachmentMetadata(
                        for: runRange,
                        on: page
                    )
                    attachments.append(
                        RDEPUBPageAttachment(
                            stringRange: runRange,
                            frame: run.frame,
                            displaySize: run.frame.size,
                            placement: metadata.placement,
                            kind: metadata.kind
                        )
                    )
                }
            }
        }

        let visibleRange = offset(layoutFrame.visibleStringRange(), by: pageOffset)

        return RDEPUBPageLayoutSnapshot(
            page: page,
            lines: lines,
            runs: runs,
            attachments: attachments,
            pageContentRange: visibleRange,
            layoutFrame: layoutFrame
        )
    }

    private static func attachmentMetadata(
        for range: NSRange,
        on page: RDEPUBTextPage
    ) -> (placement: RDEPUBTextAttachmentPlacement?, kind: RDEPUBTextAttachmentKind?) {
        guard let attachmentIndex = page.metadata.attachmentRanges.firstIndex(where: { NSIntersectionRange($0, range).length > 0 }) else {
            return (nil, nil)
        }

        let placement = page.metadata.attachmentPlacements.indices.contains(attachmentIndex)
            ? page.metadata.attachmentPlacements[attachmentIndex]
            : nil
        let metadataKind = page.metadata.attachmentKinds.indices.contains(attachmentIndex)
            ? page.metadata.attachmentKinds[attachmentIndex]
            : nil
        let resolvedKind = attachmentKind(at: range, on: page) ?? metadataKind
        return (placement, resolvedKind)
    }

    private static func attachmentKind(
        at range: NSRange,
        on page: RDEPUBTextPage
    ) -> RDEPUBTextAttachmentKind? {
        guard range.location >= 0,
              range.location < page.chapterContent.length else {
            return nil
        }
        let attributes = page.chapterContent.attributes(at: range.location, effectiveRange: nil)
        return RDEPUBAttachmentNormalizer.attachmentKind(for: attributes)
    }

    private static func offset(_ range: NSRange, by offset: Int) -> NSRange {
        guard range.location != NSNotFound else {
            return range
        }
        return NSRange(location: range.location + offset, length: range.length)
    }
#endif
}