import UIKit

#if canImport(DTCoreText)
import DTCoreText
#endif

public struct RDEPUBDTCoreTextRenderer: RDEPUBTextRenderer {
    public init() {}

    public static var isAvailable: Bool {
#if canImport(DTCoreText)
        return true
#else
        return false
#endif
    }

    public func renderChapter(
        html: String,
        baseURL: URL?,
        style: RDEPUBTextRenderStyle
    ) throws -> RDEPUBRenderedChapterContent {
#if canImport(DTCoreText)
        let markedHTML = RDEPUBTextRendererSupport.injectFragmentMarkers(into: html)
        guard let data = markedHTML.data(using: .utf8) else {
            throw RDEPUBTextRenderingError.htmlEncodingFailed
        }

        guard let rendered = makeAttributedString(from: data, baseURL: baseURL, style: style) else {
            return fallbackRenderedContent(for: markedHTML, style: style)
        }

        let attributedString = NSMutableAttributedString(attributedString: rendered)
        let fragmentOffsets = RDEPUBTextRendererSupport.extractFragmentOffsets(from: attributedString)
        RDEPUBTextRendererSupport.normalizeReadingAttributes(in: attributedString, style: style)
        return RDEPUBRenderedChapterContent(attributedString: attributedString, fragmentOffsets: fragmentOffsets)
#else
        let markedHTML = RDEPUBTextRendererSupport.injectFragmentMarkers(into: html)
        return fallbackRenderedContent(for: markedHTML, style: style)
#endif
    }

    private func fallbackRenderedContent(for html: String, style: RDEPUBTextRenderStyle) -> RDEPUBRenderedChapterContent {
        let attributedString = RDEPUBTextRendererSupport.fallbackAttributedString(for: html, style: style)
        let fragmentOffsets = RDEPUBTextRendererSupport.extractFragmentOffsets(from: attributedString)
        RDEPUBTextRendererSupport.normalizeReadingAttributes(in: attributedString, style: style)
        return RDEPUBRenderedChapterContent(attributedString: attributedString, fragmentOffsets: fragmentOffsets)
    }

#if canImport(DTCoreText)
    private func makeAttributedString(from data: Data, baseURL: URL?, style: RDEPUBTextRenderStyle) -> NSAttributedString? {
        let builder = DTHTMLAttributedStringBuilder(
            html: data,
            options: dtOptions(baseURL: baseURL, style: style),
            documentAttributes: nil
        )
        return builder?.generatedAttributedString()
    }

    private func dtOptions(baseURL: URL?, style: RDEPUBTextRenderStyle) -> [AnyHashable: Any] {
        var options: [AnyHashable: Any] = [
            NSTextSizeMultiplierDocumentOption: 1.0,
            DTDefaultFontFamily: style.font.familyName,
            DTDefaultFontName: style.font.fontName,
            DTDefaultFontSize: style.font.pointSize,
            DTDefaultLineHeightMultiplier: max((style.font.lineHeight + style.lineSpacing) / max(style.font.lineHeight, 1), 1),
            DTUseiOS6Attributes: true
        ]

        if let baseURL {
            options[NSBaseURLDocumentOption] = baseURL
        }
        if let textColor = style.textColor {
            options[DTDefaultTextColor] = textColor
        }

        return options
    }
#endif
}