import Foundation

final class RDEPUBTextSearchEngine: RDEPUBSearchEngine {
    private let textBook: RDEPUBTextBook
    private let publication: RDEPUBPublication

    init(textBook: RDEPUBTextBook, publication: RDEPUBPublication) {
        self.textBook = textBook
        self.publication = publication
    }

    func search(keyword: String) -> [RDEPUBSearchMatch] {
        let normalizedKeyword = keyword.trimmingCharacters(in: .whitespacesAndNewlines)
        guard !normalizedKeyword.isEmpty else {
            return []
        }

        var matches: [RDEPUBSearchMatch] = []
        for chapter in textBook.chapters {
            guard let chapterData = textBook.chapterData(for: chapter.href) else { continue }
            let source = chapter.attributedContent.string as NSString
            let fullLength = source.length
            guard fullLength > 0 else {
                continue
            }

            let normalizedHref = publication.resourceResolver.normalizedHref(chapter.href) ?? chapter.href
            var localMatchIndex = 0
            var searchRange = NSRange(location: 0, length: fullLength)

            while searchRange.length > 0 {
                let foundRange = source.range(of: normalizedKeyword, options: [.caseInsensitive], range: searchRange)
                guard foundRange.location != NSNotFound else {
                    break
                }

                let progressionDenominator = max(fullLength - 1, 1)
                let progression = Double(foundRange.location) / Double(progressionDenominator)
                matches.append(
                    RDEPUBSearchMatch(
                        href: normalizedHref,
                        progression: progression,
                        previewText: previewText(in: source, matchRange: foundRange),
                        localMatchIndex: localMatchIndex,
                        rangeLocation: foundRange.location,
                        rangeLength: foundRange.length,
                        rangeAnchor: chapterData.rangeAnchor(for: foundRange)
                    )
                )

                localMatchIndex += 1
                let nextLocation = foundRange.location + max(foundRange.length, 1)
                if nextLocation >= fullLength {
                    break
                }
                searchRange = NSRange(location: nextLocation, length: fullLength - nextLocation)
            }
        }

        return matches
    }

    private func previewText(in text: NSString, matchRange: NSRange) -> String {
        let previewRadius = 12
        let start = max(matchRange.location - previewRadius, 0)
        let end = min(matchRange.location + matchRange.length + previewRadius, text.length)
        let range = NSRange(location: start, length: max(end - start, 0))
        return text.substring(with: range).trimmingCharacters(in: .whitespacesAndNewlines)
    }
}