import Foundation

/// EPUB 文本搜索引擎：在分页书籍中执行全文搜索。
///
/// 实现 `RDEPUBSearchEngine` 协议，遍历所有章节的富文本内容，
/// 使用大小写不敏感匹配查找关键词，返回搜索结果列表。
/// 每个搜索结果包含进度位置、预览文本和语义锚点。
final class RDEPUBTextSearchEngine: RDEPUBSearchEngine {
    private let textBook: RDEPUBTextBook
    private let publication: RDEPUBPublication

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

    /// 在全书中搜索关键词，返回所有匹配结果。
    ///
    /// 搜索流程：
    /// 1. 遍历所有章节
    /// 2. 在每章的富文本字符串中执行大小写不敏感搜索
    /// 3. 计算匹配位置的阅读进度（progression）
    /// 4. 生成预览文本（匹配位置前后各 12 个字符）
    /// 5. 生成语义锚点（用于跨设备/跨字体精确定位）
    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
    }

    /// 生成搜索结果的预览文本：匹配位置前后各取 12 个字符
    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)
    }

    /// 无 publication 时的搜索（用于 txt 等外部文本文件）
    static func searchWithoutPublication(textBook: RDEPUBTextBook, keyword: String) -> [RDEPUBSearchMatch] {
        let normalizedKeyword = keyword.trimmingCharacters(in: .whitespacesAndNewlines)
        guard !normalizedKeyword.isEmpty else { return [] }

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

            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)
                let previewRadius = 12
                let previewStart = max(foundRange.location - previewRadius, 0)
                let previewEnd = min(foundRange.location + foundRange.length + previewRadius, fullLength)
                let previewRange = NSRange(location: previewStart, length: max(previewEnd - previewStart, 0))
                let previewText = source.substring(with: previewRange).trimmingCharacters(in: .whitespacesAndNewlines)

                matches.append(
                    RDEPUBSearchMatch(
                        href: chapter.href,
                        progression: progression,
                        previewText: previewText,
                        localMatchIndex: localMatchIndex,
                        rangeLocation: foundRange.location,
                        rangeLength: foundRange.length,
                        rangeAnchor: nil
                    )
                )

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