// RDEPUBTextAnchor.swift
// EPUB 文本锚点和范围锚点
// 定义精确的文本位置锚点（RDEPUBTextAnchor，含 fileIndex/row/column/chapterOffset/fragmentID），
// 以及文本范围锚点（RDEPUBTextRangeAnchor，起止锚点对）。
// 支持 Codable 序列化（兼容 spineIndex/fileIndex 两种 key）。

import Foundation

/// 文本锚点，精确定位到 EPUB 中的某个字符位置
/// 包含文件索引、行号、列号、章节内偏移和可选的 fragment ID
public struct RDEPUBTextAnchor: Codable, Equatable {
    /// 文件索引（等同于 spineIndex）
    public let fileIndex: Int
    /// 行号
    public let row: Int
    /// 列号（行内偏移）
    public let column: Int
    /// 章节内的绝对字符偏移量
    public let chapterOffset: Int
    /// 最近的 fragment ID（用于 URL 锚点定位）
    public let fragmentID: String?

    /// spine 索引的别名（与 fileIndex 等价）
    public var spineIndex: Int { fileIndex }

    public init(
        fileIndex: Int,
        row: Int,
        column: Int,
        chapterOffset: Int,
        fragmentID: String? = nil
    ) {
        self.fileIndex = fileIndex
        self.row = row
        self.column = column
        self.chapterOffset = chapterOffset
        self.fragmentID = fragmentID
    }

    enum CodingKeys: String, CodingKey {
        case fileIndex
        case spineIndex
        case row
        case column
        case chapterOffset
        case fragmentID
    }

    public init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        let decodedFileIndex = try container.decodeIfPresent(Int.self, forKey: .fileIndex)
            ?? container.decode(Int.self, forKey: .spineIndex)
        self.fileIndex = decodedFileIndex
        self.row = try container.decodeIfPresent(Int.self, forKey: .row) ?? 0
        self.column = try container.decodeIfPresent(Int.self, forKey: .column) ?? 0
        self.chapterOffset = try container.decode(Int.self, forKey: .chapterOffset)
        self.fragmentID = try container.decodeIfPresent(String.self, forKey: .fragmentID)
    }

    public func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(fileIndex, forKey: .fileIndex)
        try container.encode(row, forKey: .row)
        try container.encode(column, forKey: .column)
        try container.encode(chapterOffset, forKey: .chapterOffset)
        try container.encodeIfPresent(fragmentID, forKey: .fragmentID)
    }
}

/// 文本范围锚点，由起止锚点组成的区间
public struct RDEPUBTextRangeAnchor: Codable, Equatable {
    /// 起始锚点
    public let start: RDEPUBTextAnchor
    /// 结束锚点
    public let end: RDEPUBTextAnchor

    public init(start: RDEPUBTextAnchor, end: RDEPUBTextAnchor) {
        self.start = start
        self.end = end
    }

    /// 转换为 NSRange（基于 chapterOffset）
    public var nsRange: NSRange {
        NSRange(location: start.chapterOffset, length: max(end.chapterOffset - start.chapterOffset, 0))
    }
}