// RDEPUBFixedLayoutTemplate.swift
// 固定版式（Fixed Layout）HTML 模板生成器
// 根据渲染请求和 Publication 信息，将 iframe 拼装到 HTML 模板中，
// 生成适配视口尺寸和内边距的固定版式页面 HTML。

import Foundation

/// 固定版式模板生成器，负责将 spine 资源渲染为 iframe 嵌套的 HTML 页面
enum RDEPUBFixedLayoutTemplate {
    /// 根据渲染请求和 Publication 生成固定版式页面的完整 HTML
    /// - Parameters:
    ///   - request: 固定版式渲染请求（含 spread、视口尺寸、内边距、适配模式等）
    ///   - publication: EPUB 出版物，用于解析资源 URL
    /// - Returns: 完整的 HTML 字符串
    static func html(for request: RDEPUBFixedRenderRequest, publication: RDEPUBPublication) -> String {
        // 遍历 spread 中的每个资源，生成对应的 iframe pane HTML
        let panes = request.spread.resources.enumerated().compactMap { index, resource -> String? in
            guard let url = publication.resourceResolver.resourceURL(forRelativePath: resource.href)?.absoluteString else {
                return nil
            }

            // 根据 spread 中的资源数量判断页面类型：单页/左页/右页/居中
            let pageType: String
            if request.spread.resources.count == 1 {
                pageType = "single"
            } else if request.spread.resources.count == 2 {
                pageType = index == 0 ? "left" : "right"
            } else {
                pageType = "center"
            }

            return """
            <div class=\"ss-fixed-viewport\" data-page-type=\"\(pageType)\">
              <iframe class=\"ss-fixed-page\" data-page-type=\"\(pageType)\" scrolling=\"no\" src=\"\(url)\"></iframe>
            </div>
            """
        }.joined()

        // 计算视口区域（去除内边距后的可用区域）
        let background = request.backgroundColorCSS ?? "#FFFFFF"
        let viewportWidth = max(1, Int((request.viewportSize.width - request.contentInset.left - request.contentInset.right).rounded(.down)))
        let viewportHeight = max(1, Int((request.viewportSize.height - request.contentInset.top - request.contentInset.bottom).rounded(.down)))
        let insetTop = Int(request.contentInset.top.rounded(.down))
        let insetRight = Int(request.contentInset.right.rounded(.down))
        let insetBottom = Int(request.contentInset.bottom.rounded(.down))
        let insetLeft = Int(request.contentInset.left.rounded(.down))
        // 从资源仓库加载 HTML 模板并替换占位符
        return RDEPUBAssetRepository.string(
            for: .fixedLayoutTemplate,
            replacements: [
                "BACKGROUND": background,
                "INSET_TOP": String(insetTop),
                "INSET_RIGHT": String(insetRight),
                "INSET_BOTTOM": String(insetBottom),
                "INSET_LEFT": String(insetLeft),
                "VIEWPORT_WIDTH": String(viewportWidth),
                "VIEWPORT_HEIGHT": String(viewportHeight),
                "PANES": panes,
                "FIT_MODE": request.fit.rawValue,
                "FIXED_LAYOUT_READY_MESSAGE": RDEPUBJavaScriptBridgeMessage.fixedLayoutReady.rawValue
            ]
        )
    }
}