#!/usr/bin/env swift

import AppKit
import Foundation
import WebKit

enum ExportError: Error, CustomStringConvertible {
  case invalidArguments
  case snapshotFailed
  case pngEncodingFailed(String)
  case clockRegionMissing

  var description: String {
    switch self {
    case .invalidArguments:
      return "用法：export-kindle-background.swift <url> <png-output> <region-output>"
    case .snapshotFailed:
      return "网页截图失败"
    case let .pngEncodingFailed(path):
      return "PNG 编码失败：\(path)"
    case .clockRegionMissing:
      return "页面里没有找到 data-clock-region 标记"
    }
  }
}

final class SnapshotExporter: NSObject, WKNavigationDelegate {
  private let url: URL
  private let pngOutputURL: URL
  private let regionOutputURL: URL
  private let completion: (Result<Void, Error>) -> Void
  private let targetSize = CGSize(width: 1024, height: 600)

  private lazy var window: NSWindow = {
    let window = NSWindow(
      contentRect: CGRect(origin: .zero, size: targetSize),
      styleMask: [.borderless],
      backing: .buffered,
      defer: false
    )
    window.isReleasedWhenClosed = false
    window.backgroundColor = .white
    return window
  }()

  private lazy var webView: WKWebView = {
    let config = WKWebViewConfiguration()
    let view = WKWebView(frame: CGRect(origin: .zero, size: targetSize), configuration: config)
    view.navigationDelegate = self
    return view
  }()

  init(url: URL, pngOutputURL: URL, regionOutputURL: URL, completion: @escaping (Result<Void, Error>) -> Void) {
    self.url = url
    self.pngOutputURL = pngOutputURL
    self.regionOutputURL = regionOutputURL
    self.completion = completion
    super.init()
  }

  func start() {
    window.contentView = webView
    window.orderBack(nil)
    webView.load(URLRequest(url: url))
  }

  func webView(_ webView: WKWebView, didFinish _: WKNavigation!) {
    // 等页面数据与图片稳定下来，避免只截到骨架。
    DispatchQueue.main.asyncAfter(deadline: .now() + 4) {
      self.capture()
    }
  }

  private func capture() {
    let regionScript = """
      (() => {
        const node = document.querySelector('[data-clock-region="true"]');
        if (!node) return null;
        const rect = node.getBoundingClientRect();
        return {
          x: Math.round(rect.left),
          y: Math.round(rect.top),
          width: Math.round(rect.width),
          height: Math.round(rect.height)
        };
      })();
      """

    webView.evaluateJavaScript(regionScript) { value, error in
      if let error {
        self.finish(.failure(error))
        return
      }

      guard let region = value as? [String: NSNumber] else {
        self.finish(.failure(ExportError.clockRegionMissing))
        return
      }

      let snapshotConfig = WKSnapshotConfiguration()
      snapshotConfig.rect = CGRect(origin: .zero, size: self.targetSize)
      snapshotConfig.snapshotWidth = NSNumber(value: Float(self.targetSize.width))

      self.webView.takeSnapshot(with: snapshotConfig) { image, snapshotError in
        if let snapshotError {
          self.finish(.failure(snapshotError))
          return
        }

        guard let image else {
          self.finish(.failure(ExportError.snapshotFailed))
          return
        }

        do {
          try self.savePNG(image: image, to: self.pngOutputURL)
          try self.saveRegion(region: region)
          self.finish(.success(()))
        } catch {
          self.finish(.failure(error))
        }
      }
    }
  }

  private func savePNG(image: NSImage, to url: URL) throws {
    let normalizedImage = NSImage(size: NSSize(width: targetSize.width, height: targetSize.height))
    normalizedImage.lockFocus()
    image.draw(in: NSRect(origin: .zero, size: targetSize))
    normalizedImage.unlockFocus()

    guard
      let tiffRepresentation = normalizedImage.tiffRepresentation,
      let bitmap = NSBitmapImageRep(data: tiffRepresentation),
      let pngData = bitmap.representation(using: .png, properties: [:])
    else {
      throw ExportError.pngEncodingFailed(url.path)
    }

    try FileManager.default.createDirectory(at: url.deletingLastPathComponent(), withIntermediateDirectories: true)
    try pngData.write(to: url)
  }

  private func saveRegion(region: [String: NSNumber]) throws {
    let jsonObject: [String: Int] = [
      "x": region["x"]?.intValue ?? 0,
      "y": region["y"]?.intValue ?? 0,
      "width": region["width"]?.intValue ?? 0,
      "height": region["height"]?.intValue ?? 0,
    ]
    let data = try JSONSerialization.data(withJSONObject: jsonObject, options: [.prettyPrinted, .sortedKeys])
    try FileManager.default.createDirectory(at: regionOutputURL.deletingLastPathComponent(), withIntermediateDirectories: true)
    try data.write(to: regionOutputURL)
  }

  private func finish(_ result: Result<Void, Error>) {
    completion(result)
    NSApplication.shared.terminate(nil)
  }
}

guard CommandLine.arguments.count >= 4 else {
  fputs("\(ExportError.invalidArguments)\n", stderr)
  exit(1)
}

let url = URL(string: CommandLine.arguments[1])!
let pngOutputURL = URL(fileURLWithPath: CommandLine.arguments[2])
let regionOutputURL = URL(fileURLWithPath: CommandLine.arguments[3])

let app = NSApplication.shared
app.setActivationPolicy(.prohibited)

let exporter = SnapshotExporter(url: url, pngOutputURL: pngOutputURL, regionOutputURL: regionOutputURL) { result in
  switch result {
  case .success:
    print("Exported \(pngOutputURL.path)")
    print("Region saved to \(regionOutputURL.path)")
  case let .failure(error):
    fputs("\(error)\n", stderr)
    exit(1)
  }
}

exporter.start()
app.run()