//
//  PhotoPickerPreviewVC.swift
//  QuickLocation
//

import UIKit
import Photos

final class PhotoPickerPreviewVC: UIViewController, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {

    override var preferredStatusBarStyle: UIStatusBarStyle { .lightContent }

    private let assets: [PHAsset]
    private let store: PhotoPickerStore
    private var currentIndex: Int
    private var lastPageSize: CGSize = .zero

    init(assets: [PHAsset], startIndex: Int, store: PhotoPickerStore) {
        self.assets = assets
        self.store = store
        self.currentIndex = min(max(startIndex, 0), max(assets.count - 1, 0))
        super.init(nibName: nil, bundle: nil)
        modalPresentationStyle = .fullScreen
    }

    required init?(coder: NSCoder) { fatalError("init(coder:) has not been implemented") }

    private lazy var closeBtn: UIButton = {
        let btn = UIButton(type: .custom)
        btn.setImage(UIImage(named: "PhotoPicker/btn_close"), for: .normal)
        btn.extendEdgeInsets = UIEdgeInsets(top: 10, left: 10, bottom: 10, right: 10)
        btn.addTarget(self, action: #selector(tapClose), for: .touchUpInside)
        return btn
    }()

    private lazy var titleLab: UILabel = {
        let label = UILabel()
        label.text = "预览"
        label.textColor = .white
        label.font = .systemFont(ofSize: 17, weight: .medium)
        return label
    }()

    private lazy var collectionView: UICollectionView = {
        let layout = UICollectionViewFlowLayout()
        layout.scrollDirection = .horizontal
        layout.minimumLineSpacing = 0
        layout.minimumInteritemSpacing = 0
        let cv = UICollectionView(frame: .zero, collectionViewLayout: layout)
        cv.isPagingEnabled = true
        cv.showsHorizontalScrollIndicator = false
        cv.backgroundColor = .black
        cv.dataSource = self
        cv.delegate = self
        cv.register(PhotoPickerPreviewCell.self, forCellWithReuseIdentifier: "cell")
        return cv
    }()

    private lazy var pageLab: UILabel = {
        let label = UILabel()
        label.textColor = .white
        label.font = .systemFont(ofSize: 13, weight: .medium)
        label.textAlignment = .center
        label.backgroundColor = UIColor.black.withAlphaComponent(0.45)
        label.cornerRadius = 12
        label.clipsToBounds = true
        return label
    }()

    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .black
        view.addSubview(collectionView)
        view.addSubview(closeBtn)
        view.addSubview(titleLab)
        view.addSubview(pageLab)

        collectionView.layoutChain.edges()
        closeBtn.layoutChain.left(16).width(32).height(32)
        closeBtn.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 6).isActive = true
        titleLab.layoutChain.centerX().centerY(closeBtn)
        pageLab.layoutChain.centerX().width(52).height(24)
        pageLab.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor, constant: -16).isActive = true
        updatePageLabel()
    }

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        let size = collectionView.bounds.size
        guard size.width > 1 else { return }
        if size != lastPageSize {
            lastPageSize = size
            collectionView.collectionViewLayout.invalidateLayout()
        }
        guard assets.indices.contains(currentIndex) else { return }
        let offset = CGFloat(currentIndex) * size.width
        if abs(collectionView.contentOffset.x - offset) > 1 {
            collectionView.setContentOffset(CGPoint(x: offset, y: 0), animated: false)
        }
    }

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        assets.count
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath) as! PhotoPickerPreviewCell
        cell.configure(asset: assets[indexPath.item], store: store)
        return cell
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        collectionView.bounds.size
    }

    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        let width = scrollView.bounds.width
        guard width > 0 else { return }
        let index = Int(round(scrollView.contentOffset.x / width))
        let clamped = min(max(index, 0), max(assets.count - 1, 0))
        if clamped != currentIndex {
            currentIndex = clamped
            updatePageLabel()
        }
    }

    private func updatePageLabel() {
        pageLab.text = "\(currentIndex + 1)/\(max(assets.count, 1))"
    }

    @objc private func tapClose() {
        dismiss(animated: true)
    }
}

private final class PhotoPickerPreviewCell: UICollectionViewCell {
    private let imageView = UIImageView()
    private var assetId = ""
    private var requestId: PHImageRequestID = PHInvalidImageRequestID

    override init(frame: CGRect) {
        super.init(frame: frame)
        backgroundColor = .black
        imageView.contentMode = .scaleAspectFit
        contentView.addSubview(imageView)
        imageView.layoutChain.edges()
    }

    required init?(coder: NSCoder) { fatalError("init(coder:) has not been implemented") }

    func configure(asset: PHAsset, store: PhotoPickerStore) {
        if requestId != PHInvalidImageRequestID {
            store.cancelRequest(requestId)
        }
        assetId = asset.localIdentifier
        imageView.image = nil
        let size = UIScreen.main.bounds.size
        requestId = store.requestThumbnail(for: asset, size: size) { [weak self] image in
            guard let self, self.assetId == asset.localIdentifier else { return }
            self.imageView.image = image
        }
    }
}