//
//  FFPageContentView.swift
//  FFPage
//
//  Created by FFIB on 2017/10/18.
//  Copyright © 2017年 FFIB. All rights reserved.
//

import UIKit

protocol FFPageContentViewDataSource {

    func pageContentView(pageContentView: FFPageContentView, cellForItemAt index: Int) -> FFPageContentViewCell

    func numberOfSections(in pageContentView: FFPageContentView) -> Int
}

protocol FFPageContentViewDelegate {

    func pageContentView(pageContentView: FFPageContentView, didSelectItemAt index: Int)
}

@IBDesignable
open class FFPageContentView: UIScrollView, UIScrollViewDelegate {

    var dataSource: FFPageContentViewDataSource?
    var pageDelegate: FFPageContentViewDelegate?

    private var ffConstraints = [NSLayoutConstraint]()
    private var nibs = [String: UINib]()
    private var cells = [String: AnyClass]()
    var needLayout = true

    public override init(frame: CGRect) {
        super.init(frame: frame)
        configuration()
    }
    public required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        configuration()
    }

    func configuration() {
        isPagingEnabled = true
        showsHorizontalScrollIndicator = false
        showsVerticalScrollIndicator = false
        alwaysBounceVertical = false
        bounces = false
        alwaysBounceHorizontal = true
        addObserver(self, forKeyPath: "contentOffset", options: .new, context: nil)
    }

    open override func layoutSubviews() {
        if needLayout {
            reloadData()
        }
        super.layoutSubviews()
    }

    func register(nib: UINib, with identifier: String) {
        nibs[identifier] = nib
    }

    func register(cell: AnyClass, with identifier: String) {
        cells[identifier] = cell
    }

    func dequeue(with identifier: String) -> FFPageContentViewCell {
        if let nib = nibs[identifier] {
            return nib.instantiate(withOwner: self, options: nil).first as! FFPageContentViewCell
        }
        if let cell = cells[identifier], cell is FFPageContentViewCell.Type {
            return  (cell as! FFPageContentViewCell.Type).init()
        }
        fatalError("FFPageContentViewCell and identifier unmatch")
    }

    func reloadData() {
        subviews.forEach { $0.removeFromSuperview()  }
        NSLayoutConstraint.deactivate(ffConstraints)
        contentSize = CGSize(width: 0, height: 0)
        ffConstraints.removeAll()

        guard let dataSource = dataSource else { return }
        contentSize = CGSize(width: frame.width * CGFloat(dataSource.numberOfSections(in: self)), height: frame.height)

        var last: FFPageContentViewCell?
        for i in 0..<dataSource.numberOfSections(in: self) {
            var cell = dataSource.pageContentView(pageContentView: self, cellForItemAt: i)
            cell.index = i
            cell.translatesAutoresizingMaskIntoConstraints = false
            addSubview(cell)
            var subConstriants = [NSLayoutConstraint(item: cell,
                                                  attribute: .top,
                                                  relatedBy: .equal,
                                                  toItem: self,
                                                  attribute: .top,
                                                  multiplier: 1,
                                                  constant: 0),
                               NSLayoutConstraint(item: cell,
                                                  attribute: .height,
                                                  relatedBy: .equal,
                                                  toItem: self,
                                                  attribute: .height,
                                                  multiplier: 1,
                                                  constant: 0),
                               NSLayoutConstraint(item: cell,
                                                  attribute: .width,
                                                  relatedBy: .equal,
                                                  toItem: self,
                                                  attribute: .width,
                                                  multiplier: 1,
                                                  constant: 0)]
            var leadConstriant: NSLayoutConstraint
            if last == nil {
                leadConstriant = NSLayoutConstraint(item: cell,
                                                    attribute: .leading,
                                                    relatedBy: .equal,
                                                    toItem: self,
                                                    attribute: .leading,
                                                    multiplier: 1,
                                                    constant: 0)
            } else {
                leadConstriant = NSLayoutConstraint(item: cell,
                                                    attribute: .left,
                                                    relatedBy: .equal,
                                                    toItem: last,
                                                    attribute: .right,
                                                    multiplier: 1,
                                                    constant: 0)
            }
            subConstriants.append(leadConstriant)
            ffConstraints += subConstriants
            last = cell
        }
        NSLayoutConstraint.activate(ffConstraints)
        needLayout = false
    }

    open override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey: Any]?, context: UnsafeMutableRawPointer?) {
        if let point = change?[NSKeyValueChangeKey.newKey] as? CGPoint, (isTracking || isDragging || isDecelerating) {
            pageDelegate?.pageContentView(pageContentView: self, didSelectItemAt: Int(point.x / frame.width))
        }
    }

    deinit {
        removeObserver(self, forKeyPath: "contentOffset")
    }
}