//
//  WidgetHelper.swift
//  Reader
//
//  Created by Shadowfacts on 6/19/22.
//

import Foundation
import WidgetKit
import Persistence
import OSLog

private let logger = Logger(subsystem: "net.shadowfacts.Reader", category: "WidgetHelper")
private let signposter = OSSignposter(logger: logger)

struct WidgetHelper {
    private init() {}
    
    private static let maxDisplayableItems = 8
    
    static func updateWidgetData(fervorController: FervorController) async {
        // Accessing CoreData from the widget extension puts us over the memory limit, so we pre-generate all the data it needs and save it to disk
        
        let context = fervorController.persistentContainer.backgroundContext
        let prioritizedItems: [WidgetData.Item] = await context.perform {
            let req = Item.fetchRequest()
            req.sortDescriptors = [NSSortDescriptor(key: "published", ascending: false)]
            req.fetchLimit = 32
            req.predicate = NSPredicate(format: "read = NO")
            let state = signposter.beginInterval("fetch")
            var items = (try? context.fetch(req)) ?? []
            signposter.endInterval("fetch", state)
            
            var prioritizedItems: [Item] = []
            
            while prioritizedItems.count < maxDisplayableItems {
                let firstFromUnseenFeedIdx = items.firstIndex { item in
                    prioritizedItems.allSatisfy { existing in
                        existing.feed != item.feed
                    }
                }
                if let firstFromUnseenFeedIdx {
                    prioritizedItems.append(items.remove(at: firstFromUnseenFeedIdx))
                } else if let item = items.first {
                    prioritizedItems.append(item)
                    items.removeFirst()
                } else {
                    break
                }
            }

            return prioritizedItems.map {
                WidgetData.Item(id: $0.id!, feedTitle: $0.feed?.title, title: $0.title, published: $0.published)
            }
        }
        
        if let item = prioritizedItems.first {
            logger.info("Saving widget data with first item: '\(item.title ?? "<untitled>", privacy: .public)'")
        }
        
        WidgetData(recentItems: prioritizedItems).save(account: fervorController.account!)
        
        WidgetCenter.shared.reloadAllTimelines()
    }
}