//
//  TodoStore.swift
//  iris
//
//  Created by Codex.
//

import Foundation

final class TodoStore {
    private struct Persisted: Codable {
        var schema: Int?
        var items: [TodoItem]
    }

    private let queue = DispatchQueue(label: "iris.todostore.queue")
    private let fileURL: URL
    private var items: [TodoItem]

    init(filename: String = "todos_v1.json") {
        self.fileURL = Self.defaultFileURL(filename: filename)
        let persisted = Self.load(from: fileURL)
        self.items = persisted?.items ?? []
    }

    func snapshot() -> [TodoItem] {
        queue.sync { items }
    }

    @discardableResult
    func add(title: String, now: Date = Date()) -> TodoItem {
        queue.sync {
            let item = TodoItem(title: title, createdAt: now, updatedAt: now)
            items.append(item)
            save()
            return item
        }
    }

    @discardableResult
    func updateTitle(id: UUID, title: String, now: Date = Date()) -> TodoItem? {
        queue.sync {
            guard let index = items.firstIndex(where: { $0.id == id }) else { return nil }
            var item = items[index]
            item.title = title
            item.updatedAt = now
            items[index] = item
            save()
            return item
        }
    }

    @discardableResult
    func setCompleted(id: UUID, completed: Bool, now: Date = Date()) -> TodoItem? {
        queue.sync {
            guard let index = items.firstIndex(where: { $0.id == id }) else { return nil }
            var item = items[index]
            item.isCompleted = completed
            item.updatedAt = now
            item.completedAt = completed ? now : nil
            items[index] = item
            save()
            return item
        }
    }

    func delete(id: UUID) {
        queue.sync {
            items.removeAll { $0.id == id }
            save()
        }
    }

    private func save() {
        let persisted = Persisted(schema: 1, items: items)
        Self.save(persisted, to: fileURL)
    }

    private static func defaultFileURL(filename: String) -> URL {
        let fm = FileManager.default
        let base = fm.urls(for: .applicationSupportDirectory, in: .userDomainMask).first ?? fm.temporaryDirectory
        let bundle = Bundle.main.bundleIdentifier ?? "iris"
        return base
            .appendingPathComponent(bundle, isDirectory: true)
            .appendingPathComponent(filename, isDirectory: false)
    }

    private static func load(from url: URL) -> Persisted? {
        guard let data = try? Data(contentsOf: url) else { return nil }
        return try? makeDecoder().decode(Persisted.self, from: data)
    }

    private static func save(_ persisted: Persisted, to url: URL) {
        do {
            let fm = FileManager.default
            try fm.createDirectory(at: url.deletingLastPathComponent(), withIntermediateDirectories: true)
            let data = try makeEncoder().encode(persisted)
            try data.write(to: url, options: [.atomic])
        } catch {
            // Best-effort persistence.
        }
    }

    private static func makeEncoder() -> JSONEncoder {
        let encoder = JSONEncoder()
        encoder.outputFormatting = [.prettyPrinted, .withoutEscapingSlashes]
        encoder.dateEncodingStrategy = .iso8601
        return encoder
    }

    private static func makeDecoder() -> JSONDecoder {
        let decoder = JSONDecoder()
        decoder.dateDecodingStrategy = .iso8601
        return decoder
    }
}