import Foundation

public struct ProjectAutosavePolicy: Equatable, Sendable {
    public static let `default` = ProjectAutosavePolicy()

    public var minimumVersionInterval: TimeInterval
    public var versionLabel: String

    public init(
        minimumVersionInterval: TimeInterval = 300,
        versionLabel: String = "Autosave checkpoint"
    ) {
        self.minimumVersionInterval = minimumVersionInterval
        self.versionLabel = versionLabel
    }
}

public struct ProjectAutosaveResult: Equatable, Sendable {
    public var project: SongProject
    public var didCreateVersion: Bool

    public init(project: SongProject, didCreateVersion: Bool) {
        self.project = project
        self.didCreateVersion = didCreateVersion
    }
}

public actor ProjectAutosaveService {
    private let store: any ProjectStore
    private let policy: ProjectAutosavePolicy

    public init(store: any ProjectStore, policy: ProjectAutosavePolicy = .default) {
        self.store = store
        self.policy = policy
    }

    public func autosave(_ project: SongProject, at savedAt: Date = Date()) async throws -> ProjectAutosaveResult {
        var autosavedProject = project
        var didCreateVersion = false

        if shouldCreateAutosaveVersion(for: autosavedProject, at: savedAt) {
            _ = autosavedProject.createVersion(label: policy.versionLabel, createdAt: savedAt)
            didCreateVersion = true
        }

        autosavedProject.updatedAt = savedAt
        try await store.save(autosavedProject)

        return ProjectAutosaveResult(project: autosavedProject, didCreateVersion: didCreateVersion)
    }

    private func shouldCreateAutosaveVersion(for project: SongProject, at savedAt: Date) -> Bool {
        let currentSnapshot = SongProjectSnapshot(project: project)

        guard let latestVersion = project.versions.last else {
            return true
        }

        guard latestVersion.snapshot != currentSnapshot else {
            return false
        }

        return savedAt.timeIntervalSince(latestVersion.createdAt) >= policy.minimumVersionInterval
    }
}