//
//  ModelRouter.swift
//  Prisme
//
//  Author: Simon-Pierre Boucher <contact@spboucher.ai>
//

import Foundation
import FoundationModels
import Observation

/// Effort level a task declares. The router decides what actually runs —
/// no other code calls a model directly (CLAUDE.md §3).
enum Tier {
    /// Pure heuristics, zero AI. The first choice whenever it suffices.
    case none
    /// On-device Foundation Models: free, unlimited, offline.
    case local
    /// Private Cloud Compute: explicit user action only, never on
    /// sensitive-container content. Not wired yet (P2).
    case cloud
}

/// Availability of the on-device model, with a user-presentable reason.
/// AI is an enhancement: Prisme must remain a great browser without it —
/// never an error screen, never a dead button (CLAUDE.md §2).
enum LocalModelAvailability: Equatable {
    case available
    case unavailable(reason: String)
}

/// Single owner of model availability and session creation.
@MainActor
@Observable
final class ModelRouter {
    private(set) var local: LocalModelAvailability = .unavailable(reason: "")

    /// Serializes on-device inference (Neural Engine runs requests in
    /// series; more than 2 in flight only builds a hidden queue).
    let queue = InferenceQueue(maxConcurrent: 2)

    init() {
        refreshAvailability()
    }

    var isLocalAvailable: Bool { local == .available }

    func refreshAvailability() {
        switch SystemLanguageModel.default.availability {
        case .available:
            local = .available
        case .unavailable(let reason):
            local = .unavailable(reason: Self.describe(reason))
        }
    }

    private static func describe(_ reason: SystemLanguageModel.Availability.UnavailableReason) -> String {
        switch reason {
        case .deviceNotEligible:
            "Cet appareil ne prend pas en charge l'intelligence locale. Prisme reste un navigateur complet."
        case .appleIntelligenceNotEnabled:
            "Apple Intelligence est désactivé. Activez-le dans Réglages pour les résumés locaux."
        case .modelNotReady:
            "Le modèle local se prépare (téléchargement en cours). Réessayez dans quelques minutes."
        @unknown default:
            "L'intelligence locale n'est pas disponible pour le moment."
        }
    }
}