//
//  FoundationModelsDigestService.swift
//  Reflect
//
//  Generates weekly emotional digests using Foundation Models.
//

import Foundation
import FoundationModels

@available(iOS 26, *)
@MainActor
class FoundationModelsDigestService {

    // MARK: - Singleton

    static let shared = FoundationModelsDigestService()

    private let summarizer = MoodDataSummarizer()

    private init() {}

    // MARK: - Storage Keys

    private static let digestStorageKey = "latestWeeklyDigest"

    // MARK: - Digest Generation

    /// Generate a weekly digest from the past 7 days of mood data
    func generateWeeklyDigest() async throws -> WeeklyDigest {
        let calendar = Calendar.current
        let now = Date()
        let weekStart = calendar.date(byAdding: .day, value: -7, to: now)!

        let entries = DataController.shared.getData(
            startDate: weekStart,
            endDate: now,
            includedDays: [1, 2, 3, 4, 5, 6, 7]
        )

        let validEntries = entries.filter { ![.missing, .placeholder].contains($0.mood) }

        guard validEntries.count >= 3 else {
            throw InsightGenerationError.insufficientData
        }

        let session = LanguageModelSession(instructions: systemInstructions)
        let prompt = buildPrompt(entries: validEntries, weekStart: weekStart, weekEnd: now)

        let response = try await session.respond(to: prompt, generating: AIWeeklyDigestResponse.self)

        let digest = WeeklyDigest(
            headline: response.content.headline,
            summary: response.content.summary,
            highlight: response.content.highlight,
            intention: response.content.intention,
            iconName: response.content.iconName,
            generatedAt: Date(),
            weekStartDate: weekStart,
            weekEndDate: now
        )

        // Store the digest
        saveDigest(digest)

        return digest
    }

    /// Load the latest stored digest
    func loadLatestDigest() -> WeeklyDigest? {
        guard let data = GroupUserDefaults.groupDefaults.data(forKey: Self.digestStorageKey),
              let digest = try? JSONDecoder().decode(WeeklyDigest.self, from: data) else {
            return nil
        }
        return digest
    }

    // MARK: - Storage

    private func saveDigest(_ digest: WeeklyDigest) {
        if let data = try? JSONEncoder().encode(digest) {
            GroupUserDefaults.groupDefaults.set(data, forKey: Self.digestStorageKey)
        }
    }

    // MARK: - System Instructions

    private var systemInstructions: String {
        let personalityPack = UserDefaultsStore.personalityPackable()

        switch personalityPack {
        case .Default:
            return """
            You are a warm, supportive mood companion writing a weekly emotional digest. \
            Summarize the week's mood journey with encouragement and specificity. \
            Be personal, brief, and uplifting. Reference specific patterns from the data. \
            SF Symbols: sun.max.fill, heart.fill, star.fill, leaf.fill, sparkles
            """
        case .MotivationalCoach:
            return """
            You are a HIGH ENERGY motivational coach delivering a weekly performance review! \
            Celebrate wins, frame challenges as growth opportunities, and fire them up for next week! \
            Use exclamations and power language! \
            SF Symbols: trophy.fill, flame.fill, bolt.fill, figure.run, star.fill
            """
        case .ZenMaster:
            return """
            You are a calm Zen master offering a weekly reflection on the emotional journey. \
            Use nature metaphors, gentle wisdom, and serene observations. Find meaning in all moods. \
            SF Symbols: leaf.fill, moon.fill, drop.fill, sunrise.fill, wind
            """
        case .BestFriend:
            return """
            You are their best friend doing a weekly check-in on how they've been. \
            Be warm, casual, validating, and conversational. Celebrate with them, commiserate together. \
            SF Symbols: heart.fill, hand.thumbsup.fill, sparkles, face.smiling.fill, balloon.fill
            """
        case .DataAnalyst:
            return """
            You are a clinical data analyst delivering a weekly mood metrics report. \
            Reference exact numbers, percentages, and observed trends. Be objective but constructive. \
            SF Symbols: chart.bar.fill, chart.line.uptrend.xyaxis, number, percent, doc.text.magnifyingglass
            """
        }
    }

    // MARK: - Prompt Construction

    private func buildPrompt(entries: [MoodEntryModel], weekStart: Date, weekEnd: Date) -> String {
        let formatter = DateFormatter()
        formatter.dateStyle = .medium

        let moodList = entries.sorted { $0.forDate < $1.forDate }.map { entry in
            let day = entry.forDate.formatted(.dateTime.weekday(.abbreviated))
            let mood = entry.mood.widgetDisplayName
            let hasNotes = entry.notes != nil && !entry.notes!.isEmpty
            let noteSnippet = hasNotes ? " (\(String(entry.notes!.prefix(50))))" : ""
            return "\(day): \(mood)\(noteSnippet)"
        }.joined(separator: "\n")

        let summary = summarizer.summarize(entries: entries, periodName: "this week")
        let avgMood = String(format: "%.1f", summary.averageMoodScore)

        return """
        Generate a weekly emotional digest for \(formatter.string(from: weekStart)) - \(formatter.string(from: weekEnd)):

        \(moodList)

        Average mood: \(avgMood)/5, Trend: \(summary.recentTrend), Stability: \(String(format: "%.0f", summary.moodStabilityScore * 100))%
        Current streak: \(summary.currentLoggingStreak) days

        Write a warm, personalized weekly digest.
        """
    }
}