import Foundation
import SwiftData

/// Builds starter Splits from the bundled YAML exercise catalog, grouped by the
/// catalog's `split` label (Upper Body / Core / Lower Body). Written on demand
/// (never auto-seeded) through the SyncEngine — an empty cache at launch can't be
/// told apart from an iCloud library that simply hasn't downloaded yet.
enum SplitSeeder {
    /// Visual theme per starter split group, in display order.
    private static let groups: [(name: String, color: String, icon: String)] = [
        ("Upper Body", "blue", "figure.strengthtraining.traditional"),
        ("Core", "orange", "figure.core.training"),
        ("Lower Body", "green", "figure.run"),
    ]

    /// Default split source catalog (most universally applicable).
    private static let sourceFile = "bodyweight-starter.exercises.yaml"

    /// Builds the default split documents (fresh ULIDs each call).
    static func defaultSplitDocuments() -> [SplitDocument] {
        let lists = ExerciseListLoader.loadExerciseLists()
        guard let catalog = lists[sourceFile] else { return [] }

        var docs: [SplitDocument] = []
        for (order, group) in groups.enumerated() {
            let items = catalog.exercises.filter { $0.split == group.name }
            guard !items.isEmpty else { continue }

            let exercises = items.enumerated().map { idx, item in
                ExerciseDocument(
                    id: ULID.make(), name: item.name, order: idx,
                    sets: 3, reps: 10, weight: 0, loadType: LoadType.weight.rawValue,
                    durationSeconds: 0, weightLastUpdated: nil, weightReminderWeeks: 2
                )
            }
            docs.append(SplitDocument(
                schemaVersion: SplitDocument.currentSchema, id: ULID.make(),
                name: group.name, color: group.color, systemImage: group.icon, order: order,
                createdAt: Date(), updatedAt: Date(), exercises: exercises
            ))
        }
        return docs
    }

    /// Writes any starter splits whose name doesn't already exist, appended after
    /// existing splits. Idempotent against double-taps / partial prior seeds.
    @MainActor
    static func seedDefaults(into context: ModelContext, using sync: SyncEngine) async {
        let existing = (try? context.fetch(FetchDescriptor<Split>())) ?? []
        let existingNames = Set(existing.map(\.name))
        let base = existing.count

        let fresh = defaultSplitDocuments().filter { !existingNames.contains($0.name) }
        for (offset, var doc) in fresh.enumerated() {
            doc.order = base + offset
            await sync.save(split: doc)
        }
    }
}