import Foundation

// MARK: - BookDetailViewModel
// Loads book metadata, chapter index, save state, and reading progress.
// Uses @Observable (iOS 17+).

@Observable
@MainActor
final class BookDetailViewModel {
    let slug: String

    var book: Book?
    var chapters: [ChapterIndex] = []
    var inLib: Bool = false
    var saved: Bool = false
    var lastChapter: Int?

    var isLoading = false
    var isSaving  = false
    var error: String?

    init(slug: String) {
        self.slug = slug
    }

    // MARK: - Load

    func load() async {
        guard !isLoading else { return }
        isLoading = true
        error = nil
        do {
            let response = try await APIClient.shared.bookDetail(slug: slug)
            book        = response.book
            chapters    = response.chapters
            inLib       = response.inLib
            saved       = response.saved
            lastChapter = response.lastChapter
        } catch {
            if !(error is CancellationError) {
                self.error = error.localizedDescription
            }
        }
        isLoading = false
    }

    // MARK: - Toggle saved (bookmark)

    func toggleSaved() async {
        guard !isSaving else { return }
        isSaving = true
        let targetSaved = !saved
        saved = targetSaved          // optimistic update
        do {
            if targetSaved {
                try await APIClient.shared.saveBook(slug: slug)
                if !inLib { inLib = true }
            } else {
                try await APIClient.shared.unsaveBook(slug: slug)
            }
        } catch {
            saved = !targetSaved     // revert on failure
            self.error = error.localizedDescription
        }
        isSaving = false
    }

    // MARK: - Chapter helpers

    /// Title stripped of trailing " - Month DD YYYY" date suffixes.
    func displayTitle(for chapter: ChapterIndex) -> String {
        let stripped = chapter.title.strippingTrailingDate()
        if stripped.isEmpty || stripped == "Chapter \(chapter.number)" {
            return "Chapter \(chapter.number)"
        }
        return stripped
    }
}