import Foundation

// MARK: - BrowseViewModel
// Powers both the Discover shelves (BrowseView) and the full paginated grid (BrowseCategoryView).
// Uses @Observable (iOS 17+).

@Observable
@MainActor
final class BrowseViewModel {

    // MARK: - Discover shelves (BrowseView)

    var trending: [BrowseNovel] = []
    var newReleases: [BrowseNovel] = []
    var recentlyUpdated: [BrowseNovel] = []
    var ranking: [BrowseNovel] = []

    // MARK: - Paginated grid (BrowseCategoryView)

    var novels: [BrowseNovel] = []
    var currentPage = 1
    var hasNext = false

    // Filter params (BrowseCategoryView sets these before calling loadFirstPage)
    var sort: String   = "popular"
    var genre: String  = "all"
    var status: String = "all"

    // MARK: - UI state

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

    // MARK: - Discover load (fetches multiple shelves in parallel)

    func loadShelves() async {
        isLoading = true
        error = nil

        do {
            async let trendingTask       = APIClient.shared.browse(page: 1, genre: "all",   sort: "popular",  status: "all")
            async let newTask            = APIClient.shared.browse(page: 1, genre: "all",   sort: "new",      status: "all")
            async let updatedTask        = APIClient.shared.browse(page: 1, genre: "all",   sort: "update",   status: "all")
            async let rankingTask        = APIClient.shared.ranking()

            let (trendingResp, newResp, updatedResp, rankItems) = try await (
                trendingTask, newTask, updatedTask, rankingTask
            )

            trending        = Array(trendingResp.novels.prefix(12))
            newReleases     = Array(newResp.novels.prefix(12))
            recentlyUpdated = Array(updatedResp.novels.prefix(12))
            ranking         = rankItems.prefix(12).map { item in
                BrowseNovelFromRanking(item)
            }
        } catch {
            if !(error is CancellationError) {
                self.error = error.localizedDescription
            }
        }
        isLoading = false
    }

    // MARK: - Paginated category load

    func loadFirstPage() async {
        guard !isLoading else { return }
        novels = []
        currentPage = 1
        hasNext = false
        isLoading = true
        error = nil

        do {
            let resp = try await APIClient.shared.browse(
                page: 1, genre: genre, sort: sort, status: status)
            novels      = resp.novels
            currentPage = resp.page
            hasNext     = resp.hasNext
        } catch {
            if !(error is CancellationError) {
                self.error = error.localizedDescription
            }
        }
        isLoading = false
    }

    func loadNextPage() async {
        guard hasNext, !isLoadingMore, !isLoading else { return }
        isLoadingMore = true

        let next = currentPage + 1
        do {
            let resp = try await APIClient.shared.browse(
                page: next, genre: genre, sort: sort, status: status)
            novels      += resp.novels
            currentPage  = resp.page
            hasNext      = resp.hasNext
        } catch {
            // Silently ignore — user can scroll again
        }
        isLoadingMore = false
    }

    // MARK: - Ranking load (for rank sort mode)

    func loadRanking() async {
        guard !isLoading else { return }
        novels = []
        hasNext = false
        isLoading = true
        error = nil

        do {
            let items = try await APIClient.shared.ranking()
            novels = items.map { BrowseNovelFromRanking($0) }
        } catch {
            if !(error is CancellationError) {
                self.error = error.localizedDescription
            }
        }
        isLoading = false
    }
}

// MARK: - RankingItem → BrowseNovel adapter

private func BrowseNovelFromRanking(_ item: RankingItem) -> BrowseNovel {
    // Synthesise a minimal JSON blob so we can decode via the standard init
    let rankStr = "#\(item.rank)"
    let dict: [String: Any] = [
        "slug":    item.slug,
        "title":   item.title,
        "cover":   item.cover,
        "rank":    rankStr,
        "rating":  "",
        "chapters": "",
        "url":     item.sourceURL,
        "author":  item.author,
        "status":  item.status,
        "genres":  item.genres
    ]
    let data = try! JSONSerialization.data(withJSONObject: dict)
    return try! JSONDecoder.apiDecoder.decode(BrowseNovel.self, from: data)
}