import Foundation
import Observation

/// `mr list <repo> --state <s>`, paginated.
@Observable
@MainActor
final class MRListViewModel {

    let list: PagedListModel<MergeRequest>
    let repoPath: String
    private let client: GitbayClient
    var filter = MRFilter() {
        didSet {
            guard filter != oldValue else { return }
            configureList()
            // Only the free-text fields changed: debounce, so typing does
            // not fire a request per keystroke. Anything else — a picker —
            // reloads now. MRFilter has no `assignee` field: `mr list`
            // rejects it.
            var typed = oldValue
            typed.search = filter.search
            typed.author = filter.author
            if typed == filter {
                scheduleSearchReload()
            } else {
                reloadTask?.cancel()
                reloadTask = Task { await list.reload() }
            }
        }
    }

    /// Open and closed milestones for the filter picker; fetched on first use.
    private(set) var milestones: [Milestone] = []
    private var reloadTask: Task<Void, Never>?

    init(client: GitbayClient, repoPath: String) {
        self.client = client
        self.repoPath = repoPath
        list = PagedListModel(
            client: client,
            argv: ["mr", "list", repoPath] + MRFilter().flags(),
            emptyMessage: MRFilter().emptyMessage
        )
    }

    var state: LoadState<[MergeRequest]> { list.state }

    func load() async {
        reloadTask?.cancel()
        await list.reload()
    }

    /// The list's `.task`: reads only while nothing is shown yet.
    func loadIfNeeded() async {
        guard list.needsLoad else { return }
        await load()
    }

    func loadMilestones() async {
        guard milestones.isEmpty else { return }
        milestones = (try? await client.readList(
            ["milestone", "list", repoPath, "--state", "all"], of: Milestone.self
        )) ?? []
    }

    /// The repository's labels for the filter picker and its chips;
    /// fetched on first use, like the milestones.
    private(set) var labels: [IssueLabel] = []
    private(set) var colors = LabelColors()
    private var labelsLoaded = false

    func loadLabels() async {
        guard !labelsLoaded else { return }
        labelsLoaded = true
        labels = (try? await client.readList(["label", "list", repoPath], of: IssueLabel.self)) ?? []
        colors = LabelColors(labels)
    }

    private func scheduleSearchReload() {
        reloadTask?.cancel()
        reloadTask = Task {
            guard (try? await Task.sleep(for: .milliseconds(300))) != nil else { return }
            guard !Task.isCancelled else { return }
            await list.reload()
        }
    }

    private func configureList() {
        list.argv = ["mr", "list", repoPath] + filter.flags()
        list.emptyMessage = filter.emptyMessage
    }
}