import Foundation
import Observation

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

    let list: PagedListModel<Issue>
    let repoPath: String
    private let client: GitbayClient
    var filter = IssueFilter() {
        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.
            var typed = oldValue
            typed.search = filter.search
            typed.author = filter.author
            typed.assignee = filter.assignee
            if typed == filter {
                scheduleSearchReload()
            } else {
                reloadTask?.cancel()
                reloadTask = Task { await list.reload() }
            }
        }
    }

    /// This repository's labels, loaded beside the issues: the names for
    /// a picker, the colours for the chips. A failure here is not fatal —
    /// every chip then derives its colour from its name.
    private(set) var labels: [IssueLabel] = []
    private(set) var colors = LabelColors()
    /// Labels rarely change mid-session: fetch them once per view model,
    /// not on every reload.
    private var labelsLoaded = false

    /// 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: ["issue", "list", repoPath] + IssueFilter().flags(),
            emptyMessage: IssueFilter().emptyMessage
        )
    }

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

    func load() async {
        reloadTask?.cancel()
        await list.reload()
        if case .failed = list.state { return }
        guard !labelsLoaded else { return }
        labelsLoaded = true
        labels = await labelList()
        colors = LabelColors(labels)
    }

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

    private func labelList() async -> [IssueLabel] {
        (try? await client.readList(["label", "list", repoPath], of: IssueLabel.self)) ?? []
    }

    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 = ["issue", "list", repoPath] + filter.flags()
        list.emptyMessage = filter.emptyMessage
    }
}