import SwiftUI
import OrgSocialKit

/// Posts a `:MIGRATION:` entry to the user's feed, telling followers the feed has moved.
/// Per the Org Social spec, a migration post has body `"<old-url> <new-url>"` and is
/// indistinguishable from a regular post except that clients highlight it and should
/// prefer following the new URL going forward.
struct MigrationSheet: View {
    @Environment(\.dismiss) private var dismiss
    @AppStorage("publicFeedURL") private var publicFeedURL = ""
    @State private var newURL = ""
    @State private var isPosting = false
    @State private var errorMessage: String?
    @State private var finished = false

    var body: some View {
        NavigationStack {
            Form {
                Section {
                    HStack {
                        Text("Current URL").foregroundStyle(.secondary)
                        Spacer()
                        Text(publicFeedURL)
                            .font(.caption)
                            .foregroundStyle(.secondary)
                            .lineLimit(1)
                            .truncationMode(.middle)
                    }
                }
                Section("New feed URL") {
                    TextField("https://new.example.com/social.org", text: $newURL)
                        .autocorrectionDisabled()
                        .textInputAutocapitalization(.never)
                        .keyboardType(.URL)
                }
                if let errorMessage {
                    Section {
                        Label(errorMessage, systemImage: "exclamationmark.triangle")
                            .font(.footnote)
                            .foregroundStyle(.red)
                    }
                }
                if finished {
                    Section {
                        Label("Migration announced", systemImage: "checkmark.circle.fill")
                            .foregroundStyle(.green)
                    }
                }
            }
            .navigationTitle("Migrate account")
            .navigationBarTitleDisplayMode(.inline)
            .toolbar {
                ToolbarItem(placement: .cancellationAction) {
                    Button("Cancel") { dismiss() }
                }
                ToolbarItem(placement: .confirmationAction) {
                    if isPosting {
                        ProgressView()
                    } else {
                        Button("Post") { Task { await post() } }
                            .disabled(!canPost)
                    }
                }
            }
        }
    }

    private var canPost: Bool {
        !publicFeedURL.isEmpty
            && URL(string: publicFeedURL) != nil
            && URL(string: newURL) != nil
            && !isPosting
    }

    private func post() async {
        isPosting = true
        errorMessage = nil
        defer { isPosting = false }
        guard let feedURL = URL(string: publicFeedURL),
              let uploader = UploaderFactory.makeUploader() else {
            errorMessage = "Configure your vfile (or other upload method) first."
            return
        }
        do {
            let content = try await FeedFetcher().fetch(from: feedURL, bypassCache: true)
            let options = NewPostOptions.migration(from: publicFeedURL, to: newURL)
            let (updated, _) = try PostWriter().appendPost(to: content, feedURL: feedURL, options: options)
            try await uploader.upload(content: updated)
            FollowCoordinator.shared.updateCachedContent(updated)
            finished = true
            try? await Task.sleep(for: .seconds(1))
            dismiss()
        } catch {
            errorMessage = error.localizedDescription
        }
    }
}