import SwiftUI

struct PageListView: View {

    @Environment(\.language)
    private var language

    @EnvironmentObject
    private var content: Content

    @State
    private var selected: Page?

    @State
    private var showNewPageView = false

    @State
    private var newPageId = ""

    @State
    private var newPageIdIsValid = false

    private let allowedCharactersInPageId = CharacterSet.alphanumerics.union(CharacterSet(charactersIn: "-")).inverted

    private var cleanPageId: String {
        newPageId.trimmingCharacters(in: .whitespacesAndNewlines)
    }

    var body: some View {
        NavigationSplitView {
            List(content.pages, selection: $selected) { page in
                Text(page.localized(in: language).title)
                    .tag(page)
            }
            .toolbar {
                ToolbarItem(placement: .primaryAction) {
                    Button(action: { showNewPageView = true }) {
                        Label("New post", systemSymbol: .plus)
                    }
                }
            }
            .navigationSplitViewColumnWidth(min: 300, ideal: 300, max: 300)
        } content: {
            if let selected {
                PageContentView(page: selected, language: language)
                    .id(selected.id + language.rawValue)
                    .layoutPriority(1)
            } else {
                // Fallback if no item is selected
                Text("Select a page from the list")
                    .font(.largeTitle)
                    .foregroundColor(.secondary)
            }
        } detail: {
            if let selected {
                PageDetailView(page: selected)
                    .frame(maxWidth: 350)
            } else {
                EmptyView()
                    .frame(maxWidth: 350)
            }
        }
        .onAppear {
            if selected == nil {
                selected = content.pages.first
            }
        }
        .sheet(isPresented: $showNewPageView,
               onDismiss: addNewPage) {
            TextEntrySheet(
                title: "Enter the id for the new page",
                text: $newPageId,
                isValid: $newPageIdIsValid)
        }
    }

    private func isValid(id: String) -> Bool {
        let id = cleanPageId
        guard id != "" else {
            return false
        }

        guard !content.pages.contains(where: { $0.id == id }) else {
            return false
        }
        // Only allow alphanumeric characters and hyphens
        return id.rangeOfCharacter(from: allowedCharactersInPageId) == nil
    }

    private func addNewPage() {
        let id = cleanPageId
        guard isValid(id: id) else {
            return
        }

        let page = Page(
            id: id,
            isDraft: true,
            createdDate: .now,
            startDate: .now,
            endDate: nil,
            german: .init(urlString: "seite",
                          title: "Ein Titel"),
            english: .init(urlString: "page",
                           title: "A Title"),
            tags: [])
        content.pages.insert(page, at: 0)
        selected = page
    }
}

#Preview {
    PageListView()
        .environmentObject(Content.mock)
}