Gemini/Gemini-iOS/TableOfContentsView.swift

//
//  TableOfContentsView.swift
//  Gemini-iOS
//
//  Created by Shadowfacts on 12/20/20.
//

import SwiftUI
import GeminiFormat

struct TableOfContentsView: View {
    private let entries: [Entry]
    private let close: (Int?) -> Void
    
    init(document: Document, close: @escaping (Int?) -> Void) {
        let toc = TableOfContents(document: document)
        self.entries = toc.entries.flatMap { TableOfContentsView.flattenToCEntry($0) }
        self.close = close
    }
    
    private static func flattenToCEntry(_ e: TableOfContents.Entry, depth: Int = 0) -> [Entry] {
        guard case let .heading(text, level: _) = e.line else { fatalError() }
        var entries = e.children.flatMap {
            flattenToCEntry($0, depth: depth + 1)
        }
        entries.insert(Entry(title: text, lineIndex: e.lineIndex, depth: depth), at: 0)
        return entries
    }
    
    var body: some View {
        NavigationView {
            List(Array(entries.enumerated()), id: \.0) { (a) in
                Button {
                    close(a.1.lineIndex)
                } label: {
                    HStack(spacing: 0) {
                        Spacer()
                            .frame(width: CGFloat(a.1.depth * 25))
                        Text(verbatim: a.1.title)
                    }
                }
            }
            .listStyle(PlainListStyle())
            .navigationBarTitle("Table of Contents", displayMode: .inline)
            .navigationBarItems(leading: Button("Cancel", action: {
                close(nil)
            }))
        }
        .navigationViewStyle(StackNavigationViewStyle())
    }
}

extension TableOfContentsView {
    struct Entry {
        let title: String
        let lineIndex: Int
        let depth: Int
    }
}

struct TableOfContentsView_Previews: PreviewProvider {
    static var previews: some View {
        TableOfContentsView(document: Document(url: URL(string: "gemini://example.com")!, lines: [])) { (_) in }
    }
}