Gemini/GeminiRenderer/RenderingBlockView.swift

//
//  RenderingBlockView.swift
//  GeminiRenderer
//
//  Created by Shadowfacts on 7/13/20.
//

import SwiftUI
import GeminiFormat

struct RenderingBlockView: View {
    let document: Document
    let block: RenderingBlock
    let changeURL: ((URL) -> Void)?
    @State var hovering = false
    
    @Environment(\.colorScheme) var colorScheme: ColorScheme
    
    init(document: Document, block: RenderingBlock, changeURL: ((URL) -> Void)? = nil) {
        self.document = document
        self.block = block
        self.changeURL = changeURL
    }
    
    @ViewBuilder
    var body: some View {
        switch block {
        case let .text(text):
            self.text(text)
        case let .link(url, text: linkText):
            self.link(url, text: linkText)
        case let .preformatted(text, alt: _):
            preformatted(text)
        case let .heading(text, level: level):
            heading(text, level: level)
        case let .unorderedListItem(text):
            unorderedListItem(text)
        case let .quote(text):
            quote(text)
        }
    }
    
    private func text(_ text: String) -> some View {
        Text(verbatim: text)
            .font(.documentBody)
            .frame(maxWidth: .infinity, alignment: .leading)
    }
    
    private func link(_ url: URL, text: String?) -> some View {
        let text = text ?? url.absoluteString
        
        #if os(macOS)
            let buttonStyle = LinkButtonStyle()
        #elseif os(iOS)
            let buttonStyle = PlainButtonStyle()
        #endif
        
        let imageName: String
        if url.scheme == "gemini" {
            if url.host == document.url.host {
                imageName = "arrow.right"
            } else {
                imageName = "link"
            }
        } else if url.scheme == "http" || url.scheme == "https" {
            imageName = "safari"
        } else if url.scheme == "mailto" {
            imageName = "envelope"
        } else {
            imageName = "arrow.up.left.square"
        }
        
        let button: some View = Button {
            self.changeURL?(url)
        } label: {
            HStack(alignment: .firstTextBaseline, spacing: 4) {
                maybeLinkImage(name: imageName)
                
                Text(verbatim: text)
                    .font(.documentBody)
                    .foregroundColor(colorScheme == .dark ?
                                        hovering ? Color.blue.opacity(0.8) : .blue :
                                        hovering ? .blue : Color.blue.opacity(0.8))
                    .underline()
                    .frame(maxWidth: .infinity, alignment: .leading)
            }
        }
            .buttonStyle(buttonStyle)
            .onHover { hovering in
                self.hovering = hovering
            }
        
        return button.maybeHelp(url.absoluteString)
    }
    
    private func maybeLinkImage(name: String) -> AnyView {
        // can't use availability check inside view body, since buildLimitedAvailability was introduced in iOS 14 :/
        if #available(iOS 13.0, macOS 11.0, *) {
            return AnyView(Image(systemName: name).frame(minWidth: 23, alignment: .leading))
        } else {
            return AnyView(EmptyView())
        }
    }
    
    private func preformatted(_ text: String) -> some View {
        ScrollView(.horizontal) {
            Text(verbatim: text)
                .font(.documentBodyPreformatted)
                .frame(maxWidth: .infinity, alignment: .leading)
        }
    }
    
    private func heading(_ text: String, level: Document.HeadingLevel) -> some View {
        Text(verbatim: text)
            .font(level.font)
            .frame(maxWidth: .infinity, alignment: .leading)
    }
    
    private func unorderedListItem(_ text: String) -> some View {
        // todo: should this be .firstTextBaseline?
        HStack(alignment: .top, spacing: 4) {
            Text(verbatim: "\u{2022}")
            Text(verbatim: text)
                .font(.documentBody)
            Spacer()
        }.frame(maxWidth: .infinity, alignment: .leading)
    }
    
    private func quote(_ text: String) -> some View {
        HStack(spacing: 4) {
            Color.gray
                .frame(width: 4)
            Text(verbatim: text)
                .font(Font.documentBody.italic())
                .foregroundColor(.gray)
            Spacer()
        }.frame(maxWidth: .infinity, alignment: .leading)
    }
}

struct RenderingBlockView_Previews: PreviewProvider {
    static let doc = Document(url: URL(string: "gemini://localhost/test.gmi")!, lines: [.text("Some Text"), .quote("A Quote")])
    
    static var previews: some View {
        Group {
            RenderingBlockView(document: doc, block: .text("Some Text"))
            RenderingBlockView(document: doc, block: .quote("A Quote"))
        }
    }
}