//
//  ChatTranscriptView.swift
//  kordophone2
//
//  Created by James Magahern on 8/24/25.
//

import SwiftUI

struct ChatTranscriptView: View
{
    @Binding var model: ViewModel
    
    @Environment(\.xpcClient) private var xpcClient
    
    var body: some View {
        ScrollView {
            LazyVStack(spacing: 17.0) {
                ForEach($model.messages.reversed()) { message in
                    MessageCellView(message: message)
                        .id(message.id)
                        .scaleEffect(CGSize(width: 1.0, height: -1.0))
                        .transition(
                            .push(from: .bottom)
                            .combined(with: .opacity)
                        )
                }
            }
            .padding()
        }
        .scaleEffect(CGSize(width: 1.0, height: -1.0))
        .task { await watchForMessageListChanges() }
    }
    
    private func watchForMessageListChanges() async {
        for await event in xpcClient.eventStream() {
            if case let .messagesUpdated(conversationId) = event {
                if conversationId == model.displayedConversation {
                    model.setNeedsReload()
                }
            }
        }
    }
    
    // MARK: - Types
    
    @Observable
    class ViewModel
    {
        var messages: [Display.Message]
        var displayedConversation: Display.Conversation.ID? = nil
        var needsReload: Bool = true

        init(messages: [Display.Message] = []) {
            self.messages = messages
            observeDisplayedConversation()
        }
        
        private func observeDisplayedConversation() {
            withObservationTracking {
                _ = displayedConversation
            } onChange: {
                Task { @MainActor [weak self] in
                    guard let self else { return }
                    
                    setNeedsReload()
                    observeDisplayedConversation()
                }
            }
        }

        func setNeedsReload() {
            needsReload = true
            Task { @MainActor [weak self] in
                guard let self else { return }
                await reloadMessages()
            }
        }
        
        func reloadMessages() async {
            guard needsReload else { return }
            needsReload = false
            
            guard let displayedConversation else { return }
            
            do {
                let client = XPCClient()
                let clientMessages = try await client.getMessages(conversationId: displayedConversation)
                    .map { Display.Message(from: $0) }
                
                let newMessages = Set(clientMessages).subtracting(Set(self.messages))
                
                let animation: Animation? = newMessages.count == 1 ? .default : nil
                withAnimation(animation) {
                    self.messages = clientMessages
                }
            } catch {
                print("Message fetch error: \(error)")
            }
        }
    }
}

struct MessageCellView: View
{
    @Binding var message: Display.Message
    
    var body: some View {
        VStack {
            HStack(alignment: .bottom) {
                if message.isFromMe { Spacer(minLength: .minimumBubbleHorizontalPadding) }

                TextCellContentView(text: message.text, isFromMe: message.isFromMe)
                    .mask {
                        UnevenRoundedRectangle(cornerRadii: RectangleCornerRadii(
                            topLeading: message.isFromMe ? .dominantCornerRadius : .minorCornerRadius,
                            bottomLeading: .dominantCornerRadius,
                            bottomTrailing: .dominantCornerRadius,
                            topTrailing: message.isFromMe ? .minorCornerRadius : .dominantCornerRadius,
                        ))
                    }

                if !message.isFromMe { Spacer(minLength: .minimumBubbleHorizontalPadding) }
            }
        }
    }
    
    // MARK: - Types
    
    private struct TextCellContentView: View
    {
        let text: String
        let isFromMe: Bool
        
        var body: some View {
            let bubbleColor: Color = isFromMe ? .blue : Color(.systemGray)
            let textColor: Color = isFromMe ? .white : .primary
            
            HStack {
                Text(text)
                    .foregroundStyle(textColor)
                    .multilineTextAlignment(.leading)
            }
            .fixedSize(horizontal: false, vertical: true)
            .padding(.horizontal, 16.0)
            .padding(.vertical, 10.0)
            .background(bubbleColor)
        }
    }
}

fileprivate extension CGFloat {
    static let dominantCornerRadius = 16.0
    static let minorCornerRadius = 4.0
    static let minimumBubbleHorizontalPadding = 80.0
}

#Preview {
    @Previewable @State var model = ChatTranscriptView.ViewModel(messages: [
        .init(sender: .me,                 text: "Hello, how are you?"),
        .init(sender: .counterpart("Bob"), text: "I am doing fine!")
    ])
    
    ChatTranscriptView(model: $model)
}