//
//  ArtistsView.swift
//  Mobile Music Assistant
//
//  Created by Sven Hanold on 26.03.26.
//

import SwiftUI
import UIKit

struct ArtistsView: View {
    @Environment(MAService.self) private var service
    @State private var errorMessage: String?
    @State private var showError = false

    private var artists: [MAArtist] {
        service.libraryManager.artists
    }

    private var isLoading: Bool {
        service.libraryManager.isLoadingArtists
    }

    private let columns = [
        GridItem(.adaptive(minimum: 80), spacing: 8)
    ]

    /// Artists grouped by first letter; non-alphabetic names go under "#"
    private var artistsByLetter: [(String, [MAArtist])] {
        let grouped = Dictionary(grouping: artists) { artist -> String in
            let first = artist.name.prefix(1).uppercased()
            return first.first?.isLetter == true ? String(first) : "#"
        }
        return grouped.sorted {
            if $0.key == "#" { return false }
            if $1.key == "#" { return true }
            return $0.key < $1.key
        }
    }

    private var availableLetters: [String] {
        artistsByLetter.map { $0.0 }
    }

    var body: some View {
        ScrollViewReader { proxy in
            ZStack(alignment: .trailing) {
                ScrollView {
                    LazyVStack(alignment: .leading, spacing: 0) {
                        ForEach(artistsByLetter, id: \.0) { letter, letterArtists in
                            // Section header
                            Text(letter)
                                .font(.headline)
                                .fontWeight(.bold)
                                .foregroundStyle(.secondary)
                                .padding(.horizontal, 12)
                                .padding(.top, 10)
                                .padding(.bottom, 4)
                                .id(letter)

                            // Grid of artists in this section
                            LazyVGrid(columns: columns, spacing: 8) {
                                ForEach(letterArtists) { artist in
                                    NavigationLink(value: artist) {
                                        ArtistGridItem(artist: artist)
                                    }
                                    .buttonStyle(.plain)
                                    .task {
                                        await loadMoreIfNeeded(currentItem: artist)
                                    }
                                }
                            }
                            .padding(.horizontal, 12)
                            .padding(.bottom, 4)
                        }

                        if isLoading {
                            ProgressView()
                                .frame(maxWidth: .infinity)
                                .padding()
                        }
                    }
                    // Right padding leaves room for the alphabet index
                    .padding(.trailing, 24)
                }

                // Floating alphabet index on the right edge
                if !availableLetters.isEmpty {
                    AlphabetIndexView(letters: availableLetters) { letter in
                        proxy.scrollTo(letter, anchor: .top)
                    }
                    .padding(.trailing, 2)
                }
            }
        }
        .refreshable {
            await loadArtists(refresh: true)
        }
        .task {
            await loadArtists(refresh: !artists.isEmpty)
        }
        .alert("Error", isPresented: $showError) {
            Button("OK", role: .cancel) { }
        } message: {
            if let errorMessage {
                Text(errorMessage)
            }
        }
        .overlay {
            if artists.isEmpty && !isLoading {
                ContentUnavailableView(
                    "No Artists",
                    systemImage: "music.mic",
                    description: Text("Your library doesn't contain any artists yet")
                )
            }
        }
    }

    private func loadArtists(refresh: Bool) async {
        do {
            try await service.libraryManager.loadArtists(refresh: refresh)
        } catch {
            errorMessage = error.localizedDescription
            showError = true
        }
    }

    private func loadMoreIfNeeded(currentItem: MAArtist) async {
        do {
            try await service.libraryManager.loadMoreArtistsIfNeeded(currentItem: currentItem)
        } catch {
            errorMessage = error.localizedDescription
            showError = true
        }
    }
}

// MARK: - Alphabet Index

struct AlphabetIndexView: View {
    let letters: [String]
    let onSelect: (String) -> Void

    @State private var activeLetter: String?

    var body: some View {
        GeometryReader { geometry in
            let itemHeight = geometry.size.height / CGFloat(letters.count)

            ZStack {
                // Touch-responsive column
                VStack(spacing: 0) {
                    ForEach(letters, id: \.self) { letter in
                        Text(letter)
                            .font(.system(size: 11, weight: .bold))
                            .frame(width: 20, height: itemHeight)
                            .foregroundStyle(activeLetter == letter ? .white : .accentColor)
                            .background {
                                if activeLetter == letter {
                                    Circle()
                                        .fill(Color.accentColor)
                                        .frame(width: 18, height: 18)
                                }
                            }
                    }
                }
                .gesture(
                    DragGesture(minimumDistance: 0)
                        .onChanged { value in
                            let index = Int(value.location.y / itemHeight)
                            let clamped = max(0, min(letters.count - 1, index))
                            let letter = letters[clamped]
                            if activeLetter != letter {
                                activeLetter = letter
                                onSelect(letter)
                                UISelectionFeedbackGenerator().selectionChanged()
                            }
                        }
                        .onEnded { _ in
                            activeLetter = nil
                        }
                )
            }
        }
        .frame(width: 20)
    }
}

// MARK: - Artist Grid Item

struct ArtistGridItem: View {
    @Environment(MAService.self) private var service
    let artist: MAArtist

    var body: some View {
        VStack(spacing: 4) {
            CachedAsyncImage(url: service.imageProxyURL(path: artist.imageUrl, provider: artist.imageProvider, size: 128)) { image in
                image
                    .resizable()
                    .aspectRatio(contentMode: .fill)
            } placeholder: {
                Circle()
                    .fill(Color.gray.opacity(0.2))
                    .overlay {
                        Image(systemName: "music.mic")
                            .font(.system(size: 22))
                            .foregroundStyle(.secondary)
                    }
            }
            .frame(width: 76, height: 76)
            .clipShape(Circle())

            Text(artist.name)
                .font(.caption)
                .fontWeight(.medium)
                .lineLimit(1)
                .multilineTextAlignment(.center)
                .foregroundStyle(.primary)
        }
    }
}

#Preview {
    NavigationStack {
        ArtistsView()
            .environment(MAService())
    }
}