//
//  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
    var albumArtistsOnly: Bool = false
    @State private var errorMessage: String?
    @State private var showError = false
    @State private var scrollPosition: String?

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

    private var isLoading: Bool {
        albumArtistsOnly ? service.libraryManager.isLoadingAlbumArtists : service.libraryManager.isLoadingArtists
    }

    private let columns = [
        GridItem(.flexible(), spacing: 8),
        GridItem(.flexible(), spacing: 8),
        GridItem(.flexible(), 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 }
    }

    // Always show A–Z plus # so the sidebar has a consistent full height
    private let allLetters: [String] = (65...90).map { String(UnicodeScalar($0)!) } + ["#"]

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

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

                    if isLoading {
                        ProgressView()
                            .frame(maxWidth: .infinity)
                            .padding()
                    }
                }
                .padding(.trailing, 28)
            }
            .scrollPosition(id: $scrollPosition)
            .overlay(alignment: .trailing) {
                AlphabetIndexView(
                    letters: allLetters,
                    itemHeight: 17,
                    onSelect: { letter in
                        let target = "section-\(letter)"
                        scrollPosition = target
                        proxy.scrollTo(target, anchor: .top)
                    }
                )
                .padding(.vertical, 8)
                .padding(.trailing, 2)
            }
        }
        .refreshable {
            await loadArtists(refresh: true)
        }
        .task {
            if artists.isEmpty {
                await loadArtists(refresh: true)
            }
        }
        .alert("Error", isPresented: $showError) {
            Button("OK", role: .cancel) { }
        } message: {
            if let errorMessage {
                Text(errorMessage)
            }
        }
        .overlay {
            if artists.isEmpty && !isLoading {
                ContentUnavailableView(
                    albumArtistsOnly ? "No Album Artists" : "No Artists",
                    systemImage: "music.mic",
                    description: Text(albumArtistsOnly
                        ? "Your library doesn't contain any album artists yet"
                        : "Your library doesn't contain any artists yet")
                )
            }
        }
    }

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

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

// MARK: - Alphabet Index

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

    @State private var activeLetter: String?

    var body: some View {
        VStack(spacing: 0) {
            ForEach(letters, id: \.self) { letter in
                Text(letter)
                    .font(.system(size: min(13, itemHeight * 0.65), weight: .bold))
                    .frame(width: 20, height: itemHeight)
                    .padding(.top, letter == "#" ? 6 : 0)
                    .foregroundStyle(activeLetter == letter ? .white : .accentColor)
                    .background {
                        if activeLetter == letter {
                            Circle()
                                .fill(Color.accentColor)
                                .frame(width: min(18, itemHeight - 2), height: min(18, itemHeight - 2))
                        }
                    }
            }
        }
        .contentShape(Rectangle())
        .gesture(
            DragGesture(minimumDistance: 0)
                .onChanged { value in
                    let safeHeight = max(1, itemHeight)
                    let index = Int(value.location.y / safeHeight)
                    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
                }
        )
    }
}

// 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: 256)) { image in
                image
                    .resizable()
                    .aspectRatio(contentMode: .fill)
            } placeholder: {
                Circle()
                    .fill(Color.gray.opacity(0.2))
                    .overlay {
                        Image(systemName: "music.mic")
                            .font(.system(size: 30))
                            .foregroundStyle(.secondary)
                    }
            }
            .aspectRatio(1, contentMode: .fit)
            .clipShape(Circle())
            .overlay(alignment: .bottomTrailing) {
                if service.libraryManager.isFavorite(uri: artist.uri) {
                    Image(systemName: "heart.fill")
                        .font(.system(size: 12))
                        .foregroundStyle(.red)
                        .padding(4)
                }
            }

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

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