import SwiftUI

/// 搜索页 - 对应 Android 版 SearchActivity
struct SearchView: View {
    /// 搜索状态与结果管理。
    @StateObject private var viewModel = SearchViewModel()
    
    #if os(iOS)
    /// iOS 卡片网格参数。
    private let columns = [
        GridItem(.adaptive(minimum: 120, maximum: 160), spacing: 12)
    ]
    #else
    /// macOS 卡片网格参数。
    private let columns = [
        GridItem(.adaptive(minimum: 140, maximum: 180), spacing: 16)
    ]
    #endif
    
    var body: some View {
        NavigationStack {
            VStack(spacing: 0) {
                // 搜索栏
                searchBar
                
                // 内容
                if viewModel.isSearching {
                    Spacer()
                    ProgressView("搜索中...")
                        .tint(.orange)
                    Spacer()
                } else if !viewModel.results.isEmpty {
                    searchResults
                } else if viewModel.keyword.isEmpty {
                    // 输入为空时显示历史；输入非空但无结果时显示提示文案。
                    searchHistorySection
                } else if let error = viewModel.errorMessage {
                    Spacer()
                    VStack(spacing: 8) {
                        Image(systemName: "magnifyingglass")
                            .font(.largeTitle)
                            .foregroundColor(.gray)
                        Text(error)
                            .font(.subheadline)
                            .foregroundColor(.secondary)
                    }
                    Spacer()
                }
            }
            .background(Color(red: 0.08, green: 0.08, blue: 0.1))
            .navigationTitle("搜索")
            #if os(iOS)
            .navigationBarTitleDisplayMode(.inline)
            #endif
        }
    }
    
    // MARK: - 搜索栏
    
    /// 顶部搜索输入区。
    private var searchBar: some View {
        HStack(spacing: 12) {
            HStack(spacing: 10) {
                Image(systemName: "magnifyingglass")
                    .font(.system(size: 16, weight: .semibold))
                    .foregroundColor(.white.opacity(0.8))
                
                TextField("搜索影片...", text: $viewModel.keyword)
                    .textFieldStyle(.plain)
                    .font(.system(size: 16))
                    .foregroundColor(.white)
                    .submitLabel(.search)
                    .onSubmit {
                        Task { await viewModel.search() }
                    }
                    #if os(iOS)
                    .autocapitalization(.none)
                    #endif
                
                if !viewModel.keyword.isEmpty {
                    Button {
                        withAnimation {
                            viewModel.keyword = ""
                            viewModel.results = []
                        }
                    } label: {
                        Image(systemName: "xmark.circle.fill")
                            .foregroundColor(.white.opacity(0.4))
                    }
                    .buttonStyle(.plain)
                }
            }
            .padding(.horizontal, 16)
            .padding(.vertical, 12)
            .background(Color.white.opacity(0.05))
            .cornerRadius(16)
            .overlay(
                RoundedRectangle(cornerRadius: 16)
                    .stroke(LinearGradient(colors: [.orange.opacity(0.5), .clear], startPoint: .topLeading, endPoint: .bottomTrailing), lineWidth: 1)
            )
            
            Button {
                Task { await viewModel.search() }
            } label: {
                Text("搜索")
                    .font(.system(size: 15, weight: .bold))
                    .foregroundColor(.white)
                    .padding(.horizontal, 16)
                    .padding(.vertical, 12)
                    .background(LinearGradient(colors: [.orange, .red], startPoint: .leading, endPoint: .trailing))
                    .cornerRadius(14)
            }
            .buttonStyle(.plain)
        }
        .padding(.horizontal, 20)
        .padding(.top, 20)
        .padding(.bottom, 10)
    }
    
    // MARK: - 搜索结果
    
    /// 搜索结果网格。
    private var searchResults: some View {
        ScrollView {
            LazyVGrid(columns: columns, spacing: 16) {
                ForEach(viewModel.results) { video in
                    NavigationLink(value: video) {
                        VodCardView(video: video)
                    }
                    .buttonStyle(.plain)
                }
            }
            .padding(.horizontal, 20)
            .padding(.vertical, 12)
        }
        .navigationDestination(for: Movie.Video.self) { video in
            DetailView(video: video)
        }
    }
    
    // MARK: - 搜索历史
    
    /// 搜索历史区域，支持复用历史关键词与一键清空。
    private var searchHistorySection: some View {
        VStack(alignment: .leading, spacing: 12) {
            if !viewModel.searchHistory.isEmpty {
                HStack {
                    Text("搜索历史")
                        .font(.headline)
                        .foregroundColor(.white)
                    Spacer()
                    Button {
                        viewModel.clearHistory()
                    } label: {
                        HStack(spacing: 4) {
                            Image(systemName: "trash")
                            Text("清空")
                        }
                        .font(.caption)
                        .foregroundColor(.gray)
                    }
                }
                .padding(.horizontal, 20)
                .padding(.top, 16)
                
                FlowLayout(spacing: 8) {
                    ForEach(viewModel.searchHistory, id: \.self) { keyword in
                        Button {
                            viewModel.keyword = keyword
                            Task { await viewModel.search() }
                        } label: {
                            Text(keyword)
                                .font(.subheadline)
                                .foregroundColor(.white.opacity(0.8))
                                .padding(.horizontal, 14)
                                .padding(.vertical, 7)
                                .background(Color.white.opacity(0.1))
                                .cornerRadius(16)
                        }
                        .buttonStyle(.plain)
                    }
                }
                .padding(.horizontal, 20)
            }
            
            Spacer()
        }
    }
}

/// 流式布局
struct FlowLayout: Layout {
    /// 子项间距。
    var spacing: CGFloat = 8
    
    /// 计算整体尺寸。
    func sizeThatFits(proposal: ProposedViewSize, subviews: Subviews, cache: inout ()) -> CGSize {
        let result = arrangement(proposal: proposal, subviews: subviews)
        return result.size
    }
    
    /// 按计算结果放置子视图。
    func placeSubviews(in bounds: CGRect, proposal: ProposedViewSize, subviews: Subviews, cache: inout ()) {
        let result = arrangement(proposal: ProposedViewSize(width: bounds.width, height: bounds.height), subviews: subviews)
        for (index, position) in result.positions.enumerated() {
            subviews[index].place(at: CGPoint(x: bounds.minX + position.x, y: bounds.minY + position.y), proposal: .unspecified)
        }
    }
    
    /// 核心排版算法：按最大宽度逐个放置，超宽后自动换行。
    private func arrangement(proposal: ProposedViewSize, subviews: Subviews) -> (size: CGSize, positions: [CGPoint]) {
        let maxWidth = proposal.width ?? .infinity
        var positions: [CGPoint] = []
        var currentX: CGFloat = 0
        var currentY: CGFloat = 0
        var lineHeight: CGFloat = 0
        var maxX: CGFloat = 0
        
        for subview in subviews {
            let size = subview.sizeThatFits(.unspecified)
            if currentX + size.width > maxWidth && currentX > 0 {
                currentX = 0
                currentY += lineHeight + spacing
                lineHeight = 0
            }
            positions.append(CGPoint(x: currentX, y: currentY))
            lineHeight = max(lineHeight, size.height)
            currentX += size.width + spacing
            maxX = max(maxX, currentX)
        }
        
        return (CGSize(width: maxX, height: currentY + lineHeight), positions)
    }
}