import SwiftUI

/// "Ask Your Bookmarks" — the on-device RAG surface. Questions are answered by
/// Apple's on-device model, grounded in the user's bookmarks via Spotlight.
struct AskView: View {
    @State private var assistant = BookmarkAssistant()
    @State private var question = ""
    @State private var answer = ""
    @State private var isLoading = false
    @State private var errorText: String?
    @Environment(\.dismiss) private var dismiss
    @FocusState private var focused: Bool

    var body: some View {
        NavigationStack {
            Group {
                switch assistant.status {
                case .checking:
                    ProgressView()
                case .unavailable(let message):
                    PaperEmptyState(
                        title: "Unavailable",
                        systemImage: "sparkles.slash",
                        message: message
                    )
                case .ready:
                    ready
                }
            }
            .paperSurface()
            .navigationTitle("Ask Your Bookmarks")
            .navigationBarTitleDisplayMode(.inline)
            .toolbar {
                ToolbarItem(placement: .topBarTrailing) {
                    Button("Done") { dismiss() }
                        .font(PaperType.label)
                        .tint(Paper.accent)
                }
            }
        }
    }

    private var ready: some View {
        VStack(spacing: 0) {
            ScrollView {
                VStack(alignment: .leading, spacing: 16) {
                    if answer.isEmpty && !isLoading && errorText == nil {
                        PaperEmptyState(
                            title: "Ask anything",
                            systemImage: "sparkles",
                            message: "Answers come from your saved bookmarks, generated on-device."
                        )
                        .padding(.top, 40)
                    }
                    if isLoading {
                        HStack(spacing: 8) {
                            ProgressView()
                            Text("Searching your bookmarks…")
                                .font(PaperType.meta)
                                .foregroundStyle(Paper.secondary)
                        }
                    }
                    if !answer.isEmpty {
                        MarkdownAnswer(text: answer)
                            .textSelection(.enabled)
                            .frame(maxWidth: .infinity, alignment: .leading)
                    }
                    if let errorText {
                        Text(errorText)
                            .font(PaperType.meta)
                            .foregroundStyle(Paper.alarm)
                    }
                }
                .padding()
            }

            HStack(spacing: 10) {
                TextField("Ask about your bookmarks…", text: $question, axis: .vertical)
                    .font(PaperType.body)
                    .foregroundStyle(Paper.ink)
                    .lineLimit(1...4)
                    .focused($focused)
                    .submitLabel(.send)
                    .onSubmit(send)
                Button(action: send) {
                    Image(systemName: "arrow.up.circle.fill")
                        .font(.system(size: 26))
                        .foregroundStyle(Paper.accent)
                }
                .disabled(question.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty || isLoading)
            }
            .padding()
            .background(Paper.raised)
            .overlay(alignment: .top) {
                Rectangle().fill(Paper.rule.opacity(0.5)).frame(height: 0.6)
            }
        }
        .onAppear { focused = true }
    }

    private func send() {
        let q = question.trimmingCharacters(in: .whitespacesAndNewlines)
        guard !q.isEmpty, !isLoading else { return }
        question = ""
        answer = ""
        errorText = nil
        isLoading = true
        Task {
            do {
                answer = try await assistant.ask(q)
            } catch {
                errorText = error.localizedDescription
            }
            isLoading = false
        }
    }
}

/// Renders the model's answer as lightweight Markdown. SwiftUI's `Text` only
/// parses *inline* Markdown (bold/italic/code/links), so we split into block
/// elements — headings, bullet/numbered lists, paragraphs — and lay them out,
/// applying inline parsing per line.
private struct MarkdownAnswer: View {
    let text: String

    private enum Block: Hashable { case heading(String), bullet(String), paragraph(String) }

    var body: some View {
        VStack(alignment: .leading, spacing: 10) {
            ForEach(Array(blocks.enumerated()), id: \.offset) { _, block in
                switch block {
                case .heading(let line):
                    inline(line).font(PaperType.heading)
                case .bullet(let line):
                    HStack(alignment: .firstTextBaseline, spacing: 8) {
                        Text("•").foregroundStyle(Paper.tertiary)
                        inline(line).font(PaperType.body)
                    }
                case .paragraph(let line):
                    inline(line).font(PaperType.body)
                }
            }
        }
    }

    private var blocks: [Block] {
        text.split(separator: "\n", omittingEmptySubsequences: true).map { raw in
            let line = raw.trimmingCharacters(in: .whitespaces)
            if let r = line.range(of: "^#{1,6}\\s+", options: .regularExpression) {
                return .heading(String(line[r.upperBound...]))
            }
            if let r = line.range(of: "^([-*+]|\\d+\\.)\\s+", options: .regularExpression) {
                return .bullet(String(line[r.upperBound...]))
            }
            return .paragraph(line)
        }
    }

    private func inline(_ s: String) -> Text {
        let opts = AttributedString.MarkdownParsingOptions(interpretedSyntax: .inlineOnlyPreservingWhitespace)
        if let attr = try? AttributedString(markdown: s, options: opts) {
            return Text(attr)
        }
        return Text(s)
    }
}