//
//  WebPageProxy.swift
//  Prisme
//
//  Author: Simon-Pierre Boucher <contact@spboucher.ai>
//

import Foundation
import Observation
import WebKit

/// The only surface through which the rest of the app talks to a web page.
/// `WKWebView` itself never escapes `Browser/Engine` (CLAUDE.md §9): chrome
/// and tabs read observable state here and issue commands through it.
@MainActor
@Observable
final class WebPageProxy {
    /// The pooled web view currently rendering this page, if any.
    /// Set by the engine while the owning tab is on screen.
    @ObservationIgnored weak var webView: WKWebView?

    /// Fired by the engine when a main-frame load finishes. The app layer
    /// hooks history recording here; the engine stays ignorant of it.
    @ObservationIgnored var onDidFinishLoad: ((URL) -> Void)?

    /// Fired when the user picks "Sauver l'extrait" in the selection menu.
    @ObservationIgnored var onExcerptRequested: (() -> Void)?

    private(set) var url: URL?
    private(set) var title: String = ""
    private(set) var estimatedProgress: Double = 0
    private(set) var isLoading = false
    private(set) var canGoBack = false
    private(set) var canGoForward = false

    // MARK: Commands

    func load(_ url: URL) {
        webView?.load(URLRequest(url: url))
    }

    func goBack() { webView?.goBack() }
    func goForward() { webView?.goForward() }
    func reload() { webView?.reload() }
    func stopLoading() { webView?.stopLoading() }

    // MARK: Content extraction (Distiller steps 1–2, in-page)

    enum PageError: LocalizedError {
        case notAttached
        case extractionFailed

        var errorDescription: String? {
            switch self {
            case .notAttached: "L'onglet n'est pas affiché."
            case .extractionFailed: "Le contenu de la page n'a pas pu être lu."
            }
        }
    }

    /// Runs the injected extractor and returns the typed block list.
    /// Never returns raw HTML (CLAUDE.md §4).
    func extractContent() async throws -> ExtractedContent {
        guard let webView else { throw PageError.notAttached }
        let result = try await webView.evaluateJavaScript("window.__prismeExtract(400)")
        guard let json = result as? String, let data = json.data(using: .utf8) else {
            throw PageError.extractionFailed
        }
        return try JSONDecoder().decode(ExtractedContent.self, from: data)
    }

    /// The user's current text selection, with source anchor and section
    /// context. Nil when nothing is selected.
    func captureSelection() async throws -> SelectionExcerpt? {
        guard let webView else { throw PageError.notAttached }
        let result = try await webView.evaluateJavaScript("window.__prismeSelection()")
        guard let json = result as? String, let data = json.data(using: .utf8) else {
            return nil
        }
        return try? JSONDecoder().decode(SelectionExcerpt.self, from: data)
    }

    /// Scrolls the page to the DOM element a digest item was derived from —
    /// the anchor that keeps generated content honest (§7).
    func scrollToBlock(domPath: String) {
        let escaped = domPath.replacingOccurrences(of: "'", with: "")
        webView?.evaluateJavaScript("window.__prismeScrollTo('\(escaped)')")
    }

    // MARK: Engine-side state sync

    func sync(from webView: WKWebView) {
        url = webView.url
        title = webView.title ?? ""
        estimatedProgress = webView.estimatedProgress
        isLoading = webView.isLoading
        canGoBack = webView.canGoBack
        canGoForward = webView.canGoForward
    }

    func resetTransientState() {
        estimatedProgress = 0
        isLoading = false
    }
}