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

import Foundation
import WebKit

/// Reusable `WKWebView` instances, partitioned by identity container.
/// Never instantiate one web view per tab (CLAUDE.md §8): tabs check a view
/// out while visible and check it back in when they leave the screen.
@MainActor
final class WebViewPool {
    private static let maxIdlePerContainer = 3

    private let containers: IdentityContainerStore
    private let rules: ContentRuleManager

    private var idle: [IdentityContainer.ID: [WKWebView]] = [:]
    /// Weak set of every view we ever vended, so freshly compiled content
    /// rules can be applied to views already on screen.
    private let live = NSHashTable<WKWebView>.weakObjects()

    init(containers: IdentityContainerStore, rules: ContentRuleManager) {
        self.containers = containers
        self.rules = rules
    }

    func checkout(for containerID: IdentityContainer.ID) -> WKWebView {
        if let reused = idle[containerID]?.popLast() {
            return reused
        }
        let webView = makeWebView(for: containerID)
        live.add(webView)
        return webView
    }

    func checkin(_ webView: WKWebView, containerID: IdentityContainer.ID) {
        webView.stopLoading()
        var stack = idle[containerID] ?? []
        guard stack.count < Self.maxIdlePerContainer else { return }
        stack.append(webView)
        idle[containerID] = stack
    }

    /// Apply a compiled rule list to all current and future web views.
    func apply(_ ruleList: WKContentRuleList) {
        for webView in live.allObjects {
            webView.configuration.userContentController.add(ruleList)
        }
    }

    /// Extractor source is read once; it only defines functions, so the
    /// injection cost at documentEnd is negligible (CLAUDE.md §8).
    private static let extractorSource: String? = {
        guard let url = Bundle.main.url(forResource: "extractor", withExtension: "js") else { return nil }
        return try? String(contentsOf: url, encoding: .utf8)
    }()

    private func makeWebView(for containerID: IdentityContainer.ID) -> WKWebView {
        let configuration = WKWebViewConfiguration()
        configuration.websiteDataStore = containers.dataStore(for: containerID)
        configuration.allowsInlineMediaPlayback = true
        if let ruleList = rules.ruleList {
            configuration.userContentController.add(ruleList)
        }
        if let source = Self.extractorSource {
            configuration.userContentController.addUserScript(
                WKUserScript(source: source, injectionTime: .atDocumentEnd, forMainFrameOnly: true)
            )
        }

        let webView = PrismeWebView(frame: .zero, configuration: configuration)
        webView.allowsBackForwardNavigationGestures = true
        webView.isFindInteractionEnabled = true
        webView.scrollView.contentInsetAdjustmentBehavior = .always
        return webView
    }
}