import Foundation

/// Cloze-Helpers. 1:1-Port der Funktionen aus
/// `cards/packages/cards-domain/src/cloze.ts`.
///
/// **Web-Parität-Hinweis:** Web rendert Cloze client-side. Native macht
/// dasselbe, weil Server keinen Render-Endpoint dafür hat. Pure-String-
/// Manipulation, kein FSRS — Mocking gegen die TS-Implementierung via
/// Fixture-Tests.
///
/// Markup: `{{cN::answer}}` oder `{{cN::answer::hint}}`. N ist
/// 1-basierte Cluster-ID. Mehrere Cluster pro Karte → mehrere
/// Sub-Index-Reviews.
enum Cloze {
    // swiftlint:disable large_tuple

    /// Pattern für `{{cN::answer(::hint)?}}`. Pro Call konstruiert,
    /// weil `Regex` unter Strict-Concurrency nicht Sendable ist.
    /// Tuple-Output (whole-match, id, answer, hint?) ist Regex-Builder-
    /// bedingt — Lint-Regel `large_tuple` greift hier nicht.
    private static var clusterPattern: Regex<(Substring, Substring, Substring, Substring?)> {
        #/\{\{c(\d+)::([^}]*?)(?:::([^}]*?))?\}\}/#
    }

    // swiftlint:enable large_tuple

    /// Distinct Cluster-IDs, sortiert.
    static func extractClusterIds(_ text: String) -> [Int] {
        var ids = Set<Int>()
        for match in text.matches(of: clusterPattern) {
            if let n = Int(match.output.1), n >= 1 {
                ids.insert(n)
            }
        }
        return ids.sorted()
    }

    /// Hint für einen Cluster (erstes Vorkommen gewinnt).
    static func hint(for text: String, clusterId: Int) -> String? {
        for match in text.matches(of: clusterPattern) {
            if let n = Int(match.output.1), n == clusterId, let hint = match.output.3 {
                return String(hint)
            }
        }
        return nil
    }

    /// Anzahl distinct Cluster — entspricht Sub-Index-Count.
    static func subIndexCount(_ text: String) -> Int {
        extractClusterIds(text).count
    }

    /// Mapping Sub-Index → Cluster-ID.
    static func clusterId(for text: String, subIndex: Int) -> Int? {
        let ids = extractClusterIds(text)
        guard ids.indices.contains(subIndex) else { return nil }
        return ids[subIndex]
    }

    /// Prompt-Render: aktiver Cluster wird zu `[…]` (oder `[hint]`),
    /// alle anderen werden auf ihre Antwort expandiert.
    static func renderPrompt(_ text: String, activeClusterId: Int) -> String {
        text.replacing(clusterPattern) { match in
            guard let n = Int(match.output.1) else { return String(match.output.0) }
            if n == activeClusterId {
                if let hint = match.output.3 {
                    return "[\(hint)]"
                }
                return "[…]"
            }
            return String(match.output.2)
        }
    }

    /// Antwort-Render: alle Cluster expandiert. Aktiver Cluster wird
    /// als Markdown-Bold markiert.
    static func renderAnswer(_ text: String, activeClusterId: Int) -> String {
        text.replacing(clusterPattern) { match in
            guard let n = Int(match.output.1) else { return String(match.output.0) }
            let answer = String(match.output.2)
            return n == activeClusterId ? "**\(answer)**" : answer
        }
    }
}