import AppKit
import Foundation
import NaturalLanguage

public protocol WordKnowledge {
    /// A common word in Dutch or English (case-insensitive). Rare words, names and product names are not.
    func isWord(_ word: String) -> Bool
    /// A very frequent function word ("in", "de", "the", "of").
    func isFunctionWord(_ word: String) -> Bool
}

/// Splitting and normalising the left-hand side of an entry, shared by the engine and the warnings.
enum EntryKey {
    static func parts(_ source: String) -> [String] {
        source.split(whereSeparator: { $0.isWhitespace || "-‐‑–".contains($0) }).map(String.init)
    }

    /// Spacing, hyphens and case do not matter: "Cloud-Code", "cloud code" and "cloudcode" are the same source.
    static func key(_ source: String) -> String {
        parts(source).joined().lowercased()
    }
}

/// The most frequent Dutch and English function words.
enum CommonWords {
    static let english: Set<String> = [
        "a", "about", "after", "all", "also", "an", "and", "any", "are", "as", "at", "be", "because", "been", "but",
        "by", "can", "could", "did", "do", "does", "for", "from", "had", "has", "have", "he", "her", "here", "him",
        "his", "how", "i", "if", "in", "into", "is", "it", "its", "just", "me", "more", "most", "my", "no", "not",
        "now", "of", "on", "one", "only", "or", "other", "our", "out", "over", "she", "so", "some", "such", "than",
        "that", "the", "their", "them", "then", "there", "these", "they", "this", "those", "to", "up", "us", "very",
        "was", "we", "were", "what", "when", "which", "who", "will", "with", "would", "you", "your",
    ]
    static let dutch: Set<String> = [
        "aan", "al", "als", "ben", "bij", "dan", "dat", "de", "den", "der", "deze", "die", "dit", "doen", "door",
        "dus", "een", "en", "er", "ga", "had", "heb", "heeft", "hem", "het", "hier", "hij", "hoe", "ik", "in", "is",
        "ja", "je", "jij", "kan", "kon", "maar", "me", "mij", "mijn", "moet", "na", "naar", "niet", "nog", "nu",
        "of", "om", "ons", "onze", "ook", "op", "over", "te", "ten", "ter", "toch", "toen", "tot", "u", "uit", "van",
        "veel", "voor", "was", "wat", "we", "wel", "werd", "wij", "wil", "worden", "wordt", "zal", "ze", "zei",
        "zich", "zij", "zijn", "zo", "zou",
    ]
    static let all: Set<String> = english.union(dutch)
}

/// English: the on-device word list of `NaturalLanguage` (common words only, so "cloud" and "reef" are in, "anthropic" and "vercel" are not).
/// Dutch has no such list, so the spell checker decides. Function words come from the built-in list.
public final class SystemWordKnowledge: WordKnowledge, @unchecked Sendable {
    private let englishWords = NLEmbedding.wordEmbedding(for: .english)

    public init() {}

    public func isWord(_ word: String) -> Bool {
        let lowered = word.lowercased()
        guard !lowered.isEmpty else { return false }
        if let englishWords {
            if englishWords.contains(lowered) { return true }
        } else if spellChecks(lowered, language: "en") {
            return true
        }
        return spellChecks(lowered, language: "nl")
    }

    public func isFunctionWord(_ word: String) -> Bool {
        CommonWords.all.contains(word.lowercased())
    }

    private func spellChecks(_ word: String, language: String) -> Bool {
        NSSpellChecker.shared.checkSpelling(
            of: word, startingAt: 0, language: language, wrap: false,
            inSpellDocumentWithTag: 0, wordCount: nil).location == NSNotFound
    }
}