import SwiftUI

struct SearchSuggestionsView: View {
  private struct CachedTag {
    let original: Either<BooruTag, BooruSearchQuery>
    let names: [String]
  }

  var items: [Either<BooruTag, BooruSearchQuery>]
  @Binding var searchText: String

  private var lastSearchTag: String {
    String(searchText.split(separator: " ").last ?? "").lowercased()
  }

  private var cachedTags: [CachedTag] {
    items.map { item in
      switch item {
      case .left(let tag):
        return CachedTag(original: item, names: [tag.name.lowercased()])

      case .right(let query):
        return CachedTag(original: item, names: query.tags.map { $0.lowercased() })
      }
    }
  }

  private var filteredItems: [Either<BooruTag, BooruSearchQuery>] {
    let matchCandidateTag = lastSearchTag
    let matchingTagsLimit = 50

    guard !matchCandidateTag.isEmpty else { return [] }

    var seenTags = Set<String>()
    var matchingTags: [Either<BooruTag, BooruSearchQuery>] = []

    matchingTags.reserveCapacity(matchingTagsLimit)

    for tag in cachedTags {
      if matchingTags.count >= matchingTagsLimit { break }

      for name in tag.names {
        if name.contains(matchCandidateTag), seenTags.insert(name).inserted {
          matchingTags.append(tag.original)

          break
        }
      }
    }

    return matchingTags
  }

  var body: some View {
    ForEach(filteredItems, id: \.self) { item in
      switch item {
      case .left(let tag):
        Button {
          if let range = searchText.range(of: lastSearchTag, options: .backwards) {
            searchText.replaceSubrange(range, with: tag.name)
          }
        } label: {
          Text(tag.name)
        }

      case .right(let query):
        Button {
          if let range = searchText.range(of: lastSearchTag, options: .backwards),
            let matchingTag = query.tags.first(where: { $0.lowercased().contains(lastSearchTag) })
          {
            searchText.replaceSubrange(range, with: matchingTag)
          }
        } label: {
          if let matchingTag = query.tags.first(where: { $0.lowercased().contains(lastSearchTag) })
          {
            Text(matchingTag)
          } else {
            Text(query.tags.first ?? "")
          }
        }
      }
    }
  }
}