import Foundation
import SwiftUI

/// Where a name a file uses is defined, from `repo definitions`
/// (krz/gitbay#333): the first definition, and how many there are. A name defined
/// once links to its line; one defined more often to a search.
nonisolated struct Definition: Decodable, Sendable, Hashable {
    let name: String
    let count: Int
    let path: String
    let line: Int

    private static let scheme = "gitbay-definition"
    /// The index's names, as the server matches them.
    nonisolated(unsafe) private static let identifier = /[\p{L}_$][\p{L}\p{N}_$]*/

    /// `line` with each defined name marked as a link the file view opens.
    /// The highlighting stays; names the index does not define stay plain.
    static func link(_ line: AttributedString, definitions: [String: Definition]) -> AttributedString {
        guard !definitions.isEmpty else { return line }
        var out = line
        let text = String(line.characters)
        for match in text.matches(of: identifier) {
            let name = String(match.output)
            guard definitions[name] != nil,
                  let lower = AttributedString.Index(match.range.lowerBound, within: out),
                  let upper = AttributedString.Index(match.range.upperBound, within: out) else { continue }
            var components = URLComponents()
            components.scheme = scheme
            components.host = "name"
            components.path = "/" + name
            out[lower..<upper].link = components.url
            out[lower..<upper].underlineStyle = .init(pattern: .dot)
        }
        return out
    }

    /// The name a link from `link(_:definitions:)` carries; nil for any
    /// other URL.
    static func name(in url: URL) -> String? {
        guard url.scheme == scheme else { return nil }
        let path = url.path(percentEncoded: false)
        return path.hasPrefix("/") ? String(path.dropFirst()) : nil
    }
}