import Foundation

/// A parsed `NAME;PARAM=value:VALUE` content line.
///
/// vCard and iCalendar share this grammar, so both sanitizers parse through
/// this type.
struct PropertyLine {
    /// Apple exports group related properties as `item1.EMAIL` / `item1.X-ABLabel`.
    /// The group is parsed off and never re-emitted — click-wheel parsers do not
    /// understand grouping, and the labels it points at are `X-` properties that
    /// get dropped anyway.
    var name: String
    var parameters: [String]
    var value: String

    init?(_ line: String) {
        guard let colon = line.firstIndex(of: ":") else { return nil }

        let head = String(line[line.startIndex..<colon])
        value = String(line[line.index(after: colon)...])

        var segments = head.components(separatedBy: ";")
        guard var rawName = segments.first, !rawName.isEmpty else { return nil }
        segments.removeFirst()

        if let dot = rawName.lastIndex(of: ".") {
            rawName = String(rawName[rawName.index(after: dot)...])
        }

        name = rawName.uppercased()
        parameters = segments
    }

    /// The value of `name`, for parameters written as `NAME=value`.
    func parameterValue(named name: String) -> String? {
        let prefix = name.uppercased() + "="
        for parameter in parameters where parameter.uppercased().hasPrefix(prefix) {
            return String(parameter.dropFirst(prefix.count))
        }
        return nil
    }

    mutating func removeParameters(named names: [String]) {
        let prefixes = names.map { $0.uppercased() + "=" }
        parameters.removeAll { parameter in
            prefixes.contains { parameter.uppercased().hasPrefix($0) }
        }
    }

    var rendered: String {
        let head = ([name] + parameters).joined(separator: ";")
        return "\(head):\(value)"
    }
}

extension PropertyLine {
    /// Unescapes a TEXT value: `\n` to a newline, `\;` `\,` `\\` to their literals.
    static func unescape(_ value: String) -> String {
        var output = ""
        var escaped = false
        for character in value {
            if escaped {
                switch character {
                case "n", "N": output.append("\n")
                default: output.append(character)
                }
                escaped = false
            } else if character == "\\" {
                escaped = true
            } else {
                output.append(character)
            }
        }
        return output
    }
}