//
//  Token.swift
//  Metrika
//
//  Author:  Simon-Pierre Boucher
//  Contact: contact@spboucher.ai
//  Copyright © 2026 Simon-Pierre Boucher. All rights reserved.
//

/// A lexical token of the ZQL command language, carrying its 1-based
/// source column so parse errors can point at the offending position.
public struct ZQToken: Equatable, Sendable {
    public enum Kind: Equatable, Sendable {
        case identifier(String)
        case number(Double)
        case string(String)
        case comma
        case colon
        case lparen
        case rparen
        case lbracket
        case rbracket
        /// Operators: + - * / ^ = == != < <= > >= & | ! # .
        case op(String)
        case endOfLine
    }

    public let kind: Kind
    /// 1-based column of the first character of the token.
    public let column: Int

    public init(kind: Kind, column: Int) {
        self.kind = kind
        self.column = column
    }
}

extension ZQToken.Kind {
    /// Human-readable rendering used in error messages.
    public var describe: String {
        switch self {
        case .identifier(let s): return "'\(s)'"
        case .number(let n): return "number \(n)"
        case .string(let s): return "\"\(s)\""
        case .comma: return "','"
        case .colon: return "':'"
        case .lparen: return "'('"
        case .rparen: return "')'"
        case .lbracket: return "'['"
        case .rbracket: return "']'"
        case .op(let o): return "'\(o)'"
        case .endOfLine: return "end of line"
        }
    }
}