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

/// Parse failure with the 1-based source column and, where possible, a
/// suggested fix (CLAUDE.md §4: errors must cite column position and
/// suggest fixes via Levenshtein distance on known verbs).
public struct ZQParseError: Error, Equatable, Sendable, CustomStringConvertible {
    public var message: String
    public var column: Int
    public var suggestion: String?

    public init(message: String, column: Int, suggestion: String? = nil) {
        self.message = message
        self.column = column
        self.suggestion = suggestion
    }

    public var description: String {
        var text = "parse error at column \(column): \(message)"
        if let suggestion {
            text += "\n  did you mean '\(suggestion)'?"
        }
        return text
    }
}

/// Levenshtein edit distance, used to suggest the closest known verb for
/// an unrecognized command.
public func levenshteinDistance(_ a: String, _ b: String) -> Int {
    let a = Array(a), b = Array(b)
    if a.isEmpty { return b.count }
    if b.isEmpty { return a.count }

    var previous = Array(0...b.count)
    var current = [Int](repeating: 0, count: b.count + 1)

    for i in 1...a.count {
        current[0] = i
        for j in 1...b.count {
            let substitution = previous[j - 1] + (a[i - 1] == b[j - 1] ? 0 : 1)
            current[j] = min(previous[j] + 1, current[j - 1] + 1, substitution)
        }
        swap(&previous, &current)
    }
    return previous[b.count]
}