import Foundation

struct PaymvQrResult {
    let account: String
    let amount: String?
    let merchantName: String?
    let purpose: String?
}

enum PaymvQrParser {
    static func parse(_ qr: String) -> PaymvQrResult? {
        let tlvs = parseTLV(qr)

        // Tag 26: merchant account info — sub-tag 03 = account number
        var account: String?
        if let tag26 = tlvs["26"] {
            let sub = parseTLV(tag26)
            account = sub["03"]
        }

        guard let acc = account, !acc.isEmpty else { return nil }

        let amount = tlvs["54"]
        let name   = tlvs["59"]

        // Tag 62: additional data — sub-tag 08 = purpose/reference
        var purpose: String?
        if let tag62 = tlvs["62"] {
            let sub = parseTLV(tag62)
            purpose = sub["08"]
        }

        return PaymvQrResult(account: acc, amount: amount, merchantName: name, purpose: purpose)
    }

    private static func parseTLV(_ s: String) -> [String: String] {
        var result: [String: String] = [:]
        var idx = s.startIndex
        while s.distance(from: idx, to: s.endIndex) >= 4 {
            let idEnd  = s.index(idx, offsetBy: 2)
            let lenEnd = s.index(idEnd, offsetBy: 2)
            let id     = String(s[idx..<idEnd])
            guard let len = Int(s[idEnd..<lenEnd]) else { break }
            idx = lenEnd
            guard s.distance(from: idx, to: s.endIndex) >= len else { break }
            let valEnd = s.index(idx, offsetBy: len)
            result[id] = String(s[idx..<valEnd])
            idx = valEnd
        }
        return result
    }
}