package com.peachpasswords.ui.vault

/**
 * Shared card formatting/detection helpers for D2 (card type fields).
 *
 * Pure functions — no Compose, no Android deps — so they are unit-testable and
 * reusable by both EntryEditScreen (live formatting) and EntryDetailScreen
 * (masked display). Network ids match the VaultEntry.cardNetwork doc comment:
 * "visa" | "mastercard" | "amex" | "discover" | "unknown".
 */
object CardFieldUtils {

    /** Detect the network id from the leading digit(s) of a raw (digits-or-spaces) number. */
    fun detectNetwork(rawNumber: String): String {
        val digits = rawNumber.filter { it.isDigit() }
        if (digits.isEmpty()) return "unknown"
        return when {
            digits.startsWith("4") -> "visa"
            digits.length >= 2 && digits.take(2).toIntOrNull() in 51..55 -> "mastercard"
            digits.length >= 2 && digits.take(2).toIntOrNull() in 22..27 -> "mastercard"
            digits.startsWith("34") || digits.startsWith("37") -> "amex"
            digits.startsWith("6011") || digits.startsWith("65") -> "discover"
            else -> "unknown"
        }
    }

    /** Human label for a network id, e.g. "visa" -> "Visa". Blank for unknown. */
    fun networkLabel(network: String?): String = when (network) {
        "visa" -> "Visa"
        "mastercard" -> "Mastercard"
        "amex" -> "Amex"
        "discover" -> "Discover"
        else -> ""
    }

    /** Max PAN digits by network: Amex = 15, everyone else = 16. */
    fun panMaxDigits(network: String?): Int = if (network == "amex") 15 else 16

    /** CVC length by network: Amex = 4, everyone else = 3. */
    fun cvcMaxDigits(network: String?): Int = if (network == "amex") 4 else 3

    /**
     * Group a raw PAN into display chunks. Amex uses 4-6-5; all others 4-4-4-4.
     * Input may contain spaces; only digits are kept. Caps at the network max.
     */
    fun formatPan(rawNumber: String, network: String? = null): String {
        val net = network ?: detectNetwork(rawNumber)
        val digits = rawNumber.filter { it.isDigit() }.take(panMaxDigits(net))
        val groups = if (net == "amex") intArrayOf(4, 6, 5) else intArrayOf(4, 4, 4, 4)
        val out = StringBuilder()
        var i = 0
        for (g in groups) {
            if (i >= digits.length) break
            if (out.isNotEmpty()) out.append(' ')
            out.append(digits.substring(i, minOf(i + g, digits.length)))
            i += g
        }
        return out.toString()
    }

    /** Raw digits only (for storage / network detection). */
    fun digitsOnly(value: String): String = value.filter { it.isDigit() }

    /** Last 4 digits of a stored/raw PAN, or "" if fewer than 4. */
    fun last4(rawNumber: String?): String {
        val digits = (rawNumber ?: "").filter { it.isDigit() }
        return if (digits.length >= 4) digits.takeLast(4) else digits
    }

    /**
     * Masked display: groups of bullets matching the network layout with the
     * real last-4 shown, e.g. "•••• •••• •••• 4242" (Amex: "•••• •••••• •2345").
     * Falls back to a plain masked group when the stored number is short.
     */
    fun maskedPan(rawNumber: String?, network: String? = null, last4: String? = null): String {
        val digits = (rawNumber ?: "").filter { it.isDigit() }
        // Prefer the stored last4 (MF-3) over deriving it from the raw PAN at render.
        val storedTail = last4?.filter { it.isDigit() }?.takeIf { it.isNotEmpty() }
        if (digits.isEmpty() && storedTail == null) return ""
        val net = network ?: detectNetwork(digits)
        val tail = storedTail ?: if (digits.length >= 4) digits.takeLast(4) else digits
        val groups = if (net == "amex") intArrayOf(4, 6, 5) else intArrayOf(4, 4, 4, 4)
        // Build a bullet template of total length, then overlay the last-4.
        val total = groups.sum()
        val visibleFrom = (total - tail.length).coerceAtLeast(0)
        val chars = CharArray(total) { idx -> if (idx >= visibleFrom) tail[idx - visibleFrom] else '•' }
        val out = StringBuilder()
        var i = 0
        for (g in groups) {
            if (out.isNotEmpty()) out.append(' ')
            out.append(chars, i, g)
            i += g
        }
        return out.toString()
    }

    /** Auto-format expiry as "MM/YY" or "MM/YYYY": inserts "/" after 2 digits. */
    fun formatExpiry(raw: String): String {
        val digits = raw.filter { it.isDigit() }.take(6)
        return when {
            digits.length <= 2 -> digits
            else -> digits.substring(0, 2) + "/" + digits.substring(2)
        }
    }

    /** Combine stored expMonth/expYear into "MM/YY" or browser-style "MM/YYYY". */
    fun displayExpiry(expMonth: String?, expYear: String?): String {
        val mm = (expMonth ?: "").filter { it.isDigit() }.takeLast(2).padStart(2, '0').takeIf { expMonth?.isNotBlank() == true } ?: ""
        val year = (expYear ?: "").filter { it.isDigit() }.take(4)
        return if (mm.isNotBlank() && year.isNotBlank()) "$mm/$year" else (mm.takeIf { it.isNotBlank() } ?: year)
    }

    fun expiryMonth(formatted: String): String =
        formatted.filter { it.isDigit() }.take(2)

    fun expiryYear(formatted: String): String =
        formatted.filter { it.isDigit() }.drop(2).take(4)

    fun combineExpiry(month: String, year: String): String {
        val mm = month.filter { it.isDigit() }.take(2)
        val yy = year.filter { it.isDigit() }.take(4)
        return if (mm.isNotBlank() && yy.isNotBlank()) "$mm/$yy" else mm.ifBlank { yy }
    }

    /**
     * Validate a "MM/YY" or "MM/YYYY" expiry: month 01-12 and year >= current
     * 2-digit year. `currentYear2`/`currentMonth` are injected for testability.
     */
    fun isExpiryValid(formatted: String, currentYear2: Int, currentMonth: Int): Boolean {
        val digits = formatted.filter { it.isDigit() }
        if (digits.length != 4 && digits.length != 6) return false
        val mm = digits.substring(0, 2).toIntOrNull() ?: return false
        val yy = digits.takeLast(2).toIntOrNull() ?: return false
        if (mm !in 1..12) return false
        if (yy < currentYear2) return false
        if (yy == currentYear2 && mm < currentMonth) return false
        return true
    }
}