package com.peachpasswords.vault

/**
 * PeachScript outer codec — maps each payload byte to one Private-Use-Area code
 * point in U+E000..U+E0FF, and back. Byte-for-byte the browser's `peachScript.ts`:
 * byte 0 → U+E000, byte 255 → U+E0FF. The bundled PeachScript font renders those
 * 256 code points; outside Peach the string is unreadable boxes (intended).
 */
object PeachScript {
    private const val BASE = 0xE000

    /** Encode binary [bytes] to a PeachScript string (one code point per byte). */
    fun encode(bytes: ByteArray): String {
        val sb = StringBuilder(bytes.size)
        for (b in bytes) sb.appendCodePoint(BASE + (b.toInt() and 0xff))
        return sb.toString()
    }

    /**
     * Decode a PeachScript string back to bytes. Throws on any code point outside
     * U+E000..U+E0FF (edited / truncated / not PeachScript), matching the browser's
     * INVALID_PEACHSCRIPT_CHARACTER.
     */
    fun decode(str: String): ByteArray {
        val cps = str.codePoints().toArray()
        val out = ByteArray(cps.size)
        for (i in cps.indices) {
            val cp = cps[i]
            require(cp in BASE..(BASE + 0xff)) { "INVALID_PEACHSCRIPT_CHARACTER" }
            out[i] = (cp - BASE).toByte()
        }
        return out
    }

    /** Strip all whitespace before decoding (browser `normalisePeachScript`). */
    fun normalise(str: String): String = str.replace(Regex("\\s+"), "")

    /**
     * Cheap pre-flight: non-empty and every non-whitespace char is in the PUA
     * range. Used to gate the import button without throwing.
     */
    fun isPeachScript(str: String): Boolean {
        val t = normalise(str)
        if (t.isEmpty()) return false
        var i = 0
        while (i < t.length) {
            val cp = t.codePointAt(i)
            if (cp < BASE || cp > BASE + 0xff) return false
            i += Character.charCount(cp)
        }
        return true
    }
}