package de.waypointaudio.license

import org.json.JSONArray
import org.json.JSONObject

/**
 * v2.5.20 — Kanonische JSON-Serialisierung, kompatibel zum Python-Tool
 * (`canonical_json_bytes`):
 *  - Keys lexikografisch sortiert.
 *  - Trennzeichen ohne Whitespace: "," / ":".
 *  - `ensure_ascii=False` ⇒ Unicode-Strings werden nicht escapet, ausser den
 *    minimal nötigen JSON-Escapes (`\"`, `\\`, Steuerzeichen < 0x20).
 *  - `null` für JSON-Null; `JSONObject.NULL` und Kotlin-`null` gleich behandelt.
 *
 * Diese kanonische Form ist die Eingabe für die ECDSA-P256-SHA256-Signatur.
 */
internal object CanonicalJson {

    fun encode(value: Any?): String {
        val sb = StringBuilder()
        appendValue(sb, value)
        return sb.toString()
    }

    private fun appendValue(sb: StringBuilder, value: Any?) {
        when {
            value == null || value === JSONObject.NULL -> sb.append("null")
            value is Boolean -> sb.append(if (value) "true" else "false")
            value is Number -> appendNumber(sb, value)
            value is String -> appendString(sb, value)
            value is JSONObject -> appendObject(sb, value)
            value is JSONArray -> appendArray(sb, value)
            else -> appendString(sb, value.toString())
        }
    }

    private fun appendObject(sb: StringBuilder, obj: JSONObject) {
        val keys = obj.keys().asSequence().toList().sorted()
        sb.append('{')
        for ((index, key) in keys.withIndex()) {
            if (index > 0) sb.append(',')
            appendString(sb, key)
            sb.append(':')
            appendValue(sb, obj.opt(key))
        }
        sb.append('}')
    }

    private fun appendArray(sb: StringBuilder, arr: JSONArray) {
        sb.append('[')
        for (i in 0 until arr.length()) {
            if (i > 0) sb.append(',')
            appendValue(sb, arr.opt(i))
        }
        sb.append(']')
    }

    private fun appendNumber(sb: StringBuilder, n: Number) {
        when (n) {
            is Int, is Long, is Short, is Byte -> sb.append(n.toString())
            is Double -> {
                if (n.isNaN() || n.isInfinite()) {
                    sb.append("null")
                } else if (n == n.toLong().toDouble()) {
                    sb.append(n.toLong().toString())
                } else {
                    sb.append(n.toString())
                }
            }
            is Float -> appendNumber(sb, n.toDouble())
            else -> sb.append(n.toString())
        }
    }

    private fun appendString(sb: StringBuilder, s: String) {
        sb.append('"')
        for (c in s) {
            when (c.code) {
                0x22 -> sb.append("\\\"")
                0x5C -> sb.append("\\\\")
                0x08 -> sb.append("\\b")
                0x0C -> sb.append("\\f")
                0x0A -> sb.append("\\n")
                0x0D -> sb.append("\\r")
                0x09 -> sb.append("\\t")
                else -> {
                    val code = c.code
                    if (code < 0x20) {
                        sb.append("\\u%04x".format(code))
                    } else {
                        sb.append(c)
                    }
                }
            }
        }
        sb.append('"')
    }
}