/*
 * Copyright (C) 2023 NotEnoughUpdates contributors
 *
 * This file is part of NotEnoughUpdates.
 *
 * NotEnoughUpdates is free software: you can redistribute it
 * and/or modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation, either
 * version 3 of the License, or (at your option) any later version.
 *
 * NotEnoughUpdates is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with NotEnoughUpdates. If not, see <https://www.gnu.org/licenses/>.
 */

package io.github.moulberry.notenoughupdates.util

import com.google.gson.GsonBuilder
import io.github.moulberry.notenoughupdates.util.kotlin.KotlinTypeAdapterFactory
import java.util.*

object TemplateUtil {
    val gson = GsonBuilder()
        .registerTypeAdapterFactory(KotlinTypeAdapterFactory)
        .create()

    @JvmStatic
    fun getTemplatePrefix(data: String): String? {
        val decoded = maybeFromBase64Encoded(data) ?: return null
        return decoded.replaceAfter("/", "", "").ifBlank { null }
    }

    @JvmStatic
    fun intoBase64Encoded(raw: String): String {
        return Base64.getEncoder().encodeToString(raw.encodeToByteArray())
    }

    private val base64Alphabet = charArrayOf(
        'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
        'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
        'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
        'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/', '='
    )

    @JvmStatic
    fun maybeFromBase64Encoded(raw: String): String? {
        val raw = raw.trim()
        if (raw.any { it !in base64Alphabet }) {
            return null
        }
        return try {
            Base64.getDecoder().decode(raw).decodeToString()
        } catch (ex: Exception) {
            null
        }
    }


    /**
     * Returns a base64 encoded string, truncated such that for all `x`, `x.startsWith(prefix)` implies
     * `base64Encoded(x).startsWith(getPrefixComparisonSafeBase64Encoding(prefix))`
     * (however, the inverse may not always be true).
     */
    @JvmStatic
    fun getPrefixComparisonSafeBase64Encoding(prefix: String): String {
        val rawEncoded =
            Base64.getEncoder().encodeToString(prefix.encodeToByteArray())
                .replace("=", "")
        return rawEncoded.substring(0, rawEncoded.length - rawEncoded.length % 4)
    }

    @JvmStatic
    fun encodeTemplate(sharePrefix: String, data: Any): String {
        require(sharePrefix.endsWith("/"))
        return intoBase64Encoded(sharePrefix + gson.toJson(data))
    }

    @JvmStatic
    fun <T : Any> maybeDecodeTemplate(sharePrefix: String, data: String, type: Class<T>): T? {
        require(sharePrefix.endsWith("/"))
        val data = data.trim()
        if (!data.startsWith(getPrefixComparisonSafeBase64Encoding(sharePrefix)))
            return null
        val decoded = maybeFromBase64Encoded(data) ?: return null
        if (!decoded.startsWith(sharePrefix))
            return null
        return try {
            gson.fromJson(decoded.substring(sharePrefix.length), type)
        } catch (e: Exception) {
            null
        }
    }

}