package com.peachpasswords.updates

import java.util.Base64
import org.bouncycastle.crypto.params.Ed25519PublicKeyParameters
import org.bouncycastle.crypto.signers.Ed25519Signer
import org.json.JSONObject

/**
 * Public half of the Peach-vault-backed release metadata key. The private seed
 * is never shipped or read by the app. An empty value deliberately fails closed
 * until the owner provisions the generated public key in the release source.
 */
const val UPDATE_METADATA_PUBLIC_KEY_HEX = "d6a47f867d2add9c6490447c7a611c08a474a98ab7afa540f65d4347f26ba77c"

internal fun canonicalReleaseMetadataPayload(
    version: String,
    platform: String,
    url: String,
    checksumHex: String,
    provenanceSource: String,
): ByteArray = "$version\n$platform\n$url\n$checksumHex\n$version\n$platform\n$checksumHex\n$provenanceSource"
    .toByteArray(Charsets.UTF_8)

private fun decodeHex(value: String): ByteArray? {
    if (value.length != 64 || value.any { it !in "0123456789abcdefABCDEF" }) return null
    return ByteArray(32) { i ->
        value.substring(i * 2, i * 2 + 2).toInt(16).toByte()
    }
}

private fun verifySignature(publicKeyHex: String, payload: ByteArray, encoded: String): Boolean {
    val key = decodeHex(publicKeyHex) ?: return false
    val signature = runCatching { Base64.getDecoder().decode(encoded) }.getOrNull() ?: return false
    if (signature.size != 64) return false
    return runCatching {
        Ed25519Signer().apply {
            init(false, Ed25519PublicKeyParameters(key, 0))
            update(payload, 0, payload.size)
        }.verifySignature(signature)
    }.getOrDefault(false)
}

/**
 * Authenticates the platform object before [parseReleaseManifest] trusts its
 * URL, checksum, version, or notes. JSON is inspected only to locate the
 * signed fields; all semantic validation remains in the existing parser.
 */
fun parseSignedReleaseManifest(
    body: String,
    platformKey: String = ANDROID_PLATFORM_KEY,
    publicKeyHex: String = UPDATE_METADATA_PUBLIC_KEY_HEX,
): ReleaseManifest {
    val root = runCatching { JSONObject(body) }
        .getOrElse { throw ManifestFormatException("manifest is not JSON") }
    val version = root.optTextOrNull("version")
        ?: throw ManifestFormatException("signed manifest has no version")
    val platform = root.optJSONObject("platforms")?.optJSONObject(platformKey)
        ?: throw ManifestFormatException("signed manifest has no '$platformKey' artifact")
    val url = platform.optTextOrNull("url")
        ?: throw ManifestFormatException("signed artifact has no url")
    val checksum = parseArtifactChecksum(platform)
        ?: throw ManifestFormatException("signed artifact has no checksum")
    val checksumParts = checksum.split(':', limit = 2)
    val checksumHex = checksumParts.getOrNull(1)
        ?: throw ManifestFormatException("signed artifact checksum is malformed")
    val provenance = platform.optJSONObject("provenance")
        ?: throw ManifestFormatException("signed artifact has no provenance")
    val provenanceVersion = provenance.optTextOrNull("version")
        ?: throw ManifestFormatException("signed artifact provenance has no version")
    val provenancePlatform = provenance.optTextOrNull("platform")
        ?: throw ManifestFormatException("signed artifact provenance has no platform")
    val provenanceChecksum = provenance.optTextOrNull("checksum")
        ?: throw ManifestFormatException("signed artifact provenance has no checksum")
    val source = provenance.optTextOrNull("source")
        ?: throw ManifestFormatException("signed artifact provenance has no source")
    val signature = platform.optTextOrNull("signature")
        ?: throw ManifestFormatException("signed artifact has no signature")
    if (provenanceVersion != version || provenancePlatform != platformKey ||
        provenanceChecksum != checksum || checksumParts[0] != "blake3") {
        throw ManifestFormatException("signed artifact provenance does not match manifest")
    }
    if (!verifySignature(
            publicKeyHex,
            canonicalReleaseMetadataPayload(version, platformKey, url, checksumHex, source),
            signature,
        )
    ) {
        throw ManifestFormatException("release metadata signature verification failed")
    }
    return parseReleaseManifest(body, platformKey).copy(
        signature = signature,
        provenanceSource = source,
        platformKey = platformKey,
    )
}