package com.peachpasswords.codex

import kotlinx.serialization.json.Json
import java.security.MessageDigest
import java.util.Base64
import java.util.zip.Deflater
import java.util.zip.Inflater

/**
 * Pure (Android-free) Codex byte pipeline: compress → stripe → Reed-Solomon →
 * envelopes, and the inverse for restore. Kept independent of Aztec/PDF so the
 * full round-trip is unit-testable on the JVM. Port of the browser
 * `generate.ts` / `restore.ts` / `erasure.ts` byte handling.
 */
object CodexCodec {
    val json = Json { encodeDefaults = true; ignoreUnknownKeys = true }

    private val urlEncoder = Base64.getUrlEncoder().withoutPadding()
    private val urlDecoder = Base64.getUrlDecoder()

    /**
     * F4: decompression bomb guard — mirrors PeachPayloadCodec's
     * MAX_SECTION_RAW_BYTES (16 MiB). A codex payload is the same vault JSON
     * the PeachScript sections carry, so the cap is identical by definition.
     */
    const val MAX_INFLATED_BYTES = 16L * 1024 * 1024

    fun base64Url(bytes: ByteArray): String = urlEncoder.encodeToString(bytes)
    fun fromBase64Url(s: String): ByteArray = urlDecoder.decode(s)

    /** Uppercase hex of SHA-256(bytes) — per-chunk hash + vault fingerprint source. */
    fun sha256Hex(bytes: ByteArray): String {
        val digest = MessageDigest.getInstance("SHA-256").digest(bytes)
        val sb = StringBuilder(digest.size * 2)
        for (b in digest) sb.append("%02X".format(b.toInt() and 0xff))
        return sb.toString()
    }

    fun deflate(data: ByteArray): ByteArray {
        val deflater = Deflater(Deflater.BEST_COMPRESSION).apply { setInput(data); finish() }
        val out = java.io.ByteArrayOutputStream(data.size / 2 + 32)
        val buf = ByteArray(8192)
        while (!deflater.finished()) out.write(buf, 0, deflater.deflate(buf))
        deflater.end()
        return out.toByteArray()
    }

    fun inflate(data: ByteArray): ByteArray {
        val inflater = Inflater().apply { setInput(data) }
        val out = java.io.ByteArrayOutputStream(data.size * 3 + 32)
        val buf = ByteArray(8192)
        // PB-26-004: a malformed stream can return 0 bytes without finishing
        // or needing input, spinning the loop indefinitely. Treat every
        // zero-progress state as an explicit failure: needsInput means trailing
        // zero-pad; needsDictionary means a preset dictionary stream Codex
        // never produces; any other 0-return is malformed.
        while (!inflater.finished()) {
            val n = inflater.inflate(buf)
            if (n == 0) {
                if (inflater.finished()) break
                inflater.end()
                if (inflater.needsDictionary()) {
                    throw CodexException(
                        CodexErrorCode.CORRUPTED,
                        "Inflate requires a preset dictionary — Codex never produces one",
                    )
                }
                if (inflater.needsInput()) {
                    throw CodexException(
                        CodexErrorCode.CORRUPTED,
                        "Inflate input ended before the stream finished",
                    )
                }
                throw CodexException(
                    CodexErrorCode.CORRUPTED,
                    "Inflate made no progress without needing input",
                )
            }
            out.write(buf, 0, n)
            if (out.size() > MAX_INFLATED_BYTES) {
                inflater.end()
                throw CodexException(
                    CodexErrorCode.PAYLOAD_TOO_LARGE,
                    "Inflated payload exceeds the ${MAX_INFLATED_BYTES / (1024 * 1024)} MiB cap",
                )
            }
        }
        inflater.end()
        return out.toByteArray()
    }

    // ── Stripe layout ─────────────────────────────────────────────────────

    fun planStripeShardCounts(totalDataShards: Int): IntArray {
        if (totalDataShards <= 0) return IntArray(0)
        val numStripes = maxOf(1, Math.ceil(totalDataShards.toDouble() / MAX_DATA_SHARDS_PER_STRIPE).toInt())
        val base = totalDataShards / numStripes
        val remainder = totalDataShards % numStripes
        return IntArray(numStripes) { base + if (it < remainder) 1 else 0 }
    }

    data class Stripe(val dataShards: Int, val parityShards: Int, val shards: Array<ByteArray>) {
        val totalChunks: Int get() = dataShards + parityShards
    }

    /** Compress + stripe + RS-encode into envelopes for [verifyCode]. */
    fun encodeToEnvelopes(compressed: ByteArray, verifyCode: String): Pair<List<ChunkEnvelope>, CodexLayout> {
        val totalDataShards = maxOf(1, Math.ceil(compressed.size.toDouble() / CHUNK_SIZE).toInt())
        val counts = planStripeShardCounts(totalDataShards)
        val envelopes = ArrayList<ChunkEnvelope>()
        var offset = 0
        var totalData = 0
        var totalParity = 0
        for ((sIdx, dataShards) in counts.withIndex()) {
            val region = dataShards * CHUNK_SIZE
            val parityShards = computeParityShards(dataShards)
            val total = dataShards + parityShards
            val shards = Array(total) { ByteArray(CHUNK_SIZE) }
            for (d in 0 until dataShards) {
                val start = offset + d * CHUNK_SIZE
                val len = (compressed.size - start).coerceIn(0, CHUNK_SIZE)
                if (len > 0) System.arraycopy(compressed, start, shards[d], 0, len)
            }
            ReedSolomon.encode(shards, dataShards, parityShards)
            for (i in 0 until total) {
                envelopes.add(buildEnvelope(shards[i], i, total, i >= dataShards, verifyCode, sIdx, counts.size))
            }
            offset += region
            totalData += dataShards
            totalParity += parityShards
        }
        return envelopes to CodexLayout(counts.size, totalData, totalParity, totalData + totalParity)
    }

    private fun buildEnvelope(
        chunk: ByteArray, index: Int, total: Int, isParity: Boolean,
        verifyCode: String, stripe: Int, stripeCount: Int,
    ): ChunkEnvelope = ChunkEnvelope(
        v = 3, c = verifyCode, s = stripe, capS = stripeCount,
        i = index, t = total, p = isParity,
        d = base64Url(chunk), h = sha256Hex(chunk).take(32),
    )

    /**
     * Upper bound on one chunk's decoded bytes, not the generator's exact
     * [CHUNK_SIZE]: the browser's decoder derives the shard size from the
     * first scanned chunk precisely so Codexes printed before the current
     * chunk size (800 bytes) still restore, and it enforces no length of its
     * own. The bound sits above a full-range Aztec code's alphanumeric
     * capacity, so it rejects only what no barcode could have carried.
     */
    private const val MAX_CHUNK_BYTES = 4096
    private val MAX_ENCODED_CHUNK_CHARS = base64Url(ByteArray(MAX_CHUNK_BYTES)).length

    /**
     * Budget for the whole reconstructed payload. [inflate] refuses anything
     * over [MAX_INFLATED_BYTES], so a payload larger than this can never
     * succeed; the headroom covers deflate framing on a payload at the cap.
     */
    private val MAX_RECONSTRUCTED_BYTES = MAX_INFLATED_BYTES + 1024 * 1024

    private val VERIFY_CODE = Regex("PX-[0-9A-Z]{4}-[0-9A-Z]{4}")

    /**
     * Stripe ceiling implied by the inflate cap: the largest legal payload
     * divided by the largest legal stripe, rounded up. The extra stripe covers
     * deflate's own framing overhead, which can push the compressed payload a
     * fraction above the uncompressed cap.
     */
    private val MAX_STRIPES: Int =
        ((MAX_INFLATED_BYTES + MAX_DATA_SHARDS_PER_STRIPE * CHUNK_SIZE - 1) /
            (MAX_DATA_SHARDS_PER_STRIPE * CHUNK_SIZE)).toInt() + 1

    /**
     * Reject a scanned envelope whose declared geometry no real Codex can
     * produce, before anything is allocated from it (PAI-2026-002).
     *
     * The per-chunk hash covers `d` only — `t`, `S`, `s` and `i` are unauthenticated
     * integers, and reconstruction sized `Array(total)` straight from `t`. A
     * barcode with a valid hash over a tiny payload and t = Int.MAX_VALUE
     * therefore cost a multi-gigabyte allocation before it could be rejected.
     * Every bound here is the encoder's own, except the chunk size, which is a
     * ceiling rather than an exact match so older paper still restores (see
     * [MAX_CHUNK_BYTES]). [buildEnvelope] emits at most
     * [MAX_TOTAL_SHARDS_PER_STRIPE] shards per stripe and at most
     * [MAX_STRIPES] stripes.
     */
    internal fun isValidEnvelope(env: ChunkEnvelope): Boolean =
        env.v == CODEX_VERSION &&
            VERIFY_CODE.matches(env.c) &&
            env.capS in 1..MAX_STRIPES &&
            env.s in 0 until env.capS &&
            env.t in 1..MAX_TOTAL_SHARDS_PER_STRIPE &&
            env.i in 0 until env.t &&
            env.d.length in 1..MAX_ENCODED_CHUNK_CHARS &&
            (env.h.length == 16 || env.h.length == 32)

    fun verifyChunkIntegrity(env: ChunkEnvelope): Boolean {
        if (env.h.length != 16 && env.h.length != 32) return false
        return sha256Hex(fromBase64Url(env.d)).take(env.h.length).equals(env.h, ignoreCase = true)
    }

    /**
     * Reconstruct the compressed payload from scanned envelopes, tolerating
     * lost codes via Reed-Solomon. Groups by stripe, reconstructs each, then
     * concatenates the data regions in stripe order.
     */
    fun reconstructCompressed(envelopes: List<ChunkEnvelope>): ByteArray {
        val good = envelopes.filter { isValidEnvelope(it) && verifyChunkIntegrity(it) }
        if (good.isEmpty()) throw CodexException(CodexErrorCode.INSUFFICIENT_CHUNKS, "no valid chunks")
        val verifyCode = good.first().c
        val stripeCount = good.first().capS
        if (good.any { it.c != verifyCode || it.capS != stripeCount }) {
            throw CodexException(CodexErrorCode.INVALID_ENVELOPE, "mixed verify codes or stripe counts")
        }
        val byStripe = good.groupBy { it.s }
        var reconstructedBytes = 0L
        val out = java.io.ByteArrayOutputStream()
        for (sIdx in 0 until stripeCount) {
            val chunks = byStripe[sIdx]
                ?: throw CodexException(CodexErrorCode.INSUFFICIENT_CHUNKS, "stripe $sIdx missing entirely")
            val total = chunks.first().t
            if (chunks.any { it.t != total }) {
                throw CodexException(CodexErrorCode.INVALID_ENVELOPE, "mixed shard totals in stripe $sIdx")
            }
            val (dataShards, parityShards) = deriveShardCounts(total)
            val shards = Array(total) { ByteArray(0) }
            val present = BooleanArray(total)
            for (env in chunks) {
                if (env.i in 0 until total) {
                    val decoded = fromBase64Url(env.d)
                    reconstructedBytes += decoded.size
                    if (reconstructedBytes > MAX_RECONSTRUCTED_BYTES) {
                        throw CodexException(
                            CodexErrorCode.PAYLOAD_TOO_LARGE,
                            "Reconstructed payload exceeds the ${MAX_INFLATED_BYTES / (1024 * 1024)} MiB cap",
                        )
                    }
                    shards[env.i] = decoded
                    present[env.i] = true
                }
            }
            ReedSolomon.reconstruct(shards, dataShards, parityShards, present)
            for (d in 0 until dataShards) out.write(shards[d])
        }
        return out.toByteArray()
    }
}

data class CodexLayout(val stripeCount: Int, val dataChunks: Int, val parityChunks: Int, val totalChunks: Int)