package com.peachpasswords.codex

import org.junit.Assert.assertArrayEquals
import org.junit.Assert.assertEquals
import org.junit.Assert.assertTrue
import org.junit.Test
import kotlin.random.Random

class CodexCodecTest {

    @Test fun rs_recovers_dropped_shards() {
        val data = 6
        val parity = computeParityShards(data) // 2
        val size = 40
        val rng = Random(7)
        val original = Array(data) { ByteArray(size) { rng.nextInt().toByte() } }
        val shards = Array(data + parity) { i -> if (i < data) original[i].copyOf() else ByteArray(size) }
        ReedSolomon.encode(shards, data, parity)

        // Drop `parity` shards (the max tolerable) — here drop 2 data shards.
        val present = BooleanArray(data + parity) { true }
        shards[1] = ByteArray(0); present[1] = false
        shards[4] = ByteArray(0); present[4] = false
        ReedSolomon.reconstruct(shards, data, parity, present)

        for (i in 0 until data) assertArrayEquals("shard $i", original[i], shards[i])
    }

    @Test fun gf_mul_div_are_inverse() {
        for (a in 1..255) for (b in 1..255) {
            assertEquals(a, Galois.div(Galois.mul(a, b), b))
        }
    }

    @Test fun full_codec_round_trip() {
        val payload = CodexPayload(
            version = 2, verifyCode = "PX-AB12-CD34",
            vaultBlob = "x".repeat(5000), timestamp = 111, entryCount = 7,
            vaultFingerprint = "DEADBEEF".repeat(4), generatedAt = 222,
        )
        val bytes = CodexCodec.json.encodeToString(CodexPayload.serializer(), payload).toByteArray()
        val compressed = CodexCodec.deflate(bytes)
        assertArrayEquals(bytes, CodexCodec.inflate(compressed))

        val (envelopes, layout) = CodexCodec.encodeToEnvelopes(compressed, payload.verifyCode)
        assertTrue(envelopes.all { CodexCodec.verifyChunkIntegrity(it) })
        assertEquals(layout.dataChunks + layout.parityChunks, envelopes.size)

        // Lose the maximum tolerable codes in stripe 0, then rebuild.
        val parity = layout.parityChunks / layout.stripeCount
        val survivors = envelopes.toMutableList()
        repeat(parity) { survivors.removeAt(0) } // drop first `parity` data shards
        val recovered = CodexCodec.reconstructCompressed(survivors)
        val parsed = CodexCodec.json.decodeFromString(CodexPayload.serializer(), String(CodexCodec.inflate(recovered)))
        assertEquals(payload, parsed)
    }

    @Test fun corrupted_chunk_fails_integrity() {
        val (envelopes, _) = CodexCodec.encodeToEnvelopes(CodexCodec.deflate("hello world".toByteArray()), "PX-0000-0000")
        val tampered = envelopes.first().copy(d = CodexCodec.base64Url("tampered".toByteArray()))
        assertTrue(!CodexCodec.verifyChunkIntegrity(tampered))
    }

    @Test fun inflate_exactly_at_the_cap_round_trips() {
        val data = ByteArray(CodexCodec.MAX_INFLATED_BYTES.toInt()) // zeros compress to ~17 KB
        assertArrayEquals(data, CodexCodec.inflate(CodexCodec.deflate(data)))
    }

    /**
     * PAI-2026-002: the per-chunk hash covers `d` only, so a hostile code
     * passes verifyChunkIntegrity with a tiny payload and any `t`/`S`/`i` it
     * likes. Every case below used to reach Array(t) before being rejected.
     */
    private fun hostileChunk(
        total: Int = 4,
        index: Int = 0,
        stripe: Int = 0,
        stripeCount: Int = 1,
        data: ByteArray = ByteArray(CHUNK_SIZE),
        verifyCode: String = "PX-AB12-CD34",
    ): ChunkEnvelope = ChunkEnvelope(
        v = 3, c = verifyCode, s = stripe, capS = stripeCount, i = index, t = total,
        p = index >= total - 2,
        d = CodexCodec.base64Url(data),
        h = CodexCodec.sha256Hex(data).take(32),
    )

    @Test fun hostile_shard_total_is_rejected_before_allocation() {
        val hostile = hostileChunk(total = Int.MAX_VALUE)
        assertTrue("geometry is rejected", !CodexCodec.isValidEnvelope(hostile))
        val error = try {
            CodexCodec.reconstructCompressed(listOf(hostile))
            null
        } catch (e: CodexException) {
            e
        }
        assertEquals(CodexErrorCode.INSUFFICIENT_CHUNKS, error?.code)
    }

    @Test fun out_of_range_shard_and_stripe_indices_are_rejected() {
        assertTrue(!CodexCodec.isValidEnvelope(hostileChunk(total = 4, index = 4)))
        assertTrue(!CodexCodec.isValidEnvelope(hostileChunk(total = 4, index = -1)))
        assertTrue(!CodexCodec.isValidEnvelope(hostileChunk(stripe = 2, stripeCount = 2)))
        assertTrue(!CodexCodec.isValidEnvelope(hostileChunk(stripeCount = 0)))
        assertTrue(!CodexCodec.isValidEnvelope(hostileChunk(stripeCount = 100_000)))
        assertTrue(!CodexCodec.isValidEnvelope(hostileChunk(total = 256)))
    }

    @Test fun oversized_chunk_data_is_rejected() {
        // One byte past the ceiling, and far past a full-range Aztec code's capacity.
        assertTrue(!CodexCodec.isValidEnvelope(hostileChunk(data = ByteArray(4097))))
        assertTrue(!CodexCodec.isValidEnvelope(hostileChunk(data = ByteArray(64 * 1024))))
        assertTrue(CodexCodec.isValidEnvelope(hostileChunk()))
    }

    /**
     * Cross-platform: the browser's decoder derives the shard size from the
     * first scanned chunk so that Codexes printed before the current
     * [CHUNK_SIZE] (the previous value was 800 bytes) still restore, and it
     * enforces no chunk length of its own. Android's Reed-Solomon decoder
     * derives shard size the same way. Pinning the chunk length to the current
     * generator's would turn every such printed Codex into an unreadable one.
     */
    @Test fun a_codex_printed_with_an_older_chunk_size_still_restores() {
        val legacyChunkSize = 800
        val payload = ByteArray(legacyChunkSize * 2) { (it % 251).toByte() }
        // t = 4 inverts to 2 data + 2 parity shards; every shard is present, so
        // reconstruction is just the concatenation of the two data shards.
        val shards = listOf(
            payload.copyOfRange(0, legacyChunkSize),
            payload.copyOfRange(legacyChunkSize, legacyChunkSize * 2),
            ByteArray(legacyChunkSize),
            ByteArray(legacyChunkSize),
        )
        val envelopes = shards.mapIndexed { i, bytes ->
            ChunkEnvelope(
                v = 3, c = "PX-AB12-CD34", s = 0, capS = 1, i = i, t = 4,
                p = i >= 2, d = CodexCodec.base64Url(bytes),
                h = CodexCodec.sha256Hex(bytes).take(32),
            )
        }
        assertTrue("legacy envelopes are accepted", envelopes.all { CodexCodec.isValidEnvelope(it) })
        assertArrayEquals(payload, CodexCodec.reconstructCompressed(envelopes))
    }

    /**
     * Bounding each envelope is not enough on its own: a hostile Codex can
     * simply carry many valid stripes. The whole reconstruction is budgeted
     * against the inflate cap, which it can never legitimately exceed.
     */
    @Test fun a_reconstruction_past_the_inflate_cap_is_refused() {
        val chunk = ByteArray(4096) // the largest chunk a single envelope may carry
        val stripeCount = 20 // 20 × 230 × 4096 is past the 16 MiB inflate cap
        val envelopes = (0 until stripeCount).flatMap { s ->
            (0 until 230).map { i ->
                ChunkEnvelope(
                    v = 3, c = "PX-AB12-CD34", s = s, capS = stripeCount,
                    i = i, t = 230, p = false,
                    d = CodexCodec.base64Url(chunk), h = CodexCodec.sha256Hex(chunk).take(32),
                )
            }
        }
        val error = try {
            CodexCodec.reconstructCompressed(envelopes); null
        } catch (e: CodexException) {
            e
        }
        assertEquals(CodexErrorCode.PAYLOAD_TOO_LARGE, error?.code)
    }

    @Test fun malformed_verify_code_is_rejected() {
        assertTrue(!CodexCodec.isValidEnvelope(hostileChunk(verifyCode = "PX-AB12-CD3")))
        assertTrue(CodexCodec.isValidEnvelope(hostileChunk()))
    }

    @Test fun mixed_verify_codes_and_shard_totals_are_rejected() {
        val (envelopes, _) = CodexCodec.encodeToEnvelopes(
            CodexCodec.deflate("hello codex".toByteArray()),
            "PX-AB12-CD34",
        )
        val other = CodexCodec.encodeToEnvelopes(
            CodexCodec.deflate("hello codex".toByteArray()),
            "PX-ZZ99-YY88",
        ).first.first()
        var error = try {
            CodexCodec.reconstructCompressed(envelopes + other); null
        } catch (e: CodexException) {
            e
        }
        assertEquals(CodexErrorCode.INVALID_ENVELOPE, error?.code)

        val mixedTotal = envelopes.first().copy(t = envelopes.first().t + 1, i = 0)
        error = try {
            CodexCodec.reconstructCompressed(listOf(envelopes.first(), mixedTotal)); null
        } catch (e: CodexException) {
            e
        }
        assertEquals(CodexErrorCode.INVALID_ENVELOPE, error?.code)
    }

    @Test fun hostile_envelopes_are_skipped_and_real_codes_still_restore() {
        val (envelopes, _) = CodexCodec.encodeToEnvelopes(
            CodexCodec.deflate("survives hostile neighbours".toByteArray()),
            "PX-AB12-CD34",
        )
        val recovered = CodexCodec.reconstructCompressed(
            listOf(hostileChunk(total = Int.MAX_VALUE)) + envelopes +
                listOf(hostileChunk(verifyCode = "nope")),
        )
        assertEquals("survives hostile neighbours", String(CodexCodec.inflate(recovered)))
    }

    @Test fun inflate_refuses_decompression_bombs() {
        val bomb = CodexCodec.deflate(ByteArray(CodexCodec.MAX_INFLATED_BYTES.toInt() + 1))
        assertTrue("bomb compresses tiny", bomb.size < 64 * 1024)
        val error = try {
            CodexCodec.inflate(bomb)
            null
        } catch (e: CodexException) {
            e
        }
        assertEquals(CodexErrorCode.PAYLOAD_TOO_LARGE, error?.code)
    }

    /**
     * PB-26-004: a malformed compressed stream that returns 0 bytes without
     * finishing or needing input must not loop — it must fail as CORRUPTED.
     * A truncated stream (valid header, cut off mid-block) triggers exactly
     * this: the inflater has input but cannot make progress.
     */
    @Test fun inflate_rejects_malformed_no_progress_stream() {
        val valid = CodexCodec.deflate("hello world".toByteArray())
        // Truncate past the zlib header so the inflater has data but can't finish.
        val truncated = valid.copyOf(valid.size / 2)
        val error = try {
            CodexCodec.inflate(truncated)
            null
        } catch (e: CodexException) {
            e
        }
        assertEquals(CodexErrorCode.CORRUPTED, error?.code)
    }
}