import { PACKER_CODES, PackerError } from "../../error-codes.js";
import { resolvePackerMessage } from "../../i18n/messages.js";
import {
    CHUNK_HEADER_SIZE,
    CHUNK_METADATA_SIZE,
    CHUNK_VERSION_V1,
    type ChunkV1Metadata,
} from "../../types/chunked.types.js";

const FILE_ID_SIZE = 32;
const NONCE_SIZE = 24;
const AEAD_TAG_SIZE = 16;

/**
 * Encode a {@link ChunkV1Metadata} into the locked 100-byte big-endian metadata header.
 *
 * Throws `PackerError(PACKER.INVALID_FORMAT)` on any field-size mismatch.
 */
export function encodeHeader(meta: ChunkV1Metadata): Uint8Array {
    if (meta.fileId.byteLength !== FILE_ID_SIZE) {
        throw new PackerError(
            PACKER_CODES.INVALID_FORMAT,
            `fileId must be ${FILE_ID_SIZE} bytes, got ${meta.fileId.byteLength}`
        );
    }
    if (meta.nonce.byteLength !== NONCE_SIZE) {
        throw new PackerError(
            PACKER_CODES.INVALID_FORMAT,
            `nonce must be ${NONCE_SIZE} bytes, got ${meta.nonce.byteLength}`
        );
    }
    if (meta.aeadTag.byteLength !== AEAD_TAG_SIZE) {
        throw new PackerError(
            PACKER_CODES.INVALID_FORMAT,
            `aeadTag must be ${AEAD_TAG_SIZE} bytes, got ${meta.aeadTag.byteLength}`
        );
    }
    const out = new Uint8Array(CHUNK_METADATA_SIZE);
    const view = new DataView(out.buffer);
    view.setUint16(0, meta.version, false);
    out.set(meta.fileId, 2);
    view.setUint32(34, meta.chunkId, false);
    view.setUint32(38, meta.totalChunks, false);
    view.setBigUint64(42, meta.fileSize, false);
    view.setUint32(50, meta.chunkSize, false);
    view.setUint32(54, meta.payloadLen, false);
    view.setUint16(58, meta.flags, false);
    out.set(meta.nonce, 60);
    out.set(meta.aeadTag, 84);
    return out;
}

/**
 * Parse the first 100 bytes of `buf` as a v1 metadata header.
 *
 * Validates: buffer length, version=0x0001, flags=0x0000 (v1 reserved),
 * totalChunks ≥ 1, chunkId < totalChunks, chunkSize > 164, and the payloadLen
 * invariants for non-final and final chunks (PACKER-CHUNK-03).
 *
 * Field byte ranges are returned as zero-copy `Uint8Array.subarray` views into
 * `buf` — callers must not mutate.
 */
export function parseHeader(buf: Uint8Array): ChunkV1Metadata {
    if (buf.byteLength < CHUNK_METADATA_SIZE) {
        throw new PackerError(
            PACKER_CODES.INVALID_FORMAT,
            `buffer too short for metadata: ${buf.byteLength} < ${CHUNK_METADATA_SIZE}`
        );
    }
    const view = new DataView(buf.buffer, buf.byteOffset, CHUNK_METADATA_SIZE);
    const version = view.getUint16(0, false);
    if (version !== CHUNK_VERSION_V1) {
        throw new PackerError(
            PACKER_CODES.VERSION_UNSUPPORTED,
            resolvePackerMessage(
                undefined,
                "packer.error.VERSION_UNSUPPORTED.unknown-version",
                { version: `0x${version.toString(16).padStart(4, "0")}` }
            )
        );
    }
    const flags = view.getUint16(58, false);
    if (flags !== 0) {
        throw new PackerError(
            PACKER_CODES.FLAGS_RESERVED_NONZERO,
            resolvePackerMessage(
                undefined,
                "packer.error.FLAGS_RESERVED_NONZERO.nonzero"
            )
        );
    }
    const fileId = buf.subarray(2, 34);
    const chunkId = view.getUint32(34, false);
    const totalChunks = view.getUint32(38, false);
    const fileSize = view.getBigUint64(42, false);
    const chunkSize = view.getUint32(50, false);
    const payloadLen = view.getUint32(54, false);
    const nonce = buf.subarray(60, 84);
    const aeadTag = buf.subarray(84, 100);

    if (totalChunks === 0) {
        throw new PackerError(
            PACKER_CODES.INVALID_FORMAT,
            "totalChunks must be >= 1"
        );
    }
    if (chunkId >= totalChunks) {
        throw new PackerError(
            PACKER_CODES.INVALID_FORMAT,
            `chunkId=${chunkId} out of range; totalChunks=${totalChunks}`
        );
    }
    if (chunkSize <= CHUNK_HEADER_SIZE) {
        throw new PackerError(
            PACKER_CODES.INVALID_FORMAT,
            `chunkSize=${chunkSize} must exceed header size ${CHUNK_HEADER_SIZE}`
        );
    }

    const payloadPerChunk = chunkSize - CHUNK_HEADER_SIZE;
    if (chunkId < totalChunks - 1) {
        if (payloadLen !== payloadPerChunk) {
            throw new PackerError(
                PACKER_CODES.PAYLOAD_LEN_INVALID,
                resolvePackerMessage(
                    undefined,
                    "packer.error.PAYLOAD_LEN_INVALID.non-final",
                    { actual: payloadLen, expected: payloadPerChunk }
                )
            );
        }
    } else {
        const expectedFinal =
            fileSize - BigInt(chunkId) * BigInt(payloadPerChunk);
        if (BigInt(payloadLen) !== expectedFinal) {
            throw new PackerError(
                PACKER_CODES.PAYLOAD_LEN_INVALID,
                resolvePackerMessage(
                    undefined,
                    "packer.error.PAYLOAD_LEN_INVALID.final",
                    {
                        actual: payloadLen,
                        expected: expectedFinal.toString(),
                    }
                )
            );
        }
    }

    return {
        version,
        fileId,
        chunkId,
        totalChunks,
        fileSize,
        chunkSize,
        payloadLen,
        flags,
        nonce,
        aeadTag,
    };
}