// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

import type { Codec } from './registry.ts';
import { CompressionType } from '../../fb/compression-type.js';

export interface CompressionValidator {
    isValidCodecEncode(codec: Codec): boolean;
}

class Lz4FrameValidator implements CompressionValidator {
    private readonly LZ4_FRAME_MAGIC = new Uint8Array([4, 34, 77, 24]);
    private readonly MIN_HEADER_LENGTH = 7; // 4 (magic) + 2 (FLG + BD) + 1 (header checksum) = 7 min bytes

    isValidCodecEncode(codec: Codec): boolean {
        const testData = new Uint8Array([1, 2, 3, 4, 5, 6, 7, 8]);
        const compressed = codec.encode!(testData);
        return this._isValidCompressed(compressed);
    }

    private _isValidCompressed(buffer: Uint8Array): boolean {
        return (
            this._hasMinimumLength(buffer) &&
            this._hasValidMagicNumber(buffer) &&
            this._hasValidVersion(buffer)
        );
    }

    private _hasMinimumLength(buffer: Uint8Array): boolean {
        return buffer.length >= this.MIN_HEADER_LENGTH;
    }

    private _hasValidMagicNumber(buffer: Uint8Array): boolean {
        return this.LZ4_FRAME_MAGIC.every(
            (byte, i) => buffer[i] === byte
        );
    }

    private _hasValidVersion(buffer: Uint8Array): boolean {
        const flg = buffer[4];
        const versionBits = (flg & 0xC0) >> 6;
        return versionBits === 1;
    }

}

class ZstdValidator implements CompressionValidator {
    private readonly ZSTD_MAGIC = new Uint8Array([40, 181, 47, 253]);
    private readonly MIN_HEADER_LENGTH = 6; // 4 (magic) + 2 (min Frame_Header) = 6 min bytes

    isValidCodecEncode(codec: Codec): boolean {
        const testData = new Uint8Array([1, 2, 3, 4, 5, 6, 7, 8]);
        const compressed = codec.encode!(testData);
        return this._isValidCompressed(compressed);
    }

    private _isValidCompressed(buffer: Uint8Array): boolean {
        return (
            this._hasMinimumLength(buffer) &&
            this._hasValidMagicNumber(buffer)
        );
    }

    private _hasMinimumLength(buffer: Uint8Array): boolean {
        return buffer.length >= this.MIN_HEADER_LENGTH;
    }

    private _hasValidMagicNumber(buffer: Uint8Array): boolean {
        return this.ZSTD_MAGIC.every(
            (byte, i) => buffer[i] === byte
        );
    }
}

export const compressionValidators: Record<CompressionType, CompressionValidator> = {
    [CompressionType.LZ4_FRAME]: new Lz4FrameValidator(),
    [CompressionType.ZSTD]: new ZstdValidator(),
};