import { SdtfError } from '@shapediver/sdk.sdtf-core';
import { SdtfFileUtils } from '../utils/SdtfFileUtils';
import { SdtfBinaryBufferCache } from './SdtfBinaryBufferCache';

export class SdtfFileBufferCache extends SdtfBinaryBufferCache {
    private readonly fileUtils: SdtfFileUtils;

    /** The paths of all sdTF buffers of this sdTF asset are relative to the path of the JSON content file. */
    private readonly basePath: string;

    constructor(absolutePath: string) {
        super();

        this.fileUtils = new SdtfFileUtils();

        // Calculate the base path for all external buffers
        const index = absolutePath.lastIndexOf('/');
        this.basePath = absolutePath.substring(0, index);
    }

    /**
     * Loads the requested buffer from disk and updates the internal buffer cache.
     * @override
     * @protected
     */
    async acquireBuffer(
        relativePath: string | undefined,
        offset: number,
        length: number
    ): Promise<DataView> {
        let buffer;
        try {
            buffer = await this.fileUtils.readFile(`${this.basePath}/${relativePath}`);
        } catch (e) {
            throw new SdtfError(`Cannot read buffer: ${e.message}`);
        }

        // Cache the entire buffer
        this.storeInCache(
            this.calcCacheKey(relativePath),
            this.cacheIdFullBuffer,
            new DataView(buffer)
        );

        return new DataView(buffer, offset, length);
    }
}