118 lines
3.4 KiB
Plaintext
118 lines
3.4 KiB
Plaintext
/**
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* 大字段（LOB）分块缓冲（1.7.7）。
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*
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* 大文本/二进制按固定大小分块加载与编辑：
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* - 只请求可视范围内的块，避免一次性读取整列；
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* - 记录已加载块，read 拼接时若跨未加载块则抛错（提示先加载）。
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*/
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export class LobBuffer {
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private readonly totalSize: number;
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private readonly chunkSize: number;
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private readonly loaded: Map<number, string> = new Map<number, string>();
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constructor(totalSize: number, chunkSize: number) {
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if (chunkSize < 1) {
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throw new Error('chunkSize must be >= 1');
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}
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this.totalSize = totalSize < 0 ? 0 : totalSize;
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this.chunkSize = chunkSize;
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}
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size(): number {
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return this.totalSize;
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}
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chunkCount(): number {
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return Math.ceil(this.totalSize / this.chunkSize);
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}
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chunkLength(index: number): number {
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if (index < 0 || index >= this.chunkCount()) {
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return 0;
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}
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const start: number = index * this.chunkSize;
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const remaining: number = this.totalSize - start;
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return remaining < this.chunkSize ? remaining : this.chunkSize;
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}
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/** 覆盖 [offset, offset+length) 需要的块号。 */
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chunksFor(offset: number, length: number): number[] {
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if (this.totalSize === 0 || length <= 0) {
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return [];
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}
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const start: number = offset < 0 ? 0 : offset;
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const end: number = Math.min(this.totalSize, start + length);
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if (end <= start) {
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return [];
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}
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const first: number = Math.floor(start / this.chunkSize);
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const last: number = Math.floor((end - 1) / this.chunkSize);
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const out: number[] = [];
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for (let index = first; index <= last; index++) {
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out.push(index);
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}
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return out;
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}
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setChunk(index: number, data: string): void {
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if (index < 0 || index >= this.chunkCount()) {
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return;
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}
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this.loaded.set(index, data);
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}
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isLoaded(index: number): boolean {
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return this.loaded.has(index);
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}
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loadedChunks(): number {
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return this.loaded.size;
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}
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loadedBytes(): number {
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let bytes: number = 0;
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this.loaded.forEach((data: string, index: number) => {
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bytes += data.length;
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});
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return bytes;
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}
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/** 是否需要加载（覆盖范围内有未加载块）。 */
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needsLoad(offset: number, length: number): boolean {
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const chunks: number[] = this.chunksFor(offset, length);
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for (let i = 0; i < chunks.length; i++) {
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if (!this.loaded.has(chunks[i])) {
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return true;
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}
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}
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return false;
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}
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/** 读取区间；跨未加载块时抛错。 */
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read(offset: number, length: number): string {
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const start: number = offset < 0 ? 0 : offset;
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const end: number = Math.min(this.totalSize, start + length);
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if (end <= start) {
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return '';
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}
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const chunks: number[] = this.chunksFor(start, end - start);
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for (let i = 0; i < chunks.length; i++) {
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if (!this.loaded.has(chunks[i])) {
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throw new Error('chunk ' + chunks[i] + ' not loaded');
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}
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}
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let out: string = '';
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for (let i = 0; i < chunks.length; i++) {
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out += this.loaded.get(chunks[i]) as string;
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}
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const sliceStart: number = start - chunks[0] * this.chunkSize;
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const sliceEnd: number = sliceStart + (end - start);
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return out.substring(sliceStart, sliceEnd);
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}
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/** 全部块已加载。 */
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isComplete(): boolean {
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return this.chunkCount() === 0 || this.loaded.size === this.chunkCount();
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}
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}
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