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TypeScript
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475export type Rows = { readonly length: number; slice(start: number, end: number): string[] }
/** Immutable row blocks, indexed by their start row. No flattened history copy. */export class RowIndex { private blocks: { start: number; rows: readonly string[] }[] = [] length = 0
append(rows: readonly string[]): void { if (!rows.length) return this.blocks.push({ start: this.length, rows }) this.length += rows.length }
replace(row: number, text: string): void { if (row < 0 || row >= this.length) return const index = this.blockAt(row) const block = this.blocks[index]! const rows = block.rows.slice() rows[row - block.start] = text this.blocks[index] = { start: block.start, rows } }
snapshot(): Rows { const saved = new RowIndex() saved.blocks = this.blocks.slice() saved.length = this.length return saved }
private blockAt(row: number): number { let low = 0; let high = this.blocks.length while (low < high) { const middle = (low + high) >>> 1 if (this.blocks[middle]!.start <= row) low = middle + 1 else high = middle } return low - 1 }
/** O(log(blocks) + visible rows), independent of the amount of offscreen text. */ slice(start: number, end: number): string[] { start = Math.max(0, start) end = Math.min(this.length, end) if (end <= start) return [] const rows: string[] = [] for (let i = this.blockAt(start); i < this.blocks.length; i++) { const block = this.blocks[i]! if (block.start >= end) break const from = Math.max(0, start - block.start) const to = Math.min(block.rows.length, end - block.start) for (let row = from; row < to; row++) rows.push(block.rows[row]!) } return rows }}
/** A cheap view over row sources: only the requested viewport is copied. */export function joinRows(parts: readonly Rows[]): Rows { return { length: parts.reduce((sum, part) => sum + part.length, 0), slice(start, end) { const rows: string[] = [] let offset = 0 for (const part of parts) { const from = Math.max(0, start - offset) const to = Math.min(part.length, end - offset) if (to > from) rows.push(...part.slice(from, to)) offset += part.length if (offset >= end) break } return rows }, }}