text-edit-model.ts

import { assert } from "https://deno.land/std@0.149.0/testing/asserts.ts";

import fc from 'https://cdn.skypack.dev/fast-check';

type BufferPosition = {
  x: number;
  y: number;
}

type ContentIndex = {
  x: number;
  y: number;
}

type TextContent = string[][];

type TextBuffer = string[][];

function contentToBuffer(content: TextContent, lineWidth: number): TextBuffer {
  const buffer: string[][] = [];
  content.forEach(line => {
    const numBufferLines = Math.ceil(line.length / lineWidth);
    for(let i = 0; i < numBufferLines; i++) {
      const lineOffset = i * lineWidth;
      buffer.push(line.slice(lineOffset, lineOffset + lineWidth));
    }
  });
  
  return buffer;
}

function positionToContentIdx(pos: BufferPosition, content: TextContent, lineWidth: number): ContentIndex {
  let bufferX = 0;
  let bufferY = 0;
  let contentX = 0;
  let contentY = 0;
  let contentIdx: ContentIndex | null = null;

  content.forEach(line => {
    line.forEach(_ => {
      if (bufferX === pos.x && bufferY === pos.y) {
        contentIdx = {
          x: contentX,
          y: contentY,
        }
        return
      } else if (bufferX === lineWidth - 1) {
        bufferX = 0;
        bufferY += 1;
        contentX += 1;
      } else {
        bufferX += 1;
        contentX += 1;
      }
    });

    if (contentIdx !== null) {
      return
    }

    bufferX = 0;
    bufferY += 1;
    contentX = 0;
    contentY += 1;
  });

  if (contentIdx !== null) {
    return contentIdx;
  }

  console.error("Unable to find content index for position!");
  return {
    x: 0,
    y: 0
  }
}

class TextEdit {
  lineWidth;
  content: TextContent;
  cursor: BufferPosition;

  constructor(lineWidth: number = 80, content: TextContent = [[]], cursor: BufferPosition = { x: 0, y: 0 }) {
    this.lineWidth = lineWidth, this.content = content, this.cursor = cursor;
  }

  Type(char: string) {
    if (char === "\n") {
      this.content.push([]);
      this.cursor.x = 0;
      this.cursor.y += 1;
      return;
    }

    this.content[this.content.length - 1].push(char);

    if (this.cursor.x === this.lineWidth) {
      this.cursor.x = 0;
      this.cursor.y += 1;
    } else {
      this.cursor.x += 1;
    }
  }

  Click(pos: BufferPosition) {
    this.cursor = pos;
  }

  Delete() {
    const contentIdx = positionToContentIdx(this.cursor, this.content, this.lineWidth);
    const line = this.content[contentIdx.y];

    line.splice(contentIdx.x, 1);
  }

  Render() {
    return contentToBuffer(this.content, this.lineWidth);
  }
}

Deno.test("Line widths are always preserved", (_) => {
  const contentGen = fc.array(fc.array(fc.char()));
  const lineWidthGen = fc.integer({ min: 1, max: 160 });

  return fc.assert(
    fc.property(contentGen, lineWidthGen, (content: TextContent, lineWidth: number) => {
      const textEdit = new TextEdit(lineWidth, content);
      const buffer = textEdit.Render();

      assert(buffer.every(line => line.length <= lineWidth));
    })
  );
});