initial version

logic/board.ts

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+import type { SectionData, SectionPosition } from "../types/section.ts";
+import type {
+  BoardConfig,
+  BoardData,
+  CharacterPosition,
+} from "../types/board.ts";
+import { createSection } from "./section.ts";
+
+export function createBoard(config: BoardConfig): BoardData {
+  const sections: SectionData[][] = Array(config.ySections).map((_, sy) =>
+    Array(config.xSections).map((_, sx) => createSection({ sx, sy }, config))
+  );
+
+  return { config, sections };
+}
+
+export function locateSection(
+  { x, y }: CharacterPosition,
+  config: BoardConfig
+): SectionPosition {
+  return {
+    sx: Math.floor(x / config.sectionWidth),
+    sy: Math.floor(y / config.sectionHeight),
+  };
+}

logic/character.ts

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+const segmenter = new Intl.Segmenter("en", { granularity: "grapheme" });
+const cjkRegex =
+  /[\p{Unified_Ideograph}\u30A0-\u30FF\u3040-\u309F\u31F0-\u31FF]/u;
+const printableASCIIRegex = /^[\x20-\x7E]$/;
+
+export function getCharacterWidth(ch: string): number {
+  const segments = [...segmenter.segment(ch)];
+  if (segments.length !== 1)
+    throw new Error(
+      `Expected exactly one grapheme cluster, got ${segments.length}.`
+    );
+
+  const matchesASCII = ch.match(printableASCIIRegex);
+  const matchesCJK = ch.match(cjkRegex);
+
+  if (!matchesASCII && !matchesCJK) throw new Error(`Invalid character: ${ch}`);
+
+  // TODO: Support Emojis.
+  return matchesCJK ? 2 : 1;
+}

logic/section.ts

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+import { getCharacterWidth } from "../mod.ts";
+import type { BoardConfig } from "../types/board.ts";
+import { BoardChange } from "../types/change.ts";
+import type { SectionData, SectionPosition } from "../types/section.ts";
+
+export function createSection(
+  { sx, sy }: SectionPosition,
+  boardConfig: BoardConfig
+): SectionData {
+  const offsetX = sx * boardConfig.sectionWidth;
+  const offsetY = sy * boardConfig.sectionHeight;
+
+  const ch: string[][] = Array(boardConfig.sectionHeight).fill(
+    Array(boardConfig.sectionWidth).fill(boardConfig.defaultCh)
+  );
+  const color: string[][] = Array(boardConfig.sectionHeight).fill(
+    Array(boardConfig.sectionWidth).fill(boardConfig.defaultColor)
+  );
+  const bgColor: string[][] = Array(boardConfig.sectionHeight).fill(
+    Array(boardConfig.sectionWidth).fill(boardConfig.defaultBgColor)
+  );
+  const width: number[][] = Array(boardConfig.sectionHeight).fill(
+    Array(boardConfig.sectionWidth).fill(boardConfig.defaultWidth)
+  );
+
+  return { offsetX, offsetY, ch, color, bgColor, width };
+}
+
+export function applyChange(change: BoardChange, section: SectionData) {
+  const xInSection = change.x - section.offsetX;
+  const yInSection = change.y - section.offsetY;
+
+  if (change.ch) {
+    const chWidth = getCharacterWidth(change.ch);
+    section.ch[yInSection][xInSection] = change.ch;
+    section.width[yInSection][xInSection] = chWidth;
+  }
+  if (change.color) {
+    section.color[yInSection][xInSection] = change.color;
+  }
+  if (change.bg_color) {
+    section.bgColor[yInSection][xInSection] = change.bg_color;
+  }
+}