diffRendering.ts

import type { FileDiffMetadata } from "@pierre/diffs";

export const DIFF_THEME_NAMES = {
  light: "pierre-light",
  dark: "pierre-dark",
} as const;

export type DiffThemeName = (typeof DIFF_THEME_NAMES)[keyof typeof DIFF_THEME_NAMES];

export const MAX_RENDERABLE_DIFF_LINE_LENGTH = 500_000;

export function resolveDiffThemeName(theme: "light" | "dark"): DiffThemeName {
  return theme === "dark" ? DIFF_THEME_NAMES.dark : DIFF_THEME_NAMES.light;
}

const FNV_OFFSET_BASIS_32 = 0x811c9dc5;
const FNV_PRIME_32 = 0x01000193;
const SECONDARY_HASH_SEED = 0x9e3779b9;
const SECONDARY_HASH_MULTIPLIER = 0x85ebca6b;

export function fnv1a32(
  input: string,
  seed = FNV_OFFSET_BASIS_32,
  multiplier = FNV_PRIME_32,
): number {
  let hash = seed >>> 0;
  for (let index = 0; index < input.length; index += 1) {
    hash ^= input.charCodeAt(index);
    hash = Math.imul(hash, multiplier) >>> 0;
  }
  return hash >>> 0;
}

export function buildPatchCacheKey(patch: string, scope = "diff-panel"): string {
  const normalizedPatch = patch.trim();
  const primary = fnv1a32(normalizedPatch, FNV_OFFSET_BASIS_32, FNV_PRIME_32).toString(36);
  const secondary = fnv1a32(
    normalizedPatch,
    SECONDARY_HASH_SEED,
    SECONDARY_HASH_MULTIPLIER,
  ).toString(36);
  return `${scope}:${normalizedPatch.length}:${primary}:${secondary}`;
}

export function canRenderFileDiff(
  fileDiff: Pick<FileDiffMetadata, "additionLines" | "deletionLines">,
): boolean {
  return (
    fileDiff.additionLines.every((line) => line.length <= MAX_RENDERABLE_DIFF_LINE_LENGTH) &&
    fileDiff.deletionLines.every((line) => line.length <= MAX_RENDERABLE_DIFF_LINE_LENGTH)
  );
}