idk

diff.ts

@@ -0,0 +1,134 @@
+import type { DiffChunk } from "./types.ts";
+
+// ~4 chars per token is a reasonable rough estimate for code
+function estimateTokens(text: string): number {
+  return Math.ceil(text.length / 4);
+}
+
+const SKIP_EXTENSIONS = new Set([
+  "lock", "sum",
+  "map",
+  "png", "jpg", "jpeg", "gif", "svg", "ico", "webp",
+  "woff", "woff2", "ttf", "eot",
+  "pdf", "zip", "tar", "gz",
+  "bin", "exe", "dll", "so", "dylib",
+]);
+
+const SKIP_PATTERNS = [
+  /^node_modules\//,
+  /^\.git\//,
+  /\/generated\//,
+  /\.pb\.\w+$/,
+  /\.min\.[jt]s$/,
+];
+
+function shouldSkip(filename: string): boolean {
+  if (!filename.includes(".")) return true; // no extension = likely binary
+  const ext = filename.split(".").pop()!.toLowerCase();
+  return SKIP_EXTENSIONS.has(ext) || SKIP_PATTERNS.some((p) => p.test(filename));
+}
+
+const EXT_TO_LANG: Record<string, string> = {
+  ts: "TypeScript", tsx: "TypeScript",
+  js: "JavaScript", jsx: "JavaScript", mjs: "JavaScript", cjs: "JavaScript",
+  py: "Python",
+  go: "Go",
+  rs: "Rust",
+  rb: "Ruby",
+  java: "Java",
+  kt: "Kotlin", kts: "Kotlin",
+  swift: "Swift",
+  cs: "C#",
+  cpp: "C++", cc: "C++", cxx: "C++", hpp: "C++",
+  c: "C",
+  php: "PHP",
+  sh: "Shell", bash: "Shell", zsh: "Shell",
+  yaml: "YAML", yml: "YAML",
+  json: "JSON",
+  md: "Markdown",
+  sql: "SQL",
+  html: "HTML", htm: "HTML",
+  css: "CSS", scss: "CSS", sass: "CSS", less: "CSS",
+  vue: "Vue",
+  svelte: "Svelte",
+  toml: "TOML",
+  xml: "XML",
+  tf: "Terraform", hcl: "HCL",
+};
+
+function detectLanguage(filename: string): string {
+  const ext = filename.split(".").pop()?.toLowerCase() ?? "";
+  return EXT_TO_LANG[ext] ?? "plain";
+}
+
+export interface DiffFile {
+  filename: string;
+  language: string;
+  hunks: Array<{ header: string; body: string }>;
+}
+
+export function parseDiff(rawDiff: string): DiffFile[] {
+  const files: DiffFile[] = [];
+
+  const sections = rawDiff.split(/^diff --git /m).filter((s) => s.trim());
+
+  for (const section of sections) {
+    const lines = section.split("\n");
+
+    // Use +++ / --- lines — more reliable than first line for renames and paths with spaces
+    const plusLine = lines.find((l) => l.startsWith("+++ "));
+    const minusLine = lines.find((l) => l.startsWith("--- "));
+
+    let filename: string;
+    if (plusLine?.startsWith("+++ b/")) {
+      filename = plusLine.slice(6);
+    } else if (plusLine === "+++ /dev/null" && minusLine?.startsWith("--- a/")) {
+      filename = minusLine.slice(6); // deleted file — use old path
+    } else {
+      continue;
+    }
+
+    if (shouldSkip(filename)) continue;
+
+    const language = detectLanguage(filename);
+    const hunks: DiffFile["hunks"] = [];
+    let header = "";
+    let bodyLines: string[] = [];
+
+    for (const line of lines) {
+      if (line.startsWith("@@")) {
+        if (header) hunks.push({ header, body: bodyLines.join("\n") });
+        header = line;
+        bodyLines = [];
+      } else if (header) {
+        bodyLines.push(line);
+      }
+    }
+    if (header) hunks.push({ header, body: bodyLines.join("\n") });
+
+    if (hunks.length > 0) files.push({ filename, language, hunks });
+  }
+
+  return files;
+}
+
+export function chunkFile(file: DiffFile, maxTokens: number): DiffChunk[] {
+  return file.hunks.map(({ header, body }) => {
+    let hunk = body;
+
+    if (estimateTokens(body) > maxTokens) {
+      // Truncate from bottom — top of the hunk has the most useful context
+      const lines = body.split("\n");
+      const charBudget = maxTokens * 4;
+      let chars = 0;
+      let i = 0;
+      while (i < lines.length && chars + (lines[i]?.length ?? 0) + 1 <= charBudget) {
+        chars += (lines[i]?.length ?? 0) + 1;
+        i++;
+      }
+      hunk = lines.slice(0, i).join("\n");
+    }
+
+    return { filename: file.filename, language: file.language, hunk, context: header };
+  });
+}