// Minimal unified-diff / git format-patch parser for pull request render.
// Handles the real `patch` field stored on sh.tangled.repo.pull records.

export interface DiffLine {
  type: "add" | "del" | "ctx";
  text: string;
}

export interface DiffHunk {
  header: string;
  lines: DiffLine[];
}

export interface DiffFile {
  from: string;
  to: string;
  hunks: DiffHunk[];
  binary: boolean;
}

function cleanPath(p: string): string {
  return p
    .replace(/^a\//, "")
    .replace(/^b\//, "");
}

export function parsePatch(patch: string): DiffFile[] {
  if (!patch) return [];
  const files: DiffFile[] = [];
  let file: DiffFile | null = null;
  let hunk: DiffHunk | null = null;

  const lines = patch.replace(/\r\n/g, "\n").split("\n");

  for (const raw of lines) {
    const line = raw;

    if (line.startsWith("diff --git ")) {
      if (file) files.push(file);
      file = { from: "", to: "", hunks: [], binary: false };
      hunk = null;
      const m = /diff --git a\/(\S+) b\/(\S+)/.exec(line);
      file.from = m ? cleanPath(m[1]) : "";
      file.to = m ? cleanPath(m[2]) : "";
      continue;
    }

    if (!file) continue;

    if (line.startsWith("Binary files ") || line.startsWith("GIT binary patch")) {
      file.binary = true;
      continue;
    }

    if (line.startsWith("@@ ")) {
      hunk = { header: line, lines: [] };
      file.hunks.push(hunk);
      continue;
    }

    if (hunk) {
      const first = line[0];
      if (first === "+") {
        hunk.lines.push({ type: "add", text: line.slice(1) });
      } else if (first === "-") {
        hunk.lines.push({ type: "del", text: line.slice(1) });
      } else if (line === "\\ No newline at end of file") {
        hunk.lines.push({ type: "ctx", text: line });
      } else {
        hunk.lines.push({ type: "ctx", text: line });
      }
    }
  }
  if (file) files.push(file);
  return files;
}

export function patchStats(patch: string): { additions: number; deletions: number; files: number } {
  const stats = { additions: 0, deletions: 0, files: 0 };
  for (const f of parsePatch(patch)) {
    stats.files += 1;
    for (const h of f.hunks) {
      for (const l of h.lines) {
        if (l.type === "add") stats.additions += 1;
        if (l.type === "del") stats.deletions += 1;
      }
    }
  }
  return stats;
}