import type { CommitSummary } from "~/lib/types";

export type PatchKind = "diff" | "patch";

/** RFC 2822 date as git writes it. Author time zones are not kept, so dates are given in UTC. */
function mailDate(timestamp: number): string {
  return new Date(timestamp).toUTCString().replace("GMT", "+0000");
}

function withTrailingNewline(text: string): string {
  return text === "" || text.endsWith("\n") ? text : `${text}\n`;
}

/** Splits a commit message into the subject line and the body after the first blank line, like git does. */
function splitMessage(message: string): { subject: string; body: string } {
  const lines = message.replace(/\r\n/g, "\n").split("\n");
  const blank = lines.findIndex((line) => line.trim() === "");
  const subjectLines = blank === -1 ? lines : lines.slice(0, blank);
  const body =
    blank === -1
      ? ""
      : lines
          .slice(blank + 1)
          .join("\n")
          .trim();
  return { subject: subjectLines.join(" ").trim(), body };
}

/** One `git format-patch` mbox message per commit, numbered `[PATCH i/n]` when there is more than one. */
export function formatPatchSeries(
  entries: Array<{
    commit: Pick<CommitSummary, "sha" | "message" | "authorName" | "authorEmail" | "authoredAt">;
    patch: string;
  }>,
): string {
  const total = entries.length;
  return entries
    .map(({ commit, patch }, index) => {
      const { subject, body } = splitMessage(commit.message);
      const prefix = total > 1 ? `[PATCH ${index + 1}/${total}]` : "[PATCH]";
      const header = [
        `From ${commit.sha} Mon Sep 17 00:00:00 2001`,
        `From: ${commit.authorName} <${commit.authorEmail}>`,
        `Date: ${mailDate(commit.authoredAt)}`,
        `Subject: ${prefix} ${subject}`,
        "",
      ];
      const message = body ? `${body}\n` : "";
      return `${header.join("\n")}\n${message}---\n${withTrailingNewline(patch)}-- \ngitfor\n`;
    })
    .join("\n");
}

export function patchResponse(kind: PatchKind, text: string, name: string): Response {
  return new Response(text, {
    headers: {
      "content-type": kind === "patch" ? "text/x-patch; charset=utf-8" : "text/x-diff; charset=utf-8",
      "content-disposition": `inline; filename="${name}.${kind}"`,
      "x-content-type-options": "nosniff",
      "cache-control": "private, max-age=60",
    },
  });
}