// What the forge's holder does for a delivery (novox/hq ADR 0239): the commit's note under
// refs/notes/mesh-plan and the delivery's view on its pull request, asked through the seat git's verbs `note` and
// `view` (seat.ts). The forge is this module's; no delivery part writes to it itself.
//
// **The note is written in the forge's own repository, as the forge's own user.** The forge's API reads a
// note and writes none, and a push needs a clone and a credential nobody else should hold; the forge's
// container holds the bare repository and git. So the line is appended there, by `git notes append`, as the
// account the forge runs as — the mesh's own forge, never a person's or an agent's hand. Appending is
// idempotent here: a line the note already has is not added again, so asking twice adds nothing.
//
// Pure functions and an injectable runner, so this is tested without a forge.

import { execFile } from "node:child_process";
import { promisify } from "node:util";
/** How a command is run: docker on the forge's machine, or a test's. */
export type Runner = (file: string, args: string[]) => Promise<{ stdout: string; code: number }>;

const execFileP = promisify(execFile);

export const run: Runner = async (file, args) => {
  try {
    const { stdout } = await execFileP(file, args, { maxBuffer: 4 << 20 });
    return { stdout, code: 0 };
  } catch (err) {
    const e = err as { code?: number; stdout?: string };
    return { stdout: e.stdout ?? "", code: typeof e.code === "number" ? e.code : 1 };
  }
};

const name = /^[A-Za-z0-9_.-]+$/;
const sha = /^[0-9a-fA-F]{7,64}$/;
const ref = /^[a-z0-9][a-z0-9-]*$/;

/** A note line as it may be written: one line, bounded, nothing that is not text. */
export function noteLine(line: string): string {
  const one = String(line ?? "").replace(/[\r\n\t]+/g, " ").replace(/\s+/g, " ").trim();
  if (!one) throw new Error("an empty line is no note");
  return one.length > 2000 ? one.slice(0, 1999) + "…" : one;
}

/** Where the forge keeps a repository, inside its container. */
export function gitDir(owner: string, repo: string): string {
  if (!name.test(owner) || !name.test(repo)) throw new Error(`${owner}/${repo} is not a repository's name`);
  return `/data/git/repositories/${owner.toLowerCase()}/${repo.toLowerCase()}.git`;
}

/** The commands the note is read and appended with, in the forge's container, as its user. */
export function noteArgs(container: string, owner: string, repo: string, commit: string, notesRef: string, line?: string): string[] {
  if (!name.test(container)) throw new Error(`${container} is not a container's name`);
  if (!sha.test(commit)) throw new Error(`${commit} is not a commit`);
  if (!ref.test(notesRef)) throw new Error(`${notesRef} is not a notes ref`);
  const base = ["exec", "-u", "git", container, "git", "--git-dir", gitDir(owner, repo),
    "-c", "user.name=mesh", "-c", "user.email=mesh@mesh.invalid", "notes", `--ref=${notesRef}`];
  return line === undefined ? [...base, "show", commit] : [...base, "append", "-m", noteLine(line), commit];
}

/** Append a line to a commit's note, unless the note already holds it. Answers whether it was added. */
export async function appendNote(runner: Runner, container: string, owner: string, repo: string, commit: string,
  notesRef: string, line: string, heldId?: string): Promise<{ added: boolean; lines: number }> {
  const wanted = noteLine(line);
  const shown = await runner("docker", noteArgs(container, owner, repo, commit, notesRef));
  // No note yet is git's exit 1 with nothing on stdout; anything else unreadable is said.
  const lines = shown.code === 0 ? shown.stdout.split("\n").filter((l) => l.trim() !== "") : [];
  // A line that carries the act's id is the act already done, whatever else it says.
  if (lines.includes(wanted) || (heldId && lines.some((l) => l.includes(`[${heldId}]`)))) return { added: false, lines: lines.length };
  const appended = await runner("docker", noteArgs(container, owner, repo, commit, notesRef, wanted));
  if (appended.code !== 0) throw new Error(`the note on ${commit.slice(0, 8)} could not be appended (git exited ${appended.code})`);
  return { added: true, lines: lines.length + 1 };
}

/** The marker that makes one comment of a pull request the delivery's view. */
export const VIEW_MARKER = "<!-- mesh-delivery:view -->";

/** The view's body, marked: mesh-delivery writes it, this keeps exactly one of them per pull request. */
export function viewBody(body: string): string {
  const b = String(body ?? "");
  return b.includes(VIEW_MARKER) ? b : `${VIEW_MARKER}\n${b}`;
}

/** Which comment is the view: the first that carries the marker, or none yet. */
export function viewComment<T extends { id: number; body: string }>(comments: T[]): T | undefined {
  return comments.find((c) => c.body.includes(VIEW_MARKER));
}