// A pull request's merge check (novox/hq to-be 45 §9): what the forge's announcer says when a pull
// request's head moves, and what it sets as the pull request's status when the mesh says the verdict.
//
// **Before merge, never after.** Every check the mesh had ran after a merge, on a machine: a manifest the
// node-engine refuses (issue 236), an identity a real machine's name made too long (263). So each new head
// of an open pull request is announced as `pull.updated`; the controller asks the build seat to check it
// against every machine of the mesh's facts; and the verdict comes back as the controller's `checked`,
// which this sets as the head commit's status — and, when it is not a pass, as a comment saying why.
//
// Pure functions here, so they are tested without a forge; index.ts does the asking and the setting.

import type { CommitStatus, GiteaPull } from "./client.js";

/** The status context a merge check's gate is kept under: one per commit, the newest replacing the last. */
export const CHECK_CONTEXT = "mesh/merge-gate";

/** The status context of the repository's own merge-check.sh, the check's second layer (novox/hq ADR 0237). */
export const REPO_CHECK_CONTEXT = "mesh/repo-check";

/** One layer of a check, judged. */
export interface Layer {
  verdict: string;
  summary: string;
  /** The modules a merge of the change would move, as the controller's planner reckons it… */
  modules?: string[];
  /** …and those it would build after them because they stand on them. */
  dependents?: string[];
}

/** What the controller says as `checked` (mesh-controller internal/link, Checked). */
export interface Checked {
  owner: string;
  repo: string;
  number?: number;
  commit: string;
  verdict: string;
  summary: string;
  report?: string;
  id: string;
  on?: string;
  /** The gate — the modules of the mesh's graph the change touches — and the repository's own check. A
   *  controller from before the layers says neither, and its verdict is the gate's. */
  gate?: Layer;
  "repo-check"?: Layer;
  /** The change plan of the commit checked (novox/hq ADR 0238): what a merge of it would build and send. */
  plan?: ChangePlan;
  /** Set on a delivery group's composed check (novox/hq ADR 0239): not this head's merge gate. */
  group?: string;
}

/** A change plan, as the controller says it (mesh-controller internal/link, ChangePlan). */
export interface ChangePlan {
  repository: string;
  base: string;
  head: string;
  moved?: string[];
  dependents?: string[];
  new?: string[];
  unread?: string[];
  tiers?: string[][];
  machines?: { machine: string; receives?: string[]; waits?: string[] }[];
  steps?: string[];
  summary: string;
}

/** Whether a plan builds anything: a change that touches the mesh's graph. */
function builds(plan?: ChangePlan): boolean {
  return !!plan && ((plan.moved?.length ?? 0) > 0 || (plan.new?.length ?? 0) > 0);
}

/** A change plan as a person reads it on the pull request. */
export function planText(plan: ChangePlan): string {
  const lines = [`**Change plan** — ${plan.summary}`];
  (plan.tiers ?? []).forEach((tier, i) => lines.push(`- tier ${i}: ${tier.join(", ")}`));
  for (const m of plan.machines ?? []) {
    const parts: string[] = [];
    if (m.receives?.length) parts.push(`receives ${m.receives.join(", ")}`);
    if (m.waits?.length) parts.push(`waits for a person: ${m.waits.join(", ")}`);
    lines.push(`- ${m.machine}: ${parts.join("; ")}`);
  }
  for (const step of plan.steps ?? []) lines.push(`- ${step}`);
  if (plan.unread?.length) lines.push(`- read by no module's build: ${plan.unread.join(", ")}`);
  return lines.join("\n");
}

/** The heads already announced, keyed `owner/repo#number`, so a restart announces nothing twice. */
export type Announced = Record<string, string>;

/** Which open pull requests have a head not yet announced. A pull request merged or closed is not
 *  open and is never asked about. */
export function headsToAnnounce(full: string, pulls: GiteaPull[], announced: Announced): GiteaPull[] {
  return pulls.filter((p) => p.state === "open" && !!p.head_sha && announced[`${full}#${p.number}`] !== p.head_sha);
}

// **A required status is success or it blocks** (novox/hq issue 293). The forge combines `warning` as a
// failure, and a branch whose protection requires mesh/merge-gate or mesh/repo-check — with no
// administrator override — will not merge past one. So the controller's `warning`, a note and never a
// question, is set as `success` with the note in its description; only what a person must decide is a
// `failure`, with why. The mapping, verdict by verdict:
//
//   pass                                     → success
//   warning (a note: rebuild width, a problem
//     already so on the base, a script's own) → success, "pass, with a note: …"
//   repo-check, no merge-check.sh, not required → success, "no repository check defined"
//   repo-check, no merge-check.sh, required (or
//     the protection unreadable)             → failure: a person adds one, or lifts the requirement
//   fail                                     → failure
//   error, or no verdict                     → error — never a success

/** The forge's state for a verdict: an error is the forge's `error`, never a success; a warning is a note. */
function stateOf(verdict: string): CommitStatus["state"] {
  return verdict === "pass" || verdict === "warning" ? "success" : verdict === "fail" ? "failure" : "error";
}

/** How a verdict is said in a status's description: a warning as the pass with a note it is. */
function saidAs(verdict: string): string {
  return verdict === "warning" ? "pass, with a note" : verdict || "error";
}

function described(verdict: string, summary: string, modules?: string[], dependents?: string[]): string {
  // The forge keeps a short description; the rest is the comment's.
  let d = `${saidAs(verdict)}: ${summary}`;
  if (modules?.length) d += ` [${modules.join(", ")}${dependents?.length ? ` +${dependents.length} dependent(s)` : ""}]`;
  return clipped(d);
}

function clipped(d: string): string {
  d = d.replace(/\s+/g, " ").trim();
  return d.length > 140 ? d.slice(0, 139) + "…" : d;
}

/** What the forge says of a repository's own check beyond the controller's verdict, asked by index.ts only
 *  when the verdict is a warning: whether the head holds a merge-check.sh, and whether the base branch's
 *  protection requires mesh/repo-check. Unknown is undefined. */
export interface RepoCheckFacts {
  defined?: boolean;
  required?: boolean;
}

/** The description of a required repository check that is not defined. */
export const UNDEFINED_REQUIRED = "fail: mesh/repo-check is required here and this head defines no merge-check.sh — " +
  "a person adds one, or lifts the requirement from the branch's protection";

/** The repository check's status: its verdict, unless the repository defines no check at all — then
 *  success where the check is not required, and a failure for a person where it is (or may be). */
function repoStatus(repo: Layer, facts: RepoCheckFacts): CommitStatus {
  if (repo.verdict === "warning" && facts.defined === false) {
    return facts.required === false
      ? { state: "success", context: REPO_CHECK_CONTEXT, description: "no repository check defined" }
      : { state: "failure", context: REPO_CHECK_CONTEXT, description: clipped(UNDEFINED_REQUIRED) };
  }
  return { state: stateOf(repo.verdict), context: REPO_CHECK_CONTEXT, description: described(repo.verdict, repo.summary) };
}

/** Whether the repository check is a failure a person must read: failed, could not run, or required and
 *  not defined. */
function repoWrong(repo: Layer | undefined, facts: RepoCheckFacts): boolean {
  return !!repo && repoStatus(repo, facts).state !== "success";
}

/** The forge's status for the gate. */
export function statusFor(c: Checked): CommitStatus {
  const gate = c.gate ?? { verdict: c.verdict, summary: c.summary };
  // With a plan, the status says what the change does and how it was judged: "pass: builds gitea → anchor;
  // no bus step; every machine composes…".
  const description = builds(c.plan)
    ? described(gate.verdict, `${c.plan!.summary}; ${gate.summary}`)
    : described(gate.verdict, gate.summary, gate.modules, gate.dependents);
  return { state: stateOf(gate.verdict), context: CHECK_CONTEXT, description };
}

/** Every status a verdict sets: the gate's, and the repository's own check's when it was said. */
export function statusesFor(c: Checked, facts: RepoCheckFacts = {}): CommitStatus[] {
  const out = [statusFor(c)];
  const repo = c["repo-check"];
  if (repo) out.push(repoStatus(repo, facts));
  return out;
}

/** The comment a verdict leaves on its pull request, with the check's own account: the change plan of a
 *  change that builds something (novox/hq ADR 0238), and why, when the gate is not a pass or the
 *  repository's own check failed or could not run. A repository with no merge-check.sh, touching nothing,
 *  is said by its statuses alone, not by a comment on every push. */
export function commentFor(c: Checked, facts: RepoCheckFacts = {}): string | null {
  const gate = c.gate ?? { verdict: c.verdict, summary: c.summary };
  const repo = c["repo-check"];
  const wrong = repoWrong(repo, facts);
  if (gate.verdict === "pass" && !wrong && !builds(c.plan)) return null;
  const lines = [`**Merge check** at \`${c.commit.slice(0, 8)}\``, ""];
  lines.push(`- \`${CHECK_CONTEXT}\`: **${saidAs(gate.verdict).toUpperCase()}** — ${gate.summary}` +
    (gate.modules?.length ? ` (modules: ${gate.modules.join(", ")}` +
      (gate.dependents?.length ? `; built after them: ${gate.dependents.join(", ")}` : "") + ")" : ""));
  if (repo) {
    const st = repoStatus(repo, facts);
    lines.push(`- \`${REPO_CHECK_CONTEXT}\`: ` + (repo.verdict === "warning" && facts.defined === false
      ? `**${st.state === "success" ? "PASS" : "FAIL"}** — ${st.description.replace(/^fail: /, "")}`
      : `**${saidAs(repo.verdict).toUpperCase()}** — ${repo.summary}`));
  }
  if (builds(c.plan)) lines.push("", planText(c.plan!));
  const ran = c.on ? `\n\nRun by the build seat on ${c.on} as \`${c.id}\` (\`builds --log ${c.id}\`).` : "";
  const report = c.report ? `\n\n\`\`\`\n${c.report.replace(/```/g, "'''")}\n\`\`\`` : "";
  return lines.join("\n") + ran + report;
}