import { readdirSync, readFileSync } from 'node:fs';
import { join } from 'node:path';
import { OFFICER_ITEMS_DIR } from '../data-path';
import { capabilityRoots } from '../capability-sources';

// What the platform tells an agent about the surface it is speaking through.
//
// ── The problem ──
//
// The platform hosts the agent and never introduces itself. An agent gets a shell, a filesystem and a
// prompt; everything about the CLIENT on the other end has to be guessed. It writes
// `![](/home/me/chart.png)`, nothing renders, and nothing tells it why — because an `<img>` carries no
// bearer token, and it is the USER'S DEVICE that fetches the URL.
//
// That knowledge used to live as prose in a hand-written CLAUDE.md on one machine. This reads it from
// `capabilities/affordances/` instead, where it is versioned, inspectable, and contributable by a plugin.
//
// See `plugins/CLAUDE.md` for what an affordance is and what belongs in one.
//
// ── Deliberately dumb ──
//
// No filtering. Every affordance is compiled into every conversation, because the axis to filter on is
// not one dimension — for image rendering it is what the CLIENT renders, for gitea what TOOLING exists on
// the machine. Picking the wrong axis now and writing files against it costs more than loading two extra
// paragraphs. `TODO.md` carries the argument.

const YAML = (Bun as unknown as { YAML: { parse(input: string): unknown } }).YAML;

export const AFFORDANCES_DIR = join(OFFICER_ITEMS_DIR, 'affordances');

export type Affordance = {
  /** `<publisher>/<plugin>/<file>` — provenance, and unique. */
  id: string;
  name: string;
  description: string | null;
  /** An INTEGER, matching `capabilities/agents/`. Not the semver a plugin carries. */
  version: number;
  /** What is actually sent. */
  body: string;
};

function parse(raw: string): { fm: Record<string, unknown>; body: string } {
  const match = raw.match(/^---\n([\s\S]*?)\n---\n?([\s\S]*)$/);
  if (!match) return { fm: {}, body: raw.trim() };
  try {
    return { fm: (YAML.parse(match[1]!) as Record<string, unknown>) ?? {}, body: match[2]!.trim() };
  } catch {
    // A broken header is not a reason to lose the body. The agent needs the prose far more than the name,
    // and a file that vanished over a stray colon would be very hard to notice.
    return { fm: {}, body: match[2]!.trim() };
  }
}

/**
 * Every `.md` under `affordances/`, at any depth, sorted so the compiled block is stable.
 *
 * SYNCHRONOUS on purpose. `createSession` is not async, and making it so to read a few kilobytes would
 * ripple through every caller for no benefit — this runs once per session, not per request.
 */
export function loadAffordances(root: string = AFFORDANCES_DIR): Affordance[] {
  let entries: string[];
  try {
    // `recursive` because the tree is `<publisher>/<plugin>/<file>.md` and neither level is known here.
    entries = (readdirSync(root, { recursive: true }) as string[]).filter((f) => f.endsWith('.md'));
  } catch {
    // No directory yet is the ordinary state of a fresh install, not an error.
    return [];
  }

  const found = entries.sort().map((rel): Affordance | null => {
    try {
      const { fm, body } = parse(readFileSync(join(root, rel), 'utf8'));
      if (!body) return null;
      const versionRaw = fm.version;
      return {
        id: rel.replace(/\.md$/, ''),
        // Falls back to the path rather than to "Untitled": a heading naming the file beats one that
        // says nothing, and it makes a missing `name` visible without failing the load.
        name: fm.name == null ? rel.replace(/\.md$/, '') : String(fm.name),
        description: fm.description == null ? null : String(fm.description),
        version: typeof versionRaw === 'number' ? versionRaw : Number(versionRaw) || 1,
        body,
      };
    } catch {
      return null;
    }
  });

  return found.filter((a): a is Affordance => a !== null);
}

/**
 * One block for the system prompt, or null when there is nothing to say.
 *
 * `description` is NOT included — it answers "when should I reach for this", which only matters when an
 * agent chooses what to load. Everything here is already loaded, so it would be paid for and unread.
 */
export function compileAffordances(affordances: Affordance[]): string | null {
  if (!affordances.length) return null;
  return [
    '# This environment',
    '',
    'What the surface you are talking through will and will not do. Not instructions — facts about the',
    'client on the other end, which you cannot discover from the filesystem.',
    '',
    ...affordances.map((a) => `## ${a.name}\n\n${a.body}`),
  ].join('\n');
}

/** Read and compile in one step, for callers that only want the string. */
/**
 * Every affordance in force: the owner's own, plus each installed and enabled plugin's.
 *
 * Read in place rather than copied in — see `capability-sources.ts`. Unlike skills these are NOT
 * de-duplicated by name: an affordance is a paragraph of guidance, several can be true at once, and two
 * plugins describing the same surface differently is information rather than a collision.
 */
export function loadAffordancesAcross(roots: string[]): Affordance[] {
  return roots.flatMap((root) => loadAffordances(root));
}

/**
 * Read and compile in one step. Async because resolving which plugins are enabled reads the database;
 * called once per session, which is what makes that affordable.
 */
export async function affordanceBlock(): Promise<string | null> {
  return compileAffordances(loadAffordancesAcross(await capabilityRoots('affordances')));
}