/**
 * Roots and session names.
 *
 * One root directory = one sl0ppij session. The session name is derived from
 * the root's basename so that typing `sl0ppi` in ~/dev always lands in the same
 * session instead of minting another randomly-named one.
 *
 * The registry (session name -> root path) exists because a tab purpose stores
 * a path *relative to the root*, and `list-panes --json` exposes no cwd, so
 * without it there is no way back from a session to a directory. It is a
 * rebuildable index, not a source of truth: delete it and the next `up --root`
 * writes it again. It doubles as the record of which sessions are ours, which
 * is how sl0ppi avoids touching sessions it did not create.
 */

import { existsSync, mkdirSync, readFileSync, writeFileSync } from "node:fs";
import { basename, dirname, join, resolve } from "node:path";
import { homedir } from "node:os";
import { createHash } from "node:crypto";
import { isProjectDir } from "./discover.ts";

export function configDir(env: NodeJS.ProcessEnv = process.env): string {
  return env.SL0PPI_CONFIG_DIR ?? join(env.XDG_CONFIG_HOME ?? join(homedir(), ".config"), "sl0ppi");
}

export function registryPath(env?: NodeJS.ProcessEnv): string {
  return join(configDir(env), "roots.json");
}

export type Registry = Record<string, string>;

export function loadRegistry(env?: NodeJS.ProcessEnv): Registry {
  const path = registryPath(env);
  try {
    const parsed = JSON.parse(readFileSync(path, "utf8"));
    return typeof parsed === "object" && parsed !== null ? (parsed as Registry) : {};
  } catch {
    return {}; // missing or corrupt: it is an index, so rebuild rather than fail
  }
}

export function saveRegistry(registry: Registry, env?: NodeJS.ProcessEnv): void {
  const path = registryPath(env);
  mkdirSync(dirname(path), { recursive: true });
  writeFileSync(path, `${JSON.stringify(registry, null, 2)}\n`);
}

/**
 * Session name for a root.
 *
 * Sanitised to something safe to type and to pass as a session name, and
 * disambiguated with a short hash when another root already claims the name —
 * two checkouts both called `api` must not fight over one session.
 */
export function sessionNameFor(root: string, registry: Registry = {}): string {
  const cleaned = basename(resolve(root)).replace(/[^A-Za-z0-9_-]/g, "-").replace(/^-+|-+$/g, "");
  const base = cleaned.length > 0 ? cleaned : "root";
  const claimed = registry[base];
  if (claimed === undefined || resolve(claimed) === resolve(root)) return base;
  return `${base}-${createHash("sha256").update(resolve(root)).digest("hex").slice(0, 6)}`;
}

export interface ResolvedRoot {
  root: string;
  session: string;
  /** Set when the CWD is itself a project, so `sl0ppi` can focus its tab. */
  project?: string;
}

/**
 * Work out which root the user means.
 *
 *   --root DIR      -> that, explicitly
 *   inside a project-> its parent is the root, and we remember which project
 *   inside a session-> the root the session is registered against
 *   otherwise       -> the cwd is the root
 */
export function resolveRoot(options: {
  rootFlag?: string;
  cwd: string;
  sessionEnv?: string | null;
  registry?: Registry;
}): ResolvedRoot {
  const registry = options.registry ?? {};
  const cwd = resolve(options.cwd);

  if (options.rootFlag) {
    const root = resolve(options.rootFlag);
    return { root, session: sessionNameFor(root, registry) };
  }

  if (isProjectDir(cwd)) {
    const root = dirname(cwd);
    return { root, session: sessionNameFor(root, registry), project: basename(cwd) };
  }

  if (options.sessionEnv && registry[options.sessionEnv]) {
    const root = resolve(registry[options.sessionEnv] as string);
    return { root, session: options.sessionEnv };
  }

  return { root: cwd, session: sessionNameFor(cwd, registry) };
}

/** Record that `session` belongs to `root`, so later runs can find it. */
export function rememberRoot(session: string, root: string, env?: NodeJS.ProcessEnv): void {
  const registry = loadRegistry(env);
  const resolved = resolve(root);
  if (registry[session] === resolved) return;
  registry[session] = resolved;
  saveRegistry(registry, env);
}

export function rootExists(root: string): boolean {
  return existsSync(root);
}