import type { Context } from "@earendil-works/chord";
import { type FileError, getOrThrow } from "@earendil-works/pi-durable/env";
import ignore, { type Ignore } from "ignore";
import type { Environment } from "@berry/api/environment.ts";

function unavailable(error: FileError): boolean {
  return ["not_found", "not_directory", "permission_denied", "invalid"].includes(error.code);
}

function score(path: string, query: string): number {
  const text = path.toLowerCase();
  if (query.length > text.length) return -Infinity;
  let previous = Array<number>(text.length).fill(-Infinity);
  for (let q = 0; q < query.length; q++) {
    const current = Array<number>(text.length).fill(-Infinity);
    let best = -Infinity;
    for (let i = 0; i < text.length; i++) {
      if (text[i] === query[q]) {
        const boundary = i === 0 || /[/._-]/u.test(text[i - 1]) ||
          (path[i] !== text[i] && path[i - 1] === text[i - 1]);
        current[i] = (q === 0 ? -i * 0.1 : Math.max(best, (previous[i - 1] ?? -Infinity) + 8)) +
          1 + (boundary ? 6 : 0);
      }
      best = Math.max(best, previous[i]) - 1;
    }
    previous = current;
  }
  const quality = Math.max(...previous);
  if (!Number.isFinite(quality)) return -Infinity;
  const name = text.replace(/\/$/u, "").split("/").at(-1)!;
  const rank = text === query || name === query
    ? 3
    : name.startsWith(query)
    ? 2
    : name.includes(query)
    ? 1
    : 0;
  return rank * 1000 + quality - path.length * 0.01;
}

const WALK_WIDTH = 16;

/** Whether `path` names a directory, through any links; `false` where nothing can be seen. */
async function isDirectory(env: Environment, path: string, context: Context): Promise<boolean> {
  const canonical = await env.canonicalPath(path, context);
  const info = canonical.ok ? await env.fileInfo(canonical.value, context) : canonical;
  if (info.ok) return info.value.kind === "directory";
  if (unavailable(info.error)) return false;
  throw info.error;
}

/** Paths extending a reference from the environment's working directory, with directories left open. */
export async function references(
  env: Environment,
  prefix: string,
  context: Context,
): Promise<string[]> {
  if (/\s/u.test(prefix) || prefix.includes("\u0000")) return [];
  if (prefix === "~") return ["~/"];
  let base = prefix.match(/^(?:~\/|\/|(?:\.\.?\/)+)/u)?.[0] ?? "";
  let query = prefix.slice(base.length);
  let directory = getOrThrow(await env.absolutePath(base || ".", context));
  while (query.includes("/")) {
    const part = query.slice(0, query.indexOf("/") + 1);
    const next = getOrThrow(await env.joinPath([directory, part], context));
    if (!(await isDirectory(env, next, context))) break;
    base += part;
    query = query.slice(part.length);
    directory = next;
  }
  query = query.toLowerCase();
  const matches: { path: string; score: number }[] = [];
  type Rule = { root: string; matcher: Ignore };
  type Visit = { path: string; current: string; rules: Rule[] };
  async function visit({ path, current, rules: inherited }: Visit): Promise<Visit[]> {
    const entries = await env.listDir(current, context);
    if (!entries.ok) {
      if (unavailable(entries.error)) return [];
      throw entries.error;
    }
    let rules = inherited;
    const gitignore = entries.value.find((entry) => entry.name === ".gitignore");
    if (gitignore) {
      const source = await env.readTextFile(gitignore.path, context);
      if (source.ok) rules = [...rules, { root: path, matcher: ignore().add(source.value) }];
      else if (!unavailable(source.error)) throw source.error;
    }
    const next: Visit[] = [];
    for (const entry of entries.value) {
      if (/\s/u.test(entry.name) || [".git", ".jj", "node_modules"].includes(entry.name)) continue;
      const relative = path + entry.name;
      const directory = entry.kind === "directory" ||
        (entry.kind === "symlink" && await isDirectory(env, entry.path, context));
      const candidate = relative + (directory ? "/" : "");
      let ignored = false;
      for (const rule of rules) {
        const result = rule.matcher.test(candidate.slice(rule.root.length));
        if (result.ignored) ignored = true;
        else if (result.unignored) ignored = false;
      }
      if (ignored) continue;
      const quality = query === "" ? 0 : score(candidate, query);
      if (Number.isFinite(quality)) matches.push({ path: base + candidate, score: quality });
      // explicit symlink directories can be browsed, but recursive search must not follow cycles
      if (query !== "" && entry.kind === "directory") {
        next.push({ path: candidate, current: entry.path, rules });
      }
    }
    return next;
  }
  // several directories at once, as each can be a round trip to another machine
  const pending: Visit[] = [{ path: "", current: directory, rules: [] }];
  const running = new Set<Promise<void>>();
  while (pending.length > 0 || running.size > 0) {
    while (pending.length > 0 && running.size < WALK_WIDTH) {
      const visiting: Promise<void> = visit(pending.pop()!).then((next) => {
        running.delete(visiting);
        pending.push(...next);
      });
      running.add(visiting);
    }
    await Promise.race(running);
  }
  return matches.sort((a, b) => b.score - a.score || a.path.localeCompare(b.path))
    .slice(0, 50).map((match) => match.path);
}