import { mkdir, readdir, rename, stat } from "node:fs/promises";
import { join, relative, resolve } from "node:path";
import type { ServerContext } from "@stc/contracts";
import { withCourseLock } from "@stc/core";
import { readRawManifest, writeManifest, type RawManifest } from "./util/manifest";
import { slugify, uniqueId } from "./util/text";
import { extractFrame, type Tools } from "./media";

export interface ImportEnv { [k: string]: string | undefined }
/** `env` supplies only tool paths and transcription credentials (STC_FFMPEG, STC_FFPROBE, STC_TRANSCRIBE_KEY, _MODEL). */
export interface ImportOptions { env?: ImportEnv }

export interface Deps {
  ctx: ServerContext;
  env: ImportEnv;
  tools: Tools;
  /** AppConfig.python (STC_PYTHON). */
  python: string;
  /** AppConfig.importRoots (STC_IMPORT_ROOTS). */
  importRoots: string[];
  /** AppConfig.transcribeUrl (STC_TRANSCRIBE_URL). */
  transcribeUrl: string | null;
}

export const coursesDir = (d: Deps) => resolve(d.ctx.config.importedCoursesDir ?? resolve(d.ctx.config.dataDir, "courses"));
export const cacheDir = (d: Deps) => resolve(d.ctx.config.cacheDir ?? resolve(d.ctx.config.dataDir, "cache"));
const studioRepo = (d: Deps, id: string) => join(d.ctx.config.studioReposDir ?? resolve(d.ctx.config.dataDir, "studio", "repos"), `${id}.git`);
export const deckCacheDir = (d: Deps, courseId: string, deckId: string) => join(cacheDir(d), "decks", courseId, deckId);
export const coverCacheDir = (d: Deps, courseId: string) => join(cacheDir(d), "covers", courseId);
export const transcriptCacheDir = (d: Deps, courseId: string) => join(cacheDir(d), "transcripts", courseId);

export const isPlainId = (s: string) => /^[a-z0-9][a-z0-9-]*$/.test(s);

/** A fresh course id from a title, unique among managed folders and every course the server already knows. */
export async function freshCourseId(d: Deps, wanted: string | undefined, title: string): Promise<string> {
  if (wanted !== undefined) {
    if (!isPlainId(wanted)) throw new Error(`invalid courseId "${wanted}" (use lowercase letters, digits and dashes)`);
    // Studio repos share the id space (ruling R9): refuse an id the studio already uses, even before it is published.
    if (await exists(join(coursesDir(d), wanted)) || await exists(studioRepo(d, wanted)) || d.ctx.courses.get(wanted)) throw new Error(`a course with id "${wanted}" already exists`);
    return wanted;
  }
  const taken = new Set<string>(d.ctx.courses.list().map((c) => c.id));
  for (const e of await readdir(coursesDir(d)).catch(() => [] as string[])) taken.add(e);
  const repos = d.ctx.config.studioReposDir ?? resolve(d.ctx.config.dataDir, "studio", "repos");
  for (const e of await readdir(repos).catch(() => [] as string[])) if (e.endsWith(".git")) taken.add(e.slice(0, -4));
  return uniqueId(slugify(title), (x) => taken.has(x));
}

export async function exists(p: string): Promise<boolean> {
  return stat(p).then(() => true, () => false);
}

/** Scratch folder on the same filesystem as the courses, so finished work is moved in with one rename. */
export async function stageDir(d: Deps, label: string): Promise<string> {
  const dir = resolve(d.ctx.config.dataDir, "tmp", `${label}-${Bun.randomUUIDv7()}`);
  await mkdir(dir, { recursive: true });
  return dir;
}

export async function publishCourse(d: Deps, stage: string, id: string): Promise<string> {
  await mkdir(coursesDir(d), { recursive: true });
  const dest = join(coursesDir(d), id);
  await rename(stage, dest);
  return dest;
}

export interface ManagedCourse { id: string; dir: string; manifest: RawManifest }

export const STUDIO_OWNED = "this course is now edited in the studio; add files there instead";

/**
 * Runs importer work that changes an existing course under the course lock shared with the studio (core
 * `withCourseLock`), after checking, inside the lock, that the course is still an importer folder. A conversion to a
 * studio course therefore either waits for the job, or the job fails cleanly with STUDIO_OWNED and writes nothing.
 */
export function withManagedCourse<T>(d: Deps, courseId: string | undefined, fn: (c: ManagedCourse) => Promise<T>): Promise<T> {
  return withCourseLock(courseId ?? "", async () => fn(await managedCourse(d, courseId)));
}

/** An existing course the importer may add to. Only folders directly under <dataDir>/courses qualify: overlays and authored repos are never edited. */
export async function managedCourse(d: Deps, courseId: string | undefined): Promise<ManagedCourse> {
  if (!courseId) throw new Error("options.courseId is required: choose the course to add to");
  if (isPlainId(courseId) && (await exists(studioRepo(d, courseId)))) throw new Error(STUDIO_OWNED);
  const dir = join(coursesDir(d), courseId);
  const rel = relative(coursesDir(d), dir);
  if (!isPlainId(courseId) || rel.startsWith("..") || !(await exists(join(dir, "stcourse.yaml")))) {
    throw new Error(`course "${courseId}" is not an imported course under ${coursesDir(d)}; the importer only edits courses it created`);
  }
  const manifest = await readRawManifest(dir);
  if (manifest.id !== courseId) throw new Error(`course folder "${courseId}" has manifest id "${manifest.id}"`);
  return { id: courseId, dir, manifest };
}

/** Reloads the repository and turns load problems into warnings. */
export async function finish(d: Deps, id: string, warnings: string[]): Promise<void> {
  await d.ctx.courses.reload(id);
  const c = d.ctx.courses.get(id);
  if (!c) {
    warnings.push(`course "${id}" is not visible to the server: add ${coursesDir(d)} to STC_COURSE_DIRS`);
    return;
  }
  for (const diag of c.diagnostics) warnings.push(`${diag.level}: ${diag.message}${diag.path ? ` (${diag.path})` : ""}`);
}

export async function saveManifest(dir: string, manifest: RawManifest): Promise<void> {
  await writeManifest(dir, manifest);
}

export function sourceBlock(kind: string, origin: string) {
  return { kind, origin, importedAt: new Date().toISOString() };
}

/** Writes up to `count` frame candidates from evenly spaced clips; returns the candidate file names. Failures are skipped. */
export async function frameCandidates(d: Deps, courseId: string, clips: string[], count = 3): Promise<string[]> {
  const out: string[] = [];
  const n = Math.min(count, clips.length);
  for (let i = 0; i < n; i++) {
    const name = `frame-${i + 1}.jpg`;
    try {
      await extractFrame(d.tools, clips[Math.floor((i * clips.length) / n)]!, join(coverCacheDir(d, courseId), name), 0.2);
      out.push(name);
    } catch { /* a bad clip must not fail the import */ }
  }
  return out;
}