import { Injectable, NotFoundException } from "@nestjs/common";
import { readdirSync, statSync } from "node:fs";
import { extname, join } from "node:path";
import { eq } from "drizzle-orm";
import { DatabaseService } from "../database/database.service.js";
import { books, libraries } from "../database/schema.js";
import { JobsService } from "../jobs/jobs.service.js";
import { extractMetadata } from "./metadata.js";
import { OpenLibraryService } from "./open-library.service.js";

@Injectable()
export class ScannerService {
  constructor(
    private readonly database: DatabaseService,
    private readonly jobs: JobsService,
    private readonly openLibrary: OpenLibraryService
  ) {}

  enqueueLibraryScan(libraryId: number) {
    const library = this.database.db.select().from(libraries).where(eq(libraries.id, libraryId)).get();
    if (!library) {
      throw new NotFoundException("Library not found");
    }
    const job = this.jobs.create("library-scan", `Scanning ${library.path}`);
    setImmediate(() => {
      void this.scanLibrary(job.id, library).catch((error) => this.jobs.markFailed(job.id, error));
    });
    return job;
  }

  private async scanLibrary(jobId: number, library: typeof libraries.$inferSelect): Promise<void> {
    this.jobs.markRunning(jobId, `Scanning ${library.path}`);
    let count = 0;
    for (const filePath of walkBooks(library.path)) {
      await this.ingestFile(library.id, filePath);
      count += 1;
    }
    this.jobs.markSucceeded(jobId, `Scanned ${count} file(s)`);
  }

  private async ingestFile(libraryId: number, filePath: string): Promise<void> {
    const stats = statSync(filePath);
    let metadata = extractMetadata(filePath, this.database.config.storageDir);
    if (this.database.config.openLibraryEnabled) {
      try {
        metadata = { ...metadata, ...(await this.openLibrary.enrich(metadata)) };
      } catch {
        // Remote enrichment is opportunistic; local ingestion must stay deterministic.
      }
    }

    const now = this.database.now();
    const format: "epub" | "pdf" = extname(filePath).toLowerCase() === ".epub" ? "epub" : "pdf";
    const existing = this.database.db.select({ id: books.id }).from(books).where(eq(books.filePath, filePath)).get();
    const values = {
      libraryId,
      title: metadata.title,
      author: metadata.author,
      description: metadata.description,
      isbn: metadata.isbn,
      language: metadata.language,
      publisher: metadata.publisher,
      publishedDate: metadata.publishedDate,
      format,
      filePath,
      coverPath: metadata.coverPath,
      fileSize: stats.size,
      fileMtime: stats.mtime.toISOString(),
      updatedAt: now
    };

    existing
      ? this.database.db.update(books).set(values).where(eq(books.id, existing.id)).returning().get()
      : this.database.db.insert(books).values({ ...values, createdAt: now }).returning().get();
  }
}

function* walkBooks(root: string): Generator<string> {
  for (const entry of readdirSync(root, { withFileTypes: true })) {
    const path = join(root, entry.name);
    if (entry.isDirectory()) {
      yield* walkBooks(path);
      continue;
    }
    if (!entry.isFile()) continue;
    const extension = extname(entry.name).toLowerCase();
    if (extension === ".epub" || extension === ".pdf") {
      yield path;
    }
  }
}