import { NextRequest, NextResponse } from "next/server";
import path from "node:path";
import fs from "node:fs";
import fsp from "node:fs/promises";
import os from "node:os";
import { Readable } from "node:stream";
import { pipeline } from "node:stream/promises";
import yauzl from "yauzl";
import { assertLocalRequest } from "@/lib/api/localOnly";
import { importDatabaseTables, restoreDatabaseSnapshot } from "@/lib/backup/importDb";

export const runtime = "nodejs";
export const dynamic = "force-dynamic";
export const maxDuration = 3600;

const ROOT = process.cwd();

// Folders the export route ships and that we expect to restore. zipPrefix is
// the path inside the archive; absDir is where it lives on disk.
const TARGETS: Array<{ zipPrefix: string; absDir: string }> = [
  { zipPrefix: "library", absDir: path.join(ROOT, "library") },
  { zipPrefix: "data/thumbs", absDir: path.join(ROOT, "data", "thumbs") },
  { zipPrefix: "data/portraits", absDir: path.join(ROOT, "data", "portraits") },
  { zipPrefix: "data/category-covers", absDir: path.join(ROOT, "data", "category-covers") },
  { zipPrefix: "data/collection-covers", absDir: path.join(ROOT, "data", "collection-covers") },
];

function openZip(zipPath: string): Promise<yauzl.ZipFile> {
  return new Promise((resolve, reject) => {
    yauzl.open(zipPath, { lazyEntries: true, autoClose: false }, (err, zf) => {
      if (err || !zf) return reject(err ?? new Error("Failed to open zip"));
      resolve(zf);
    });
  });
}

function readEntryStream(zf: yauzl.ZipFile, entry: yauzl.Entry): Promise<Readable> {
  return new Promise((resolve, reject) => {
    zf.openReadStream(entry, (err, stream) => {
      if (err || !stream) return reject(err ?? new Error("Failed to open entry stream"));
      resolve(stream);
    });
  });
}

// Reject zip-slip / path-traversal entries: the resolved destination must
// stay strictly inside the staging root. Without this, a crafted entry
// named "../../etc/passwd" would write outside the staging folder.
function safeJoin(root: string, rel: string): string | null {
  const resolved = path.resolve(root, rel);
  const rel2 = path.relative(root, resolved);
  if (rel2.startsWith("..") || path.isAbsolute(rel2)) return null;
  return resolved;
}

async function extractAll(zipPath: string, stagingRoot: string): Promise<void> {
  const zf = await openZip(zipPath);
  try {
    await new Promise<void>((resolve, reject) => {
      zf.on("error", reject);
      zf.on("end", resolve);
      zf.on("entry", async (entry: yauzl.Entry) => {
        try {
          const isDir = /\/$/.test(entry.fileName);
          const dest = safeJoin(stagingRoot, entry.fileName);
          if (!dest) {
            // Skip suspicious entries silently and continue.
            zf.readEntry();
            return;
          }
          if (isDir) {
            await fsp.mkdir(dest, { recursive: true });
            zf.readEntry();
            return;
          }
          await fsp.mkdir(path.dirname(dest), { recursive: true });
          const rs = await readEntryStream(zf, entry);
          await pipeline(rs, fs.createWriteStream(dest));
          zf.readEntry();
        } catch (e) {
          reject(e);
        }
      });
      zf.readEntry();
    });
  } finally {
    zf.close();
  }
}

async function rollbackMediaSwap(
  renamedBackups: Array<{ from: string; to: string }>,
  movedTargets: string[],
  ts: string,
): Promise<string[]> {
  const errors: string[] = [];
  for (const tgt of [...TARGETS].reverse()) {
    const backup = renamedBackups.find((r) => r.from === tgt.absDir);
    const wasMoved = movedTargets.includes(tgt.zipPrefix);
    if (!backup && !wasMoved) continue;

    if (wasMoved) {
      try {
        await fsp.access(tgt.absDir);
        await fsp.rename(tgt.absDir, `${tgt.absDir}.failed-restore-${ts}`);
      } catch (e) {
        if ((e as NodeJS.ErrnoException).code !== "ENOENT") {
          errors.push(`Could not move failed ${tgt.zipPrefix}: ${(e as Error).message}`);
        }
      }
    }

    if (backup) {
      try {
        await fsp.rename(backup.to, backup.from);
      } catch (e) {
        errors.push(`Could not restore backup ${backup.to}: ${(e as Error).message}`);
      }
    }
  }
  return errors;
}

export async function POST(req: NextRequest) {
  const blocked = assertLocalRequest(req);
  if (blocked) return blocked;

  if (!req.body) {
    return NextResponse.json({ error: "Missing request body" }, { status: 400 });
  }

  const tmpDir = await fsp.mkdtemp(path.join(os.tmpdir(), "pinkudex-import-"));
  const tmpZip = path.join(tmpDir, "upload.zip");
  const staging = path.join(tmpDir, "staging");

  try {
    // 1) Stream upload to disk. Buffering a multi-GB upload in memory is a
    // non-starter; piping the request body straight to a file is constant-RAM.
    await pipeline(
      Readable.fromWeb(req.body as unknown as import("node:stream/web").ReadableStream),
      fs.createWriteStream(tmpZip),
    );

    // 2) Extract everything to staging. If anything throws here we abort
    // before touching live state.
    await fsp.mkdir(staging, { recursive: true });
    await extractAll(tmpZip, staging);

    // 3) Read database.json and validate.
    const dbJsonPath = path.join(staging, "database.json");
    let dbJsonRaw: string;
    try {
      dbJsonRaw = await fsp.readFile(dbJsonPath, "utf8");
    } catch {
      return NextResponse.json(
        { error: "Archive is missing database.json — not a Pinkudex library export." },
        { status: 400 },
      );
    }
    let parsed: { tables?: Record<string, unknown[]> };
    try {
      parsed = JSON.parse(dbJsonRaw);
    } catch {
      return NextResponse.json({ error: "database.json is not valid JSON." }, { status: 400 });
    }
    const tables = parsed.tables;
    if (!tables || typeof tables !== "object") {
      return NextResponse.json({ error: "database.json missing 'tables' object." }, { status: 400 });
    }
    if (!Array.isArray(tables.actresses) && !Array.isArray(tables.images)) {
      return NextResponse.json(
        { error: "database.json is missing core tables." },
        { status: 400 },
      );
    }

    // 4) Import DB. On failure the helper restores a pre-import .bak snapshot
    // and we abort BEFORE swapping any folders so live media is untouched.
    const dbResult = await importDatabaseTables(tables);
    if (!dbResult.ok) {
      return NextResponse.json(
        {
          error: `Database import failed: ${dbResult.error}`,
          snapshotName: dbResult.snapshotPath ? path.basename(dbResult.snapshotPath) : null,
          hint: "Media folders were not modified. The DB was rolled back from the pre-import snapshot.",
        },
        { status: 500 },
      );
    }

    // 5) Swap media folders. Existing folders renamed to *.pre-restore-<ts>
    // for manual rollback. New folders moved out of staging into place.
    const ts = new Date().toISOString().replace(/[:.]/g, "-");
    const renamedBackups: Array<{ from: string; to: string }> = [];
    const movedTargets: string[] = [];

    try {
      for (const tgt of TARGETS) {
        const stagedSrc = path.join(staging, tgt.zipPrefix);
        let stagedExists = false;
        try {
          const st = await fsp.stat(stagedSrc);
          stagedExists = st.isDirectory();
        } catch {}
        if (!stagedExists) continue;

        // Rename existing folder if present.
        try {
          await fsp.access(tgt.absDir);
          const backupPath = `${tgt.absDir}.pre-restore-${ts}`;
          await fsp.rename(tgt.absDir, backupPath);
          renamedBackups.push({ from: tgt.absDir, to: backupPath });
        } catch {
          // Didn't exist — fine.
        }

        await fsp.mkdir(path.dirname(tgt.absDir), { recursive: true });
        await fsp.rename(stagedSrc, tgt.absDir);
        movedTargets.push(tgt.zipPrefix);
      }
    } catch (e) {
      const rollbackErrors = await rollbackMediaSwap(renamedBackups, movedTargets, ts);
      if (dbResult.snapshotPath) {
        try {
          await restoreDatabaseSnapshot(dbResult.snapshotPath);
        } catch (restoreErr) {
          rollbackErrors.push(`Could not restore DB snapshot: ${(restoreErr as Error).message}`);
        }
      }
      return NextResponse.json(
        {
          error: `Library restore failed during media swap: ${(e as Error).message}`,
          dbSnapshotName: dbResult.snapshotPath ? path.basename(dbResult.snapshotPath) : null,
          mediaBackupNames: renamedBackups.map((r) => path.basename(r.to)),
          rollbackErrors,
        },
        { status: 500 },
      );
    }

    return NextResponse.json({
      ok: true,
      counts: dbResult.counts,
      errors: dbResult.errors,
      dbSnapshotName: dbResult.snapshotPath ? path.basename(dbResult.snapshotPath) : null,
      mediaRestored: movedTargets,
      mediaBackupNames: renamedBackups.map((r) => path.basename(r.to)),
    });
  } catch (e) {
    return NextResponse.json(
      { error: `Library restore failed: ${(e as Error).message}` },
      { status: 500 },
    );
  } finally {
    fsp.rm(tmpDir, { recursive: true, force: true }).catch(() => {});
  }
}