/**
 * Storage backend migration core. The CLI in `scripts/migrate-storage.ts` and
 * the admin API at `/api/v1/admin/storage/migrate` both call `runMigration()`
 * here, so behaviour is identical regardless of trigger.
 *
 * See docs/berth-recommender-and-pdf-plan.md §4.7a + §14.9a for the contract.
 */

import { createHash } from 'node:crypto';
import { statfs } from 'node:fs/promises';
import { Readable } from 'node:stream';

import { and, eq, isNull, sql } from 'drizzle-orm';

import { db } from '@/lib/db';
import { systemSettings } from '@/lib/db/schema/system';

import { FilesystemBackend } from './filesystem';
import { resetStorageBackendCache, type StorageBackend, type StorageBackendName } from './index';
import { S3Backend } from './s3';

// ─── tables to walk ─────────────────────────────────────────────────────────

export interface StorageKeyTable {
  table: string;
  /** Column name holding the storage key (always `storage_key` going forward). */
  keyColumn: string;
  /** Primary-key column for per-row progress markers. */
  pkColumn: string;
  /** Optional content-type column (lets the target backend persist Content-Type). */
  contentTypeColumn?: string;
}

/**
 * Tables that hold blob references the migration script must walk.
 *
 * Column naming is intentionally inconsistent across the schema for historical
 * reasons:
 *   - `files.storage_path`             (oldest table, named before §4.7a rename)
 *   - `berth_pdf_versions.storage_key` (Phase 6b - followed the new convention)
 *   - `brochure_versions.storage_key`  (Phase 6b)
 *   - `gdpr_exports.storage_key`       (worker-uploaded export bundle)
 *
 * None of these tables carry a per-row content-type column today
 * (`files.mime_type` exists but isn't the same semantics - it's the
 * original-upload mime, not the stored object's Content-Type header). The
 * migration falls back to `application/octet-stream` when
 * `contentTypeColumn` is omitted; the byte stream is what matters for the
 * sha256-verified round-trip and the original Content-Type is already
 * persisted on the source object's S3 metadata.
 *
 * The `report_snapshots` table called out in the audit does not exist yet.
 * Add it here when it lands.
 */
export const TABLES_WITH_STORAGE_KEYS: StorageKeyTable[] = [
  { table: 'files', keyColumn: 'storage_path', pkColumn: 'id' },
  { table: 'berth_pdf_versions', keyColumn: 'storage_key', pkColumn: 'id' },
  { table: 'brochure_versions', keyColumn: 'storage_key', pkColumn: 'id' },
  { table: 'gdpr_exports', keyColumn: 'storage_key', pkColumn: 'id' },
  // Last-resort recovery: pg_dump artefacts from the BackupService. The
  // audit caught these were missing - flipping the storage backend used
  // to silently orphan every backup, dark-blacking the recovery path.
  { table: 'backup_jobs', keyColumn: 'storage_path', pkColumn: 'id' },
];

const ADVISORY_LOCK_KEY = 0xc7000a01;

// ─── helpers ────────────────────────────────────────────────────────────────

interface CliArgs {
  from: StorageBackendName;
  to: StorageBackendName;
  dryRun: boolean;
}

export function parseArgs(argv: string[]): CliArgs {
  const args: Partial<CliArgs> = { dryRun: false };
  for (let i = 0; i < argv.length; i++) {
    const a = argv[i];
    if (a === '--dry-run') args.dryRun = true;
    else if (a === '--from') args.from = argv[++i] as StorageBackendName;
    else if (a === '--to') args.to = argv[++i] as StorageBackendName;
  }
  if (!args.from || !args.to || (args.from !== 's3' && args.from !== 'filesystem')) {
    throw new Error('Usage: --from s3|filesystem --to s3|filesystem [--dry-run]');
  }
  if (args.to !== 's3' && args.to !== 'filesystem') {
    throw new Error('--to must be s3 or filesystem');
  }
  if (args.from === args.to) {
    throw new Error('--from and --to must differ');
  }
  return args as CliArgs;
}

async function ensureProgressTable(): Promise<void> {
  await db.execute(sql`
    CREATE TABLE IF NOT EXISTS _storage_migration_progress (
      table_name text NOT NULL,
      row_pk text NOT NULL,
      storage_key text NOT NULL,
      sha256 text NOT NULL,
      size_bytes bigint NOT NULL,
      migrated_at timestamptz NOT NULL DEFAULT now(),
      PRIMARY KEY (table_name, row_pk)
    )
  `);
}

function rowsOf(result: unknown): unknown[] {
  if (Array.isArray(result)) return result;
  const r = result as { rows?: unknown[] } | null;
  return r?.rows ?? [];
}

async function isRowMigrated(tableName: string, pk: string): Promise<boolean> {
  const res = await db.execute(sql`
    SELECT 1 FROM _storage_migration_progress
    WHERE table_name = ${tableName} AND row_pk = ${pk}
    LIMIT 1
  `);
  return rowsOf(res).length > 0;
}

async function markRowMigrated(
  tableName: string,
  pk: string,
  key: string,
  sha256: string,
  sizeBytes: number,
): Promise<void> {
  await db.execute(sql`
    INSERT INTO _storage_migration_progress (table_name, row_pk, storage_key, sha256, size_bytes)
    VALUES (${tableName}, ${pk}, ${key}, ${sha256}, ${sizeBytes})
    ON CONFLICT (table_name, row_pk) DO NOTHING
  `);
}

export interface RowRef {
  tableName: string;
  pk: string;
  key: string;
  contentType: string;
}

async function listKeysFor(tbl: StorageKeyTable): Promise<RowRef[]> {
  const ctSelect = tbl.contentTypeColumn ? `, ${tbl.contentTypeColumn} as content_type` : '';
  const result = await db.execute(
    sql.raw(
      `SELECT ${tbl.pkColumn} as pk, ${tbl.keyColumn} as key${ctSelect}
       FROM ${tbl.table}
       WHERE ${tbl.keyColumn} IS NOT NULL`,
    ),
  );
  const rows = rowsOf(result) as Array<{ pk: unknown; key: unknown; content_type?: unknown }>;
  return rows.map((r) => ({
    tableName: tbl.table,
    pk: String(r.pk),
    key: String(r.key),
    contentType:
      typeof r.content_type === 'string' && r.content_type.length > 0
        ? r.content_type
        : 'application/octet-stream',
  }));
}

/**
 * Inventory every blob reference across all blob-bearing tables. Used by the
 * full-backup exporter (Phase 4a) to enumerate what to bundle. `excludeTables`
 * lets the exporter drop `backup_jobs` so a full export doesn't recursively
 * include prior backup artefacts.
 */
export async function collectStorageRefs(opts?: { excludeTables?: string[] }): Promise<RowRef[]> {
  const exclude = new Set(opts?.excludeTables ?? []);
  const all: RowRef[] = [];
  for (const tbl of TABLES_WITH_STORAGE_KEYS) {
    if (exclude.has(tbl.table)) continue;
    all.push(...(await listKeysFor(tbl)));
  }
  return all;
}

// ─── streaming + sha256 verify ──────────────────────────────────────────────

/**
 * Stream a file from `source` -> `target` while computing sha256 of the bytes
 * actually written. Re-fetches the target object and verifies a second time
 * to catch storage-side corruption.
 */
export async function copyAndVerify(
  source: StorageBackend,
  target: StorageBackend,
  ref: RowRef,
): Promise<{ sha256: string; sizeBytes: number }> {
  const stream = await source.get(ref.key);
  const chunks: Buffer[] = [];
  for await (const chunk of stream as Readable) {
    chunks.push(Buffer.isBuffer(chunk) ? chunk : Buffer.from(chunk as string));
  }
  const buffer = Buffer.concat(chunks);
  const sha256 = createHash('sha256').update(buffer).digest('hex');

  const putResult = await target.put(ref.key, buffer, {
    contentType: ref.contentType,
    sha256,
    sizeBytes: buffer.length,
  });
  if (putResult.sha256 !== sha256) {
    throw new Error(`sha256 mismatch on put for ${ref.tableName}/${ref.pk}`);
  }

  // Re-fetch from the target and verify a second time.
  const verifyStream = await target.get(ref.key);
  const verifyChunks: Buffer[] = [];
  for await (const chunk of verifyStream as Readable) {
    verifyChunks.push(Buffer.isBuffer(chunk) ? chunk : Buffer.from(chunk as string));
  }
  const verifyBuf = Buffer.concat(verifyChunks);
  const verifySha = createHash('sha256').update(verifyBuf).digest('hex');
  if (verifySha !== sha256) {
    throw new Error(`sha256 mismatch after round-trip for ${ref.tableName}/${ref.pk} (${ref.key})`);
  }
  return { sha256, sizeBytes: buffer.length };
}

// ─── pre-flight ─────────────────────────────────────────────────────────────

async function freeBytesAt(rootPath: string): Promise<number> {
  const s = await statfs(rootPath);
  return Number(s.bavail) * Number(s.bsize);
}

async function flipBackendSetting(target: StorageBackendName, userId: string): Promise<void> {
  const existing = await db.query.systemSettings.findFirst({
    where: and(eq(systemSettings.key, 'storage_backend'), isNull(systemSettings.portId)),
  });
  if (existing) {
    await db
      .update(systemSettings)
      .set({ value: target, updatedBy: userId, updatedAt: new Date() })
      .where(and(eq(systemSettings.key, 'storage_backend'), isNull(systemSettings.portId)));
  } else {
    await db.insert(systemSettings).values({
      key: 'storage_backend',
      value: target,
      portId: null,
      updatedBy: userId,
    });
  }
  resetStorageBackendCache();
}

// ─── main ───────────────────────────────────────────────────────────────────

export interface MigrationOptions {
  from: StorageBackendName;
  to: StorageBackendName;
  dryRun: boolean;
  /** Skip the file copy and just flip the active backend pointer.
   *  Existing files become inaccessible until they're migrated later
   *  or the backend is reverted. Rare - surfaced in the admin UI as
   *  a clearly-warned alternative to switch + migrate. */
  skipMigration?: boolean;
  /** Override for tests. */
  source?: StorageBackend;
  target?: StorageBackend;
  /** Audit user id. */
  userId?: string;
}

export interface MigrationResult {
  rowsConsidered: number;
  rowsMigrated: number;
  rowsSkippedAlreadyDone: number;
  totalBytes: number;
  flipped: boolean;
  dryRun: boolean;
}

export async function runMigration(opts: MigrationOptions): Promise<MigrationResult> {
  const lockResult = await db.execute(sql`SELECT pg_try_advisory_lock(${ADVISORY_LOCK_KEY}) as ok`);
  const lockRows = rowsOf(lockResult) as Array<{ ok: boolean }>;
  if (!lockRows[0]?.ok) {
    throw new Error('Could not acquire storage migration advisory lock');
  }

  try {
    await ensureProgressTable();

    let rowsConsidered = 0;
    let rowsMigrated = 0;
    let rowsSkippedAlreadyDone = 0;
    let totalBytes = 0;

    // Skip-migration shortcut: don't touch storage at all, just flip
    // the active-backend pointer. Existing files become unreachable
    // until a future migration. Surfaced as a clearly-warned option
    // in the admin UI; almost never the right choice.
    if (opts.skipMigration && !opts.dryRun) {
      await flipBackendSetting(opts.to, opts.userId ?? 'cli:migrate-storage');
      return {
        rowsConsidered: 0,
        rowsMigrated: 0,
        rowsSkippedAlreadyDone: 0,
        totalBytes: 0,
        flipped: true,
        dryRun: false,
      };
    }

    const source = opts.source ?? (await buildBackendForMigration(opts.from));
    const target = opts.target ?? (await buildBackendForMigration(opts.to));

    for (const tbl of TABLES_WITH_STORAGE_KEYS) {
      const refs = await listKeysFor(tbl);
      rowsConsidered += refs.length;

      // Pre-flight free-disk check when target is filesystem.
      if (opts.to === 'filesystem' && target instanceof FilesystemBackend) {
        const heads = await Promise.all(
          refs.map((r) => source.head(r.key).then((h) => h?.sizeBytes ?? 0)),
        );
        const sumBytes = heads.reduce((a, b) => a + b, 0);
        const free = await freeBytesAt(process.cwd());
        if (free < sumBytes * 1.2) {
          throw new Error(
            `Insufficient disk: need ${Math.round(sumBytes / 1e6)}MB + 20% margin, have ${Math.round(free / 1e6)}MB free`,
          );
        }
      }

      for (const ref of refs) {
        if (await isRowMigrated(ref.tableName, ref.pk)) {
          rowsSkippedAlreadyDone += 1;
          continue;
        }
        if (opts.dryRun) {
          const head = await source.head(ref.key);
          totalBytes += head?.sizeBytes ?? 0;
          continue;
        }
        const { sha256, sizeBytes } = await copyAndVerify(source, target, ref);
        await markRowMigrated(ref.tableName, ref.pk, ref.key, sha256, sizeBytes);
        rowsMigrated += 1;
        totalBytes += sizeBytes;
      }
    }

    let flipped = false;
    if (!opts.dryRun) {
      await flipBackendSetting(opts.to, opts.userId ?? 'cli:migrate-storage');
      flipped = true;
    }

    return {
      rowsConsidered,
      rowsMigrated,
      rowsSkippedAlreadyDone,
      totalBytes,
      flipped,
      dryRun: opts.dryRun,
    };
  } finally {
    await db.execute(sql`SELECT pg_advisory_unlock(${ADVISORY_LOCK_KEY})`);
  }
}

async function buildBackendForMigration(name: StorageBackendName): Promise<StorageBackend> {
  if (name === 'filesystem') {
    return FilesystemBackend.create({
      root: process.env.STORAGE_FILESYSTEM_ROOT ?? './storage',
      proxyHmacSecretEncrypted: null,
    });
  }
  return S3Backend.create({});
}