import { createHash, randomBytes, timingSafeEqual } from 'node:crypto';
import type { Database, GoogleConnection, GoogleOauthFlow } from '@pig/db';
import { activities, googleConnections, googleOauthFlows } from '@pig/db';
import { and, eq, gt, isNull } from 'drizzle-orm';
import type { Principal } from '../lib/auth';
import { decryptSecret, encryptionReady, encryptSecret } from '../lib/secrets';
import { MutationError } from '../lib/mutation';
import {
  MAX_IMPORT_CELL_CHARS,
  MAX_IMPORT_COLUMNS,
  MAX_IMPORT_ROWS,
  normaliseTabularRows,
  type ParsedTable,
} from './tabular-import';

export const GOOGLE_OAUTH_SCOPES = [
  'https://www.googleapis.com/auth/drive.metadata.readonly',
  'https://www.googleapis.com/auth/spreadsheets.readonly',
] as const;
const GOOGLE_AUTHORIZATION_ENDPOINT = 'https://accounts.google.com/o/oauth2/v2/auth';
const GOOGLE_TOKEN_ENDPOINT = 'https://oauth2.googleapis.com/token';
const GOOGLE_REVOCATION_ENDPOINT = 'https://oauth2.googleapis.com/revoke';
const GOOGLE_DRIVE_FILES_ENDPOINT = 'https://www.googleapis.com/drive/v3/files';
const GOOGLE_SHEETS_ENDPOINT = 'https://sheets.googleapis.com/v4/spreadsheets';
const OAUTH_FLOW_TTL_MS = 10 * 60 * 1_000;
const ACCESS_TOKEN_SKEW_MS = 60 * 1_000;
const DRIVE_PAGE_SIZE = 50;
const PKCE_PURPOSE = 'google-oauth:pkce-verifier';
const REFRESH_TOKEN_PURPOSE = 'google-oauth:refresh-token';
const ACCESS_TOKEN_PURPOSE = 'google-oauth:access-token';

export interface GoogleSheetsConfig {
  clientId?: string;
  clientSecret?: string;
  redirectUri?: string;
  encryptionKey?: string;
  publicUrl: string;
}

export interface GoogleConnectionMetadata {
  configured: boolean;
  connected: boolean;
  connectedAt: string | null;
  scopes: string[];
}

export interface GoogleDriveFile {
  id: string;
  name: string;
  modifiedTime: string | null;
}

export interface GoogleSheetMetadata {
  sheetId: number;
  title: string;
  rowCount: number;
  columnCount: number;
}

interface GoogleTokenResponse {
  access_token?: string;
  expires_in?: number;
  refresh_token?: string;
  scope?: string;
  token_type?: string;
  error?: string;
}

interface DriveListResponse {
  files?: { id?: string; name?: string; modifiedTime?: string }[];
  nextPageToken?: string;
  incompleteSearch?: boolean;
}

interface SpreadsheetMetadataResponse {
  properties?: { title?: string };
  sheets?: {
    properties?: {
      sheetId?: number;
      title?: string;
      sheetType?: string;
      hidden?: boolean;
      gridProperties?: { rowCount?: number; columnCount?: number };
    };
  }[];
}

interface ValuesResponse {
  values?: unknown[][];
}

export class GoogleApiError extends Error {
  constructor(
    message: string,
    readonly status: number,
    readonly reconnectRequired = false,
  ) {
    super(message);
    this.name = 'GoogleApiError';
  }
}

export class GoogleSheetsService {
  constructor(
    private readonly db: Database,
    private readonly config: GoogleSheetsConfig,
    private readonly fetchImpl: typeof fetch = fetch,
  ) {}

  configured(): boolean {
    return Boolean(
      this.config.clientId &&
      this.config.clientSecret &&
      this.config.redirectUri &&
      encryptionReady(this.config.encryptionKey),
    );
  }

  async connectionMetadata(userId: string): Promise<GoogleConnectionMetadata> {
    const [connection] = await this.db
      .select()
      .from(googleConnections)
      .where(eq(googleConnections.userId, userId))
      .limit(1);
    return googleConnectionMetadata(this.configured(), connection);
  }

  async beginOAuth(principal: Principal, now = new Date()): Promise<{ authorizationUrl: string; browserBinding: string }> {
    this.requireConfigured();
    const state = randomBytes(32).toString('base64url');
    const browserBinding = randomBytes(32).toString('base64url');
    const verifier = randomBytes(32).toString('base64url');
    const challenge = createHash('sha256').update(verifier).digest('base64url');
    await this.db.insert(googleOauthFlows).values({
      userId: principal.userId,
      stateHash: oauthStateHash(state),
      browserBindingHash: oauthStateHash(browserBinding),
      pkceVerifierEncrypted: encryptSecret(verifier, this.config.encryptionKey, PKCE_PURPOSE),
      expiresAt: new Date(now.getTime() + OAUTH_FLOW_TTL_MS),
      createdAt: now,
    });
    return {
      authorizationUrl: buildGoogleAuthorizationUrl({
        clientId: this.config.clientId!,
        redirectUri: this.config.redirectUri!,
        state,
        challenge,
      }),
      browserBinding,
    };
  }

  async completeOAuth(input: { state: string; code: string; browserBinding: string }, now = new Date()): Promise<void> {
    this.requireConfigured();
    const [flow] = await this.db
      .update(googleOauthFlows)
      .set({ consumedAt: now })
      .where(and(
        eq(googleOauthFlows.stateHash, oauthStateHash(input.state)),
        isNull(googleOauthFlows.consumedAt),
        gt(googleOauthFlows.expiresAt, now),
      ))
      .returning();
    if (!flow || !oauthFlowMatches(flow, input.state, input.browserBinding, now)) {
      throw new MutationError('invalid_oauth_state', 'The Google authorization request is invalid or expired.', 400);
    }
    const verifier = decryptSecret(
      flow.pkceVerifierEncrypted,
      this.config.encryptionKey,
      PKCE_PURPOSE,
    );
    const token = await this.exchangeToken(new URLSearchParams({
      client_id: this.config.clientId!,
      client_secret: this.config.clientSecret!,
      code: input.code,
      code_verifier: verifier,
      grant_type: 'authorization_code',
      redirect_uri: this.config.redirectUri!,
    }));
    if (!token.access_token) {
      throw new GoogleApiError('Google did not return an access token. Connect again.', 502, true);
    }
    const [existing] = await this.db
      .select()
      .from(googleConnections)
      .where(eq(googleConnections.userId, flow.userId))
      .limit(1);
    const refreshTokenEncrypted = token.refresh_token
      ? encryptSecret(token.refresh_token, this.config.encryptionKey, REFRESH_TOKEN_PURPOSE)
      : existing?.refreshTokenEncrypted;
    if (!refreshTokenEncrypted) {
      throw new GoogleApiError('Google did not grant offline access. Connect again and approve access.', 502, true);
    }
    const expiresAt = token.expires_in
      ? new Date(now.getTime() + token.expires_in * 1_000)
      : null;
    const scopes = token.scope?.split(/\s+/).filter(Boolean) ?? [...GOOGLE_OAUTH_SCOPES];
    await this.db.transaction(async (tx) => {
      await tx.insert(googleConnections).values({
        userId: flow.userId,
        refreshTokenEncrypted,
        accessTokenEncrypted: encryptSecret(token.access_token!, this.config.encryptionKey, ACCESS_TOKEN_PURPOSE),
        accessTokenExpiresAt: expiresAt,
        scopes,
        connectedAt: now,
        updatedAt: now,
      }).onConflictDoUpdate({
        target: googleConnections.userId,
        set: {
          refreshTokenEncrypted,
          accessTokenEncrypted: encryptSecret(token.access_token!, this.config.encryptionKey, ACCESS_TOKEN_PURPOSE),
          accessTokenExpiresAt: expiresAt,
          scopes,
          connectedAt: now,
          updatedAt: now,
        },
      });
      await tx.insert(activities).values({
        type: 'note',
        subject: 'Connected Google Sheets import',
        actorUserId: flow.userId,
        source: 'manual',
        occurredAt: now,
        meta: { action: 'integration.connected', integration: 'google_sheets' },
      });
    });
  }

  async disconnect(principal: Principal, now = new Date()): Promise<void> {
    const [connection] = await this.db
      .select()
      .from(googleConnections)
      .where(eq(googleConnections.userId, principal.userId))
      .limit(1);
    if (!connection) return;
    const token = decryptSecret(
      connection.refreshTokenEncrypted,
      this.config.encryptionKey,
      REFRESH_TOKEN_PURPOSE,
    );
    const response = await this.fetchImpl(GOOGLE_REVOCATION_ENDPOINT, {
      method: 'POST',
      headers: { 'content-type': 'application/x-www-form-urlencoded' },
      body: new URLSearchParams({ token }),
    });
    if (!response.ok && response.status !== 400) {
      throw new GoogleApiError('Google access could not be revoked. Try again.', response.status);
    }
    await this.db.transaction(async (tx) => {
      await tx.delete(googleConnections).where(eq(googleConnections.userId, principal.userId));
      await tx.insert(activities).values({
        type: 'note',
        subject: 'Disconnected Google Sheets import',
        actorUserId: principal.userId,
        source: 'manual',
        occurredAt: now,
        meta: { action: 'integration.disconnected', integration: 'google_sheets' },
      });
    });
  }

  async listSpreadsheets(
    userId: string,
    options: { pageToken?: string; search?: string },
  ): Promise<{ files: GoogleDriveFile[]; nextPageToken: string | null; incomplete: boolean }> {
    const token = await this.accessToken(userId);
    const query = [
      "mimeType='application/vnd.google-apps.spreadsheet'",
      'trashed=false',
      ...(options.search?.trim()
        ? [`name contains '${escapeDriveQuery(options.search.trim().slice(0, 100))}'`]
        : []),
    ].join(' and ');
    const url = new URL(GOOGLE_DRIVE_FILES_ENDPOINT);
    url.searchParams.set('q', query);
    url.searchParams.set('spaces', 'drive');
    url.searchParams.set('orderBy', 'modifiedTime desc,name_natural');
    url.searchParams.set('pageSize', String(DRIVE_PAGE_SIZE));
    url.searchParams.set('fields', 'files(id,name,modifiedTime),nextPageToken,incompleteSearch');
    url.searchParams.set('supportsAllDrives', 'true');
    url.searchParams.set('includeItemsFromAllDrives', 'true');
    if (options.pageToken) url.searchParams.set('pageToken', options.pageToken);
    const body = await this.googleJson<DriveListResponse>(url, token, 'Google Drive could not list spreadsheets.');
    return {
      files: (body.files ?? []).flatMap((file) => file.id && file.name
        ? [{ id: file.id, name: file.name, modifiedTime: file.modifiedTime ?? null }]
        : []),
      nextPageToken: body.nextPageToken ?? null,
      incomplete: body.incompleteSearch === true,
    };
  }

  async spreadsheetMetadata(
    userId: string,
    spreadsheetId: string,
  ): Promise<{ title: string; sheets: GoogleSheetMetadata[] }> {
    const token = await this.accessToken(userId);
    const url = new URL(`${GOOGLE_SHEETS_ENDPOINT}/${encodeURIComponent(spreadsheetId)}`);
    url.searchParams.set(
      'fields',
      'properties(title),sheets(properties(sheetId,title,index,sheetType,hidden,gridProperties(rowCount,columnCount)))',
    );
    const body = await this.googleJson<SpreadsheetMetadataResponse>(url, token, 'Google Sheets could not read spreadsheet metadata.');
    const sheets = (body.sheets ?? []).flatMap((sheet) => {
      const properties = sheet.properties;
      if (
        !properties ||
        properties.sheetType !== 'GRID' ||
        properties.hidden ||
        properties.sheetId == null ||
        !properties.title
      ) return [];
      return [{
        sheetId: properties.sheetId,
        title: properties.title,
        rowCount: properties.gridProperties?.rowCount ?? 0,
        columnCount: properties.gridProperties?.columnCount ?? 0,
      }];
    });
    return { title: body.properties?.title ?? 'Google spreadsheet', sheets };
  }

  async readTable(
    userId: string,
    input: { spreadsheetId: string; sheetId: number; range: string },
  ): Promise<ParsedTable> {
    const metadata = await this.spreadsheetMetadata(userId, input.spreadsheetId);
    const sheet = metadata.sheets.find((candidate) => candidate.sheetId === input.sheetId);
    if (!sheet) throw new MutationError('google_sheet_not_found', 'The selected visible grid sheet no longer exists.', 404);
    const bounded = parseBoundedGoogleRange(input.range, {
      rowCount: sheet.rowCount,
      columnCount: sheet.columnCount,
    });
    const a1 = `'${sheet.title.replace(/'/g, "''")}'!${bounded.a1}`;
    const token = await this.accessToken(userId);
    const url = new URL(
      `${GOOGLE_SHEETS_ENDPOINT}/${encodeURIComponent(input.spreadsheetId)}/values/${encodeURIComponent(a1)}`,
    );
    url.searchParams.set('majorDimension', 'ROWS');
    // Formatted values expose cached/display results, never executable formula source.
    url.searchParams.set('valueRenderOption', 'FORMATTED_VALUE');
    const body = await this.googleJson<ValuesResponse>(url, token, 'Google Sheets could not read the selected range.');
    const table = normaliseGoogleValues(body.values ?? [], bounded.columns);
    return {
      fileName: `Google Sheets · ${metadata.title} · ${sheet.title} · ${bounded.a1}`,
      sheetName: sheet.title,
      ...table,
    };
  }

  private async accessToken(userId: string, now = new Date()): Promise<string> {
    const [connection] = await this.db
      .select()
      .from(googleConnections)
      .where(eq(googleConnections.userId, userId))
      .limit(1);
    if (!connection) throw new GoogleApiError('Connect Google Sheets before selecting a spreadsheet.', 409, true);
    if (
      connection.accessTokenEncrypted &&
      connection.accessTokenExpiresAt &&
      connection.accessTokenExpiresAt.getTime() > now.getTime() + ACCESS_TOKEN_SKEW_MS
    ) {
      return decryptSecret(connection.accessTokenEncrypted, this.config.encryptionKey, ACCESS_TOKEN_PURPOSE);
    }
    this.requireConfigured();
    const refreshToken = decryptSecret(
      connection.refreshTokenEncrypted,
      this.config.encryptionKey,
      REFRESH_TOKEN_PURPOSE,
    );
    const token = await this.exchangeToken(new URLSearchParams({
      client_id: this.config.clientId!,
      client_secret: this.config.clientSecret!,
      refresh_token: refreshToken,
      grant_type: 'refresh_token',
    }));
    if (!token.access_token) throw new GoogleApiError('Google access expired. Connect again.', 401, true);
    await this.db.update(googleConnections).set({
      accessTokenEncrypted: encryptSecret(token.access_token, this.config.encryptionKey, ACCESS_TOKEN_PURPOSE),
      accessTokenExpiresAt: token.expires_in
        ? new Date(now.getTime() + token.expires_in * 1_000)
        : null,
      updatedAt: now,
    }).where(eq(googleConnections.userId, userId));
    return token.access_token;
  }

  private async exchangeToken(parameters: URLSearchParams): Promise<GoogleTokenResponse> {
    const response = await this.fetchImpl(GOOGLE_TOKEN_ENDPOINT, {
      method: 'POST',
      headers: { 'content-type': 'application/x-www-form-urlencoded' },
      body: parameters,
    });
    if (!response.ok) {
      throw new GoogleApiError('Google authorization failed. Connect again.', response.status, true);
    }
    return await response.json() as GoogleTokenResponse;
  }

  private async googleJson<T>(url: URL, token: string, message: string): Promise<T> {
    const response = await this.fetchImpl(url, {
      headers: { authorization: `Bearer ${token}` },
    });
    if (!response.ok) {
      throw new GoogleApiError(message, response.status, response.status === 401 || response.status === 403);
    }
    return await response.json() as T;
  }

  private requireConfigured(): void {
    if (!this.configured()) {
      throw new MutationError(
        'google_not_configured',
        'Google Sheets import requires OAuth credentials and the settings encryption key.',
        503,
      );
    }
  }
}

export function oauthStateHash(state: string): string {
  return createHash('sha256').update(state).digest('hex');
}

export function oauthFlowMatches(
  flow: Pick<GoogleOauthFlow, 'stateHash' | 'browserBindingHash' | 'expiresAt' | 'consumedAt'>,
  state: string,
  browserBinding: string,
  now: Date,
): boolean {
  if (!flow.consumedAt || flow.consumedAt.getTime() !== now.getTime() || flow.expiresAt <= now) return false;
  const expected = Buffer.from(flow.stateHash, 'hex');
  const actual = Buffer.from(oauthStateHash(state), 'hex');
  const expectedBinding = Buffer.from(flow.browserBindingHash, 'hex');
  const actualBinding = Buffer.from(oauthStateHash(browserBinding), 'hex');
  return (
    expected.length === actual.length &&
    timingSafeEqual(expected, actual) &&
    expectedBinding.length === actualBinding.length &&
    timingSafeEqual(expectedBinding, actualBinding)
  );
}

export function buildGoogleAuthorizationUrl(input: {
  clientId: string;
  redirectUri: string;
  state: string;
  challenge: string;
}): string {
  const url = new URL(GOOGLE_AUTHORIZATION_ENDPOINT);
  url.searchParams.set('client_id', input.clientId);
  url.searchParams.set('redirect_uri', input.redirectUri);
  url.searchParams.set('response_type', 'code');
  url.searchParams.set('scope', GOOGLE_OAUTH_SCOPES.join(' '));
  url.searchParams.set('state', input.state);
  url.searchParams.set('code_challenge', input.challenge);
  url.searchParams.set('code_challenge_method', 'S256');
  url.searchParams.set('access_type', 'offline');
  url.searchParams.set('include_granted_scopes', 'true');
  url.searchParams.set('prompt', 'consent');
  return url.toString();
}

export function googleConnectionMetadata(
  configured: boolean,
  connection: GoogleConnection | undefined,
): GoogleConnectionMetadata {
  return {
    configured,
    connected: Boolean(connection),
    connectedAt: connection?.connectedAt.toISOString() ?? null,
    scopes: connection?.scopes ?? [],
  };
}

export interface BoundedGoogleRange {
  a1: string;
  rows: number;
  columns: number;
}

export function parseBoundedGoogleRange(
  value: string,
  grid?: { rowCount: number; columnCount: number },
): BoundedGoogleRange {
  const match = value.trim().match(/^([A-Za-z]{1,3})([1-9]\d*):([A-Za-z]{1,3})([1-9]\d*)$/);
  if (!match) {
    throw new MutationError('invalid_google_range', 'Use a rectangular A1 range such as A1:H500.', 400);
  }
  const startColumn = columnNumber(match[1]!);
  const endColumn = columnNumber(match[3]!);
  const startRow = Number(match[2]);
  const endRow = Number(match[4]);
  if (endColumn < startColumn || endRow < startRow) {
    throw new MutationError('invalid_google_range', 'The range end must follow its start.', 400);
  }
  const columns = endColumn - startColumn + 1;
  const rows = endRow - startRow + 1;
  if (columns > MAX_IMPORT_COLUMNS || rows > MAX_IMPORT_ROWS + 1) {
    throw new MutationError(
      'google_range_too_large',
      `Select at most ${MAX_IMPORT_COLUMNS} columns and ${MAX_IMPORT_ROWS + 1} rows including the header.`,
      400,
    );
  }
  if (grid && (endColumn > grid.columnCount || endRow > grid.rowCount)) {
    throw new MutationError('google_range_outside_sheet', 'The selected range extends beyond the sheet grid.', 400);
  }
  return { a1: `${match[1]!.toUpperCase()}${startRow}:${match[3]!.toUpperCase()}${endRow}`, rows, columns };
}

export function normaliseGoogleValues(
  values: readonly (readonly unknown[])[],
  requestedColumns: number,
): Omit<ParsedTable, 'fileName' | 'sheetName'> {
  const table = values.map((row) => {
    if (row.length > requestedColumns) {
      throw new MutationError('invalid_google_values', 'Google returned cells outside the requested range.', 502);
    }
    return row.map((value) => normaliseGoogleCell(value));
  });
  return normaliseTabularRows(table, [
    'Google formula source was not imported; formula cells use only their formatted cached result.',
  ]);
}

function normaliseGoogleCell(value: unknown): string {
  if (value == null) return '';
  if (typeof value === 'boolean') return value ? 'true' : 'false';
  if (typeof value === 'number') {
    if (!Number.isFinite(value)) throw new MutationError('invalid_google_values', 'Google returned a non-finite number.', 502);
    return String(value);
  }
  if (typeof value === 'string') {
    if (value.length > MAX_IMPORT_CELL_CHARS) {
      throw new MutationError('google_cell_too_large', `A Google Sheets cell exceeds ${MAX_IMPORT_CELL_CHARS} characters.`, 400);
    }
    return value;
  }
  throw new MutationError('invalid_google_values', 'Google returned an unsupported cell value.', 502);
}

function columnNumber(letters: string): number {
  let result = 0;
  for (const letter of letters.toUpperCase()) result = result * 26 + letter.charCodeAt(0) - 64;
  return result;
}

function escapeDriveQuery(value: string): string {
  return value.replace(/\\/g, '\\\\').replace(/'/g, "\\'");
}