import type { Knex } from 'knex';
import type { IClientContract } from '@alga-psa/types';
import { v4 as uuidv4 } from 'uuid';
import type { ClientContractAssignmentCreateInput } from './types';
import { assertBoardScopedTicketStatusSelection } from '../lib/boardScopedTicketStatusValidation';
import { deriveClientContractStatus } from './clientContractStatus';

type RenewalMode = NonNullable<IClientContract['renewal_mode']>;

const DEFAULT_RENEWAL_MODE: RenewalMode = 'manual';
const DEFAULT_NOTICE_PERIOD_DAYS = 30;
const MS_PER_DAY = 24 * 60 * 60 * 1000;
const MAX_ABSOLUTE_DAYS_UNTIL_DUE = 36500;

const normalizeRenewalMode = (value: unknown): RenewalMode | undefined => {
  return value === 'none' || value === 'manual' || value === 'auto' ? value : undefined;
};

const normalizeNonNegativeInteger = (value: unknown): number | undefined => {
  if (value === null || value === undefined) return undefined;
  const numeric = typeof value === 'string' ? Number(value) : value;
  if (typeof numeric !== 'number' || !Number.isFinite(numeric)) return undefined;
  return Math.max(0, Math.trunc(numeric));
};

const normalizePositiveInteger = (value: unknown): number | undefined => {
  const normalized = normalizeNonNegativeInteger(value);
  return normalized !== undefined && normalized > 0 ? normalized : undefined;
};

const normalizeDateOnly = (value: unknown): string | undefined => {
  if (value === null || value === undefined) return undefined;
  if (value instanceof Date) {
    if (Number.isNaN(value.getTime())) return undefined;
    return value.toISOString().slice(0, 10);
  }
  if (typeof value !== 'string') return undefined;

  const trimmed = value.trim();
  if (!trimmed) return undefined;
  if (/^\d{4}-\d{2}-\d{2}$/.test(trimmed)) return trimmed;
  if (trimmed.includes('T')) {
    return trimmed.slice(0, 10);
  }
  return undefined;
};

const findMixedCurrencyActiveAssignment = async (
  knexOrTrx: Knex | Knex.Transaction,
  tenant: string,
  params: {
    clientId: string;
    targetCurrencyCode?: string | null;
  }
): Promise<{ currency_code: string; contract_name: string | null } | null> => {
  const targetCurrencyCode =
    typeof params.targetCurrencyCode === 'string' && params.targetCurrencyCode.trim().length > 0
      ? params.targetCurrencyCode.trim()
      : null;
  if (!targetCurrencyCode) return null;

  const rows = await knexOrTrx('client_contracts as cc')
    .join('contracts as c', function joinContracts() {
      this.on('cc.contract_id', '=', 'c.contract_id').andOn('cc.tenant', '=', 'c.tenant');
    })
    .where({
      'cc.client_id': params.clientId,
      'cc.tenant': tenant,
      'cc.is_active': true,
      'c.is_active': true,
    })
    .whereNot('c.currency_code', targetCurrencyCode)
    .select('cc.start_date', 'cc.end_date', 'c.currency_code', 'c.contract_name');

  const activeRow = rows.find((row: {
    start_date: string | null;
    end_date: string | null;
    currency_code?: string | null;
  }) => deriveClientContractStatus({
    isActive: true,
    startDate: row.start_date,
    endDate: row.end_date,
  }) === 'active');
  if (!activeRow || typeof activeRow.currency_code !== 'string' || activeRow.currency_code.trim().length === 0) {
    return null;
  }

  return {
    currency_code: activeRow.currency_code,
    contract_name: typeof activeRow.contract_name === 'string' ? activeRow.contract_name : null,
  };
};

const subtractDaysFromDateOnly = (dateOnly: string, days: number): string | undefined => {
  if (!Number.isInteger(days) || days < 0) return undefined;
  const parsed = new Date(`${dateOnly}T00:00:00.000Z`);
  if (Number.isNaN(parsed.getTime())) return undefined;
  return new Date(parsed.getTime() - days * MS_PER_DAY).toISOString().slice(0, 10);
};

const createClampedUtcDate = (year: number, monthIndex: number, dayOfMonth: number): Date => {
  const lastDayOfMonth = new Date(Date.UTC(year, monthIndex + 1, 0)).getUTCDate();
  const clampedDay = Math.min(dayOfMonth, lastDayOfMonth);
  return new Date(Date.UTC(year, monthIndex, clampedDay));
};

export const computeNextEvergreenReviewAnchorDate = (params: {
  startDate: string;
  now?: string | Date;
}): string | undefined => {
  const normalizedStartDate = normalizeDateOnly(params.startDate);
  if (!normalizedStartDate) return undefined;

  const start = new Date(`${normalizedStartDate}T00:00:00.000Z`);
  if (Number.isNaN(start.getTime())) return undefined;

  const normalizedNow = normalizeDateOnly(params.now instanceof Date ? params.now.toISOString() : params.now);
  const nowBase = normalizedNow
    ? new Date(`${normalizedNow}T00:00:00.000Z`)
    : new Date(new Date().toISOString().slice(0, 10) + 'T00:00:00.000Z');
  if (Number.isNaN(nowBase.getTime())) return undefined;

  const month = start.getUTCMonth();
  const day = start.getUTCDate();
  const thisYearCandidate = createClampedUtcDate(nowBase.getUTCFullYear(), month, day);
  const nextAnchor =
    thisYearCandidate.getTime() >= nowBase.getTime()
      ? thisYearCandidate
      : createClampedUtcDate(nowBase.getUTCFullYear() + 1, month, day);

  return nextAnchor.toISOString().slice(0, 10);
};

export const computeEvergreenDecisionDueDate = (params: {
  startDate: string;
  noticePeriodDays: number;
  now?: string | Date;
}): string | undefined => {
  const anchorDate = computeNextEvergreenReviewAnchorDate({
    startDate: params.startDate,
    now: params.now,
  });
  if (!anchorDate) return undefined;

  const normalizedNoticePeriodDays = normalizeNonNegativeInteger(params.noticePeriodDays);
  if (normalizedNoticePeriodDays === undefined) return undefined;

  return subtractDaysFromDateOnly(anchorDate, normalizedNoticePeriodDays);
};

export const computeEvergreenCycleBounds = (params: {
  startDate: string;
  now?: string | Date;
}): { cycleStart: string; cycleEnd: string } | undefined => {
  const normalizedStartDate = normalizeDateOnly(params.startDate);
  if (!normalizedStartDate) return undefined;

  const start = new Date(`${normalizedStartDate}T00:00:00.000Z`);
  if (Number.isNaN(start.getTime())) return undefined;

  const anchorDate = computeNextEvergreenReviewAnchorDate({
    startDate: normalizedStartDate,
    now: params.now,
  });
  if (!anchorDate) return undefined;

  const anchor = new Date(`${anchorDate}T00:00:00.000Z`);
  if (Number.isNaN(anchor.getTime())) return undefined;

  const previousAnchor = createClampedUtcDate(
    anchor.getUTCFullYear() - 1,
    start.getUTCMonth(),
    start.getUTCDate()
  );
  const cycleStartDate = previousAnchor.getTime() < start.getTime() ? start : previousAnchor;

  return {
    cycleStart: cycleStartDate.toISOString().slice(0, 10),
    cycleEnd: anchorDate,
  };
};

export const computeDaysUntilDate = (params: {
  targetDate: string;
  now?: string | Date;
}): number | undefined => {
  const normalizedTargetDate = normalizeDateOnly(params.targetDate);
  if (!normalizedTargetDate) return undefined;

  const target = new Date(`${normalizedTargetDate}T00:00:00.000Z`);
  if (Number.isNaN(target.getTime())) return undefined;

  const normalizedNow = normalizeDateOnly(params.now instanceof Date ? params.now.toISOString() : params.now);
  const nowBase = normalizedNow
    ? new Date(`${normalizedNow}T00:00:00.000Z`)
    : new Date(new Date().toISOString().slice(0, 10) + 'T00:00:00.000Z');
  if (Number.isNaN(nowBase.getTime())) return undefined;

  const rawDaysUntilDue = Math.round((target.getTime() - nowBase.getTime()) / MS_PER_DAY);
  if (!Number.isFinite(rawDaysUntilDue)) return undefined;

  return Math.max(
    -MAX_ABSOLUTE_DAYS_UNTIL_DUE,
    Math.min(MAX_ABSOLUTE_DAYS_UNTIL_DUE, rawDaysUntilDue)
  );
};

const RENEWAL_DEFAULT_SELECTIONS = [
  'dbs.default_renewal_mode as tenant_default_renewal_mode',
  'dbs.default_notice_period_days as tenant_default_notice_period_days',
];

const withRenewalDefaultsJoin = (
  query: Knex.QueryBuilder
): Knex.QueryBuilder => {
  return query.leftJoin('default_billing_settings as dbs', function joinDefaultBillingSettings() {
    this.on('cc.tenant', '=', 'dbs.tenant');
  });
};

export const normalizeClientContract = (row: any): IClientContract => {
  if (!row) return row;

  const normalized = { ...row } as Record<string, unknown>;

  if (normalized.contract_billing_frequency !== undefined && normalized.billing_frequency === undefined) {
    normalized.billing_frequency = normalized.contract_billing_frequency;
  }

  const renewalMode = normalizeRenewalMode(normalized.renewal_mode);
  const noticePeriodDays = normalizeNonNegativeInteger(normalized.notice_period_days);
  const renewalTermMonths = normalizePositiveInteger(normalized.renewal_term_months);
  const useTenantDefaults =
    typeof normalized.use_tenant_renewal_defaults === 'boolean'
      ? normalized.use_tenant_renewal_defaults
      : true;

  const tenantDefaultRenewalMode =
    normalizeRenewalMode(normalized.tenant_default_renewal_mode) ?? DEFAULT_RENEWAL_MODE;
  const tenantDefaultNoticePeriodDays =
    normalizeNonNegativeInteger(normalized.tenant_default_notice_period_days) ?? DEFAULT_NOTICE_PERIOD_DAYS;

  normalized.renewal_mode = renewalMode;
  normalized.notice_period_days = noticePeriodDays;
  normalized.renewal_term_months = renewalTermMonths;
  normalized.use_tenant_renewal_defaults = useTenantDefaults;
  normalized.effective_renewal_mode = useTenantDefaults
    ? tenantDefaultRenewalMode
    : renewalMode ?? tenantDefaultRenewalMode;
  normalized.effective_notice_period_days = useTenantDefaults
    ? tenantDefaultNoticePeriodDays
    : noticePeriodDays ?? tenantDefaultNoticePeriodDays;

  const normalizedEndDate = normalizeDateOnly(normalized.end_date);
  const normalizedStartDate = normalizeDateOnly(normalized.start_date);
  const effectiveNoticePeriodDays = normalizeNonNegativeInteger(normalized.effective_notice_period_days);
  const effectiveRenewalMode = normalizeRenewalMode(normalized.effective_renewal_mode);
  const isInactiveAssignment = normalized.is_active !== true;
  const shouldSkipForLifecycleState = isInactiveAssignment;
  normalized.evergreen_review_anchor_date =
    !shouldSkipForLifecycleState && !normalizedEndDate && normalizedStartDate
      ? computeNextEvergreenReviewAnchorDate({ startDate: normalizedStartDate })
      : undefined;
  const shouldSkipDecisionDueDate =
    shouldSkipForLifecycleState || (effectiveRenewalMode === 'none' && !normalized.evergreen_review_anchor_date);
  normalized.decision_due_date =
    shouldSkipDecisionDueDate
      ? undefined
      : normalizedEndDate && effectiveNoticePeriodDays !== undefined
      ? subtractDaysFromDateOnly(normalizedEndDate, effectiveNoticePeriodDays)
      : !normalizedEndDate && normalizedStartDate && effectiveNoticePeriodDays !== undefined
        ? computeEvergreenDecisionDueDate({
            startDate: normalizedStartDate,
            noticePeriodDays: effectiveNoticePeriodDays,
          })
      : undefined;
  if (normalizedEndDate && normalizedStartDate) {
    normalized.renewal_cycle_start = normalizedStartDate;
    normalized.renewal_cycle_end = normalizedEndDate;
  } else if (!normalizedEndDate && normalizedStartDate && normalized.evergreen_review_anchor_date) {
    const evergreenCycleBounds = computeEvergreenCycleBounds({ startDate: normalizedStartDate });
    normalized.renewal_cycle_start = evergreenCycleBounds?.cycleStart;
    normalized.renewal_cycle_end = evergreenCycleBounds?.cycleEnd;
  } else {
    normalized.renewal_cycle_start = undefined;
    normalized.renewal_cycle_end = undefined;
  }
  normalized.renewal_cycle_key = normalized.decision_due_date
    ? normalizedEndDate
      ? normalized.renewal_cycle_end
        ? `fixed-term:${normalized.renewal_cycle_end as string}`
        : undefined
      : normalized.renewal_cycle_end
        ? `evergreen:${normalized.renewal_cycle_end as string}`
        : undefined
    : undefined;
  normalized.days_until_due = normalized.decision_due_date
    ? computeDaysUntilDate({ targetDate: normalized.decision_due_date as string })
    : undefined;
  normalized.assignment_status = deriveClientContractStatus({
    isActive: normalized.is_active === true,
    startDate: normalizedStartDate ?? null,
    endDate: normalizedEndDate ?? null,
  });

  delete normalized.tenant_default_renewal_mode;
  delete normalized.tenant_default_notice_period_days;

  return normalized as unknown as IClientContract;
};

export const dedupeClientContractsByRenewalCycle = (
  rows: IClientContract[]
): IClientContract[] => {
  const deduped = new Map<string, IClientContract>();

  for (const row of rows) {
    const cycleKey = row.renewal_cycle_key;
    if (!cycleKey) {
      deduped.set(`${row.tenant}:${row.client_contract_id}`, row);
      continue;
    }

    const dedupeKey = `${row.tenant}:${row.client_contract_id}:${cycleKey}`;
    if (!deduped.has(dedupeKey)) {
      deduped.set(dedupeKey, row);
    }
  }

  return [...deduped.values()];
};

export async function getClientContracts(
  knexOrTrx: Knex | Knex.Transaction,
  tenant: string,
  clientId: string
): Promise<IClientContract[]> {
  const baseQuery = knexOrTrx('client_contracts as cc')
    .leftJoin('contracts as c', function joinContracts() {
      this.on('cc.contract_id', '=', 'c.contract_id').andOn('cc.tenant', '=', 'c.tenant');
    })
    .where({ 'cc.client_id': clientId, 'cc.tenant': tenant, 'cc.is_active': true })
    .orderBy('cc.start_date', 'desc');

  const rows = await withRenewalDefaultsJoin(baseQuery).select([
    'cc.*',
    'c.billing_frequency as contract_billing_frequency',
    'c.status as contract_status',
    ...RENEWAL_DEFAULT_SELECTIONS,
  ]);

  return dedupeClientContractsByRenewalCycle(rows.map(normalizeClientContract));
}

export async function getActiveClientContractsByClientIds(
  knexOrTrx: Knex | Knex.Transaction,
  tenant: string,
  clientIds: string[]
): Promise<IClientContract[]> {
  if (clientIds.length === 0) return [];

  const baseQuery = knexOrTrx('client_contracts as cc')
    .leftJoin('contracts as c', function joinContracts() {
      this.on('cc.contract_id', '=', 'c.contract_id').andOn('cc.tenant', '=', 'c.tenant');
    })
    .whereIn('cc.client_id', clientIds)
    .andWhere({ 'cc.tenant': tenant, 'cc.is_active': true })
    .orderBy([
      { column: 'cc.client_id', order: 'asc' },
      { column: 'cc.start_date', order: 'desc' },
    ]);

  const rows = await withRenewalDefaultsJoin(baseQuery).select([
    'cc.*',
    'c.billing_frequency as contract_billing_frequency',
    'c.status as contract_status',
    ...RENEWAL_DEFAULT_SELECTIONS,
  ]);

  return dedupeClientContractsByRenewalCycle(rows.map(normalizeClientContract));
}

export async function getClientContractById(
  knexOrTrx: Knex | Knex.Transaction,
  tenant: string,
  clientContractId: string
): Promise<IClientContract | null> {
  const baseQuery = knexOrTrx('client_contracts as cc')
    .leftJoin('contracts as c', function joinContracts() {
      this.on('cc.contract_id', '=', 'c.contract_id').andOn('cc.tenant', '=', 'c.tenant');
    })
    .where({ 'cc.client_contract_id': clientContractId, 'cc.tenant': tenant });

  const row = await withRenewalDefaultsJoin(baseQuery)
    .select([
      'cc.*',
      'c.billing_frequency as contract_billing_frequency',
      'c.status as contract_status',
      ...RENEWAL_DEFAULT_SELECTIONS,
    ])
    .first();

  return row ? normalizeClientContract(row) : null;
}

export async function getDetailedClientContract(
  knexOrTrx: Knex | Knex.Transaction,
  tenant: string,
  clientContractId: string
): Promise<any | null> {
  const baseQuery = knexOrTrx('client_contracts as cc')
    .join('contracts as c', function joinContracts() {
      this.on('cc.contract_id', '=', 'c.contract_id').andOn('cc.tenant', '=', 'c.tenant');
    })
    .where({ 'cc.client_contract_id': clientContractId, 'cc.tenant': tenant });

  const clientContract = await withRenewalDefaultsJoin(baseQuery).select(
    [
      'cc.*',
      'c.contract_name',
      'c.contract_description',
      'c.billing_frequency as contract_billing_frequency',
      'c.status as contract_status',
      ...RENEWAL_DEFAULT_SELECTIONS,
    ]
  )
    .first();

  if (!clientContract) return null;

  const normalized = normalizeClientContract(clientContract);

  const contractLines = await knexOrTrx('client_contracts as cc')
    .join('contract_lines as cl', function joinContractLines() {
      this.on('cc.contract_id', '=', 'cl.contract_id').andOn('cc.tenant', '=', 'cl.tenant');
    })
    .where({
      'cc.client_contract_id': clientContractId,
      'cc.tenant': tenant,
    })
    .distinct('cl.contract_line_id', 'cl.contract_line_name')
    .select('cl.contract_line_name');

  return {
    ...normalized,
    contract_line_names: contractLines.map((line) => line.contract_line_name),
    contract_line_count: contractLines.length,
  };
}

export async function createClientContractAssignment(
  knexOrTrx: Knex | Knex.Transaction,
  tenant: string,
  input: ClientContractAssignmentCreateInput
): Promise<IClientContract> {
  const clientExists = await knexOrTrx('clients').where({ client_id: input.client_id, tenant }).first();
  if (!clientExists) {
    throw new Error(`Client ${input.client_id} not found`);
  }

  const contractQuery = knexOrTrx('contracts')
    .where({ contract_id: input.contract_id, tenant });
  if (input.is_active) {
    contractQuery.andWhere({ is_active: true });
  }
  const contractExists = await contractQuery.first();
  if (!contractExists) {
    throw new Error(`Contract ${input.contract_id} not found or inactive`);
  }

  if (input.is_active) {
    const targetCurrencyCode =
      typeof (contractExists as { currency_code?: string | null }).currency_code === 'string'
        ? (contractExists as { currency_code: string }).currency_code
        : null;
    const mixedCurrencyConflict = await findMixedCurrencyActiveAssignment(knexOrTrx, tenant, {
      clientId: input.client_id,
      targetCurrencyCode,
    });
    if (mixedCurrencyConflict) {
      const contractLabel = mixedCurrencyConflict.contract_name
        ? ` ("${mixedCurrencyConflict.contract_name}")`
        : '';
      throw new Error(
        `Client already has an active contract in ${mixedCurrencyConflict.currency_code}${contractLabel}. ` +
        `Cannot create a contract in ${targetCurrencyCode}. Mixed-currency contracts for the same client are not supported.`
      );
    }
  }

  const timestamp = new Date().toISOString();
  const insertPayload: Record<string, unknown> = {
    client_contract_id: uuidv4(),
    client_id: input.client_id,
    contract_id: input.contract_id,
    template_contract_id: null,
    start_date: input.start_date,
    end_date: input.end_date,
    is_active: input.is_active,
    tenant,
    created_at: timestamp,
    updated_at: timestamp,
  };

  await assertBoardScopedTicketStatusSelection({
    trx: knexOrTrx,
    tenant,
    boardId: input.renewal_ticket_board_id ?? null,
    statusId: input.renewal_ticket_status_id ?? null,
    statusLabel: 'Renewal ticket status',
  });

  if (input.renewal_mode === 'none' || input.renewal_mode === 'manual' || input.renewal_mode === 'auto') {
    insertPayload.renewal_mode = input.renewal_mode;
  }
  if (Number.isInteger(input.notice_period_days) && (input.notice_period_days as number) >= 0) {
    insertPayload.notice_period_days = input.notice_period_days;
  }
  if (Number.isInteger(input.renewal_term_months) && (input.renewal_term_months as number) > 0) {
    insertPayload.renewal_term_months = input.renewal_term_months;
  }
  if (typeof input.use_tenant_renewal_defaults === 'boolean') {
    insertPayload.use_tenant_renewal_defaults = input.use_tenant_renewal_defaults;
  }

  const [
    hasRenewalDueDateActionPolicy,
    hasRenewalTicketBoard,
    hasRenewalTicketStatus,
    hasRenewalTicketPriority,
    hasRenewalTicketAssignee,
    hasPoRequired,
    hasPoNumber,
    hasPoAmount,
  ] = await Promise.all([
    (knexOrTrx as any).schema?.hasColumn?.('client_contracts', 'renewal_due_date_action_policy'),
    (knexOrTrx as any).schema?.hasColumn?.('client_contracts', 'renewal_ticket_board_id'),
    (knexOrTrx as any).schema?.hasColumn?.('client_contracts', 'renewal_ticket_status_id'),
    (knexOrTrx as any).schema?.hasColumn?.('client_contracts', 'renewal_ticket_priority'),
    (knexOrTrx as any).schema?.hasColumn?.('client_contracts', 'renewal_ticket_assignee_id'),
    (knexOrTrx as any).schema?.hasColumn?.('client_contracts', 'po_required'),
    (knexOrTrx as any).schema?.hasColumn?.('client_contracts', 'po_number'),
    (knexOrTrx as any).schema?.hasColumn?.('client_contracts', 'po_amount'),
  ]);

  if (hasRenewalDueDateActionPolicy) {
    insertPayload.renewal_due_date_action_policy = input.renewal_due_date_action_policy ?? null;
  }
  if (hasRenewalTicketBoard) {
    insertPayload.renewal_ticket_board_id = input.renewal_ticket_board_id ?? null;
  }
  if (hasRenewalTicketStatus) {
    insertPayload.renewal_ticket_status_id = input.renewal_ticket_status_id ?? null;
  }
  if (hasRenewalTicketPriority) {
    insertPayload.renewal_ticket_priority = input.renewal_ticket_priority ?? null;
  }
  if (hasRenewalTicketAssignee) {
    insertPayload.renewal_ticket_assignee_id = input.renewal_ticket_assignee_id ?? null;
  }

  if (hasPoRequired) insertPayload.po_required = Boolean(input.po_required);
  if (hasPoNumber) insertPayload.po_number = input.po_number ?? null;
  if (hasPoAmount) insertPayload.po_amount = input.po_amount ?? null;

  const [created] = await knexOrTrx<IClientContract>('client_contracts').insert(insertPayload).returning('*');
  return normalizeClientContract(created);
}

export async function updateClientContractAssignment(
  knexOrTrx: Knex | Knex.Transaction,
  tenant: string,
  clientContractId: string,
  updateData: Partial<IClientContract>
): Promise<IClientContract> {
  const existing = await getClientContractById(knexOrTrx, tenant, clientContractId);
  if (!existing) {
    throw new Error(`Client contract ${clientContractId} not found`);
  }

  const sanitized: Partial<IClientContract> = {
    ...updateData,
    tenant: undefined as any,
    client_contract_id: undefined as any,
    client_id: undefined as any,
    contract_id: undefined as any,
    created_at: undefined as any,
    updated_at: new Date().toISOString() as any,
  };

  const effectiveRenewalTicketBoardId =
    updateData.renewal_ticket_board_id !== undefined
      ? updateData.renewal_ticket_board_id ?? null
      : existing.renewal_ticket_board_id ?? null;
  const effectiveRenewalTicketStatusId =
    updateData.renewal_ticket_status_id !== undefined
      ? updateData.renewal_ticket_status_id ?? null
      : existing.renewal_ticket_status_id ?? null;

  await assertBoardScopedTicketStatusSelection({
    trx: knexOrTrx,
    tenant,
    boardId: effectiveRenewalTicketBoardId,
    statusId: effectiveRenewalTicketStatusId,
    statusLabel: 'Renewal ticket status',
  });

  if (updateData.start_date !== undefined && updateData.start_date !== existing.start_date) {
    const contract = await knexOrTrx('contracts')
      .where({ contract_id: existing.contract_id, tenant })
      .first();

    if (contract && contract.is_active) {
      throw new Error('Start date cannot be changed for active contracts. Set the contract to draft first.');
    }
  }

  const [updated] = await knexOrTrx<IClientContract>('client_contracts')
    .where({ tenant, client_contract_id: clientContractId })
    .update(sanitized as any)
    .returning('*');

  if (!updated) {
    throw new Error(`Client contract ${clientContractId} not found`);
  }

  return normalizeClientContract(updated);
}