package businessscope

import (
	"context"
	"database/sql"
	"fmt"
	"strings"
	"time"
)

// candidateQuery deliberately derives the active lease lifecycle from delivery and
// return task facts. vehicle_lease_order_record remains an independent customer
// ownership check, but its last_return_time is not authoritative: saving a return
// draft currently updates that aggregate field before the return is completed.
const candidateQuery = `SELECT
  dv.vehicle_id,
  v.id,
  COALESCE(v.vin, ''),
  COALESCE(v.plate_number, dv.plate_number, r.plate_number, ''),
  r.customer_id,
  ci.id,
  dv.contract_id,
  co.id,
  COALESCE(co.other_customer_id, co.customer_id),
  COALESCE(co.contract_code, r.contract_code, ''),
  COALESCE(co.project_name, r.project_name, ''),
  COALESCE(vs.operation_status, ''),
  dv.delivery_time,
  dv.update_time
FROM delivery_vehicle dv
LEFT JOIN vehicle_info v ON v.id = dv.vehicle_id AND v.del_flag = '0'
LEFT JOIN vehicle_lease_order_record r ON r.vehicle_id = dv.vehicle_id AND r.del_flag = '0'
LEFT JOIN customer_info ci ON ci.id = r.customer_id AND ci.del_flag = '0'
LEFT JOIN vehicle_lease_contract_info co ON co.id = dv.contract_id AND co.del_flag = '0'
LEFT JOIN vehicle_status vs ON vs.vehicle_id = dv.vehicle_id AND vs.del_flag = '0'
WHERE dv.del_flag = '0'
  AND dv.delivery_status IN (2, 3)
  AND dv.vehicle_id IS NOT NULL
  AND dv.delivery_time IS NOT NULL
  AND NOT EXISTS (
    SELECT 1
    FROM delivery_vehicle newer
    WHERE newer.del_flag = '0'
      AND newer.vehicle_id = dv.vehicle_id
      AND newer.vehicle_id IS NOT NULL
      AND (
        COALESCE(newer.delivery_time, '1000-01-01') > COALESCE(dv.delivery_time, '1000-01-01')
        OR (
          COALESCE(newer.delivery_time, '1000-01-01') = COALESCE(dv.delivery_time, '1000-01-01')
          AND newer.id > dv.id
        )
      )
  )
  AND NOT EXISTS (
    SELECT 1
    FROM return_vehicle_task rt
    WHERE rt.delivery_vehicle_id = dv.id
      AND rt.del_flag = '0'
      AND rt.status IN (2, 3, 5)
  )
ORDER BY dv.vehicle_id, dv.id, r.id`

func ReadCandidates(ctx context.Context, db *sql.DB) ([]Candidate, error) {
	connection, err := db.Conn(ctx)
	if err != nil {
		return nil, fmt.Errorf("acquire OneOS connection: %w", err)
	}
	defer connection.Close()
	if err := VerifyReadOnlyGrants(ctx, connection); err != nil {
		return nil, err
	}
	if _, err := connection.ExecContext(ctx, `SET SESSION TRANSACTION READ ONLY`); err != nil {
		return nil, fmt.Errorf("force OneOS session read only: %w", err)
	}
	if _, err := connection.ExecContext(ctx, `SET SESSION MAX_EXECUTION_TIME = 10000`); err != nil {
		return nil, fmt.Errorf("set OneOS query timeout: %w", err)
	}
	tx, err := connection.BeginTx(ctx, &sql.TxOptions{Isolation: sql.LevelRepeatableRead, ReadOnly: true})
	if err != nil {
		return nil, fmt.Errorf("begin OneOS read-only snapshot: %w", err)
	}
	defer tx.Rollback()
	rows, err := tx.QueryContext(ctx, candidateQuery)
	if err != nil {
		return nil, fmt.Errorf("query OneOS customer vehicle candidates: %w", err)
	}
	defer rows.Close()
	candidates := make([]Candidate, 0, 1024)
	for rows.Next() {
		var vehicleID, vehicleProfileID, customerID, customerProfileID sql.NullInt64
		var contractID, contractProfileID, effectiveCustomerID sql.NullInt64
		var vin, plate, contractCode, projectName, operationStatus string
		var scopeStart time.Time
		var updatedAt sql.NullTime
		if err := rows.Scan(
			&vehicleID, &vehicleProfileID, &vin, &plate, &customerID, &customerProfileID,
			&contractID, &contractProfileID, &effectiveCustomerID, &contractCode, &projectName,
			&operationStatus, &scopeStart, &updatedAt,
		); err != nil {
			return nil, fmt.Errorf("scan OneOS scope candidate: %w", err)
		}
		candidate := Candidate{
			RowNumber: len(candidates) + 1,
			VehicleID: vehicleID.Int64, VehiclePresent: vehicleID.Valid && vehicleProfileID.Valid,
			VIN: vin, PlateNumber: plate,
			CustomerID: customerID.Int64, CustomerPresent: customerID.Valid,
			CustomerProfileExists: customerProfileID.Valid,
			ContractID:            contractID.Int64, ContractPresent: contractID.Valid,
			ContractProfileExists: contractProfileID.Valid,
			EffectiveCustomerID:   effectiveCustomerID.Int64, EffectiveCustomerSet: effectiveCustomerID.Valid,
			ContractCode: contractCode, ProjectName: projectName, OperationStatus: operationStatus,
			ScopeStartAt: scopeStart,
		}
		if updatedAt.Valid {
			value := updatedAt.Time
			candidate.SourceUpdatedAt = &value
		}
		candidates = append(candidates, candidate)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("iterate OneOS scope candidates: %w", err)
	}
	if err := tx.Commit(); err != nil {
		return nil, fmt.Errorf("finish OneOS read-only snapshot: %w", err)
	}
	return candidates, nil
}

func VerifyReadOnlyGrants(ctx context.Context, connection *sql.Conn) error {
	rows, err := connection.QueryContext(ctx, `SHOW GRANTS FOR CURRENT_USER`)
	if err != nil {
		return fmt.Errorf("inspect OneOS database grants: %w", err)
	}
	defer rows.Close()
	grants := make([]string, 0)
	for rows.Next() {
		var grant string
		if err := rows.Scan(&grant); err != nil {
			return fmt.Errorf("scan OneOS database grant: %w", err)
		}
		grants = append(grants, grant)
	}
	if err := rows.Err(); err != nil {
		return fmt.Errorf("iterate OneOS database grants: %w", err)
	}
	if err := ValidateReadOnlyGrants(grants); err != nil {
		return fmt.Errorf("OneOS database account is not read-only: %w", err)
	}
	return nil
}

func ValidateReadOnlyGrants(grants []string) error {
	if len(grants) == 0 {
		return fmt.Errorf("SHOW GRANTS returned no rows")
	}
	allowedSelectScopes := map[string]bool{
		"LN_ASSET_MANAGEMENT.VEHICLE_LEASE_ORDER_RECORD":  true,
		"LN_ASSET_MANAGEMENT.DELIVERY_VEHICLE":            true,
		"LN_ASSET_MANAGEMENT.RETURN_VEHICLE_TASK":         true,
		"LN_ASSET_MANAGEMENT.VEHICLE_INFO":                true,
		"LN_ASSET_MANAGEMENT.CUSTOMER_INFO":               true,
		"LN_ASSET_MANAGEMENT.VEHICLE_LEASE_CONTRACT_INFO": true,
		"LN_ASSET_MANAGEMENT.VEHICLE_STATUS":              true,
	}
	for _, raw := range grants {
		grant := strings.ToUpper(strings.TrimSpace(raw))
		if strings.HasPrefix(grant, "SET DEFAULT ROLE ") {
			return fmt.Errorf("role-based grants are not accepted; grant SELECT directly to the sync account")
		}
		if !strings.HasPrefix(grant, "GRANT ") {
			return fmt.Errorf("unsupported grant statement")
		}
		onIndex := strings.Index(grant, " ON ")
		if onIndex < 0 {
			return fmt.Errorf("unsupported role or dynamic grant")
		}
		privileges := strings.TrimSpace(strings.TrimPrefix(grant[:onIndex], "GRANT "))
		toIndex := strings.Index(grant[onIndex+4:], " TO ")
		if toIndex < 0 {
			return fmt.Errorf("unsupported grant scope")
		}
		scope := strings.ReplaceAll(strings.TrimSpace(grant[onIndex+4:onIndex+4+toIndex]), "`", "")
		for _, privilege := range strings.Split(privileges, ",") {
			privilege = strings.TrimSpace(privilege)
			switch privilege {
			case "USAGE":
				if scope != "*.*" {
					return fmt.Errorf("USAGE has unsupported scope %q", scope)
				}
			case "SELECT":
				if !allowedSelectScopes[scope] {
					return fmt.Errorf("SELECT scope %q is not required by the sync query", scope)
				}
			default:
				return fmt.Errorf("disallowed privilege %q", privilege)
			}
		}
	}
	return nil
}