Expression and Conversion System

trait ImplicitExpressionConversions {
  // Window operation constants
  implicit val UNBOUNDED_ROW: Expression
  implicit val UNBOUNDED_RANGE: Expression
  implicit val CURRENT_ROW: Expression
  implicit val CURRENT_RANGE: Expression
  
  // Field reference creation
  def $(name: String): Expression
  def col(name: String): Expression
  
  // Literal creation
  def lit(v: Any): Expression
  def lit(v: Any, dataType: DataType): Expression
  
  // Function calls
  def call(path: String, params: Expression*): Expression
  def call(function: UserDefinedFunction, params: Expression*): Expression
  def call(function: Class[_ <: UserDefinedFunction], params: Expression*): Expression
  def callSql(sqlExpression: String): Expression
}

implicit class WithOperations(e: Expression) extends ImplicitExpressionOperations {
  def expr: Expression = e
}

implicit class UnresolvedFieldExpression(s: Symbol) extends ImplicitExpressionOperations {
  def expr: Expression = unresolvedRef(s.name)
}

val fieldExpr = 'myField  // Creates field reference from symbol

implicit class AnyWithOperations[T](e: T)(implicit toExpr: T => Expression) 
  extends ImplicitExpressionOperations {
  def expr: Expression = toExpr(e)
}

implicit class LiteralLongExpression(l: Long) extends ImplicitExpressionOperations
implicit class LiteralByteExpression(b: Byte) extends ImplicitExpressionOperations  
implicit class LiteralShortExpression(s: Short) extends ImplicitExpressionOperations
implicit class LiteralIntExpression(i: Int) extends ImplicitExpressionOperations
implicit class LiteralFloatExpression(f: Float) extends ImplicitExpressionOperations
implicit class LiteralDoubleExpression(d: Double) extends ImplicitExpressionOperations
implicit class LiteralStringExpression(str: String) extends ImplicitExpressionOperations
implicit class LiteralBooleanExpression(bool: Boolean) extends ImplicitExpressionOperations

val expr = 42.asInstanceOf[Int] + 10  // Arithmetic operations on literals

implicit class ScalarFunctionCall(scalarFunction: ScalarFunction) {
  def apply(params: Expression*): Expression
}

implicit class TableFunctionCall(tableFunction: TableFunction[_]) {
  def apply(params: Expression*): Expression
}

implicit class ImperativeAggregateFunctionCall(aggregateFunction: ImperativeAggregateFunction[_, _]) {
  def apply(params: Expression*): Expression
}

implicit class FieldExpression(sc: StringContext) {
  def $(args: Any*): Expression  // String interpolation: $"fieldName"
}

$"userId"           // Simple field reference
$"user.address"     // Nested field reference  
$"items[0].price"   // Array element access

implicit def byte2Literal(b: Byte): Expression
implicit def short2Literal(s: Short): Expression
implicit def int2Literal(i: Int): Expression
implicit def long2Literal(l: Long): Expression
implicit def double2Literal(d: Double): Expression
implicit def float2Literal(f: Float): Expression
implicit def string2Literal(str: String): Expression
implicit def boolean2Literal(bool: Boolean): Expression
implicit def javaByte2Literal(b: JByte): Expression
implicit def javaShort2Literal(s: JShort): Expression
implicit def javaInt2Literal(i: JInteger): Expression
implicit def javaLong2Literal(l: JLong): Expression
implicit def javaDouble2Literal(d: JDouble): Expression
implicit def javaFloat2Literal(f: JFloat): Expression
implicit def javaBoolean2Literal(bool: JBoolean): Expression

implicit def sqlDate2Literal(d: Date): Expression
implicit def sqlTime2Literal(t: Time): Expression
implicit def sqlTimestamp2Literal(t: Timestamp): Expression
implicit def localDate2Literal(d: LocalDate): Expression
implicit def localTime2Literal(t: LocalTime): Expression
implicit def localDateTime2Literal(dt: LocalDateTime): Expression

implicit def seq2ArrayConstructor(seq: Seq[Expression]): Expression
implicit def map2MapConstructor(map: Map[Expression, Expression]): Expression

implicit def bigDecimal2Literal(bd: JBigDecimal): Expression
implicit def row2Literal(row: Row): Expression
implicit def list2ArrayConstructor(list: JList[Expression]): Expression
implicit def map2MapConstructor(map: JMap[Expression, Expression]): Expression

def $(name: String): Expression                    // Create field reference
def col(name: String): Expression                  // Alias for $()

def lit(v: Any): Expression                       // Create literal from any value  
def lit(v: Any, dataType: DataType): Expression      // Create typed literal

def call(path: String, params: Expression*): Expression                      // Call catalog function
def call(function: UserDefinedFunction, params: Expression*): Expression     // Call inline function
def call(function: Class[_ <: UserDefinedFunction], params: Expression*): Expression  // Call UDF class  
def callSql(sqlExpression: String): Expression                              // Execute SQL expression

import org.apache.flink.table.api._

// Field references
val userId = $"userId"
val userField = col("user")

// Literals  
val constValue = lit(42)
val constString = lit("hello")

// Mixed operations
val result = $"price" * 1.1 + lit(5.0)

// Built-in function call
val upperName = call("UPPER", $"name")

// User-defined function
class MyUDF extends ScalarFunction {
  def eval(value: String): String = value.toUpperCase
}
val myUdf = new MyUDF()
val result = call(myUdf, $"name")

// SQL expression
val sqlResult = callSql("CURRENT_TIMESTAMP")

// Using symbols for field names (legacy approach)
val field1 = 'userId         // Equivalent to $"userId"
val field2 = 'user_name      // Equivalent to $"user_name"

// Using window constants
import org.apache.flink.table.api._

val windowSpec = Over
  .partitionBy($"userId")
  .orderBy($"timestamp")
  .preceding(UNBOUNDED_RANGE)
  .following(CURRENT_ROW)

// Array construction from Scala sequence
val items = Seq(lit(1), lit(2), lit(3))
val arrayExpr = items  // Implicitly converted to array constructor

// Map construction
val mapData = Map(lit("key1") -> lit("value1"), lit("key2") -> lit("value2"))
val mapExpr = mapData  // Implicitly converted to map constructor