Expression System

/**
 * Reference a table column by name
 * @param name Column name
 * @return Expression referencing the column
 */
public static Expression $(String name);

/**
 * Create a literal value expression
 * @param value Constant value (String, Number, Boolean, etc.)
 * @return Expression representing the literal value
 */
public static Expression lit(Object value);

/**
 * Create a null literal of specific type
 * @param dataType Type of the null value
 * @return Expression representing typed null
 */
public static Expression nullOf(DataType dataType);

/**
 * Create a range expression for array slicing
 * @param start Start index (inclusive)
 * @param end End index (exclusive)
 * @return Range expression for array operations
 */
public static Expression range(int start, int end);

import static org.apache.flink.table.api.Expressions.*;

// Column references
Expression userId = $("user_id");
Expression userName = $("name");

// Literals
Expression hundred = lit(100);
Expression greeting = lit("Hello");
Expression pi = lit(3.14159);
Expression isActive = lit(true);

// Null values
Expression nullString = nullOf(DataTypes.STRING());
Expression nullTimestamp = nullOf(DataTypes.TIMESTAMP());

// Basic arithmetic
public Expression plus(Object other);
public Expression minus(Object other);
public Expression times(Object other);
public Expression dividedBy(Object other);
public Expression mod(Object other);

// Unary operations  
public Expression unaryMinus();
public Expression unaryPlus();

// Power and mathematical functions
public Expression power(Object exponent);
public Expression abs();
public Expression sqrt();
public Expression exp();
public Expression log();
public Expression log10();
public Expression log2();
public Expression ln();

// Trigonometric functions
public Expression sin();
public Expression cos();
public Expression tan();
public Expression asin();
public Expression acos();
public Expression atan();
public Expression sinh();
public Expression cosh();
public Expression tanh();

// Rounding functions
public Expression ceil();
public Expression floor();
public Expression round();
public Expression round(int scale);

// Basic calculations
Expression totalPrice = $("quantity").times($("unit_price"));
Expression discount = $("price").times(lit(0.1));
Expression finalPrice = $("price").minus(discount);

// Mathematical functions
Expression distance = $("x").power(lit(2)).plus($("y").power(lit(2))).sqrt();
Expression logValue = $("value").log();
Expression roundedPrice = $("price").round(2);

// Equality comparisons
public Expression isEqual(Object other);
public Expression isNotEqual(Object other);

// Ordering comparisons
public Expression isGreater(Object other);
public Expression isGreaterOrEqual(Object other);
public Expression isLess(Object other);
public Expression isLessOrEqual(Object other);

// Null checks
public Expression isNull();
public Expression isNotNull();

// Range operations
public Expression between(Object lower, Object upper);
public Expression notBetween(Object lower, Object upper);

// Set membership
public Expression in(Object... values);
public Expression notIn(Object... values);

// Age filtering
Expression adults = $("age").isGreaterOrEqual(lit(18));
Expression seniors = $("age").between(lit(65), lit(100));

// Price comparisons
Expression expensive = $("price").isGreater(lit(1000));
Expression affordable = $("price").isLessOrEqual(lit(100));

// Null handling
Expression hasEmail = $("email").isNotNull();
Expression validUser = $("name").isNotNull().and($("email").isNotNull());

// Category filtering
Expression popularCategories = $("category").in(lit("electronics"), lit("books"), lit("clothing"));

/**
 * Logical AND operation
 * @param other Expression to AND with
 * @return Boolean expression representing AND result
 */
public Expression and(Object other);

/**
 * Logical OR operation
 * @param other Expression to OR with
 * @return Boolean expression representing OR result
 */
public Expression or(Object other);

/**
 * Logical NOT operation
 * @return Boolean expression representing NOT result
 */
public Expression not();

// Complex filtering conditions
Expression validOrder = $("amount").isGreater(lit(0))
    .and($("status").isEqual(lit("confirmed")))
    .and($("customer_id").isNotNull());

Expression weekendOrEvening = $("day_of_week").in(lit("Saturday"), lit("Sunday"))
    .or($("hour").isGreaterOrEqual(lit(18)));

Expression notCancelled = $("status").isNotEqual(lit("cancelled"));

// Case conversion
public Expression upperCase();
public Expression lowerCase();
public Expression initCap();

// String manipulation
public Expression substring(int start);
public Expression substring(int start, int length);
public Expression trim();
public Expression ltrim();
public Expression rtrim();
public Expression repeat(int times);
public Expression reverse();

// String operations
public Expression concat(Object... others);
public Expression length();
public Expression charLength();
public Expression position(String substring);
public Expression overlay(String replacement, int start);
public Expression overlay(String replacement, int start, int length);

// Pattern matching
public Expression like(String pattern);
public Expression notLike(String pattern);
public Expression similar(String pattern);
public Expression notSimilar(String pattern);
public Expression rlike(String pattern);

// String splitting and parsing
public Expression split(String delimiter);
public Expression regexpReplace(String pattern, String replacement);
public Expression regexpExtract(String pattern);
public Expression regexpExtract(String pattern, int group);

// Text processing
Expression cleanName = $("name").trim().upperCase();
Expression firstName = $("full_name").split(lit(" ")).at(lit(0));
Expression emailDomain = $("email").regexpExtract(lit("@(.+)"), lit(1));

// Pattern matching
Expression gmailUsers = $("email").like(lit("%@gmail.com"));
Expression phoneNumbers = $("phone").rlike(lit("\\d{3}-\\d{3}-\\d{4}"));

// String construction
Expression fullAddress = $("street").concat(lit(", ")).concat($("city")).concat(lit(", ")).concat($("state"));

// Current time functions
public static Expression currentTimestamp();
public static Expression currentDate();
public static Expression currentTime();
public static Expression localTimestamp();
public static Expression localTime();

// Extraction functions
public Expression year();
public Expression quarter();
public Expression month();
public Expression week();
public Expression dayOfYear();
public Expression dayOfMonth();
public Expression dayOfWeek();
public Expression hour();
public Expression minute();
public Expression second();

// Date/time arithmetic
public Expression plus(IntervalUnit unit, int amount);
public Expression minus(IntervalUnit unit, int amount);
public Expression plus(Expression interval);
public Expression minus(Expression interval);

// Conversion functions
public Expression toDate();
public Expression toTime();
public Expression toTimestamp();
public Expression toTimestampLtz();

// Formatting functions
public Expression dateFormat(String format);
public Expression timestampDiff(TimePointUnit unit, Expression other);

// Date extraction
Expression orderYear = $("order_date").year();
Expression orderMonth = $("order_date").month();
Expression orderHour = $("created_at").hour();

// Date arithmetic
Expression oneWeekLater = $("start_date").plus(IntervalUnit.WEEK, 1);
Expression ageInYears = currentDate().minus($("birth_date")).dividedBy(lit(365));

// Time-based filtering
Expression recentOrders = $("order_date").isGreater(currentTimestamp().minus(IntervalUnit.DAY, 7));
Expression businessHours = $("created_at").hour().between(lit(9), lit(17));

// Date formatting
Expression formattedDate = $("order_date").dateFormat(lit("yyyy-MM-dd"));

// Array access
public Expression at(Object index);
public Expression cardinality();

// Array manipulation
public Expression element();
public Expression slice(int start, int end);

// Array predicates
public Expression exists(Expression predicate);
public Expression forall(Expression predicate);

// Array element access
Expression firstTag = $("tags").at(lit(0));
Expression tagCount = $("tags").cardinality();

// Array operations
Expression hasImportantTag = $("tags").exists($("item").like(lit("important%")));
Expression recentTags = $("tags").slice(lit(0), lit(5));

// JSON extraction
public Expression jsonValue(String path);
public Expression jsonValue(String path, JsonValueOnEmptyOrError onEmpty, 
                          JsonValueOnEmptyOrError onError);
public Expression jsonQuery(String path);
public Expression jsonExists(String path);

// JSON type checking
public Expression isJson();
public Expression isJson(JsonType type);

// JSON data extraction
Expression customerName = $("json_data").jsonValue(lit("$.customer.name"));
Expression orderItems = $("order_json").jsonQuery(lit("$.items[*]"));
Expression hasShipping = $("order_json").jsonExists(lit("$.shipping"));

// JSON validation
Expression validJson = $("data").isJson();
Expression jsonObject = $("data").isJson(JsonType.OBJECT);

/**
 * Simple CASE WHEN expression
 * @param condition Boolean expression
 * @param thenValue Value when condition is true
 * @param elseValue Value when condition is false
 * @return Conditional expression
 */
public static Expression when(Expression condition, Object thenValue, Object elseValue);

/**
 * Multi-branch CASE expression
 * @param condition First condition
 * @param thenValue Value for first condition
 * @return CaseExpression for chaining additional when clauses
 */
public static CaseExpression when(Expression condition, Object thenValue);

public interface CaseExpression extends Expression {
    public CaseExpression when(Expression condition, Object thenValue);
    public Expression otherwise(Object elseValue);
}

/**
 * Null coalescing - return first non-null value
 * @param expressions Expressions to check in order
 * @return First non-null expression value
 */
public static Expression coalesce(Expression... expressions);

/**
 * Null-safe equality check
 * @param left Left expression
 * @param right Right expression
 * @return Boolean indicating null-safe equality
 */
public static Expression nullIf(Expression left, Expression right);

// Simple conditional
Expression priceCategory = when($("price").isGreater(lit(100)), lit("expensive"), lit("affordable"));

// Multi-branch case
Expression ageGroup = when($("age").isLess(lit(18)), lit("minor"))
    .when($("age").isLess(lit(65)), lit("adult"))
    .otherwise(lit("senior"));

// Null handling
Expression displayName = coalesce($("nickname"), $("first_name"), lit("Anonymous"));
Expression cleanValue = nullIf($("value"), lit(""));

// Count functions
public Expression count();
public Expression countDistinct();

// Numeric aggregations
public Expression sum();
public Expression avg();
public Expression min();
public Expression max();
public Expression stddev();
public Expression variance();

// String aggregations
public Expression concat(String delimiter);
public Expression listAgg();
public Expression listAgg(String delimiter);

// Collection functions
public Expression collect();
public Expression mode();

// Numeric aggregations
Table orderSummary = orders
    .groupBy($("customer_id"))
    .select($("customer_id"),
            $("amount").sum().as("total_spent"),
            $("order_id").count().as("order_count"),
            $("amount").avg().as("avg_order_value"));

// String aggregations
Table customerTags = orders
    .groupBy($("customer_id"))
    .select($("customer_id"),
            $("product_category").listAgg(lit(", ")).as("categories"));

// Ranking functions
public Expression rowNumber();
public Expression rank();
public Expression denseRank();
public Expression percentRank();

// Value functions
public Expression lag(int offset);
public Expression lag(int offset, Object defaultValue);
public Expression lead(int offset);
public Expression lead(int offset, Object defaultValue);
public Expression firstValue();
public Expression lastValue();
public Expression nthValue(int n);

// Ranking within groups
Table rankedProducts = sales
    .window(Over.partitionBy($("category")).orderBy($("sales").desc()).as("w"))
    .select($("product"), $("category"), $("sales"),
            $("sales").rank().over($("w")).as("sales_rank"));

// Time series analysis
Table timeSeriesData = events
    .window(Over.partitionBy($("user_id")).orderBy($("timestamp")).as("w"))
    .select($("user_id"), $("value"), $("timestamp"),
            $("value").lag(1).over($("w")).as("previous_value"));