feat(parser): extend Parser with parseIsSuffix and parseInSuffix

src/main/kotlin/kestrel/sql/parser/Parser.kt

@@ -1348,6 +1348,14 @@ class Parser(private val tokens: List<Token>) {
     private fun parseComparison(): Expression {
         var left = parseAdditive()
         while (true) {
+            val negated = match(TokenType.Not)
+            left = when {
+                check(TokenType.In) -> { advance(); parseInSuffix(left, negated) }
+                check(TokenType.Between) -> { advance(); parseBetweenSuffix(left, negated) }
+                check(TokenType.Like) -> { advance(); parseLikeSuffix(left, negated) }
+                negated -> throw error("expected IN, BETWEEN, or LIKE after NOT", peek())
+                check(TokenType.Is) -> { advance(); parseIsSuffix(left) }
+                else -> {
                     val operator = when {
                         check(TokenType.Equal) -> BinaryOperator.Equal
                         check(TokenType.NotEqual) -> BinaryOperator.NotEqual
@@ -1355,12 +1363,46 @@ class Parser(private val tokens: List<Token>) {
                         check(TokenType.LessEqual) -> BinaryOperator.LessEqual
                         check(TokenType.Greater) -> BinaryOperator.Greater
                         check(TokenType.GreaterEqual) -> BinaryOperator.GreaterEqual
-                else -> break
+                        else -> return left
                     }
                     advance()
-            left = BinaryExpression(operator, left, parseAdditive())
+                    BinaryExpression(operator, left, parseAdditive())
                 }
-        return left
+            }
+        }
+    }
+
+    private fun parseIsSuffix(left: Expression): Expression {
+        val negated = match(TokenType.Not)
+        expect(TokenType.Null, "expected NULL after IS" + if (negated) " NOT" else "")
+        return IsNullExpression(left, negated)
+    }
+
+    private fun parseInSuffix(left: Expression, negated: Boolean): Expression {
+        expect(TokenType.LeftParen, "expected '(' after IN")
+        if (check(TokenType.Select)) {
+            val select = parseSelect()
+            expect(TokenType.RightParen, "expected ')' after IN subquery")
+            return InSubqueryExpression(left, select, negated)
+        }
+        val values = mutableListOf<Expression>()
+        do {
+            values.add(parseExpression())
+        } while (match(TokenType.Comma))
+        expect(TokenType.RightParen, "expected ')' after IN list")
+        return InExpression(left, values, negated)
+    }
+
+    private fun parseBetweenSuffix(left: Expression, negated: Boolean): Expression {
+        val low = parseAdditive()
+        expect(TokenType.And, "expected AND in BETWEEN")
+        val high = parseAdditive()
+        return BetweenExpression(left, low, high, negated)
+    }
+
+    private fun parseLikeSuffix(left: Expression, negated: Boolean): Expression {
+        val pattern = parseAdditive()
+        return LikeExpression(left, pattern, negated)
     }
 
     private fun parseAdditive(): Expression {
@@ -1378,7 +1420,7 @@ class Parser(private val tokens: List<Token>) {
     }
 
     private fun parseMultiplicative(): Expression {
-        var left = parseUnary()
+        var left = parseCollate()
         while (true) {
             val operator = when {
                 check(TokenType.Star) -> BinaryOperator.Multiply
@@ -1386,11 +1428,30 @@ class Parser(private val tokens: List<Token>) {
                 else -> break
             }
             advance()
-            left = BinaryExpression(operator, left, parseUnary())
+            left = BinaryExpression(operator, left, parseCollate())
         }
         return left
     }
 
+    /**
+     * `expr COLLATE name` - sits between unary and multiplicative in precedence, matching
+     * SQLite's own grammar (binds tighter than every arithmetic/comparison operator, but looser
+     * than unary `-`/`NOT`, so `-x COLLATE NOCASE` is `(-x) COLLATE NOCASE` and
+     * `a || b COLLATE NOCASE` would apply to `b` alone). Left-associative chaining
+     * (`x COLLATE A COLLATE B`) is accepted like SQLite accepts it - only the last one written
+     * has any effect, since each wraps the previous [CollateExpression] as its own operand.
+     */
+    private fun parseCollate(): Expression {
+        var expression = parseUnary()
+        while (match(TokenType.Collate)) {
+            val nameToken = expect(TokenType.Identifier, "expected a collation name after COLLATE")
+            val collation = Collation.fromName(nameToken.lexeme)
+                ?: throw error("no such collating sequence: ${nameToken.lexeme}", nameToken)
+            expression = CollateExpression(expression, collation)
+        }
+        return expression
+    }
+
     private fun parseUnary(): Expression {
         if (match(TokenType.Minus)) {
             return UnaryExpression(UnaryOperator.Negate, parseUnary())
@@ -1419,6 +1480,27 @@ class Parser(private val tokens: List<Token>) {
             TokenType.Null -> {
                 advance(); LiteralExpression(Value.NullValue)
             }
+            TokenType.Parameter -> {
+                advance()
+                val index = token.intValue!!
+                if (index < 1) throw error("parameter index must be >= 1 but was $index", token)
+                ParameterExpression(index.toInt())
+            }
+            TokenType.Case -> parseCase()
+            TokenType.Exists -> parseExists()
+            TokenType.Cast -> parseCast()
+            // LEFT/RIGHT are otherwise reserved (LEFT/RIGHT JOIN), but LEFT(str, n)/RIGHT(str, n) are
+            // real, commonly expected scalar functions - only valid here as a call, never as a bare
+            // column reference, so a missing '(' is unconditionally an error rather than falling back
+            // to ColumnExpression like the TokenType.Identifier branch below does.
+            TokenType.Left -> {
+                advance()
+                if (check(TokenType.LeftParen)) parseFunctionCall(token.lexeme) else throw error("expected '(' after LEFT", peek())
+            }
+            TokenType.Right -> {
+                advance()
+                if (check(TokenType.LeftParen)) parseFunctionCall(token.lexeme) else throw error("expected '(' after RIGHT", peek())
+            }
             TokenType.Identifier -> {
                 advance()
                 when {
@@ -1429,19 +1511,71 @@ class Parser(private val tokens: List<Token>) {
             }
             TokenType.LeftParen -> {
                 advance()
+                if (check(TokenType.Select)) {
+                    val select = parseSelect()
+                    expect(TokenType.RightParen, "expected ')' after subquery")
+                    ScalarSubqueryExpression(select)
+                } else {
                     val expression = parseExpression()
                     expect(TokenType.RightParen, "expected ')' after expression")
                     expression
                 }
+            }
             else -> throw error("expected an expression but found '${describe(token)}'", token)
         }
     }
 
+    private fun parseCase(): Expression {
+        expect(TokenType.Case, "expected CASE")
+        val operand = if (!check(TokenType.When)) parseExpression() else null
+        val branches = mutableListOf<CaseBranch>()
+        while (match(TokenType.When)) {
+            val condition = parseExpression()
+            expect(TokenType.Then, "expected THEN after CASE condition")
+            val result = parseExpression()
+            branches.add(CaseBranch(condition, result))
+        }
+        if (branches.isEmpty()) throw error("expected at least one WHEN clause in CASE expression", peek())
+        val elseExpression = if (match(TokenType.Else)) parseExpression() else null
+        expect(TokenType.End, "expected END to close CASE expression")
+        return CaseExpression(operand, branches, elseExpression)
+    }
+
+    private fun parseCast(): Expression {
+        expect(TokenType.Cast, "expected CAST")
+        expect(TokenType.LeftParen, "expected '(' after CAST")
+        val operand = parseExpression()
+        expect(TokenType.As, "expected AS in CAST")
+        val spec = parseTypeSpec()
+        expect(TokenType.RightParen, "expected ')' after CAST target type")
+        return CastExpression(operand, spec.type, spec.precision, spec.scale)
+    }
+
+    private fun parseExists(): Expression {
+        expect(TokenType.Exists, "expected EXISTS")
+        expect(TokenType.LeftParen, "expected '(' after EXISTS")
+        val select = parseSelect()
+        expect(TokenType.RightParen, "expected ')' after EXISTS subquery")
+        return ExistsExpression(select)
+    }
+
     private fun parseFunctionCall(name: String): Expression {
         expect(TokenType.LeftParen, "expected '(' after function name")
-        if (match(TokenType.Star)) {
-            expect(TokenType.RightParen, "expected ')' after '*'")
-            return FunctionExpression(name, argument = null, star = true)
+        val upperName = name.uppercase()
+        if (upperName == "STRING_AGG") return parseStringAggCall(name)
+        val isAggregate = upperName in AGGREGATE_FUNCTIONS
+        var star = false
+        var distinct = false
+        val arguments = mutableListOf<Expression>()
+        if (isAggregate && match(TokenType.Distinct)) {
+            distinct = true
+            arguments.add(parseExpression())
+        } else if (isAggregate && match(TokenType.Star)) {
+            star = true
+        } else if (!check(TokenType.RightParen)) {
+            do {
+                arguments.add(parseExpression())
+            } while (match(TokenType.Comma))
         }
         val argument = parseExpression()
         expect(TokenType.RightParen, "expected ')' after function argument")