feat(engine): extend Evaluator with evaluateBetween and evaluateLike

src/main/kotlin/kestrel/engine/Evaluator.kt

@@ -284,6 +284,62 @@ class Evaluator(
             if (candidate is Value.NullValue) {
                 sawNull = true
                 continue
+            }
+            if (compareOperands(operand, candidate, collation) == 0) return Value.BooleanValue(!expression.negated)
+        }
+        return if (sawNull) Value.NullValue else Value.BooleanValue(expression.negated)
+    }
+
+    private fun evaluateBetween(expression: BetweenExpression): Value {
+        val operand = evaluate(expression.operand)
+        val low = evaluate(expression.low)
+        val high = evaluate(expression.high)
+        if (operand is Value.NullValue || low is Value.NullValue || high is Value.NullValue) return Value.NullValue
+        val withinRange = compareOperands(operand, low, pairCollation(expression.operand, expression.low)) >= 0 &&
+            compareOperands(operand, high, pairCollation(expression.operand, expression.high)) <= 0
+        return Value.BooleanValue(if (expression.negated) !withinRange else withinRange)
+    }
+
+    private fun evaluateLike(expression: LikeExpression): Value {
+        val operand = evaluate(expression.operand)
+        val pattern = evaluate(expression.pattern)
+        if (operand is Value.NullValue || pattern is Value.NullValue) return Value.NullValue
+        if (operand !is Value.TextValue || pattern !is Value.TextValue) {
+            throw KestrelException("LIKE requires text operands but got ${operand.typeName} and ${pattern.typeName}")
+        }
+        val matches = likeToRegex(pattern.value).matches(operand.value)
+        return Value.BooleanValue(if (expression.negated) !matches else matches)
+    }
+
+    private fun likeToRegex(pattern: String): Regex {
+        val builder = StringBuilder("(?s)")
+        for (character in pattern) {
+            when (character) {
+                '%' -> builder.append(".*")
+                '_' -> builder.append(".")
+                else -> builder.append(Regex.escape(character.toString()))
+            }
+        }
+        return Regex(builder.toString())
+    }
+
+    private fun evaluateCase(expression: CaseExpression): Value {
+        val operand = expression.operand?.let { evaluate(it) }
+        for (branch in expression.branches) {
+            val matched = if (operand != null) {
+                if (operand is Value.NullValue) {
+                    false
+                } else {
+                    val candidate = evaluate(branch.condition)
+                    candidate !is Value.NullValue &&
+                        compareOperands(operand, candidate, pairCollation(expression.operand!!, branch.condition)) == 0
+                }
+            } else {
+                asBooleanOrNull(evaluate(branch.condition)) == true
+            }
+            if (matched) return evaluate(branch.result)
+        }
+        return expression.elseExpression?.let { evaluate(it) } ?: Value.NullValue
     }
 
     private fun evaluateColumn(expression: ColumnExpression): Value {
@@ -298,6 +354,7 @@ class Evaluator(
             UnaryOperator.Negate -> when (operand) {
                 is Value.IntegerValue -> Value.IntegerValue(-operand.value)
                 is Value.RealValue -> Value.RealValue(-operand.value)
+                is Value.DecimalValue -> Value.DecimalValue(-operand.value)
                 else -> throw KestrelException("unary minus requires a numeric operand but got ${operand.typeName}")
             }
             UnaryOperator.Not -> when (operand) {
@@ -317,7 +374,7 @@ class Evaluator(
         return when (operator) {
             BinaryOperator.Add, BinaryOperator.Subtract,
             BinaryOperator.Multiply, BinaryOperator.Divide -> evaluateArithmetic(operator, left, right)
-            else -> evaluateComparison(operator, left, right)
+            else -> evaluateComparison(operator, left, right, pairCollation(expression.left, expression.right))
         }
     }
 
@@ -347,6 +404,12 @@ class Evaluator(
 
     private fun evaluateArithmetic(operator: BinaryOperator, left: Value, right: Value): Value {
         if (left is Value.NullValue || right is Value.NullValue) return Value.NullValue
+        if (left is Value.DateValue || right is Value.DateValue) {
+            return evaluateDateArithmetic(operator, left, right)
+        }
+        if (left is Value.DecimalValue || right is Value.DecimalValue) {
+            return evaluateDecimalArithmetic(operator, left, right)
+        }
         if (!isNumeric(left) || !isNumeric(right)) {
             throw KestrelException("arithmetic requires numeric operands but got ${left.typeName} and ${right.typeName}")
         }
@@ -382,9 +445,9 @@ class Evaluator(
         )
     }
 
-    private fun evaluateComparison(operator: BinaryOperator, left: Value, right: Value): Value {
+    private fun evaluateComparison(operator: BinaryOperator, left: Value, right: Value, collation: Collation): Value {
         if (left is Value.NullValue || right is Value.NullValue) return Value.NullValue
-        val ordering = compareOperands(left, right)
+        val ordering = compareOperands(left, right, collation)
         val result = when (operator) {
             BinaryOperator.Equal -> ordering == 0
             BinaryOperator.NotEqual -> ordering != 0
@@ -397,14 +460,59 @@ class Evaluator(
         return Value.BooleanValue(result)
     }
 
-    private fun compareOperands(left: Value, right: Value): Int = when {
+    /**
+     * [collation] only ever changes the outcome for two [Value.TextValue]s - every other pairing
+     * ignores it, matching SQLite (COLLATE is meaningless outside of text comparison). Defaults to
+     * [Collation.Binary] (this engine's behavior before COLLATE existed) at every call site that
+     * has no [CollateExpression] to resolve one from.
+     */
+    private fun compareOperands(left: Value, right: Value, collation: Collation = Collation.Binary): Int = when {
         left is Value.IntegerValue && right is Value.IntegerValue -> left.value.compareTo(right.value)
+        left is Value.DecimalValue || right is Value.DecimalValue -> {
+            val a = decimalOf(left) ?: throw KestrelException("cannot compare ${left.typeName} with ${right.typeName}")
+            val b = decimalOf(right) ?: throw KestrelException("cannot compare ${left.typeName} with ${right.typeName}")
+            a.compareTo(b)
+        }
         isNumeric(left) && isNumeric(right) -> asDouble(left).compareTo(asDouble(right))
-        left is Value.TextValue && right is Value.TextValue -> left.value.compareTo(right.value)
+        left is Value.TextValue && right is Value.TextValue -> collation.compare(left.value, right.value)
         left is Value.BooleanValue && right is Value.BooleanValue -> left.value.compareTo(right.value)
+        left is Value.DateValue && right is Value.DateValue -> left.value.compareTo(right.value)
         else -> throw KestrelException("cannot compare ${left.typeName} with ${right.typeName}")
     }
 
+    /** The [Collation] an explicit `COLLATE` on [expression] itself names, or `null` when it is not a [CollateExpression] at all. */
+    private fun explicitCollationOf(expression: Expression): Collation? = (expression as? CollateExpression)?.collation
+
+    /**
+     * [expression]'s own declared `COLLATE` (see [kestrel.catalog.Column.collation]) when it is a
+     * bare [ColumnExpression] whose [resolver] reports one - `null` for anything else, including a
+     * column that never declared one at all ([ColumnResolver.declaredCollation] reporting
+     * [Collation.Binary], its class default, is treated the exact same as reporting nothing: a
+     * column that never opted into a non-default sequence should not out-rank an operand on the
+     * *other* side of a comparison that did, purely by virtue of appearing on the left - see
+     * [pairCollation]).
+     */
+    private fun columnDeclaredCollationOf(expression: Expression): Collation? =
+        (expression as? ColumnExpression)?.let { resolver?.declaredCollation(it) }?.takeIf { it != Collation.Binary }
+
+    /**
+     * The [Collation] [expression] compares with on its own, combining both of [pairCollation]'s
+     * tiers into one - used where there is only a single operand to consult
+     * ([evaluateIn]/[evaluateInSubquery]'s list/subquery operand), which can still tell "no COLLATE
+     * here at all" apart from "explicitly COLLATE BINARY" (both [explicitCollationOf] and
+     * [columnDeclaredCollationOf] return `null` only for the former).
+     */
+    private fun collationOf(expression: Expression): Collation? = explicitCollationOf(expression) ?: columnDeclaredCollationOf(expression)
+
+    /**
+     * Delegates to the shared [kestrel.engine.pairCollation] (SQLite's two-tier binary-comparison
+     * rule) bound to this evaluator's own [resolver] - see that function's doc for the precedence
+     * rule itself and why it must stay two separate passes rather than one combined
+     * [collationOf]-per-side check.
+     */
+    private fun pairCollation(left: Expression, right: Expression): Collation =
+        kestrel.engine.pairCollation(left, right) { resolver?.declaredCollation(it) }
+
     private fun isNumeric(value: Value): Boolean = value is Value.IntegerValue || value is Value.RealValue
 
     private fun asDouble(value: Value): Double = when (value) {
@@ -412,4 +520,47 @@ class Evaluator(
         is Value.RealValue -> value.value
         else -> error("not a numeric value")
     }
+
+    private fun decimalOf(value: Value): BigDecimal? = when (value) {
+        is Value.DecimalValue -> value.value
+        is Value.IntegerValue -> BigDecimal(value.value)
+        is Value.RealValue -> BigDecimal.valueOf(value.value)
+        else -> null
+    }
+
+    private fun evaluateDateArithmetic(operator: BinaryOperator, left: Value, right: Value): Value = when {
+        left is Value.DateValue && right is Value.DateValue -> when (operator) {
+            BinaryOperator.Subtract -> Value.IntegerValue(left.value.toEpochDay() - right.value.toEpochDay())
+            else -> throw KestrelException("DATE ${operator.symbol} DATE is not supported; only subtraction (day difference) is")
+        }
+        left is Value.DateValue && right is Value.IntegerValue -> when (operator) {
+            BinaryOperator.Add -> Value.DateValue(left.value.plusDays(right.value))
+            BinaryOperator.Subtract -> Value.DateValue(left.value.minusDays(right.value))
+            else -> throw KestrelException("DATE only supports + and - with an INTEGER day offset")
+        }
+        left is Value.IntegerValue && right is Value.DateValue && operator == BinaryOperator.Add ->
+            Value.DateValue(right.value.plusDays(left.value))
+        else -> throw KestrelException("arithmetic requires numeric operands but got ${left.typeName} and ${right.typeName}")
+    }
+
+    private fun evaluateDecimalArithmetic(operator: BinaryOperator, left: Value, right: Value): Value {
+        val a = decimalOf(left) ?: throw KestrelException("arithmetic requires numeric operands but got ${left.typeName} and ${right.typeName}")
+        val b = decimalOf(right) ?: throw KestrelException("arithmetic requires numeric operands but got ${left.typeName} and ${right.typeName}")
+        return Value.DecimalValue(
+            when (operator) {
+                BinaryOperator.Add -> a + b
+                BinaryOperator.Subtract -> a - b
+                BinaryOperator.Multiply -> a * b
+                BinaryOperator.Divide -> {
+                    if (b.signum() == 0) throw KestrelException("division by zero")
+                    a.divide(b, maxOf(a.scale(), b.scale(), MIN_DIVISION_SCALE), RoundingMode.HALF_UP)
+                }
+                else -> error("unreachable arithmetic operator")
+            }
+        )
+    }
+
+    private companion object {
+        const val MIN_DIVISION_SCALE = 10
+    }
 }