Monitor Conditions (#5048)

server/monitor-conditions/evaluator.js

@@ -0,0 +1,71 @@
+const { ConditionExpressionGroup, ConditionExpression, LOGICAL } = require("./expression");
+const { operatorMap } = require("./operators");
+
+/**
+ * @param {ConditionExpression} expression Expression to evaluate
+ * @param {object} context Context to evaluate against; These are values for variables in the expression
+ * @returns {boolean} Whether the expression evaluates true or false
+ * @throws {Error}
+ */
+function evaluateExpression(expression, context) {
+    /**
+     * @type {import("./operators").ConditionOperator|null}
+     */
+    const operator = operatorMap.get(expression.operator) || null;
+    if (operator === null) {
+        throw new Error("Unexpected expression operator ID '" + expression.operator + "'. Expected one of [" + operatorMap.keys().join(",") + "]");
+    }
+
+    if (!Object.prototype.hasOwnProperty.call(context, expression.variable)) {
+        throw new Error("Variable missing in context: " + expression.variable);
+    }
+
+    return operator.test(context[expression.variable], expression.value);
+}
+
+/**
+ * @param {ConditionExpressionGroup} group Group of expressions to evaluate
+ * @param {object} context Context to evaluate against; These are values for variables in the expression
+ * @returns {boolean} Whether the group evaluates true or false
+ * @throws {Error}
+ */
+function evaluateExpressionGroup(group, context) {
+    if (!group.children.length) {
+        throw new Error("ConditionExpressionGroup must contain at least one child.");
+    }
+
+    let result = null;
+
+    for (const child of group.children) {
+        let childResult;
+
+        if (child instanceof ConditionExpression) {
+            childResult = evaluateExpression(child, context);
+        } else if (child instanceof ConditionExpressionGroup) {
+            childResult = evaluateExpressionGroup(child, context);
+        } else {
+            throw new Error("Invalid child type in ConditionExpressionGroup. Expected ConditionExpression or ConditionExpressionGroup");
+        }
+
+        if (result === null) {
+            result = childResult; // Initialize result with the first child's result
+        } else if (child.andOr === LOGICAL.OR) {
+            result = result || childResult;
+        } else if (child.andOr === LOGICAL.AND) {
+            result = result && childResult;
+        } else {
+            throw new Error("Invalid logical operator in child of ConditionExpressionGroup. Expected 'and' or 'or'. Got '" + group.andOr + "'");
+        }
+    }
+
+    if (result === null) {
+        throw new Error("ConditionExpressionGroup did not result in a boolean.");
+    }
+
+    return result;
+}
+
+module.exports = {
+    evaluateExpression,
+    evaluateExpressionGroup,
+};