/**
 * Given an Espree Node, returns true if the node is a component.
 *
 * @param {espree.Node} node Node to check.
 *
 * @return {boolean} Whether node is a component.
 */
function isComponent( node ) {
	// Assume function component by naming convention of UpperCamelCase.
	if (
		node.type === 'FunctionDeclaration' &&
		node.id &&
		/^[A-Z]/.test( node.id.name )
	) {
		return true;
	}

	// Assume class component by extends name `Component`.
	if ( node.type === 'ClassDeclaration' && node.superClass ) {
		let superClassName;
		switch ( node.superClass.type ) {
			case 'Identifier':
				superClassName = node.superClass.name;
				break;

			case 'MemberExpression':
				superClassName = node.superClass.property.name;
				break;
		}

		if ( superClassName === 'Component' ) {
			return true;
		}
	}

	return false;
}

module.exports = {
	meta: {
		type: 'problem',
		schema: [],
	},
	create( context ) {
		return {
			'CallExpression[callee.name="setTimeout"]'( node ) {
				// If the result of a `setTimeout` call is assigned to a
				// variable, assume the timer ID is handled by a cancellation.
				const hasAssignment =
					node.parent.type === 'AssignmentExpression' ||
					node.parent.type === 'VariableDeclarator';
				if ( hasAssignment ) {
					return;
				}

				let isInComponent = false;

				let parent = node;
				while ( ( parent = parent.parent ) ) {
					if ( isComponent( parent ) ) {
						isInComponent = true;
						break;
					}
				}

				// Only consider `setTimeout` which occur within a component.
				if ( ! isInComponent ) {
					return;
				}

				// Consider whether `setTimeout` is a reference to the global
				// by checking references to see if `setTimeout` resolves to a
				// variable in scope.
				const { references } = context.getScope();
				const hasResolvedReference = references.some(
					( reference ) =>
						reference.identifier.name === 'setTimeout' &&
						!! reference.resolved &&
						reference.resolved.scope.type !== 'global'
				);

				if ( hasResolvedReference ) {
					return;
				}

				context.report(
					node,
					'setTimeout in a component must be cancelled on unmount'
				);
			},
		};
	},
};