/**
 * Traverse up through the chain of parent AST nodes returning the first parent
 * the predicate returns a truthy value for.
 *
 * @param {Object}   sourceNode The AST node to search from.
 * @param {Function} predicate  A predicate invoked for each parent.
 *
 * @return {Object | undefined} The first encountered parent node where the predicate
 *                    returns a truthy value.
 */
function findParent( sourceNode, predicate ) {
	if ( ! sourceNode.parent ) {
		return;
	}

	if ( predicate( sourceNode.parent ) ) {
		return sourceNode.parent;
	}

	return findParent( sourceNode.parent, predicate );
}

/**
 * Tests whether the IS_GUTENBERG_PLUGIN variable is used as the condition for an
 * if statement or ternary, triggering a violation if not.
 *
 * @example
 * ```js
 * // good
 * if ( process.env.IS_GUTENBERG_PLUGIN ) {
 *
 * // bad
 * const isFeatureActive = process.env.IS_GUTENBERG_PLUGIN;
 * ```
 *
 * @param {Object} node    The IS_GUTENBERG_PLUGIN identifier node.
 * @param {Object} context The eslint context object.
 */
function isUsedInConditional( node, context ) {
	const conditionalParent = findParent( node, ( candidate ) =>
		[ 'IfStatement', 'ConditionalExpression' ].includes( candidate.type )
	);

	if ( ! conditionalParent ) {
		return false;
	}

	// Allow for whitespace as prettier sometimes breaks this on separate lines.
	const textRegex = /^\s*!?\s*process\s*\.\s*env\s*\.\s*IS_GUTENBERG_PLUGIN$/;
	const testSource = context.getSource( conditionalParent.test );

	if ( ! textRegex.test( testSource ) ) {
		return false;
	}

	return true;
}

const ERROR_MESSAGE =
	'The `process.env.IS_GUTENBERG_PLUGIN` constant should only be used as the condition in an if statement or ternary expression.';

module.exports = {
	meta: {
		type: 'problem',
		schema: [],
	},
	create( context ) {
		return {
			Identifier( node ) {
				// Bypass any identifiers with a node name different to `IS_GUTENBERG_PLUGIN`.
				if ( node.name !== 'IS_GUTENBERG_PLUGIN' ) {
					return;
				}

				if ( ! isUsedInConditional( node, context ) ) {
					context.report( node, ERROR_MESSAGE );
				}
			},
			// Check for literals, e.g. when 'IS_GUTENBERG_PLUGIN' is used as a string via something like 'window[ 'IS_GUTENBERG_PLUGIN' ]'.
			Literal( node ) {
				// Bypass any identifiers with a node value different to `IS_GUTENBERG_PLUGIN`.
				if ( node.value !== 'IS_GUTENBERG_PLUGIN' ) {
					return;
				}

				if ( node.parent && node.parent.type === 'MemberExpression' ) {
					if ( ! isUsedInConditional( node, context ) ) {
						context.report( node, ERROR_MESSAGE );
					}
				}
			},
		};
	},
};