/**
 * Helper functions that help test things to do with the index catalog.
 */
export var IndexCatalogHelpers = (function() {
    /**
     * Returns the index specification with the name 'indexName' if it is present in the
     * 'indexSpecs' array, and returns null otherwise.
     */
    function getIndexSpecByName(indexSpecs, indexName) {
        if (typeof indexName !== "string") {
            throw new Error("'indexName' parameter must be a string, but got " + tojson(indexName));
        }

        const found = indexSpecs.filter(spec => spec.name === indexName);

        if (found.length > 1) {
            throw new Error("Found multiple indexes with name '" + indexName +
                            "': " + tojson(indexSpecs));
        }
        return (found.length === 1) ? found[0] : null;
    }

    /**
     * Returns the index specification with the key pattern 'keyPattern' and the collation
     * 'collation' if it is present in the 'indexSpecs' array, and returns null otherwise.
     *
     * The 'collation' parameter is optional and is only required to be specified when multiple
     * indexes with the same key pattern exist.
     */
    function getIndexSpecByKeyPattern(indexSpecs, keyPattern, collation) {
        const collationWasSpecified = arguments.length >= 3;
        const foundByKeyPattern = indexSpecs.filter(spec => {
            return bsonWoCompare(spec.key, keyPattern) === 0;
        });

        if (!collationWasSpecified) {
            if (foundByKeyPattern.length > 1) {
                throw new Error(
                    "Found multiple indexes with key pattern " + tojson(keyPattern) +
                    " and 'collation' parameter was not specified: " + tojson(indexSpecs));
            }
            return (foundByKeyPattern.length === 1) ? foundByKeyPattern[0] : null;
        }

        const foundByKeyPatternAndCollation = foundByKeyPattern.filter(spec => {
            if (collation.locale === "simple") {
                // The simple collation is not explicitly stored in the index catalog, so we expect
                // the "collation" field to be absent.
                return !spec.hasOwnProperty("collation");
            }
            return bsonWoCompare(spec.collation, collation) === 0;
        });

        if (foundByKeyPatternAndCollation.length > 1) {
            throw new Error("Found multiple indexes with key pattern" + tojson(keyPattern) +
                            " and collation " + tojson(collation) + ": " + tojson(indexSpecs));
        }
        return (foundByKeyPatternAndCollation.length === 1) ? foundByKeyPatternAndCollation[0]
                                                            : null;
    }

    function createSingleIndex(coll, key, parameters) {
        return coll.getDB().runCommand(
            {createIndexes: coll.getName(), indexes: [Object.assign({key: key}, parameters)]});
    }

    function createIndexAndVerifyWithDrop(coll, key, parameters) {
        coll.dropIndexes();
        assert.commandWorked(createSingleIndex(coll, key, parameters));
        assert.neq(
            null,
            getIndexSpecByName(coll.getIndexes(), parameters.name),
            () =>
                `Could not find index with name ${parameters.name}: ${tojson(coll.getIndexes())}`);
    }

    return {
        findByName: getIndexSpecByName,
        findByKeyPattern: getIndexSpecByKeyPattern,
        createSingleIndex: createSingleIndex,
        createIndexAndVerifyWithDrop: createIndexAndVerifyWithDrop,
    };
})();