import _ from "lodash";
import type {
    BUN_MARIADB_DatabaseSchemaType,
    BUN_MARIADB_TableSchemaType,
    CreateDBSchemaParams,
} from "../../types";

/**
 * Topologically order tables so referenced (parent) tables come before the
 * tables that reference them. Declaration order is kept wherever the FK
 * graph allows it.
 *
 * - Self references (e.g. `comments.parent_comment_id`) are ignored.
 * - References to tables outside the schema are ignored.
 * - Cycles do not throw: a table already on the current path is skipped,
 *   so every table is still emitted exactly once. Foreign keys are created
 *   after all tables exist, so cycles are safe to sync.
 */
export default async function orderDBSchema({
    db_schema,
}: CreateDBSchemaParams): Promise<BUN_MARIADB_DatabaseSchemaType> {
    const new_db_schema = _.cloneDeep(db_schema);
    const tables = new_db_schema.tables;

    const tables_by_name = new Map<string, BUN_MARIADB_TableSchemaType>();
    for (const table of tables) {
        if (table) tables_by_name.set(table.tableName, table);
    }

    const ordered: BUN_MARIADB_TableSchemaType[] = [];
    const visited = new Set<string>();
    const visiting = new Set<string>();

    function visit(table: BUN_MARIADB_TableSchemaType) {
        if (visited.has(table.tableName) || visiting.has(table.tableName)) {
            return;
        }

        visiting.add(table.tableName);

        for (const field of table.fields || []) {
            const dst_table_name = field?.foreignKey?.destinationTableName;

            if (!dst_table_name || dst_table_name === table.tableName) {
                continue;
            }

            const fk_table = tables_by_name.get(dst_table_name);

            if (fk_table) {
                visit(fk_table);
            }
        }

        visiting.delete(table.tableName);
        visited.add(table.tableName);
        ordered.push(table);
    }

    for (const table of tables) {
        if (table) visit(table);
    }

    new_db_schema.tables = ordered;

    return new_db_schema;
}