Rule engine, resolves #96

[jeroenrinzema]

This pull request introduces a new SQL query builder system for user and event segmentation rules in the Nexus service. The changes add a robust, type-safe way to define, compose, and generate PostgreSQL queries from a tree of rule definitions, supporting complex user and event attribute filtering, frequency/event-based rules, and JSONB path access. The system is modular, with clear separation for rule types, operators, and query construction logic.

Core Rule Model and Types:

• Introduced a comprehensive rules package defining Rule, RuleSet, Frequency, Period, and all supported operators, types, and groups, with methods for SQL type mapping and rule tree navigation.

Query Builder Architecture:

• Added the QueryBuilder struct with methods to generate SQL and arguments from a RuleSet, supporting both full SELECT queries and WHERE clause fragments.

Rule Parsing and SQL Construction:

• Implemented recursive rule parsing in rule.go, including logic for logical wrappers (AND/OR), user attribute rules, and flexible JSONB/dot/bracket path resolution for nested attributes, with correct PostgreSQL type casting.
• Provided robust path parsing using regular expressions to support both dot and bracket notation for JSONB columns.

Comparison and Event Rule Handling:

• Added a flexible comparison builder supporting all defined operators (equality, existence, string, array, date, etc.), with special handling for arrays and type casting.
• Implemented event rule SQL generation, including support for event attribute filters, project scoping, and frequency-based event conditions with rolling time window logic.

These changes lay the foundation for advanced, composable rule-based segmentation with strong type safety and SQL correctness.

References:
[1] [2] [3] [4] [5]

[Copilot]

Pull request overview

This PR introduces a comprehensive SQL query builder system for the Nexus service, enabling type-safe construction of PostgreSQL queries from rule definitions. The implementation supports user attribute filtering, event-based rules, frequency conditions, and complex JSONB path navigation with proper type casting.

Key Changes

• Added a rule model with type definitions, operators, and tree navigation methods
• Implemented a query builder that recursively constructs SQL from rule trees
• Added support for nested JSONB paths using dot and bracket notation

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 16 comments.

Show a summary per file

File	Description
services/nexus/internal/rules/rules.go	Defines core rule types, operators, and period configurations with SQL mapping methods
services/nexus/internal/rules/query/query.go	Implements the QueryBuilder for generating SELECT queries and WHERE clauses
services/nexus/internal/rules/query/rule.go	Handles recursive rule parsing and JSONB path resolution for nested attributes
services/nexus/internal/rules/query/event.go	Builds event-based SQL with frequency conditions and time window logic
services/nexus/internal/rules/query/comparison.go	Constructs SQL comparison expressions for various operators and types
services/nexus/internal/rules/query/query_test.go	Comprehensive test coverage for all query builder functionality