flynn/src/routing/policy.ts

export type RoutingPath = 'fast' | 'llm';

export interface RoutingPolicyConfig {
  enabled: boolean;
  fastPathThreshold: number;
  llmThreshold: number;
  defaultPath: RoutingPath;
}

export interface RoutingDecisionInput {
  confidence: number | null;
}

export interface RoutingDecision {
  path: RoutingPath;
  reason: 'disabled' | 'no_match' | 'high_confidence' | 'low_confidence' | 'mid_confidence';
}

export class RoutingPolicy {
  private readonly config: RoutingPolicyConfig;

  constructor(config: RoutingPolicyConfig) {
    this.config = config;
  }

  isEnabled(): boolean {
    return this.config.enabled;
  }

  decide(input: RoutingDecisionInput): RoutingDecision {
    if (!this.config.enabled) {
      return {
        path: this.config.defaultPath,
        reason: 'disabled',
      };
    }

    if (input.confidence === null) {
      return {
        path: this.config.defaultPath,
        reason: 'no_match',
      };
    }

    if (input.confidence >= this.config.fastPathThreshold) {
      return {
        path: 'fast',
        reason: 'high_confidence',
      };
    }

    if (input.confidence <= this.config.llmThreshold) {
      return {
        path: 'llm',
        reason: 'low_confidence',
      };
    }

    return {
      path: this.config.defaultPath,
      reason: 'mid_confidence',
    };
  }
}