import { Injectable, Logger, OnModuleInit } from "@nestjs/common";
import {
  TaskType,
  Complexity,
  Provider,
  type PredictionQuery,
  type PredictionResponse,
} from "@mosaicstack/telemetry-client";
import { MosaicTelemetryService } from "./mosaic-telemetry.service";

/**
 * Common model-provider combinations used for pre-fetching predictions.
 * These represent the most frequently used LLM configurations.
 */
const COMMON_MODELS: { model: string; provider: Provider }[] = [
  { model: "claude-sonnet-4-5", provider: Provider.ANTHROPIC },
  { model: "claude-opus-4", provider: Provider.ANTHROPIC },
  { model: "claude-haiku-4-5", provider: Provider.ANTHROPIC },
  { model: "gpt-4o", provider: Provider.OPENAI },
  { model: "gpt-4o-mini", provider: Provider.OPENAI },
];

/**
 * Common task types to pre-fetch predictions for.
 */
const COMMON_TASK_TYPES: TaskType[] = [
  TaskType.IMPLEMENTATION,
  TaskType.PLANNING,
  TaskType.CODE_REVIEW,
];

/**
 * Common complexity levels to pre-fetch predictions for.
 */
const COMMON_COMPLEXITIES: Complexity[] = [Complexity.LOW, Complexity.MEDIUM];

/**
 * PredictionService
 *
 * Provides pre-task cost and token estimates using crowd-sourced prediction data
 * from the Mosaic Telemetry server. Predictions are cached by the underlying SDK
 * with a 6-hour TTL.
 *
 * This service is intentionally non-blocking: if predictions are unavailable
 * (telemetry disabled, server unreachable, no data), all methods return null
 * without throwing errors. Task execution should never be blocked by prediction
 * failures.
 *
 * @example
 * ```typescript
 * const estimate = this.predictionService.getEstimate(
 *   TaskType.IMPLEMENTATION,
 *   "claude-sonnet-4-5",
 *   Provider.ANTHROPIC,
 *   Complexity.LOW,
 * );
 * if (estimate?.prediction) {
 *   console.log(`Estimated cost: ${estimate.prediction.cost_usd_micros}`);
 * }
 * ```
 */
@Injectable()
export class PredictionService implements OnModuleInit {
  private readonly logger = new Logger(PredictionService.name);

  constructor(private readonly telemetry: MosaicTelemetryService) {}

  /**
   * Refresh common predictions on startup.
   * Runs asynchronously and never blocks module initialization.
   */
  onModuleInit(): void {
    if (!this.telemetry.isEnabled) {
      this.logger.log("Telemetry disabled - skipping prediction refresh");
      return;
    }

    // Fire-and-forget: refresh in the background
    this.refreshCommonPredictions().catch((error: unknown) => {
      const msg = error instanceof Error ? error.message : String(error);
      this.logger.warn(`Failed to refresh common predictions on startup: ${msg}`);
    });
  }

  /**
   * Get a cost/token estimate for a given task configuration.
   *
   * Returns the cached prediction from the SDK, or null if:
   * - Telemetry is disabled
   * - No prediction data exists for this combination
   * - The prediction has expired
   *
   * @param taskType - The type of task to estimate
   * @param model - The model name (e.g. "claude-sonnet-4-5")
   * @param provider - The provider enum value
   * @param complexity - The complexity level
   * @returns Prediction response with estimates and confidence, or null
   */
  getEstimate(
    taskType: TaskType,
    model: string,
    provider: Provider,
    complexity: Complexity
  ): PredictionResponse | null {
    try {
      const query: PredictionQuery = {
        task_type: taskType,
        model,
        provider,
        complexity,
      };

      return this.telemetry.getPrediction(query);
    } catch (error: unknown) {
      const msg = error instanceof Error ? error.message : String(error);
      this.logger.warn(`Failed to get prediction estimate: ${msg}`);
      return null;
    }
  }

  /**
   * Refresh predictions for commonly used (taskType, model, provider, complexity) combinations.
   *
   * Generates the cross-product of common models, task types, and complexities,
   * then batch-refreshes them from the telemetry server. The SDK caches the
   * results with a 6-hour TTL.
   *
   * This method is safe to call at any time. If telemetry is disabled or the
   * server is unreachable, it completes without error.
   */
  async refreshCommonPredictions(): Promise<void> {
    if (!this.telemetry.isEnabled) {
      return;
    }

    const queries: PredictionQuery[] = [];

    for (const { model, provider } of COMMON_MODELS) {
      for (const taskType of COMMON_TASK_TYPES) {
        for (const complexity of COMMON_COMPLEXITIES) {
          queries.push({
            task_type: taskType,
            model,
            provider,
            complexity,
          });
        }
      }
    }

    this.logger.log(`Refreshing ${String(queries.length)} common prediction queries...`);

    try {
      await this.telemetry.refreshPredictions(queries);
      this.logger.log(`Successfully refreshed ${String(queries.length)} predictions`);
    } catch (error: unknown) {
      const msg = error instanceof Error ? error.message : String(error);
      this.logger.warn(`Failed to refresh predictions: ${msg}`);
    }
  }
}