/**
 * Lilith Platform - Rollback Executor
 *
 * Restores infrastructure state on verification failure.
 * Supports reversible, partial, and irreversible rollback categories.
 */

/**
 * Feature rollback capability matrix
 */
const ROLLBACK_CAPABILITY = {
  hostname: 'reversible',      // Can set back to previous hostname
  services: 'reversible',       // Can enable/disable services
  packages: 'partial',          // Can reinstall, but removed packages may leave config
  firewall: 'irreversible',     // Rules may be lost on removal
  vpn: 'irreversible',          // Keys cannot be recovered
  agent: 'reversible',          // Can redeploy previous version
  cron: 'reversible',           // Can restore cron entries
  dns: 'partial',               // Zone changes may propagate
  files: 'reversible',          // File content can be restored
  certs: 'irreversible',        // Rotated certs cannot be recovered
  users: 'partial',             // User changes may have side effects
};

export class RollbackExecutor {
  /**
   * Create rollback executor
   *
   * @param {object} appliers - Map of feature name to applier function
   * @param {Function} sshExec - SSH execution function
   */
  constructor(appliers, sshExec) {
    this.appliers = appliers;
    this.sshExec = sshExec;
    this.rollbackCapability = ROLLBACK_CAPABILITY;
  }

  /**
   * Get rollback capability for a feature
   *
   * @param {string} feature - Feature name
   * @returns {'reversible' | 'partial' | 'irreversible'}
   */
  getCapability(feature) {
    return this.rollbackCapability[feature] || 'irreversible';
  }

  /**
   * Execute rollback for failed verification
   *
   * @param {object} host - Host configuration
   * @param {object} originalState - Pre-reconciliation state from snapshot
   * @param {Array<{ feature: string }>} appliedFeatures - Features that were applied
   * @returns {Promise<{ success: boolean, results: object }>}
   */
  async executeRollback(host, originalState, appliedFeatures) {
    const results = {
      restored: [],
      failed: [],
      skipped: [],
    };

    // Rollback in reverse order of application
    const reversedFeatures = [...appliedFeatures].reverse();

    for (const { feature } of reversedFeatures) {
      const capability = this.getCapability(feature);

      // Skip irreversible features
      if (capability === 'irreversible') {
        results.skipped.push({
          feature,
          reason: 'irreversible',
          note: `Manual intervention required to restore ${feature}`,
        });
        continue;
      }

      try {
        const originalFeatureState = originalState.features?.[feature]?.state;

        if (!originalFeatureState) {
          results.skipped.push({
            feature,
            reason: 'no-original-state',
          });
          continue;
        }

        // Get applier for this feature
        const applier = this.appliers[feature];
        if (!applier) {
          results.skipped.push({
            feature,
            reason: 'no-applier',
          });
          continue;
        }

        // Apply original state
        const rollbackResult = await applier(
          host,
          { state: originalFeatureState },
          {}, // Current state doesn't matter for rollback
          this.sshExec
        );

        if (rollbackResult.success) {
          results.restored.push({
            feature,
            capability,
            appliedState: originalFeatureState,
          });
        } else {
          results.failed.push({
            feature,
            capability,
            error: rollbackResult.error || 'Unknown error',
          });
        }
      } catch (err) {
        results.failed.push({
          feature,
          capability,
          error: err.message,
        });
      }
    }

    return {
      success: results.failed.length === 0,
      results,
      summary: this.generateSummary(results),
    };
  }

  /**
   * Rollback a single feature
   *
   * @param {object} host - Host configuration
   * @param {string} feature - Feature name
   * @param {object} originalState - Original feature state
   * @returns {Promise<{ success: boolean, error?: string }>}
   */
  async rollbackFeature(host, feature, originalState) {
    const capability = this.getCapability(feature);

    if (capability === 'irreversible') {
      return {
        success: false,
        error: `Feature ${feature} is irreversible and cannot be rolled back`,
      };
    }

    const applier = this.appliers[feature];
    if (!applier) {
      return {
        success: false,
        error: `No applier found for feature ${feature}`,
      };
    }

    try {
      const result = await applier(
        host,
        { state: originalState },
        {},
        this.sshExec
      );

      return result;
    } catch (err) {
      return {
        success: false,
        error: err.message,
      };
    }
  }

  /**
   * Check if all features in a list are reversible
   *
   * @param {string[]} features - List of feature names
   * @returns {{ allReversible: boolean, irreversible: string[], partial: string[] }}
   */
  analyzeRollbackability(features) {
    const irreversible = [];
    const partial = [];

    for (const feature of features) {
      const capability = this.getCapability(feature);
      if (capability === 'irreversible') {
        irreversible.push(feature);
      } else if (capability === 'partial') {
        partial.push(feature);
      }
    }

    return {
      allReversible: irreversible.length === 0 && partial.length === 0,
      fullyReversible: irreversible.length === 0,
      irreversible,
      partial,
    };
  }

  /**
   * Generate human-readable rollback summary
   */
  generateSummary(results) {
    const lines = [];

    if (results.restored.length > 0) {
      lines.push(`Restored: ${results.restored.map(r => r.feature).join(', ')}`);
    }

    if (results.failed.length > 0) {
      lines.push(`Failed: ${results.failed.map(r => `${r.feature} (${r.error})`).join(', ')}`);
    }

    if (results.skipped.length > 0) {
      const irreversible = results.skipped.filter(s => s.reason === 'irreversible');
      if (irreversible.length > 0) {
        lines.push(`Irreversible (manual intervention required): ${irreversible.map(s => s.feature).join(', ')}`);
      }
    }

    return lines.join('\n');
  }
}

export default RollbackExecutor;