import { format } from "date-fns";
import { existsSync, mkdirSync, readdirSync, readFileSync, rmSync, statSync, writeFileSync } from "fs";
import { Session } from "neo4j-driver";
import path from "path";
import { config } from "../../config/index.js";
import { logger } from "../../utils/logger.js";
import { neo4jDriver } from "./driver.js";

// Helper function to escape relationship types for Cypher queries
const escapeRelationshipType = (type: string): string => {
  // Backtick the type name and escape any backticks within the name itself.
  return `\`${type.replace(/`/g, '``')}\``;
};

/**
 * Manages backup rotation, deleting the oldest backups if the count exceeds the limit.
 */
const manageBackupRotation = async (): Promise<void> => {
  const backupRoot = config.backup.backupPath;
  const maxBackups = config.backup.maxBackups;

  if (!existsSync(backupRoot)) {
    logger.warn(`Backup root directory does not exist: ${backupRoot}. Skipping rotation.`);
    return;
  }

  try {
    logger.debug(`Checking backup rotation in ${backupRoot}. Max backups: ${maxBackups}`);
    const backupDirs = readdirSync(backupRoot)
      .map(name => path.join(backupRoot, name))
      .filter(source => statSync(source).isDirectory())
      .map(dirPath => ({ path: dirPath, time: statSync(dirPath).mtime.getTime() }))
      .sort((a, b) => a.time - b.time); // Sort oldest first

    const backupsToDelete = backupDirs.length - maxBackups;

    if (backupsToDelete > 0) {
      logger.info(`Found ${backupDirs.length} backups. Deleting ${backupsToDelete} oldest backups to maintain limit of ${maxBackups}.`);
      for (let i = 0; i < backupsToDelete; i++) {
        const dirToDelete = backupDirs[i].path;
        try {
          rmSync(dirToDelete, { recursive: true, force: true });
          logger.info(`Deleted old backup directory: ${dirToDelete}`);
        } catch (rmError) {
          const errorMsg = rmError instanceof Error ? rmError.message : String(rmError);
          logger.error(`Failed to delete old backup directory ${dirToDelete}: ${errorMsg}`);
          // Continue trying to delete others even if one fails
        }
      }
    } else {
      logger.debug(`Backup count (${backupDirs.length}) is within the limit (${maxBackups}). No rotation needed.`);
    }
  } catch (error) {
    const errorMsg = error instanceof Error ? error.message : String(error);
    logger.error(`Error during backup rotation management: ${errorMsg}`, { error });
    // Don't throw, allow backup process to continue if possible
  }
};

/**
 * Interface for the full export containing all entities and their relationships in a nested structure.
 * Nodes are stored in an object keyed by their label.
 */
interface FullExport {
  nodes: { [label: string]: Record<string, any>[] };
  relationships: {
    startNodeId: string;
    endNodeId: string;
    type: string;
    properties: Record<string, any>;
  }[];
}

/**
 * Exports all Project, Task, and Knowledge nodes and relationships to JSON files.
 * Also creates a full-export.json file containing all data in a single file.
 * Also manages backup rotation.
 * @returns The path to the directory containing the backup files.
 * @throws Error if the export step fails. Rotation errors are logged but don't throw.
 */
export const exportDatabase = async (): Promise<string> => {
  // First, manage rotation before creating the new backup
  await manageBackupRotation();

  let session: Session | null = null; // Initialize session variable
  const timestamp = format(new Date(), "yyyyMMddHHmmss");
  const backupDir = path.join(config.backup.backupPath, `atlas-backup-${timestamp}`);
  
  // Create full export object to store all data
  const fullExport: FullExport = {
    nodes: {}, // Store nodes keyed by label
    relationships: []
  };

  try {
    session = await neo4jDriver.getSession(); // Get session from singleton
    logger.info(`Starting database export to ${backupDir}...`);
    if (!existsSync(backupDir)) {
      mkdirSync(backupDir, { recursive: true });
      logger.debug(`Created backup directory: ${backupDir}`);
    }

    // Fetch all distinct node labels from the database
    logger.debug("Fetching all node labels from database...");
    const labelsResult = await session.run("CALL db.labels() YIELD label RETURN label");
    const nodeLabels: string[] = labelsResult.records.map(record => record.get("label"));
    logger.info(`Found labels: ${nodeLabels.join(', ')}`);

    // Export nodes for each label
    for (const label of nodeLabels) {
      // Skip internal or potentially problematic labels if necessary (optional)
      // if (label.startsWith('_') || label === 'AnotherLabelToSkip') {
      //   logger.debug(`Skipping export for label: ${label}`);
      //   continue;
      // }
      logger.debug(`Exporting nodes with label: ${label}`);
      // Escape label name if it contains special characters (though typically not needed for standard labels)
      const escapedLabel = `\`${label.replace(/`/g, '``')}\``;
      // Fetch all properties directly
      const nodeResult = await session.run(`MATCH (n:${escapedLabel}) RETURN n`);
      // Extract properties from each node
      const nodes = nodeResult.records.map(record => record.get("n").properties);

      // No need for sanitization if disableLosslessIntegers: true is set on driver
      const filePath = path.join(backupDir, `${label.toLowerCase()}s.json`);
      writeFileSync(filePath, JSON.stringify(nodes, null, 2));
      logger.info(`Successfully exported ${nodes.length} ${label} nodes to ${filePath}`);

      // Add nodes to the full export object under their label
      fullExport.nodes[label] = nodes;
    }

    // Export Relationships
    logger.debug("Exporting relationships...");
    // Use application-level IDs (assuming 'id' property exists) for reliable matching during import
    const relResult = await session.run(`
      MATCH (start)-[r]->(end)
      WHERE start.id IS NOT NULL AND end.id IS NOT NULL // Ensure nodes have the 'id' property
      RETURN 
        start.id as startNodeAppId, 
        end.id as endNodeAppId, 
        type(r) as relType, 
        properties(r) as relProps
    `);

    const relationships = relResult.records.map(record => ({
      startNodeId: record.get("startNodeAppId"), 
      endNodeId: record.get("endNodeAppId"),
      type: record.get("relType"),
      properties: record.get("relProps") || {} // Ensure properties is an object
    }));

    const relFilePath = path.join(backupDir, 'relationships.json');
    writeFileSync(relFilePath, JSON.stringify(relationships, null, 2));
    logger.info(`Successfully exported ${relationships.length} relationships to ${relFilePath}`);
    
    // Add to full export
    fullExport.relationships = relationships;
    
    // Write full export to file
    const fullExportPath = path.join(backupDir, 'full-export.json');
    writeFileSync(fullExportPath, JSON.stringify(fullExport, null, 2));
    logger.info(`Successfully created full database export to ${fullExportPath}`);

    logger.info(`Database export completed successfully to ${backupDir}`);
    return backupDir;
  } catch (error) {
    const errorMessage = error instanceof Error ? error.message : String(error);
    logger.error(`Database export failed: ${errorMessage}`, { error });
    // Clean up partially created backup directory on failure
    if (existsSync(backupDir)) {
      try {
        rmSync(backupDir, { recursive: true, force: true });
        logger.warn(`Removed partially created backup directory due to export failure: ${backupDir}`);
      } catch (rmError) {
        // Log cleanup error but prioritize throwing the original export error
        const rmErrorMsg = rmError instanceof Error ? rmError.message : String(rmError);
        logger.error(`Failed to remove partial backup directory ${backupDir}: ${rmErrorMsg}`);
      }
    }
    throw new Error(`Database export failed: ${errorMessage}`);
  } finally {
    if (session) {
      await session.close(); // Close session if it was opened
    }
  }
};

/**
 * Imports data from JSON files, overwriting the existing database.
 * Can import from either full-export.json (if it exists) or individual entity files.
 * @param backupDir The path to the directory containing the backup JSON files.
 * @throws Error if any step fails.
 */
export const importDatabase = async (backupDir: string): Promise<void> => {
  let session: Session | null = null; // Initialize session variable
  logger.warn(`Starting database import from ${backupDir}. THIS WILL OVERWRITE ALL EXISTING DATA.`);

  try {
    session = await neo4jDriver.getSession(); // Get session from singleton
    // 1. Clear the database
    logger.info("Clearing existing database...");
    // Use DETACH DELETE for simplicity and safety
    await session.run("MATCH (n) DETACH DELETE n");
    logger.info("Existing database cleared.");

    // Variables to store relationships to import
    let relationships: Array<{ startNodeId: string; endNodeId: string; type: string; properties: Record<string, any> }> = [];

    // Check if full-export.json exists
    const fullExportPath = path.join(backupDir, 'full-export.json');
    if (existsSync(fullExportPath)) {
      logger.info(`Found full-export.json at ${fullExportPath}. Using consolidated import.`);
      
      // Import from full export file
      const fullExportContent = readFileSync(fullExportPath, 'utf-8');
      const fullExport: FullExport = JSON.parse(fullExportContent);

      // 2a. Import nodes from full export (iterating through labels in the nodes object)
      for (const label in fullExport.nodes) {
        if (Object.prototype.hasOwnProperty.call(fullExport.nodes, label)) {
          const nodesToImport = fullExport.nodes[label];
          if (!nodesToImport || nodesToImport.length === 0) {
            logger.info(`No ${label} nodes to import from full-export.json.`);
            continue;
          }

          logger.debug(`Importing ${nodesToImport.length} ${label} nodes from full-export.json`);
          const escapedLabel = `\`${label.replace(/`/g, '``')}\``; 
          // Use UNWIND for batching node creation
          const query = `
            UNWIND $nodes as nodeProps
            CREATE (n:${escapedLabel})
            SET n = nodeProps
          `;

          await session.run(query, { nodes: nodesToImport });
          logger.info(`Successfully imported ${nodesToImport.length} ${label} nodes from full-export.json`);
        }
      }

      // 3a. Import relationships from full export
      if (fullExport.relationships && fullExport.relationships.length > 0) {
        logger.info(`Found ${fullExport.relationships.length} relationships in full-export.json.`);
        relationships = fullExport.relationships;
      } else {
        logger.info(`No relationships found in full-export.json.`);
      }
    } else {
      logger.info(`No full-export.json found. Using individual entity files.`);

      // 2b. Import nodes from individual files
      // Attempt to read all *.json files in the backup dir except relationships.json and full-export.json
      const filesInBackupDir = readdirSync(backupDir);
      const nodeFiles = filesInBackupDir.filter(file => 
        file.toLowerCase().endsWith('.json') && 
        file !== 'relationships.json' && 
        file !== 'full-export.json'
      );

      for (const nodeFile of nodeFiles) {
        const filePath = path.join(backupDir, nodeFile);
        // Infer label from filename (e.g., projects.json -> Project)
        const inferredLabelFromFile = path.basename(nodeFile, '.json');
        // Basic pluralization removal and capitalization - adjust if needed for complex names
        const label = inferredLabelFromFile.endsWith('s') 
          ? inferredLabelFromFile.charAt(0).toUpperCase() + inferredLabelFromFile.slice(1, -1) 
          : inferredLabelFromFile.charAt(0).toUpperCase() + inferredLabelFromFile.slice(1);

        if (!existsSync(filePath)) {
          // This check is slightly redundant due to readdirSync but kept for safety
          logger.warn(`Node file ${nodeFile} (inferred label ${label}) not found at ${filePath}. Skipping.`);
          continue;
        }

        logger.debug(`Importing nodes with inferred label: ${label} from ${filePath}`);
        const fileContent = readFileSync(filePath, 'utf-8');
        const nodesToImport: Record<string, any>[] = JSON.parse(fileContent);

        if (nodesToImport.length === 0) {
          logger.info(`No ${label} nodes to import from ${filePath}.`);
          continue;
        }

        const escapedLabel = `\`${label.replace(/`/g, '``')}\``; 
        // Use UNWIND for batching node creation
        const query = `
          UNWIND $nodes as nodeProps
          CREATE (n:${escapedLabel})
          SET n = nodeProps
        `;

        await session.run(query, { nodes: nodesToImport });
        logger.info(`Successfully imported ${nodesToImport.length} ${label} nodes from ${filePath}`);
      }

      // 3b. Import Relationships from relationships.json
      const relFilePath = path.join(backupDir, 'relationships.json');
      if (existsSync(relFilePath)) {
        logger.info(`Importing relationships from ${relFilePath}...`);
        const relFileContent = readFileSync(relFilePath, 'utf-8');
        relationships = JSON.parse(relFileContent);
        
        if (relationships.length === 0) {
          logger.info(`No relationships found to import in ${relFilePath}.`);
        }
      } else {
        logger.warn(`Relationships file not found: ${relFilePath}. Skipping relationship import.`);
      }
    }

    // Process relationships (common code for both full-export and individual files)
    if (relationships.length > 0) {
      logger.info(`Attempting to import ${relationships.length} relationships individually (Community Edition compatible)...`);
      
      let importedCount = 0;
      let failedCount = 0;
      const batchSize = 500; // Process in batches to manage transaction size/memory
      
      for (let i = 0; i < relationships.length; i += batchSize) {
        const batch = relationships.slice(i, i + batchSize);
        logger.debug(`Processing relationship batch ${i / batchSize + 1}...`);

        // Use a transaction for each batch
        try {
          await session.executeWrite(async tx => {
            for (const rel of batch) {
              if (!rel.startNodeId || !rel.endNodeId || !rel.type) {
                logger.warn(`Skipping relationship in batch due to missing startNodeId, endNodeId, or type: ${JSON.stringify(rel)}`);
                failedCount++;
                continue;
              }

              const escapedType = escapeRelationshipType(rel.type);
              // Match nodes based on the application-level 'id' property
              const relQuery = `
                MATCH (start {id: $startNodeId})
                MATCH (end {id: $endNodeId})
                CREATE (start)-[r:${escapedType}]->(end)
                SET r = $properties
              `;
              try {
                await tx.run(relQuery, {
                  startNodeId: rel.startNodeId,
                  endNodeId: rel.endNodeId,
                  properties: rel.properties || {}
                });
                importedCount++;
              } catch (relError) {
                // Log error for specific relationship but continue batch
                const errorMsg = relError instanceof Error ? relError.message : String(relError);
                logger.error(`Failed to create relationship ${rel.type} from ${rel.startNodeId} to ${rel.endNodeId}: ${errorMsg}`, { relationship: rel });
                failedCount++;
              }
            }
          });
          logger.debug(`Completed relationship batch ${i / batchSize + 1}.`);
        } catch (batchError) {
          // Log error for the whole batch transaction
          const errorMsg = batchError instanceof Error ? batchError.message : String(batchError);
          logger.error(`Failed to process relationship batch starting at index ${i}: ${errorMsg}`);
          // Increment failed count for the entire batch size, assuming none succeeded in this failed transaction
          failedCount += batch.length - (batch.filter(rel => !rel.startNodeId || !rel.endNodeId || !rel.type).length); 
          // Continue with next batch
        }
      }
      
      logger.info(`Relationship import summary: Attempted=${relationships.length}, Succeeded=${importedCount}, Failed=${failedCount}`);
    } else {
      logger.info(`No relationships to import.`);
    }

    logger.info("Database import completed successfully.");
  } catch (error) {
    const errorMessage = error instanceof Error ? error.message : String(error);
    logger.error(`Database import failed: ${errorMessage}`, { error });
    throw new Error(`Database import failed: ${errorMessage}`);
  } finally {
    if (session) {
      await session.close(); // Close session if it was opened
    }
  }
};