import type { Database } from "@atbb/db";
import { forums, backfillProgress, backfillErrors, users } from "@atbb/db";
import { eq, asc, gt } from "drizzle-orm";
import { AtpAgent } from "@atproto/api";
import { CursorManager } from "./cursor-manager.js";
import type { AppConfig } from "./config.js";
import type { Indexer } from "./indexer.js";
import { isProgrammingError } from "./errors.js";
import type { Logger } from "@atbb/logger";

/**
 * Maps AT Proto collection NSIDs to Indexer handler method names.
 * Order matters: sync forum-owned records first (FK dependencies).
 */
// These collections define the sync order. Used by performBackfill() in Task 6.
export const FORUM_OWNED_COLLECTIONS = [
  "space.atbb.forum.forum",
  "space.atbb.forum.category",
  "space.atbb.forum.board",
  "space.atbb.forum.role",
  "space.atbb.modAction",
] as const;

export const USER_OWNED_COLLECTIONS = [
  "space.atbb.membership",
  "space.atbb.post",
] as const;

const COLLECTION_HANDLER_MAP: Record<string, string> = {
  "space.atbb.post": "handlePostCreate",
  "space.atbb.forum.forum": "handleForumCreate",
  "space.atbb.forum.category": "handleCategoryCreate",
  "space.atbb.forum.board": "handleBoardCreate",
  "space.atbb.forum.role": "handleRoleCreate",
  "space.atbb.membership": "handleMembershipCreate",
  "space.atbb.modAction": "handleModActionCreate",
};

export enum BackfillStatus {
  NotNeeded = "not_needed",
  CatchUp = "catch_up",
  FullSync = "full_sync",
}

export interface BackfillResult {
  backfillId: bigint;
  type: BackfillStatus;
  didsProcessed: number;
  recordsIndexed: number;
  errors: number;
  durationMs: number;
}

export interface SyncStats {
  recordsFound: number;
  recordsIndexed: number;
  errors: number;
}

export class BackfillManager {
  private cursorManager: CursorManager;
  private isRunning = false;
  private indexer: Indexer | null = null;

  constructor(
    private db: Database,
    private config: AppConfig,
    private logger: Logger,
  ) {
    this.cursorManager = new CursorManager(db, logger);
  }

  /**
   * Inject the Indexer instance. Called during AppContext wiring.
   */
  setIndexer(indexer: Indexer): void {
    this.indexer = indexer;
  }

  /**
   * Sync all records from a single (DID, collection) pair via listRecords.
   * Feeds each record through the matching Indexer handler.
   */
  async syncRepoRecords(
    did: string,
    collection: string,
    agent: AtpAgent
  ): Promise<SyncStats> {
    const stats: SyncStats = { recordsFound: 0, recordsIndexed: 0, errors: 0 };
    const handlerName = COLLECTION_HANDLER_MAP[collection];

    if (!handlerName || !this.indexer) {
      this.logger.error("backfill.sync_skipped", {
        event: "backfill.sync_skipped",
        did,
        collection,
        reason: !handlerName ? "unknown_collection" : "indexer_not_set",
      });
      stats.errors = 1;
      return stats;
    }

    const handler = (this.indexer as any)[handlerName].bind(this.indexer);
    const delayMs = 1000 / this.config.backfillRateLimit;
    let cursor: string | undefined;

    try {
      do {
        const response = await agent.com.atproto.repo.listRecords({
          repo: did,
          collection,
          limit: 100,
          cursor,
        });

        const records = response.data.records;
        stats.recordsFound += records.length;

        for (const record of records) {
          try {
            const rkey = record.uri.split("/").pop()!;
            const event = {
              did,
              commit: { rkey, cid: record.cid, record: record.value },
            };
            await handler(event);
            stats.recordsIndexed++;
          } catch (error) {
            if (isProgrammingError(error)) throw error;
            stats.errors++;
            this.logger.error("backfill.record_error", {
              event: "backfill.record_error",
              did,
              collection,
              uri: record.uri,
              error: error instanceof Error ? error.message : String(error),
            });
          }
        }

        cursor = response.data.cursor;

        // Rate limiting: delay between page fetches
        if (cursor) {
          await new Promise((resolve) => setTimeout(resolve, delayMs));
        }
      } while (cursor);
    } catch (error) {
      stats.errors++;
      this.logger.error("backfill.pds_error", {
        event: "backfill.pds_error",
        did,
        collection,
        error: error instanceof Error ? error.message : String(error),
      });
    }

    return stats;
  }

  /**
   * Determine if backfill is needed based on cursor state and DB contents.
   */
  async checkIfNeeded(cursor: bigint | null): Promise<BackfillStatus> {
    // No cursor at all → first startup or wiped cursor
    if (cursor === null) {
      this.logger.info("backfill.decision", {
        event: "backfill.decision",
        status: BackfillStatus.FullSync,
        reason: "no_cursor",
      });
      return BackfillStatus.FullSync;
    }

    // Check if DB has forum data (consistency check)
    let forum: { rkey: string } | undefined;
    try {
      const results = await this.db
        .select()
        .from(forums)
        .where(eq(forums.rkey, "self"))
        .limit(1);
      forum = results[0];
    } catch (error) {
      this.logger.error("backfill.decision", {
        event: "backfill.decision",
        status: BackfillStatus.FullSync,
        reason: "db_query_failed",
        error: error instanceof Error ? error.message : String(error),
      });
      return BackfillStatus.FullSync;
    }

    if (!forum) {
      this.logger.info("backfill.decision", {
        event: "backfill.decision",
        status: BackfillStatus.FullSync,
        reason: "db_inconsistency",
        cursorTimestamp: cursor.toString(),
      });
      return BackfillStatus.FullSync;
    }

    // Check cursor age
    const ageHours = this.cursorManager.getCursorAgeHours(cursor)!;
    if (ageHours > this.config.backfillCursorMaxAgeHours) {
      this.logger.info("backfill.decision", {
        event: "backfill.decision",
        status: BackfillStatus.CatchUp,
        reason: "cursor_too_old",
        cursorAgeHours: Math.round(ageHours),
        thresholdHours: this.config.backfillCursorMaxAgeHours,
        cursorTimestamp: cursor.toString(),
      });
      return BackfillStatus.CatchUp;
    }

    this.logger.info("backfill.decision", {
      event: "backfill.decision",
      status: BackfillStatus.NotNeeded,
      reason: "cursor_fresh",
      cursorAgeHours: Math.round(ageHours),
    });
    return BackfillStatus.NotNeeded;
  }

  /**
   * Check if a backfill is currently running.
   */
  getIsRunning(): boolean {
    return this.isRunning;
  }

  /**
   * Create an AtpAgent pointed at the forum's PDS.
   * Extracted as a private method for test mocking.
   */
  private createAgentForPds(): AtpAgent {
    return new AtpAgent({ service: this.config.pdsUrl });
  }

  /**
   * Create a progress row and return its ID.
   * Use this before performBackfill when you need the ID immediately (e.g., for a 202 response).
   * Pass the returned ID as existingRowId to performBackfill to skip duplicate row creation.
   */
  async prepareBackfillRow(type: BackfillStatus): Promise<bigint> {
    const [row] = await this.db
      .insert(backfillProgress)
      .values({
        status: "in_progress",
        backfillType: type,
        startedAt: new Date(),
      })
      .returning({ id: backfillProgress.id });
    return row.id;
  }

  /**
   * Query the backfill_progress table for any row with status = 'in_progress'.
   * Returns the first such row, or null if none exists.
   */
  async checkForInterruptedBackfill() {
    try {
      const [row] = await this.db
        .select()
        .from(backfillProgress)
        .where(eq(backfillProgress.status, "in_progress"))
        .limit(1);

      return row ?? null;
    } catch (error) {
      if (isProgrammingError(error)) throw error;
      this.logger.error("backfill.check_interrupted.failed", {
        event: "backfill.check_interrupted.failed",
        error: error instanceof Error ? error.message : String(error),
        note: "Could not check for interrupted backfills — assuming none",
      });
      return null;
    }
  }

  /**
   * Resume a CatchUp backfill from its last checkpoint (lastProcessedDid).
   * Only processes users with DID > lastProcessedDid.
   * Does NOT re-run Phase 1 (forum-owned collections).
   */
  async resumeBackfill(interrupted: typeof backfillProgress.$inferSelect): Promise<BackfillResult> {
    if (this.isRunning) {
      throw new Error("Backfill is already in progress");
    }

    this.isRunning = true;
    const startTime = Date.now();
    let totalIndexed = interrupted.recordsIndexed;
    let totalErrors = 0;
    let didsProcessed = interrupted.didsProcessed;

    this.logger.info("backfill.resuming", {
      event: "backfill.resuming",
      backfillId: interrupted.id.toString(),
      lastProcessedDid: interrupted.lastProcessedDid,
      didsProcessed: interrupted.didsProcessed,
      didsTotal: interrupted.didsTotal,
    });

    try {
      const agent = this.createAgentForPds();

      if (interrupted.backfillType !== BackfillStatus.CatchUp) {
        // FullSync cannot be resumed from a checkpoint — it must re-run from scratch
        throw new Error(
          "Interrupted FullSync cannot be resumed. Re-trigger via /api/admin/backfill?force=full_sync."
        );
      }

      if (interrupted.lastProcessedDid) {
        // Resume: fetch users after lastProcessedDid
        // TODO(ATB-13): Paginate for large forums
        const remainingUsers = await this.db
          .select({ did: users.did })
          .from(users)
          .where(gt(users.did, interrupted.lastProcessedDid))
          .orderBy(asc(users.did));

        for (let i = 0; i < remainingUsers.length; i += this.config.backfillConcurrency) {
          const batch = remainingUsers.slice(i, i + this.config.backfillConcurrency);
          const backfillId = interrupted.id;

          const batchResults = await Promise.allSettled(
            batch.map(async (user) => {
              let userIndexed = 0;
              let userErrors = 0;
              for (const collection of USER_OWNED_COLLECTIONS) {
                const stats = await this.syncRepoRecords(user.did, collection, agent);
                userIndexed += stats.recordsIndexed;
                if (stats.errors > 0) {
                  userErrors += stats.errors;
                  await this.db.insert(backfillErrors).values({
                    backfillId,
                    did: user.did,
                    collection,
                    errorMessage: `${stats.errors} record(s) failed`,
                    createdAt: new Date(),
                  });
                }
              }
              return { indexed: userIndexed, errors: userErrors };
            })
          );

          // Aggregate results after settlement, including DID for debuggability
          batchResults.forEach((result, i) => {
            if (result.status === "fulfilled") {
              totalIndexed += result.value.indexed;
              totalErrors += result.value.errors;
            } else {
              totalErrors++;
              this.logger.error("backfill.resume.batch_user_failed", {
                event: "backfill.resume.batch_user_failed",
                backfillId: backfillId.toString(),
                did: batch[i].did,
                error: result.reason instanceof Error ? result.reason.message : String(result.reason),
              });
            }
          });

          didsProcessed += batch.length;

          try {
            await this.db
              .update(backfillProgress)
              .set({
                didsProcessed,
                recordsIndexed: totalIndexed,
                lastProcessedDid: batch[batch.length - 1].did,
              })
              .where(eq(backfillProgress.id, backfillId));
          } catch (checkpointError) {
            if (isProgrammingError(checkpointError)) throw checkpointError;
            this.logger.warn("backfill.resume.checkpoint_failed", {
              event: "backfill.resume.checkpoint_failed",
              backfillId: backfillId.toString(),
              didsProcessed,
              error: checkpointError instanceof Error ? checkpointError.message : String(checkpointError),
              note: "Checkpoint save failed — continuing backfill. Resume may reprocess this batch.",
            });
          }
        }
      }

      // Mark completed
      await this.db
        .update(backfillProgress)
        .set({
          status: "completed",
          didsProcessed,
          recordsIndexed: totalIndexed,
          completedAt: new Date(),
        })
        .where(eq(backfillProgress.id, interrupted.id));

      const result: BackfillResult = {
        backfillId: interrupted.id,
        type: interrupted.backfillType as BackfillStatus,
        didsProcessed,
        recordsIndexed: totalIndexed,
        errors: totalErrors,
        durationMs: Date.now() - startTime,
      };

      const resumeEvent = totalErrors > 0 ? "backfill.resume.completed_with_errors" : "backfill.resume.completed";
      this.logger.info(resumeEvent, {
        event: resumeEvent,
        ...result,
        backfillId: result.backfillId.toString(),
      });

      return result;
    } catch (error) {
      // Best-effort: mark as failed
      try {
        await this.db
          .update(backfillProgress)
          .set({
            status: "failed",
            errorMessage: error instanceof Error ? error.message : String(error),
            completedAt: new Date(),
          })
          .where(eq(backfillProgress.id, interrupted.id));
      } catch (updateError) {
        this.logger.error("backfill.resume.failed_status_update_error", {
          event: "backfill.resume.failed_status_update_error",
          backfillId: interrupted.id.toString(),
          error: updateError instanceof Error ? updateError.message : String(updateError),
        });
      }

      this.logger.error("backfill.resume.failed", {
        event: "backfill.resume.failed",
        backfillId: interrupted.id.toString(),
        error: error instanceof Error ? error.message : String(error),
      });
      throw error;
    } finally {
      this.isRunning = false;
    }
  }

  /**
   * Execute a backfill operation.
   * Phase 1: Syncs forum-owned collections from the Forum DID.
   * Phase 2 (CatchUp only): Syncs user-owned collections from all known users.
   *
   * @param existingRowId - If provided (from prepareBackfillRow), skips creating a new progress row.
   */
  async performBackfill(type: BackfillStatus, existingRowId?: bigint): Promise<BackfillResult> {
    if (this.isRunning) {
      throw new Error("Backfill is already in progress");
    }

    this.isRunning = true;
    const startTime = Date.now();
    let backfillId: bigint | undefined = existingRowId;
    let totalIndexed = 0;
    let totalErrors = 0;
    let didsProcessed = 0;

    try {
      // Create progress row only if not pre-created by prepareBackfillRow
      if (backfillId === undefined) {
        const [row] = await this.db
          .insert(backfillProgress)
          .values({
            status: "in_progress",
            backfillType: type,
            startedAt: new Date(),
          })
          .returning({ id: backfillProgress.id });
        backfillId = row.id;
      }
      // Capture in const so TypeScript can narrow through async closures
      const resolvedBackfillId: bigint = backfillId;

      const agent = this.createAgentForPds();

      // Phase 1: Sync forum-owned collections from Forum DID
      for (const collection of FORUM_OWNED_COLLECTIONS) {
        const stats = await this.syncRepoRecords(
          this.config.forumDid,
          collection,
          agent
        );
        totalIndexed += stats.recordsIndexed;
        totalErrors += stats.errors;
        if (stats.errors > 0) {
          await this.db.insert(backfillErrors).values({
            backfillId: resolvedBackfillId,
            did: this.config.forumDid,
            collection,
            errorMessage: `${stats.errors} record(s) failed`,
            createdAt: new Date(),
          });
        }
      }

      // Phase 2: For CatchUp, sync user-owned records from known DIDs
      if (type === BackfillStatus.CatchUp) {
        // TODO(ATB-13): Paginate for large forums — currently loads all DIDs into memory
        const knownUsers = await this.db
          .select({ did: users.did })
          .from(users)
          .orderBy(asc(users.did));

        const didsTotal = knownUsers.length;

        await this.db
          .update(backfillProgress)
          .set({ didsTotal })
          .where(eq(backfillProgress.id, backfillId));

        // Process in batches of backfillConcurrency
        for (let i = 0; i < knownUsers.length; i += this.config.backfillConcurrency) {
          const batch = knownUsers.slice(i, i + this.config.backfillConcurrency);

          const batchResults = await Promise.allSettled(
            batch.map(async (user) => {
              let userIndexed = 0;
              let userErrors = 0;
              for (const collection of USER_OWNED_COLLECTIONS) {
                const stats = await this.syncRepoRecords(user.did, collection, agent);
                userIndexed += stats.recordsIndexed;
                if (stats.errors > 0) {
                  userErrors += stats.errors;
                  await this.db.insert(backfillErrors).values({
                    backfillId: resolvedBackfillId,
                    did: user.did,
                    collection,
                    errorMessage: `${stats.errors} record(s) failed`,
                    createdAt: new Date(),
                  });
                }
              }
              return { indexed: userIndexed, errors: userErrors };
            })
          );

          // Aggregate results after settlement, including DID for debuggability
          batchResults.forEach((result, i) => {
            if (result.status === "fulfilled") {
              totalIndexed += result.value.indexed;
              totalErrors += result.value.errors;
            } else {
              totalErrors++;
              this.logger.error("backfill.batch_user_failed", {
                event: "backfill.batch_user_failed",
                backfillId: resolvedBackfillId.toString(),
                did: batch[i].did,
                error: result.reason instanceof Error ? result.reason.message : String(result.reason),
              });
            }
          });

          didsProcessed += batch.length;

          try {
            await this.db
              .update(backfillProgress)
              .set({
                didsProcessed,
                recordsIndexed: totalIndexed,
                lastProcessedDid: batch[batch.length - 1].did,
              })
              .where(eq(backfillProgress.id, backfillId));
          } catch (checkpointError) {
            if (isProgrammingError(checkpointError)) throw checkpointError;
            this.logger.warn("backfill.checkpoint_failed", {
              event: "backfill.checkpoint_failed",
              backfillId: resolvedBackfillId.toString(),
              didsProcessed,
              error: checkpointError instanceof Error ? checkpointError.message : String(checkpointError),
              note: "Checkpoint save failed — continuing backfill. Resume may reprocess this batch.",
            });
          }

          this.logger.info("backfill.progress", {
            event: "backfill.progress",
            backfillId: backfillId.toString(),
            type,
            didsProcessed,
            didsTotal,
            recordsIndexed: totalIndexed,
            elapsedMs: Date.now() - startTime,
          });
        }
      }

      // Mark completed
      await this.db
        .update(backfillProgress)
        .set({
          status: "completed",
          didsProcessed,
          recordsIndexed: totalIndexed,
          completedAt: new Date(),
        })
        .where(eq(backfillProgress.id, backfillId));

      const result: BackfillResult = {
        backfillId: resolvedBackfillId,
        type,
        didsProcessed,
        recordsIndexed: totalIndexed,
        errors: totalErrors,
        durationMs: Date.now() - startTime,
      };

      const completedEvent = totalErrors > 0 ? "backfill.completed_with_errors" : "backfill.completed";
      this.logger.info(completedEvent, {
        event: completedEvent,
        ...result,
        backfillId: result.backfillId.toString(),
      });

      return result;
    } catch (error) {
      // Best-effort: mark progress row as failed (if it was created)
      if (backfillId !== undefined) {
        try {
          await this.db
            .update(backfillProgress)
            .set({
              status: "failed",
              errorMessage: error instanceof Error ? error.message : String(error),
              completedAt: new Date(),
            })
            .where(eq(backfillProgress.id, backfillId));
        } catch (updateError) {
          this.logger.error("backfill.failed_status_update_error", {
            event: "backfill.failed_status_update_error",
            backfillId: backfillId.toString(),
            error: updateError instanceof Error ? updateError.message : String(updateError),
          });
        }
      }

      this.logger.error("backfill.failed", {
        event: "backfill.failed",
        backfillId: backfillId !== undefined ? backfillId.toString() : "not_created",
        error: error instanceof Error ? error.message : String(error),
      });
      throw error;
    } finally {
      this.isRunning = false;
    }
  }
}