import { Db } from 'mongodb'
import { readdir } from 'node:fs/promises'
import { join } from 'node:path'
import { pathToFileURL } from 'node:url'

export abstract class MongoMigration {
  protected db: Db

  constructor(db: Db) {
    this.db = db
  }

  abstract up(): Promise<void>
  abstract down(): Promise<void>
}

export class MigratorRunner {
  private db: Db
  private migrationsPath: string

  constructor(db: Db, migrationsPath: string) {
    this.db = db
    this.migrationsPath = migrationsPath
  }

  private get migrationsCollection() {
    return this.db.collection('_migrations')
  }

  async run(): Promise<string[]> {
    const files = await this.getMigrationFiles()
    const executed = await this.getExecutedMigrations()
    const pending = files.filter((f) => !executed.includes(f))

    if (pending.length === 0) {
      return []
    }

    const batch = await this.getNextBatch()
    const ran: string[] = []

    for (const file of pending) {
      const migration = await this.loadMigration(file)
      await migration.up()
      await this.migrationsCollection.insertOne({
        name: file,
        batch,
        executed_at: new Date(),
      })
      ran.push(file)
    }

    return ran
  }

  async rollback(): Promise<string[]> {
    const lastBatch = await this.getLastBatch()
    if (lastBatch === 0) return []

    const migrations = await this.migrationsCollection
      .find({ batch: lastBatch })
      .sort({ executed_at: -1 })
      .toArray()

    const rolledBack: string[] = []
    for (const record of migrations) {
      const migration = await this.loadMigration(record.name)
      await migration.down()
      await this.migrationsCollection.deleteOne({ _id: record._id })
      rolledBack.push(record.name)
    }

    return rolledBack
  }

  async status(): Promise<{ name: string; batch: number | null; ran: boolean }[]> {
    const files = await this.getMigrationFiles()
    const executed = await this.migrationsCollection.find({}).toArray()
    const executedMap = new Map(executed.map((e) => [e.name, e.batch]))

    return files.map((file) => ({
      name: file,
      batch: executedMap.get(file) ?? null,
      ran: executedMap.has(file),
    }))
  }

  private async getMigrationFiles(): Promise<string[]> {
    try {
      const files = await readdir(this.migrationsPath)
      return files.filter((f) => f.endsWith('.ts') || f.endsWith('.js')).sort()
    } catch {
      return []
    }
  }

  private async getExecutedMigrations(): Promise<string[]> {
    const docs = await this.migrationsCollection.find({}).toArray()
    return docs.map((d) => d.name)
  }

  private async getNextBatch(): Promise<number> {
    const last = await this.getLastBatch()
    return last + 1
  }

  private async getLastBatch(): Promise<number> {
    const doc = await this.migrationsCollection.find({}).sort({ batch: -1 }).limit(1).toArray()
    return doc.length > 0 ? doc[0].batch : 0
  }

  private async loadMigration(file: string): Promise<MongoMigration> {
    const filePath = join(this.migrationsPath, file)
    const fileUrl = pathToFileURL(filePath).href
    const module = await import(fileUrl)
    const MigrationClass = module.default
    return new MigrationClass(this.db)
  }
}