import { createClient } from '@/lib/supabase/client'
import type { FlowchartNode, FlowchartEdge } from '@/types/flowchart'

export type AuditActionType =
  | 'node_add'
  | 'node_update'
  | 'node_delete'
  | 'edge_add'
  | 'edge_update'
  | 'edge_delete'

type PendingAuditEntry = {
  actionType: AuditActionType
  entityId: string
  previousState: unknown | null
  newState: unknown | null
  timer: ReturnType<typeof setTimeout>
}

const DEBOUNCE_MS = 1000

export class AuditTrailRecorder {
  private projectId: string
  private userId: string
  private previousNodes: Map<string, string> // node ID -> JSON string
  private previousEdges: Map<string, string> // edge ID -> JSON string
  private pending: Map<string, PendingAuditEntry> // entityId -> pending entry
  private isDestroyed = false

  constructor(projectId: string, userId: string) {
    this.projectId = projectId
    this.userId = userId
    this.previousNodes = new Map()
    this.previousEdges = new Map()
    this.pending = new Map()
  }

  /** Initialize with the current state (no audit entries are created for initial state) */
  initialize(nodes: FlowchartNode[], edges: FlowchartEdge[]): void {
    this.previousNodes.clear()
    this.previousEdges.clear()
    nodes.forEach((node) => {
      this.previousNodes.set(node.id, JSON.stringify(node))
    })
    edges.forEach((edge) => {
      this.previousEdges.set(edge.id, JSON.stringify(edge))
    })
  }

  /** Record changes by diffing current state against previous state */
  recordNodeChanges(currentNodes: FlowchartNode[]): void {
    if (this.isDestroyed) return

    const currentMap = new Map<string, string>()
    currentNodes.forEach((node) => {
      currentMap.set(node.id, JSON.stringify(node))
    })

    // Detect additions and updates
    for (const [id, serialized] of currentMap) {
      const previous = this.previousNodes.get(id)
      if (!previous) {
        // Node was added
        this.scheduleWrite(id, 'node_add', null, JSON.parse(serialized))
      } else if (previous !== serialized) {
        // Node was updated
        this.scheduleWrite(id, 'node_update', JSON.parse(previous), JSON.parse(serialized))
      }
    }

    // Detect deletions
    for (const [id, serialized] of this.previousNodes) {
      if (!currentMap.has(id)) {
        this.scheduleWrite(id, 'node_delete', JSON.parse(serialized), null)
      }
    }

    // Update previous state
    this.previousNodes = currentMap
  }

  /** Record edge changes by diffing current state against previous state */
  recordEdgeChanges(currentEdges: FlowchartEdge[]): void {
    if (this.isDestroyed) return

    const currentMap = new Map<string, string>()
    currentEdges.forEach((edge) => {
      currentMap.set(edge.id, JSON.stringify(edge))
    })

    // Detect additions and updates
    for (const [id, serialized] of currentMap) {
      const previous = this.previousEdges.get(id)
      if (!previous) {
        // Edge was added
        this.scheduleWrite(id, 'edge_add', null, JSON.parse(serialized))
      } else if (previous !== serialized) {
        // Edge was updated
        this.scheduleWrite(id, 'edge_update', JSON.parse(previous), JSON.parse(serialized))
      }
    }

    // Detect deletions
    for (const [id, serialized] of this.previousEdges) {
      if (!currentMap.has(id)) {
        this.scheduleWrite(id, 'edge_delete', JSON.parse(serialized), null)
      }
    }

    // Update previous state
    this.previousEdges = currentMap
  }

  /** Clean up resources */
  destroy(): void {
    this.isDestroyed = true
    // Flush all pending writes immediately
    for (const [entityId, entry] of this.pending) {
      clearTimeout(entry.timer)
      this.writeEntry(entry)
      this.pending.delete(entityId)
    }
  }

  private scheduleWrite(
    entityId: string,
    actionType: AuditActionType,
    previousState: unknown | null,
    newState: unknown | null
  ): void {
    // If there's already a pending write for this entity, cancel it and update
    const existing = this.pending.get(entityId)
    if (existing) {
      clearTimeout(existing.timer)
      // For debounced updates, keep the original previousState but use latest newState
      // For type changes (e.g., add then delete within 1s), use the new action type
      const mergedPreviousState = existing.actionType === 'node_add' || existing.actionType === 'edge_add'
        ? null // If it was just added, there's no real previous state
        : existing.previousState
      const mergedActionType = this.mergeActionTypes(existing.actionType, actionType)

      // If an entity was added and then deleted within the debounce window, skip entirely
      if (mergedActionType === null) {
        this.pending.delete(entityId)
        return
      }

      const entry: PendingAuditEntry = {
        actionType: mergedActionType,
        entityId,
        previousState: mergedPreviousState,
        newState,
        timer: setTimeout(() => {
          this.pending.delete(entityId)
          this.writeEntry(entry)
        }, DEBOUNCE_MS),
      }
      this.pending.set(entityId, entry)
    } else {
      const entry: PendingAuditEntry = {
        actionType,
        entityId,
        previousState,
        newState,
        timer: setTimeout(() => {
          this.pending.delete(entityId)
          this.writeEntry(entry)
        }, DEBOUNCE_MS),
      }
      this.pending.set(entityId, entry)
    }
  }

  /** Merge two sequential action types for the same entity */
  private mergeActionTypes(
    first: AuditActionType,
    second: AuditActionType
  ): AuditActionType | null {
    // add + delete = no-op (entity never really existed)
    if (
      (first === 'node_add' && second === 'node_delete') ||
      (first === 'edge_add' && second === 'edge_delete')
    ) {
      return null
    }
    // add + update = still an add (with the updated state)
    if (
      (first === 'node_add' && second === 'node_update') ||
      (first === 'edge_add' && second === 'edge_update')
    ) {
      return first
    }
    // For all other cases, use the second (latest) action type
    return second
  }

  /** Fire-and-forget write to Supabase */
  private writeEntry(entry: PendingAuditEntry): void {
    if (this.isDestroyed) return

    const supabase = createClient()
    supabase
      .from('audit_trail')
      .insert({
        project_id: this.projectId,
        user_id: this.userId,
        action_type: entry.actionType,
        entity_id: entry.entityId,
        previous_state: entry.previousState,
        new_state: entry.newState,
      })
      .then(({ error }) => {
        if (error) {
          console.error('[AuditTrail] Failed to write audit entry:', error)
        }
      })
  }
}