brainy/src/graph/pathfinding.ts

/**
 * Advanced Graph Pathfinding Algorithms
 * Provides shortest path, multi-hop traversal, and path ranking
 */

// Graph pathfinding doesn't need to import from coreTypes

export interface GraphNode {
  id: string
  [key: string]: any
}

export interface GraphEdge {
  source: string
  target: string
  type: string
  weight: number
  metadata?: any
}

export interface Path {
  nodes: string[]
  edges: GraphEdge[]
  totalWeight: number
  length: number
}

export interface PathfindingOptions {
  maxDepth?: number
  maxPaths?: number
  bidirectional?: boolean
  weightField?: string
  relationshipTypes?: string[]
  nodeFilter?: (node: GraphNode) => boolean
  edgeFilter?: (edge: GraphEdge) => boolean
}

export class GraphPathfinding {
  private adjacencyList: Map<string, Map<string, GraphEdge[]>> = new Map()
  private nodes: Map<string, GraphNode> = new Map()
  
  /**
   * Add a node to the graph
   */
  public addNode(node: GraphNode): void {
    this.nodes.set(node.id, node)
    if (!this.adjacencyList.has(node.id)) {
      this.adjacencyList.set(node.id, new Map())
    }
  }
  
  /**
   * Add an edge to the graph
   */
  public addEdge(edge: GraphEdge): void {
    // Ensure nodes exist
    if (!this.adjacencyList.has(edge.source)) {
      this.adjacencyList.set(edge.source, new Map())
    }
    if (!this.adjacencyList.has(edge.target)) {
      this.adjacencyList.set(edge.target, new Map())
    }
    
    // Add edge to adjacency list
    const sourceEdges = this.adjacencyList.get(edge.source)!
    if (!sourceEdges.has(edge.target)) {
      sourceEdges.set(edge.target, [])
    }
    sourceEdges.get(edge.target)!.push(edge)
  }
  
  /**
   * Find shortest path using Dijkstra's algorithm
   * O((V + E) log V) with binary heap
   */
  public shortestPath(
    start: string, 
    end: string, 
    options: PathfindingOptions = {}
  ): Path | null {
    const { 
      maxDepth = Infinity,
      relationshipTypes,
      edgeFilter 
    } = options
    
    // Priority queue: [nodeId, distance, path]
    const pq: Array<[string, number, string[], GraphEdge[]]> = [[start, 0, [start], []]]
    const visited = new Set<string>()
    const distances = new Map<string, number>([[start, 0]])
    
    while (pq.length > 0) {
      // Sort by distance (simple array, could optimize with heap)
      pq.sort((a, b) => a[1] - b[1])
      const [current, distance, path, edges] = pq.shift()!
      
      if (visited.has(current)) continue
      visited.add(current)
      
      // Found target
      if (current === end) {
        return {
          nodes: path,
          edges,
          totalWeight: distance,
          length: path.length - 1
        }
      }
      
      // Max depth reached
      if (path.length > maxDepth) continue
      
      // Explore neighbors
      const neighbors = this.adjacencyList.get(current)
      if (!neighbors) continue
      
      for (const [neighbor, edgeList] of neighbors) {
        if (visited.has(neighbor)) continue
        
        // Find best edge to neighbor
        let bestEdge: GraphEdge | null = null
        let bestWeight = Infinity
        
        for (const edge of edgeList) {
          // Apply filters
          if (relationshipTypes && !relationshipTypes.includes(edge.type)) continue
          if (edgeFilter && !edgeFilter(edge)) continue
          
          if (edge.weight < bestWeight) {
            bestWeight = edge.weight
            bestEdge = edge
          }
        }
        
        if (!bestEdge) continue
        
        const newDistance = distance + bestWeight
        const currentBest = distances.get(neighbor) ?? Infinity
        
        if (newDistance < currentBest) {
          distances.set(neighbor, newDistance)
          pq.push([
            neighbor,
            newDistance,
            [...path, neighbor],
            [...edges, bestEdge]
          ])
        }
      }
    }
    
    return null // No path found
  }
  
  /**
   * Find all paths between two nodes
   * Uses DFS with cycle detection
   */
  public allPaths(
    start: string,
    end: string,
    options: PathfindingOptions = {}
  ): Path[] {
    const { 
      maxDepth = 10,
      maxPaths = 100,
      relationshipTypes,
      edgeFilter 
    } = options
    
    const paths: Path[] = []
    const visited = new Set<string>()
    
    const dfs = (
      current: string,
      path: string[],
      edges: GraphEdge[],
      weight: number
    ): void => {
      if (paths.length >= maxPaths) return
      if (path.length > maxDepth) return
      
      if (current === end && path.length > 1) {
        paths.push({
          nodes: [...path],
          edges: [...edges],
          totalWeight: weight,
          length: path.length - 1
        })
        return
      }
      
      visited.add(current)
      
      const neighbors = this.adjacencyList.get(current)
      if (neighbors) {
        for (const [neighbor, edgeList] of neighbors) {
          if (visited.has(neighbor)) continue
          
          for (const edge of edgeList) {
            // Apply filters
            if (relationshipTypes && !relationshipTypes.includes(edge.type)) continue
            if (edgeFilter && !edgeFilter(edge)) continue
            
            dfs(
              neighbor,
              [...path, neighbor],
              [...edges, edge],
              weight + edge.weight
            )
          }
        }
      }
      
      visited.delete(current)
    }
    
    dfs(start, [start], [], 0)
    
    // Sort paths by weight
    paths.sort((a, b) => a.totalWeight - b.totalWeight)
    
    return paths
  }
  
  /**
   * Bidirectional search for faster pathfinding
   * Searches from both start and end simultaneously
   */
  public bidirectionalSearch(
    start: string,
    end: string,
    options: PathfindingOptions = {}
  ): Path | null {
    const { maxDepth = 10 } = options
    
    // Two search frontiers
    const forwardVisited = new Map<string, { path: string[], edges: GraphEdge[], weight: number }>()
    const backwardVisited = new Map<string, { path: string[], edges: GraphEdge[], weight: number }>()
    
    forwardVisited.set(start, { path: [start], edges: [], weight: 0 })
    backwardVisited.set(end, { path: [end], edges: [], weight: 0 })
    
    const forwardQueue = [start]
    const backwardQueue = [end]
    
    let depth = 0
    
    while (
      (forwardQueue.length > 0 || backwardQueue.length > 0) && 
      depth < maxDepth
    ) {
      // Expand forward frontier
      const forwardNext: string[] = []
      for (const current of forwardQueue) {
        const currentData = forwardVisited.get(current)!
        const neighbors = this.adjacencyList.get(current)
        
        if (neighbors) {
          for (const [neighbor, edges] of neighbors) {
            if (forwardVisited.has(neighbor)) continue
            
            const bestEdge = edges[0] // TODO: Select best edge
            forwardVisited.set(neighbor, {
              path: [...currentData.path, neighbor],
              edges: [...currentData.edges, bestEdge],
              weight: currentData.weight + bestEdge.weight
            })
            
            // Check if we met the backward search
            if (backwardVisited.has(neighbor)) {
              const forward = forwardVisited.get(neighbor)!
              const backward = backwardVisited.get(neighbor)!
              
              // Combine paths
              const fullPath = [
                ...forward.path,
                ...backward.path.slice(1).reverse()
              ]
              
              // Reverse backward edges and combine
              const backwardEdgesReversed = backward.edges
                .map(e => ({
                  ...e,
                  source: e.target,
                  target: e.source
                }))
                .reverse()
              
              return {
                nodes: fullPath,
                edges: [...forward.edges, ...backwardEdgesReversed],
                totalWeight: forward.weight + backward.weight,
                length: fullPath.length - 1
              }
            }
            
            forwardNext.push(neighbor)
          }
        }
      }
      
      // Expand backward frontier
      const backwardNext: string[] = []
      for (const current of backwardQueue) {
        const currentData = backwardVisited.get(current)!
        
        // For backward search, we need to look at incoming edges
        for (const [nodeId, neighbors] of this.adjacencyList) {
          const edges = neighbors.get(current)
          if (!edges) continue
          
          if (backwardVisited.has(nodeId)) continue
          
          const bestEdge = edges[0] // TODO: Select best edge
          backwardVisited.set(nodeId, {
            path: [...currentData.path, nodeId],
            edges: [...currentData.edges, bestEdge],
            weight: currentData.weight + bestEdge.weight
          })
          
          // Check if we met the forward search
          if (forwardVisited.has(nodeId)) {
            const forward = forwardVisited.get(nodeId)!
            const backward = backwardVisited.get(nodeId)!
            
            // Combine paths
            const fullPath = [
              ...forward.path,
              ...backward.path.slice(1).reverse()
            ]
            
            // Reverse backward edges and combine
            const backwardEdgesReversed = backward.edges
              .map(e => ({
                ...e,
                source: e.target,
                target: e.source
              }))
              .reverse()
            
            return {
              nodes: fullPath,
              edges: [...forward.edges, ...backwardEdgesReversed],
              totalWeight: forward.weight + backward.weight,
              length: fullPath.length - 1
            }
          }
          
          backwardNext.push(nodeId)
        }
      }
      
      forwardQueue.splice(0, forwardQueue.length, ...forwardNext)
      backwardQueue.splice(0, backwardQueue.length, ...backwardNext)
      depth++
    }
    
    return null
  }
  
  /**
   * Multi-hop traversal (e.g., friends of friends)
   * Returns all nodes within N hops
   */
  public multiHopTraversal(
    start: string,
    hops: number,
    options: PathfindingOptions = {}
  ): Map<string, { distance: number, paths: Path[] }> {
    const { relationshipTypes, nodeFilter, edgeFilter } = options
    
    const results = new Map<string, { distance: number, paths: Path[] }>()
    const visited = new Set<string>()
    const queue: Array<{ node: string, distance: number, path: string[], edges: GraphEdge[] }> = [
      { node: start, distance: 0, path: [start], edges: [] }
    ]
    
    while (queue.length > 0) {
      const { node, distance, path, edges } = queue.shift()!
      
      if (distance > hops) continue
      
      // Record this node
      if (!results.has(node)) {
        results.set(node, { distance, paths: [] })
      }
      results.get(node)!.paths.push({
        nodes: path,
        edges,
        totalWeight: edges.reduce((sum, e) => sum + e.weight, 0),
        length: path.length - 1
      })
      
      if (distance === hops) continue
      
      // Explore neighbors
      const neighbors = this.adjacencyList.get(node)
      if (neighbors) {
        for (const [neighbor, edgeList] of neighbors) {
          // Apply node filter
          if (nodeFilter) {
            const neighborNode = this.nodes.get(neighbor)
            if (neighborNode && !nodeFilter(neighborNode)) continue
          }
          
          for (const edge of edgeList) {
            // Apply filters
            if (relationshipTypes && !relationshipTypes.includes(edge.type)) continue
            if (edgeFilter && !edgeFilter(edge)) continue
            
            queue.push({
              node: neighbor,
              distance: distance + 1,
              path: [...path, neighbor],
              edges: [...edges, edge]
            })
          }
        }
      }
    }
    
    return results
  }
  
  /**
   * Find connected components using DFS
   */
  public connectedComponents(): Array<Set<string>> {
    const visited = new Set<string>()
    const components: Array<Set<string>> = []
    
    const dfs = (node: string, component: Set<string>): void => {
      visited.add(node)
      component.add(node)
      
      const neighbors = this.adjacencyList.get(node)
      if (neighbors) {
        for (const neighbor of neighbors.keys()) {
          if (!visited.has(neighbor)) {
            dfs(neighbor, component)
          }
        }
      }
    }
    
    for (const node of this.adjacencyList.keys()) {
      if (!visited.has(node)) {
        const component = new Set<string>()
        dfs(node, component)
        components.push(component)
      }
    }
    
    return components
  }
  
  /**
   * Calculate PageRank for all nodes
   * Useful for ranking importance in the graph
   */
  public pageRank(iterations: number = 100, damping: number = 0.85): Map<string, number> {
    const nodes = Array.from(this.adjacencyList.keys())
    const n = nodes.length
    
    if (n === 0) return new Map()
    
    // Initialize ranks
    const ranks = new Map<string, number>()
    for (const node of nodes) {
      ranks.set(node, 1 / n)
    }
    
    // Calculate outgoing edge counts
    const outDegree = new Map<string, number>()
    for (const [node, neighbors] of this.adjacencyList) {
      let count = 0
      for (const edges of neighbors.values()) {
        count += edges.length
      }
      outDegree.set(node, count)
    }
    
    // Iterate PageRank algorithm
    for (let i = 0; i < iterations; i++) {
      const newRanks = new Map<string, number>()
      
      for (const node of nodes) {
        let rank = (1 - damping) / n
        
        // Sum contributions from incoming edges
        for (const [source, neighbors] of this.adjacencyList) {
          if (neighbors.has(node)) {
            const sourceRank = ranks.get(source) ?? 0
            const sourceOutDegree = outDegree.get(source) ?? 1
            rank += damping * (sourceRank / sourceOutDegree)
          }
        }
        
        newRanks.set(node, rank)
      }
      
      // Update ranks
      for (const [node, rank] of newRanks) {
        ranks.set(node, rank)
      }
    }
    
    return ranks
  }
  
  /**
   * Clear the graph
   */
  public clear(): void {
    this.adjacencyList.clear()
    this.nodes.clear()
  }
}