Blame for apps/api/src/network/graph.service.ts

import { Injectable, Logger, OnModuleInit } from "@nestjs/common";
import { PrismaService } from "../prisma/prisma.service";

/**
 * Graph Node Types
 */
type GraphNode = 
    | { type: "guest"; id: string; data: any }
    | { type: "podcast"; id: string; data: any }
    | { type: "host"; id: string; data: any };

type GraphEdge = {
    source: string;
    target: string;
    type: "appeared_on" | "hosted" | "booked" | "knows" | "similar_to";
    weight: number;
    metadata?: Record<string, any>;
};

/**
 * Social Graph Service
 * 
 * Manages the "who knows who" graph for the Verified Guest Network.
 * Enables features like:
 * - "Podcasters who booked X also booked Y"
 * - Guest recommendations based on network proximity
 * - Trust paths between hosts and guests
 * 
 * African Context: Emphasizes community connections and tech hub networks
 */
@Injectable()
export class GraphService implements OnModuleInit {
    private readonly logger = new Logger(GraphService.name);

    // In-memory adjacency list for fast traversal
    // Backed by the graph_edges table for persistence across restarts
    private adjacencyList: Map<string, Map<string, GraphEdge>> = new Map();

    constructor(private readonly prisma: PrismaService) {}

    async onModuleInit() {
        await this.loadEdgesFromDatabase();
    }

    /**
     * Load all graph edges from the database into memory on startup.
     */
    private async loadEdgesFromDatabase(): Promise<void> {
        try {
            const edges = await this.prisma.graphEdge.findMany();
            for (const edge of edges) {
                const sourceId = edge.source;
                const targetId = edge.target;
                const storedEdge: GraphEdge = {
                    source: edge.source,
                    target: edge.target,
                    type: edge.type as GraphEdge["type"],
                    weight: edge.weight,
                    metadata: edge.metadata as Record<string, any>,
                };

                if (!this.adjacencyList.has(sourceId)) {
                    this.adjacencyList.set(sourceId, new Map());
                }
                this.adjacencyList.get(sourceId)!.set(targetId, storedEdge);

                // Restore reverse edges for bidirectional types
                if (edge.type === "knows" || edge.type === "similar_to" || edge.type === "appeared_on") {
                    const reverseEdge = { ...storedEdge, source: edge.target, target: edge.source };
                    if (!this.adjacencyList.has(edge.target)) {
                        this.adjacencyList.set(edge.target, new Map());
                    }
                    this.adjacencyList.get(edge.target)!.set(edge.source, reverseEdge);
                }

                // Restore node data from metadata if available
                if (edge.source.startsWith("guest:") || edge.source.startsWith("podcast:")) {
                    const edges = this.adjacencyList.get(edge.source)!;
                    if (edge.metadata && typeof edge.metadata === "object") {
                        const meta = edge.metadata as Record<string, any>;
                        if (meta.nodeData) {
                            (edges as any).nodeData = meta.nodeData;
                        }
                    }
                }
            }
            this.logger.log(`Loaded ${edges.length} graph edges from database`);
        } catch (error) {
            this.logger.warn("Failed to load graph edges from database, starting with empty graph", error);
        }
    }

    /**
     * Ingest a guest profile into the graph
     */
    async ingestProfile(profileId: string): Promise<void> {
        this.logger.log(`Ingesting profile ${profileId} into graph`);

        const profile = await this.prisma.guestPublicProfile.findUnique({
            where: { id: profileId },
            include: {
                expertiseTags: true,
                bookingHistory: true,
            },
        });

        if (!profile) {
            this.logger.warn(`Profile ${profileId} not found`);
            return;
        }

        // Add guest node
        this.addNode({
            type: "guest",
            id: `guest:${profileId}`,
            data: {
                name: profile.headline,
                country: profile.country,
                expertise: profile.expertiseTags.map((t) => t.name),
                tier: profile.tier,
            },
        });

        // Add appeared_on edges from booking history
        for (const booking of profile.bookingHistory) {
            const podcastNodeId = `podcast:${booking.podcastName}`;
            
            // Add podcast node if not exists
            this.addNode({
                type: "podcast",
                id: podcastNodeId,
                data: { name: booking.podcastName },
            });

            // Add appeared_on edge
            this.addEdge({
                source: `guest:${profileId}`,
                target: podcastNodeId,
                type: "appeared_on",
                weight: 1,
                metadata: {
                    date: booking.appearedAt,
                    topics: booking.topicsDiscussed,
                },
            });
        }

        // Calculate similarity edges to other guests
        await this.calculateSimilarityEdges(profileId, profile.expertiseTags);

        this.logger.log(`Profile ${profileId} ingested successfully`);
    }

    /**
     * Add a node to the graph
     */
    private addNode(node: GraphNode): void {
        if (!this.adjacencyList.has(node.id)) {
            this.adjacencyList.set(node.id, new Map());
        }
        // Store node data in the adjacency list entry
        const edges = this.adjacencyList.get(node.id)!;
        (edges as any).nodeData = node.data;
    }

    /**
     * Add an edge to the graph
     */
    private addEdge(edge: GraphEdge): void {
        // Add forward edge
        if (!this.adjacencyList.has(edge.source)) {
            this.adjacencyList.set(edge.source, new Map());
        }
        this.adjacencyList.get(edge.source)!.set(edge.target, edge);

        // Add reverse edge for undirected relationships (including appeared_on)
        if (edge.type === "knows" || edge.type === "similar_to" || edge.type === "appeared_on") {
            const reverseEdge = { ...edge, source: edge.target, target: edge.source };
            if (!this.adjacencyList.has(edge.target)) {
                this.adjacencyList.set(edge.target, new Map());
            }
            this.adjacencyList.get(edge.target)!.set(edge.source, reverseEdge);
        }

        // Persist to database
        this.persistEdge(edge).catch(err =>
            this.logger.error(`Failed to persist graph edge`, err),
        );
    }

    /**
     * Persist a graph edge to the database.
     */
    private async persistEdge(edge: GraphEdge): Promise<void> {
        try {
            await this.prisma.graphEdge.upsert({
                where: {
                    source_target_type: {
                        source: edge.source,
                        target: edge.target,
                        type: edge.type,
                    },
                },
                create: {
                    source: edge.source,
                    target: edge.target,
                    type: edge.type,
                    weight: edge.weight,
                    metadata: (edge.metadata || {}) as any,
                },
                update: {
                    weight: edge.weight,
                    metadata: (edge.metadata || {}) as any,
                },
            });
        } catch (error) {
            this.logger.error(`Failed to persist edge ${edge.source} -> ${edge.target} (${edge.type})`, error);
        }
    }

    /**
     * Calculate similarity edges based on shared expertise and geography
     */
    private async calculateSimilarityEdges(
        profileId: string,
        expertiseTags: { name: string }[]
    ): Promise<void> {
        const expertiseNames = expertiseTags.map((t) => t.name);
        
        if (expertiseNames.length === 0) return;

        // Find other guests with similar expertise
        const similarGuests = await this.prisma.guestPublicProfile.findMany({
            where: {
                id: { not: profileId },
                isPublic: true,
                expertiseTags: {
                    some: {
                        name: { in: expertiseNames },
                    },
                },
            },
            include: {
                expertiseTags: true,
            },
            take: 20,
        });

        for (const other of similarGuests) {
            const otherExpertise = other.expertiseTags.map((t) => t.name);
            const sharedExpertise = expertiseNames.filter((e) => 
                otherExpertise.includes(e)
            );
            
            if (sharedExpertise.length > 0) {
                const similarityScore = sharedExpertise.length / 
                    Math.max(expertiseNames.length, otherExpertise.length);

                this.addEdge({
                    source: `guest:${profileId}`,
                    target: `guest:${other.id}`,
                    type: "similar_to",
                    weight: similarityScore,
                    metadata: {
                        sharedExpertise,
                        score: similarityScore,
                    },
                });
            }
        }
    }

    /**
     * Get recommendations based on graph proximity
     * "Podcasters who booked X also booked Y"
     */
    async getRecommendations(
        profileId: string,
        limit = 5
    ): Promise<Array<{
        guestId: string;
        reason: string;
        score: number;
    }>> {
        const nodeId = `guest:${profileId}`;
        const scores = new Map<string, number>();
        const reasons = new Map<string, string[]>();

        // Get guests who appeared on the same podcasts
        const appearedOn = this.getNeighbors(nodeId, "appeared_on");
        
        for (const podcastId of appearedOn) {
            const coGuests = this.getNeighbors(podcastId, "appeared_on")
                .filter((g) => g !== nodeId);
            
            for (const coGuest of coGuests) {
                const guestId = coGuest.replace("guest:", "");
                const currentScore = scores.get(guestId) || 0;
                scores.set(guestId, currentScore + 1);
                
                if (!reasons.has(guestId)) {
                    reasons.set(guestId, []);
                }
                const podcastName = this.getNodeData(podcastId)?.name || "a podcast";
                reasons.get(guestId)!.push(`Appeared on ${podcastName}`);
            }
        }

        // Get similar guests
        const similar = this.getNeighbors(nodeId, "similar_to");
        for (const simGuest of similar) {
            const guestId = simGuest.replace("guest:", "");
            const edge = this.getEdge(nodeId, simGuest);
            const currentScore = scores.get(guestId) || 0;
            const weight = edge?.weight || 0.5;
            scores.set(guestId, currentScore + weight);
            
            if (!reasons.has(guestId)) {
                reasons.set(guestId, []);
            }
            const shared = edge?.metadata?.sharedExpertise || ["similar expertise"];
            reasons.get(guestId)!.push(`Shares expertise in ${shared.slice(0, 2).join(", ")}`);
        }

        // Sort by score and return top recommendations
        const sorted = Array.from(scores.entries())
            .sort((a, b) => b[1] - a[1])
            .slice(0, limit);

        return sorted.map(([guestId, score]) => ({
            guestId,
            reason: [...new Set(reasons.get(guestId) || [])].join("; "),
            score,
        }));
    }

    /**
     * Find the shortest path between two guests (trust path)
     */
    async findTrustPath(
        fromProfileId: string,
        toProfileId: string
    ): Promise<string[] | null> {
        const start = `guest:${fromProfileId}`;
        const end = `guest:${toProfileId}`;

        if (!this.adjacencyList.has(start) || !this.adjacencyList.has(end)) {
            return null;
        }

        // BFS for shortest path
        const queue: Array<{ node: string; path: string[] }> = [{ node: start, path: [start] }];
        const visited = new Set<string>();

        while (queue.length > 0) {
            const { node, path } = queue.shift()!;

            if (node === end) {
                return path.map((n) => n.replace("guest:", "").replace("podcast:", ""));
            }

            if (visited.has(node)) continue;
            visited.add(node);

            const neighbors = this.adjacencyList.get(node);
            if (neighbors) {
                for (const [neighbor] of Array.from(neighbors.entries())) {
                    if (!visited.has(neighbor)) {
                        queue.push({ node: neighbor, path: [...path, neighbor] });
                    }
                }
            }
        }

        return null; // No path found
    }

    /**
     * Get network statistics for a profile
     */
    async getNetworkStats(profileId: string): Promise<{
        connections: number;
        reach: number;
        centrality: number;
        communities: string[];
    }> {
        const nodeId = `guest:${profileId}`;
        
        if (!this.adjacencyList.has(nodeId)) {
            return { connections: 0, reach: 0, centrality: 0, communities: [] };
        }

        const directConnections = this.adjacencyList.get(nodeId)!.size;
        
        // Calculate 2-hop reach
        const visited = new Set<string>();
        visited.add(nodeId);
        
        const neighbors = this.getAllNeighbors(nodeId);
        for (const n of Array.from(neighbors)) {
            visited.add(n);
        }
        
        for (const n of Array.from(neighbors)) {
            const secondHop = this.getAllNeighbors(n);
            for (const sh of Array.from(secondHop)) {
                visited.add(sh);
            }
        }

        // Identify communities (tech hubs, countries, expertise areas)
        const communities = this.identifyCommunities(nodeId);

        return {
            connections: directConnections,
            reach: visited.size - 1, // exclude self
            centrality: this.calculateCentrality(nodeId),
            communities,
        };
    }

    /**
     * Get guests in the same network/community
     */
    async getCommunityMembers(
        communityType: "country" | "expertise" | "hub",
        value: string,
        limit = 20
    ): Promise<string[]> {
        const members: string[] = [];

        for (const [nodeId, edges] of Array.from(this.adjacencyList.entries())) {
            if (!nodeId.startsWith("guest:")) continue;
            
            const data = (edges as any).nodeData;
            if (!data) continue;

            if (communityType === "country" && data.country === value) {
                members.push(nodeId.replace("guest:", ""));
            } else if (communityType === "expertise" && data.expertise?.includes(value)) {
                members.push(nodeId.replace("guest:", ""));
            }
        }

        return members.slice(0, limit);
    }

    /**
     * Get neighbors by edge type
     */
    private getNeighbors(nodeId: string, edgeType: string): string[] {
        const edges = this.adjacencyList.get(nodeId);
        if (!edges) return [];

        return Array.from(edges.entries())
            .filter(([, edge]) => edge.type === edgeType)
            .map(([target]) => target);
    }

    /**
     * Get all neighbors regardless of edge type
     */
    private getAllNeighbors(nodeId: string): string[] {
        const edges = this.adjacencyList.get(nodeId);
        if (!edges) return [];
        return Array.from(edges.keys());
    }

    /**
     * Get edge between two nodes
     */
    private getEdge(source: string, target: string): GraphEdge | undefined {
        return this.adjacencyList.get(source)?.get(target);
    }

    /**
     * Get node data
     */
    private getNodeData(nodeId: string): any {
        const edges = this.adjacencyList.get(nodeId);
        if (!edges) return null;
        return (edges as any).nodeData;
    }

    /**
     * Identify communities the node belongs to
     */
    private identifyCommunities(nodeId: string): string[] {
        const data = this.getNodeData(nodeId);
        if (!data) return [];

        const communities: string[] = [];
        
        if (data.country) {
            communities.push(`${data.country} Community`);
        }
        
        if (data.expertise) {
            // Group by top expertise areas
            communities.push(...data.expertise.slice(0, 2).map((e: string) => `${e} Network`));
        }

        return communities;
    }

    /**
     * Calculate a simple centrality score
     */
    private calculateCentrality(nodeId: string): number {
        const direct = this.adjacencyList.get(nodeId)?.size || 0;
        
        // Count unique 2-hop connections
        const twoHop = new Set<string>();
        const neighbors = this.getAllNeighbors(nodeId);
        
        for (const n of neighbors) {
            const secondHop = this.getAllNeighbors(n);
            for (const sh of secondHop) {
                if (sh !== nodeId) {
                    twoHop.add(sh);
                }
            }
        }

        // Simple centrality: combination of direct and 2-hop
        return direct + twoHop.size * 0.5;
    }

    /**
     * Get graph health stats
     */
    getStats(): {
        nodes: number;
        edges: number;
        guests: number;
        podcasts: number;
    } {
        let edges = 0;
        let guests = 0;
        let podcasts = 0;

        for (const [nodeId] of Array.from(this.adjacencyList.entries())) {
            if (nodeId.startsWith("guest:")) guests++;
            if (nodeId.startsWith("podcast:")) podcasts++;
            edges += this.adjacencyList.get(nodeId)!.size;
        }

        return {
            nodes: this.adjacencyList.size,
            edges: edges / 2, // undirected
            guests,
            podcasts,
        };
    }
}