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

/**
 * Represents a knowledge entry that matches a link target
 */
export interface ResolvedEntry {
  id: string;
  title: string;
}

/**
 * Service for resolving wiki-style links to knowledge entries
 *
 * Resolution strategy (in order of priority):
 * 1. Exact title match (case-sensitive)
 * 2. Slug match
 * 3. Fuzzy title match (case-insensitive)
 *
 * Supports workspace scoping via RLS
 */
@Injectable()
export class LinkResolutionService {
  constructor(private readonly prisma: PrismaService) {}

  /**
   * Resolve a single link target to a knowledge entry ID
   *
   * @param workspaceId - The workspace scope
   * @param target - The link target (title or slug)
   * @returns The entry ID if resolved, null if not found or ambiguous
   */
  async resolveLink(
    workspaceId: string,
    target: string
  ): Promise<string | null> {
    // Validate input
    if (!target || typeof target !== "string") {
      return null;
    }

    // Trim whitespace
    const trimmedTarget = target.trim();

    // Reject empty or whitespace-only strings
    if (trimmedTarget.length === 0) {
      return null;
    }

    // 1. Try exact title match (case-sensitive)
    const exactMatch = await this.prisma.knowledgeEntry.findFirst({
      where: {
        workspaceId,
        title: trimmedTarget,
      },
      select: {
        id: true,
      },
    });

    if (exactMatch) {
      return exactMatch.id;
    }

    // 2. Try slug match
    const slugMatch = await this.prisma.knowledgeEntry.findUnique({
      where: {
        workspaceId_slug: {
          workspaceId,
          slug: trimmedTarget,
        },
      },
      select: {
        id: true,
      },
    });

    if (slugMatch) {
      return slugMatch.id;
    }

    // 3. Try fuzzy match (case-insensitive)
    const fuzzyMatches = await this.prisma.knowledgeEntry.findMany({
      where: {
        workspaceId,
        title: {
          mode: "insensitive",
          equals: trimmedTarget,
        },
      },
      select: {
        id: true,
        title: true,
      },
    });

    // Return null if no matches or multiple matches (ambiguous)
    if (fuzzyMatches.length === 0) {
      return null;
    }

    if (fuzzyMatches.length > 1) {
      // Ambiguous match - multiple entries with similar titles
      return null;
    }

    return fuzzyMatches[0].id;
  }

  /**
   * Resolve multiple link targets in batch
   *
   * @param workspaceId - The workspace scope
   * @param targets - Array of link targets
   * @returns Map of target to resolved entry ID (null if not found)
   */
  async resolveLinks(
    workspaceId: string,
    targets: string[]
  ): Promise<Record<string, string | null>> {
    const result: Record<string, string | null> = {};

    // Deduplicate targets
    const uniqueTargets = Array.from(new Set(targets));

    // Resolve each target
    for (const target of uniqueTargets) {
      const resolved = await this.resolveLink(workspaceId, target);
      result[target] = resolved;
    }

    return result;
  }

  /**
   * Get all entries that could match a link target (for disambiguation UI)
   *
   * @param workspaceId - The workspace scope
   * @param target - The link target
   * @returns Array of matching entries
   */
  async getAmbiguousMatches(
    workspaceId: string,
    target: string
  ): Promise<ResolvedEntry[]> {
    const trimmedTarget = target.trim();

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

    const matches = await this.prisma.knowledgeEntry.findMany({
      where: {
        workspaceId,
        title: {
          mode: "insensitive",
          equals: trimmedTarget,
        },
      },
      select: {
        id: true,
        title: true,
      },
    });

    return matches;
  }
}