/**
 * @module mcp-server/tools/transit
 * MCP Tool: Transit and upstream analysis — diversity, cost, optimization.
 *
 * Analyzes an ASN's upstream providers, evaluates transit diversity,
 * and provides recommendations for peering vs. transit decisions.
 */

import { z } from "zod";
import type { ASN } from "../../types/common.js";

// ── Tool Schemas ─────────────────────────────────────────

/** Input schema for upstream analysis */
export const upstreamAnalysisSchema = z.object({
  asn: z
    .union([z.string(), z.number()])
    .describe("ASN to analyze upstreams for (e.g., 13335 or 'AS13335')"),
  includeHistory: z
    .boolean()
    .optional()
    .default(false)
    .describe("Include historical upstream changes"),
});

/** Input schema for transit diversity assessment */
export const transitDiversitySchema = z.object({
  asn: z
    .union([z.string(), z.number()])
    .describe("ASN to assess transit diversity for"),
  minimumUpstreams: z
    .number()
    .optional()
    .default(2)
    .describe("Minimum recommended number of upstreams"),
});

/** Input schema for peering vs. transit comparison */
export const peeringVsTransitSchema = z.object({
  sourceAsn: z
    .union([z.string(), z.number()])
    .describe("Your ASN"),
  targetAsn: z
    .union([z.string(), z.number()])
    .describe("Target ASN to evaluate peering with"),
  estimatedTrafficGbps: z
    .number()
    .optional()
    .describe("Estimated bilateral traffic in Gbps"),
  transitCostPerMbps: z
    .number()
    .optional()
    .describe("Current transit cost per Mbps (USD)"),
});

// ── Result Types ─────────────────────────────────────────

/** Upstream provider information */
export interface UpstreamProvider {
  readonly asn: ASN;
  readonly name: string;
  readonly relationship: "transit" | "peer" | "partial-transit";
  readonly prefixesVia: number;
  readonly percentOfPaths: number;
  readonly firstSeen: string;
  readonly lastSeen: string;
  readonly stability: "stable" | "intermittent" | "new";
}

/** Upstream analysis result */
export interface UpstreamAnalysis {
  readonly asn: ASN;
  readonly name: string;
  readonly upstreams: ReadonlyArray<UpstreamProvider>;
  readonly upstreamCount: number;
  readonly transitProviders: ReadonlyArray<UpstreamProvider>;
  readonly singleHomedPrefixes: ReadonlyArray<string>;
  readonly recommendations: ReadonlyArray<string>;
}

/** Transit diversity assessment */
export interface TransitDiversityReport {
  readonly asn: ASN;
  readonly name: string;
  readonly upstreamCount: number;
  readonly diversityScore: number;
  readonly singlePointsOfFailure: ReadonlyArray<{
    readonly description: string;
    readonly severity: "critical" | "high" | "medium" | "low";
    readonly affectedPrefixes: ReadonlyArray<string>;
  }>;
  readonly geographicDiversity: {
    readonly countries: ReadonlyArray<string>;
    readonly continents: ReadonlyArray<string>;
    readonly score: number;
  };
  readonly recommendations: ReadonlyArray<string>;
}

/** Peering vs. transit cost comparison */
export interface PeeringVsTransitComparison {
  readonly sourceAsn: ASN;
  readonly targetAsn: ASN;
  readonly targetName: string;
  readonly currentPath: {
    readonly asPath: ReadonlyArray<ASN>;
    readonly hopCount: number;
    readonly transitProviders: ReadonlyArray<string>;
  };
  readonly peeringPath: {
    readonly commonIXs: ReadonlyArray<string>;
    readonly commonFacilities: ReadonlyArray<string>;
    readonly estimatedRttReductionMs: number;
  };
  readonly costAnalysis: {
    readonly currentMonthlyCostUsd: number | null;
    readonly estimatedPeeringSetupCostUsd: number;
    readonly estimatedMonthlySavingsUsd: number | null;
    readonly breakEvenMonths: number | null;
  };
  readonly recommendation: string;
}

// ── Tool Handlers ────────────────────────────────────────

/**
 * Analyze upstream providers for an ASN.
 *
 * Identifies all transit providers, evaluates their role in routing,
 * and highlights single-homed prefixes.
 *
 * @param input - Validated analysis parameters
 * @returns Upstream analysis with provider details
 *
 * @example
 * ```
 * > Show me the upstream providers for AS32934 (Meta)
 *
 * Returns: List of transit providers, percentage of paths via each,
 * stability assessment, and single-homed prefix warnings.
 * ```
 */
export async function handleUpstreamAnalysis(
  input: z.infer<typeof upstreamAnalysisSchema>
): Promise<UpstreamAnalysis> {
  // TODO: Query bgp.he.net and RIPE Stat for upstream data
  // TODO: Query CAIDA for AS relationship classification
  // TODO: Cross-reference with BGP state from Route Views
  // TODO: Calculate path percentages and stability metrics

  const _input = input;

  return {
    asn: 0, // TODO: parseASN(input.asn)
    name: "",
    upstreams: [],
    upstreamCount: 0,
    transitProviders: [],
    singleHomedPrefixes: [],
    recommendations: [
      "Consider adding a second transit provider for redundancy",
      "Evaluate peering at shared IXPs to reduce transit dependency",
    ],
  };
}

/**
 * Assess transit diversity and resilience for an ASN.
 *
 * Evaluates single points of failure, geographic diversity, and
 * provides a diversity score.
 *
 * @param input - Validated assessment parameters
 * @returns Diversity report with risk assessment
 */
export async function handleTransitDiversity(
  input: z.infer<typeof transitDiversitySchema>
): Promise<TransitDiversityReport> {
  // TODO: Analyze upstream paths for redundancy
  // TODO: Check geographic distribution of upstreams
  // TODO: Identify single points of failure
  // TODO: Score diversity (0-100)

  const _input = input;

  return {
    asn: 0,
    name: "",
    upstreamCount: 0,
    diversityScore: 0,
    singlePointsOfFailure: [],
    geographicDiversity: {
      countries: [],
      continents: [],
      score: 0,
    },
    recommendations: [],
  };
}

/**
 * Compare peering directly vs. using transit to reach a target ASN.
 *
 * Evaluates whether establishing a direct peering session would be
 * beneficial in terms of latency, cost, and reliability.
 *
 * @param input - Validated comparison parameters
 * @returns Cost/benefit analysis with recommendation
 *
 * @example
 * ```
 * > What would change if AS32934 peered directly with AS13335
 * > instead of using transit?
 *
 * Returns: Current path analysis, common IX/facility overlap,
 * estimated latency improvement, and cost comparison.
 * ```
 */
export async function handlePeeringVsTransit(
  input: z.infer<typeof peeringVsTransitSchema>
): Promise<PeeringVsTransitComparison> {
  // TODO: Get current BGP path between source and target
  // TODO: Find common IXPs and facilities via PeeringDB
  // TODO: Estimate latency reduction from direct peering
  // TODO: Calculate cost comparison if traffic estimate provided

  return {
    sourceAsn: 0, // TODO: parseASN(input.sourceAsn)
    targetAsn: 0, // TODO: parseASN(input.targetAsn)
    targetName: "",
    currentPath: {
      asPath: [],
      hopCount: 0,
      transitProviders: [],
    },
    peeringPath: {
      commonIXs: [],
      commonFacilities: [],
      estimatedRttReductionMs: 0,
    },
    costAnalysis: {
      currentMonthlyCostUsd: input.transitCostPerMbps != null && input.estimatedTrafficGbps != null
        ? input.transitCostPerMbps * input.estimatedTrafficGbps * 1000
        : null,
      estimatedPeeringSetupCostUsd: 0,
      estimatedMonthlySavingsUsd: null,
      breakEvenMonths: null,
    },
    recommendation: "Insufficient data — provide traffic and cost estimates for a full comparison.",
  };
}
