/**
 * GRAPH_REPORT.md generator
 *
 * Produces a human-readable audit report from the knowledge graph:
 *   - Corpus summary
 *   - God nodes (most-connected entities)
 *   - Community overview
 *   - Surprising connections
 *   - Suggested questions
 */

import type { KnowledgeGraph } from "./graph.ts";
import type { GraphStats } from "./types.ts";

interface Surprise {
  source: string;
  target: string;
  relation: string;
  reason: string;
}

export function generateReport(
  kg: KnowledgeGraph,
  stats: GraphStats,
  root: string,
  fileCount: number,
  byExtension: Record<string, number>,
): string {
  const lines: string[] = [];

  lines.push("# Mind Place Report");
  lines.push("");
  lines.push(`Generated from \`${root}\``);
  lines.push("");

  // Corpus
  lines.push("## Corpus");
  lines.push("");
  lines.push(`- **Files scanned:** ${fileCount}`);
  if (Object.keys(byExtension).length > 0) {
    lines.push(`- **Languages:** ${Object.entries(byExtension).map(([ext, n]) => `${n} ${ext}`).join(", ")}`);
  }
  lines.push("");

  // Graph stats
  lines.push("## Graph Statistics");
  lines.push("");
  lines.push(`| Metric | Value |`);
  lines.push(`|--------|-------|`);
  lines.push(`| Nodes | ${stats.nodeCount} |`);
  lines.push(`| Edges | ${stats.edgeCount} |`);
  lines.push(`| Communities | ${stats.communityCount} |`);
  lines.push(`| Avg. Degree | ${stats.nodeCount > 0 ? (stats.edgeCount * 2 / stats.nodeCount).toFixed(1) : "0"} |`);
  lines.push("");

  // God nodes
  lines.push("## God Nodes");
  lines.push("");
  lines.push("The most-connected entities - these are the architectural pillars:");
  lines.push("");
  lines.push("| # | Node | Type | Connections | File |");
  lines.push("|---|------|------|-------------|------|");
  for (let i = 0; i < stats.godNodes.length; i++) {
    const god = stats.godNodes[i];
    const node = kg.nodes.get(god.id);
    lines.push(`| ${i + 1} | **${god.label}** | ${node?.type ?? "?"} | ${god.degree} | \`${node?.sourceFile ?? "?"}\` |`);
  }
  lines.push("");

  // Community overview
  if (stats.communityCount > 1) {
    lines.push("## Communities");
    lines.push("");
    lines.push("The graph was partitioned into these subsystems:");

    // Gather community info with named labels
    const commMap = new Map<number, { size: number; top: string[]; label: string }>();
    for (const node of kg.nodes.values()) {
      if (node.community === undefined) continue;
      const c = commMap.get(node.community) ?? { size: 0, top: [], label: "" };
      c.size++;
      if (c.top.length < 3) c.top.push(node.label);
      // Use the highest-centrality node as the community label
      if (!c.label || (node.centrality ?? 0) > (kg.nodes.get(c.label)?.centrality ?? 0)) {
        c.label = node.label;
      }
      commMap.set(node.community, c);
    }

    lines.push("");
    lines.push("| Community | Size | Key Members |");
    lines.push("|-----------|------|-------------|");
    for (const [, info] of [...commMap.entries()].sort((a, b) => b[1].size - a[1].size)) {
      lines.push(`| **${info.label}** | ${info.size} | ${info.top.join(", ")} |`);
    }
    lines.push("");
  }

  // Surprising connections
  const surprises = findSurprises(kg);
  if (surprises.length > 0) {
    lines.push("## Surprising Connections");
    lines.push("");
    for (const s of surprises.slice(0, 10)) {
      lines.push(`- **${s.source}** → \`${s.relation}\` → **${s.target}**: ${s.reason}`);
    }
    lines.push("");
  }

  // Suggested questions
  const questions = suggestQuestions(kg, stats);
  if (questions.length > 0) {
    lines.push("## Suggested Questions");
    lines.push("");
    for (const q of questions.slice(0, 8)) {
      lines.push(`- ${q}`);
    }
    lines.push("");
  }

  lines.push("---");
  lines.push(`_Report generated by pi-mindplace · Use \`mindplace_query\` to explore the graph_`);
  lines.push("");

  return lines.join("\n");
}

function findSurprises(kg: KnowledgeGraph): Surprise[] {
  const surprises: Surprise[] = [];
  const communities = new Map<string, number>();
  for (const node of kg.nodes.values()) {
    if (node.community !== undefined) communities.set(node.id, node.community);
  }

  // Map community ID to its best label
  const commLabels = new Map<number, string>();
  for (const node of kg.nodes.values()) {
    if (node.community === undefined) continue;
    const best = commLabels.get(node.community);
    const bestNode = best ? kg.nodes.get(best) : null;
    if (!best || (node.centrality ?? 0) > (bestNode?.centrality ?? 0)) {
      commLabels.set(node.community, node.id);
    }
  }

  function commName(id: string): string {
    const c = communities.get(id);
    if (c === undefined) return "?";
    const bestId = commLabels.get(c);
    return bestId ? (kg.nodes.get(bestId)?.label ?? `C${c}`) : `C${c}`;
  }

  for (const edge of kg.edges) {
    const sc = communities.get(edge.source);
    const tc = communities.get(edge.target);
    if (sc !== undefined && tc !== undefined && sc !== tc) {
      const srcLabel = kg.nodes.get(edge.source)?.label ?? edge.source;
      const tgtLabel = kg.nodes.get(edge.target)?.label ?? edge.target;
      if (edge.confidence !== "EXTRACTED") continue;
      surprises.push({
        source: srcLabel,
        target: tgtLabel,
        relation: edge.relation,
        reason: `Cross-community bridge between "${commName(edge.source)}" and "${commName(edge.target)}"`,
      });
    }
  }

  return surprises;
}

function suggestQuestions(kg: KnowledgeGraph, stats: GraphStats): string[] {
  const questions: string[] = [];

  // Questions about god nodes
  const top = stats.godNodes.slice(0, 3);
  if (top.length >= 2) {
    questions.push(`How does **${top[0].label}** connect to **${top[1].label}**?`);
  }
  if (top.length >= 1) {
    questions.push(`What calls **${top[0].label}** and what does it depend on?`);
  }

  // Cross-community bridges
  const communities = new Map<number, string[]>();
  for (const node of kg.nodes.values()) {
    if (node.community === undefined) continue;
    const c = communities.get(node.community) ?? [];
    c.push(node.label);
    communities.set(node.community, c);
  }

  const commEntries = [...communities.entries()].sort((a, b) => b[1].length - a[1].length);
  if (commEntries.length >= 2) {
    const examples = commEntries.slice(0, 2).map(c => c[1][0]);
    if (examples.length >= 2) {
      questions.push(`Trace the data flow between **${examples[0]}** and **${examples[1]}**`);
    }
  }

  // Type-based questions
  const importEdges = kg.edges.filter(e => e.relation === "imports").length;
  if (importEdges > 5) {
    questions.push(`Which modules have the most dependencies?`);
  }
  questions.push(`Show me the architecture of the \`${top[0]?.label ?? "main"}\` subsystem`);
  questions.push(`What is the most heavily connected module in the codebase?`);

  return questions;
}