import { NextRequest, NextResponse } from 'next/server'
import prisma from '@/lib/prisma'
import { auth } from '@/auth'

// ── Stopwords FR + EN ─────────────────────────────────────────────────────────
const STOPWORDS = new Set([
  'le','la','les','de','du','des','un','une','et','en','au','aux','ce','se',
  'sa','son','ses','mon','ma','mes','ton','ta','tes','que','qui','quoi','dont',
  'il','elle','ils','elles','nous','vous','je','tu','on','par','pour','sur',
  'sous','avec','dans','est','sont','pas','ne','plus','très','tout','comme',
  'mais','donc','car','cet','cette','ces','leur','leurs','note','notes',
  'the','a','an','and','or','but','in','on','at','to','for','of','with','by',
  'from','is','are','was','were','be','been','have','has','had','do','does',
  'did','will','would','could','should','may','might','this','that','these',
  'those','it','its','they','them','their','he','she','we','you','not','no',
  'so','if','as','up','out','about','also','just','can','all','any','get',
])

function stripHtml(html: string): string {
  return html.replace(/<[^>]+>/g, ' ').replace(/&\w+;/g, ' ')
}

function extractKeywords(text: string): Set<string> {
  return new Set(
    stripHtml(text)
      .toLowerCase()
      .split(/[\s\p{P}]+/u)
      .filter(w => w.length >= 3 && !STOPWORDS.has(w) && !/^\d+$/.test(w))
  )
}

function jaccardSimilarity(a: Set<string>, b: Set<string>): number {
  if (a.size === 0 || b.size === 0) return 0
  let intersection = 0
  for (const w of a) if (b.has(w)) intersection++
  return intersection / (a.size + b.size - intersection)
}

type EdgeType = 'title_mention' | 'shared_label' | 'jaccard'

interface GraphEdge { source: string; target: string; weight: number; type: EdgeType }

// GET /api/graph — connexions automatiques à 3 niveaux
export async function GET(request: NextRequest) {
  const session = await auth()
  if (!session?.user?.id) return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })

  const userId = session.user.id
  const { searchParams } = new URL(request.url)
  const notebookId = searchParams.get('notebookId') || undefined

  const notes = await prisma.note.findMany({
    where: { userId, trashedAt: null, ...(notebookId ? { notebookId } : {}) },
    select: {
      id: true, title: true, content: true, notebookId: true, createdAt: true,
      labelRelations: { select: { id: true } },
      notebook: { select: { id: true, name: true } },
    },
  })

  if (notes.length === 0) return NextResponse.json({ nodes: [], edges: [] })

  const ids = notes.map(n => n.id)

  // Pré-calcul
  const keywordsMap = new Map<string, Set<string>>()
  const labelMap    = new Map<string, Set<string>>()
  for (const note of notes) {
    keywordsMap.set(note.id, extractKeywords(`${note.title ?? ''} ${note.content}`))
    labelMap.set(note.id, new Set(note.labelRelations.map((l: any) => l.id)))
  }

  const edgeMap = new Map<string, GraphEdge>()
  function upsertEdge(a: string, b: string, weight: number, type: EdgeType) {
    const key = a < b ? `${a}--${b}` : `${b}--${a}`
    const ex = edgeMap.get(key)
    if (!ex || ex.weight < weight) edgeMap.set(key, { source: a < b ? a : b, target: a < b ? b : a, weight, type })
  }

  // ── Niveau 1 : Title Mention (comme Obsidian "unlinked mentions") ──────────
  for (const noteA of notes) {
    const title = (noteA.title ?? '').trim().toLowerCase()
    if (title.length < 3) continue
    const escaped = title.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')
    const re = new RegExp(`\\b${escaped}\\b`, 'i')
    for (const noteB of notes) {
      if (noteA.id === noteB.id) continue
      if (re.test(stripHtml(noteB.content))) upsertEdge(noteA.id, noteB.id, 1.0, 'title_mention')
    }
  }

  // ── Niveau 2 : Labels partagés ────────────────────────────────────────────
  for (let i = 0; i < ids.length; i++) {
    for (let j = i + 1; j < ids.length; j++) {
      const la = labelMap.get(ids[i])!
      const lb = labelMap.get(ids[j])!
      const shared = [...la].filter(l => lb.has(l)).length
      if (shared > 0) upsertEdge(ids[i], ids[j], Math.min(0.5 + shared * 0.15, 0.9), 'shared_label')
    }
  }

  // ── Niveau 3 : Jaccard (désactivé > 500 notes) ───────────────────────────
  if (notes.length <= 500) {
    for (let i = 0; i < ids.length; i++) {
      const kwI = keywordsMap.get(ids[i])!
      const candidates: { j: number; score: number }[] = []
      for (let j = i + 1; j < ids.length; j++) {
        const score = jaccardSimilarity(kwI, keywordsMap.get(ids[j])!)
        if (score >= 0.12) candidates.push({ j, score })
      }
      candidates.sort((a, b) => b.score - a.score).slice(0, 10)
        .forEach(({ j, score }) => upsertEdge(ids[i], ids[j], score * 0.8, 'jaccard'))
    }
  }

  const degreeMap = new Map<string, number>()
  for (const e of edgeMap.values()) {
    degreeMap.set(e.source, (degreeMap.get(e.source) ?? 0) + 1)
    degreeMap.set(e.target, (degreeMap.get(e.target) ?? 0) + 1)
  }

  const nodes = notes.map(n => ({
    id: n.id,
    title: n.title || 'Sans titre',
    notebookId: n.notebookId,
    createdAt: n.createdAt,
    degree: degreeMap.get(n.id) ?? 0,
  }))

  // Build clusters (notebooks)
  const notebookMap = new Map<string, string>()
  for (const n of notes) {
    if (n.notebook) notebookMap.set(n.notebook.id, n.notebook.name)
  }
  const clusters = [...notebookMap.entries()].map(([id, name]) => ({ id, name }))

  return NextResponse.json({ nodes, edges: Array.from(edgeMap.values()), clusters })
}