import { NextRequest, NextResponse } from 'next/server'
import { auth } from '@/auth'
import { getSystemConfig } from '@/lib/config'
import { getTagsProvider } from '@/lib/ai/factory'

export async function POST(request: NextRequest) {
  try {
    const session = await auth()
    if (!session?.user?.id) {
      return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
    }

    const { existingContent, resourceText, mode, language, format } = await request.json()

    if (!resourceText || typeof resourceText !== 'string') {
      return NextResponse.json({ error: 'resourceText is required' }, { status: 400 })
    }
    if (!mode || !['complete', 'merge'].includes(mode)) {
      return NextResponse.json({ error: 'mode must be "complete" or "merge"' }, { status: 400 })
    }

    const lang = language || 'fr'
    const outputFormat = format === 'html' ? 'HTML (with proper tags like <h2>, <p>, <ul>, <li>)' : 'Markdown (with ##, -, **, etc.)'
    const config = await getSystemConfig()
    const provider = getTagsProvider(config)

    let prompt: string

    if (mode === 'complete') {
      // Add missing info from resource without rewriting the existing note
      prompt = `You are an expert note editor. Your task is to enrich an existing note by adding relevant information from a provided resource, WITHOUT modifying or rewriting the existing content.

LANGUAGE RULE: Respond in ${lang}. Match the language of the existing note.
FORMAT RULE: Respond in ${outputFormat}.

EXISTING NOTE:
---
${existingContent || '(empty note)'}
---

RESOURCE TO INTEGRATE:
---
${resourceText}
---

INSTRUCTIONS:
- Keep ALL existing note content exactly as-is at the top
- Append ONLY new, non-redundant information from the resource below the existing content
- Use a clear separator (e.g., "---" or a new section heading) between existing and new content
- Skip information already covered in the existing note
- Format the new content consistently with the existing note style and the requested FORMAT RULE
- Respond ONLY with the enriched note content, no explanations`
    } else {
      // Merge: intelligently rewrite integrating both sources
      prompt = `You are an expert note writer. Your task is to intelligently merge an existing note with a resource into a single, coherent, well-structured document.

LANGUAGE RULE: Respond in ${lang}. Match the language of the existing note.
FORMAT RULE: Respond in ${outputFormat}.

EXISTING NOTE:
---
${existingContent || '(empty note)'}
---

RESOURCE TO INTEGRATE:
---
${resourceText}
---

INSTRUCTIONS:
- Combine both sources into one cohesive, well-organized document
- Eliminate redundancy — include each piece of information only once
- Preserve the key ideas from both sources
- Maintain a logical structure with clear headings if appropriate
- Keep the tone and style consistent with the requested FORMAT RULE
- Respond ONLY with the merged content, no meta-commentary or explanations`
    }

    const enrichedContent = await provider.generateText(prompt)

    return NextResponse.json({ enrichedContent: enrichedContent.trim() })
  } catch (error: any) {
    console.error('[enrich-from-resource] Error:', error)
    return NextResponse.json(
      { error: error.message || 'Failed to enrich content' },
      { status: 500 }
    )
  }
}