Book‑Builder

A mobile‑first web app and workflow toolkit that turns your big, nested outline into a polished manuscript. It combines Next.js + Tailwind for the UI, n8n for orchestration, Supabase for the data layer, and Fly.io for hosting. It leverages an advanced LLM like GPT-4.1 (or similar models with large context windows, e.g., 1 million tokens) for its intelligence, offering a blend of power, cost-effectiveness, and smart content generation.

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What It Does

Phase	Purpose	Key Workflow
1. World‑Building	Capture facts about characters, lore, timelines. Extract triples & store them for semantic recall.	/webhook/world-builder
2. Multi‑Level Outlining	Nest writing‑formula steps (Hero's Journey, etc.) 3–4 layers deep.	/webhook/outline-generator
3. Draft Writing	Generate, iterate, and commit prose for each section.	/webhook/draft-generator

Each phase is a standalone n8n workflow with its own webhook, so you can toggle between them in the mobile UI.

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🖼️ High‑Level Architecture

Mobile PWA (Next.js)  <----->  Supabase Edge Functions  <----->  Supabase Postgres
                                       |                                |  (pgvector, ltree)
                                       |                                |
                             +---------------------+
                             |  n8n (Fly.io)       |
                             |  – World Builder    |
                             |  – Outliner         |
                             |  – Draft Writer     |
                             +---------------------+
                                       |
                                       |
                                 LLM (GPT-4.1)

Front End

• Next.js / React – routes & API proxies.
• Tailwind CSS – utility‑first, mobile‑first.
• Headless UI + react‑swipeable – swipe drawers for TOC & settings.
• React Query – caching & realtime updates.

Orchestration

• n8n – three modular workflows (one per phase) exposed via webhooks.

Data Layer

• Supabase Postgres – single source‑of‑truth with pgvector + ltree.
• Realtime – push section updates to the UI.
• Auth – row‑level security.

Hosting

• Fly.io – Dockerized deployments for both Next.js and n8n.

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Database Schema (Supabase)

Core Tables

Table	Purpose	Highlight Columns
sections	Outline & manuscript tree	id, parent_id, position (ltree), title, is_title (bool), content_type (outline|draft|final), formula_layer, text, outline_notes
formulas	Writing‑cycle templates	id, name, mood_id, template, default_length, default_temp
moods	Voice & style snippets	id, label, prompt_snippet
entities	Characters / objects / places	id, type, name, attributes (jsonb), biography
facts	RDF‑style triples	id, subject_id, predicate, object, started_at, ended_at, context_section
embeddings	Semantic search	id, section_id, vector (pgvector)

Indexes & Extensions

• ltree on sections.position – fast subtree queries.
• Full‑text index on sections.text.
• pgvector on embeddings.vector for similarity search.
• JSONB GIN on entities.attributes.

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n8n Workflows

1. World‑Building (/webhook/world-builder)

1. Webhook → Function (normalize) → Airtable/Supabase upsert entities
2. HTTP Request to LLM → extract triples & attributes
3. SplitInBatches → insert into facts
4. Respond with JSON form for UI pre‑fill

2. Outline Generator (/webhook/outline-generator)

1. Fetch current context (parent section)
2. For each formula step: HTTP → LLM to get sub‑outline (requires very detailed prompts).
3. Merge & write into sections (content_type=outline)
4. Return updated outline JSON

3. Draft Writer (/webhook/draft-generator)

1. Build prompt from sections, moods, formulas (requires very detailed prompts).
2. HTTP → LLM generate prose.
3. Engage in an iterative refinement process with the user, allowing for multiple rounds of feedback and LLM-driven revisions (individual revisions are not stored).
4. Commit final text (content_type=final) + Git mirror (optional).
5. Slack/email notification

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Getting Started

Prerequisites

• Node >= 18
• Docker & Fly CLI
• Supabase account (free tier OK)
• n8n cloud or self‑host

Environment Variables

# /.env
SUPABASE_URL=…
SUPABASE_ANON_KEY=…
N8N_WEBHOOK_URL=https://<flyapp>.fly.dev/webhook/
OPENAI_API_KEY=…

Local Dev

yarn install
supabase start    # spin up local Postgres
npx supabase db push   # apply schema
npx supabase gen types typescript --local
yarn dev          # next dev on http://localhost:3000

Deploy

fly launch        # generates fly.toml
fly deploy        # pushes Next.js
fly scale vm shared-cpu-1x

For n8n, either:

• Use n8n Cloud → set N8N_WEBHOOK_URL accordingly, or
• fly launch a second app with the n8n Docker image.

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Development Tips

• Cursor AI: prompt it to scaffold React components & API routes.
• Detailed Prompts: Crafting highly detailed and specific prompts for the LLM is crucial for achieving desired outputs in all phases.
• Branch‑per‑chapter workflow: use Supabase RLS + Git history to prevent merge pain.
• Error Handling: every AI call in n8n gets an error branch → Slack.
• Testing: Thoroughly test workflows, potentially using mock LLM responses for consistency and focusing on data integrity within Supabase.

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Roadmap / Nice‑To‑Haves

• Visual timeline Gantt chart for facts & events
• Embedding‑powered "similar scene" suggestions

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📄 License

MIT © Jeff Steele