feat: Add extensible submit provider system with Kattis support

[yuuhikaze]

Submit Provider System

This PR introduces a generic submission system for competitive programming judges, with Kattis as the first implementation.

🎯 Overview

Adds the ability to submit solutions directly from Neovim to online judges through an extensible provider architecture. Users can now compete on Kattis without leaving their editor!

Features

• 🔌 Extensible Provider System - Easy to add support for other judges (Codeforces, AtCoder, USACO, etc.)
• 🚀 Async/Non-blocking - Uses vim.loop.spawn() for all network operations, Neovim stays responsive
• 📁 Multi-file Submissions - File picker (snacks.nvim preferred, nui.nvim fallback) for Java/Kotlin projects
• 📊 Live Status Tracking - Background polling with test case progress
• 🎨 Beautiful Notifications - Clean 3-step notification flow (works great with noice.nvim!)
• ✅ Production Ready - Comprehensive QA, handles edge cases, proper resource cleanup
• ✅ Opt-in Providers - Users must explicitly enable providers to prevent unwanted errors

🖼️ Demo

Shows both failed (Wrong Answer with test case count) and successful (Accepted) submission workflows. Notifications styled with noice.nvim.

🔧 Architecture

Provider Interface

---@class competitest.SubmitProvider
---@field name string
---@field supports_multiple_files boolean
---@field setup fun(config: table): boolean, string?
---@field can_submit fun(bufnr: integer, opts): boolean, string?
---@field submit fun(bufnr: integer, opts, callback)
---@field submit_multiple fun(files: string[], opts, callback)?
---@field get_status fun(submission_id: string, callback)?

Files Added

• lua/competitest/submit/init.lua - Provider registry and orchestration
• lua/competitest/submit/ui.lua - File picker (snacks/nui)
• lua/competitest/submit/providers/kattis.lua - Kattis implementation
• Updates to commands.lua, config.lua, utils.lua for integration

📝 Usage

Commands

:CompetiTest submit [provider] [problem_id]
:CompetiTest submit_multiple [provider] [problem_id]

Configuration

⚠️ Providers are opt-in - you must explicitly enable them:

require('competitest').setup({
  submit = {
    kattis = {
      enable = true,  -- REQUIRED to use provider, in this case, Kattis
      config_file = vim.fn.expand('~/.kattisrc'),  -- this is the default, can be changed
    },
  },
})

Without enable = true, the Kattis provider won't be initialized and you won't get errors if .kattisrc is missing.

Kattis Setup

1. Download .kattisrc from https://open.kattis.com/download/kattisrc
2. Place in ~/.kattisrc (or specify in config)
3. Submit: :CompetiTest submit kattis (auto-detects problem ID from filename)

🎨 Notification Flow

1. "Submitting..." - Immediate feedback
2. "Submitted successfully! - View: [URL]" - Upload complete with submission link
3. "Accepted" or "Wrong Answer (failed 3/10 test cases)" - Final result with details

Recommended: Use noice.nvim for beautiful styled notifications with icons (✓ for success, ✕ for errors).

🔒 Implementation Details

Async Safety

• All HTTP via vim.loop.spawn("curl", ...) - no blocking
• Proper callback chains with vim.schedule_wrap()
• Resource cleanup: timers, pipes, handles (with is_closing() checks)
• Retry logic for transient network errors

Kattis Provider

• Parses .kattisrc (supports both : and = delimiters)
• Language auto-detection from file extension (with fallback)
• Mainclass detection for Java/Kotlin/Scala
• Problem ID from filename (lowercase)
• Status polling every 250ms, max 60s timeout
• Test case visualization: [....x.?] notation

Provider Loading (Opt-in)

• Providers are only loaded if explicitly enabled in config
• enable = true required in provider config table
• Provider setup() called immediately during registration
• User gets immediate feedback if provider configuration is invalid
• No warnings or errors for unconfigured providers

🧪 Testing

Tested on:

• Kattis open.kattis.com
• Single-file submissions (Python, Zig, Rust, C++)
• Multi-file submissions (Java)
• Both successful and failed submissions
• Network errors and timeouts

🚀 Future Extensions

The provider system makes it easy to add:

• Codeforces - Login via API, submit with session cookies
• AtCoder - Similar to Codeforces
• USACO - Submit via web form
• LeetCode - GraphQL API integration

📚 Related

• Original Kattis CLI: https://github.com/Kattis/kattis-cli
• Addresses feature request from community for submission support

✅ Checklist

• Code follows existing style and patterns
• LuaCATS type annotations
• Async-safe (no blocking calls)
• Resource cleanup (timers, pipes, handles)
• Tested with real submissions
• Works with existing competitest.nvim features
• No new required dependencies (only system curl)
• Providers are opt-in to prevent unwanted errors

---

Note: This PR is ready for review and merge. The provider system is production-ready and has been thoroughly tested. Future providers can be added incrementally without breaking changes.

🤖 Generated with Claude Code

Co-Authored-By: Claude noreply@anthropic.com

[yuuhikaze]

Ok so I added the opt-in behavior I mentioned on the previous PR
It got closed because I got banned from GitHub haha (system's fault)
Please tell me @xeluxee if you need me to change something