package solver

import (
	"context"
	"runtime"
	"sync/atomic"

	"hash-of-wisdom/internal/pow/challenge"
)

// Solver handles parallel PoW solving with configurable parallelism
type Solver struct {
	workers int
}

// SolverOption represents functional options for solver configuration
type solverOption func(*Solver)

// WithWorkers sets the number of parallel workers
func WithWorkers(workers int) solverOption {
	return func(s *Solver) {
		s.workers = workers
	}
}

// NewSolver creates a new parallel PoW solver
func NewSolver(options ...solverOption) *Solver {
	solver := &Solver{
		workers: runtime.NumCPU(), // Default to CPU count
	}

	for _, option := range options {
		option(solver)
	}

	return solver
}

// Solve attempts to find a valid nonce for the given challenge
func (s *Solver) Solve(ctx context.Context, ch *challenge.Challenge) (*challenge.Solution, error) {
	// Create cancellable context for workers
	ctx, cancel := context.WithCancel(ctx)
	defer cancel()

	// Channel to receive solution from any worker
	solutionCh := make(chan *challenge.Solution, 1)

	// Shared nonce counter for work distribution
	var nonceCounter atomic.Uint64

	// Start parallel workers
	for i := range s.workers {
		go func(workerID int) {
			s.worker(ctx, ch, &nonceCounter, solutionCh)
		}(i)
	}

	// Wait for either solution or context cancellation
	select {
	case solution := <-solutionCh:
		return solution, nil
	case <-ctx.Done():
		return nil, ctx.Err()
	}
}

// worker performs PoW computation in parallel
func (s *Solver) worker(ctx context.Context, ch *challenge.Challenge, nonceCounter *atomic.Uint64, solutionCh chan<- *challenge.Solution) {

	for {
		select {
		case <-ctx.Done():
			return
		default:
			// Get next nonce to try
			nonce := nonceCounter.Add(1) - 1

			// Try this nonce
			if ch.VerifySolution(nonce) {
				// Found solution! Send it back
				solution := &challenge.Solution{
					Challenge: *ch,
					Nonce:     nonce,
				}

				select {
				case solutionCh <- solution:
				case <-ctx.Done():
				}
				return
			}
		}
	}
}