package jobs

import (
	"context"
	"encoding/json"
	"fmt"
	"sync"
)

// Handler defines the function signature for executing a job.
type Handler func(ctx context.Context, payload json.RawMessage) error

// Runner manages the registration and execution of worker job handlers.
type Runner struct {
	mu       sync.RWMutex
	handlers map[Kind]Handler
}

// NewRunner creates a new Runner instance.
func NewRunner() *Runner {
	return &Runner{
		handlers: make(map[Kind]Handler),
	}
}

// Register registers a handler for a specific job kind.
func (r *Runner) Register(kind Kind, handler Handler) {
	r.mu.Lock()
	defer r.mu.Unlock()
	r.handlers[kind] = handler
}

// Len returns the number of registered handlers.
func (r *Runner) Len() int {
	r.mu.RLock()
	defer r.mu.RUnlock()
	return len(r.handlers)
}

// Execute dispatches the job to its registered handler and executes it.
// It checks context cancellation and handles panics gracefully.
func (r *Runner) Execute(ctx context.Context, job Job) error {
	r.mu.RLock()
	handler, exists := r.handlers[job.Kind]
	r.mu.RUnlock()

	if !exists {
		return fmt.Errorf("unknown job kind: %s", job.Kind)
	}

	// Check context before starting
	if err := ctx.Err(); err != nil {
		return err
	}

	return r.executeWithPanicRecovery(ctx, handler, job.Payload)
}

func (r *Runner) executeWithPanicRecovery(ctx context.Context, handler Handler, payload json.RawMessage) (err error) {
	defer func() {
		if rec := recover(); rec != nil {
			err = fmt.Errorf("job panicked: %v", rec)
		}
	}()
	return handler(ctx, payload)
}