// Package errorbus provides a channel-based error bus implementation.
package errorbus

import (
	"context"
	"runtime"
	"sync"

	"git.dcentral.systems/toolz/goplt/pkg/errorbus"
	"git.dcentral.systems/toolz/goplt/pkg/logger"
)

// ChannelBus implements a channel-based error bus.
type ChannelBus struct {
	errors    chan errorWithContext
	logger    logger.Logger
	done      chan struct{}
	wg        sync.WaitGroup
	once      sync.Once
	closeOnce sync.Once
}

type errorWithContext struct {
	err   error
	ctx   context.Context
	stack []byte
}

// NewChannelBus creates a new channel-based error bus.
func NewChannelBus(log logger.Logger, bufferSize int) *ChannelBus {
	if bufferSize <= 0 {
		bufferSize = 100
	}

	bus := &ChannelBus{
		errors: make(chan errorWithContext, bufferSize),
		logger: log,
		done:   make(chan struct{}),
	}

	// Start background consumer
	bus.wg.Add(1)
	go bus.consume()

	return bus
}

// Publish publishes an error to the error bus.
func (b *ChannelBus) Publish(ctx context.Context, err error) {
	if err == nil {
		return
	}

	// Capture stack trace
	stack := make([]byte, 4096)
	n := runtime.Stack(stack, false)
	stack = stack[:n]

	select {
	case b.errors <- errorWithContext{
		err:   err,
		ctx:   ctx,
		stack: stack,
	}:
		// Successfully queued
	default:
		// Channel is full, log directly to avoid blocking
		b.logger.Error("Error bus channel full, logging directly",
			logger.String("error", err.Error()),
		)
	}
}

// consume consumes errors from the channel and logs them.
func (b *ChannelBus) consume() {
	defer b.wg.Done()

	for {
		select {
		case errCtx := <-b.errors:
			b.handleError(errCtx)
		case <-b.done:
			return
		}
	}
}

// handleError handles a single error by logging it with context.
func (b *ChannelBus) handleError(errCtx errorWithContext) {
	fields := []logger.Field{
		logger.String("error", errCtx.err.Error()),
	}

	// Extract request ID from context
	if requestID := extractRequestID(errCtx.ctx); requestID != "" {
		fields = append(fields, logger.String("request_id", requestID))
	}

	// Extract user ID from context
	if userID := extractUserID(errCtx.ctx); userID != "" {
		fields = append(fields, logger.String("user_id", userID))
	}

	// Add stack trace for debugging
	if len(errCtx.stack) > 0 {
		fields = append(fields, logger.String("stack", string(errCtx.stack)))
	}

	b.logger.Error("Error captured by error bus", fields...)

	// TODO: In Epic 6, add Sentry integration here
	// if b.sentryClient != nil {
	//     b.sentryClient.CaptureException(errCtx.err, ...)
	// }
}

// extractRequestID extracts request ID from context.
func extractRequestID(ctx context.Context) string {
	if ctx == nil {
		return ""
	}
	// Try common context key patterns
	if val := ctx.Value("request_id"); val != nil {
		if str, ok := val.(string); ok {
			return str
		}
	}
	if val := ctx.Value("RequestID"); val != nil {
		if str, ok := val.(string); ok {
			return str
		}
	}
	return ""
}

// extractUserID extracts user ID from context.
func extractUserID(ctx context.Context) string {
	if ctx == nil {
		return ""
	}
	// Try common context key patterns
	if val := ctx.Value("user_id"); val != nil {
		if str, ok := val.(string); ok {
			return str
		}
	}
	if val := ctx.Value("UserID"); val != nil {
		if str, ok := val.(string); ok {
			return str
		}
	}
	return ""
}

// Close closes the error bus and waits for all errors to be processed.
func (b *ChannelBus) Close() error {
	b.once.Do(func() {
		close(b.done)
	})
	b.wg.Wait()
	b.closeOnce.Do(func() {
		close(b.errors)
	})
	return nil
}

// Ensure ChannelBus implements ErrorPublisher
var _ errorbus.ErrorPublisher = (*ChannelBus)(nil)