// Package queue provides task queue functionality
package queue

import (
	"errors"
	"fmt"
	"strings"
)

// ErrorCategory represents the type of error encountered
type ErrorCategory string

// Error categories for task classification and retry logic
const (
	ErrorNetwork    ErrorCategory = "network"    // Network connectivity issues
	ErrorResource   ErrorCategory = "resource"   // Resource exhaustion (OOM, disk full)
	ErrorRateLimit  ErrorCategory = "rate_limit" // Rate limiting or throttling
	ErrorAuth       ErrorCategory = "auth"       // Authentication/authorization failures
	ErrorValidation ErrorCategory = "validation" // Input validation errors
	ErrorTimeout    ErrorCategory = "timeout"    // Operation timeout
	ErrorPermanent  ErrorCategory = "permanent"  // Non-retryable errors
	ErrorUnknown    ErrorCategory = "unknown"    // Unclassified errors
)

// TaskError wraps an error with category and context
type TaskError struct {
	Category ErrorCategory
	Message  string
	Cause    error
	Context  map[string]string
}

func (e *TaskError) Error() string {
	if e.Cause != nil {
		return fmt.Sprintf("[%s] %s: %v", e.Category, e.Message, e.Cause)
	}
	return fmt.Sprintf("[%s] %s", e.Category, e.Message)
}

func (e *TaskError) Unwrap() error {
	return e.Cause
}

// NewTaskError creates a new categorized error
func NewTaskError(category ErrorCategory, message string, cause error) *TaskError {
	return &TaskError{
		Category: category,
		Message:  message,
		Cause:    cause,
		Context:  make(map[string]string),
	}
}

// ClassifyError categorizes an error for retry logic
func ClassifyError(err error) ErrorCategory {
	if err == nil {
		return ErrorUnknown
	}

	// Check if already classified
	var taskErr *TaskError
	if errors.As(err, &taskErr) {
		return taskErr.Category
	}

	errStr := strings.ToLower(err.Error())

	// Network errors (retryable)
	networkIndicators := []string{
		"connection refused",
		"connection reset",
		"connection timeout",
		"no route to host",
		"network unreachable",
		"temporary failure",
		"dns",
		"dial tcp",
		"i/o timeout",
	}
	for _, indicator := range networkIndicators {
		if strings.Contains(errStr, indicator) {
			return ErrorNetwork
		}
	}

	// Resource errors (retryable after delay)
	resourceIndicators := []string{
		"out of memory",
		"oom",
		"no space left",
		"disk full",
		"resource temporarily unavailable",
		"too many open files",
		"cannot allocate memory",
	}
	for _, indicator := range resourceIndicators {
		if strings.Contains(errStr, indicator) {
			return ErrorResource
		}
	}

	// Rate limiting (retryable with backoff)
	rateLimitIndicators := []string{
		"rate limit",
		"too many requests",
		"throttle",
		"quota exceeded",
		"429",
	}
	for _, indicator := range rateLimitIndicators {
		if strings.Contains(errStr, indicator) {
			return ErrorRateLimit
		}
	}

	// Timeout errors (retryable)
	timeoutIndicators := []string{
		"timeout",
		"deadline exceeded",
		"context deadline",
	}
	for _, indicator := range timeoutIndicators {
		if strings.Contains(errStr, indicator) {
			return ErrorTimeout
		}
	}

	// Authentication errors (not retryable)
	authIndicators := []string{
		"unauthorized",
		"forbidden",
		"authentication failed",
		"invalid credentials",
		"access denied",
		"401",
		"403",
	}
	for _, indicator := range authIndicators {
		if strings.Contains(errStr, indicator) {
			return ErrorAuth
		}
	}

	// Validation errors (not retryable)
	validationIndicators := []string{
		"invalid input",
		"validation failed",
		"bad request",
		"malformed",
		"400",
	}
	for _, indicator := range validationIndicators {
		if strings.Contains(errStr, indicator) {
			return ErrorValidation
		}
	}

	// Default to unknown
	return ErrorUnknown
}

// IsRetryable determines if an error category should be retried
func IsRetryable(category ErrorCategory) bool {
	switch category {
	case ErrorNetwork, ErrorResource, ErrorRateLimit, ErrorTimeout, ErrorUnknown:
		return true
	case ErrorAuth, ErrorValidation, ErrorPermanent:
		return false
	default:
		return false
	}
}

// GetUserMessage returns a user-friendly error message with suggestions
func GetUserMessage(category ErrorCategory, err error) string {
	messages := map[ErrorCategory]string{
		ErrorNetwork: "Network connectivity issue. Please check your network " +
			"connection and try again.",
		ErrorResource: "System resource exhausted. The system may be under heavy load. " +
			"Try again later or contact support.",
		ErrorRateLimit:  "Rate limit exceeded. Please wait a moment before retrying.",
		ErrorAuth:       "Authentication failed. Please check your API key or credentials.",
		ErrorValidation: "Invalid input. Please review your request and correct any errors.",
		ErrorTimeout: "Operation timed out. The task may be too complex or the system is slow. " +
			"Try again or simplify the request.",
		ErrorPermanent: "A permanent error occurred. This task cannot be retried automatically.",
		ErrorUnknown:   "An unexpected error occurred. If this persists, please contact support.",
	}

	baseMsg := messages[category]
	if err != nil {
		return fmt.Sprintf("%s (Details: %v)", baseMsg, err)
	}
	return baseMsg
}

// RetryDelay calculates the retry delay based on error category and retry count
func RetryDelay(category ErrorCategory, retryCount int) int {
	switch category {
	case ErrorRateLimit:
		// Longer backoff for rate limits
		return intMin(300, 10*(1<<retryCount)) // 10s, 20s, 40s, 80s, up to 300s
	case ErrorResource:
		// Medium backoff for resource issues
		return intMin(120, 5*(1<<retryCount)) // 5s, 10s, 20s, 40s, up to 120s
	case ErrorNetwork, ErrorTimeout:
		// Standard exponential backoff
		return 1 << retryCount // 1s, 2s, 4s, 8s, etc
	case ErrorAuth, ErrorValidation, ErrorPermanent:
		// No retry for auth, validation, or permanent errors
		return 0
	case ErrorUnknown:
		// Conservative backoff for unknown errors
		return 1 << retryCount
	default:
		// Fallback for any unexpected categories
		return 1 << retryCount
	}
}

func intMin(a, b int) int {
	if a < b {
		return a
	}
	return b
}