// Package errors provides a unified error model for the Cyrene platform.
// All errors flowing through the system should use AppError or its subtypes.
// This ensures consistent error codes, user-friendly messages, and HTTP status mapping.
package errors

import (
	"fmt"
	"net/http"
)

// AppError is the unified application error type.
type AppError struct {
	Code     string // Machine-readable error code (e.g., "USER_NOT_FOUND")
	Message  string // Human-readable message (safe to show to users)
	Cause    error  // Original error (internal only, not exposed to clients)
	HTTPCode int    // HTTP status code
}

// Error implements the error interface.
func (e *AppError) Error() string {
	if e.Cause != nil {
		return fmt.Sprintf("[%s] %s: %v", e.Code, e.Message, e.Cause)
	}
	return fmt.Sprintf("[%s] %s", e.Code, e.Message)
}

// Unwrap returns the underlying cause error.
func (e *AppError) Unwrap() error {
	return e.Cause
}

// --- Pre-defined common errors ---

// NewNotFound creates a NOT_FOUND error.
func NewNotFound(message string) *AppError {
	return &AppError{Code: "NOT_FOUND", Message: message, HTTPCode: http.StatusNotFound}
}

// NewUnauthorized creates an UNAUTHORIZED error.
func NewUnauthorized(message string) *AppError {
	return &AppError{Code: "UNAUTHORIZED", Message: message, HTTPCode: http.StatusUnauthorized}
}

// NewForbidden creates a FORBIDDEN error.
func NewForbidden(message string) *AppError {
	return &AppError{Code: "FORBIDDEN", Message: message, HTTPCode: http.StatusForbidden}
}

// NewBadRequest creates a BAD_REQUEST error.
func NewBadRequest(message string) *AppError {
	return &AppError{Code: "BAD_REQUEST", Message: message, HTTPCode: http.StatusBadRequest}
}

// NewConflict creates a CONFLICT error.
func NewConflict(message string) *AppError {
	return &AppError{Code: "CONFLICT", Message: message, HTTPCode: http.StatusConflict}
}

// NewTooManyRequests creates a TOO_MANY_REQUESTS error.
func NewTooManyRequests(message string) *AppError {
	return &AppError{Code: "TOO_MANY_REQUESTS", Message: message, HTTPCode: http.StatusTooManyRequests}
}

// NewInternal creates an INTERNAL error with a generic message for clients.
// The cause is logged internally but not exposed.
func NewInternal(message string, cause error) *AppError {
	return &AppError{Code: "INTERNAL", Message: message, HTTPCode: http.StatusInternalServerError, Cause: cause}
}

// NewValidation creates a VALIDATION error.
func NewValidation(message string) *AppError {
	return &AppError{Code: "VALIDATION", Message: message, HTTPCode: http.StatusBadRequest}
}

// --- Constructors with cause ---

// Wrap wraps an existing error with an application error.
func Wrap(err error, code, message string, httpCode int) *AppError {
	return &AppError{Code: code, Message: message, HTTPCode: httpCode, Cause: err}
}

// WrapNotFound wraps an error as NOT_FOUND.
func WrapNotFound(err error, message string) *AppError {
	return &AppError{Code: "NOT_FOUND", Message: message, HTTPCode: http.StatusNotFound, Cause: err}
}

// WrapBadRequest wraps an error as BAD_REQUEST.
func WrapBadRequest(err error, message string) *AppError {
	return &AppError{Code: "BAD_REQUEST", Message: message, HTTPCode: http.StatusBadRequest, Cause: err}
}

// WrapInternal wraps an error as INTERNAL.
func WrapInternal(err error, message string) *AppError {
	return &AppError{Code: "INTERNAL", Message: message, HTTPCode: http.StatusInternalServerError, Cause: err}
}

// --- Helpers ---

// IsAppError checks if the error is an AppError.
func IsAppError(err error) (*AppError, bool) {
	if err == nil {
		return nil, false
	}
	ae, ok := err.(*AppError)
	return ae, ok
}

// StatusCode extracts the HTTP status code from an error.
// Returns 500 if the error is not an AppError.
func StatusCode(err error) int {
	if ae, ok := IsAppError(err); ok {
		return ae.HTTPCode
	}
	return http.StatusInternalServerError
}

// Message extracts the user-safe message from an error.
// Returns a generic message if the error is not an AppError.
func Message(err error) string {
	if ae, ok := IsAppError(err); ok {
		return ae.Message
	}
	return "Internal server error"
}

// Code extracts the machine-readable error code.
// Returns "INTERNAL" if the error is not an AppError.
func Code(err error) string {
	if ae, ok := IsAppError(err); ok {
		return ae.Code
	}
	return "INTERNAL"
}

// --- Sentinel errors for quick checks ---

var (
	// ErrUnauthorized is a pre-built unauthorized error.
	ErrUnauthorized = &AppError{Code: "UNAUTHORIZED", Message: "Authentication required", HTTPCode: http.StatusUnauthorized}

	// ErrForbidden is a pre-built forbidden error.
	ErrForbidden = &AppError{Code: "FORBIDDEN", Message: "Insufficient permissions", HTTPCode: http.StatusForbidden}

	// ErrInternal is a pre-built internal error.
	ErrInternal = &AppError{Code: "INTERNAL", Message: "Internal server error", HTTPCode: http.StatusInternalServerError}
)

// IsCode checks if the error has the given error code.
func IsCode(err error, code string) bool {
	if ae, ok := IsAppError(err); ok {
		return ae.Code == code
	}
	return false
}

// IsNotFound checks if the error is a NOT_FOUND error.
func IsNotFound(err error) bool {
	return IsCode(err, "NOT_FOUND")
}