package valid

import (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"sort"
	"strings"
	"text/template"
)

var (
	// ErrStructPointer is the error that a struct being validated is not specified as a pointer.
	ErrStructPointer = errors.New("only a pointer to a struct can be validated")
)

// ErrorTag is the struct tag name used to customize the error field name for a struct field.
var ErrorTag = "json"

// Error interface represents an validation error
type Error interface {
	Error() string
	Code() string
	Message() string
	SetMessage(string) Error
	Params() map[string]interface{}
	SetParams(map[string]interface{}) Error
}

// InternalError represents an error that should NOT be treated as a validation error.
type InternalError interface {
	error
	InternalError() error
}

type internalError struct {
	error
}

// NewInternalError wraps a given error into an InternalError.
func NewInternalError(err error) InternalError {
	return internalError{error: err}
}

// InternalError returns the actual error that it wraps around.
func (e internalError) InternalError() error {
	return e.error
}

// Errors represents the validation errors that are indexed by struct field names, map or slice keys.
// values are Error or Errors (for map, slice and array error value is Errors).
type Errors map[string]error

// Error returns the error string of Errors.
func (es Errors) Error() string {
	if len(es) == 0 {
		return ""
	}

	keys := make([]string, len(es))
	i := 0
	for key := range es {
		keys[i] = key
		i++
	}
	sort.Strings(keys)

	var s strings.Builder
	for i, key := range keys {
		if i > 0 {
			s.WriteString("; ")
		}
		if errs, ok := es[key].(Errors); ok {
			_, _ = fmt.Fprintf(&s, "%v: (%v)", key, errs)
		} else {
			_, _ = fmt.Fprintf(&s, "%v: %v", key, es[key].Error())
		}
	}
	s.WriteString(".")
	return s.String()
}

// MarshalJSON converts the Errors into a valid JSON.
func (es Errors) MarshalJSON() ([]byte, error) {
	errs := map[string]interface{}{}
	for key, err := range es {
		if ms, ok := err.(json.Marshaler); ok {
			errs[key] = ms
		} else {
			errs[key] = err.Error()
		}
	}
	return json.Marshal(errs)
}

// Filter removes all nils from Errors and returns back the updated Errors as an error.
// If the length of Errors becomes 0, it will return nil.
func (es Errors) Filter() error {
	for key, value := range es {
		if value == nil {
			delete(es, key)
		}
	}
	if len(es) == 0 {
		return nil
	}
	return es
}

// NewError create new validation error.
func NewError(code, message string) Error {
	return ErrorObject{
		code:    code,
		message: message,
	}
}

// Assert that our ErrorObject implements the Error interface.
var _ Error = ErrorObject{}

// ErrorObject is the default validation error
// that implements the Error interface.
type ErrorObject struct {
	code    string
	message string
	params  map[string]interface{}
}

// SetCode set the error's translation code.
func (e ErrorObject) SetCode(code string) Error {
	e.code = code
	return e
}

// Code get the error's translation code.
func (e ErrorObject) Code() string {
	return e.code
}

// SetParams set the error's params.
func (e ErrorObject) SetParams(params map[string]interface{}) Error {
	e.params = params
	return e
}

// AddParam add parameter to the error's parameters.
func (e ErrorObject) AddParam(name string, value interface{}) Error {
	if e.params == nil {
		e.params = make(map[string]interface{})
	}

	e.params[name] = value
	return e
}

// Params returns the error's params.
func (e ErrorObject) Params() map[string]interface{} {
	return e.params
}

// SetMessage set the error's message.
func (e ErrorObject) SetMessage(message string) Error {
	e.message = message
	return e
}

// Message return the error's message.
func (e ErrorObject) Message() string {
	return e.message
}

// Error returns the error message.
func (e ErrorObject) Error() string {
	if len(e.params) == 0 {
		return e.message
	}

	res := bytes.Buffer{}
	_ = template.Must(template.New("err").Parse(e.message)).Execute(&res, e.params)

	return res.String()
}

// ErrFieldPointer is the error that a field is not specified as a pointer.
type ErrFieldPointer int

// Error returns the error string of ErrFieldPointer.
func (e ErrFieldPointer) Error() string {
	return fmt.Sprintf("field #%v must be specified as a pointer", int(e))
}

// ErrFieldNotFound is the error that a field cannot be found in the struct.
type ErrFieldNotFound int

// Error returns the error string of ErrFieldNotFound.
func (e ErrFieldNotFound) Error() string {
	return fmt.Sprintf("field #%v cannot be found in the struct", int(e))
}