package errcode

import (
	"fmt"
	"net/http"
	"strings"
	"sync"
)

// ErrorCode represents the error type. The errors are serialized via strings
// and the integer format may change and should *never* be exported.
type ErrorCode int

// ErrorDescriptor provides relevant information about a given error code.
type ErrorDescriptor struct {
	// Code is the error code that this descriptor describes.
	Code ErrorCode

	// Value provides a unique, string key, often captilized with
	// underscores, to identify the error code. This value is used as the
	// keyed value when serializing api errors.
	Value string

	// Message is a short, human readable decription of the error condition
	// included in API responses.
	Message string

	// Description provides a complete account of the errors purpose, suitable
	// for use in documentation.
	Description string

	// HTTPStatusCode provides the http status code that is associated with
	// this error condition.
	HTTPStatusCode int
}

var (
	errorCodeToDescriptors = map[ErrorCode]ErrorDescriptor{}
	idToDescriptors        = map[string]ErrorDescriptor{}
	groupToDescriptors     = map[string][]ErrorDescriptor{}
)

// ErrorCodeUnknown is a generic error that can be used as a last
// resort if there is no situation-specific error message that can be used
var ErrorCodeUnknown = Register("registry.api.errcode", ErrorDescriptor{
	Value:   "UNKNOWN",
	Message: "unknown error",
	Description: `Generic error returned when the error does not have an
									        API classification.`,
	HTTPStatusCode: http.StatusInternalServerError,
})

var nextCode = 1000
var registerLock sync.Mutex

// Register will make the passed-in error known to the environment and
// return a new ErrorCode
func Register(group string, descriptor ErrorDescriptor) ErrorCode {
	registerLock.Lock()
	defer registerLock.Unlock()
	code := ErrorCode(nextCode)

	descriptor.Code = code

	if _, ok := idToDescriptors[descriptor.Value]; ok {
		panic(fmt.Sprintf("ErrorValue %s is already registered", descriptor.Value))
	}
	if _, ok := errorCodeToDescriptors[descriptor.Code]; ok {
		panic(fmt.Sprintf("ErrorCode %d is already registered", descriptor.Code))
	}

	groupToDescriptors[group] = append(groupToDescriptors[group], descriptor)
	errorCodeToDescriptors[code] = descriptor
	idToDescriptors[descriptor.Value] = descriptor

	nextCode++
	return code
}

// ParseErrorCode returns the value by the string error code.
// `ErrorCodeUnknown` will be returned if the error is not known.
func ParseErrorCode(value string) ErrorCode {
	ed, ok := idToDescriptors[value]
	if ok {
		return ed.Code
	}

	return ErrorCodeUnknown
}

// GetGroupNames returns the list of Error group names that are registered
func GetGroupNames() []string {
	keys := []string{}

	for k := range groupToDescriptors {
		keys = append(keys, k)
	}
	return keys
}

// GetErrorCodeGroup returns the named group of error descriptors
func GetErrorCodeGroup(name string) []ErrorDescriptor {
	return groupToDescriptors[name]
}

// Descriptor returns the descriptor for the error code.
func (ec ErrorCode) Descriptor() ErrorDescriptor {
	d, ok := errorCodeToDescriptors[ec]

	if !ok {
		return ErrorCodeUnknown.Descriptor()
	}

	return d
}

// String returns the canonical identifier for this error code.
func (ec ErrorCode) String() string {
	return ec.Descriptor().Value
}

// Message returned the human-readable error message for this error code.
func (ec ErrorCode) Message() string {
	return ec.Descriptor().Message
}

// MarshalText encodes the receiver into UTF-8-encoded text and returns the
// result.
func (ec ErrorCode) MarshalText() (text []byte, err error) {
	return []byte(ec.String()), nil
}

// UnmarshalText decodes the form generated by MarshalText.
func (ec *ErrorCode) UnmarshalText(text []byte) error {
	desc, ok := idToDescriptors[string(text)]

	if !ok {
		desc = ErrorCodeUnknown.Descriptor()
	}

	*ec = desc.Code

	return nil
}

// Error provides a wrapper around ErrorCode with extra Details provided.
type Error struct {
	Code   ErrorCode   `json:"code"`
	Detail interface{} `json:"detail,omitempty"`
}

// Error returns a human readable representation of the error.
func (e Error) Error() string {
	return fmt.Sprintf("%s: %s",
		strings.ToLower(strings.Replace(e.Code.String(), "_", " ", -1)),
		e.Code.Message())
}

// Message returned the human-readable error message for this Error
func (e Error) Message() string {
	return e.Code.Message()
}

// Errors provides the envelope for multiple errors and a few sugar methods
// for use within the application.
type Errors []Error

// NewError creates a new Error struct based on the passed-in info
func NewError(code ErrorCode, details ...interface{}) Error {
	if len(details) > 1 {
		panic("please specify zero or one detail items for this error")
	}

	var detail interface{}
	if len(details) > 0 {
		detail = details[0]
	}

	if err, ok := detail.(error); ok {
		detail = err.Error()
	}

	return Error{
		Code:   code,
		Detail: detail,
	}
}

func (errs Errors) Error() string {
	switch len(errs) {
	case 0:
		return "<nil>"
	case 1:
		return errs[0].Error()
	default:
		msg := "errors:\n"
		for _, err := range errs {
			msg += err.Error() + "\n"
		}
		return msg
	}
}

// Len returns the current number of errors.
func (errs Errors) Len() int {
	return len(errs)
}