package xerrors

import (
	"encoding/json"
	"fmt"

	"code.nochebuena.dev/einherjar/contracts/errs"
)

// Compile-time proof that *Err satisfies the contracts interfaces consumed by logz.
var _ errs.CodedError = (*Err)(nil)
var _ errs.ContextualError = (*Err)(nil)

// Err is a structured application error carrying a Code, a human-readable
// message, an optional cause, and optional key-value context fields.
//
// It implements the standard error interface, errors.Unwrap for cause chaining,
// and json.Marshaler for API responses. It also satisfies errs.CodedError and
// errs.ContextualError from contracts, enabling logz to enrich log records
// automatically without importing this package.
//
// Use the builder methods WithContext, WithError, and WithPlatformCode to attach
// additional information after construction:
//
//	err := xerrors.New(xerrors.ErrInvalidInput, "validation failed").
//	    WithContext("field", "email").
//	    WithContext("rule", "required").
//	    WithError(cause)
type Err struct {
	code         Code
	message      string
	err          error
	fields       map[string]any
	platformCode string
}

// New creates an Err with the given code and message. No cause is set.
func New(code Code, message string) *Err {
	return &Err{code: code, message: message}
}

// Wrap creates an Err that wraps an existing error with a code and message.
// The wrapped error is accessible via errors.Is, errors.As, and Err.Unwrap.
func Wrap(code Code, message string, err error) *Err {
	return &Err{code: code, message: message, err: err}
}

// InvalidInput creates an Err with ErrInvalidInput code.
func InvalidInput(msg string, args ...any) *Err {
	return New(ErrInvalidInput, fmt.Sprintf(msg, args...))
}

// OutOfRange creates an Err with ErrOutOfRange code.
func OutOfRange(msg string, args ...any) *Err { return New(ErrOutOfRange, fmt.Sprintf(msg, args...)) }

// Unauthorized creates an Err with ErrUnauthorized code.
func Unauthorized(msg string, args ...any) *Err {
	return New(ErrUnauthorized, fmt.Sprintf(msg, args...))
}

// PermissionDenied creates an Err with ErrPermissionDenied code.
func PermissionDenied(msg string, args ...any) *Err {
	return New(ErrPermissionDenied, fmt.Sprintf(msg, args...))
}

// NotFound creates an Err with ErrNotFound code.
func NotFound(msg string, args ...any) *Err { return New(ErrNotFound, fmt.Sprintf(msg, args...)) }

// AlreadyExists creates an Err with ErrAlreadyExists code.
func AlreadyExists(msg string, args ...any) *Err {
	return New(ErrAlreadyExists, fmt.Sprintf(msg, args...))
}

// Aborted creates an Err with ErrAborted code.
func Aborted(msg string, args ...any) *Err { return New(ErrAborted, fmt.Sprintf(msg, args...)) }

// Gone creates an Err with ErrGone code.
func Gone(msg string, args ...any) *Err { return New(ErrGone, fmt.Sprintf(msg, args...)) }

// PreconditionFailed creates an Err with ErrPreconditionFailed code.
func PreconditionFailed(msg string, args ...any) *Err {
	return New(ErrPreconditionFailed, fmt.Sprintf(msg, args...))
}

// RateLimited creates an Err with ErrRateLimited code.
func RateLimited(msg string, args ...any) *Err { return New(ErrRateLimited, fmt.Sprintf(msg, args...)) }

// Cancelled creates an Err with ErrCancelled code.
func Cancelled(msg string, args ...any) *Err { return New(ErrCancelled, fmt.Sprintf(msg, args...)) }

// Internal creates an Err with ErrInternal code.
func Internal(msg string, args ...any) *Err { return New(ErrInternal, fmt.Sprintf(msg, args...)) }

// DataLoss creates an Err with ErrDataLoss code.
func DataLoss(msg string, args ...any) *Err { return New(ErrDataLoss, fmt.Sprintf(msg, args...)) }

// NotImplemented creates an Err with ErrNotImplemented code.
func NotImplemented(msg string, args ...any) *Err {
	return New(ErrNotImplemented, fmt.Sprintf(msg, args...))
}

// Unavailable creates an Err with ErrUnavailable code.
func Unavailable(msg string, args ...any) *Err { return New(ErrUnavailable, fmt.Sprintf(msg, args...)) }

// DeadlineExceeded creates an Err with ErrDeadlineExceeded code.
func DeadlineExceeded(msg string, args ...any) *Err {
	return New(ErrDeadlineExceeded, fmt.Sprintf(msg, args...))
}

// WithContext adds a key-value pair to the error's context fields and returns
// the receiver for chaining. Calling it multiple times with the same key
// overwrites the previous value.
func (e *Err) WithContext(key string, value any) *Err {
	if e.fields == nil {
		e.fields = make(map[string]any)
	}
	e.fields[key] = value
	return e
}

// WithError sets the underlying cause and returns the receiver for chaining.
func (e *Err) WithError(err error) *Err {
	e.err = err
	return e
}

// WithPlatformCode sets a platform-level error code and returns the receiver
// for chaining. Platform codes are domain-specific identifiers (e.g.
// "EMPLOYEE_NOT_FOUND") intended for consuming applications — such as a
// frontend — that need to map errors to localised user-facing messages.
//
// Platform codes are optional. Errors that have no user-actionable meaning
// (e.g. 500 internal errors) should not carry one.
func (e *Err) WithPlatformCode(code string) *Err {
	e.platformCode = code
	return e
}

// Code returns the typed error code.
func (e *Err) Code() Code { return e.code }

// Message returns the human-readable error message.
func (e *Err) Message() string { return e.message }

// PlatformCode returns the platform-level error code, or "" if none was set.
func (e *Err) PlatformCode() string { return e.platformCode }

// Fields returns a shallow copy of the context fields.
// Returns an empty (non-nil) map if no fields have been set.
func (e *Err) Fields() map[string]any {
	if len(e.fields) == 0 {
		return map[string]any{}
	}
	out := make(map[string]any, len(e.fields))
	for k, v := range e.fields {
		out[k] = v
	}
	return out
}

// Detailed returns a verbose string useful for debugging.
// Format: "code: X | message: Y | cause: Z | fields: {...}"
func (e *Err) Detailed() string {
	s := fmt.Sprintf("code: %s | message: %s", e.code, e.message)
	if e.err != nil {
		s = fmt.Sprintf("%s | cause: %v", s, e.err)
	}
	if len(e.fields) > 0 {
		s = fmt.Sprintf("%s | fields: %v", s, e.fields)
	}
	return s
}

// Error implements the error interface.
// Format: "INVALID_ARGUMENT: username is required → original cause"
func (e *Err) Error() string {
	base := fmt.Sprintf("%s: %s", e.code, e.message)
	if e.err != nil {
		base = fmt.Sprintf("%s → %v", base, e.err)
	}
	return base
}

// Unwrap returns the underlying cause, enabling errors.Is and errors.As
// to walk the full cause chain.
func (e *Err) Unwrap() error { return e.err }

// ErrorCode satisfies errs.CodedError. logz calls this to append error_code
// to log records without importing this package.
func (e *Err) ErrorCode() string { return string(e.code) }

// ErrorContext satisfies errs.ContextualError. logz calls this to append
// context fields to log records. The returned map is read-only by logz;
// use Fields() if you need a safe copy.
func (e *Err) ErrorContext() map[string]any { return e.fields }

// MarshalJSON implements json.Marshaler.
// Output: {"code":"NOT_FOUND","platform_code":"...","message":"...","fields":{...}}
// platform_code and fields are omitted when empty.
func (e *Err) MarshalJSON() ([]byte, error) {
	return json.Marshal(struct {
		Code         string         `json:"code"`
		PlatformCode string         `json:"platform_code,omitempty"`
		Message      string         `json:"message"`
		Fields       map[string]any `json:"fields,omitempty"`
	}{
		Code:         string(e.code),
		PlatformCode: e.platformCode,
		Message:      e.message,
		Fields:       e.fields,
	})
}