package query

import (
	"encoding/json"
	"errors"
)

// Response represents a list of statement results.
type Response struct {
	Results []*Result
	Err     error
}

// MarshalJSON encodes a Response struct into JSON.
func (r Response) MarshalJSON() ([]byte, error) {
	// Define a struct that outputs "error" as a string.
	var o struct {
		Results []*Result `json:"results,omitempty"`
		Err     string    `json:"error,omitempty"`
	}

	// Copy fields to output struct.
	o.Results = r.Results
	if r.Err != nil {
		o.Err = r.Err.Error()
	}

	return json.Marshal(&o)
}

// UnmarshalJSON decodes the data into the Response struct.
func (r *Response) UnmarshalJSON(b []byte) error {
	var o struct {
		Results []*Result `json:"results,omitempty"`
		Err     string    `json:"error,omitempty"`
	}

	err := json.Unmarshal(b, &o)
	if err != nil {
		return err
	}
	r.Results = o.Results
	if o.Err != "" {
		r.Err = errors.New(o.Err)
	}
	return nil
}

// Error returns the first error from any statement.
// Returns nil if no errors occurred on any statements.
func (r *Response) Error() error {
	if r.Err != nil {
		return r.Err
	}
	for _, rr := range r.Results {
		if rr.Err != nil {
			return rr.Err
		}
	}
	return nil
}