myth/json.go

/*
Copyright (c) 2012, Jason Moiron

 Permission is hereby granted, free of charge, to any person
 obtaining a copy of this software and associated documentation
 files (the "Software"), to deal in the Software without
 restriction, including without limitation the rights to use,
 copy, modify, merge, publish, distribute, sublicense, and/or sell
 copies of the Software, and to permit persons to whom the
 Software is furnished to do so, subject to the following
 conditions:

 The above copyright notice and this permission notice shall be
 included in all copies or substantial portions of the Software.

 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 OTHER DEALINGS IN THE SOFTWARE.
 // */
// https://github.com/jmoiron/jsonq

package myth

import (
	"bytes"
	"encoding/json"
	"fmt"
	"strconv"
)

// JSONQuery is an object that enables querying of a Go map with a simple
// positional query language.
type JSONQuery struct {
	data map[string]interface{}
}

// NewJSONQuery creates a new JSONQuery obj from []byte.
func NewJSONQuery(data []byte) (jq *JSONQuery, err error) {
	obj := make(map[string]interface{})
	// bytes.NewReader(data) strings.NewReader(jsonstring)
	dec := json.NewDecoder(bytes.NewReader(data))
	err = dec.Decode(&obj)
	if err != nil {
		return
	}

	jq = new(JSONQuery)
	jq.data = obj
	return
}

// Bool extracts a bool the JSONQuery
func (jq *JSONQuery) Bool(s ...string) (bool, error) {
	val, err := rquery(jq.data, s...)
	if err != nil {
		return false, err
	}
	return boolFromInterface(val)
}

// Float extracts a float from the JsonQuery
func (jq *JSONQuery) Float(s ...string) (float64, error) {
	val, err := rquery(jq.data, s...)
	if err != nil {
		return 0.0, err
	}
	return floatFromInterface(val)
}

// Int extracts an int from the JsonQuery
func (jq *JSONQuery) Int(s ...string) (int, error) {
	val, err := rquery(jq.data, s...)
	if err != nil {
		return 0, err
	}
	return intFromInterface(val)
}

// String extracts a string from the JsonQuery
func (jq *JSONQuery) String(s ...string) (string, error) {
	val, err := rquery(jq.data, s...)
	if err != nil {
		return "", err
	}
	return stringFromInterface(val)
}

// Object extracts a json object from the JsonQuery
func (jq *JSONQuery) Object(s ...string) (map[string]interface{}, error) {
	val, err := rquery(jq.data, s...)
	if err != nil {
		return map[string]interface{}{}, err
	}
	return objectFromInterface(val)
}

// Array extracts a []interface{} from the JsonQuery
func (jq *JSONQuery) Array(s ...string) ([]interface{}, error) {
	val, err := rquery(jq.data, s...)
	if err != nil {
		return []interface{}{}, err
	}
	return arrayFromInterface(val)
}

// Interface extracts an interface{} from the JsonQuery
func (jq *JSONQuery) Interface(s ...string) (interface{}, error) {
	val, err := rquery(jq.data, s...)
	if err != nil {
		return nil, err
	}
	return val, nil
}

// ArrayOfStrings extracts an array of strings from some json
func (jq *JSONQuery) ArrayOfStrings(s ...string) ([]string, error) {
	array, err := jq.Array(s...)
	if err != nil {
		return []string{}, err
	}
	toReturn := make([]string, len(array))
	for index, val := range array {
		toReturn[index], err = stringFromInterface(val)
		if err != nil {
			return toReturn, err
		}
	}
	return toReturn, nil
}

// ArrayOfInts extracts an array of ints from some json
func (jq *JSONQuery) ArrayOfInts(s ...string) ([]int, error) {
	array, err := jq.Array(s...)
	if err != nil {
		return []int{}, err
	}
	toReturn := make([]int, len(array))
	for index, val := range array {
		toReturn[index], err = intFromInterface(val)
		if err != nil {
			return toReturn, err
		}
	}
	return toReturn, nil
}

// ArrayOfFloats extracts an array of float64s from some json
func (jq *JSONQuery) ArrayOfFloats(s ...string) ([]float64, error) {
	array, err := jq.Array(s...)
	if err != nil {
		return []float64{}, err
	}
	toReturn := make([]float64, len(array))
	for index, val := range array {
		toReturn[index], err = floatFromInterface(val)
		if err != nil {
			return toReturn, err
		}
	}
	return toReturn, nil
}

// ArrayOfBools extracts an array of bools from some json
func (jq *JSONQuery) ArrayOfBools(s ...string) ([]bool, error) {
	array, err := jq.Array(s...)
	if err != nil {
		return []bool{}, err
	}
	toReturn := make([]bool, len(array))
	for index, val := range array {
		toReturn[index], err = boolFromInterface(val)
		if err != nil {
			return toReturn, err
		}
	}
	return toReturn, nil
}

// ArrayOfObjects extracts an array of map[string]interface{} (objects) from some json
func (jq *JSONQuery) ArrayOfObjects(s ...string) ([]map[string]interface{}, error) {
	array, err := jq.Array(s...)
	if err != nil {
		return []map[string]interface{}{}, err
	}
	toReturn := make([]map[string]interface{}, len(array))
	for index, val := range array {
		toReturn[index], err = objectFromInterface(val)
		if err != nil {
			return toReturn, err
		}
	}
	return toReturn, nil
}

// ArrayOfArrays extracts an array of []interface{} (arrays) from some json
func (jq *JSONQuery) ArrayOfArrays(s ...string) ([][]interface{}, error) {
	array, err := jq.Array(s...)
	if err != nil {
		return [][]interface{}{}, err
	}
	toReturn := make([][]interface{}, len(array))
	for index, val := range array {
		toReturn[index], err = arrayFromInterface(val)
		if err != nil {
			return toReturn, err
		}
	}
	return toReturn, nil
}

// Matrix2D is an alias for ArrayOfArrays
func (jq *JSONQuery) Matrix2D(s ...string) ([][]interface{}, error) {
	return jq.ArrayOfArrays(s...)
}

// Recursively query a decoded json blob
func rquery(blob interface{}, s ...string) (interface{}, error) {
	var (
		val interface{}
		err error
	)
	val = blob
	for _, q := range s {
		val, err = query(val, q)
		if err != nil {
			return nil, err
		}
	}
	switch val.(type) {
	case nil:
		return nil, fmt.Errorf("nil value")
	}
	return val, nil
}

// query a json blob for a single field or index.  If query is a string, then
// the blob is treated as a json object (map[string]interface{}).  If query is
// an integer, the blob is treated as a json array ([]interface{}).  Any kind
// of key or index error will result in a nil return value with an error set.
func query(blob interface{}, query string) (interface{}, error) {
	index, err := strconv.Atoi(query)
	// if it's an integer, then we treat the current interface as an array
	if err == nil {
		switch blob.(type) {
		case []interface{}:
		default:
			return nil, fmt.Errorf("Array index on non-array")
		}
		if len(blob.([]interface{})) > index {
			return blob.([]interface{})[index], nil
		}
		return nil, fmt.Errorf("Array index %d out of bounds", index)
	}

	// blob is likely an object, but verify first
	switch blob.(type) {
	case map[string]interface{}:
	default:
		return nil, fmt.Errorf("Object lookup \"%s\" on non-object", query)
	}

	val, ok := blob.(map[string]interface{})[query]
	if !ok {
		return nil, fmt.Errorf("Object does not contain field %s", query)
	}
	return val, nil
}

// stringFromInterface converts an interface{} to a string and returns an error if types don't match.
func stringFromInterface(val interface{}) (string, error) {
	switch val.(type) {
	case string:
		return val.(string), nil
	}
	return "", fmt.Errorf("Expected string value for String, got \"%v\"", val)
}

// boolFromInterface converts an interface{} to a bool and returns an error if types don't match.
func boolFromInterface(val interface{}) (bool, error) {
	switch val.(type) {
	case bool:
		return val.(bool), nil
	}
	return false, fmt.Errorf("Expected boolean value for Bool, got \"%v\"", val)
}

// floatFromInterface converts an interface{} to a float64 and returns an error if types don't match.
func floatFromInterface(val interface{}) (float64, error) {
	switch val.(type) {
	case float64:
		return val.(float64), nil
	case int:
		return float64(val.(int)), nil
	case string:
		fval, err := strconv.ParseFloat(val.(string), 64)
		if err == nil {
			return fval, nil
		}
	}
	return 0.0, fmt.Errorf("Expected numeric value for Float, got \"%v\"", val)
}

// intFromInterface converts an interface{} to an int and returns an error if types don't match.
func intFromInterface(val interface{}) (int, error) {
	switch val.(type) {
	case float64:
		return int(val.(float64)), nil
	case string:
		ival, err := strconv.ParseFloat(val.(string), 64)
		if err == nil {
			return int(ival), nil
		}
	case int:
		return val.(int), nil
	}
	return 0, fmt.Errorf("Expected numeric value for Int, got \"%v\"", val)
}

// objectFromInterface converts an interface{} to a map[string]interface{} and returns an error if types don't match.
func objectFromInterface(val interface{}) (map[string]interface{}, error) {
	switch val.(type) {
	case map[string]interface{}:
		return val.(map[string]interface{}), nil
	}
	return map[string]interface{}{}, fmt.Errorf("Expected json object for Object, got \"%v\"", val)
}

// arrayFromInterface converts an interface{} to an []interface{} and returns an error if types don't match.
func arrayFromInterface(val interface{}) ([]interface{}, error) {
	switch val.(type) {
	case []interface{}:
		return val.([]interface{}), nil
	}
	return []interface{}{}, fmt.Errorf("Expected json array for Array, got \"%v\"", val)
}