// Copyright (c) 2019 Ashley Jeffs
//
// 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.

// Package gabs implements a wrapper around creating and parsing unknown or
// dynamic map structures resulting from JSON parsing.
package gabs

import (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"io/ioutil"
	"strconv"
	"strings"
)

//------------------------------------------------------------------------------

var (
	// ErrOutOfBounds indicates an index was out of bounds.
	ErrOutOfBounds = errors.New("out of bounds")

	// ErrNotObjOrArray is returned when a target is not an object or array type
	// but needs to be for the intended operation.
	ErrNotObjOrArray = errors.New("not an object or array")

	// ErrNotObj is returned when a target is not an object but needs to be for
	// the intended operation.
	ErrNotObj = errors.New("not an object")

	// ErrInvalidQuery is returned when a seach query was not valid.
	ErrInvalidQuery = errors.New("invalid search query")

	// ErrNotArray is returned when a target is not an array but needs to be for
	// the intended operation.
	ErrNotArray = errors.New("not an array")

	// ErrPathCollision is returned when creating a path failed because an
	// element collided with an existing value.
	ErrPathCollision = errors.New("encountered value collision whilst building path")

	// ErrInvalidInputObj is returned when the input value was not a
	// map[string]interface{}.
	ErrInvalidInputObj = errors.New("invalid input object")

	// ErrInvalidInputText is returned when the input data could not be parsed.
	ErrInvalidInputText = errors.New("input text could not be parsed")

	// ErrNotFound is returned when a query leaf is not found.
	ErrNotFound = errors.New("field not found")

	// ErrInvalidPath is returned when the filepath was not valid.
	ErrInvalidPath = errors.New("invalid file path")

	// ErrInvalidBuffer is returned when the input buffer contained an invalid
	// JSON string.
	ErrInvalidBuffer = errors.New("input buffer contained invalid JSON")
)

//------------------------------------------------------------------------------

// JSONPointerToSlice parses a JSON pointer path
// (https://tools.ietf.org/html/rfc6901) and returns the path segments as a
// slice.
//
// Because the characters '~' (%x7E) and '/' (%x2F) have special meanings in
// gabs paths, '~' needs to be encoded as '~0' and '/' needs to be encoded as
// '~1' when these characters appear in a reference key.
func JSONPointerToSlice(path string) ([]string, error) {
	if len(path) < 1 {
		return nil, errors.New("failed to resolve JSON pointer: path must not be empty")
	}
	if path[0] != '/' {
		return nil, errors.New("failed to resolve JSON pointer: path must begin with '/'")
	}
	hierarchy := strings.Split(path, "/")[1:]
	for i, v := range hierarchy {
		v = strings.Replace(v, "~1", "/", -1)
		v = strings.Replace(v, "~0", "~", -1)
		hierarchy[i] = v
	}
	return hierarchy, nil
}

// DotPathToSlice returns a slice of path segments parsed out of a dot path.
//
// Because the characters '~' (%x7E) and '.' (%x2E) have special meanings in
// gabs paths, '~' needs to be encoded as '~0' and '.' needs to be encoded as
// '~1' when these characters appear in a reference key.
func DotPathToSlice(path string) []string {
	hierarchy := strings.Split(path, ".")
	for i, v := range hierarchy {
		v = strings.Replace(v, "~1", ".", -1)
		v = strings.Replace(v, "~0", "~", -1)
		hierarchy[i] = v
	}
	return hierarchy
}

//------------------------------------------------------------------------------

// Container references a specific element within a wrapped structure.
type Container struct {
	object interface{}
}

// Data returns the underlying value of the target element in the wrapped
// structure.
func (g *Container) Data() interface{} {
	if g == nil {
		return nil
	}
	return g.object
}

//------------------------------------------------------------------------------

func (g *Container) searchStrict(allowWildcard bool, hierarchy ...string) (*Container, error) {
	object := g.Data()
	for target := 0; target < len(hierarchy); target++ {
		pathSeg := hierarchy[target]
		if mmap, ok := object.(map[string]interface{}); ok {
			object, ok = mmap[pathSeg]
			if !ok {
				return nil, fmt.Errorf("failed to resolve path segment '%v': key '%v' was not found", target, pathSeg)
			}
		} else if marray, ok := object.([]interface{}); ok {
			if allowWildcard && pathSeg == "*" {
				tmpArray := []interface{}{}
				for _, val := range marray {
					if (target + 1) >= len(hierarchy) {
						tmpArray = append(tmpArray, val)
					} else if res := Wrap(val).Search(hierarchy[target+1:]...); res != nil {
						tmpArray = append(tmpArray, res.Data())
					}
				}
				if len(tmpArray) == 0 {
					return nil, nil
				}
				return &Container{tmpArray}, nil
			}
			index, err := strconv.Atoi(pathSeg)
			if err != nil {
				return nil, fmt.Errorf("failed to resolve path segment '%v': found array but segment value '%v' could not be parsed into array index: %v", target, pathSeg, err)
			}
			if index < 0 {
				return nil, fmt.Errorf("failed to resolve path segment '%v': found array but index '%v' is invalid", target, pathSeg)
			}
			if len(marray) <= index {
				return nil, fmt.Errorf("failed to resolve path segment '%v': found array but index '%v' exceeded target array size of '%v'", target, pathSeg, len(marray))
			}
			object = marray[index]
		} else {
			return nil, fmt.Errorf("failed to resolve path segment '%v': field '%v' was not found", target, pathSeg)
		}
	}
	return &Container{object}, nil
}

// Search attempts to find and return an object within the wrapped structure by
// following a provided hierarchy of field names to locate the target.
//
// If the search encounters an array then the next hierarchy field name must be
// either a an integer which is interpreted as the index of the target, or the
// character '*', in which case all elements are searched with the remaining
// search hierarchy and the results returned within an array.
func (g *Container) Search(hierarchy ...string) *Container {
	c, _ := g.searchStrict(true, hierarchy...)
	return c
}

// Path searches the wrapped structure following a path in dot notation,
// segments of this path are searched according to the same rules as Search.
//
// Because the characters '~' (%x7E) and '.' (%x2E) have special meanings in
// gabs paths, '~' needs to be encoded as '~0' and '.' needs to be encoded as
// '~1' when these characters appear in a reference key.
func (g *Container) Path(path string) *Container {
	return g.Search(DotPathToSlice(path)...)
}

// JSONPointer parses a JSON pointer path (https://tools.ietf.org/html/rfc6901)
// and either returns a *gabs.Container containing the result or an error if the
// referenced item could not be found.
//
// Because the characters '~' (%x7E) and '/' (%x2F) have special meanings in
// gabs paths, '~' needs to be encoded as '~0' and '/' needs to be encoded as
// '~1' when these characters appear in a reference key.
func (g *Container) JSONPointer(path string) (*Container, error) {
	hierarchy, err := JSONPointerToSlice(path)
	if err != nil {
		return nil, err
	}
	return g.searchStrict(false, hierarchy...)
}

// S is a shorthand alias for Search.
func (g *Container) S(hierarchy ...string) *Container {
	return g.Search(hierarchy...)
}

// Exists checks whether a field exists within the hierarchy.
func (g *Container) Exists(hierarchy ...string) bool {
	return g.Search(hierarchy...) != nil
}

// ExistsP checks whether a dot notation path exists.
func (g *Container) ExistsP(path string) bool {
	return g.Exists(DotPathToSlice(path)...)
}

// Index attempts to find and return an element within a JSON array by an index.
func (g *Container) Index(index int) *Container {
	if array, ok := g.Data().([]interface{}); ok {
		if index >= len(array) {
			return nil
		}
		return &Container{array[index]}
	}
	return nil
}

// Children returns a slice of all children of an array element. This also works
// for objects, however, the children returned for an object will be in a random
// order and you lose the names of the returned objects this way. If the
// underlying container value isn't an array or map nil is returned.
func (g *Container) Children() []*Container {
	if array, ok := g.Data().([]interface{}); ok {
		children := make([]*Container, len(array))
		for i := 0; i < len(array); i++ {
			children[i] = &Container{array[i]}
		}
		return children
	}
	if mmap, ok := g.Data().(map[string]interface{}); ok {
		children := []*Container{}
		for _, obj := range mmap {
			children = append(children, &Container{obj})
		}
		return children
	}
	return nil
}

// ChildrenMap returns a map of all the children of an object element. IF the
// underlying value isn't a object then an empty map is returned.
func (g *Container) ChildrenMap() map[string]*Container {
	if mmap, ok := g.Data().(map[string]interface{}); ok {
		children := make(map[string]*Container, len(mmap))
		for name, obj := range mmap {
			children[name] = &Container{obj}
		}
		return children
	}
	return map[string]*Container{}
}

//------------------------------------------------------------------------------

// Set attempts to set the value of a field located by a hierarchy of field
// names. If the search encounters an array then the next hierarchy field name
// is interpreted as an integer index of an existing element, or the character
// '-', which indicates a new element appended to the end of the array.
//
// Any parts of the hierarchy that do not exist will be constructed as objects.
// This includes parts that could be interpreted as array indexes.
//
// Returns a container of the new value or an error.
func (g *Container) Set(value interface{}, hierarchy ...string) (*Container, error) {
	if g == nil {
		return nil, errors.New("failed to resolve path, container is nil")
	}
	if len(hierarchy) == 0 {
		g.object = value
		return g, nil
	}
	if g.object == nil {
		g.object = map[string]interface{}{}
	}
	object := g.object

	for target := 0; target < len(hierarchy); target++ {
		pathSeg := hierarchy[target]
		if mmap, ok := object.(map[string]interface{}); ok {
			if target == len(hierarchy)-1 {
				object = value
				mmap[pathSeg] = object
			} else if object = mmap[pathSeg]; object == nil {
				mmap[pathSeg] = map[string]interface{}{}
				object = mmap[pathSeg]
			}
		} else if marray, ok := object.([]interface{}); ok {
			if pathSeg == "-" {
				if target < 1 {
					return nil, errors.New("unable to append new array index at root of path")
				}
				if target == len(hierarchy)-1 {
					object = value
				} else {
					object = map[string]interface{}{}
				}
				marray = append(marray, object)
				if _, err := g.Set(marray, hierarchy[:target]...); err != nil {
					return nil, err
				}
			} else {
				index, err := strconv.Atoi(pathSeg)
				if err != nil {
					return nil, fmt.Errorf("failed to resolve path segment '%v': found array but segment value '%v' could not be parsed into array index: %v", target, pathSeg, err)
				}
				if index < 0 {
					return nil, fmt.Errorf("failed to resolve path segment '%v': found array but index '%v' is invalid", target, pathSeg)
				}
				if len(marray) <= index {
					return nil, fmt.Errorf("failed to resolve path segment '%v': found array but index '%v' exceeded target array size of '%v'", target, pathSeg, len(marray))
				}
				if target == len(hierarchy)-1 {
					object = value
					marray[index] = object
				} else if object = marray[index]; object == nil {
					return nil, fmt.Errorf("failed to resolve path segment '%v': field '%v' was not found", target, pathSeg)
				}
			}
		} else {
			return nil, ErrPathCollision
		}
	}
	return &Container{object}, nil
}

// SetP sets the value of a field at a path using dot notation, any parts
// of the path that do not exist will be constructed, and if a collision occurs
// with a non object type whilst iterating the path an error is returned.
func (g *Container) SetP(value interface{}, path string) (*Container, error) {
	return g.Set(value, DotPathToSlice(path)...)
}

// SetIndex attempts to set a value of an array element based on an index.
func (g *Container) SetIndex(value interface{}, index int) (*Container, error) {
	if array, ok := g.Data().([]interface{}); ok {
		if index >= len(array) {
			return nil, ErrOutOfBounds
		}
		array[index] = value
		return &Container{array[index]}, nil
	}
	return nil, ErrNotArray
}

// SetJSONPointer parses a JSON pointer path
// (https://tools.ietf.org/html/rfc6901) and sets the leaf to a value. Returns
// an error if the pointer could not be resolved due to missing fields.
func (g *Container) SetJSONPointer(value interface{}, path string) (*Container, error) {
	hierarchy, err := JSONPointerToSlice(path)
	if err != nil {
		return nil, err
	}
	return g.Set(value, hierarchy...)
}

// Object creates a new JSON object at a target path. Returns an error if the
// path contains a collision with a non object type.
func (g *Container) Object(hierarchy ...string) (*Container, error) {
	return g.Set(map[string]interface{}{}, hierarchy...)
}

// ObjectP creates a new JSON object at a target path using dot notation.
// Returns an error if the path contains a collision with a non object type.
func (g *Container) ObjectP(path string) (*Container, error) {
	return g.Object(DotPathToSlice(path)...)
}

// ObjectI creates a new JSON object at an array index. Returns an error if the
// object is not an array or the index is out of bounds.
func (g *Container) ObjectI(index int) (*Container, error) {
	return g.SetIndex(map[string]interface{}{}, index)
}

// Array creates a new JSON array at a path. Returns an error if the path
// contains a collision with a non object type.
func (g *Container) Array(hierarchy ...string) (*Container, error) {
	return g.Set([]interface{}{}, hierarchy...)
}

// ArrayP creates a new JSON array at a path using dot notation. Returns an
// error if the path contains a collision with a non object type.
func (g *Container) ArrayP(path string) (*Container, error) {
	return g.Array(DotPathToSlice(path)...)
}

// ArrayI creates a new JSON array within an array at an index. Returns an error
// if the element is not an array or the index is out of bounds.
func (g *Container) ArrayI(index int) (*Container, error) {
	return g.SetIndex([]interface{}{}, index)
}

// ArrayOfSize creates a new JSON array of a particular size at a path. Returns
// an error if the path contains a collision with a non object type.
func (g *Container) ArrayOfSize(size int, hierarchy ...string) (*Container, error) {
	a := make([]interface{}, size)
	return g.Set(a, hierarchy...)
}

// ArrayOfSizeP creates a new JSON array of a particular size at a path using
// dot notation. Returns an error if the path contains a collision with a non
// object type.
func (g *Container) ArrayOfSizeP(size int, path string) (*Container, error) {
	return g.ArrayOfSize(size, DotPathToSlice(path)...)
}

// ArrayOfSizeI create a new JSON array of a particular size within an array at
// an index. Returns an error if the element is not an array or the index is out
// of bounds.
func (g *Container) ArrayOfSizeI(size, index int) (*Container, error) {
	a := make([]interface{}, size)
	return g.SetIndex(a, index)
}

// Delete an element at a path, an error is returned if the element does not
// exist or is not an object. In order to remove an array element please use
// ArrayRemove.
func (g *Container) Delete(hierarchy ...string) error {
	if g == nil || g.object == nil {
		return ErrNotObj
	}
	if len(hierarchy) == 0 {
		return ErrInvalidQuery
	}

	object := g.object
	target := hierarchy[len(hierarchy)-1]
	if len(hierarchy) > 1 {
		object = g.Search(hierarchy[:len(hierarchy)-1]...).Data()
	}

	if obj, ok := object.(map[string]interface{}); ok {
		if _, ok = obj[target]; !ok {
			return ErrNotFound
		}
		delete(obj, target)
		return nil
	}
	if array, ok := object.([]interface{}); ok {
		if len(hierarchy) < 2 {
			return errors.New("unable to delete array index at root of path")
		}
		index, err := strconv.Atoi(target)
		if err != nil {
			return fmt.Errorf("failed to parse array index '%v': %v", target, err)
		}
		if index >= len(array) {
			return ErrOutOfBounds
		}
		if index < 0 {
			return ErrOutOfBounds
		}
		array = append(array[:index], array[index+1:]...)
		g.Set(array, hierarchy[:len(hierarchy)-1]...)
		return nil
	}
	return ErrNotObjOrArray
}

// DeleteP deletes an element at a path using dot notation, an error is returned
// if the element does not exist.
func (g *Container) DeleteP(path string) error {
	return g.Delete(DotPathToSlice(path)...)
}

// MergeFn merges two objects using a provided function to resolve collisions.
//
// The collision function receives two interface{} arguments, destination (the
// original object) and source (the object being merged into the destination).
// Which ever value is returned becomes the new value in the destination object
// at the location of the collision.
func (g *Container) MergeFn(source *Container, collisionFn func(destination, source interface{}) interface{}) error {
	var recursiveFnc func(map[string]interface{}, []string) error
	recursiveFnc = func(mmap map[string]interface{}, path []string) error {
		for key, value := range mmap {
			newPath := append(path, key)
			if g.Exists(newPath...) {
				existingData := g.Search(newPath...).Data()
				switch t := value.(type) {
				case map[string]interface{}:
					switch existingVal := existingData.(type) {
					case map[string]interface{}:
						if err := recursiveFnc(t, newPath); err != nil {
							return err
						}
					default:
						if _, err := g.Set(collisionFn(existingVal, t), newPath...); err != nil {
							return err
						}
					}
				default:
					if _, err := g.Set(collisionFn(existingData, t), newPath...); err != nil {
						return err
					}
				}
			} else {
				// path doesn't exist. So set the value
				if _, err := g.Set(value, newPath...); err != nil {
					return err
				}
			}
		}
		return nil
	}
	if mmap, ok := source.Data().(map[string]interface{}); ok {
		return recursiveFnc(mmap, []string{})
	}
	return nil
}

// Merge a source object into an existing destination object. When a collision
// is found within the merged structures (both a source and destination object
// contain the same non-object keys) the result will be an array containing both
// values, where values that are already arrays will be expanded into the
// resulting array.
//
// It is possible to merge structures will different collision behaviours with
// MergeFn.
func (g *Container) Merge(source *Container) error {
	return g.MergeFn(source, func(dest, source interface{}) interface{} {
		destArr, destIsArray := dest.([]interface{})
		sourceArr, sourceIsArray := source.([]interface{})
		if destIsArray {
			if sourceIsArray {
				return append(destArr, sourceArr...)
			}
			return append(destArr, source)
		}
		if sourceIsArray {
			return append(append([]interface{}{}, dest), sourceArr...)
		}
		return []interface{}{dest, source}
	})
}

//------------------------------------------------------------------------------

/*
Array modification/search - Keeping these options simple right now, no need for
anything more complicated since you can just cast to []interface{}, modify and
then reassign with Set.
*/

// ArrayAppend attempts to append a value onto a JSON array at a path. If the
// target is not a JSON array then it will be converted into one, with its
// original contents set to the first element of the array.
func (g *Container) ArrayAppend(value interface{}, hierarchy ...string) error {
	if array, ok := g.Search(hierarchy...).Data().([]interface{}); ok {
		array = append(array, value)
		_, err := g.Set(array, hierarchy...)
		return err
	}

	newArray := []interface{}{}
	if d := g.Search(hierarchy...).Data(); d != nil {
		newArray = append(newArray, d)
	}
	newArray = append(newArray, value)

	_, err := g.Set(newArray, hierarchy...)
	return err
}

// ArrayAppendP attempts to append a value onto a JSON array at a path using dot
// notation. If the target is not a JSON array then it will be converted into
// one, with its original contents set to the first element of the array.
func (g *Container) ArrayAppendP(value interface{}, path string) error {
	return g.ArrayAppend(value, DotPathToSlice(path)...)
}

// ArrayConcat attempts to append a value onto a JSON array at a path. If the
// target is not a JSON array then it will be converted into one, with its
// original contents set to the first element of the array.
//
// ArrayConcat differs from ArrayAppend in that it will expand a value type
// []interface{} during the append operation, resulting in concatenation of each
// element, rather than append as a single element of []interface{}.
func (g *Container) ArrayConcat(value interface{}, hierarchy ...string) error {
	var array []interface{}
	if d := g.Search(hierarchy...).Data(); d != nil {
		if targetArray, ok := d.([]interface{}); !ok {
			// If the data exists, and it is not a slice of interface,
			// append it as the first element of our new array.
			array = append(array, d)
		} else {
			// If the data exists, and it is a slice of interface,
			// assign it to our variable.
			array = targetArray
		}
	}

	switch v := value.(type) {
	case []interface{}:
		// If we have been given a slice of interface, expand it when appending.
		array = append(array, v...)
	default:
		array = append(array, v)
	}

	_, err := g.Set(array, hierarchy...)

	return err
}

// ArrayConcatP attempts to append a value onto a JSON array at a path using dot
// notation. If the target is not a JSON array then it will be converted into one,
// with its original contents set to the first element of the array.
//
// ArrayConcatP differs from ArrayAppendP in that it will expand a value type
// []interface{} during the append operation, resulting in concatenation of each
// element, rather than append as a single element of []interface{}.
func (g *Container) ArrayConcatP(value interface{}, path string) error {
	return g.ArrayConcat(value, DotPathToSlice(path)...)
}

// ArrayRemove attempts to remove an element identified by an index from a JSON
// array at a path.
func (g *Container) ArrayRemove(index int, hierarchy ...string) error {
	if index < 0 {
		return ErrOutOfBounds
	}
	array, ok := g.Search(hierarchy...).Data().([]interface{})
	if !ok {
		return ErrNotArray
	}
	if index < len(array) {
		array = append(array[:index], array[index+1:]...)
	} else {
		return ErrOutOfBounds
	}
	_, err := g.Set(array, hierarchy...)
	return err
}

// ArrayRemoveP attempts to remove an element identified by an index from a JSON
// array at a path using dot notation.
func (g *Container) ArrayRemoveP(index int, path string) error {
	return g.ArrayRemove(index, DotPathToSlice(path)...)
}

// ArrayElement attempts to access an element by an index from a JSON array at a
// path.
func (g *Container) ArrayElement(index int, hierarchy ...string) (*Container, error) {
	if index < 0 {
		return nil, ErrOutOfBounds
	}
	array, ok := g.Search(hierarchy...).Data().([]interface{})
	if !ok {
		return nil, ErrNotArray
	}
	if index < len(array) {
		return &Container{array[index]}, nil
	}
	return nil, ErrOutOfBounds
}

// ArrayElementP attempts to access an element by an index from a JSON array at
// a path using dot notation.
func (g *Container) ArrayElementP(index int, path string) (*Container, error) {
	return g.ArrayElement(index, DotPathToSlice(path)...)
}

// ArrayCount counts the number of elements in a JSON array at a path.
func (g *Container) ArrayCount(hierarchy ...string) (int, error) {
	if array, ok := g.Search(hierarchy...).Data().([]interface{}); ok {
		return len(array), nil
	}
	return 0, ErrNotArray
}

// ArrayCountP counts the number of elements in a JSON array at a path using dot
// notation.
func (g *Container) ArrayCountP(path string) (int, error) {
	return g.ArrayCount(DotPathToSlice(path)...)
}

//------------------------------------------------------------------------------

func walkObject(path string, obj map[string]interface{}, flat map[string]interface{}) {
	for elePath, v := range obj {
		if len(path) > 0 {
			elePath = path + "." + elePath
		}
		switch t := v.(type) {
		case map[string]interface{}:
			walkObject(elePath, t, flat)
		case []interface{}:
			walkArray(elePath, t, flat)
		default:
			flat[elePath] = t
		}
	}
}

func walkArray(path string, arr []interface{}, flat map[string]interface{}) {
	for i, ele := range arr {
		elePath := strconv.Itoa(i)
		if len(path) > 0 {
			elePath = path + "." + elePath
		}
		switch t := ele.(type) {
		case map[string]interface{}:
			walkObject(elePath, t, flat)
		case []interface{}:
			walkArray(elePath, t, flat)
		default:
			flat[elePath] = t
		}
	}
}

// Flatten a JSON array or object into an object of key/value pairs for each
// field, where the key is the full path of the structured field in dot path
// notation matching the spec for the method Path.
//
// E.g. the structure `{"foo":[{"bar":"1"},{"bar":"2"}]}` would flatten into the
// object: `{"foo.0.bar":"1","foo.1.bar":"2"}`.
//
// Returns an error if the target is not a JSON object or array.
func (g *Container) Flatten() (map[string]interface{}, error) {
	flattened := map[string]interface{}{}
	switch t := g.Data().(type) {
	case map[string]interface{}:
		walkObject("", t, flattened)
	case []interface{}:
		walkArray("", t, flattened)
	default:
		return nil, ErrNotObjOrArray
	}
	return flattened, nil
}

//------------------------------------------------------------------------------

// Bytes marshals an element to a JSON []byte blob.
func (g *Container) Bytes() []byte {
	if bytes, err := json.Marshal(g.Data()); err == nil {
		return bytes
	}
	return []byte("null")
}

// BytesIndent marshals an element to a JSON []byte blob formatted with a prefix
// and indent string.
func (g *Container) BytesIndent(prefix string, indent string) []byte {
	if g.object != nil {
		if bytes, err := json.MarshalIndent(g.Data(), prefix, indent); err == nil {
			return bytes
		}
	}
	return []byte("null")
}

// String marshals an element to a JSON formatted string.
func (g *Container) String() string {
	return string(g.Bytes())
}

// StringIndent marshals an element to a JSON string formatted with a prefix and
// indent string.
func (g *Container) StringIndent(prefix string, indent string) string {
	return string(g.BytesIndent(prefix, indent))
}

// EncodeOpt is a functional option for the EncodeJSON method.
type EncodeOpt func(e *json.Encoder)

// EncodeOptHTMLEscape sets the encoder to escape the JSON for html.
func EncodeOptHTMLEscape(doEscape bool) EncodeOpt {
	return func(e *json.Encoder) {
		e.SetEscapeHTML(doEscape)
	}
}

// EncodeOptIndent sets the encoder to indent the JSON output.
func EncodeOptIndent(prefix string, indent string) EncodeOpt {
	return func(e *json.Encoder) {
		e.SetIndent(prefix, indent)
	}
}

// EncodeJSON marshals an element to a JSON formatted []byte using a variant
// list of modifier functions for the encoder being used. Functions for
// modifying the output are prefixed with EncodeOpt, e.g. EncodeOptHTMLEscape.
func (g *Container) EncodeJSON(encodeOpts ...EncodeOpt) []byte {
	var b bytes.Buffer
	encoder := json.NewEncoder(&b)
	encoder.SetEscapeHTML(false) // Do not escape by default.
	for _, opt := range encodeOpts {
		opt(encoder)
	}
	if err := encoder.Encode(g.object); err != nil {
		return []byte("null")
	}
	result := b.Bytes()
	if len(result) > 0 {
		result = result[:len(result)-1]
	}
	return result
}

// New creates a new gabs JSON object.
func New() *Container {
	return &Container{map[string]interface{}{}}
}

// Wrap an already unmarshalled JSON object (or a new map[string]interface{})
// into a *Container.
func Wrap(root interface{}) *Container {
	return &Container{root}
}

// ParseJSON unmarshals a JSON byte slice into a *Container.
func ParseJSON(sample []byte) (*Container, error) {
	var gabs Container

	if err := json.Unmarshal(sample, &gabs.object); err != nil {
		return nil, err
	}

	return &gabs, nil
}

// ParseJSONDecoder applies a json.Decoder to a *Container.
func ParseJSONDecoder(decoder *json.Decoder) (*Container, error) {
	var gabs Container

	if err := decoder.Decode(&gabs.object); err != nil {
		return nil, err
	}

	return &gabs, nil
}

// ParseJSONFile reads a file and unmarshals the contents into a *Container.
func ParseJSONFile(path string) (*Container, error) {
	if len(path) > 0 {
		cBytes, err := ioutil.ReadFile(path)
		if err != nil {
			return nil, err
		}

		container, err := ParseJSON(cBytes)
		if err != nil {
			return nil, err
		}

		return container, nil
	}
	return nil, ErrInvalidPath
}

// ParseJSONBuffer reads a buffer and unmarshals the contents into a *Container.
func ParseJSONBuffer(buffer io.Reader) (*Container, error) {
	var gabs Container
	jsonDecoder := json.NewDecoder(buffer)
	if err := jsonDecoder.Decode(&gabs.object); err != nil {
		return nil, err
	}

	return &gabs, nil
}

// MarshalJSON returns the JSON encoding of this container. This allows
// structs which contain Container instances to be marshaled using
// json.Marshal().
func (g *Container) MarshalJSON() ([]byte, error) {
	return json.Marshal(g.Data())
}

//------------------------------------------------------------------------------