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// Copyright 2010 The Go Authors.  All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package json implements encoding and decoding of JSON objects as defined in
// RFC 4627.
//
// See "JSON and Go" for an introduction to this package:
// http://blog.golang.org/2011/01/json-and-go.html
package json

import (
        "bytes"
        "encoding/base64"
        "math"
        "reflect"
        "runtime"
        "sort"
        "strconv"
        "sync"
        "unicode"
        "unicode/utf8"
)

// Marshal returns the JSON encoding of v.
//
// Marshal traverses the value v recursively.
// If an encountered value implements the Marshaler interface
// and is not a nil pointer, Marshal calls its MarshalJSON method
// to produce JSON.  The nil pointer exception is not strictly necessary
// but mimics a similar, necessary exception in the behavior of
// UnmarshalJSON.
//
// Otherwise, Marshal uses the following type-dependent default encodings:
//
// Boolean values encode as JSON booleans.
//
// Floating point and integer values encode as JSON numbers.
//
// String values encode as JSON strings, with each invalid UTF-8 sequence
// replaced by the encoding of the Unicode replacement character U+FFFD.
// The angle brackets "<" and ">" are escaped to "\u003c" and "\u003e"
// to keep some browsers from misinterpreting JSON output as HTML.
//
// Array and slice values encode as JSON arrays, except that
// []byte encodes as a base64-encoded string.
//
// Struct values encode as JSON objects. Each exported struct field
// becomes a member of the object unless
//   - the field's tag is "-", or
//   - the field is empty and its tag specifies the "omitempty" option.
// The empty values are false, 0, any
// nil pointer or interface value, and any array, slice, map, or string of
// length zero. The object's default key string is the struct field name
// but can be specified in the struct field's tag value. The "json" key in
// struct field's tag value is the key name, followed by an optional comma
// and options. Examples:
//
//   // Field is ignored by this package.
//   Field int `json:"-"`
//
//   // Field appears in JSON as key "myName".
//   Field int `json:"myName"`
//
//   // Field appears in JSON as key "myName" and
//   // the field is omitted from the object if its value is empty,
//   // as defined above.
//   Field int `json:"myName,omitempty"`
//
//   // Field appears in JSON as key "Field" (the default), but
//   // the field is skipped if empty.
//   // Note the leading comma.
//   Field int `json:",omitempty"`
//
// The "string" option signals that a field is stored as JSON inside a
// JSON-encoded string.  This extra level of encoding is sometimes
// used when communicating with JavaScript programs:
//
//    Int64String int64 `json:",string"`
//
// The key name will be used if it's a non-empty string consisting of
// only Unicode letters, digits, dollar signs, percent signs, hyphens,
// underscores and slashes.
//
// Map values encode as JSON objects.
// The map's key type must be string; the object keys are used directly
// as map keys.
//
// Pointer values encode as the value pointed to.
// A nil pointer encodes as the null JSON object.
//
// Interface values encode as the value contained in the interface.
// A nil interface value encodes as the null JSON object.
//
// Channel, complex, and function values cannot be encoded in JSON.
// Attempting to encode such a value causes Marshal to return
// an InvalidTypeError.
//
// JSON cannot represent cyclic data structures and Marshal does not
// handle them.  Passing cyclic structures to Marshal will result in
// an infinite recursion.
//
func Marshal(v interface{}) ([]byte, error) {
        e := &encodeState{}
        err := e.marshal(v)
        if err != nil {
                return nil, err
        }
        return e.Bytes(), nil
}

// MarshalIndent is like Marshal but applies Indent to format the output.
func MarshalIndent(v interface{}, prefix, indent string) ([]byte, error) {
        b, err := Marshal(v)
        if err != nil {
                return nil, err
        }
        var buf bytes.Buffer
        err = Indent(&buf, b, prefix, indent)
        if err != nil {
                return nil, err
        }
        return buf.Bytes(), nil
}

// MarshalForHTML is like Marshal but applies HTMLEscape to the output.
func MarshalForHTML(v interface{}) ([]byte, error) {
        b, err := Marshal(v)
        if err != nil {
                return nil, err
        }
        var buf bytes.Buffer
        HTMLEscape(&buf, b)
        return buf.Bytes(), nil
}

// HTMLEscape appends to dst the JSON-encoded src with <, >, and &
// characters inside string literals changed to \u003c, \u003e, \u0026
// so that the JSON will be safe to embed inside HTML <script> tags.
// For historical reasons, web browsers don't honor standard HTML
// escaping within <script> tags, so an alternative JSON encoding must
// be used.
func HTMLEscape(dst *bytes.Buffer, src []byte) {
        // < > & can only appear in string literals,
        // so just scan the string one byte at a time.
        start := 0
        for i, c := range src {
                if c == '<' || c == '>' || c == '&' {
                        if start < i {
                                dst.Write(src[start:i])
                        }
                        dst.WriteString(`\u00`)
                        dst.WriteByte(hex[c>>4])
                        dst.WriteByte(hex[c&0xF])
                        start = i + 1
                }
        }
        if start < len(src) {
                dst.Write(src[start:])
        }
}

// Marshaler is the interface implemented by objects that
// can marshal themselves into valid JSON.
type Marshaler interface {
        MarshalJSON() ([]byte, error)
}

type UnsupportedTypeError struct {
        Type reflect.Type
}

func (e *UnsupportedTypeError) Error() string {
        return "json: unsupported type: " + e.Type.String()
}

type UnsupportedValueError struct {
        Value reflect.Value
        Str   string
}

func (e *UnsupportedValueError) Error() string {
        return "json: unsupported value: " + e.Str
}

type InvalidUTF8Error struct {
        S string
}

func (e *InvalidUTF8Error) Error() string {
        return "json: invalid UTF-8 in string: " + strconv.Quote(e.S)
}

type MarshalerError struct {
        Type reflect.Type
        Err  error
}

func (e *MarshalerError) Error() string {
        return "json: error calling MarshalJSON for type " + e.Type.String() + ": " + e.Err.Error()
}

type interfaceOrPtrValue interface {
        IsNil() bool
        Elem() reflect.Value
}

var hex = "0123456789abcdef"

// An encodeState encodes JSON into a bytes.Buffer.
type encodeState struct {
        bytes.Buffer // accumulated output
        scratch      [64]byte
}

func (e *encodeState) marshal(v interface{}) (err error) {
        defer func() {
                if r := recover(); r != nil {
                        if _, ok := r.(runtime.Error); ok {
                                panic(r)
                        }
                        err = r.(error)
                }
        }()
        e.reflectValue(reflect.ValueOf(v))
        return nil
}

func (e *encodeState) error(err error) {
        panic(err)
}

var byteSliceType = reflect.TypeOf([]byte(nil))

func isEmptyValue(v reflect.Value) bool {
        switch v.Kind() {
        case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
                return v.Len() == 0
        case reflect.Bool:
                return !v.Bool()
        case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
                return v.Int() == 0
        case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
                return v.Uint() == 0
        case reflect.Float32, reflect.Float64:
                return v.Float() == 0
        case reflect.Interface, reflect.Ptr:
                return v.IsNil()
        }
        return false
}

func (e *encodeState) reflectValue(v reflect.Value) {
        e.reflectValueQuoted(v, false)
}

// reflectValueQuoted writes the value in v to the output.
// If quoted is true, the serialization is wrapped in a JSON string.
func (e *encodeState) reflectValueQuoted(v reflect.Value, quoted bool) {
        if !v.IsValid() {
                e.WriteString("null")
                return
        }

        m, ok := v.Interface().(Marshaler)
        if !ok {
                // T doesn't match the interface. Check against *T too.
                if v.Kind() != reflect.Ptr && v.CanAddr() {
                        m, ok = v.Addr().Interface().(Marshaler)
                        if ok {
                                v = v.Addr()
                        }
                }
        }
        if ok && (v.Kind() != reflect.Ptr || !v.IsNil()) {
                b, err := m.MarshalJSON()
                if err == nil {
                        // copy JSON into buffer, checking validity.
                        err = Compact(&e.Buffer, b)
                }
                if err != nil {
                        e.error(&MarshalerError{v.Type(), err})
                }
                return
        }

        writeString := (*encodeState).WriteString
        if quoted {
                writeString = (*encodeState).string
        }

        switch v.Kind() {
        case reflect.Bool:
                x := v.Bool()
                if x {
                        writeString(e, "true")
                } else {
                        writeString(e, "false")
                }

        case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
                b := strconv.AppendInt(e.scratch[:0], v.Int(), 10)
                if quoted {
                        writeString(e, string(b))
                } else {
                        e.Write(b)
                }
        case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
                b := strconv.AppendUint(e.scratch[:0], v.Uint(), 10)
                if quoted {
                        writeString(e, string(b))
                } else {
                        e.Write(b)
                }
        case reflect.Float32, reflect.Float64:
                f := v.Float()
                if math.IsInf(f, 0) || math.IsNaN(f) {
                        e.error(&UnsupportedValueError{v, strconv.FormatFloat(f, 'g', -1, v.Type().Bits())})
                }
                b := strconv.AppendFloat(e.scratch[:0], f, 'g', -1, v.Type().Bits())
                if quoted {
                        writeString(e, string(b))
                } else {
                        e.Write(b)
                }
        case reflect.String:
                if quoted {
                        sb, err := Marshal(v.String())
                        if err != nil {
                                e.error(err)
                        }
                        e.string(string(sb))
                } else {
                        e.string(v.String())
                }

        case reflect.Struct:
                e.WriteByte('{')
                first := true
                for _, ef := range encodeFields(v.Type()) {
                        fieldValue := v.Field(ef.i)
                        if ef.omitEmpty && isEmptyValue(fieldValue) {
                                continue
                        }
                        if first {
                                first = false
                        } else {
                                e.WriteByte(',')
                        }
                        e.string(ef.tag)
                        e.WriteByte(':')
                        e.reflectValueQuoted(fieldValue, ef.quoted)
                }
                e.WriteByte('}')

        case reflect.Map:
                if v.Type().Key().Kind() != reflect.String {
                        e.error(&UnsupportedTypeError{v.Type()})
                }
                if v.IsNil() {
                        e.WriteString("null")
                        break
                }
                e.WriteByte('{')
                var sv stringValues = v.MapKeys()
                sort.Sort(sv)
                for i, k := range sv {
                        if i > 0 {
                                e.WriteByte(',')
                        }
                        e.string(k.String())
                        e.WriteByte(':')
                        e.reflectValue(v.MapIndex(k))
                }
                e.WriteByte('}')

        case reflect.Slice:
                if v.IsNil() {
                        e.WriteString("null")
                        break
                }
                if v.Type().Elem().Kind() == reflect.Uint8 {
                        // Byte slices get special treatment; arrays don't.
                        s := v.Bytes()
                        e.WriteByte('"')
                        if len(s) < 1024 {
                                // for small buffers, using Encode directly is much faster.
                                dst := make([]byte, base64.StdEncoding.EncodedLen(len(s)))
                                base64.StdEncoding.Encode(dst, s)
                                e.Write(dst)
                        } else {
                                // for large buffers, avoid unnecessary extra temporary
                                // buffer space.
                                enc := base64.NewEncoder(base64.StdEncoding, e)
                                enc.Write(s)
                                enc.Close()
                        }
                        e.WriteByte('"')
                        break
                }
                // Slices can be marshalled as nil, but otherwise are handled
                // as arrays.
                fallthrough
        case reflect.Array:
                e.WriteByte('[')
                n := v.Len()
                for i := 0; i < n; i++ {
                        if i > 0 {
                                e.WriteByte(',')
                        }
                        e.reflectValue(v.Index(i))
                }
                e.WriteByte(']')

        case reflect.Interface, reflect.Ptr:
                if v.IsNil() {
                        e.WriteString("null")
                        return
                }
                e.reflectValue(v.Elem())

        default:
                e.error(&UnsupportedTypeError{v.Type()})
        }
        return
}

func isValidTag(s string) bool {
        if s == "" {
                return false
        }
        for _, c := range s {
                switch c {
                case '$', '-', '_', '/', '%':
                        // Acceptable
                default:
                        if !unicode.IsLetter(c) && !unicode.IsDigit(c) {
                                return false
                        }
                }
        }
        return true
}

// stringValues is a slice of reflect.Value holding *reflect.StringValue.
// It implements the methods to sort by string.
type stringValues []reflect.Value

func (sv stringValues) Len() int           { return len(sv) }
func (sv stringValues) Swap(i, j int)      { sv[i], sv[j] = sv[j], sv[i] }
func (sv stringValues) Less(i, j int) bool { return sv.get(i) < sv.get(j) }
func (sv stringValues) get(i int) string   { return sv[i].String() }

func (e *encodeState) string(s string) (int, error) {
        len0 := e.Len()
        e.WriteByte('"')
        start := 0
        for i := 0; i < len(s); {
                if b := s[i]; b < utf8.RuneSelf {
                        if 0x20 <= b && b != '\\' && b != '"' && b != '<' && b != '>' {
                                i++
                                continue
                        }
                        if start < i {
                                e.WriteString(s[start:i])
                        }
                        switch b {
                        case '\\', '"':
                                e.WriteByte('\\')
                                e.WriteByte(b)
                        case '\n':
                                e.WriteByte('\\')
                                e.WriteByte('n')
                        case '\r':
                                e.WriteByte('\\')
                                e.WriteByte('r')
                        default:
                                // This encodes bytes < 0x20 except for \n and \r,
                                // as well as < and >. The latter are escaped because they
                                // can lead to security holes when user-controlled strings
                                // are rendered into JSON and served to some browsers.
                                e.WriteString(`\u00`)
                                e.WriteByte(hex[b>>4])
                                e.WriteByte(hex[b&0xF])
                        }
                        i++
                        start = i
                        continue
                }
                c, size := utf8.DecodeRuneInString(s[i:])
                if c == utf8.RuneError && size == 1 {
                        e.error(&InvalidUTF8Error{s})
                }
                i += size
        }
        if start < len(s) {
                e.WriteString(s[start:])
        }
        e.WriteByte('"')
        return e.Len() - len0, nil
}

// encodeField contains information about how to encode a field of a
// struct.
type encodeField struct {
        i         int // field index in struct
        tag       string
        quoted    bool
        omitEmpty bool
}

var (
        typeCacheLock     sync.RWMutex
        encodeFieldsCache = make(map[reflect.Type][]encodeField)
)

// encodeFields returns a slice of encodeField for a given
// struct type.
func encodeFields(t reflect.Type) []encodeField {
        typeCacheLock.RLock()
        fs, ok := encodeFieldsCache[t]
        typeCacheLock.RUnlock()
        if ok {
                return fs
        }

        typeCacheLock.Lock()
        defer typeCacheLock.Unlock()
        fs, ok = encodeFieldsCache[t]
        if ok {
                return fs
        }

        v := reflect.Zero(t)
        n := v.NumField()
        for i := 0; i < n; i++ {
                f := t.Field(i)
                if f.PkgPath != "" {
                        continue
                }
                var ef encodeField
                ef.i = i
                ef.tag = f.Name

                tv := f.Tag.Get("json")
                if tv != "" {
                        if tv == "-" {
                                continue
                        }
                        name, opts := parseTag(tv)
                        if isValidTag(name) {
                                ef.tag = name
                        }
                        ef.omitEmpty = opts.Contains("omitempty")
                        ef.quoted = opts.Contains("string")
                }
                fs = append(fs, ef)
        }
        encodeFieldsCache[t] = fs
        return fs
}