/*
 * Copyright 2021 ByteDance Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package ast

import (
    `sync`
    `unicode/utf8`
)

const (
    _MaxBuffer = 1024    // 1KB buffer size
)

func quoteString(e *[]byte, s string) {
    *e = append(*e, '"')
    start := 0
    for i := 0; i < len(s); {
        if b := s[i]; b < utf8.RuneSelf {
            if safeSet[b] {
                i++
                continue
            }
            if start < i {
                *e = append(*e, s[start:i]...)
            }
            *e = append(*e, '\\')
            switch b {
            case '\\', '"':
                *e = append(*e, b)
            case '\n':
                *e = append(*e, 'n')
            case '\r':
                *e = append(*e, 'r')
            case '\t':
                *e = append(*e, 't')
            default:
                // This encodes bytes < 0x20 except for \t, \n and \r.
                // If escapeHTML is set, it also escapes <, >, and &
                // because they can lead to security holes when
                // user-controlled strings are rendered into JSON
                // and served to some browsers.
                *e = append(*e, `u00`...)
                *e = append(*e, hex[b>>4])
                *e = append(*e, hex[b&0xF])
            }
            i++
            start = i
            continue
        }
        c, size := utf8.DecodeRuneInString(s[i:])
        // if c == utf8.RuneError && size == 1 {
        //     if start < i {
        //         e.Write(s[start:i])
        //     }
        //     e.WriteString(`\ufffd`)
        //     i += size
        //     start = i
        //     continue
        // }
        if c == '\u2028' || c == '\u2029' {
            if start < i {
                *e = append(*e, s[start:i]...)
            }
            *e = append(*e, `\u202`...)
            *e = append(*e, hex[c&0xF])
            i += size
            start = i
            continue
        }
        i += size
    }
    if start < len(s) {
        *e = append(*e, s[start:]...)
    }
    *e = append(*e, '"')
}

var bytesPool   = sync.Pool{}

func (self *Node) MarshalJSON() ([]byte, error) {
    buf := newBuffer()
    err := self.encode(buf)
    if err != nil {
        freeBuffer(buf)
        return nil, err
    }

    ret := make([]byte, len(*buf))
    copy(ret, *buf)
    freeBuffer(buf)
    return ret, err
}

func newBuffer() *[]byte {
    if ret := bytesPool.Get(); ret != nil {
        return ret.(*[]byte)
    } else {
        buf := make([]byte, 0, _MaxBuffer)
        return &buf
    }
}

func freeBuffer(buf *[]byte) {
    *buf = (*buf)[:0]
    bytesPool.Put(buf)
}

func (self *Node) encode(buf *[]byte) error {
    if self.IsRaw() {
        return self.encodeRaw(buf)
    }
    switch self.Type() {
        case V_NONE  : return ErrNotExist
        case V_ERROR : return self.Check()
        case V_NULL  : return self.encodeNull(buf)
        case V_TRUE  : return self.encodeTrue(buf)
        case V_FALSE : return self.encodeFalse(buf)
        case V_ARRAY : return self.encodeArray(buf)
        case V_OBJECT: return self.encodeObject(buf)
        case V_STRING: return self.encodeString(buf)
        case V_NUMBER: return self.encodeNumber(buf)
        case V_ANY   : return self.encodeInterface(buf)
        default      : return ErrUnsupportType 
    }
}

func (self *Node) encodeRaw(buf *[]byte) error {
    raw, err := self.Raw()
    if err != nil {
        return err
    }
    *buf = append(*buf, raw...)
    return nil
}

func (self *Node) encodeNull(buf *[]byte) error {
    *buf = append(*buf, bytesNull...)
    return nil
}

func (self *Node) encodeTrue(buf *[]byte) error {
    *buf = append(*buf, bytesTrue...)
    return nil
}

func (self *Node) encodeFalse(buf *[]byte) error {
    *buf = append(*buf, bytesFalse...)
    return nil
}

func (self *Node) encodeNumber(buf *[]byte) error {
    str := self.toString()
    *buf = append(*buf, str...)
    return nil
}

func (self *Node) encodeString(buf *[]byte) error {
    if self.l == 0 {
        *buf = append(*buf, '"', '"')
        return nil
    }

    quote(buf, self.toString())
    return nil
}

func (self *Node) encodeArray(buf *[]byte) error {
    if self.isLazy() {
        if err := self.skipAllIndex(); err != nil {
            return err
        }
    }

    nb := self.len()
    if nb == 0 {
        *buf = append(*buf, bytesArray...)
        return nil
    }
    
    *buf = append(*buf, '[')

    var started bool
    for i := 0; i < nb; i++ {
        n := self.nodeAt(i)
        if !n.Exists() {
            continue
        }
        if started {
            *buf = append(*buf, ',')
        }
        started = true
        if err := n.encode(buf); err != nil {
            return err
        }
    }

    *buf = append(*buf, ']')
    return nil
}

func (self *Pair) encode(buf *[]byte) error {
    if len(*buf) == 0 {
        *buf = append(*buf, '"', '"', ':')
        return self.Value.encode(buf)
    }

    quote(buf, self.Key)
    *buf = append(*buf, ':')

    return self.Value.encode(buf)
}

func (self *Node) encodeObject(buf *[]byte) error {
    if self.isLazy() {
        if err := self.skipAllKey(); err != nil {
            return err
        }
    }
    
    nb := self.len()
    if nb == 0 {
        *buf = append(*buf, bytesObject...)
        return nil
    }
    
    *buf = append(*buf, '{')

    var started bool
    for i := 0; i < nb; i++ {
        n := self.pairAt(i)
        if n == nil || !n.Value.Exists() {
            continue
        }
        if started {
            *buf = append(*buf, ',')
        }
        started = true
        if err := n.encode(buf); err != nil {
            return err
        }
    }

    *buf = append(*buf, '}')
    return nil
}
