package content

import (
	"bytes"
	"encoding/base64"

	"github.com/mleku/transit/chk"
	"github.com/mleku/transit/errorf"
	"github.com/mleku/transit/text"
)

var BinaryPrefix = []byte("base64:")

// C is a content field for an event.T that can be binary or text, if set to binary, it encodes
// to base64 URL format (with padding). Binary coded values have the prefix "base64:" prefix.
// Setting binary should be done in accordance with the mimetype being a binary mimetype.
type C struct {
	Val    []byte
	Binary bool
}

// New creates a new mime.Type based on input string or bytes of value.
func New[V []byte | string](c V, binary bool) (content *C) {
	content = &C{Val: []byte(c), Binary: binary}
	return
}

func (c *C) MarshalJSON() (b []byte, err error) {
	if c.Binary {
		b = make([]byte, base64.URLEncoding.EncodedLen(len(c.Val))+2+len(BinaryPrefix))
		copy(b[1:], BinaryPrefix)
		base64.URLEncoding.Encode(b[1+len(BinaryPrefix):len(b)-1], c.Val)
		b[0] = '"'
		b[len(b)-1] = '"'
	} else {
		b = append(append([]byte{'"'}, text.Escape(nil, c.Val)...), '"')
	}
	return
}

func (c *C) UnmarshalJSON(b []byte) (err error) {
	b = b[1:]
	if bytes.HasPrefix(b, BinaryPrefix) {
		c.Binary = true
		// remove quotes and binary prefix
		b = b[len(BinaryPrefix) : len(b)-1]
		var n int
		// we use AppendDecode to avoid needing to trim pad bytes
		if c.Val, err = base64.URLEncoding.AppendDecode(c.Val, b); chk.E(err) {
			err = errorf.E("error: decoding failed at %d: %s", n, err.Error())
			return
		}
		c.Binary = true
	} else {
		b = b[:len(b)-1]
		c.Val = b
		c.Val = text.Unescape(c.Val)
		c.Binary = false
	}
	return
}