package yqlib

import (
	"bytes"
	"encoding/base64"
	"io"
	"strings"

	yaml "gopkg.in/yaml.v3"
)

type base64Padder struct {
	count uint64
	io.Reader
}

func (c *base64Padder) pad(buf []byte) (int, error) {
	pad := strings.Repeat("=", int(4-c.count%4))
	n, err := strings.NewReader(pad).Read(buf)
	c.count += uint64(n)
	return n, err
}

func (c *base64Padder) Read(buf []byte) (int, error) {
	n, err := c.Reader.Read(buf)
	c.count += uint64(n)

	if err == io.EOF && c.count%4 != 0 {
		return c.pad(buf)
	}
	return n, err
}

type base64Decoder struct {
	reader       io.Reader
	finished     bool
	readAnything bool
	encoding     base64.Encoding
}

func NewBase64Decoder() Decoder {
	return &base64Decoder{finished: false, encoding: *base64.StdEncoding}
}

func (dec *base64Decoder) Init(reader io.Reader) error {
	dec.reader = &base64Padder{Reader: reader}
	dec.readAnything = false
	dec.finished = false
	return nil
}

func (dec *base64Decoder) Decode() (*CandidateNode, error) {
	if dec.finished {
		return nil, io.EOF
	}
	base64Reader := base64.NewDecoder(&dec.encoding, dec.reader)
	buf := new(bytes.Buffer)

	if _, err := buf.ReadFrom(base64Reader); err != nil {
		return nil, err
	}
	if buf.Len() == 0 {
		dec.finished = true

		// if we've read _only_ an empty string, lets return that
		// otherwise if we've already read some bytes, and now we get
		// an empty string, then we are done.
		if dec.readAnything {
			return nil, io.EOF
		}
	}
	dec.readAnything = true
	return &CandidateNode{
		Node: &yaml.Node{
			Kind:  yaml.ScalarNode,
			Tag:   "!!str",
			Value: buf.String(),
		},
	}, nil
}