package tpp

import (
	"bytes"
	"context"
)


type Preprocessor struct {
	tengo *Tengo
	tags [2][]byte
	preTag byte
}

// Get the new preprocessor with default options.
func New(tengo *Tengo ) *Preprocessor {
	pp := &Preprocessor{}
	pp.tengo = tengo
	pp.tags = [2][]byte{
		[]byte("{{"),
		[]byte("}}"),
	}
	pp.preTag = '#'
	return pp
}

func (pp *Preprocessor) Process(
	ctx context.Context,
	recompile bool,
	filePath string,
	data []byte,
) ([]byte, error) {
	//var b bytes.Buffer
	preCode := []byte(nil)
	texts := [][]byte{}
	codes := [][]byte{}
	pref := append(pp.tags[0], pp.preTag)
	if bytes.HasPrefix(data, pref) {
		idxEnd := bytes.Index(data, pp.tags[1])
		if idxEnd < 0 {
			return nil, UnexpectedError{
				What: "pre-code start tag",
			}
		}
		preCode = data[len(pref):idxEnd]
		//texts = append(texts, []byte{})
		data = data[idxEnd+len(pp.tags[1]):]
	}
	for {
		idxStart := bytes.Index(data, pp.tags[0])
		idxEnd := bytes.Index(data, pp.tags[1])
		//fmt.Printf("cock %d %d %d\n", last, idxStart, idxEnd)
		if idxStart < 0 {
			if idxEnd >= 0 {
				return nil, UnexpectedError{
					What: "end tag",
				}
			}
			texts = append(texts, data)
			break
		} else if idxEnd < 0 {
			return nil, UnexpectedError{
				What: "start tag",
			}
		}

		text := data[:idxStart]
		texts = append(texts, text)

		code := data[idxStart+len(pp.tags[0]):idxEnd]
		codes = append(codes, code)

		data = data[idxEnd + len(pp.tags[1]):]
	}

	ret, err := pp.tengo.Eval(
		ctx,
		recompile,
		filePath,
		texts,
		preCode,
		codes,
	)
	if err != nil {
		return nil, err
	}

	return ret, nil
}