package pp

import (
	"strings"
	"fmt"
)

type Preprocessor struct {
	evaler Evaler
	tags [2]string
}

// Get the new preprocessor with default options.
func NewPp(evaler Evaler) *Preprocessor {
	pp := &Preprocessor{
		tags: evaler.Tags(),
	}
	pp.evaler = evaler
	return pp
}

func (pp *Preprocessor) Process(filePath string, data string) (string, error) {
	var b strings.Builder
	last := 0
	texts := []string{}
	codes := []string{}
	for {
		idxStart := strings.Index(data[last:], pp.tags[0])
		idxEnd := strings.Index(data[last:], pp.tags[1])
		//fmt.Printf("cock %d %d %d\n", last, idxStart, idxEnd)
		if idxStart < 0 {
			if idxEnd >= 0 {
				return "", UnexpectedError{
					What: "end tag",
				}
			}
			texts = append(texts, data[last:])
			break
		} else if idxEnd < 0 {
			return "", UnexpectedError{
				What: "start tag",
			}
		}
		text := data[last:idxStart]
		texts = append(texts, text)

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

		data = data[idxEnd + len(pp.tags[1]):]
		/*if len(data) > 0 && data[0] == '\n' {
			data = data[1:]
		}*/
	}
	codeRets, err := pp.evaler.Eval(filePath, codes)
	if err != nil {
		return "", err
	}

	for i, codeRet := range codeRets {
		fmt.Fprint(&b, texts[i])
		fmt.Fprintf(&b, codeRet)
	}
	fmt.Fprint(&b, texts[len(codeRets)])

	return b.String(), nil
}