package emdbed

import (
	"fmt"
	"io"
	"os"
	"path/filepath"
	"regexp"
	"strings"
)

var (
	start = regexp.MustCompile(`(?m)^<!--\s*emdbed:\s*([^\s]+)\s*(~[\w]+)?\s*(?:(/[^/]+/|L\d+)\s*(/[^/]+/|L\d+)?)?\s*-->$`)
	end   = regexp.MustCompile(`(?m)^<!--\s*/emdbed\s*-->$`)
)

// ConvertFile is a helper for converting a file on disk
func ConvertFile(path string) (string, error) {
	fi, err := os.Open(path)
	if err != nil {
		return "", err
	}
	defer fi.Close()
	return Convert(filepath.Dir(path), fi)
}

// Convert converts an io.Reader with respect to a base directory
func Convert(dir string, file io.Reader) (string, error) {
	data, err := io.ReadAll(file)
	if err != nil {
		return "", err
	}
	contents := string(data)

	var out strings.Builder
	starts := start.FindAllStringSubmatchIndex(contents, -1)
	ends := end.FindAllStringIndex(contents, -1)
	if len(starts) != len(ends) {
		return "", fmt.Errorf("start selectors (%d) != end selectors (%d)", len(starts), len(ends))
	}
	var last int
	for idx, start := range starts {
		out.WriteString(contents[last:start[1]])

		relPath := contents[start[2]:start[3]]
		fileContents, err := os.ReadFile(filepath.Join(dir, relPath))
		if err != nil {
			return "", err
		}

		lang := strings.TrimPrefix(filepath.Ext(relPath), ".")
		if start[4] != -1 {
			lang = contents[start[4]+1 : start[5]]
		}

		var startSel string
		if start[6] != -1 {
			startSel = contents[start[6]:start[7]]
		}
		var endSel string
		if start[8] != -1 {
			endSel = contents[start[8]:start[9]]
		}

		e := emdbed{
			name:     relPath,
			contents: string(fileContents),
			language: lang,
			start:    startSel,
			end:      endSel,
		}
		sel, err := e.Selection()
		if err != nil {
			return "", err
		}
		out.WriteString(fmt.Sprintf("\n```%s\n%s\n```\n", e.language, sel))
		last = ends[idx][0]
	}
	out.WriteString(contents[last:])
	return out.String(), nil
}