package emdbed

import (
	"fmt"
	"regexp"
	"strconv"
	"strings"
)

var endline = regexp.MustCompile(`(?m)$`)

type emdbed struct {
	name     string
	contents string
	language string
	start    string
	end      string
}

func (e emdbed) line(line int, end bool) (int, error) {
	if line == 1 && !end {
		return 0, nil
	}
	indexes := endline.FindAllStringIndex(e.contents, -1)
	if len(indexes) < line {
		return 0, fmt.Errorf("file %q has no line %d", e.name, line)
	}
	dec := 1
	if !end {
		dec++
	}
	var inc int
	if !end {
		inc++
	}
	return indexes[line-dec][0] + inc, nil
}

func (e emdbed) regex(pattern string, end bool) (int, error) {
	re, err := regexp.Compile(pattern)
	if err != nil {
		return 0, err
	}
	match := re.FindStringIndex(e.contents)
	if match == nil {
		return 0, fmt.Errorf("file %q has no match for pattern %q", e.name, pattern)
	}
	var inc int
	if end {
		inc++
	}
	return match[0] + inc, nil
}

func (e emdbed) selector(selector string, end bool) (int, error) {
	switch {
	case strings.HasPrefix(selector, "L"):
		line, err := strconv.Atoi(selector[1:])
		if err != nil {
			return 0, err
		}
		return e.line(line, end)
	case strings.HasPrefix(selector, "/"):
		pattern := strings.Trim(selector, "/")
		return e.regex(pattern, end)
	default:
		return 0, fmt.Errorf("unknown selector %q", selector)
	}
}

func (e emdbed) Start() (int, error) {
	if e.start == "" {
		return 0, nil
	}
	return e.selector(e.start, false)
}

func (e emdbed) End() (int, error) {
	if e.end == "" {
		return len(e.contents), nil
	}
	return e.selector(e.end, true)
}

func (e emdbed) Selection() (string, error) {
	start, err := e.Start()
	if err != nil {
		return "", err
	}
	end, err := e.End()
	if err != nil {
		return "", err
	}
	return e.contents[start:end], nil
}