package ticket

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

// taskCheckboxRe matches GFM/YouTrack-style task list items:
//
//	- [ ] unchecked
//	- [x] checked
//	* [X] also accepted
var taskCheckboxRe = regexp.MustCompile(`^(\s*)([-*+])\s+\[([ xX])\](\s*)(.*)$`)

// Checkbox is one task-list item inside a Markdown description.
type Checkbox struct {
	Line    int    // 0-based line index in the source
	Checked bool
	Text    string // label after the checkbox marker
}

// ListCheckboxes returns all task-list items in markdown source order.
func ListCheckboxes(markdown string) []Checkbox {
	if markdown == "" {
		return nil
	}
	lines := strings.Split(markdown, "\n")
	var out []Checkbox
	for i, line := range lines {
		m := taskCheckboxRe.FindStringSubmatch(line)
		if m == nil {
			continue
		}
		out = append(out, Checkbox{
			Line:    i,
			Checked: m[3] == "x" || m[3] == "X",
			Text:    m[5],
		})
	}
	return out
}

// ToggleCheckbox flips the checked state of the checkbox at index
// (0-based among ListCheckboxes results) and returns the updated markdown.
func ToggleCheckbox(markdown string, index int) (string, error) {
	boxes := ListCheckboxes(markdown)
	if index < 0 || index >= len(boxes) {
		return markdown, fmt.Errorf("checkbox %d: not found", index)
	}
	lines := strings.Split(markdown, "\n")
	lineIdx := boxes[index].Line
	m := taskCheckboxRe.FindStringSubmatch(lines[lineIdx])
	if m == nil {
		return markdown, fmt.Errorf("checkbox %d: line changed", index)
	}
	mark := " "
	if !(m[3] == "x" || m[3] == "X") {
		mark = "x"
	}
	lines[lineIdx] = m[1] + m[2] + " [" + mark + "]" + m[4] + m[5]
	return strings.Join(lines, "\n"), nil
}