package main

import (
	"fmt"
	"strings"

	"github.com/cqroot/prompt/constants"
	"github.com/cqroot/prompt/multichoose"
)

// Scrolling theme for cqroot/prompt. Allows items to be scrolled through
// using the arrow keys.
//
// choices is a list of strings to display.
// cursor is the index of the currently selected item.
// isSelected is a function that returns true if the item at the given index
func ThemeScroll(choices []string, cursor int, isSelected multichoose.IsSelected) string {
	s := strings.Builder{}
	s.WriteString("\n")

	lenChoices := len(choices)
	index := cursor
	limit := 10
	start := 0
	end := limit

	// Create a slice of items to display
	if lenChoices > limit {
		if index < limit/2 {
			end = limit
		} else if index >= limit/2 && index <= lenChoices-limit/2 {
			start = index - limit/2
			end = index + limit/2
			index = limit / 2
		} else {
			start = lenChoices - limit
			end = lenChoices
			index = limit - (lenChoices - index)
		}
	}

	// Loop through the slice and display each item.
	// We will determine if the item is selected or not by calling isSelected
	// with the index of the item, but since we're only displaying a slice of
	// the items we need to offset the index.
	for i, choice := range choices[start:end] {
		// offset represents the index of the item in the original list
		offset := i + start

		// Check if the item is the one at the cursor's location
		isCursor := index == i

		// Render item according to its state (selected + cursor / selected / normal)
		if isSelected(offset) {
			if isCursor {
				s.WriteString(constants.DefaultSelectedItemStyle.Render(fmt.Sprintf("[x] %s", choice)))
			} else {
				s.WriteString(constants.DefaultItemStyle.Render(fmt.Sprintf("[x] %s", choice)))
			}
		} else {
			if isCursor {
				s.WriteString(constants.DefaultSelectedItemStyle.Render(fmt.Sprintf("[•] %s", choice)))
			} else {
				s.WriteString(constants.DefaultItemStyle.Render(fmt.Sprintf("[ ] %s", choice)))
			}
		}

		s.WriteString("\n")
	}

	return s.String()
}