package json

import (
	"errors"
)

// ParsePath takes a JSONPath string and returns a slice of strings representing the path segments.
func ParsePath(path string) ([]string, error) {
	buf := newBuffer([]byte(path))
	result := make([]string, 0)

	for {
		b, err := buf.current()
		if err != nil {
			break
		}

		switch {
		case b == dollarSign || b == atSign:
			result = append(result, string(b))
			buf.step()

		case b == dot:
			buf.step()

			if next, _ := buf.current(); next == dot {
				buf.step()
				result = append(result, "..")

				extractNextSegment(buf, &result)
			} else {
				extractNextSegment(buf, &result)
			}

		case b == bracketOpen:
			start := buf.index
			buf.step()

			for {
				if buf.index >= buf.length || buf.data[buf.index] == bracketClose {
					break
				}

				buf.step()
			}

			if buf.index >= buf.length {
				return nil, errors.New("unexpected end of path")
			}

			segment := string(buf.sliceFromIndices(start+1, buf.index))
			result = append(result, segment)

			buf.step()

		default:
			buf.step()
		}
	}

	return result, nil
}

// extractNextSegment extracts the segment from the current index
// to the next significant character and adds it to the resulting slice.
func extractNextSegment(buf *buffer, result *[]string) {
	start := buf.index
	buf.skipToNextSignificantToken()

	if buf.index <= start {
		return
	}

	segment := string(buf.sliceFromIndices(start, buf.index))
	if segment != "" {
		*result = append(*result, segment)
	}
}