package terrace

import (
	"errors"
)

// LineData holds the parsed information from each line.
type LineData struct {
	// Which character is being used for indentation.
	Indent rune
	// How many indent characters are present in the current line.
	Level int
	// The number of characters before the start of the line's "head" section.
	OffsetHead int
	// The number of characters before the start of the line's "tail" section.
	OffsetTail int
}

// NewLineData initializes a LineData instance with default values.
func NewLineData(indent rune) *LineData {
	return &LineData{
		Indent:     indent,
		Level:      0,
		OffsetHead: 0,
		OffsetTail: 0,
	}
}

// ParseLine is the core Terrace parser function, sets level, offsetHead, and offsetTail in a LineData object based on the passed line.
func ParseLine(line string, lineData *LineData) error {
	if lineData == nil {
		return errors.New("'lineData' must be a non-nil pointer to a LineData struct")
	}
	if lineData.Indent == 0 {
		return errors.New("'lineData.Indent' must be a single character")
	}

	if len(line) == 0 {
		lineData.OffsetHead = 0
		lineData.OffsetTail = 0
	} else {
		level := 0
		for _, char := range line {
			if char == lineData.Indent {
				level++
			} else {
				break
			}
		}
		lineData.Level = level
		lineData.OffsetHead = level
		lineData.OffsetTail = level

		for lineData.OffsetTail < len(line) && line[lineData.OffsetTail] != ' ' {
			lineData.OffsetTail++
		}
	}

	return nil
}