Method Extract

postgres/parser/pgdate/field_extract.go:108–276

Extract is the top-level function. It attempts to break the input string into a collection of date/time fields in order to populate a fieldExtract.

(s string)

// string into a collection of date/time fields in order to populate a
// fieldExtract.
func (fe *fieldExtract) Extract(s string) error {
	// Break the string into alphanumeric chunks.
	textChunks := make([]stringChunk, fieldMaximum)
	count, _ := chunk(s, textChunks)

	if count < 0 {
		return inputErrorf("too many fields in input")
	} else if count == 0 {
		return inputErrorf("empty or blank input")
	}

	// Create a place to store extracted numeric info.
	numbers := make([]numberChunk, 0, fieldMaximum)

	appendNumber := func(prefix, number string) error {
		v, err := strconv.Atoi(number)
		if err != nil {
			return err
		}

		// Allow exactly one non-whitespace separator.
		s := ' '
		for _, r := range prefix {
			switch {
			case s == ' ':
				s = r
			case unicode.IsSpace(r):
			// Ignore whitespace characters.
			default:
				return inputErrorf(`detected multiple separators in "%s""`, prefix)
			}
		}

		numbers = append(numbers, numberChunk{separator: s, v: v, magnitude: len(number)})
		return nil
	}

	var leftoverText string

	// First, we'll try to pluck out any keywords that exist in the input.
	// If a chunk is not a keyword or other special-case pattern, it
	// must be a numeric value, which we'll pluck out for a second
	// pass. If we see certain sentinel values, we'll pick them out,
	// but keep going to ensure that the user hasn't written something
	// like "epoch infinity".
	for idx, chunk := range textChunks[:count] {
		match := strings.ToLower(chunk.Match)

		switch match {
		case keywordEpoch:
			if err := fe.matchedSentinel(TimeEpoch, match); err != nil {
				return err
			}

		case keywordInfinity:
			if strings.HasSuffix(chunk.NotMatch, "-") {
				if err := fe.matchedSentinel(TimeNegativeInfinity, match); err != nil {
					return err