1 files changed, 68 insertions, 0 deletions
diff --git a/coords.go b/coords.go
new file mode 100644
index 0000000..ee13dba
--- /dev/null
+++ b/coords.go
@@ -0,0 +1,68 @@
+/*
+coords calculates coordinates for spreadsheets.
+*/
+package coords
+
+import (
+	"errors"
+	"fmt"
+)
+
+const (
+	maxCols      = 16384
+	maxAlphabets = (maxCols / 26) - 1
+)
+
+// ColAlpha returns an alpha representation of a column index.
+// index is an integer - ColAlpha(0) returns "A", etc.
+func ColIndexToAlpha(index int) (string, error) {
+	max := len(colstream) - 1
+	if index <= max {
+		return colstream[index], nil
+	} else {
+		msg := fmt.Sprintf("cannot have more than %d columns", max)
+		return "", errors.New(msg)
+	}
+}
+
+var colstream = cols(maxAlphabets)
+
+// ColLettersToIndex converts an alpha column
+// reference to a zero-based numeric column identifier.
+func ColAlphaToIndex(letters string) (int, error) {
+	max := len(colstream) - 1
+	for i, v := range colstream {
+		if i > max {
+			msg := fmt.Sprintf("Cannot exceed maximum of %d", max)
+			return 0, errors.New(msg)
+		}
+		if v == letters {
+			return i, nil
+		}
+	}
+	return 0, errors.New("Cannot find requested string.")
+}
+
+//alphabet generates all the letters of the alphabet.
+func alphabet() []string {
+	letters := make([]string, 26)
+	for idx := range letters {
+		letters[idx] = string('A' + byte(idx))
+	}
+	return letters
+}
+
+//cols generates the alpha column component of Excel cell references
+//Adds n alphabets to the first (A..Z) alphabet.
+func cols(n int) []string {
+	out := alphabet()
+	alen := len(out)
+	tmp := make([]string, alen)
+	copy(tmp, out)
+	for cycle := 0; cycle < n; cycle++ {
+		for y := 0; y < alen; y++ {
+			out = append(out, out[(cycle+2)-2]+tmp[y])
+		}
+	}
+	return out
+}