Stream to Excel table (#530)

* Support all datatypes for StreamWriter

* Support setting styles with StreamWriter

**NOTE:** This is a breaking change. Values are now explicitly
passed as a []interface{} for simplicity. We also let styles to be
set at the same time.

* Create function to write stream into a table

* Write rows directly to buffer

Avoiding the xml.Encoder makes the streamer faster and use less
memory.

Using the included benchmark, the results went from:

> BenchmarkStreamWriter-4   514  2576155 ns/op  454918 B/op  6592 allocs/op

down to:

> BenchmarkStreamWriter-4  1614   777480 ns/op  147608 B/op  5570 allocs/op

* Use AddTable instead of SetTable

This requires reading the cells after they have been written,
which requires additional structure for the temp file.

As a bonus, we now efficiently allocate only one buffer when
reading the file back into memory, using the same approach
as ioutil.ReadFile.

* Use an exported Cell type to handle inline styles for StreamWriter

1 files changed, 20 insertions, 3 deletions

diff --git a/adjust.go b/adjust.go
index c15d4b4..69ded1b 100644
--- a/adjust.go
+++ b/adjust.go
@@ -196,10 +196,14 @@ func (f *File) adjustAutoFilterHelper(dir adjustDirection, coordinates []int, nu
 // areaRefToCoordinates provides a function to convert area reference to a
 // pair of coordinates.
 func (f *File) areaRefToCoordinates(ref string) ([]int, error) {
-	coordinates := make([]int, 4)
 	rng := strings.Split(ref, ":")
-	firstCell := rng[0]
-	lastCell := rng[1]
+	return areaRangeToCoordinates(rng[0], rng[1])
+}
+
+// areaRangeToCoordinates provides a function to convert cell range to a
+// pair of coordinates.
+func areaRangeToCoordinates(firstCell, lastCell string) ([]int, error) {
+	coordinates := make([]int, 4)
 	var err error
 	coordinates[0], coordinates[1], err = CellNameToCoordinates(firstCell)
 	if err != nil {
@@ -209,6 +213,19 @@ func (f *File) areaRefToCoordinates(ref string) ([]int, error) {
 	return coordinates, err
 }
 
+func sortCoordinates(coordinates []int) error {
+	if len(coordinates) != 4 {
+		return errors.New("coordinates length must be 4")
+	}
+	if coordinates[2] < coordinates[0] {
+		coordinates[2], coordinates[0] = coordinates[0], coordinates[2]
+	}
+	if coordinates[3] < coordinates[1] {
+		coordinates[3], coordinates[1] = coordinates[1], coordinates[3]
+	}
+	return nil
+}
+
 // coordinatesToAreaRef provides a function to convert a pair of coordinates
 // to area reference.
 func (f *File) coordinatesToAreaRef(coordinates []int) (string, error) {