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package csv
import (
encoding "encoding/csv"
"io"
)
type Writer interface {
Header() []string // Answer the header of the stream.
Blank() Record // Provide a blank record compatible with the stream.
Write(r Record) error // Write a single record into the underying stream.
Error() error // Return the final error.
Close(err error) error // Close the writer with the specified error.
}
// A constructor for a writer using the specified header.
// By convention, passing a nil to the Builder returns a Writer
// which will release any underlying resources held by the builder
// when Close(error) is called.
type WriterBuilder func(header []string) Writer
type writer struct {
header []string
builder RecordBuilder
encoder *encoding.Writer
closer io.Closer
err error
}
// Answer a Writer for the CSV stream constrained by specified header, using the specified encoding writer
func WithCsvWriter(w *encoding.Writer, c io.Closer) WriterBuilder {
return func(header []string) Writer {
result := &writer{
header: header,
builder: NewRecordBuilder(header),
encoder: w,
closer: c,
}
result.err = result.encoder.Write(header)
return result
}
}
// Answer a Writer for the CSV stream constrained by the specified header, using the specified io writer.
func WithIoWriter(w io.WriteCloser) WriterBuilder {
return WithCsvWriter(encoding.NewWriter(w), w)
}
// Answer a Writer for the CSV stream constrained by the specified header, using the specified io writer and delimiter.
func WithIoWriterAndDelimiter(w io.WriteCloser, delimiter rune) WriterBuilder {
writer := encoding.NewWriter(w)
writer.Comma = delimiter
return WithCsvWriter(writer, w)
}
// Answer the header that constrains the output stream
func (w *writer) Header() []string {
return w.header
}
// Answer a blank record for the output stream
func (w *writer) Blank() Record {
return w.builder(make([]string, len(w.header), len(w.header)))
}
// Write a record into the underlying stream.
func (w *writer) Write(r Record) error {
if w.err != nil {
return w.err
}
h := r.Header()
var d []string
if len(h) > 0 && len(w.header) == len(h) && &h[0] == &w.header[0] {
// optimisation to avoid copying or iterating over slice in default case
d = r.AsSlice()
} else {
// fallback in case where the stream and the record have a different header
d := make([]string, len(w.header), len(w.header))
for i, k := range w.header {
d[i] = r.Get(k)
}
}
return w.encoder.Write(d)
}
func (w *writer) Error() error {
return w.err
}
// Close the stream and propagate an error
func (w *writer) Close(err error) error {
w.encoder.Flush()
if err == nil {
err = w.encoder.Error()
}
w.err = err
if w.closer != nil {
return w.closer.Close()
} else {
return nil
}
}
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