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grate/grate.go
2021-02-12 10:50:33 -05:00

82 lines
2.2 KiB
Go

// Package grate opens tabular data files (such as spreadsheets and delimited plaintext files)
// and allows programmatic access to the data contents in a consistent interface.
package grate
import (
"errors"
"log"
"sort"
)
// Source represents a set of data collections.
type Source interface {
// List the individual data tables within this source.
List() ([]string, error)
// Get a Collection from the source by name.
Get(name string) (Collection, error)
}
// Collection represents an iterable collection of records.
type Collection interface {
// Next advances to the next record of content.
// It MUST be called prior to any Scan().
Next() bool
// Strings extracts values from the current record into a list of strings.
Strings() []string
// Scan extracts values from the current record into the provided arguments
// Arguments must be pointers to one of 5 supported types:
// bool, int, float64, string, or time.Time
// If invalid, returns ErrInvalidScanType
Scan(args ...interface{}) error
// IsEmpty returns true if there are no data values.
IsEmpty() bool
// Err returns the last error that occured.
Err() error
}
// OpenFunc defines a Source's instantiation function.
// It should return ErrNotInFormat immediately if filename is not of the correct file type.
type OpenFunc func(filename string) (Source, error)
// Open a tabular data file and return a Source for accessing it's contents.
func Open(filename string) (Source, error) {
for _, o := range srcTable {
src, err := o.op(filename)
if err == nil {
return src, nil
}
if !errors.Is(err, ErrNotInFormat) {
return nil, err
}
if Debug {
log.Println(" ", filename, "is not in", o.name, "format")
}
}
return nil, ErrUnknownFormat
}
type srcOpenTab struct {
name string
pri int
op OpenFunc
}
var srcTable = make([]*srcOpenTab, 0, 20)
// Register the named source as a grate datasource implementation.
func Register(name string, priority int, opener OpenFunc) error {
if Debug {
log.Println("Registering the", name, "format at priority", priority)
}
srcTable = append(srcTable, &srcOpenTab{name: name, pri: priority, op: opener})
sort.Slice(srcTable, func(i, j int) bool {
return srcTable[i].pri < srcTable[j].pri
})
return nil
}