okit/observer/local.go

// Copyright (C) 2022 The OKit Authors
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
// IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE
// OR OTHER DEALINGS IN THE SOFTWARE.

package observer

import (
	"bufio"
	"io"
	"os"

	"go.pitz.tech/okit/format"
	"go.pitz.tech/okit/pb"
)

// LocalOption defines a mechanism that allows properties of the observer to be overridden or configured.
type LocalOption func(l *local)

// Output configures the output of the local observer to point to the provided writer.
func Output(writer io.Writer) LocalOption {
	return func(l *local) {
		l.output = bufio.NewWriter(writer)
	}
}

// Format configures how the information is written to the target writer.
func Format(fmt string) LocalOption {
	return func(l *local) {
		switch fmt {
		case "json":
			l.format = format.JSON{}
		default:
			l.format = format.Text{}
		}
	}
}

// Local creates an Observer that writes logs to an output stream using a configured format.
func Local(opts ...LocalOption) Observer {
	l := &local{
		output: bufio.NewWriter(os.Stdout),
		format: format.Text{},
	}

	for _, o := range opts {
		o(l)
	}

	return l
}

type local struct {
	output *bufio.Writer
	format format.Marshaler
}

func (l *local) Observe(entries []*pb.Entry) {
	// TODO: how to handle internal errors

	for _, entry := range entries {
		_ = l.format.Marshal(l.output, entry)
	}

	_ = l.output.Flush()
}