format.go

// Copyright 2015 PingCAP, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.

package format

import (
	"fmt"
	"io"
)

const (
	st0 = iota
	stBOL
	stPERC
	stBOLPERC
)

// Formatter is an io.Writer extended formatter by a fmt.Printf like function Format.
type Formatter interface {
	io.Writer
	Format(format string, args ...interface{}) (n int, errno error)
}

type indentFormatter struct {
	io.Writer
	indent      []byte
	indentLevel int
	state       int
}

// IndentFormatter returns a new Formatter which interprets %i and %u in the
// Format() formats string as indent and unindent commands. The commands can
// nest. The Formatter writes to io.Writer 'w' and inserts one 'indent'
// string per current indent level value.
// Behaviour of commands reaching negative indent levels is undefined.
//  IndentFormatter(os.Stdout, "\t").Format("abc%d%%e%i\nx\ny\n%uz\n", 3)
// output:
//  abc3%e
//      x
//      y
//  z
// The Go quoted string literal form of the above is:
//  "abc%%e\n\tx\n\tx\nz\n"
// The commands can be scattered between separate invocations of Format(),
// i.e. the formatter keeps track of the indent level and knows if it is
// positioned on start of a line and should emit indentation(s).
// The same output as above can be produced by e.g.:
//  f := IndentFormatter(os.Stdout, " ")
//  f.Format("abc%d%%e%i\nx\n", 3)
//  f.Format("y\n%uz\n")
func IndentFormatter(w io.Writer, indent string) Formatter {
	return &indentFormatter{w, []byte(indent), 0, stBOL}
}

func (f *indentFormatter) format(flat bool, format string, args ...interface{}) (n int, errno error) {
	buf := []byte{}
	for i := 0; i < len(format); i++ {
		c := format[i]
		switch f.state {
		case st0:
			switch c {
			case '\n':
				cc := c
				if flat && f.indentLevel != 0 {
					cc = ' '
				}
				buf = append(buf, cc)
				f.state = stBOL
			case '%':
				f.state = stPERC
			default:
				buf = append(buf, c)
			}
		case stBOL:
			switch c {
			case '\n':
				cc := c
				if flat && f.indentLevel != 0 {
					cc = ' '
				}
				buf = append(buf, cc)
			case '%':
				f.state = stBOLPERC
			default:
				if !flat {
					for i := 0; i < f.indentLevel; i++ {
						buf = append(buf, f.indent...)
					}
				}
				buf = append(buf, c)
				f.state = st0
			}
		case stBOLPERC:
			switch c {
			case 'i':
				f.indentLevel++
				f.state = stBOL
			case 'u':
				f.indentLevel--
				f.state = stBOL
			default:
				if !flat {
					for i := 0; i < f.indentLevel; i++ {
						buf = append(buf, f.indent...)
					}
				}
				buf = append(buf, '%', c)
				f.state = st0
			}
		case stPERC:
			switch c {
			case 'i':
				f.indentLevel++
				f.state = st0
			case 'u':
				f.indentLevel--
				f.state = st0
			default:
				buf = append(buf, '%', c)
				f.state = st0
			}
		default:
			panic("unexpected state")
		}
	}
	switch f.state {
	case stPERC, stBOLPERC:
		buf = append(buf, '%')
	}
	return f.Write([]byte(fmt.Sprintf(string(buf), args...)))
}

// Format implements Format interface.
func (f *indentFormatter) Format(format string, args ...interface{}) (n int, errno error) {
	return f.format(false, format, args...)
}

type flatFormatter indentFormatter

// FlatFormatter returns a newly created Formatter with the same functionality as the one returned
// by IndentFormatter except it allows a newline in the 'format' string argument of Format
// to pass through if the indent level is current zero.
//
// If the indent level is non-zero then such new lines are changed to a space character.
// There is no indent string, the %i and %u format verbs are used solely to determine the indent level.
//
// The FlatFormatter is intended for flattening of normally nested structure textual representation to
// a one top level structure per line form.
//  FlatFormatter(os.Stdout, " ").Format("abc%d%%e%i\nx\ny\n%uz\n", 3)
// output in the form of a Go quoted string literal:
//  "abc3%%e x y z\n"
func FlatFormatter(w io.Writer) Formatter {
	return (*flatFormatter)(IndentFormatter(w, "").(*indentFormatter))
}

// Format implements Format interface.
func (f *flatFormatter) Format(format string, args ...interface{}) (n int, errno error) {
	return (*indentFormatter)(f).format(true, format, args...)
}