IOS–like "section" command

section.go

// Copyright 2017 Google 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
//
// https://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,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package main

import (
	"bufio"
	"fmt"
	"os"
	"strings"
	"unicode"
)

func Readln(ch chan string, f *os.File) {
	// Reads 'f' and outputs one line at a time to 'ch'

	defer close(ch)

	scanner := bufio.NewScanner(os.Stdin)
	for scanner.Scan() {
		ch <- scanner.Text()
	}

	if err := scanner.Err(); err != nil {
		fmt.Fprintln(os.Stderr, "reading stdin:", err)
	}
}

func NotSpace(c rune) bool {
	return !unicode.IsSpace(c)
}

func main() {
	searchstr := strings.Join(os.Args[1:], " ")

	ch := make(chan string, 16)
	go Readln(ch, os.Stdin)

	// Indent level where our search term is at
	lvl := -1

	for line := range ch {
		// Find the current indent level
		cur := strings.IndexFunc(line, NotSpace)

		// Look for our search string and print it
		if strings.Index(line, searchstr) != -1 {
			fmt.Println(line)

			// Save our indent level
			if lvl == -1 || cur < lvl {
				lvl = cur
			}
		} else {
			if lvl != -1 && cur > lvl {
				// If we're more indented than the search term, print line
				fmt.Println(line)
			} else {
				// Found an outdented line. Cancel search.
				lvl = -1
			}
		}

	}
}