From e98e155f38bc6e4643df1160a17752e9ab198cf5 Mon Sep 17 00:00:00 2001
From: do-i-need-a-username <>
Date: Mon, 11 Dec 2023 10:49:07 +1000
Subject: [PATCH] handle stdin

---
 .gitignore |  1 +
 README.md  | 39 ++++++++++++++++++++++---------
 input.json | 17 ++++++++++++++
 main.go    | 67 +++++++++++++++++++++++-------------------------------
 4 files changed, 75 insertions(+), 49 deletions(-)
 create mode 100644 input.json

diff --git a/.gitignore b/.gitignore
index 14d287f..b684f36 100644
--- a/.gitignore
+++ b/.gitignore
@@ -20,3 +20,4 @@
 # Go workspace file
 go.work
 bin/**
+*.ndjson
diff --git a/README.md b/README.md
index b15e108..a0f8ac5 100644
--- a/README.md
+++ b/README.md
@@ -5,12 +5,12 @@
 [![codecov](https://codecov.io/gh/do-i-need-a-username/j2ndj/branch/main/graph/badge.svg?token=ZQZQZQZQZQ)](https://codecov.io/gh/do-i-need-a-username/j2ndj)
 [![Go Reference](https://pkg.go.dev/badge/github.com/do-i-need-a-username/j2ndj.svg)](https://pkg.go.dev/github.com/do-i-need-a-username/j2ndj)
 
-Converts a json file to [ndjson](https://ndjson.org/) file. (New Line Delimited JSON)
+Converts json to [ndjson](https://ndjson.org/), New Line Delimited JSON.
 
 ## Installation ##
 
 ```bash
-# Install go
+# Install with go
 go install github.com/do-i-need-a-username/j2ndj@latest
 ```
 
@@ -20,13 +20,30 @@ go install github.com/do-i-need-a-username/j2ndj@latest
 # find install path
 which j2ndj
 /Users/myuser/go/bin/j2ndj
-# Run the command with output file
-/Users/myuser/go/bin/j2ndj -input /tmp/logs.json -output /tmp/nd_logs.ndjson
-# ls
-# logs.json   nd_logs.ndjson
-
-# Run the command with output file inferred from input file
-/Users/myuser/go/bin/j2ndj -input /tmp/logs.json
-# ls
-# logs.json   logs.ndjson
+
+# stdin t ostdout
+cat input.json | ./bin/j2ndj
+{"age":30,"city":"New York","name":"John Doe"}
+{"age":28,"city":"Los Angeles","name":"Jane Doe"}
+{"age":35,"city":"Chicago","name":"Bob Smith"}
+
+# stdin to output file
+cat input.json | ./bin/j2ndj -output=./output.ndjson
+
+# input file to stdout
+./bin/j2ndj -input=./input.json
+{"age":30,"city":"New York","name":"John Doe"}
+{"age":28,"city":"Los Angeles","name":"Jane Doe"}
+{"age":35,"city":"Chicago","name":"Bob Smith"}
+
+# input file to output file
+./bin/j2ndj -input=./input.json -output=./output.ndjson
+```
+
+## Alternative ##
+
+Use jq to convert json to ndjson
+
+```bash
+jq -c '.[]' input.json > output.ndjson
 ```
diff --git a/input.json b/input.json
new file mode 100644
index 0000000..1f60a5f
--- /dev/null
+++ b/input.json
@@ -0,0 +1,17 @@
+[
+    {
+        "name": "John Doe",
+        "age": 30,
+        "city": "New York"
+    },
+    {
+        "name": "Jane Doe",
+        "age": 28,
+        "city": "Los Angeles"
+    },
+    {
+        "name": "Bob Smith",
+        "age": 35,
+        "city": "Chicago"
+    }
+]
diff --git a/main.go b/main.go
index aab034f..05a0c3e 100644
--- a/main.go
+++ b/main.go
@@ -1,3 +1,7 @@
+// run converts JSON to NDJSON format.
+// It reads the input JSON file or standard input if no input file is provided.
+// It writes the output to the specified file or standard output if no output file is provided.
+// The function returns an error if any error occurs during the conversion process.
 package main
 
 import (
@@ -6,8 +10,6 @@ import (
 	"fmt"
 	"io"
 	"os"
-	"path/filepath"
-	"strings"
 )
 
 var (
@@ -17,61 +19,50 @@ var (
 
 // Convert json to ndjson
 func run() error {
-	flag.Usage = func() {
-		fmt.Printf("Usage of %s:\n", os.Args[0])
-		fmt.Println("Converts a json file to a New Line Delimited JSON (ndjson) file.")
-		fmt.Println("Flags:")
-		flag.PrintDefaults()
-	}
-
-	flag.Parse()
+	var reader io.Reader
+	var writer io.Writer
 
 	if *input == "" {
-		flag.Usage()
-		os.Exit(1)
+		reader = os.Stdin
+	} else {
+		file, err := os.Open(*input)
+		if err != nil {
+			return fmt.Errorf("Error opening input file: %w", err)
+		}
+		defer file.Close()
+		reader = file
 	}
 
-	jsonFile, err := os.Open(*input)
-	if err != nil {
-		fmt.Println("Error opening file:", err)
-		os.Exit(1)
+	if *output == "" {
+		writer = os.Stdout
+	} else {
+		file, err := os.Create(*output)
+		if err != nil {
+			return fmt.Errorf("Error creating output file: %w", err)
+		}
+		defer file.Close()
+		writer = file
 	}
-	defer jsonFile.Close()
 
-	byteValue, err := io.ReadAll(jsonFile)
+	byteValue, err := io.ReadAll(reader)
 	if err != nil {
-		fmt.Println("Error reading file:", err)
-		os.Exit(1)
+		return fmt.Errorf("Error reading from input: %w", err)
 	}
 
 	var result []map[string]interface{}
 	err = json.Unmarshal(byteValue, &result)
 	if err != nil {
-		fmt.Println("Error parsing JSON:", err)
-		os.Exit(1)
-	}
-
-	outputFileName := *output
-	if outputFileName == "" {
-		outputFileName = strings.TrimSuffix(*input, filepath.Ext(*input)) + ".ndjson"
-	}
-	outputFile, err := os.Create(outputFileName)
-	if err != nil {
-		fmt.Println("Error creating output file:", err)
-		os.Exit(1)
+		return fmt.Errorf("Error decoding JSON from input: %w", err)
 	}
-	defer outputFile.Close()
 
 	for _, item := range result {
 		jsonStr, err := json.Marshal(item)
 		if err != nil {
-			fmt.Println("Error converting to JSON:", err)
-			os.Exit(1)
+			return fmt.Errorf("Error converting to JSON: %w", err)
 		}
-		_, err = outputFile.WriteString(string(jsonStr) + "\n")
+		_, err = writer.Write([]byte(string(jsonStr) + "\n"))
 		if err != nil {
-			fmt.Println("Error writing to output file:", err)
-			os.Exit(1)
+			return fmt.Errorf("Error writing to output: %w", err)
 		}
 	}