Exercise - Read and write to files

7 minutes

You can also use the File class in .NET to write data to files and read data from files.

You're almost finished creating a .NET masterpiece for Tailwind Traders. So far, your code reads any directory, finds all .json files, and creates a totals.txt file.

In this exercise, you complete the project by reading the .json files, adding up the store totals, and writing the grand total to the totals.txt file.

Add System.Text.Json to the project

Using the terminal, add Json.NET to the project.
```
dotnet add package System.Text.Json
```

Prepare for sales data

At the top of Program.cs, add using Newtonsoft.Json:
```
using System.Text.Json;
```
In Program.cs directly under the FindFiles method, add a new record that models the sales.json data:
```
record SalesData (double Total);
```

Create a method to calculate sales totals

In Program.cs, just before the record line that you added in the previous step, create a new function that calculates the sales total. This method should take an IEnumerable<string> of file paths that it can iterate over.
```
double CalculateSalesTotal(IEnumerable<string> salesFiles)
{
    double salesTotal = 0;

    // READ FILES LOOP

    return salesTotal;
}
```

Within that method, replace // READ FILES LOOP with a loop that iterates over the salesFiles, reads the file, parses the content as JSON, and then increments the salesTotal variable with the total value from the file:

double CalculateSalesTotal(IEnumerable<string> salesFiles)
{
    double salesTotal = 0;

    // Loop over each file path in salesFiles
    foreach (var file in salesFiles)
    {      
        // Read the contents of the file
        string salesJson = File.ReadAllText(file);

        // Parse the contents as JSON
        SalesData? data = JsonSerializer.Deserialize<SalesData?>(salesJson);

        // Add the amount found in the Total field to the salesTotal variable
        salesTotal += data?.Total ?? 0;
    }

    return salesTotal;
}

Call the CalculateSalesTotals method

In the Program.cs file, add a call to the CalculateSalesTotal function just above the File.WriteAllText call:

var currentDirectory = Directory.GetCurrentDirectory();
var storesDir = Path.Combine(currentDirectory, "stores");

var salesTotalDir = Path.Combine(currentDirectory, "salesTotalDir");
Directory.CreateDirectory(salesTotalDir);

var salesFiles = FindFiles(storesDir);

var salesTotal = CalculateSalesTotal(salesFiles); // Add this line of code

File.WriteAllText(Path.Combine(salesTotalDir, "totals.txt"), String.Empty);

Write the total to the totals.txt file

In the Program.cs file, modify the File.WriteAllText block to write the value of the salesTotal variable to the totals.txt file. While you're at it, change the File.WriteAllText call to File.AppendAllText so nothing in the file gets overwritten.

var currentDirectory = Directory.GetCurrentDirectory();            
var storesDir = Path.Combine(currentDirectory, "stores");

var salesTotalDir = Path.Combine(currentDirectory, "salesTotalDir");
Directory.CreateDirectory(salesTotalDir);            

var salesFiles = FindFiles(storesDir);

var salesTotal = CalculateSalesTotal(salesFiles);

File.AppendAllText(Path.Combine(salesTotalDir, "totals.txt"), $"{salesTotal}{Environment.NewLine}");

Press Ctrl+S / Cmd+S to save the Program.cs file.

Run the program

Run the program from the terminal:
```
dotnet run
```
There's no output from the program. If you look in the salesTotalDir/totals.txt file, you find the total of all the sales from the sales.json file.
Run the program from the terminal again.
```
dotnet run
```
Select the salesTotalDir/totals.txt file.

The totals.txt file now has a second line. Every time you run the program, the totals are added up again and a new line is written to the file.

Outstanding work! You've written a smart, robust, and handy tool that Tailwind Traders can use to process all of its stores' sales every night. In the next unit, we'll review what you learned and a few tips to remember.

Got stuck?

If you got stuck during this exercise, here's the full code for this project:

using Newtonsoft.Json; 

var currentDirectory = Directory.GetCurrentDirectory();
var storesDirectory = Path.Combine(currentDirectory, "stores");

var salesTotalDir = Path.Combine(currentDirectory, "salesTotalDir");
Directory.CreateDirectory(salesTotalDir);   

var salesFiles = FindFiles(storesDirectory);

var salesTotal = CalculateSalesTotal(salesFiles);

File.AppendAllText(Path.Combine(salesTotalDir, "totals.txt"), $"{salesTotal}{Environment.NewLine}");

IEnumerable<string> FindFiles(string folderName)
{
    List<string> salesFiles = new List<string>();

    var foundFiles = Directory.EnumerateFiles(folderName, "*", SearchOption.AllDirectories);

    foreach (var file in foundFiles)
    {
        var extension = Path.GetExtension(file);
        if (extension == ".json")
        {
            salesFiles.Add(file);
        }
    }

    return salesFiles;
}

double CalculateSalesTotal(IEnumerable<string> salesFiles)
{
    double salesTotal = 0;
    
    // Loop over each file path in salesFiles
    foreach (var file in salesFiles)
    {      
        // Read the contents of the file
        string salesJson = File.ReadAllText(file);
    
        // Parse the contents as JSON
        SalesData? data = JsonConvert.DeserializeObject<SalesData?>(salesJson);
    
        // Add the amount found in the Total field to the salesTotal variable
        salesTotal += data?.Total ?? 0;
    }
    
    return salesTotal;
}

record SalesData (double Total);