package main

import (
	"math/rand/v2"
	"os"
	"path/filepath"
)

func makeOutputDir() {
	// Default to just "output"
	err := os.Mkdir("output", 0755)
	check(err, "cannot make directory")
}

func glitchImage(inputFile string, outputFile string, shitSize int64, iterations int64) error {
	// Ensure the output directory exists
	makeOutputDir()

	// Prepend the "output" directory to the output file
	outputFilePath := filepath.Join("output", outputFile)

	// Open the source file for reading
	source, err := os.Open(inputFile)
	check(err, "failed to open source file: %w")
	defer source.Close()

	// Create a new file for writing the glitched copy
	destination, err := os.Create(outputFilePath)
	check(err, "failed to create output file: %w")
	defer destination.Close()

	// Copy the contents of the source file to the destination
	_, err = destination.ReadFrom(source)
	check(err, "failed to copy file contents: %w")

	// Get the Stat() of the destination file
	fileInfo, err := destination.Stat()
	check(err, "failed to get file info: %w")

	// Get the size of the destination file
	fileSize := fileInfo.Size()

	// Generate a random offset within the file
	var i int64
	for i = 0; i < iterations; i++ {
		offset := rand.Int64N(fileSize)

		// Seek to the random offset in the destination file
		_, err = destination.Seek(offset, 0)
		check(err, "failed to seek to random offset: %w")

		// Generate random data and write it in
		shit := make([]byte, shitSize)
		_, err = destination.Write(shit)
		check(err, "failed to write shit data: %w")

		// fmt.Printf("Successfully wrote %d bytes of shit at offset %d in file %s\n", shitSize, offset, outputFilePath)
	}
	return nil
}