DSV to JSON converter (Swift)

dsv-json.swift

import Foundation

var args = CommandLine.arguments
let name = args.removeFirst()

func printUsage() {
    print(
"Usage: \(name) [FILE] -d DELIM [-o OUT_FILE]"
    )
}

guard let filePath = args.first else {
    printUsage()
    print("Input file required.")
    exit(1)
}

guard var i = args.firstIndex(of: "-d"), args.count - 1 > i else {
    printUsage()
    print("Expected delimiter")
    exit(1)
}

var delimiter = args[i + 1]
var nameComponents = filePath.components(separatedBy: ".")
nameComponents[nameComponents.count - 1] = "json"
var outFilePath = nameComponents.joined(separator: ".")

if let i = args.firstIndex(of: "-o"), args.count - 1 > i {
    outFilePath = args[i + 1]
}

if delimiter == "\\t" {
    delimiter = "\t"
}

var columns = [String: [String]]()
let contents: String
do {
    contents = try String(contentsOfFile: filePath, encoding: .utf8)
} catch let error {
    print("Error reading file \(filePath): \(error)")
    exit(1)
}

let lines = contents.components(separatedBy: .newlines)
guard let firstLine = lines.first else {
    print("Missing keys in DSV file.")
    exit(1)
}

let keys = firstLine.components(separatedBy: delimiter)
keys.forEach { word in
    columns[word] = []
}

for (i, line) in lines.dropFirst().enumerated() {
    let values = line.components(separatedBy: delimiter)
    if values.count < keys.count {
        print("Skipping line \(i + 2) because it has \(values.count) values for \(keys.count) keys")
    }

    for (key, value) in zip(keys, values) {
        columns[key]!.append(value)
    }
}

if let data = try? JSONEncoder().encode(columns) {
    let url = URL(fileURLWithPath: outFilePath)
    do {
        try data.write(to: url)
    } catch let err {
        print("Cannot write to \(outFilePath): \(err)")
    }
} else {
    print("Cannot encode JSON data.")
    exit(1)
}