A script for an Alfred qalc workflow

qalc.swift

#!/usr/bin/env bash
/*/../usr/bin/true
source="$0"
compiled="$0".cache
if [[ "$source" -nt "$compiled" ]]; then
    swiftc "$source" -o "$compiled" || exit
fi
"$compiled" "$@"
exit
*/

import Foundation

extension String {
    subscript(value: PartialRangeUpTo<Int>) -> Substring {
        get {
            return self[..<index(startIndex, offsetBy: value.upperBound)]
        }
    }

    subscript(value: PartialRangeThrough<Int>) -> Substring {
        get {
            return self[...index(startIndex, offsetBy: value.upperBound)]
        }
    }

    subscript(value: PartialRangeFrom<Int>) -> Substring {
        get {
            return self[index(startIndex, offsetBy: value.lowerBound)...]
        }
    }
}

public struct StderrOutputStream: TextOutputStream {
    public mutating func write(_ string: String) { fputs(string, stderr) }
}
public var STDERR = StderrOutputStream()

let ENV = ProcessInfo.processInfo.environment

struct Item: Encodable {
    var valid: Bool
    var uid: String
    var title: String
    var subtitle: String?
    var arg: String?
    var text: Text?

    struct Text: Encodable {
        var copy: String
        var largetype: String
    }
}

struct Response: Encodable {
    let items: [Item]
}

func respond(_ items: [Item]) throws {
    let d = try JSONEncoder().encode(Response(items: items))
    let s = String(decoding: d, as: UTF8.self)
    print(s)
}

func respond(_ item: Item) throws {
    try respond([item])
}

func system(stdin: Data? = nil, _ cmd: String...) throws -> String {
    let p = Process()
    p.executableURL = URL(fileURLWithPath: cmd[0])
    p.arguments = Array(cmd[1...])
    p.standardOutput = Pipe()

    if let d = stdin {
        let input = Pipe()
        p.standardInput = input

        input.fileHandleForWriting.write(d)
        input.fileHandleForWriting.closeFile()
    }

    try p.run()
    p.waitUntilExit()
    let d = (p.standardOutput as! Pipe).fileHandleForReading.readDataToEndOfFile()
    return String(decoding: d, as: UTF8.self)
}

var q = CommandLine.arguments[1]
if q == "" { q = "0" }
print(q, to: &STDERR)

struct QalcError: LocalizedError {
    let message: String

    var errorDescription: String? { return message }
}

do {
    let history = ((try? String(contentsOfFile: ENV["alfred_workflow_data"]! + "/history").components(separatedBy: "\n")) ?? []).enumerated()
    let varsString = history.map { "variable r\($0.offset) \($0.element)" }.joined(separator: "\n")
    let vars = Data(varsString.utf8)
    print(varsString, to: &STDERR)

    let out = try system(stdin: vars, "/usr/local/bin/qalc", "+u8", "-f", "-", "-s", "update_exchange_rates 1days", q)

    print(out, to: &STDERR)
    let lines = out.components(separatedBy: "\n")

    let errorPrefix = "error: "
    let warningPrefix = "warning: "

    let result: String
    let warning: String?

    if out.starts(with: errorPrefix) {
        throw QalcError(message: String(lines[0][errorPrefix.count...]))
    } else if out.starts(with: warningPrefix) {
        warning = String(lines[0][warningPrefix.count...])
        result = lines[1]
    } else {
        warning = nil
        result = lines[0]
    }

    let resultValue = result.components(separatedBy: " = ")[1]

    let resultItem = Item(
        valid: true,
        uid: "swift-result",
        title: result,
        subtitle: warning,
        arg: resultValue,
        text: Item.Text(
            copy: resultValue,
            largetype: result
        )
    )

    let historyItems = history.map {
        Item(
            valid: true,
            uid: UUID().uuidString,
            title: "\($0.element)",
            subtitle: "r\($0.offset) - history",
            arg: $0.element,
            text: Item.Text(
                copy: resultValue,
                largetype: resultValue
            )
        )
    }

    try respond([resultItem] + historyItems)
} catch {
    print("\(error)", to: &STDERR)
    try! respond(
        Item(
            valid: false,
            uid: "rip",
            title: "\(error.localizedDescription)",
            subtitle: "error",
            arg: nil,
            text: nil
        )
    )
}