https://platform.openai.com/docs/introduction

ChatService.swift

import c // https://github.com/0xOpenBytes/c
import o // https://github.com/0xOpenBytes/o
import Plugin // https://github.com/0xLeif/Plugin
import Foundation

class ChatService: Pluginable {
    enum Constants {
        enum Model {
            static let davinci = "text-davinci-003"
        }

        static let apiKey = "KEY_HERE"
    }

    enum ChatError: String, LocalizedError {
        case noData = "No Data"
        case noChoices = "No AI Choices"
    }

    /**
     {
       "id": "cmpl-uqkvlQyYK7bGYrRHQ0eXlWi7",
       "object": "text_completion",
       "created": 1589478378,
       "model": "text-davinci-003",
       "choices": [
         {
           "text": "\n\nThis is indeed a test",
           "index": 0,
           "logprobs": null,
           "finish_reason": "length"
         }
       ],
       "usage": {
         "prompt_tokens": 5,
         "completion_tokens": 7,
         "total_tokens": 12
       }
     }
     */
    enum JSONKeys {
        enum Root: String {
            case id, object, created, model, choices, usage
        }

        enum Choices: String {
            case text, index, logprobs, finish_reason
        }

        enum Usage: String {
            case prompt_tokens, completion_tokens, total_tokens
        }
    }

    typealias ChatServicePluginPayload = c.JSON<JSONKeys.Root>

    var plugins: [any Plugin]

    init(plugins: [any Plugin] = []) {
        self.plugins = plugins
    }

    func completion(for prompt: String) async throws -> String {
        struct Payload: Codable {
            let model: String
            let prompt: String
            let max_tokens: Int
            let temperature: Int
        }

        let body = try JSONEncoder().encode(
            Payload(
                model: Constants.Model.davinci,
                prompt: prompt,
                max_tokens: 2048,
                temperature: 0
            )
        )

        /*
         curl https://api.openai.com/v1/completions \
           -H 'Content-Type: application/json' \
           -H 'Authorization: Bearer YOUR_API_KEY' \
           -d '{
           "model": "text-davinci-003",
           "prompt": "Say this is a test",
           "max_tokens": 7,
           "temperature": 0
         }'
         */
        let dataResponse = try await o.url.post(
            url: URL(string: "https://api.openai.com/v1/completions")!,
            body: body,
            headerFields: [
                "Content-Type": "application/json",
                "Authorization": "Bearer \(Constants.apiKey)"
            ]
        )

        guard
            let data = dataResponse.data
        else {
            throw ChatError.noData
        }

        let json = c.JSON<JSONKeys.Root>(data: data)

        try await handle(value: json)

        guard
            let choices = json.array(.choices, keyed: JSONKeys.Choices.self),
            let firstChoice = choices.first?.get(.text, as: String.self)
        else {
            throw ChatError.noChoices
        }

        return firstChoice
    }
}