gramora/gramora/Services/EmailWriterService.swift

import Foundation

protocol EmailWriterServicing {
    func generateEmail(
        prompt: String,
        subject: String,
        emailType: EmailType,
        tone: EmailTone
    ) async throws -> String
}

struct EmailWriterService: EmailWriterServicing {
    private let openAI: OpenAIChatServicing

    init(openAI: OpenAIChatServicing = OpenAIChatService()) {
        self.openAI = openAI
    }

    func generateEmail(
        prompt: String,
        subject: String,
        emailType: EmailType,
        tone: EmailTone
    ) async throws -> String {
        let trimmed = prompt.trimmingCharacters(in: .whitespacesAndNewlines)
        guard !trimmed.isEmpty else {
            throw OpenAIServiceError.apiError("Describe what the email should say.")
        }

        var userPrompt = "Email type: \(emailType.title)\nTone: \(tone.title)\n"
        let trimmedSubject = subject.trimmingCharacters(in: .whitespacesAndNewlines)
        if !trimmedSubject.isEmpty {
            userPrompt += "Subject: \(trimmedSubject)\n"
        }
        userPrompt += "\nContent instructions:\n\(trimmed)"

        return try await openAI.completeText(
            systemPrompt: """
            You are a professional email writer. Write a complete, ready-to-send email based on the \
            user's instructions. Include a subject line only if one was not already provided. \
            Return only the email text with no preamble or explanation.
            """,
            userPrompt: userPrompt
        )
    }
}