app_for_reddit/Reddit App/Services/PostGenerationService.swift

import Foundation

protocol PostGenerationServiceProtocol: Sendable {
    func generatePost(from draft: PostDraft) async throws -> GeneratedPost
}

enum PostGenerationError: LocalizedError {
    case emptyTopic
    case emptySubreddit

    var errorDescription: String? {
        switch self {
        case .emptyTopic: "Enter a topic or keywords for AI generation."
        case .emptySubreddit: "Enter a subreddit to tailor the post."
        }
    }
}

struct MockPostGenerationService: PostGenerationServiceProtocol {
    func generatePost(from draft: PostDraft) async throws -> GeneratedPost {
        guard !draft.subreddit.trimmingCharacters(in: .whitespaces).isEmpty else {
            throw PostGenerationError.emptySubreddit
        }
        guard !draft.topic.trimmingCharacters(in: .whitespaces).isEmpty else {
            throw PostGenerationError.emptyTopic
        }

        try await Task.sleep(for: .milliseconds(900))

        let subreddit = draft.subreddit.replacingOccurrences(of: "r/", with: "")
        let topic = draft.topic.trimmingCharacters(in: .whitespaces)
        let tone = draft.tone.title.lowercased()

        let title = makeTitle(topic: topic, subreddit: subreddit, tone: draft.tone)
        let body = makeBody(
            topic: topic,
            subreddit: subreddit,
            tone: tone,
            postType: draft.postType
        )
        let flair = suggestFlair(for: draft.postType, subreddit: subreddit)

        return GeneratedPost(title: title, body: body, suggestedFlair: flair)
    }

    private func makeTitle(topic: String, subreddit: String, tone: PostTone) -> String {
        switch tone {
        case .humorous:
            "I tried \(topic) so you don't have to — r/\(subreddit) was not wrong"
        case .professional:
            "Analysis: \(topic) — findings from r/\(subreddit)"
        case .informative:
            "Everything you need to know about \(topic) [Guide]"
        case .controversial:
            "Unpopular opinion: \(topic) is overrated. Change my mind."
        case .storytelling:
            "How \(topic) completely changed my perspective"
        case .casual:
            "Anyone else obsessed with \(topic) lately?"
        }
    }

    private func makeBody(
        topic: String,
        subreddit: String,
        tone: String,
        postType: RedditPostType
    ) -> String {
        switch postType {
        case .text:
            """
            Hey r/\(subreddit),

            I've been diving deep into **\(topic)** and wanted to share what I've learned.

            **Key points:**
            - Started exploring this after seeing it trending here
            - The community's take has been incredibly helpful
            - Still have a few open questions (see below)

            **My experience:**
            This started as a casual experiment but turned into something I genuinely care about. Would love to hear how others in this subreddit approach \(topic).

            **Questions for the community:**
            1. What's your go-to resource for \(topic)?
            2. Any common mistakes beginners should avoid?
            3. Who else here is working on something similar?

            Written in a \(tone) tone — happy to refine based on feedback!
            """
        case .image:
            "Caption: A visual breakdown of \(topic) — details in the comments. Let me know what you think!"
        case .link:
            "Found this great resource on \(topic). Thought r/\(subreddit) would find it useful. Summary in comments."
        case .video:
            "Just watched this breakdown of \(topic) and had to share. The section at 3:42 really nails it."
        case .poll:
            "Curious where r/\(subreddit) stands on \(topic). Vote below!"
        }
    }

    private func suggestFlair(for postType: RedditPostType, subreddit: String) -> String {
        switch postType {
        case .text: "Discussion"
        case .image: "Media"
        case .link: "News"
        case .video: "Video"
        case .poll: "Poll"
        }
    }
}