app_for_reddit/Reddit App/Services/PostGenerationService.swift

import Foundation

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

enum PostGenerationServiceFactory {
    static func makeDefault() -> any PostGenerationServiceProtocol {
        if let apiKey = AIConfiguration.apiKey {
            return OpenAIPostGenerationService(apiKey: apiKey)
        }
        return MockPostGenerationService()
    }
}

enum PostGenerationError: LocalizedError {
    case emptyTopic
    case emptySubreddit
    case invalidSubreddit
    case apiUnavailable(String)
    case invalidResponse

    var errorDescription: String? {
        switch self {
        case .emptyTopic:
            "Enter a topic or keywords for AI generation."
        case .emptySubreddit:
            "Enter a subreddit to tailor the post."
        case .invalidSubreddit:
            "Subreddit names must be 3–21 characters and use only letters, numbers, or underscores."
        case .apiUnavailable(let message):
            message
        case .invalidResponse:
            "The AI returned an unexpected response. Please try again."
        }
    }
}

// MARK: - OpenAI

struct OpenAIPostGenerationService: PostGenerationServiceProtocol {
    let apiKey: String
    var model: String = "gpt-4o-mini"

    func generatePost(from draft: PostDraft) async throws -> GeneratedPost {
        try PostDraftValidator.validateForGeneration(topic: draft.topic, subreddit: draft.subreddit)

        let subreddit = PostDraftValidator.normalizedSubreddit(draft.subreddit)
        let topic = draft.topic.trimmingCharacters(in: .whitespaces)
        let prompt = buildPrompt(draft: draft, subreddit: subreddit, topic: topic)

        var request = URLRequest(url: URL(string: "https://api.openai.com/v1/chat/completions")!)
        request.httpMethod = "POST"
        request.setValue("Bearer \(apiKey)", forHTTPHeaderField: "Authorization")
        request.setValue("application/json", forHTTPHeaderField: "Content-Type")

        let body: [String: Any] = [
            "model": model,
            "temperature": 0.8,
            "response_format": ["type": "json_object"],
            "messages": [
                [
                    "role": "system",
                    "content": """
                    You write Reddit posts. Respond with JSON only using keys:
                    title (string, max 300 chars), body (string), suggestedFlair (string or null), \
                    pollOptions (array of 2-6 strings when post type is poll, otherwise null).
                    Respect NSFW, spoiler, and OC tags. Match the requested tone and post type.
                    """,
                ],
                ["role": "user", "content": prompt],
            ],
        ]
        request.httpBody = try JSONSerialization.data(withJSONObject: body)

        let (data, response) = try await URLSession.shared.data(for: request)
        guard let http = response as? HTTPURLResponse else {
            throw PostGenerationError.apiUnavailable("Couldn't reach the AI service.")
        }

        if http.statusCode == 401 {
            throw PostGenerationError.apiUnavailable("Invalid OpenAI API key.")
        }
        guard (200 ... 299).contains(http.statusCode) else {
            let message = String(data: data, encoding: .utf8) ?? "HTTP \(http.statusCode)"
            throw PostGenerationError.apiUnavailable("AI request failed: \(message)")
        }

        return try parseResponse(data, postType: draft.postType)
    }

    private func buildPrompt(draft: PostDraft, subreddit: String, topic: String) -> String {
        var lines = [
            "Subreddit: r/\(subreddit)",
            "Post type: \(draft.postType.title)",
            "Topic: \(topic)",
            "Tone: \(draft.tone.title)",
        ]

        if draft.isNSFW { lines.append("Tag: NSFW") }
        if draft.isSpoiler { lines.append("Tag: Spoiler") }
        if draft.isOC { lines.append("Tag: Original Content") }
        if !draft.flair.isEmpty { lines.append("Preferred flair: \(draft.flair)") }

        switch draft.postType {
        case .text:
            lines.append("Write a full text post with markdown formatting.")
        case .image:
            lines.append("Write a short image caption and optional supporting context in body.")
        case .link:
            lines.append("Write a link post description explaining why r/\(subreddit) should care.")
        case .video:
            lines.append("Write a video post description with a compelling hook.")
        case .poll:
            lines.append("Write poll context in body and provide \(draft.pollOptions.count) distinct poll options.")
        }

        return lines.joined(separator: "\n")
    }

    private func parseResponse(_ data: Data, postType: RedditPostType) throws -> GeneratedPost {
        struct APIEnvelope: Decodable {
            struct Choice: Decodable {
                struct Message: Decodable {
                    let content: String
                }
                let message: Message
            }
            let choices: [Choice]
        }

        struct Payload: Decodable {
            let title: String
            let body: String
            let suggestedFlair: String?
            let pollOptions: [String]?
        }

        let envelope = try JSONDecoder().decode(APIEnvelope.self, from: data)
        guard let content = envelope.choices.first?.message.content.data(using: .utf8) else {
            throw PostGenerationError.invalidResponse
        }

        let payload = try JSONDecoder().decode(Payload.self, from: content)
        let title = String(payload.title.prefix(PostDraftValidator.maxTitleLength))
        let body = String(payload.body.prefix(PostDraftValidator.maxBodyLength))

        var pollOptions = payload.pollOptions
        if postType == .poll {
            pollOptions = pollOptions?.map {
                $0.trimmingCharacters(in: .whitespaces)
            }.filter { !$0.isEmpty }
            if let pollOptions, pollOptions.count < 2 {
                throw PostGenerationError.invalidResponse
            }
        } else {
            pollOptions = nil
        }

        return GeneratedPost(
            title: title,
            body: body,
            suggestedFlair: payload.suggestedFlair,
            pollOptions: pollOptions
        )
    }
}

// MARK: - Mock

struct MockPostGenerationService: PostGenerationServiceProtocol {
    func generatePost(from draft: PostDraft) async throws -> GeneratedPost {
        try PostDraftValidator.validateForGeneration(topic: draft.topic, subreddit: draft.subreddit)

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

        let subreddit = PostDraftValidator.normalizedSubreddit(draft.subreddit)
        let topic = draft.topic.trimmingCharacters(in: .whitespaces)
        let tone = draft.tone.title.lowercased()

        let title = makeTitle(topic: topic, subreddit: subreddit, tone: draft.tone, tags: draft)
        let body = makeBody(
            topic: topic,
            subreddit: subreddit,
            tone: tone,
            postType: draft.postType,
            tags: draft
        )
        let flair = suggestFlair(for: draft.postType, draft: draft)
        let pollOptions = draft.postType == .poll ? makePollOptions(topic: topic, subreddit: subreddit) : nil

        return GeneratedPost(
            title: String(title.prefix(PostDraftValidator.maxTitleLength)),
            body: String(body.prefix(PostDraftValidator.maxBodyLength)),
            suggestedFlair: flair,
            pollOptions: pollOptions
        )
    }

    private func makeTitle(
        topic: String,
        subreddit: String,
        tone: PostTone,
        tags: PostDraft
    ) -> String {
        let prefix = tags.isNSFW ? "[NSFW] " : ""
        let base: 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?"
        }
        return prefix + base
    }

    private func makeBody(
        topic: String,
        subreddit: String,
        tone: String,
        postType: RedditPostType,
        tags: PostDraft
    ) -> String {
        var sections: [String] = []

        if tags.isSpoiler {
            sections.append("> **Spoiler warning** — details below.")
        }
        if tags.isOC {
            sections.append("*Original content — created by me.*")
        }

        let core: 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:
            """
            Visual breakdown of **\(topic)** — hope this helps someone in r/\(subreddit).

            Happy to answer questions in the comments!
            """
        case .link:
            """
            Found this resource on **\(topic)** and thought r/\(subreddit) would find it useful.

            **Why it matters:** concise overview with practical takeaways for this community.
            """
        case .video:
            """
            Just watched this breakdown of **\(topic)** and had to share with r/\(subreddit).

            The section that really nails it is around the middle — curious if you agree.
            """
        case .poll:
            """
            Curious where r/\(subreddit) stands on **\(topic)**. Vote below and share your reasoning!
            """
        }

        sections.append(core)
        return sections.joined(separator: "\n\n")
    }

    private func makePollOptions(topic: String, subreddit: String) -> [String] {
        [
            "Love it — best thing for r/\(subreddit)",
            "It's fine, but overhyped",
            "Not for me",
            "Still figuring out \(topic)",
        ]
    }

    private func suggestFlair(for postType: RedditPostType, draft: PostDraft) -> String {
        if !draft.flair.isEmpty { return draft.flair }
        if draft.isNSFW { return "NSFW" }
        return switch postType {
        case .text: "Discussion"
        case .image: "Media"
        case .link: "News"
        case .video: "Video"
        case .poll: "Poll"
        }
    }
}