import Foundation

public struct PrivateApplicationRules: Equatable, Sendable {
    public let content: String

    public init?(content: String?) {
        guard let content else { return nil }

        let trimmedContent = content.trimmingCharacters(in: .whitespacesAndNewlines)
        guard !trimmedContent.isEmpty else { return nil }

        self.content = trimmedContent
    }
}

public protocol ApplicationRuleProviding: Sendable {
    func privateApplicationRules() throws -> PrivateApplicationRules?
}

public struct StaticApplicationRuleProvider: ApplicationRuleProviding {
    private let rules: PrivateApplicationRules?

    public init(rules: PrivateApplicationRules?) {
        self.rules = rules
    }

    public func privateApplicationRules() throws -> PrivateApplicationRules? {
        rules
    }
}

public final class ApplicationRuleInjectingAIService: AIService, Sendable {
    private let baseService: any AIService
    private let ruleProvider: any ApplicationRuleProviding

    public init(
        baseService: any AIService,
        ruleProvider: any ApplicationRuleProviding
    ) {
        self.baseService = baseService
        self.ruleProvider = ruleProvider
    }

    public func generateSongProject(from request: SongProjectGenerationRequest) async throws -> SongProjectGenerationResult {
        try await baseService.generateSongProject(from: requestWithInjectedRules(request))
    }

    public func reviseLyrics(from request: LyricsRevisionRequest) async throws -> LyricsRevisionResult {
        try await baseService.reviseLyrics(from: requestWithInjectedRules(request))
    }

    public func proposeProjectUpdate(from request: SongProjectUpdateRequest) async throws -> SongProjectUpdateResult {
        try await baseService.proposeProjectUpdate(from: requestWithInjectedRules(request))
    }

    private func requestWithInjectedRules(_ request: SongProjectGenerationRequest) throws -> SongProjectGenerationRequest {
        var request = request
        request.context.injectPrivateApplicationRules(try ruleProvider.privateApplicationRules())
        return request
    }

    private func requestWithInjectedRules(_ request: LyricsRevisionRequest) throws -> LyricsRevisionRequest {
        var request = request
        request.context.injectPrivateApplicationRules(try ruleProvider.privateApplicationRules())
        return request
    }

    private func requestWithInjectedRules(_ request: SongProjectUpdateRequest) throws -> SongProjectUpdateRequest {
        var request = request
        request.context.injectPrivateApplicationRules(try ruleProvider.privateApplicationRules())
        return request
    }
}