import Foundation

public final class SongProjectGenerationDirector: Sendable {
    private let aiService: any AIService

    public init(aiService: any AIService) {
        self.aiService = aiService
    }

    public func generateCompleteProject(
        fromIdea idea: String,
        seedProject: SongProject? = nil,
        discussionMode: ConversationMode = .auto,
        conversation: [AIConversationMessage] = [],
        localeIdentifier: String? = nil,
        generatedAt: Date = Date()
    ) async throws -> SongProjectGenerationResult {
        let trimmedIdea = idea.trimmingCharacters(in: .whitespacesAndNewlines)
        guard !trimmedIdea.isEmpty else {
            throw SongProjectGenerationDirectorError.emptyIdea
        }

        let request = SongProjectGenerationRequest(
            context: AIRequestContext(
                userInstruction: trimmedIdea,
                conversation: conversation,
                localeIdentifier: localeIdentifier
            ),
            seedProject: seedProject,
            discussionMode: discussionMode
        )
        let result = try await aiService.generateSongProject(from: request)
        let project = normalizeGeneratedProject(
            result.project,
            idea: trimmedIdea,
            seedProject: seedProject,
            discussionMode: discussionMode,
            generatedAt: generatedAt
        )

        return SongProjectGenerationResult(
            project: project,
            notes: result.notes,
            followUpQuestions: result.followUpQuestions
        )
    }

    private func normalizeGeneratedProject(
        _ generatedProject: SongProject,
        idea: String,
        seedProject: SongProject?,
        discussionMode: ConversationMode,
        generatedAt: Date
    ) -> SongProject {
        let normalizedIdea = generatedProject.idea.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty
            ? idea
            : generatedProject.idea

        guard let seedProject else {
            var project = generatedProject
            project.idea = normalizedIdea
            project.conversationMode = discussionMode
            project.updatedAt = generatedAt
            return project
        }

        let update = SongProjectAIUpdateMerger().apply(
            snapshot: SongProjectSnapshot(project: generatedProject),
            changedScopes: SongProjectUpdateScope.allCases,
            to: seedProject,
            updatedAt: generatedAt
        )
        var project = update.project
        project.title = generatedProject.title
        project.idea = normalizedIdea
        project.conversationMode = discussionMode
        project.moods = generatedProject.moods
        return project
    }
}

public enum SongProjectGenerationDirectorError: Error, Equatable, Sendable {
    case emptyIdea
}