import Foundation

public enum SessionState: String, Codable, Sendable {
    case open      // accepting captures
    case archived  // its PDF has been built and sent; kept forever, never deleted
}

/// The manifest persisted as session.json alongside the PNGs.
public struct CaptureSession: Codable, Sendable, Identifiable, Equatable {
    public let id: UUID
    public let createdAt: Date
    public private(set) var state: SessionState
    public private(set) var captures: [Capture]
    /// Set when the PDF is built, so a re-send reuses the same file.
    public private(set) var pdfFileName: String?

    public init(
        id: UUID,
        createdAt: Date,
        state: SessionState,
        captures: [Capture],
        pdfFileName: String?
    ) {
        self.id = id
        self.createdAt = createdAt
        self.state = state
        self.captures = captures
        self.pdfFileName = pdfFileName
    }

    public var isEmpty: Bool {
        captures.isEmpty
    }

    /// max(sequence)+1, or 1 when empty.
    public var nextSequence: Int {
        (captures.map(\.sequence).max() ?? 0) + 1
    }

    /// Value-semantic: returns a new session; does not mutate `self`.
    public func appending(_ capture: Capture) -> CaptureSession {
        CaptureSession(
            id: id,
            createdAt: createdAt,
            state: state,
            captures: captures + [capture],
            pdfFileName: pdfFileName
        )
    }

    /// Value-semantic: returns a new session; does not mutate `self`.
    /// Sequence numbers of remaining captures are left unchanged.
    public func removing(captureID: UUID) -> CaptureSession {
        CaptureSession(
            id: id,
            createdAt: createdAt,
            state: state,
            captures: captures.filter { $0.id != captureID },
            pdfFileName: pdfFileName
        )
    }

    /// Value-semantic: returns a new session; does not mutate `self`.
    public func markArchived(pdfFileName: String) -> CaptureSession {
        CaptureSession(
            id: id,
            createdAt: createdAt,
            state: .archived,
            captures: captures,
            pdfFileName: pdfFileName
        )
    }
}