import AppKit

private final class TopAlignedView: NSView {
    override var isFlipped: Bool { true }  // so the scroll view starts at the top
}

/// Side panel: every effect with a checkbox, and the sliders of the ones that are switched on.
final class Panel: NSObject {
    static let width: CGFloat = 230

    let view = NSScrollView()
    private let stack = NSStackView()
    private let statusLabel = NSTextField(labelWithString: "")
    private let renderer: Renderer

    init(renderer: Renderer) {
        self.renderer = renderer
        super.init()
        stack.orientation = .vertical
        stack.alignment = .leading
        stack.spacing = 4
        stack.translatesAutoresizingMaskIntoConstraints = false

        let document = TopAlignedView()
        document.translatesAutoresizingMaskIntoConstraints = false
        document.addSubview(stack)
        view.documentView = document
        view.hasVerticalScroller = true
        view.drawsBackground = false
        NSLayoutConstraint.activate([
            view.widthAnchor.constraint(equalToConstant: Panel.width),
            document.widthAnchor.constraint(equalTo: view.contentView.widthAnchor),
            stack.topAnchor.constraint(equalTo: document.topAnchor, constant: 14),
            stack.leadingAnchor.constraint(equalTo: document.leadingAnchor, constant: 14),
            stack.trailingAnchor.constraint(equalTo: document.trailingAnchor, constant: -14),
            stack.bottomAnchor.constraint(equalTo: document.bottomAnchor, constant: -14),
        ])
        statusLabel.font = .boldSystemFont(ofSize: 11)
        statusLabel.textColor = .systemRed
        rebuild()
    }

    private func label(_ text: String, dim: Bool = true) -> NSTextField {
        let field = NSTextField(labelWithString: text)
        field.font = .systemFont(ofSize: 11)
        field.textColor = dim ? .secondaryLabelColor : .labelColor
        return field
    }

    func rebuild() {
        stack.arrangedSubviews.forEach { $0.removeFromSuperview() }
        statusLabel.stringValue = renderer.status
        stack.addArrangedSubview(statusLabel)

        for (layerIndex, layer) in renderer.layers.enumerated() {
            let title = layer.error == nil ? layer.name : "\(layer.name)  (shader error)"
            let checkbox = NSButton(checkboxWithTitle: title, target: self, action: #selector(toggled(_:)))
            checkbox.state = layer.enabled ? .on : .off
            checkbox.tag = layerIndex
            checkbox.font = .systemFont(ofSize: 13, weight: .medium)
            stack.addArrangedSubview(checkbox)
            guard layer.enabled else { continue }

            for (paramIndex, param) in layer.params.enumerated() {
                let slider = NSSlider(value: Double(param.value), minValue: Double(param.min), maxValue: Double(param.max),
                                      target: self, action: #selector(sliderMoved(_:)))
                slider.tag = layerIndex * maxParams + paramIndex
                slider.controlSize = .small
                stack.addArrangedSubview(label(param.name))
                stack.addArrangedSubview(slider)
                slider.widthAnchor.constraint(equalTo: stack.widthAnchor).isActive = true
            }
            stack.setCustomSpacing(12, after: stack.arrangedSubviews.last!)
        }
        if renderer.layers.isEmpty { stack.addArrangedSubview(label("no .metal files found")) }

        stack.setCustomSpacing(16, after: stack.arrangedSubviews.last!)
        stack.addArrangedSubview(label("s  screenshot\nr  record\nq  quit"))
    }

    func refreshStatus() {
        statusLabel.stringValue = renderer.status
    }

    @objc private func toggled(_ checkbox: NSButton) {
        renderer.setEnabled(checkbox.tag, checkbox.state == .on)
    }

    @objc private func sliderMoved(_ slider: NSSlider) {
        renderer.setParam(layer: slider.tag / maxParams, param: slider.tag % maxParams, value: Float(slider.doubleValue))
    }
}