import AppKit
import SwiftUI

/// **The board popover's Background tab** (03-board-ui.md § Board popover ▸ Background tab, settled
/// 2026-08-07) — two surfaces sharing one tab, one manual and one generated.
///
/// ### Color
///
/// The `StyleEditorView` embed, re-homed here unchanged from the pre-tab popover body: same target
/// (`.board`), same `showsSymbols: false` (the inline `SymbolPicker` beside the rename field owns the
/// board's glyph, so a second symbol grid here would make the glyph read as two settings), same write
/// path (`StyleCommand.apply` → `BoardStore.applyStyle` + `StyleRecents.record`). It brings its own
/// header ("Background") and its own inset (`StyleEditorLayout.popover(...).padding`), so nothing
/// here pads around it — the anti-double-pad rule `BoardInfoView.inset`'s doc names.
///
/// ### Generated
///
/// A `FacetsRecipe` names a picture (`Backgrounds/FacetsRecipe.swift`); this section is the four
/// filters that narrow one (tone, hue strategy, mesh density, saturation) plus one seed per hue,
/// minted fresh on appear and re-minted by Reroll. Every swatch previews the exact recipe a click
/// would apply — same filters, same seed, only the pixel width differs (384 for the strip, 3072 for
/// the file) — so "what's clicked is what lands" (`FacetsGenerator`'s own claim).

// MARK: - Filters

/// **The generated picker's filter state**, and the pure mapping from it (plus a hue and a seed) to a
/// `FacetsRecipe` — pulled out of the view so the default-tone rule and the recipe assembly are each
/// assertable without a popover on screen (`BoardBackgroundFiltersTests`).
struct BoardBackgroundFilters: Equatable {

    var tone: FacetsRecipe.Tone
    var colors: FacetsRecipe.Strategy
    var mesh: FacetsRecipe.Density
    var saturation: FacetsRecipe.Saturation

    /// The picker's opening state: mono colours, medium mesh, mid saturation always — only tone
    /// follows the system, which is `defaultTone(colorScheme:)`'s own job.
    static func initial(colorScheme: ColorScheme) -> BoardBackgroundFilters {
        BoardBackgroundFilters(
            tone: defaultTone(colorScheme: colorScheme), colors: .mono, mesh: .medium, saturation: .mid
        )
    }

    /// Light appearance opens on Tone Light, dark on Tone Dark — read once, at first appearance, so a
    /// picker opened on a dark-mode Mac starts on swatches that read correctly against the popover
    /// around them rather than ones chosen for the other appearance. `.light` covers every
    /// `ColorScheme` case but `.dark` — there is no third case today.
    static func defaultTone(colorScheme: ColorScheme) -> FacetsRecipe.Tone {
        colorScheme == .dark ? .dark : .light
    }

    /// One hue's recipe under these filters and a given seed — the whole of "click a swatch, get a
    /// board".
    func recipe(hue: FacetsRecipe.Hue, seed: UInt64) -> FacetsRecipe {
        FacetsRecipe(hue: hue, strategy: colors, density: mesh, tone: tone, saturation: saturation, seed: seed)
    }
}

// MARK: - The tab

struct BoardBackgroundTabView: View {

    let store: BoardStore
    let recents: StyleRecents

    /// The popover's own padding figure (`BoardInfoView.inset`), matching `BoardInfoTabView`'s own
    /// parameter — everything here that does not already carry its own inset (the Generated section)
    /// pads by this amount instead of restating the derivation.
    let inset: CGFloat

    @Environment(\.colorScheme) private var colorScheme
    @Environment(\.colorSchemeContrast) private var contrast

    @State private var filters = BoardBackgroundFilters.initial(colorScheme: .light)

    /// One seed per hue, in wheel order — minted on appear and re-minted by Reroll. A filter change
    /// leaves these alone (same geometry, new treatment); Reroll is the one gesture that changes them
    /// (new geometry).
    @State private var seeds: [FacetsRecipe.Hue: UInt64] = [:]

    /// The carousel's previews, keyed by hue — absent until the render for the current
    /// `(filters, seeds)` pair lands, which is what the placeholder chip is for.
    @State private var previews: [FacetsRecipe.Hue: CGImage] = [:]

    /// Whether a swatch's 3072px render is in flight — every swatch disables and the header grows a
    /// small spinner for the duration, so a second click cannot race the first.
    @State private var isApplying = false

    private var pointSize: CGFloat { CardWindowMetrics.bodyPointSize }
    private let swatchWidth: CGFloat = 96
    private var swatchHeight: CGFloat { (swatchWidth * 10 / 16).rounded() }
    private let swatchCornerRadius: CGFloat = 6

    var body: some View {
        VStack(alignment: .leading, spacing: 0) {
            // Always the board, whatever is selected. The ⌥⌘S anchor is the selection-aware one
            // ("nothing selected = the board"); this embed is the surface that exists *because* the
            // board is a style target, so it can have no other target (§ Styling ▸ Controls: "the
            // board popover's target is the board itself"). No symbol section — the inline
            // `SymbolPicker` beside the rename field above owns the board glyph.
            StyleEditorView(store: store, recents: recents, target: .board, showsSymbols: false)

            Divider()

            generatedSection
                .padding(inset)
        }
        .onAppear {
            filters.tone = BoardBackgroundFilters.defaultTone(colorScheme: colorScheme)
            if seeds.isEmpty { seeds = Self.mintSeeds() }
        }
        .task(id: previewKey) {
            await renderPreviews()
        }
    }

    // MARK: - Generated section

    private var generatedSection: some View {
        VStack(alignment: .leading, spacing: StyleEditorLayout.wellSpacing(bodyPointSize: pointSize)) {
            HStack(spacing: 6) {
                sectionHeader("Generated")
                if isApplying {
                    ProgressView()
                        .controlSize(.small)
                        .accessibilityLabel("Applying")
                }
                Spacer()
                Button {
                    reroll()
                } label: {
                    Image(systemName: "arrow.clockwise")
                }
                .buttonStyle(.borderless)
                .accessibilityLabel("New variations")
            }

            Grid(alignment: .leadingFirstTextBaseline, horizontalSpacing: 8, verticalSpacing: 6) {
                filterRow("Tone", selection: $filters.tone) { $0 == .light ? "Light" : "Dark" }
                filterRow("Colors", selection: $filters.colors, label: colorsLabel)
                filterRow("Mesh", selection: $filters.mesh, label: meshLabel)
                filterRow("Saturation", selection: $filters.saturation, label: saturationLabel)
            }

            carousel
        }
        .font(.callout)
        // The whole section disables as one surface under the read-only lock — the same coarse rule
        // `StyleEditorView` applies to itself just above: an editor whose gestures would be refused
        // should not look available, and there is nothing here worth half-enabling (a filter nobody
        // can commit is not a useful control to leave live).
        .disabled(!store.acceptsBoardMutations)
    }

    private func sectionHeader(_ title: String) -> some View {
        Text(title)
            .font(.subheadline.weight(.semibold))
    }

    /// One filter: a trailing-aligned label — matching the Info tab's row shape — beside a compact
    /// segmented picker. The label is hidden from VoiceOver; the picker's own title (identical text)
    /// is what it announces, so nothing is read twice.
    private func filterRow<Value>(
        _ title: String,
        selection: Binding<Value>,
        label: @escaping (Value) -> String
    ) -> some View where Value: Hashable, Value: CaseIterable, Value.AllCases: RandomAccessCollection {
        GridRow {
            Text(title)
                .foregroundStyle(.secondary)
                .gridColumnAlignment(.trailing)
                .accessibilityHidden(true)
            Picker(title, selection: selection) {
                ForEach(Array(Value.allCases), id: \.self) { value in
                    Text(label(value)).tag(value)
                }
            }
            .pickerStyle(.segmented)
            .labelsHidden()
            .controlSize(.small)
        }
    }

    private func colorsLabel(_ value: FacetsRecipe.Strategy) -> String {
        switch value {
        case .mono: "Mono"
        case .duo: "Duo"
        case .trio: "Trio"
        }
    }

    private func meshLabel(_ value: FacetsRecipe.Density) -> String {
        switch value {
        case .coarse: "Coarse"
        case .medium: "Medium"
        case .fine: "Fine"
        }
    }

    private func saturationLabel(_ value: FacetsRecipe.Saturation) -> String {
        switch value {
        case .soft: "Soft"
        case .mid: "Mid"
        case .rich: "Rich"
        }
    }

    // MARK: - Carousel

    private var carousel: some View {
        ScrollView(.horizontal, showsIndicators: false) {
            HStack(spacing: StyleEditorLayout.wellSpacing(bodyPointSize: pointSize)) {
                ForEach(FacetsRecipe.Hue.allCases, id: \.self) { hue in
                    swatch(hue)
                }
            }
        }
    }

    private func swatch(_ hue: FacetsRecipe.Hue) -> some View {
        Button {
            apply(hue)
        } label: {
            swatchFace(hue)
        }
        .buttonStyle(.plain)
        // Layered on top of the section's own disabling: this half additionally freezes every swatch
        // for the one gesture already running, so a second click cannot race the first's write.
        .disabled(isApplying)
        .opacity(isApplying ? 0.6 : 1)
        .help(hue.displayName)
        .accessibilityLabel("\(hue.displayName) — set generated background")
    }

    @ViewBuilder
    private func swatchFace(_ hue: FacetsRecipe.Hue) -> some View {
        Group {
            if let image = previews[hue] {
                Image(decorative: image, scale: 1)
                    .resizable()
                    .aspectRatio(contentMode: .fill)
            } else {
                // The pending placeholder: the recipe's own primary colour, so the strip reads as
                // "still painting this picture" rather than as a hole — and is already the right
                // colour if the render never manages to beat a quick reroll.
                chip(hue)
            }
        }
        .frame(width: swatchWidth, height: swatchHeight)
        .clipShape(RoundedRectangle(cornerRadius: swatchCornerRadius))
        .overlay(
            RoundedRectangle(cornerRadius: swatchCornerRadius)
                .strokeBorder(.separator, lineWidth: Accommodations.borderWidth(1, contrast: contrast))
        )
    }

    private func chip(_ hue: FacetsRecipe.Hue) -> Color {
        guard let seed = seeds[hue] else { return Color(nsColor: .textBackgroundColor) }
        let components = filters.recipe(hue: hue, seed: seed).primaryColor.components
        return Color(red: components.red, green: components.green, blue: components.blue)
    }

    // MARK: - Rendering and applying

    private struct PreviewKey: Equatable {
        var filters: BoardBackgroundFilters
        var seeds: [FacetsRecipe.Hue: UInt64]
    }

    private var previewKey: PreviewKey { PreviewKey(filters: filters, seeds: seeds) }

    /// The strip's eight previews, off the main actor — `FacetsGenerator.render` is pure, so this is
    /// exactly the render `apply(_:)` below would do at 3072px, just smaller and for every hue at
    /// once. Re-runs whenever `previewKey` changes (`.task(id:)`), which a filter edit or a Reroll
    /// both do — the same detach-and-await shape `BoardInfoTabView`'s disk walk uses.
    private func renderPreviews() async {
        previews = [:]
        let filters = self.filters
        let seeds = self.seeds
        let rendered = await Task.detached(priority: .utility) { () -> [FacetsRecipe.Hue: CGImage] in
            var rendered: [FacetsRecipe.Hue: CGImage] = [:]
            for hue in FacetsRecipe.Hue.allCases {
                guard let seed = seeds[hue] else { continue }
                if let image = FacetsGenerator.render(recipe: filters.recipe(hue: hue, seed: seed), pixelWidth: 384) {
                    rendered[hue] = image
                }
            }
            return rendered
        }.value
        // `.task(id:)` cancels this task when the key moves on, but cancellation is cooperative and
        // the detached render finishes regardless — without this gate a slow stale strip could land
        // *after* the newer key's own renders and quietly replace them.
        guard !Task.isCancelled else { return }
        previews = rendered
    }

    /// A swatch, clicked: the same recipe the preview showed, rendered at the file's own width and
    /// written through the one gesture every generated background lands through
    /// (`BoardStore.applyGeneratedBackground`). Failures — a `nil` render, a refused write under the
    /// lock — leave the board exactly as it was; the write path's own banners cover the write half.
    private func apply(_ hue: FacetsRecipe.Hue) {
        guard let seed = seeds[hue] else { return }
        let recipe = filters.recipe(hue: hue, seed: seed)
        isApplying = true
        Task {
            let data = await Task.detached(priority: .userInitiated) {
                FacetsGenerator.pngData(recipe: recipe, pixelWidth: 3072)
            }.value
            if let data {
                _ = store.applyGeneratedBackground(png: data, colorHex: recipe.primaryColorHex)
            }
            isApplying = false
        }
    }

    private static func mintSeeds() -> [FacetsRecipe.Hue: UInt64] {
        Dictionary(uniqueKeysWithValues: FacetsRecipe.Hue.allCases.map { ($0, UInt64.random(in: UInt64.min...UInt64.max)) })
    }

    private func reroll() {
        seeds = Self.mintSeeds()
    }
}

// MARK: - Hue display names

private extension FacetsRecipe.Hue {
    /// The wheel's own names, capitalized for the carousel's `.help` and accessibility label — the
    /// same eight words 03-board-ui.md's faceted-gallery notes use.
    var displayName: String {
        switch self {
        case .clay: "Clay"
        case .amber: "Amber"
        case .olive: "Olive"
        case .forest: "Forest"
        case .teal: "Teal"
        case .sky: "Sky"
        case .iris: "Iris"
        case .rose: "Rose"
        }
    }
}