lanework/Kanban/UI/Palette.swift

import AppKit
import SwiftUI

/// The colour vocabulary the `background` and `iconColor` fields are written in
/// (03-board-ui.md § Styling ▸ Capabilities): **a kebab-case palette name, or a `#RRGGBB[AA]`
/// hex**. This file is the single source for the name→hex mapping — the pathfinder's twelve icon
/// tints and twelve backgrounds, carried over verbatim as the starting point ("The pathfinder's
/// palettes (12 icon tints, 12 backgrounds) carry over").
///
/// ### Lenient, never an error
///
/// A stored value is *cosmetic*, so an unrecognized one is not a load failure, not a warning, and
/// not a placeholder colour: resolution simply yields `nil` and the call site falls back to its
/// own default — no stripe for a card `background`, the standard secondary tint for an
/// `iconColor` (03 § Card face). The bytes on disk are left exactly as written until the author
/// changes them, which is what makes "custom hex is not pickable in-app but stays fully honored
/// from disk" (03 § Controls) true in both directions: curated in-app, unlimited on disk.
///
/// Names are matched **exactly** — kebab-case as the tables below spell them. `Background` is not
/// `background`, and a near-miss degrades like any other unknown value rather than guessing at
/// what the author meant.
struct PaletteColor: Identifiable, Sendable {
    /// Kebab-case, exactly as written to frontmatter.
    let name: String
    let hex: String
    var id: String { name }
}

enum Palette {

    /// Icon-tint palette (`iconColor`).
    static let foregrounds: [PaletteColor] = [
        PaletteColor(name: "obsidian", hex: "#000000"),
        PaletteColor(name: "aluminum", hex: "#9B9B9B"),
        PaletteColor(name: "soapstone", hex: "#D5D5D5"),
        PaletteColor(name: "chalk", hex: "#FFFFFF"),
        PaletteColor(name: "carnation", hex: "#FF576C"),
        PaletteColor(name: "rich-grapefruit", hex: "#FF864C"),
        PaletteColor(name: "smokey-tangerine", hex: "#E5A334"),
        PaletteColor(name: "fern", hex: "#50B23D"),
        PaletteColor(name: "light-teal", hex: "#00B7B7"),
        PaletteColor(name: "deep-sky-blue", hex: "#0084E5"),
        PaletteColor(name: "pale-violet", hex: "#8C59C5"),
        PaletteColor(name: "deep-cool-granite", hex: "#597199"),
    ]

    /// Background palette (`background`) — the twelve wells the style editor will offer, "every
    /// pair AA-verified at design time" (03-board-ui.md § Styling ▸ Controls).
    static let backgrounds: [PaletteColor] = [
        PaletteColor(name: "obsidian", hex: "#000000"),
        PaletteColor(name: "shale", hex: "#5B5B5B"),
        PaletteColor(name: "aluminum", hex: "#9B9B9B"),
        PaletteColor(name: "chalk", hex: "#FFFFFF"),
        PaletteColor(name: "light-cayenne", hex: "#B6071E"),
        PaletteColor(name: "light-mocha", hex: "#B73C14"),
        PaletteColor(name: "smokey-mocha", hex: "#674611"),
        PaletteColor(name: "smokey-fern", hex: "#145312"),
        PaletteColor(name: "dark-teal", hex: "#005152"),
        PaletteColor(name: "smokey-ocean", hex: "#003168"),
        PaletteColor(name: "smokey-rich-eggplant", hex: "#290659"),
        PaletteColor(name: "intense-cool-shale", hex: "#1F2E45"),
    ]
}

// The pathfinder's panel round-trip helpers (`NSColor.paletteHexString`, `Palette.name(forHex:)`)
// and its swatch drawing are deliberately not ported yet: nothing writes a colour until the style
// editor lands, and an unused writer is a claim about a surface that doesn't exist. The styling
// card brings them back when the editor needs them.

extension Palette {

    /// Resolves a stored value — a palette name, or a hand-written `#RRGGBB`/`#RRGGBBAA` hex —
    /// searching the icon tints first, then the backgrounds. **Both tables answer either field**:
    /// the split is what each *picker* offers, not a namespace, so a hand-written
    /// `background: carnation` resolves rather than reading as garbage.
    ///
    /// `nil` means unrecognized, which is a rendering instruction ("use your default"), never an
    /// error — see this file's leading comment.
    static func nsColor(for value: String) -> NSColor? {
        if value.hasPrefix("#") { return NSColor(paletteHex: value) }
        guard let hex = (foregrounds + backgrounds).first(where: { $0.name == value })?.hex else { return nil }
        return NSColor(paletteHex: hex)
    }

    /// SwiftUI variant of `nsColor(for:)` — what the views actually call.
    static func color(named name: String) -> Color? {
        nsColor(for: name).map { Color(nsColor: $0) }
    }

    /// The lenient read of a whole frontmatter field: a missing or malformed `background` /
    /// `iconColor` resolves exactly like an unrecognized one — there is no colour, so use the
    /// default.
    ///
    /// Folding all three `FieldValue` shapes into one `nil` mirrors `ItemSymbol.name(_:fallback:)`
    /// and keeps every call site free of the distinction, which no renderer has a use for.
    static func color(for field: FieldValue<String>) -> Color? {
        guard let value = field.value else { return nil }
        return color(named: value)
    }
}

// MARK: - Hex → colour

extension NSColor {
    /// `#RRGGBB` or `#RRGGBBAA` → `NSColor` in **sRGB** — the colour space the hex digits name,
    /// so a value hand-written from a screenshot or a design tool renders as the same colour the
    /// author sampled. Returns `nil` for anything else: a missing `#`, a short or long digit run,
    /// or a non-hex character.
    convenience init?(paletteHex hex: String) {
        var string = hex
        if string.hasPrefix("#") { string.removeFirst() }
        var alpha: CGFloat = 1
        if string.count == 8 {
            guard let alphaByte = UInt32(string.suffix(2), radix: 16) else { return nil }
            alpha = CGFloat(alphaByte) / 255
            string.removeLast(2)
        }
        guard string.count == 6, let value = UInt32(string, radix: 16) else { return nil }
        self.init(
            srgbRed: CGFloat((value >> 16) & 0xFF) / 255,
            green: CGFloat((value >> 8) & 0xFF) / 255,
            blue: CGFloat(value & 0xFF) / 255,
            alpha: alpha
        )
    }
}