import SwiftUI

/// # Typography — the SF type ramp (FROZEN public surface)
///
/// All font choices come from `DS.Typography`. The ramp maps to Apple's
/// semantic text styles so everything scales with Dynamic Type (the a11y
/// audit's "keep it scalable" point). Numbers/dimensions/cost/`cols×rows`/
/// timestamps use `mono(_:)` — SF Mono with tabular figures — so columns line
/// up and digits don't jitter as values change (matches the existing
/// `TelemetryChips`/`Timeline` convention, now centralized).
extension DS {
    enum Typography {

        // ── Proportional ramp (Dynamic-Type scaling, semantic styles) ───────

        /// Screen hero title.
        static let largeTitle = Font.largeTitle
        /// Section / prominent title.
        static let title = Font.title2
        /// Emphasis / card heading.
        static let headline = Font.headline
        /// Default body text.
        static let body = Font.body
        /// Slightly smaller body (secondary actions).
        static let callout = Font.callout
        /// Meta / caption text.
        static let caption = Font.caption

        // ── Monospaced (numbers, dimensions, timestamps) ────────────────────

        /// SF Mono + tabular figures at the given text style (default `.body`).
        /// Use for anything numeric that must align or not jump: `cols×rows`,
        /// device/client counts, `$cost`, context %, relative timestamps.
        static func mono(_ style: Font.TextStyle = .body) -> Font {
            .system(style, design: .monospaced).monospacedDigit()
        }

        /// The canonical meta-number font: caption-sized mono + tabular.
        static let metaMono = mono(.caption)

        // ── Dynamic Type clamp for dense numerics (T-iOS-34) ────────────────

        /// Upper bound applied to **numeric / meta** text only (telemetry chips,
        /// `dsMetaText` rows: `ctx 92% · $0.1234 · 161×50`).
        ///
        /// Prose scales all the way to `.accessibility5` — that is the point of
        /// Dynamic Type and nothing here caps it. Tabular numerics are different:
        /// they live in one-line rows next to a status badge, and at AX4/AX5 a
        /// single chip row becomes three wrapped lines that push the row's real
        /// content off screen. Capping them at `.accessibility2` (already ~2×
        /// the default size) keeps the meta line legible AND keeps the row's
        /// primary text — the session name — visible.
        ///
        /// Pinned in `DynamicTypeLayoutTests` both as a policy value and
        /// behaviorally (AX2 and AX5 must measure the same height).
        static let numericClamp: DynamicTypeSize = .accessibility2
    }
}

// MARK: - MetaText style

/// Secondary + monospaced-tabular styling for a row's numeric meta line
/// ("N 台设备在看 · 161×50"). Apply via `.dsMetaText()`.
///
/// T-iOS-34 · carries the `numericClamp` so every meta line in the app gets the
/// same Dynamic Type ceiling from ONE place (per-screen clamps would drift).
struct MetaText: ViewModifier {
    func body(content: Content) -> some View {
        content
            .font(DS.Typography.metaMono)
            .foregroundStyle(DS.Palette.textSecondary)
            .dynamicTypeSize(...DS.Typography.numericClamp)
    }
}

extension View {
    /// Style a meta/number line as secondary monospaced-tabular text.
    func dsMetaText() -> some View {
        modifier(MetaText())
    }
}