use crate::ui::theme::Theme;
use iris::prelude::*;

const MAX_LINES: f32 = 6.0;
const APPROX_LINE_HEIGHT_DP: f32 = 24.0;
const FIELD_PAD_DP: f32 = 12.0;

/// `field` is exposed so the caller can read its content on submit
/// (`field(rsc).text()`) and clear it afterward (`field(rsc).set("")`).
pub struct Composer {
    pub field: WeakWidget<TextEdit>,
    /// The bar's own outer padding -- only `bottom` is ever changed, by
    /// [`Self::set_bottom_inset`]. A `Pad` around the whole bar rather than
    /// a rebuilt tree, because `field` lives inside it and cannot be
    /// re-added to a new wrapper once it is strongly owned here.
    outer_pad: WeakWidget<Pad>,
}

pub struct BuiltComposer {
    pub composer: Composer,
    pub widget: WeakWidget,
}

impl Composer {
    /// Called by the platform shell (Android's `on_insets_changed`, e.g.)
    /// whenever the space below the bar changes: the IME's own inset while
    /// it is open, the navigation-bar inset otherwise. Takes a plain
    /// `f32` in the caller's own physical-pixel units rather than an
    /// Android-specific insets type, so this crate stays usable from the
    /// winit backend too, which has no navigation bar to report.
    /// Rewrites the existing `Pad` in place (marking it dirty through the
    /// ordinary `Widgets::get_mut` path) instead of swapping in a new one,
    /// so the field's focus, selection and in-progress text are untouched.
    pub fn set_bottom_inset(&self, rsc: &mut impl UiRsc, inset: f32) {
        if let Some(pad) = rsc.ui_mut().widgets.get_mut(&self.outer_pad) {
            pad.padding.bottom = Len::abs(inset);
            pad.exact_region = true;
        }
    }
}

/// Returns the composer plus its own bar as a **weak** id -- the caller
/// (`lib.rs::build`) embeds it in the screen's own top-level tuple, whose
/// `set_root` performs the one real strong registration. Calling
/// `.add_strong`/`.upgrade` a second time on an id already strong-owned
/// panics ("was already added", `core/src/widget/like.rs:12`) -- the same
/// mistake this box's `row.rs` first made with its sender-label header, see
/// that file's comment for the fuller account.
pub fn build_composer<Rsc: HasEvents>(rsc: &mut Rsc, theme: &Theme) -> BuiltComposer
where
    Rsc::State: FocusHost,
{
    let field = wtext("")
        .editable(EditMode::MultiLine)
        .text_align(Align::LEFT)
        .wrap(true)
        .size(18)
        .color(theme.text.clone())
        .attr::<Selectable>(())
        .label("Message")
        .add(rsc);

    // Without any mask at all the overflow paints *above* the bar, over
    // the transcript: measured at 58px of stray text for a 475px message
    // in a 417px box.
    let content = field
        .width(rest(1))
        .scrollable(Axis::Y, Pin::End)
        .pad(dp(FIELD_PAD_DP))
        .max_height(dp(APPROX_LINE_HEIGHT_DP * MAX_LINES + FIELD_PAD_DP * 2.0))
        .width(rest(1))
        .masked_by(rect(theme.composer_surface.clone()))
        .add(rsc);

    let outer_pad: WeakWidget<Pad> = content.pad(Padding::ZERO).add(rsc);

    BuiltComposer {
        composer: Composer { field, outer_pad },
        widget: outer_pad,
    }
}