//! Theme-aware progress slider with hover-activated numeric entry.
//!
//! **Purpose:** Provides one compact numeric control for every Iced panel, matching the egui
//! `PlainSlider` interaction model without relying on the deprecated Iced `Component` API.
//! **Logic & Workflow:** An Iced Canvas retains transient drag/edit state, maps pointer positions
//! to stepped values, captures numeric keyboard input while hovered, and draws a recessed track,
//! gradient value fill, spinner arrows, centered text, and hover elevation.
//! **Interaction model:**
//!   - Click and drag anywhere on the track to adjust the value.
//!   - Type any numeric character while hovering to start direct text input.
//!   - Press `Enter` to commit the typed value, `Escape` to cancel.
//!   - Click the spinner arrows for single-step increments/decrements.
//! **Side Effects / Dependencies:** Emits caller-provided messages; all state remains local to the
//! widget tree and all colors derive from `ThemeColors`.

use crate::theme::ThemeColors;
use iced::keyboard::{self, key::Named, Key};
use iced::mouse;
use iced::widget::canvas::{self, Canvas, Frame, Path, Stroke};
use iced::{alignment, border, Element, Length, Pixels, Point, Rectangle, Size};
use std::sync::Arc;

const CONTROL_HEIGHT: f32 = 22.0;
const SPINNER_WIDTH: f32 = 24.0;

/// Persistent interaction state for one slider instance.
#[derive(Debug, Default)]
pub(crate) struct State {
    dragging: bool,
    editing: bool,
    buffer: String,
}

/// Canvas program describing one plain slider.
#[derive(Clone)]
struct PlainSlider<Message> {
    label: String,
    value: f32,
    range: std::ops::RangeInclusive<f32>,
    step: f32,
    suffix: String,
    decimals: usize,
    colors: ThemeColors,
    on_change: Arc<dyn Fn(f32) -> Message>,
}

impl<Message> std::fmt::Debug for PlainSlider<Message> {
    fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        formatter
            .debug_struct("PlainSlider")
            .field("label", &self.label)
            .field("value", &self.value)
            .field("range", &self.range)
            .field("step", &self.step)
            .field("suffix", &self.suffix)
            .field("decimals", &self.decimals)
            .finish_non_exhaustive()
    }
}

impl<Message> PlainSlider<Message> {
    /// Formats the current value for centered display.
    fn format_value(&self, value: f32) -> String {
        let displayed = if self.suffix == "%" {
            value * 100.0
        } else {
            value
        };
        let value = format!("{:.*}", self.decimals, displayed);
        if self.suffix.is_empty() {
            format!("{}: {}", self.label, value)
        } else if self.suffix == "%" {
            format!("{}: {}%", self.label, value)
        } else {
            format!("{}: {} {}", self.label, value, self.suffix)
        }
    }

    /// Parses an edit buffer, normalizes percentages, and clamps to the slider range.
    fn parse_value(&self, raw: &str) -> Option<f32> {
        let numeric = raw
            .trim()
            .trim_end_matches(&self.suffix)
            .trim()
            .replace(',', ".");
        let parsed = numeric.parse::<f32>().ok()?;
        let value = if self.suffix == "%" {
            parsed / 100.0
        } else {
            parsed
        };
        Some(self.snap(value))
    }

    /// Snaps a value to the configured step relative to the range minimum.
    fn snap(&self, value: f32) -> f32 {
        let min = *self.range.start();
        let max = *self.range.end();
        if self.step > f32::EPSILON {
            (min + ((value - min) / self.step).round() * self.step).clamp(min, max)
        } else {
            value.clamp(min, max)
        }
    }

    /// Maps a horizontal cursor coordinate to a stepped value.
    fn value_at(&self, x: f32, width: f32) -> f32 {
        let track_width = (width - SPINNER_WIDTH).max(1.0);
        let fraction = (x / track_width).clamp(0.0, 1.0);
        self.snap(*self.range.start() + (*self.range.end() - *self.range.start()) * fraction)
    }

    /// Computes the slider value for the current cursor position while dragging.
    ///
    /// **Purpose:** Allow an active drag to continue updating even when the cursor moves
    /// slightly outside the widget bounds, so 0 % and 100 % can always be reached.
    /// **Logic & Workflow:** If the cursor is inside the widget bounds, use its local X.
    /// Otherwise fall back to the global cursor position and convert it to widget-local
    /// X by subtracting `bounds.x`. Clamp the resulting X to the draggable track width.
    /// **Arguments:** `cursor` is the current mouse cursor; `bounds` is the widget rectangle.
    /// **Returns:** The stepped value at the clamped cursor position.
    fn drag_value(&self, cursor: mouse::Cursor, bounds: Rectangle) -> f32 {
        let track_width = (bounds.width - SPINNER_WIDTH).max(1.0);
        let x = match cursor.position_in(bounds) {
            Some(local) => local.x,
            None => cursor.position().map_or(0.0, |p| p.x - bounds.x),
        }
        .clamp(0.0, track_width);
        self.value_at(x, bounds.width)
    }

    /// Returns the normalized fill fraction for the current value.
    fn fraction(&self) -> f32 {
        let span = *self.range.end() - *self.range.start();
        if span.abs() <= f32::EPSILON {
            0.0
        } else {
            ((self.value - *self.range.start()) / span).clamp(0.0, 1.0)
        }
    }

    /// Starts direct numeric editing with one typed character.
    fn begin_typing(state: &mut State, text: &str) -> bool {
        if is_numeric_fragment(text) {
            state.editing = true;
            state.buffer.clear();
            state.buffer.push_str(text);
            true
        } else {
            false
        }
    }
}

impl<Message> canvas::Program<Message> for PlainSlider<Message> {
    type State = State;

    fn draw(
        &self,
        state: &Self::State,
        renderer: &iced::Renderer,
        _theme: &iced::Theme,
        bounds: Rectangle,
        cursor: mouse::Cursor,
    ) -> Vec<canvas::Geometry> {
        let mut frame = Frame::new(renderer, bounds.size());
        let hovered = cursor.is_over(bounds);
        let radius = border::Radius::from(4.0);
        let outer = Path::rounded_rectangle(Point::ORIGIN, bounds.size(), radius);

        if hovered {
            for expansion in [3.0_f32, 2.0, 1.0] {
                let mut shadow = self.colors.accent;
                shadow.a = 0.035 * (4.0 - expansion);
                let path = Path::rounded_rectangle(
                    Point::new(-expansion, -expansion),
                    Size::new(
                        bounds.width + expansion * 2.0,
                        bounds.height + expansion * 2.0,
                    ),
                    border::Radius::from(4.0 + expansion),
                );
                frame.stroke(&path, Stroke::default().with_color(shadow).with_width(1.0));
            }
        }

        frame.fill(&outer, self.colors.recessed());

        let track_width = (bounds.width - SPINNER_WIDTH).max(0.0);
        let fill_width = track_width * self.fraction();
        if fill_width > 0.0 {
            let mut fill = self.colors.accent;
            fill.a = if self.colors.is_light { 0.30 } else { 0.25 };
            let fill_rect = Path::rounded_rectangle(Point::new(0.0, 0.0), Size::new(fill_width, bounds.height), radius);
            frame.fill(&fill_rect, fill);
        }

        frame.stroke(
            &outer,
            Stroke::default()
                .with_color(if hovered {
                    self.colors.accent
                } else {
                    self.colors.border_high
                })
                .with_width(1.0),
        );
        frame.stroke(
            &Path::rectangle(
                Point::new(track_width, 1.0),
                Size::new(1.0, (bounds.height - 2.0).max(0.0)),
            ),
            Stroke::default()
                .with_color(self.colors.border_low)
                .with_width(1.0),
        );

        let center_x = track_width / 2.0;
        let display = if state.editing {
            format!("{}|", state.buffer)
        } else {
            self.format_value(self.value)
        };
        frame.fill_text(canvas::Text {
            content: display,
            position: Point::new(center_x, bounds.height / 2.0),
            color: self.colors.text_primary,
            size: Pixels(12.0),
            horizontal_alignment: alignment::Horizontal::Center,
            vertical_alignment: alignment::Vertical::Center,
            ..Default::default()
        });

        let spinner_x = track_width + SPINNER_WIDTH / 2.0;
        for (center_y, upward) in [(6.5, true), (15.5, false)] {
            let path = Path::new(|builder| {
                if upward {
                    builder.move_to(Point::new(spinner_x, center_y - 2.5));
                    builder.line_to(Point::new(spinner_x - 3.0, center_y + 2.0));
                    builder.line_to(Point::new(spinner_x + 3.0, center_y + 2.0));
                } else {
                    builder.move_to(Point::new(spinner_x, center_y + 2.5));
                    builder.line_to(Point::new(spinner_x - 3.0, center_y - 2.0));
                    builder.line_to(Point::new(spinner_x + 3.0, center_y - 2.0));
                }
                builder.close();
            });
            frame.fill(&path, self.colors.text_secondary);
        }

        vec![frame.into_geometry()]
    }

    fn update(
        &self,
        state: &mut Self::State,
        event: canvas::Event,
        bounds: Rectangle,
        cursor: mouse::Cursor,
    ) -> (canvas::event::Status, Option<Message>) {
        let local = cursor.position_in(bounds);

        match event {
            canvas::Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Left)) => {
                let Some(position) = local else {
                    if state.editing {
                        state.editing = false;
                        state.buffer.clear();
                    }
                    return (canvas::event::Status::Ignored, None);
                };

                // Spinner arrows remain step controls.
                if position.x >= bounds.width - SPINNER_WIDTH {
                    let direction = if position.y < bounds.height / 2.0 {
                        1.0
                    } else {
                        -1.0
                    };
                    let value = self.snap(self.value + self.step.max(f32::EPSILON) * direction);
                    return (
                        canvas::event::Status::Captured,
                        Some((self.on_change)(value)),
                    );
                }

                // Anywhere else on the track starts a drag; explicit edit mode
                // is no longer required before typing.
                state.editing = false;
                state.buffer.clear();
                state.dragging = true;
                let value = self.value_at(position.x, bounds.width);
                (
                    canvas::event::Status::Captured,
                    Some((self.on_change)(value)),
                )
            }
            canvas::Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Right)) => {
                // Right click outside edit mode is ignored; while editing it cancels.
                if state.editing {
                    state.editing = false;
                    state.buffer.clear();
                    return (canvas::event::Status::Captured, None);
                }
                (canvas::event::Status::Ignored, None)
            }
            canvas::Event::Mouse(mouse::Event::CursorMoved { .. }) if state.dragging => {
                let value = self.drag_value(cursor, bounds);
                return (
                    canvas::event::Status::Captured,
                    Some((self.on_change)(value)),
                );
            }
            canvas::Event::Mouse(mouse::Event::ButtonReleased(mouse::Button::Left)) => {
                if state.dragging {
                    state.dragging = false;
                    return (canvas::event::Status::Captured, None);
                }
                (canvas::event::Status::Ignored, None)
            }
            canvas::Event::Keyboard(keyboard::Event::KeyPressed { key, text, .. })
                if local.is_some() || state.editing =>
            {
                if state.editing {
                    match key {
                        Key::Named(Named::Enter) => {
                            let value = self.parse_value(&state.buffer);
                            state.editing = false;
                            state.buffer.clear();
                            return (
                                canvas::event::Status::Captured,
                                value.map(|value| (self.on_change)(value)),
                            );
                        }
                        Key::Named(Named::Escape) => {
                            state.editing = false;
                            state.buffer.clear();
                            return (canvas::event::Status::Captured, None);
                        }
                        Key::Named(Named::Backspace) => {
                            state.buffer.pop();
                            return (canvas::event::Status::Captured, None);
                        }
                        _ => {}
                    }
                    if let Some(text) = text.filter(|text| is_numeric_fragment(text)) {
                        state.buffer.push_str(&text);
                        return (canvas::event::Status::Captured, None);
                    }
                } else if let Some(text) = text.filter(|text| is_numeric_fragment(text)) {
                    // Typing while hovering immediately starts editing; no click needed.
                    PlainSlider::<Message>::begin_typing(state, &text);
                    return (canvas::event::Status::Captured, None);
                }
                (canvas::event::Status::Ignored, None)
            }
            _ => (canvas::event::Status::Ignored, None),
        }
    }

    fn mouse_interaction(
        &self,
        _state: &Self::State,
        bounds: Rectangle,
        cursor: mouse::Cursor,
    ) -> mouse::Interaction {
        if cursor.is_over(bounds) {
            mouse::Interaction::Pointer
        } else {
            mouse::Interaction::default()
        }
    }
}

/// Builds a theme-aware slider element.
///
/// **Arguments:** Label/value/range define the numeric control; `step`, `suffix`, and `decimals`
/// control interaction and formatting; `colors` is the active palette; `on_change` creates the
/// parent message. **Returns:** A fill-width 22 px slider. **Side Effects:** None until interaction.
pub fn plain_slider<Message>(
    label: impl Into<String>,
    value: f32,
    range: std::ops::RangeInclusive<f32>,
    step: f32,
    suffix: impl Into<String>,
    decimals: usize,
    colors: ThemeColors,
    on_change: impl Fn(f32) -> Message + 'static,
) -> Element<'static, Message>
where
    Message: 'static,
{
    Canvas::new(PlainSlider {
        label: label.into(),
        value,
        range,
        step,
        suffix: suffix.into(),
        decimals,
        colors,
        on_change: Arc::new(on_change),
    })
    .width(Length::Fill)
    .height(Length::Fixed(CONTROL_HEIGHT))
    .into()
}

/// Returns whether text can be appended to a numeric edit buffer.
fn is_numeric_fragment(text: &str) -> bool {
    !text.is_empty()
        && text
            .chars()
            .all(|character| character.is_ascii_digit() || matches!(character, '.' | ',' | '-'))
}

#[cfg(test)]
mod tests {
    use super::{is_numeric_fragment, PlainSlider, State};
    use crate::theme::{ThemeColors, ThemePreset};

    fn test_slider(suffix: &str) -> PlainSlider<()> {
        PlainSlider {
            label: "Opacity".to_string(),
            value: 0.5,
            range: 0.0..=1.0,
            step: 0.01,
            suffix: suffix.to_string(),
            decimals: 0,
            colors: ThemeColors::get(ThemePreset::Photopea),
            on_change: std::sync::Arc::new(|_| ()),
        }
    }

    #[test]
    fn percentage_format_parse_and_clamp_are_stable() {
        let slider = test_slider("%");
        assert_eq!(slider.format_value(0.5), "Opacity: 50%");
        assert_eq!(slider.parse_value("75"), Some(0.75));
        assert_eq!(slider.parse_value("150"), Some(1.0));
    }

    #[test]
    fn hover_typing_accepts_only_numeric_fragments() {
        let mut state = State::default();
        assert!(PlainSlider::<()>::begin_typing(&mut state, "-"));
        assert!(state.editing);
        assert_eq!(state.buffer, "-");
        assert!(is_numeric_fragment("12.5"));
        assert!(!is_numeric_fragment("px"));
    }

    #[test]
    fn pointer_mapping_respects_endpoints_and_step() {
        let slider = test_slider("");
        assert_eq!(slider.value_at(0.0, 124.0), 0.0);
        assert_eq!(slider.value_at(100.0, 124.0), 1.0);
        assert!((slider.value_at(33.0, 124.0) - 0.33).abs() < 1e-6);
    }

    #[test]
    fn pointer_mapping_clamps_outside_track() {
        let slider = test_slider("");
        assert_eq!(slider.value_at(-10.0, 124.0), 0.0);
        assert_eq!(slider.value_at(120.0, 124.0), 1.0);
    }
}