use crate::{
    Align2, AsIdSalt, Color32, Context, CursorIcon, Id, IdSalt, NumExt as _, Pos2, Rect, Response,
    Sense, Shape, Ui, UiBuilder, UiKind, UiStackInfo, Vec2, Vec2b, pos2, vec2,
};

#[derive(Clone, Copy, Debug)]
#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
pub(crate) struct State {
    /// This is the size that the user has picked by dragging the resize handles.
    /// This may be smaller and/or larger than the actual size.
    /// For instance, the user may have tried to shrink too much (not fitting the contents).
    /// Or the user requested a large area, but the content don't need that much space.
    pub(crate) desired_size: Vec2,

    /// Actual size of content last frame
    last_content_size: Vec2,

    /// Externally requested size (e.g. by Window) for the next frame
    pub(crate) requested_size: Option<Vec2>,

    /// Minimum content width measured by a sizing pass at the start of the current
    /// interactive resize. We clamp `desired_size.x` against this for the rest of
    /// the drag so the user can't shrink the window past what the content actually
    /// needs. Reset to `None` whenever a drag is not in progress.
    #[cfg_attr(feature = "serde", serde(default))]
    min_content_width: Option<f32>,
}

impl State {
    pub fn load(ctx: &Context, id: Id) -> Option<Self> {
        ctx.data_mut(|d| d.get_persisted(id))
    }

    pub fn store(self, ctx: &Context, id: Id) {
        ctx.data_mut(|d| d.insert_persisted(id, self));
    }
}

/// A region that can be resized by dragging the bottom right corner.
#[derive(Clone, Copy, Debug)]
#[must_use = "You should call .show()"]
pub struct Resize {
    id: Option<Id>,
    id_salt: Option<IdSalt>,

    /// If false, we are no enabled
    resizable: Vec2b,

    pub(crate) min_size: Vec2,
    pub(crate) max_size: Vec2,

    pub(crate) default_size: Vec2,

    with_stroke: bool,
}

impl Default for Resize {
    fn default() -> Self {
        Self {
            id: None,
            id_salt: None,
            resizable: Vec2b::TRUE,
            min_size: Vec2::splat(16.0),
            max_size: Vec2::splat(f32::INFINITY),
            default_size: vec2(320.0, 128.0), // TODO(emilk): preferred size of [`Resize`] area.
            with_stroke: true,
        }
    }
}

impl Resize {
    /// Assign an explicit and globally unique id.
    #[inline]
    pub fn id(mut self, id: Id) -> Self {
        self.id = Some(id);
        self
    }

    /// A source for the unique [`Id`], e.g. `.id_salt("second_resize_area")` or `.id_salt(loop_index)`.
    #[inline]
    pub fn id_salt(mut self, id_salt: impl AsIdSalt) -> Self {
        self.id_salt = Some(IdSalt::new(id_salt));
        self
    }

    /// Preferred / suggested width. Actual width will depend on contents.
    ///
    /// Examples:
    /// * if the contents is text, this will decide where we break long lines.
    /// * if the contents is a canvas, this decides the width of it,
    /// * if the contents is some buttons, this is ignored and we will auto-size.
    #[inline]
    pub fn default_width(mut self, width: f32) -> Self {
        self.default_size.x = width;
        self
    }

    /// Preferred / suggested height. Actual height will depend on contents.
    ///
    /// Examples:
    /// * if the contents is a [`crate::ScrollArea`] then this decides the maximum size.
    /// * if the contents is a canvas, this decides the height of it,
    /// * if the contents is text and buttons, then the `default_height` is ignored
    ///   and the height is picked automatically..
    #[inline]
    pub fn default_height(mut self, height: f32) -> Self {
        self.default_size.y = height;
        self
    }

    #[inline]
    pub fn default_size(mut self, default_size: impl Into<Vec2>) -> Self {
        self.default_size = default_size.into();
        self
    }

    /// Won't shrink to smaller than this
    #[inline]
    pub fn min_size(mut self, min_size: impl Into<Vec2>) -> Self {
        self.min_size = min_size.into();
        self
    }

    /// Won't shrink to smaller than this
    #[inline]
    pub fn min_width(mut self, min_width: f32) -> Self {
        self.min_size.x = min_width;
        self
    }

    /// Won't shrink to smaller than this
    #[inline]
    pub fn min_height(mut self, min_height: f32) -> Self {
        self.min_size.y = min_height;
        self
    }

    /// Won't expand to larger than this
    #[inline]
    pub fn max_size(mut self, max_size: impl Into<Vec2>) -> Self {
        self.max_size = max_size.into();
        self
    }

    /// Won't expand to larger than this
    #[inline]
    pub fn max_width(mut self, max_width: f32) -> Self {
        self.max_size.x = max_width;
        self
    }

    /// Won't expand to larger than this
    #[inline]
    pub fn max_height(mut self, max_height: f32) -> Self {
        self.max_size.y = max_height;
        self
    }

    /// Can you resize it with the mouse?
    ///
    /// Note that a window can still auto-resize.
    ///
    /// Default is `true`.
    #[inline]
    pub fn resizable(mut self, resizable: impl Into<Vec2b>) -> Self {
        self.resizable = resizable.into();
        self
    }

    #[inline]
    pub fn is_resizable(&self) -> Vec2b {
        self.resizable
    }

    /// Not manually resizable, just takes the size of its contents.
    /// Text will not wrap, but will instead make your window width expand.
    pub fn auto_sized(self) -> Self {
        self.min_size(Vec2::ZERO)
            .default_size(Vec2::splat(f32::INFINITY))
            .resizable(false)
    }

    #[inline]
    pub fn fixed_size(mut self, size: impl Into<Vec2>) -> Self {
        let size = size.into();
        self.default_size = size;
        self.min_size = size;
        self.max_size = size;
        self.resizable = Vec2b::FALSE;
        self
    }

    #[inline]
    pub fn with_stroke(mut self, with_stroke: bool) -> Self {
        self.with_stroke = with_stroke;
        self
    }
}

struct Prepared {
    id: Id,
    corner_id: Option<Id>,

    /// The top-left corner, or the top-right one with `grip_on_left`.
    anchor: Pos2,

    /// The resize grip is at the bottom-left ([`crate::Style::right_to_left`]).
    grip_on_left: bool,

    state: State,
    content_ui: Ui,
    sizing_pass: bool,
}

/// A rect of `size` with its top-left corner at `anchor`,
/// or its top-right corner with `grip_on_left`.
fn anchored_rect(anchor: Pos2, size: Vec2, grip_on_left: bool) -> Rect {
    if grip_on_left {
        Rect::from_min_size(pos2(anchor.x - size.x, anchor.y), size)
    } else {
        Rect::from_min_size(anchor, size)
    }
}

impl Resize {
    fn begin(&self, ui: &mut Ui) -> Prepared {
        // With the grip at the bottom-left, the right edge stays put while resizing.
        let grip_on_left = ui.style().right_to_left && self.resizable.any();
        let available = ui.available_rect_before_wrap();
        let anchor = if grip_on_left {
            available.right_top()
        } else {
            available.min
        };
        let id = self.id.unwrap_or_else(|| {
            let id_salt = self.id_salt.unwrap_or_else(|| IdSalt::new("resize"));
            ui.make_persistent_id(id_salt)
        });

        let mut state = State::load(ui.ctx(), id).unwrap_or_else(|| {
            ui.request_repaint(); // counter frame delay

            let default_size = self
                .default_size
                .at_least(self.min_size)
                .at_most(self.max_size)
                .at_most(
                    ui.ctx().content_rect().size() - ui.spacing().window_margin.sum(), // hack for windows
                )
                .round_ui();

            State {
                desired_size: default_size,
                last_content_size: vec2(0.0, 0.0),
                requested_size: None,
                min_content_width: None,
            }
        });

        state.desired_size = state
            .desired_size
            .at_least(self.min_size)
            .at_most(self.max_size)
            .round_ui();

        let mut user_requested_size = state.requested_size.take();

        let corner_id = self.resizable.any().then(|| id.with("__resize_corner"));

        if let Some(corner_id) = corner_id
            && let Some(corner_response) = ui.ctx().read_response(corner_id)
            && let Some(pointer_pos) = corner_response.interact_pointer_pos()
        {
            // Respond to the interaction early to avoid frame delay.
            let mut size = pointer_pos - anchor;
            if grip_on_left {
                size.x = -size.x;
            }
            user_requested_size = Some(size + 0.5 * corner_response.rect.size());
        }

        let is_actively_resizing = user_requested_size.is_some();

        // Drag just started: we don't yet know what the content's minimum width is.
        // Run a one-frame sizing pass below to discover it.
        let needs_sizing_pass = is_actively_resizing && state.min_content_width.is_none();

        if let Some(mut user_requested_size) = user_requested_size {
            if let Some(min_width) = state.min_content_width {
                user_requested_size.x = user_requested_size.x.at_least(min_width);
            }
            state.desired_size = user_requested_size;
        } else {
            // We are not being actively resized, so auto-expand to include size of last frame.
            // This prevents auto-shrinking if the contents contain width-filling widgets (separators etc)
            // but it makes a lot of interactions with [`Window`]s nicer.
            state.desired_size = state.desired_size.max(state.last_content_size);
            // Drag ended (if any). Forget the cached min so the next drag re-measures it,
            // in case content changed.
            state.min_content_width = None;
        }

        state.desired_size = state
            .desired_size
            .at_least(self.min_size)
            .at_most(self.max_size);

        // ------------------------------

        // For the sizing pass, offer the tightest possible rect so widgets shrink to
        // their natural minimum. We render the frame invisibly and discard it so the
        // user never sees the squished layout; the measured min then clamps drags.
        let inner_rect = if needs_sizing_pass {
            ui.ctx().request_discard("Resize sizing pass");
            anchored_rect(
                anchor,
                Vec2::new(self.min_size.x, state.desired_size.y),
                grip_on_left,
            )
        } else {
            anchored_rect(anchor, state.desired_size, grip_on_left)
        };

        let mut content_clip_rect = inner_rect;

        // If we pull the resize handle to shrink, we want to TRY to shrink it.
        // After laying out the contents, we might be much bigger.
        // In those cases we don't want the clip_rect to be smaller, because
        // then we will clip the contents of the region even thought the result gets larger. This is simply ugly!
        // So we use the memory of last_content_size to make the clip rect large enough.
        content_clip_rect.max = content_clip_rect
            .max
            .max(inner_rect.min + state.last_content_size);

        content_clip_rect = content_clip_rect.intersect(ui.clip_rect()); // Respect parent region

        let mut ui_builder = UiBuilder::new()
            .ui_stack_info(UiStackInfo::new(UiKind::Resize))
            .max_rect(inner_rect);
        if needs_sizing_pass {
            ui_builder = ui_builder.sizing_pass();
        }
        let mut content_ui = ui.new_child(ui_builder);
        content_ui.set_clip_rect(content_clip_rect);

        Prepared {
            id,
            corner_id,
            anchor,
            grip_on_left,
            state,
            content_ui,
            sizing_pass: needs_sizing_pass,
        }
    }

    pub fn show<R>(self, ui: &mut Ui, add_contents: impl FnOnce(&mut Ui) -> R) -> R {
        let mut prepared = self.begin(ui);
        let ret = add_contents(&mut prepared.content_ui);
        self.end(ui, prepared);
        ret
    }

    fn end(self, ui: &mut Ui, prepared: Prepared) {
        let Prepared {
            id,
            corner_id,
            anchor,
            grip_on_left,
            mut state,
            content_ui,
            sizing_pass,
        } = prepared;

        if sizing_pass {
            // Remember the measured minimum so we can clamp the user's drag on subsequent frames.
            // Don't touch `last_content_size`, it should keep reflecting the previously
            // rendered content.
            state.min_content_width = Some(content_ui.min_size().x);
        } else {
            state.last_content_size = content_ui.min_size();
        }

        // ------------------------------

        let mut size = state.last_content_size;
        for d in 0..2 {
            if self.with_stroke || self.resizable[d] {
                // We show how large we are,
                // so we must follow the contents:

                state.desired_size[d] = state.desired_size[d].max(state.last_content_size[d]);

                // We are as large as we look
                size[d] = state.desired_size[d];
            } else {
                // Probably a window.
                size[d] = state.last_content_size[d];
            }
        }
        // The content's top-left corner, or its top-right one when the grip is on the left.
        let anchor = if grip_on_left {
            pos2(anchor.x, content_ui.min_rect().top())
        } else {
            content_ui.min_rect().left_top()
        };
        let outer_rect = anchored_rect(anchor, size, grip_on_left);
        ui.advance_cursor_after_rect(outer_rect);

        // ------------------------------

        let corner_response = if let Some(corner_id) = corner_id {
            // We do the corner interaction last to place it on top of the content:
            let corner_size = Vec2::splat(ui.visuals().resize_corner_size);
            let corner_rect = if grip_on_left {
                Rect::from_min_size(
                    outer_rect.left_bottom() - vec2(0.0, corner_size.y),
                    corner_size,
                )
            } else {
                Rect::from_min_size(outer_rect.right_bottom() - corner_size, corner_size)
            };
            Some(ui.interact(corner_rect, corner_id, Sense::drag()))
        } else {
            None
        };

        // ------------------------------

        if self.with_stroke && corner_response.is_some() {
            let rect = anchored_rect(anchor, state.desired_size, grip_on_left);
            let rect = rect.expand(2.0); // breathing room for content
            ui.painter().add(Shape::rect_stroke(
                rect,
                3.0,
                ui.visuals().widgets.noninteractive.bg_stroke,
                epaint::StrokeKind::Inside,
            ));
        }

        if let Some(corner_response) = corner_response {
            paint_resize_corner(ui, &corner_response);

            if corner_response.hovered() || corner_response.dragged() {
                ui.set_cursor_icon(if grip_on_left {
                    CursorIcon::ResizeNeSw
                } else {
                    CursorIcon::ResizeNwSe
                });
            }
        }

        state.store(ui.ctx(), id);

        #[cfg(debug_assertions)]
        if ui.global_style().debug.show_resize {
            ui.debug_painter().debug_rect(
                anchored_rect(anchor, state.desired_size, grip_on_left),
                Color32::GREEN,
                "desired_size",
            );
            ui.debug_painter().debug_rect(
                anchored_rect(anchor, state.last_content_size, grip_on_left),
                Color32::LIGHT_BLUE,
                "last_content_size",
            );
        }
    }
}

use emath::GuiRounding as _;
use epaint::Stroke;

/// Paints a resize grip in the bottom-right corner of `response.rect`,
/// or the bottom-left one with [`crate::Style::right_to_left`].
pub fn paint_resize_corner(ui: &Ui, response: &Response) {
    let stroke = ui.style().interact(response).fg_stroke;
    let corner = if ui.style().right_to_left {
        Align2::LEFT_BOTTOM
    } else {
        Align2::RIGHT_BOTTOM
    };
    paint_resize_corner_with_style(ui, &response.rect, stroke.color, corner);
}

pub fn paint_resize_corner_with_style(
    ui: &Ui,
    rect: &Rect,
    color: impl Into<Color32>,
    corner: Align2,
) {
    let painter = ui.painter();
    let cp = corner
        .pos_in_rect(rect)
        .round_to_pixels(ui.pixels_per_point());
    let mut w = 2.0;
    let stroke = Stroke {
        width: 1.0, // Set width to 1.0 to prevent overlapping
        color: color.into(),
    };

    while w <= rect.width() && w <= rect.height() {
        painter.line_segment(
            [
                pos2(cp.x - w * corner.x().to_sign(), cp.y),
                pos2(cp.x, cp.y - w * corner.y().to_sign()),
            ],
            stroke,
        );
        w += 4.0;
    }
}