//! Provide higher-level abstraction to draw things on backends.

use crate::backend::Backend;
use crate::direction::Orientation;
use crate::rect::Rect;
use crate::theme::{
    BorderStyle, ColorPair, ColorStyle, Effect, PaletteColor, Style, Theme,
};
use crate::utils::lines::simple::{prefix, suffix};
use crate::with::With;
use crate::Vec2;

use enumset::EnumSet;
use std::cell::Cell;
use std::cmp::min;
use unicode_segmentation::UnicodeSegmentation;
use unicode_width::UnicodeWidthStr;

/// Convenient interface to draw on a subset of the screen.
///
/// The area it can print on is defined by `offset` and `size`.
///
/// The part of the content it will print is defined by `content_offset`
/// and `size`.
#[derive(Clone)]
pub struct Printer<'a, 'b> {
    /// Offset into the window this printer should start drawing at.
    ///
    /// A print request at `x` will really print at `x + offset`.
    pub offset: Vec2,

    /// Size of the area we are allowed to draw on.
    ///
    /// Anything outside of this should be discarded.
    ///
    /// The view being drawn can ingore this, but anything further than that
    /// will be ignored.
    pub output_size: Vec2,

    /// Size allocated to the view.
    ///
    /// This should be the same value as the one given in the last call to
    /// `View::layout`.
    pub size: Vec2,

    /// Offset into the view for this printer.
    ///
    /// The view being drawn can ignore this, but anything to the top-left of
    /// this will actually be ignored, so it can be used to skip this part.
    ///
    /// A print request `x`, will really print at `x - content_offset`.
    pub content_offset: Vec2,

    /// Whether the view to draw is currently focused or not.
    pub focused: bool,

    /// Whether the view to draw is currently enabled or not.
    pub enabled: bool,

    /// Currently used theme
    pub theme: &'a Theme,

    /// Current color pair used by the parent view.
    current_color: Cell<ColorPair>,

    /// Backend used to actually draw things
    backend: &'b dyn Backend,
}

impl<'a, 'b> Printer<'a, 'b> {
    /// Creates a new printer on the given window.
    ///
    /// But nobody needs to know that.
    #[doc(hidden)]
    pub fn new<T: Into<Vec2>>(
        size: T,
        theme: &'a Theme,
        backend: &'b dyn Backend,
    ) -> Self {
        let size = size.into();
        Printer {
            offset: Vec2::zero(),
            content_offset: Vec2::zero(),
            output_size: size,
            size,
            focused: true,
            enabled: true,
            theme,
            backend,
            current_color: Cell::new(ColorPair::from_256colors(0, 0)),
        }
    }

    /// Clear the screen.
    ///
    /// It will discard anything drawn before.
    ///
    /// Users rarely need to call this directly.
    pub fn clear(&self) {
        self.backend
            .clear(self.theme.palette[PaletteColor::Background]);
    }

    /// Prints some styled text at the given position.
    pub fn print_styled<S>(
        &self,
        start: S,
        text: crate::utils::span::SpannedStr<'_, Style>,
    ) where
        S: Into<Vec2>,
    {
        let Vec2 { mut x, y } = start.into();
        for span in text.spans() {
            self.with_style(*span.attr, |printer| {
                printer.print_with_width((x, y), span.content, |_| span.width);
                x += span.width;
            });
        }
    }

    // TODO: use &mut self? We don't *need* it, but it may make sense.
    // We don't want people to start calling prints in parallel?
    /// Prints some text at the given position
    pub fn print<S: Into<Vec2>>(&self, start: S, text: &str) {
        self.print_with_width(start, text, UnicodeWidthStr::width);
    }

    /// Prints some text, using the given callback to compute width.
    ///
    /// Mostly used with `UnicodeWidthStr::width`.
    /// If you already know the width, you can give it as a constant instead.
    fn print_with_width<S, F>(&self, start: S, text: &str, width: F)
    where
        S: Into<Vec2>,
        F: FnOnce(&str) -> usize,
    {
        // Where we are asked to start printing. Oh boy. It's not that simple.
        let start = start.into();

        // We accept requests between `content_offset` and
        // `content_offset + output_size`.
        if !start.strictly_lt(self.output_size + self.content_offset) {
            return;
        }

        // If start < content_offset, part of the text will not be visible.
        // This is the part of the text that's hidden:
        // (It should always be smaller than the content offset)
        let hidden_part = self.content_offset.saturating_sub(start);
        if hidden_part.y > 0 {
            // Since we are printing a single line, there's nothing we can do.
            return;
        }

        let mut text_width = width(text);

        // If we're waaaay too far left, just give up.
        if hidden_part.x > text_width {
            return;
        }

        let mut text = text;
        let mut start = start;

        if hidden_part.x > 0 {
            // We have to drop hidden_part.x width from the start of the string.
            // prefix() may be too short if there's a double-width character.
            // So instead, keep the suffix and drop the prefix.

            // TODO: use a different prefix method that is *at least* the width
            // (and not *at most*)
            let tail =
                suffix(text.graphemes(true), text_width - hidden_part.x, "");
            let skipped_len = text.len() - tail.length;
            let skipped_width = text_width - tail.width;
            assert_eq!(text[..skipped_len].width(), skipped_width);

            // This should be equal most of the time, except when there's a double
            // character preventing us from splitting perfectly.
            assert!(skipped_width >= hidden_part.x);

            // Drop part of the text, and move the cursor correspondingly.
            text = &text[skipped_len..];
            start = start + (skipped_width, 0);
            text_width -= skipped_width;
        }

        assert!(start.fits(self.content_offset));

        // What we did before should guarantee that this won't overflow.
        start = start - self.content_offset;

        // Do we have enough room for the entire line?
        let room = self.output_size.x - start.x;

        if room < text_width {
            // Drop the end of the text if it's too long
            // We want the number of CHARACTERS, not bytes.
            // (Actually we want the "width" of the string, see unicode-width)
            let prefix_len = prefix(text.graphemes(true), room, "").length;
            text = &text[..prefix_len];
            assert!(text.width() <= room);
        }

        let start = start + self.offset;
        self.backend.print_at(start, text);
    }

    /// Prints a vertical line using the given character.
    pub fn print_vline<T: Into<Vec2>>(
        &self,
        start: T,
        height: usize,
        c: &str,
    ) {
        let start = start.into();

        // Here again, we can abort if we're trying to print too far right or
        // too low.
        if !start.strictly_lt(self.output_size + self.content_offset) {
            return;
        }

        // hidden_part describes how far to the top left of the viewport we are.
        let hidden_part = self.content_offset.saturating_sub(start);
        if hidden_part.x > 0 || hidden_part.y >= height {
            // We're printing a single column, so we can't do much here.
            return;
        }

        // Skip `hidden_part`
        let start = start + hidden_part;
        assert!(start.fits(self.content_offset));

        let height = height - hidden_part.y;

        // What we did before ensures this won't overflow.
        let start = start - self.content_offset;

        // Don't go overboard
        let height = min(height, self.output_size.y - start.y);

        let start = start + self.offset;
        for y in 0..height {
            self.backend.print_at(start + (0, y), c);
        }
    }

    /// Prints a line using the given character.
    pub fn print_line<T: Into<Vec2>>(
        &self,
        orientation: Orientation,
        start: T,
        length: usize,
        c: &str,
    ) {
        match orientation {
            Orientation::Vertical => self.print_vline(start, length, c),
            Orientation::Horizontal => self.print_hline(start, length, c),
        }
    }

    /// Prints a horizontal line using the given character.
    pub fn print_hline<T: Into<Vec2>>(&self, start: T, width: usize, c: &str) {
        let start = start.into();

        // Nothing to be done if the start if too far to the bottom/right
        if !start.strictly_lt(self.output_size + self.content_offset) {
            return;
        }

        let hidden_part = self.content_offset.saturating_sub(start);
        if hidden_part.y > 0 || hidden_part.x >= width {
            // We're printing a single line, so we can't do much here.
            return;
        }

        // Skip `hidden_part`
        let start = start + hidden_part;
        assert!(start.fits(self.content_offset));

        let width = width - hidden_part.x;

        // Don't go too far
        let start = start - self.content_offset;

        // Don't write too much if we're close to the end
        let repetitions = min(width, self.output_size.x - start.x) / c.width();

        let start = start + self.offset;
        self.backend.print_at_rep(start, repetitions, c);
    }

    /// Returns the color currently used by the parent view.
    pub fn current_color(&self) -> ColorPair {
        self.current_color.get()
    }

    /// Call the given closure with a colored printer,
    /// that will apply the given color on prints.
    ///
    /// # Examples
    ///
    /// ```rust
    /// # use cursive_core::Printer;
    /// # use cursive_core::theme;
    /// # use cursive_core::backend;
    /// # let b = backend::Dummy::init();
    /// # let t = theme::load_default();
    /// # let printer = Printer::new((6,4), &t, &*b);
    /// printer.with_color(theme::ColorStyle::highlight(), |printer| {
    ///     printer.print((0, 0), "This text is highlighted!");
    /// });
    /// ```
    pub fn with_color<F>(&self, c: ColorStyle, f: F)
    where
        F: FnOnce(&Printer),
    {
        let old = self.current_color.get();
        let new = c.resolve(&self.theme.palette, old);

        self.current_color.set(new);
        self.backend.set_color(new);

        f(self);

        self.backend.set_color(old);
        self.current_color.set(old)
    }

    /// Call the given closure with a styled printer,
    /// that will apply the given style on prints.
    pub fn with_style<F, T>(&self, style: T, f: F)
    where
        F: FnOnce(&Printer),
        T: Into<Style>,
    {
        let style = style.into();

        let color = style.color;
        let effects = style.effects;

        self.with_color(color, |printer| {
            printer.with_effects(effects, f);
        });
    }

    /// Call the given closure with a modified printer
    /// that will apply the given effect on prints.
    pub fn with_effect<F>(&self, effect: Effect, f: F)
    where
        F: FnOnce(&Printer),
    {
        self.backend.set_effect(effect);
        f(self);
        self.backend.unset_effect(effect);
    }

    /// Call the given closure with a modified printer
    /// that will apply the given theme on prints.
    pub fn with_theme<F>(&self, theme: &Theme, f: F)
    where
        F: FnOnce(&Printer),
    {
        f(&self.theme(theme));
    }

    /// Create a new sub-printer with the given theme.
    pub fn theme<'c>(&self, theme: &'c Theme) -> Printer<'c, 'b>
    where
        'a: 'c,
    {
        Printer {
            theme,
            ..self.clone()
        }
    }

    /// Call the given closure with a modified printer
    /// that will apply each given effect on prints.
    pub fn with_effects<F>(&self, effects: EnumSet<Effect>, f: F)
    where
        F: FnOnce(&Printer),
    {
        match effects.iter().next() {
            None => f(self),
            Some(effect) => {
                let mut effects = effects;
                effects.remove(effect);

                self.with_effect(effect, |s| s.with_effects(effects, f));
            }
        }
    }

    /// Prints a rectangular box.
    ///
    /// If `invert` is `true`, and the theme uses `Outset` borders, then the
    /// box will use an "inset" style instead.
    ///
    /// # Examples
    ///
    /// ```rust
    /// # use cursive_core::Printer;
    /// # use cursive_core::theme;
    /// # use cursive_core::backend;
    /// # let b = backend::Dummy::init();
    /// # let t = theme::load_default();
    /// # let printer = Printer::new((6,4), &t, &*b);
    /// printer.print_box((0, 0), (6, 4), false);
    /// ```
    pub fn print_box<T: Into<Vec2>, S: Into<Vec2>>(
        &self,
        start: T,
        size: S,
        invert: bool,
    ) {
        let start = start.into();
        let size = size.into();

        if size.x < 2 || size.y < 2 {
            return;
        }
        let size = size - (1, 1);

        self.with_high_border(invert, |s| {
            s.print(start, "┌");
            s.print(start + size.keep_y(), "└");
            s.print_hline(start + (1, 0), size.x - 1, "─");
            s.print_vline(start + (0, 1), size.y - 1, "│");
        });

        self.with_low_border(invert, |s| {
            s.print(start + size.keep_x(), "┐");
            s.print(start + size, "┘");
            s.print_hline(start + (1, 0) + size.keep_y(), size.x - 1, "─");
            s.print_vline(start + (0, 1) + size.keep_x(), size.y - 1, "│");
        });
    }

    /// Runs the given function using a color depending on the theme.
    ///
    /// * If the theme's borders is `None`, return without calling `f`.
    /// * If the theme's borders is "outset" and `invert` is `false`,
    ///   use `ColorStyle::Tertiary`.
    /// * Otherwise, use `ColorStyle::Primary`.
    pub fn with_high_border<F>(&self, invert: bool, f: F)
    where
        F: FnOnce(&Printer),
    {
        let color = match self.theme.borders {
            BorderStyle::None => return,
            BorderStyle::Outset if !invert => ColorStyle::tertiary(),
            _ => ColorStyle::primary(),
        };

        self.with_color(color, f);
    }

    /// Runs the given function using a color depending on the theme.
    ///
    /// * If the theme's borders is `None`, return without calling `f`.
    /// * If the theme's borders is "outset" and `invert` is `true`,
    ///   use `ColorStyle::tertiary()`.
    /// * Otherwise, use `ColorStyle::primary()`.
    pub fn with_low_border<F>(&self, invert: bool, f: F)
    where
        F: FnOnce(&Printer),
    {
        let color = match self.theme.borders {
            BorderStyle::None => return,
            BorderStyle::Outset if invert => ColorStyle::tertiary(),
            _ => ColorStyle::primary(),
        };

        self.with_color(color, f);
    }

    /// Apply a selection style and call the given function.
    ///
    /// * If `selection` is `false`, simply uses `ColorStyle::primary()`.
    /// * If `selection` is `true`:
    ///     * If the printer currently has the focus,
    ///       uses `ColorStyle::highlight()`.
    ///     * Otherwise, uses `ColorStyle::highlight_inactive()`.
    pub fn with_selection<F: FnOnce(&Printer)>(&self, selection: bool, f: F) {
        self.with_color(
            if selection {
                if self.focused {
                    ColorStyle::highlight()
                } else {
                    ColorStyle::highlight_inactive()
                }
            } else {
                ColorStyle::inherit_parent()
            },
            f,
        );
    }

    /// Prints a horizontal delimiter with side border `├` and `┤`.
    pub fn print_hdelim<T>(&self, start: T, len: usize)
    where
        T: Into<Vec2>,
    {
        let start = start.into();
        self.print(start, "├");
        self.print_hline(start + (1, 0), len.saturating_sub(2), "─");
        self.print(start + (len.saturating_sub(1), 0), "┤");
    }

    /// Returns a sub-printer with the given offset.
    ///
    /// It will print in an area slightly to the bottom/right.
    pub fn offset<S>(&self, offset: S) -> Self
    where
        S: Into<Vec2>,
    {
        let offset = offset.into();
        self.clone().with(|s| {
            // If we are drawing a part of the content,
            // let's reduce this first.
            let consumed = Vec2::min(s.content_offset, offset);

            let offset = offset - consumed;
            s.content_offset = s.content_offset - consumed;

            s.offset = s.offset + offset;

            s.output_size = s.output_size.saturating_sub(offset);
            s.size = s.size.saturating_sub(offset);
        })
    }

    /// Returns a new sub-printer inheriting the given focus.
    ///
    /// If `self` is focused and `focused == true`, the child will be focused.
    ///
    /// Otherwise, he will be unfocused.
    pub fn focused(&self, focused: bool) -> Self {
        self.clone().with(|s| {
            s.focused &= focused;
        })
    }

    /// Returns a new sub-printer inheriting the given enabled state.
    ///
    /// If `self` is enabled and `enabled == true`, the child will be enabled.
    ///
    /// Otherwise, he will be disabled.
    pub fn enabled(&self, enabled: bool) -> Self {
        self.clone().with(|s| s.enabled &= enabled)
    }

    /// Returns a new sub-printer for the given viewport.
    ///
    /// This is a combination of offset + cropped.
    pub fn windowed(&self, viewport: Rect) -> Self {
        self.offset(viewport.top_left()).cropped(viewport.size())
    }

    /// Returns a new sub-printer with a cropped area.
    ///
    /// The new printer size will be the minimum of `size` and its current size.
    ///
    /// Any size reduction happens at the bottom-right.
    pub fn cropped<S>(&self, size: S) -> Self
    where
        S: Into<Vec2>,
    {
        self.clone().with(|s| {
            let size = size.into();
            s.output_size = Vec2::min(s.output_size, size);
            s.size = Vec2::min(s.size, size);
        })
    }

    /// Returns a new sub-printer with a cropped area.
    ///
    /// The new printer size will be the minimum of `size` and its current size.
    ///
    /// The view will stay centered.
    ///
    /// Note that if shrinking by an odd number, the view will round to the top-left.
    pub fn cropped_centered<S>(&self, size: S) -> Self
    where
        S: Into<Vec2>,
    {
        let size = size.into();
        let borders = self.size.saturating_sub(size);
        let half_borders = borders / 2;

        self.cropped(size - half_borders).offset(half_borders)
    }

    /// Returns a new sub-printer with a shrinked area.
    ///
    /// The printer size will be reduced by the given border from the bottom-right.
    pub fn shrinked<S>(&self, borders: S) -> Self
    where
        S: Into<Vec2>,
    {
        self.cropped(self.size.saturating_sub(borders))
    }

    /// Returns a new sub-printer with a shrinked area.
    ///
    /// The printer size will be reduced by the given border, and will stay centered.
    ///
    /// Note that if shrinking by an odd number, the view will round to the top-left.
    pub fn shrinked_centered<S>(&self, borders: S) -> Self
    where
        S: Into<Vec2>,
    {
        let borders = borders.into();
        let half_borders = borders / 2;

        self.shrinked(borders - half_borders).offset(half_borders)
    }

    /// Returns a new sub-printer with a content offset.
    ///
    /// This is useful for parent views that only show a subset of their
    /// child, like `ScrollView`.
    pub fn content_offset<S>(&self, offset: S) -> Self
    where
        S: Into<Vec2>,
    {
        self.clone().with(|s| {
            s.content_offset = s.content_offset + offset;
        })
    }

    /// Returns a sub-printer with a different inner size.
    ///
    /// This will not change the actual output size, but will appear bigger to
    /// users of this printer.
    ///
    /// Useful to give to children who think they're big, but really aren't.
    pub fn inner_size<S>(&self, size: S) -> Self
    where
        S: Into<Vec2>,
    {
        self.clone().with(|s| {
            s.size = size.into();
        })
    }
}