// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License in the LICENSE-APACHE file or at:
//     https://www.apache.org/licenses/LICENSE-2.0

//! Methods using positioned glyphs

use super::TextDisplay;
use crate::conv::to_usize;
use crate::fonts::{fonts, FontId, ScaledFaceRef};
use crate::{Glyph, Vec2};

/// Effect formatting marker
#[derive(Clone, Debug, Default, PartialEq)]
pub struct Effect<X> {
    /// Index in text at which formatting becomes active
    ///
    /// (Note that we use `u32` not `usize` since it can be assumed text length
    /// will never exeed `u32::MAX`.)
    pub start: u32,
    /// Effect flags
    pub flags: EffectFlags,
    /// User payload
    pub aux: X,
}

bitflags::bitflags! {
    /// Text effects
    #[derive(Default)]
    pub struct EffectFlags: u32 {
        /// Glyph is underlined
        const UNDERLINE = 1 << 0;
        /// Glyph is crossed through by a centre-line
        const STRIKETHROUGH = 1 << 1;
    }
}

/// Used to return the position of a glyph with associated metrics
#[derive(Copy, Clone, Debug, Default, PartialEq)]
pub struct MarkerPos {
    /// (x, y) coordinate of glyph
    pub pos: Vec2,
    /// Ascent (subtract from y to get top)
    pub ascent: f32,
    /// Descent (subtract from y to get bottom)
    pub descent: f32,
    level: u8,
}

impl MarkerPos {
    /// Returns the embedding level
    ///
    /// According to Unicode Technical Report #9, the embedding level is
    /// guaranteed to be between 0 and 125 (inclusive), with a default level of
    /// zero and where odd levels are right-to-left.
    #[inline]
    pub fn embedding_level(&self) -> u8 {
        self.level
    }

    /// Returns true if the cursor is left-to-right
    #[inline]
    pub fn is_ltr(&self) -> bool {
        self.level % 2 == 0
    }

    /// Returns true if the cursor is right-to-left
    #[inline]
    pub fn is_rtl(&self) -> bool {
        self.level % 2 == 1
    }
}

pub struct MarkerPosIter {
    v: [MarkerPos; 2],
    a: usize,
    b: usize,
}

impl MarkerPosIter {
    /// Directly access the slice of results
    ///
    /// The result excludes elements removed by iteration.
    pub fn as_slice(&self) -> &[MarkerPos] {
        &self.v[self.a..self.b]
    }
}

impl Iterator for MarkerPosIter {
    type Item = MarkerPos;

    #[inline]
    fn next(&mut self) -> Option<Self::Item> {
        if self.a < self.b {
            let i = self.a;
            self.a = i + 1;
            Some(self.v[i])
        } else {
            None
        }
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        let len = self.b - self.a;
        (len, Some(len))
    }
}

impl DoubleEndedIterator for MarkerPosIter {
    #[inline]
    fn next_back(&mut self) -> Option<Self::Item> {
        if self.a < self.b {
            let i = self.b - 1;
            self.b = i;
            Some(self.v[i])
        } else {
            None
        }
    }
}

impl ExactSizeIterator for MarkerPosIter {}

impl TextDisplay {
    /// Find the starting position (top-left) of the glyph at the given index
    ///
    /// The index should be no greater than the text length. It is not required
    /// to be on a code-point boundary. Returns an iterator over matching
    /// positions. Length of results is guaranteed to be one of 0, 1 or 2:
    ///
    /// -   0 if the index is not included in any run of text (probably only
    ///     possible within a multi-byte line break or beyond the text length)
    /// -   1 is the normal case
    /// -   2 if the index is at the end of one run of text *and* at the start
    ///     of another; these positions may be the same or may not be (over
    ///     line breaks and with bidirectional text). If only a single position
    ///     is desired, usually the latter is preferred (via `next_back()`).
    ///
    /// Note: if the text's bounding rect does not start at the origin, then
    /// the coordinates of the top-left corner should be added to the result(s).
    /// The result is also not guaranteed to be within the expected window
    /// between 0 and `self.env().bounds`. The user should clamp the result.
    pub fn text_glyph_pos(&self, index: usize) -> MarkerPosIter {
        assert!(self.action.is_ready(), "kas-text::TextDisplay: not ready");

        let mut v: [MarkerPos; 2] = Default::default();
        let (a, mut b) = (0, 0);
        let mut push_result = |pos, ascent, descent, level| {
            v[b] = MarkerPos {
                pos,
                ascent,
                descent,
                level,
            };
            b += 1;
        };

        // We don't care too much about performance: use a naive search strategy
        'a: for run_part in &self.wrapped_runs {
            if index > to_usize(run_part.text_end) {
                continue;
            }

            let glyph_run = &self.runs[to_usize(run_part.glyph_run)];
            let sf = fonts().get(glyph_run.font_id).scale_by_dpu(glyph_run.dpu);

            // If index is at the end of a run, we potentially get two matches.
            if index == to_usize(run_part.text_end) {
                let i = if glyph_run.level.is_ltr() {
                    run_part.glyph_range.end()
                } else {
                    run_part.glyph_range.start()
                };
                let pos = if i < glyph_run.glyphs.len() {
                    glyph_run.glyphs[i].position
                } else {
                    // NOTE: for RTL we only hit this case if glyphs.len() == 0
                    Vec2(glyph_run.caret, 0.0)
                };

                let pos = run_part.offset + pos;
                push_result(pos, sf.ascent(), sf.descent(), glyph_run.level.number());
                continue;
            }

            // else: index < to_usize(run_part.text_end)
            let pos = 'b: loop {
                if glyph_run.level.is_ltr() {
                    for glyph in glyph_run.glyphs[run_part.glyph_range.to_std()].iter().rev() {
                        if to_usize(glyph.index) <= index {
                            break 'b glyph.position;
                        }
                    }
                } else {
                    for glyph in glyph_run.glyphs[run_part.glyph_range.to_std()].iter() {
                        if to_usize(glyph.index) <= index {
                            let mut pos = glyph.position;
                            pos.0 += sf.h_advance(glyph.id);
                            break 'b pos;
                        }
                    }
                }
                break 'a;
            };

            let pos = run_part.offset + pos;
            push_result(pos, sf.ascent(), sf.descent(), glyph_run.level.number());
            break;
        }

        MarkerPosIter { v, a, b }
    }

    /// Get the number of glyphs
    ///
    /// This method is a simple memory-read.
    #[inline]
    pub fn num_glyphs(&self) -> usize {
        to_usize(self.num_glyphs)
    }

    /// Yield a sequence of positioned glyphs
    ///
    /// Glyphs are yielded in undefined order by a call to `f`. The number of
    /// glyphs yielded will equal [`TextDisplay::num_glyphs`]. This may be used as
    /// follows:
    /// ```no_run
    /// # use kas_text::{Glyph, Text, Environment, TextApi, TextApiExt};
    /// # fn draw(_: Vec<(f32, Glyph)>) {}
    /// let mut text = Text::new_single("Some example text");
    /// text.prepare();
    ///
    /// let mut glyphs = Vec::with_capacity(text.num_glyphs());
    /// text.glyphs(|_, _, height, glyph| glyphs.push((height, glyph)));
    /// draw(glyphs);
    /// ```
    ///
    /// This method has fairly low cost: `O(n)` in the number of glyphs with
    /// low overhead.
    ///
    /// One must call [`TextDisplay::prepare`] before this method.
    pub fn glyphs<F: FnMut(FontId, f32, f32, Glyph)>(&self, mut f: F) {
        assert!(self.action.is_ready(), "kas-text::TextDisplay: not ready");

        // self.wrapped_runs is in logical order
        for run_part in self.wrapped_runs.iter().cloned() {
            let run = &self.runs[to_usize(run_part.glyph_run)];
            let font_id = run.font_id;
            let dpu = run.dpu.0;
            let height = run.height;

            for mut glyph in run.glyphs[run_part.glyph_range.to_std()].iter().cloned() {
                glyph.position = glyph.position + run_part.offset;
                f(font_id, dpu, height, glyph);
            }
        }
    }

    /// Like [`TextDisplay::glyphs`] but with added effects
    ///
    /// If the list `effects` is empty or has have first entry with `start > 0`,
    /// a default-constructed `Effect<X>` token is used.
    /// The user payload `X` is simply passed
    /// through to `f` and `g` calls and may be useful for colour information.
    ///
    /// The callback `f` receives `font_id, dpu, height, glyph, i, aux` where
    /// `dpu` and `height` are both measures of the font size (pixels per font
    /// unit and pixels per height, respectively), and `i` is the index within
    /// `effects` (or `usize::MAX` when a default-constructed effect token is
    /// used).
    ///
    /// The callback `g` receives positioning for each underline/strikethrough
    /// segment: `x1, x2, y_top, h` where `h` is the thickness (height). Note
    /// that it is possible to have `h < 1.0` and `y_top, y_top + h` to round to
    /// the same number; the renderer is responsible for ensuring such lines
    /// are actually visible. The last parameters are `i, aux` as for `f`.
    ///
    /// Note: this is significantly more computationally expensive than
    /// [`TextDisplay::glyphs`]. Optionally one may choose to cache the result,
    /// though this is not really necessary.
    pub fn glyphs_with_effects<X, F, G>(&self, effects: &[Effect<X>], mut f: F, mut g: G)
    where
        X: Copy + Default,
        F: FnMut(FontId, f32, f32, Glyph, usize, X),
        G: FnMut(f32, f32, f32, f32, usize, X),
    {
        assert!(self.action.is_ready(), "kas-text::TextDisplay: not ready");
        let fonts = fonts();

        let mut effect_cur = usize::MAX;
        let mut effect_next = 0;
        let mut next_start = effects
            .get(effect_next)
            .map(|e| e.start)
            .unwrap_or(u32::MAX);

        // self.wrapped_runs is in logical order
        for run_part in self.wrapped_runs.iter().cloned() {
            if run_part.glyph_range.len() == 0 {
                continue;
            }

            let run = &self.runs[to_usize(run_part.glyph_run)];
            let font_id = run.font_id;
            let dpu = run.dpu.0;
            let height = run.height;

            let mut underline = None;
            let mut strikethrough = None;

            let ltr = run.level.is_ltr();
            if !ltr {
                let last_index = run.glyphs[run_part.glyph_range.start()].index;
                while effects
                    .get(effect_next)
                    .map(|e| e.start <= last_index)
                    .unwrap_or(false)
                {
                    effect_cur = effect_next;
                    effect_next += 1;
                }
                next_start = effects
                    .get(effect_next)
                    .map(|e| e.start)
                    .unwrap_or(u32::MAX);
            }
            let mut fmt = effects
                .get(effect_cur)
                .cloned()
                .unwrap_or(Default::default());

            if !fmt.flags.is_empty() {
                let sf = fonts.get(run.font_id).scale_by_dpu(run.dpu);
                let glyph = &run.glyphs[run_part.glyph_range.start()];
                let position = glyph.position + run_part.offset;
                if fmt.flags.contains(EffectFlags::UNDERLINE) {
                    if let Some(metrics) = sf.underline_metrics() {
                        let y_top = position.1 - metrics.position;
                        let h = metrics.thickness;
                        let x1 = position.0;
                        underline = Some((x1, y_top, h, fmt.aux));
                    }
                }
                if fmt.flags.contains(EffectFlags::STRIKETHROUGH) {
                    if let Some(metrics) = sf.strikethrough_metrics() {
                        let y_top = position.1 - metrics.position;
                        let h = metrics.thickness;
                        let x1 = position.0;
                        strikethrough = Some((x1, y_top, h, fmt.aux));
                    }
                }
            }

            for mut glyph in run.glyphs[run_part.glyph_range.to_std()].iter().cloned() {
                glyph.position = glyph.position + run_part.offset;

                // If run is RTL, glyph index is decreasing
                if (ltr && next_start <= glyph.index) || (!ltr && fmt.start > glyph.index) {
                    if ltr {
                        loop {
                            effect_cur = effect_next;
                            effect_next += 1;
                            if effects
                                .get(effect_next)
                                .map(|e| e.start > glyph.index)
                                .unwrap_or(true)
                            {
                                break;
                            }
                        }
                        next_start = effects
                            .get(effect_next)
                            .map(|e| e.start)
                            .unwrap_or(u32::MAX);
                    } else {
                        loop {
                            effect_cur = effect_cur.wrapping_sub(1);
                            if effects.get(effect_cur).map(|e| e.start).unwrap_or(0) <= glyph.index
                            {
                                break;
                            }
                        }
                    }
                    fmt = effects
                        .get(effect_cur)
                        .cloned()
                        .unwrap_or(Default::default());

                    if underline.is_some() != fmt.flags.contains(EffectFlags::UNDERLINE) {
                        let sf = fonts.get(run.font_id).scale_by_dpu(run.dpu);
                        if let Some((x1, y_top, h, aux)) = underline {
                            let x2 = glyph.position.0;
                            g(x1, x2, y_top, h, effect_cur, aux);
                            underline = None;
                        } else if let Some(metrics) = sf.underline_metrics() {
                            let y_top = glyph.position.1 - metrics.position;
                            let h = metrics.thickness;
                            let x1 = glyph.position.0;
                            underline = Some((x1, y_top, h, fmt.aux));
                        }
                    }
                    if strikethrough.is_some() != fmt.flags.contains(EffectFlags::STRIKETHROUGH) {
                        let sf = fonts.get(run.font_id).scale_by_dpu(run.dpu);
                        if let Some((x1, y_top, h, aux)) = strikethrough {
                            let x2 = glyph.position.0;
                            g(x1, x2, y_top, h, effect_cur, aux);
                            strikethrough = None;
                        } else if let Some(metrics) = sf.strikethrough_metrics() {
                            let y_top = glyph.position.1 - metrics.position;
                            let h = metrics.thickness;
                            let x1 = glyph.position.0;
                            strikethrough = Some((x1, y_top, h, fmt.aux));
                        }
                    }
                }

                f(font_id, dpu, height, glyph, effect_cur, fmt.aux);
            }

            // In case of RTL, we need to correct the value for the next run
            effect_cur = effect_next.wrapping_sub(1);

            if let Some((x1, y_top, h, aux)) = underline {
                let x2 = if run_part.glyph_range.end() < run.glyphs.len() {
                    run.glyphs[run_part.glyph_range.end()].position.0
                } else {
                    run.caret
                } + run_part.offset.0;
                g(x1, x2, y_top, h, effect_cur, aux);
            }
            if let Some((x1, y_top, h, aux)) = strikethrough {
                let x2 = if run_part.glyph_range.end() < run.glyphs.len() {
                    run.glyphs[run_part.glyph_range.end()].position.0
                } else {
                    run.caret
                } + run_part.offset.0;
                g(x1, x2, y_top, h, effect_cur, aux);
            }
        }
    }

    /// Yield a sequence of rectangles to highlight a given range, by lines
    ///
    /// Rectangles span to end and beginning of lines when wrapping lines.
    /// (Note: gaps are possible between runs in the first and last lines. This
    /// is a defect which should be fixed but low priority and trickier than it
    /// might seem due to bi-directional text allowing re-ordering of runs.)
    ///
    /// This locates the ends of a range as with [`TextDisplay::text_glyph_pos`], but
    /// yields a separate rect for each "run" within this range (where "run" is
    /// a line or part of a line). Rects are represented by the top-left
    /// vertex and the bottom-right vertex.
    ///
    /// Note: if the text's bounding rect does not start at the origin, then
    /// the coordinates of the top-left corner should be added to the result(s).
    /// The result is also not guaranteed to be within the expected window
    /// between 0 and `self.env().bounds`. The user should clamp the result.
    pub fn highlight_lines(&self, range: std::ops::Range<usize>) -> Vec<(Vec2, Vec2)> {
        assert!(self.action.is_ready(), "kas-text::TextDisplay: not ready");
        if range.len() == 0 {
            return vec![];
        }

        let mut lines = self.lines.iter();
        let mut rects = Vec::with_capacity(self.lines.len());
        let rbound = self.width;

        // Find the first line
        let mut cur_line = 'l1: loop {
            while let Some(line) = lines.next() {
                if line.text_range.includes(range.start) {
                    break 'l1 line;
                }
            }
            return vec![];
        };

        if range.start > cur_line.text_range.start() || range.end <= cur_line.text_range.end() {
            self.highlight_run_range(range.clone(), cur_line.run_range.to_std(), &mut rects);
            if !rects.is_empty() && range.end > cur_line.text_range.end() {
                // find the rect nearest the line's end and extend
                let mut nearest = 0;
                let first_run = cur_line.run_range.start();
                let glyph_run = to_usize(self.wrapped_runs[first_run].glyph_run);
                if self.runs[glyph_run].level.is_ltr() {
                    let mut dist = rbound - (rects[0].1).0;
                    for i in 1..rects.len() {
                        let d = rbound - (rects[i].1).0;
                        if d < dist {
                            nearest = i;
                            dist = d;
                        }
                    }
                    (rects[nearest].1).0 = rbound;
                } else {
                    let mut dist = (rects[0].0).0;
                    for i in 1..rects.len() {
                        let d = (rects[i].0).0;
                        if d < dist {
                            nearest = i;
                            dist = d;
                        }
                    }
                    (rects[nearest].0).0 = 0.0;
                }
            }
        } else {
            let a = Vec2(0.0, cur_line.top);
            let b = Vec2(rbound, cur_line.bottom);
            rects.push((a, b));
        }

        if range.end > cur_line.text_range.end() {
            while let Some(line) = lines.next() {
                if range.end <= line.text_range.end() {
                    cur_line = line;
                    break;
                }

                let a = Vec2(0.0, line.top);
                let b = Vec2(rbound, line.bottom);
                rects.push((a, b));
            }

            if cur_line.text_range.start() < range.end {
                self.highlight_run_range(range, cur_line.run_range.to_std(), &mut rects);
            }
        }

        rects
    }

    /// Yield a sequence of rectangles to highlight a given range, by runs
    ///
    /// Rectangles tightly fit each "run" (piece) of text highlighted. (As an
    /// artifact, the highlighting may leave gaps between runs. This may or may
    /// not change in the future.)
    ///
    /// This locates the ends of a range as with [`TextDisplay::text_glyph_pos`], but
    /// yields a separate rect for each "run" within this range (where "run" is
    /// is a line or part of a line). Rects are represented by the top-left
    /// vertex and the bottom-right vertex.
    ///
    /// Note: if the text's bounding rect does not start at the origin, then
    /// the coordinates of the top-left corner should be added to the result(s).
    /// The result is also not guaranteed to be within the expected window
    /// between 0 and `self.env().bounds`. The user should clamp the result.
    #[inline]
    pub fn highlight_runs(&self, range: std::ops::Range<usize>) -> Vec<(Vec2, Vec2)> {
        assert!(self.action.is_ready(), "kas-text::TextDisplay: not ready");
        if range.len() == 0 {
            return vec![];
        }

        let mut rects = Vec::with_capacity(self.wrapped_runs.len());
        self.highlight_run_range(range, 0..usize::MAX, &mut rects);
        rects
    }

    /// Produce highlighting rectangles within a range of runs
    ///
    /// Warning: runs are in logical order which does not correspond to display
    /// order. As a result, the order of results (on a line) is not known.
    fn highlight_run_range(
        &self,
        range: std::ops::Range<usize>,
        run_range: std::ops::Range<usize>,
        rects: &mut Vec<(Vec2, Vec2)>,
    ) {
        let mut push_rect = |mut a: Vec2, mut b: Vec2, sf: ScaledFaceRef| {
            a.1 -= sf.ascent();
            b.1 -= sf.descent();
            rects.push((a, b));
        };
        let mut a;

        let mut i = run_range.start;
        'b: loop {
            if i >= run_range.end {
                return;
            }
            let run_part = &self.wrapped_runs[i];
            if range.start >= to_usize(run_part.text_end) {
                i += 1;
                continue;
            }

            let glyph_run = &self.runs[to_usize(run_part.glyph_run)];
            let sf = fonts().get(glyph_run.font_id).scale_by_dpu(glyph_run.dpu);

            // else: range.start < to_usize(run_part.text_end)
            if glyph_run.level.is_ltr() {
                for glyph in glyph_run.glyphs[run_part.glyph_range.to_std()].iter().rev() {
                    if to_usize(glyph.index) <= range.start {
                        a = glyph.position;
                        break 'b;
                    }
                }
                a = Vec2::ZERO;
            } else {
                for glyph in glyph_run.glyphs[run_part.glyph_range.to_std()].iter() {
                    if to_usize(glyph.index) <= range.start {
                        a = glyph.position;
                        a.0 += sf.h_advance(glyph.id);
                        break 'b;
                    }
                }
                a = Vec2(glyph_run.caret, 0.0);
            }
            break 'b;
        }

        let mut first = true;
        'a: while i < run_range.end {
            let run_part = &self.wrapped_runs[i];
            let offset = run_part.offset;
            let glyph_run = &self.runs[to_usize(run_part.glyph_run)];
            let sf = fonts().get(glyph_run.font_id).scale_by_dpu(glyph_run.dpu);

            if !first {
                a = if glyph_run.level.is_ltr() {
                    if run_part.glyph_range.start() < glyph_run.glyphs.len() {
                        glyph_run.glyphs[run_part.glyph_range.start()].position
                    } else {
                        Vec2::ZERO
                    }
                } else {
                    if run_part.glyph_range.end() < glyph_run.glyphs.len() {
                        glyph_run.glyphs[run_part.glyph_range.end()].position
                    } else {
                        Vec2(glyph_run.caret, 0.0)
                    }
                };
            }
            first = false;

            if range.end >= to_usize(run_part.text_end) {
                let b;
                if glyph_run.level.is_ltr() {
                    if run_part.glyph_range.end() < glyph_run.glyphs.len() {
                        b = glyph_run.glyphs[run_part.glyph_range.end()].position;
                    } else {
                        b = Vec2(glyph_run.caret, 0.0);
                    }
                } else {
                    let p = if run_part.glyph_range.start() < glyph_run.glyphs.len() {
                        glyph_run.glyphs[run_part.glyph_range.start()].position
                    } else {
                        // NOTE: for RTL we only hit this case if glyphs.len() == 0
                        Vec2(glyph_run.caret, 0.0)
                    };
                    b = Vec2(a.0, p.1);
                    a.0 = p.0;
                };

                push_rect(a + offset, b + offset, sf);
                i += 1;
                continue;
            }

            // else: range.end < to_usize(run_part.text_end)
            let b;
            'c: loop {
                if glyph_run.level.is_ltr() {
                    for glyph in glyph_run.glyphs[run_part.glyph_range.to_std()].iter().rev() {
                        if to_usize(glyph.index) <= range.end {
                            b = glyph.position;
                            break 'c;
                        }
                    }
                } else {
                    for glyph in glyph_run.glyphs[run_part.glyph_range.to_std()].iter() {
                        if to_usize(glyph.index) <= range.end {
                            let mut p = glyph.position;
                            p.0 += sf.h_advance(glyph.id);
                            b = Vec2(a.0, p.1);
                            a.0 = p.0;
                            break 'c;
                        }
                    }
                }
                break 'a;
            }

            push_rect(a + offset, b + offset, sf);
            break;
        }
    }
}