use crate::{px, FontId, FontRun, Pixels, PlatformTextSystem};
use collections::HashMap;
use std::{iter, sync::Arc};

pub struct LineWrapper {
    platform_text_system: Arc<dyn PlatformTextSystem>,
    pub(crate) font_id: FontId,
    pub(crate) font_size: Pixels,
    cached_ascii_char_widths: [Option<Pixels>; 128],
    cached_other_char_widths: HashMap<char, Pixels>,
}

impl LineWrapper {
    pub const MAX_INDENT: u32 = 256;

    pub fn new(
        font_id: FontId,
        font_size: Pixels,
        text_system: Arc<dyn PlatformTextSystem>,
    ) -> Self {
        Self {
            platform_text_system: text_system,
            font_id,
            font_size,
            cached_ascii_char_widths: [None; 128],
            cached_other_char_widths: HashMap::default(),
        }
    }

    pub fn wrap_line<'a>(
        &'a mut self,
        line: &'a str,
        wrap_width: Pixels,
    ) -> impl Iterator<Item = Boundary> + 'a {
        let mut width = px(0.);
        let mut first_non_whitespace_ix = None;
        let mut indent = None;
        let mut last_candidate_ix = 0;
        let mut last_candidate_width = px(0.);
        let mut last_wrap_ix = 0;
        let mut prev_c = '\0';
        let mut char_indices = line.char_indices();
        iter::from_fn(move || {
            for (ix, c) in char_indices.by_ref() {
                if c == '\n' {
                    continue;
                }

                if prev_c == ' ' && c != ' ' && first_non_whitespace_ix.is_some() {
                    last_candidate_ix = ix;
                    last_candidate_width = width;
                }

                if c != ' ' && first_non_whitespace_ix.is_none() {
                    first_non_whitespace_ix = Some(ix);
                }

                let char_width = self.width_for_char(c);
                width += char_width;
                if width > wrap_width && ix > last_wrap_ix {
                    if let (None, Some(first_non_whitespace_ix)) = (indent, first_non_whitespace_ix)
                    {
                        indent = Some(
                            Self::MAX_INDENT.min((first_non_whitespace_ix - last_wrap_ix) as u32),
                        );
                    }

                    if last_candidate_ix > 0 {
                        last_wrap_ix = last_candidate_ix;
                        width -= last_candidate_width;
                        last_candidate_ix = 0;
                    } else {
                        last_wrap_ix = ix;
                        width = char_width;
                    }

                    if let Some(indent) = indent {
                        width += self.width_for_char(' ') * indent as f32;
                    }

                    return Some(Boundary::new(last_wrap_ix, indent.unwrap_or(0)));
                }
                prev_c = c;
            }

            None
        })
    }

    #[inline(always)]
    fn width_for_char(&mut self, c: char) -> Pixels {
        if (c as u32) < 128 {
            if let Some(cached_width) = self.cached_ascii_char_widths[c as usize] {
                cached_width
            } else {
                let width = self.compute_width_for_char(c);
                self.cached_ascii_char_widths[c as usize] = Some(width);
                width
            }
        } else {
            if let Some(cached_width) = self.cached_other_char_widths.get(&c) {
                *cached_width
            } else {
                let width = self.compute_width_for_char(c);
                self.cached_other_char_widths.insert(c, width);
                width
            }
        }
    }

    fn compute_width_for_char(&self, c: char) -> Pixels {
        let mut buffer = [0; 4];
        let buffer = c.encode_utf8(&mut buffer);
        self.platform_text_system
            .layout_line(
                buffer,
                self.font_size,
                &[FontRun {
                    len: 1,
                    font_id: self.font_id,
                }],
            )
            .width
    }
}

#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub struct Boundary {
    pub ix: usize,
    pub next_indent: u32,
}

impl Boundary {
    fn new(ix: usize, next_indent: u32) -> Self {
        Self { ix, next_indent }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::{font, TestAppContext, TestDispatcher};
    use rand::prelude::*;

    #[test]
    fn test_wrap_line() {
        let dispatcher = TestDispatcher::new(StdRng::seed_from_u64(0));
        let cx = TestAppContext::new(dispatcher);

        cx.update(|cx| {
            let text_system = cx.text_system().clone();
            let mut wrapper = LineWrapper::new(
                text_system.font_id(&font("Courier")).unwrap(),
                px(16.),
                text_system.platform_text_system.clone(),
            );
            assert_eq!(
                wrapper
                    .wrap_line("aa bbb cccc ddddd eeee", px(72.))
                    .collect::<Vec<_>>(),
                &[
                    Boundary::new(7, 0),
                    Boundary::new(12, 0),
                    Boundary::new(18, 0)
                ],
            );
            assert_eq!(
                wrapper
                    .wrap_line("aaa aaaaaaaaaaaaaaaaaa", px(72.0))
                    .collect::<Vec<_>>(),
                &[
                    Boundary::new(4, 0),
                    Boundary::new(11, 0),
                    Boundary::new(18, 0)
                ],
            );
            assert_eq!(
                wrapper
                    .wrap_line("     aaaaaaa", px(72.))
                    .collect::<Vec<_>>(),
                &[
                    Boundary::new(7, 5),
                    Boundary::new(9, 5),
                    Boundary::new(11, 5),
                ]
            );
            assert_eq!(
                wrapper
                    .wrap_line("                            ", px(72.))
                    .collect::<Vec<_>>(),
                &[
                    Boundary::new(7, 0),
                    Boundary::new(14, 0),
                    Boundary::new(21, 0)
                ]
            );
            assert_eq!(
                wrapper
                    .wrap_line("          aaaaaaaaaaaaaa", px(72.))
                    .collect::<Vec<_>>(),
                &[
                    Boundary::new(7, 0),
                    Boundary::new(14, 3),
                    Boundary::new(18, 3),
                    Boundary::new(22, 3),
                ]
            );
        });
    }

    // todo!("move this to a test on TextSystem::layout_text")
    // todo! repeat this test
    // #[test]
    // fn test_wrap_shaped_line() {
    //     App::test().run(|cx| {
    //         let text_system = cx.text_system().clone();

    //         let normal = TextRun {
    //             len: 0,
    //             font: font("Helvetica"),
    //             color: Default::default(),
    //             underline: Default::default(),
    //         };
    //         let bold = TextRun {
    //             len: 0,
    //             font: font("Helvetica").bold(),
    //             color: Default::default(),
    //             underline: Default::default(),
    //         };

    //         impl TextRun {
    //             fn with_len(&self, len: usize) -> Self {
    //                 let mut this = self.clone();
    //                 this.len = len;
    //                 this
    //             }
    //         }

    //         let text = "aa bbb cccc ddddd eeee".into();
    //         let lines = text_system
    //             .layout_text(
    //                 &text,
    //                 px(16.),
    //                 &[
    //                     normal.with_len(4),
    //                     bold.with_len(5),
    //                     normal.with_len(6),
    //                     bold.with_len(1),
    //                     normal.with_len(7),
    //                 ],
    //                 None,
    //             )
    //             .unwrap();
    //         let line = &lines[0];

    //         let mut wrapper = LineWrapper::new(
    //             text_system.font_id(&normal.font).unwrap(),
    //             px(16.),
    //             text_system.platform_text_system.clone(),
    //         );
    //         assert_eq!(
    //             wrapper
    //                 .wrap_shaped_line(&text, &line, px(72.))
    //                 .collect::<Vec<_>>(),
    //             &[
    //                 ShapedBoundary {
    //                     run_ix: 1,
    //                     glyph_ix: 3
    //                 },
    //                 ShapedBoundary {
    //                     run_ix: 2,
    //                     glyph_ix: 3
    //                 },
    //                 ShapedBoundary {
    //                     run_ix: 4,
    //                     glyph_ix: 2
    //                 }
    //             ],
    //         );
    //     });
    // }
}