use iced_core as core;

use crate::core::text::highlighter::{self, Format};
use crate::core::{Color, Font};

use std::ops::Range;
use syntect::highlighting;
use syntect::parsing;

pub struct Highlighter {
    syntaxes: parsing::SyntaxSet,
    syntax: parsing::SyntaxReference,
    theme: highlighting::Theme,
    caches: Vec<(parsing::ParseState, parsing::ScopeStack)>,
    current_line: usize,
}

const LINES_PER_SNAPSHOT: usize = 50;

impl highlighter::Highlighter for Highlighter {
    type Settings = Settings;
    type Highlight = Highlight;

    type Iterator<'a> =
        Box<dyn Iterator<Item = (Range<usize>, Self::Highlight)> + 'a>;

    fn new(settings: &Self::Settings) -> Self {
        let syntaxes = parsing::SyntaxSet::load_defaults_nonewlines();

        let syntax = syntaxes
            .find_syntax_by_token(&settings.extension)
            .unwrap_or_else(|| syntaxes.find_syntax_plain_text());

        let theme = highlighting::ThemeSet::load_defaults()
            .themes
            .remove(settings.theme.key())
            .unwrap();

        let parser = parsing::ParseState::new(syntax);
        let stack = parsing::ScopeStack::new();

        Highlighter {
            syntax: syntax.clone(),
            syntaxes,
            theme,
            caches: vec![(parser, stack)],
            current_line: 0,
        }
    }

    fn update(&mut self, new_settings: &Self::Settings) {
        self.syntax = self
            .syntaxes
            .find_syntax_by_token(&new_settings.extension)
            .unwrap_or_else(|| self.syntaxes.find_syntax_plain_text())
            .clone();

        self.theme = highlighting::ThemeSet::load_defaults()
            .themes
            .remove(new_settings.theme.key())
            .unwrap();

        // Restart the highlighter
        self.change_line(0);
    }

    fn change_line(&mut self, line: usize) {
        let snapshot = line / LINES_PER_SNAPSHOT;

        if snapshot <= self.caches.len() {
            self.caches.truncate(snapshot);
            self.current_line = snapshot * LINES_PER_SNAPSHOT;
        } else {
            self.caches.truncate(1);
            self.current_line = 0;
        }

        let (parser, stack) =
            self.caches.last().cloned().unwrap_or_else(|| {
                (
                    parsing::ParseState::new(&self.syntax),
                    parsing::ScopeStack::new(),
                )
            });

        self.caches.push((parser, stack));
    }

    fn highlight_line(&mut self, line: &str) -> Self::Iterator<'_> {
        if self.current_line / LINES_PER_SNAPSHOT >= self.caches.len() {
            let (parser, stack) =
                self.caches.last().expect("Caches must not be empty");

            self.caches.push((parser.clone(), stack.clone()));
        }

        self.current_line += 1;

        let (parser, stack) =
            self.caches.last_mut().expect("Caches must not be empty");

        let ops = parser.parse_line(line, &self.syntaxes).unwrap_or_default();

        let highlighter = highlighting::Highlighter::new(&self.theme);

        Box::new(
            ScopeRangeIterator {
                ops,
                line_length: line.len(),
                index: 0,
                last_str_index: 0,
            }
            .filter_map(move |(range, scope)| {
                let _ = stack.apply(&scope);

                if range.is_empty() {
                    None
                } else {
                    Some((
                        range,
                        Highlight(
                            highlighter.style_mod_for_stack(&stack.scopes),
                        ),
                    ))
                }
            }),
        )
    }

    fn current_line(&self) -> usize {
        self.current_line
    }
}

#[derive(Debug, Clone, PartialEq)]
pub struct Settings {
    pub theme: Theme,
    pub extension: String,
}

pub struct Highlight(highlighting::StyleModifier);

impl Highlight {
    pub fn color(&self) -> Option<Color> {
        self.0.foreground.map(|color| {
            Color::from_rgba8(color.r, color.g, color.b, color.a as f32 / 255.0)
        })
    }

    pub fn font(&self) -> Option<Font> {
        None
    }

    pub fn to_format(&self) -> Format<Font> {
        Format {
            color: self.color(),
            font: self.font(),
        }
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Theme {
    SolarizedDark,
    InspiredGitHub,
    Base16Mocha,
}

impl Theme {
    pub const ALL: &[Self] =
        &[Self::SolarizedDark, Self::InspiredGitHub, Self::Base16Mocha];

    fn key(&self) -> &'static str {
        match self {
            Theme::InspiredGitHub => "InspiredGitHub",
            Theme::Base16Mocha => "base16-mocha.dark",
            Theme::SolarizedDark => "Solarized (dark)",
        }
    }
}

impl std::fmt::Display for Theme {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Theme::InspiredGitHub => write!(f, "Inspired GitHub"),
            Theme::Base16Mocha => write!(f, "Mocha"),
            Theme::SolarizedDark => write!(f, "Solarized Dark"),
        }
    }
}

pub struct ScopeRangeIterator {
    ops: Vec<(usize, parsing::ScopeStackOp)>,
    line_length: usize,
    index: usize,
    last_str_index: usize,
}

impl Iterator for ScopeRangeIterator {
    type Item = (std::ops::Range<usize>, parsing::ScopeStackOp);

    fn next(&mut self) -> Option<Self::Item> {
        if self.index > self.ops.len() {
            return None;
        }

        let next_str_i = if self.index == self.ops.len() {
            self.line_length
        } else {
            self.ops[self.index].0
        };

        let range = self.last_str_index..next_str_i;
        self.last_str_index = next_str_i;

        let op = if self.index == 0 {
            parsing::ScopeStackOp::Noop
        } else {
            self.ops[self.index - 1].1.clone()
        };

        self.index += 1;
        Some((range, op))
    }
}