use alacritty_terminal::term::search::Match;
use alacritty_terminal::term::Term;

use crate::config::ui_config::{Hint, HintAction};
use crate::display::content::RegexMatches;

/// Percentage of characters in the hints alphabet used for the last character.
const HINT_SPLIT_PERCENTAGE: f32 = 0.5;

/// Keyboard regex hint state.
pub struct HintState {
    /// Hint currently in use.
    hint: Option<Hint>,

    /// Alphabet for hint labels.
    alphabet: String,

    /// Visible matches.
    matches: RegexMatches,

    /// Key label for each visible match.
    labels: Vec<Vec<char>>,

    /// Keys pressed for hint selection.
    keys: Vec<char>,
}

impl HintState {
    /// Initialize an inactive hint state.
    pub fn new<S: Into<String>>(alphabet: S) -> Self {
        Self {
            alphabet: alphabet.into(),
            hint: Default::default(),
            matches: Default::default(),
            labels: Default::default(),
            keys: Default::default(),
        }
    }

    /// Check if a hint selection is in progress.
    pub fn active(&self) -> bool {
        self.hint.is_some()
    }

    /// Start the hint selection process.
    pub fn start(&mut self, hint: Hint) {
        self.hint = Some(hint);
    }

    /// Cancel the hint highlighting process.
    fn stop(&mut self) {
        self.matches.clear();
        self.labels.clear();
        self.keys.clear();
        self.hint = None;
    }

    /// Update the visible hint matches and key labels.
    pub fn update_matches<T>(&mut self, term: &Term<T>) {
        let hint = match self.hint.as_mut() {
            Some(hint) => hint,
            None => return,
        };

        // Find visible matches.
        self.matches = hint.regex.with_compiled(|regex| RegexMatches::new(term, regex));

        // Cancel highlight with no visible matches.
        if self.matches.is_empty() {
            self.stop();
            return;
        }

        let mut generator = HintLabels::new(&self.alphabet, HINT_SPLIT_PERCENTAGE);
        let match_count = self.matches.len();
        let keys_len = self.keys.len();

        // Get the label for each match.
        self.labels.resize(match_count, Vec::new());
        for i in (0..match_count).rev() {
            let mut label = generator.next();
            if label.len() >= keys_len && label[..keys_len] == self.keys[..] {
                self.labels[i] = label.split_off(keys_len);
            } else {
                self.labels[i] = Vec::new();
            }
        }
    }

    /// Handle keyboard input during hint selection.
    pub fn keyboard_input<T>(&mut self, term: &Term<T>, c: char) -> Option<HintMatch> {
        match c {
            // Use backspace to remove the last character pressed.
            '\x08' | '\x1f' => {
                self.keys.pop();
            },
            // Cancel hint highlighting on ESC.
            '\x1b' => self.stop(),
            _ => (),
        }

        // Update the visible matches.
        self.update_matches(term);

        let hint = self.hint.as_ref()?;

        // Find the last label starting with the input character.
        let mut labels = self.labels.iter().enumerate().rev();
        let (index, label) = labels.find(|(_, label)| !label.is_empty() && label[0] == c)?;

        // Check if the selected label is fully matched.
        if label.len() == 1 {
            let bounds = self.matches[index].clone();
            let action = hint.action.clone();

            self.stop();

            Some(HintMatch { action, bounds })
        } else {
            // Store character to preserve the selection.
            self.keys.push(c);

            None
        }
    }

    /// Hint key labels.
    pub fn labels(&self) -> &Vec<Vec<char>> {
        &self.labels
    }

    /// Visible hint regex matches.
    pub fn matches(&self) -> &RegexMatches {
        &self.matches
    }

    /// Update the alphabet used for hint labels.
    pub fn update_alphabet(&mut self, alphabet: &str) {
        if self.alphabet != alphabet {
            self.alphabet = alphabet.to_owned();
            self.keys.clear();
        }
    }
}

/// Hint match which was selected by the user.
pub struct HintMatch {
    /// Action for handling the text.
    pub action: HintAction,

    /// Terminal range matching the hint.
    pub bounds: Match,
}

/// Generator for creating new hint labels.
struct HintLabels {
    /// Full character set available.
    alphabet: Vec<char>,

    /// Alphabet indices for the next label.
    indices: Vec<usize>,

    /// Point separating the alphabet's head and tail characters.
    ///
    /// To make identification of the tail character easy, part of the alphabet cannot be used for
    /// any other position.
    ///
    /// All characters in the alphabet before this index will be used for the last character, while
    /// the rest will be used for everything else.
    split_point: usize,
}

impl HintLabels {
    /// Create a new label generator.
    ///
    /// The `split_ratio` should be a number between 0.0 and 1.0 representing the percentage of
    /// elements in the alphabet which are reserved for the tail of the hint label.
    fn new(alphabet: impl Into<String>, split_ratio: f32) -> Self {
        let alphabet: Vec<char> = alphabet.into().chars().collect();
        let split_point = ((alphabet.len() - 1) as f32 * split_ratio.min(1.)) as usize;

        Self { indices: vec![0], split_point, alphabet }
    }

    /// Get the characters for the next label.
    fn next(&mut self) -> Vec<char> {
        let characters = self.indices.iter().rev().map(|index| self.alphabet[*index]).collect();
        self.increment();
        characters
    }

    /// Increment the character sequence.
    fn increment(&mut self) {
        // Increment the last character; if it's not at the split point we're done.
        let tail = &mut self.indices[0];
        if *tail < self.split_point {
            *tail += 1;
            return;
        }
        *tail = 0;

        // Increment all other characters in reverse order.
        let alphabet_len = self.alphabet.len();
        for index in self.indices.iter_mut().skip(1) {
            if *index + 1 == alphabet_len {
                // Reset character and move to the next if it's already at the limit.
                *index = self.split_point + 1;
            } else {
                // If the character can be incremented, we're done.
                *index += 1;
                return;
            }
        }

        // Extend the sequence with another character when nothing could be incremented.
        self.indices.push(self.split_point + 1);
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn hint_label_generation() {
        let mut generator = HintLabels::new("0123", 0.5);

        assert_eq!(generator.next(), vec!['0']);
        assert_eq!(generator.next(), vec!['1']);

        assert_eq!(generator.next(), vec!['2', '0']);
        assert_eq!(generator.next(), vec!['2', '1']);
        assert_eq!(generator.next(), vec!['3', '0']);
        assert_eq!(generator.next(), vec!['3', '1']);

        assert_eq!(generator.next(), vec!['2', '2', '0']);
        assert_eq!(generator.next(), vec!['2', '2', '1']);
        assert_eq!(generator.next(), vec!['2', '3', '0']);
        assert_eq!(generator.next(), vec!['2', '3', '1']);
        assert_eq!(generator.next(), vec!['3', '2', '0']);
        assert_eq!(generator.next(), vec!['3', '2', '1']);
        assert_eq!(generator.next(), vec!['3', '3', '0']);
        assert_eq!(generator.next(), vec!['3', '3', '1']);

        assert_eq!(generator.next(), vec!['2', '2', '2', '0']);
        assert_eq!(generator.next(), vec!['2', '2', '2', '1']);
        assert_eq!(generator.next(), vec!['2', '2', '3', '0']);
        assert_eq!(generator.next(), vec!['2', '2', '3', '1']);
        assert_eq!(generator.next(), vec!['2', '3', '2', '0']);
        assert_eq!(generator.next(), vec!['2', '3', '2', '1']);
        assert_eq!(generator.next(), vec!['2', '3', '3', '0']);
        assert_eq!(generator.next(), vec!['2', '3', '3', '1']);
        assert_eq!(generator.next(), vec!['3', '2', '2', '0']);
        assert_eq!(generator.next(), vec!['3', '2', '2', '1']);
        assert_eq!(generator.next(), vec!['3', '2', '3', '0']);
        assert_eq!(generator.next(), vec!['3', '2', '3', '1']);
        assert_eq!(generator.next(), vec!['3', '3', '2', '0']);
        assert_eq!(generator.next(), vec!['3', '3', '2', '1']);
        assert_eq!(generator.next(), vec!['3', '3', '3', '0']);
        assert_eq!(generator.next(), vec!['3', '3', '3', '1']);
    }
}