use std::cmp::max;

use crate::chars::{Char, CharClass};
use crate::{Config, Matcher};

pub(crate) const SCORE_MATCH: u16 = 16;
pub(crate) const PENALTY_GAP_START: u16 = 3;
pub(crate) const PENALTY_GAP_EXTENSION: u16 = 1;
/// If the prefer_prefix option is enabled we want to penalize
/// the initial gap. The prefix should not be too much  
pub(crate) const PREFIX_BONUS_SCALE: u16 = 2;
pub(crate) const MAX_PREFIX_BONUS: u16 = BONUS_BOUNDARY;

// We prefer matches at the beginning of a word, but the bonus should not be
// too great to prevent the longer acronym matches from always winning over
// shorter fuzzy matches. The bonus point here was specifically chosen that
// the bonus is cancelled when the gap between the acronyms grows over
// 8 characters, which is approximately the average length of the words found
// in web2 dictionary and my file system.
pub(crate) const BONUS_BOUNDARY: u16 = SCORE_MATCH / 2;

// Edge-triggered bonus for matches in camelCase words.
// Their value should be BONUS_BOUNDARY - PENALTY_GAP_EXTENSION = 7.
// However, this priporitzes camel case over non-camel case.
// In fzf/skim this is not a problem since they score off the max
// consecutive bonus. However, we don't do that (because its incorrect)
// so to avoids prioritizing camel we use a lower bonus. I think that's fine
// usually camel case is wekaer boundary than actual wourd boundaries anyway
// This also has the nice sideeffect of perfectly balancing out
// camel case, snake case and the consecutive version of the word
pub(crate) const BONUS_CAMEL123: u16 = BONUS_BOUNDARY - PENALTY_GAP_START;

/// Although bonus point for non-word characters is non-contextual, we need it
/// for computing bonus points for consecutive chunks starting with a non-word
/// character.
pub(crate) const BONUS_NON_WORD: u16 = BONUS_BOUNDARY;

// Minimum bonus point given to characters in consecutive chunks.
// Note that bonus points for consecutive matches shouldn't have needed if we
// used fixed match score as in the original algorithm.
pub(crate) const BONUS_CONSECUTIVE: u16 = PENALTY_GAP_START + PENALTY_GAP_EXTENSION;

// The first character in the typed pattern usually has more significance
// than the rest so it's important that it appears at special positions where
// bonus points are given, e.g. "to-go" vs. "ongoing" on "og" or on "ogo".
// The amount of the extra bonus should be limited so that the gap penalty is
// still respected.
pub(crate) const BONUS_FIRST_CHAR_MULTIPLIER: u16 = 2;

impl Config {
    #[inline]
    pub(crate) fn bonus_for(&self, prev_class: CharClass, class: CharClass) -> u16 {
        if class > CharClass::Delimiter {
            // transition from non word to word
            match prev_class {
                CharClass::Whitespace => return self.bonus_boundary_white,
                CharClass::Delimiter => return self.bonus_boundary_delimiter,
                CharClass::NonWord => return BONUS_BOUNDARY,
                _ => (),
            }
        }
        if prev_class == CharClass::Lower && class == CharClass::Upper
            || prev_class != CharClass::Number && class == CharClass::Number
        {
            // camelCase letter123
            BONUS_CAMEL123
        } else if class == CharClass::Whitespace {
            self.bonus_boundary_white
        } else if class == CharClass::NonWord {
            BONUS_NON_WORD
        } else {
            0
        }
    }
}
impl Matcher {
    #[inline(always)]
    pub(crate) fn bonus_for(&self, prev_class: CharClass, class: CharClass) -> u16 {
        self.config.bonus_for(prev_class, class)
    }

    pub(crate) fn calculate_score<const INDICES: bool, H: Char + PartialEq<N>, N: Char>(
        &mut self,
        haystack: &[H],
        needle: &[N],
        start: usize,
        end: usize,
        indices: &mut Vec<u32>,
    ) -> u16 {
        if INDICES {
            indices.reserve(needle.len());
        }

        let mut prev_class = start
            .checked_sub(1)
            .map(|i| haystack[i].char_class(&self.config))
            .unwrap_or(self.config.initial_char_class);
        let mut needle_iter = needle.iter();
        let mut needle_char = *needle_iter.next().unwrap();

        let mut in_gap = false;
        let mut consecutive = 1;

        // unrolled the first iteration to make applying the first char multiplier less awkward
        if INDICES {
            indices.push(start as u32)
        }
        let class = haystack[start].char_class(&self.config);
        let mut first_bonus = self.bonus_for(prev_class, class);
        let mut score = SCORE_MATCH + first_bonus * BONUS_FIRST_CHAR_MULTIPLIER;
        prev_class = class;
        needle_char = *needle_iter.next().unwrap_or(&needle_char);

        for (i, c) in haystack[start + 1..end].iter().enumerate() {
            let (c, class) = c.char_class_and_normalize(&self.config);
            if c == needle_char {
                if INDICES {
                    indices.push(i as u32 + start as u32 + 1)
                }
                let mut bonus = self.bonus_for(prev_class, class);
                if consecutive != 0 {
                    if bonus >= BONUS_BOUNDARY && bonus > first_bonus {
                        first_bonus = bonus
                    }
                    bonus = max(max(bonus, first_bonus), BONUS_CONSECUTIVE);
                } else {
                    first_bonus = bonus;
                }
                score += SCORE_MATCH + bonus;
                in_gap = false;
                consecutive += 1;
                if let Some(&next) = needle_iter.next() {
                    needle_char = next;
                }
            } else {
                let penalty = if in_gap {
                    PENALTY_GAP_EXTENSION
                } else {
                    PENALTY_GAP_START
                };
                score = score.saturating_sub(penalty);
                in_gap = true;
                consecutive = 0;
            }
            prev_class = class;
        }
        if self.config.prefer_prefix {
            if start != 0 {
                let penalty = PENALTY_GAP_START
                    + PENALTY_GAP_START * (start - 1).min(u16::MAX as usize) as u16;
                score += MAX_PREFIX_BONUS.saturating_sub(penalty / PREFIX_BONUS_SCALE);
            } else {
                score += MAX_PREFIX_BONUS;
            }
        }
        score
    }
}
