use std::cmp::Ordering;

use itertools::Itertools;
use serde::{Deserialize, Serialize};

use crate::{criterion::AttributeState, distance_between_two_points};

#[derive(Debug, Clone, PartialEq)]
pub enum ScoreDetails {
    Words(Words),
    Typo(Typo),
    Proximity(Rank),
    Fid(Rank),
    Position(Rank),
    ExactAttribute(ExactAttribute),
    ExactWords(ExactWords),
    Sort(Sort),
    Vector(Vector),
    GeoSort(GeoSort),

    /// Returned when we don't have the time to finish applying all the subsequent ranking-rules
    Skipped,

    /// A document that has been explicitly pinned to a specific position in the results.
    /// Pinned documents are placed at their target position regardless of their ranking score.
    /// This variant acts as a marker: it does not participate in score-based comparisons but
    /// carries the target position so downstream consumers like federated merge can detect and
    /// handle pinned documents appropriately.
    Pin {
        position: u32,
    },
}

#[derive(Clone, Copy)]
pub enum ScoreValue<'a> {
    Score(f64),
    Sort(&'a Sort),
    GeoSort(&'a GeoSort),
}

enum RankOrValue<'a> {
    Rank(Rank),
    Sort(&'a Sort),
    GeoSort(&'a GeoSort),
    Score(f64),
}

#[derive(Clone, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub enum WeightedScoreValue {
    WeightedScore(f64),
    Sort { asc: bool, value: serde_json::Value },
    GeoSort { asc: bool, distance: Option<f64> },
    VectorSort(f64),
}

impl ScoreDetails {
    pub fn local_score(&self) -> Option<f64> {
        self.rank().map(Rank::local_score)
    }

    pub fn rank(&self) -> Option<Rank> {
        match self {
            ScoreDetails::Words(details) => Some(details.rank()),
            ScoreDetails::Typo(details) => Some(details.rank()),
            ScoreDetails::Proximity(details) => Some(*details),
            ScoreDetails::Fid(details) => Some(*details),
            ScoreDetails::Position(details) => Some(*details),
            ScoreDetails::ExactAttribute(details) => Some(details.rank()),
            ScoreDetails::ExactWords(details) => Some(details.rank()),
            ScoreDetails::Sort(_) => None,
            ScoreDetails::GeoSort(_) => None,
            ScoreDetails::Vector(_) => None,
            ScoreDetails::Skipped => Some(Rank { rank: 0, max_rank: 1 }),
            ScoreDetails::Pin { .. } => None,
        }
    }

    /// Calculate the global score of the details.
    ///
    /// It is computed from the ranks of the ranking rules, excluding the sort/geo sort rules.
    /// If the details contain a semantic score (ScoreDetails::Vector), it is used instead of the ranking score.
    ///
    /// note: this function expects a maximum of one semantic score, otherwise only the last one will be used.
    pub fn global_score<'a>(details: impl Iterator<Item = &'a Self> + 'a) -> f64 {
        // Filter out only the ranking scores (Rank values) and exclude sort/geo sort.
        // Pin is a placement directive, not a score — it is filtered out upfront.
        let mut semantic_score = None;
        let ranking_ranks =
            details.filter_map(ScoreDetails::rank_or_value).filter_map(|rank_or_value| {
                match rank_or_value {
                    RankOrValue::Rank(rank) => Some(rank),
                    RankOrValue::Score(score) => {
                        semantic_score = Some(score);
                        None
                    }
                    RankOrValue::Sort(_) => None,
                    RankOrValue::GeoSort(_) => None,
                }
            });

        let ranking_score = Rank::global_score(ranking_ranks);

        // If we have semantic score, use it, otherwise use ranking score
        semantic_score.unwrap_or(ranking_score)
    }

    pub fn score_values<'a>(
        details: impl Iterator<Item = &'a Self> + 'a,
    ) -> impl Iterator<Item = ScoreValue<'a>> + 'a {
        // Pin is a placement directive, not a score — filter it out before entering
        // the rank_or_value pipeline.
        details
            .filter_map(ScoreDetails::rank_or_value)
            .coalesce(|left, right| match (left, right) {
                (RankOrValue::Rank(left), RankOrValue::Rank(right)) => {
                    Ok(RankOrValue::Rank(Rank::merge(left, right)))
                }
                (left, right) => Err((left, right)),
            })
            .map(|rank_or_value| match rank_or_value {
                RankOrValue::Rank(r) => ScoreValue::Score(r.local_score()),
                RankOrValue::Sort(s) => ScoreValue::Sort(s),
                RankOrValue::GeoSort(g) => ScoreValue::GeoSort(g),
                RankOrValue::Score(s) => ScoreValue::Score(s),
            })
    }

    pub fn weighted_score_values<'a>(
        details: impl Iterator<Item = &'a Self> + 'a,
        weight: f64,
    ) -> impl Iterator<Item = WeightedScoreValue> + 'a {
        details
            .filter_map(ScoreDetails::rank_or_value)
            .coalesce(|left, right| match (left, right) {
                (RankOrValue::Rank(left), RankOrValue::Rank(right)) => {
                    Ok(RankOrValue::Rank(Rank::merge(left, right)))
                }
                (left, right) => Err((left, right)),
            })
            .map(move |rank_or_value| match rank_or_value {
                RankOrValue::Rank(r) => WeightedScoreValue::WeightedScore(r.local_score() * weight),
                RankOrValue::Sort(s) => {
                    WeightedScoreValue::Sort { asc: s.ascending, value: s.value.clone() }
                }
                RankOrValue::GeoSort(g) => {
                    WeightedScoreValue::GeoSort { asc: g.ascending, distance: g.distance() }
                }
                RankOrValue::Score(s) => WeightedScoreValue::VectorSort(s * weight),
            })
    }

    fn rank_or_value(&self) -> Option<RankOrValue<'_>> {
        match self {
            ScoreDetails::Words(w) => Some(RankOrValue::Rank(w.rank())),
            ScoreDetails::Typo(t) => Some(RankOrValue::Rank(t.rank())),
            ScoreDetails::Proximity(p) => Some(RankOrValue::Rank(*p)),
            ScoreDetails::Fid(f) => Some(RankOrValue::Rank(*f)),
            ScoreDetails::Position(p) => Some(RankOrValue::Rank(*p)),
            ScoreDetails::ExactAttribute(e) => Some(RankOrValue::Rank(e.rank())),
            ScoreDetails::ExactWords(e) => Some(RankOrValue::Rank(e.rank())),
            ScoreDetails::Sort(sort) => Some(RankOrValue::Sort(sort)),
            ScoreDetails::GeoSort(geosort) => Some(RankOrValue::GeoSort(geosort)),
            ScoreDetails::Vector(vector) => Some(RankOrValue::Score(
                vector.similarity.as_ref().map(|s| *s as f64).unwrap_or(0.0f64),
            )),
            ScoreDetails::Skipped => Some(RankOrValue::Rank(Rank { rank: 0, max_rank: 1 })),
            // Pin is filtered out before reaching rank_or_value() — see global_score(),
            // score_values(), and weighted_score_values().
            ScoreDetails::Pin { .. } => None,
        }
    }

    /// Panics
    ///
    /// - If Position is not preceded by Fid
    /// - If Exactness is not preceded by ExactAttribute
    pub fn to_json_map<'a>(
        attribute_state: AttributeState,
        details: impl Iterator<Item = &'a Self>,
    ) -> serde_json::Map<String, serde_json::Value> {
        let mut order = 0;
        let mut fid_details = None;
        let mut details_map = serde_json::Map::default();
        for details in details {
            match details {
                ScoreDetails::Words(words) => {
                    let words_details = serde_json::json!({
                            "order": order,
                            "matchingWords": words.matching_words,
                            "maxMatchingWords": words.max_matching_words,
                            "score": words.rank().local_score(),
                    });
                    details_map.insert("words".into(), words_details);
                    order += 1;
                }
                ScoreDetails::Typo(typo) => {
                    let typo_details = serde_json::json!({
                        "order": order,
                        "typoCount": typo.typo_count,
                        "maxTypoCount": typo.max_typo_count,
                        "score": typo.rank().local_score(),
                    });
                    details_map.insert("typo".into(), typo_details);
                    order += 1;
                }
                ScoreDetails::Proximity(proximity) => {
                    let proximity_details = serde_json::json!({
                        "order": order,
                        "score": proximity.local_score(),
                    });
                    details_map.insert("proximity".into(), proximity_details);
                    order += 1;
                }
                ScoreDetails::Fid(fid) => {
                    match attribute_state {
                        AttributeState::Unified => {
                            // copy the rank for future use in Position.
                            fid_details = Some(*fid);
                            // In this case, fid is a virtual rule always followed by the "position" rule
                            let fid_details = serde_json::json!({
                                "order": order,
                                "attributeRankingOrderScore": fid.local_score(),
                            });
                            details_map.insert("attribute".into(), fid_details);
                        }
                        AttributeState::Separated => {
                            let fid_details = serde_json::json!({
                                "order": order,
                                "score": fid.local_score(),
                            });
                            details_map.insert("attributeRank".into(), fid_details);
                        }
                    }

                    order += 1;
                }
                ScoreDetails::Position(position) => {
                    match attribute_state {
                        AttributeState::Unified => {
                            // In this case, position is a virtual rule always preceded by the "fid" rule
                            let attribute_details = details_map
                                .get_mut("attribute")
                                .expect("position not preceded by attribute");
                            let attribute_details = attribute_details
                                .as_object_mut()
                                .expect("attribute details was not an object");
                            let Some(fid_details) = fid_details else {
                                unimplemented!("position not preceded by attribute");
                            };

                            attribute_details.insert(
                                "queryWordDistanceScore".into(),
                                position.local_score().into(),
                            );
                            let score =
                                Rank::global_score([fid_details, *position].iter().copied());
                            attribute_details.insert("score".into(), score.into());

                            // do not update the order since this was already done by fid
                        }
                        AttributeState::Separated => {
                            let word_position_details = serde_json::json!({
                                "order": order,
                                "score": position.local_score(),
                            });
                            details_map.insert("wordPosition".into(), word_position_details);
                            order += 1;
                        }
                    }
                }
                ScoreDetails::ExactAttribute(exact_attribute) => {
                    let exactness_details = serde_json::json!({
                        "order": order,
                        "matchType": exact_attribute,
                        "score": exact_attribute.rank().local_score(),
                    });
                    details_map.insert("exactness".into(), exactness_details);
                    order += 1;
                }
                ScoreDetails::ExactWords(details) => {
                    // For now, exactness is a virtual rule always preceded by the "ExactAttribute" rule
                    let exactness_details = details_map
                        .get_mut("exactness")
                        .expect("Exactness not preceded by exactAttribute");
                    let exactness_details = exactness_details
                        .as_object_mut()
                        .expect("exactness details was not an object");
                    if exactness_details.get("matchType").expect("missing 'matchType'")
                        == &serde_json::json!(ExactAttribute::NoExactMatch)
                    {
                        let score = Rank::global_score(
                            [ExactAttribute::NoExactMatch.rank(), details.rank()].iter().copied(),
                        );
                        // tiny detail, but we want the score to be the last displayed field,
                        // so we're removing it here, adding the other fields, then adding the new score
                        exactness_details.remove("score");
                        exactness_details
                            .insert("matchingWords".into(), details.matching_words.into());
                        exactness_details
                            .insert("maxMatchingWords".into(), details.max_matching_words.into());
                        exactness_details.insert("score".into(), score.into());
                    }
                    // do not update the order since this was already done by exactAttribute
                }
                ScoreDetails::Sort(details) => {
                    let sort = if details.redacted {
                        format!("<hidden-rule-{order}>")
                    } else {
                        format!(
                            "{}:{}",
                            details.field_name,
                            if details.ascending { "asc" } else { "desc" }
                        )
                    };
                    let value =
                        if details.redacted { "<hidden>".into() } else { details.value.clone() };
                    let sort_details = serde_json::json!({
                        "order": order,
                        "value": value,
                    });
                    details_map.insert(sort, sort_details);
                    order += 1;
                }
                ScoreDetails::GeoSort(details) => {
                    let sort = format!(
                        "_geoPoint({}, {}):{}",
                        details.target_point[0],
                        details.target_point[1],
                        if details.ascending { "asc" } else { "desc" }
                    );
                    let point = if let Some(value) = details.value {
                        serde_json::json!({ "lat": value[0], "lng": value[1]})
                    } else {
                        serde_json::Value::Null
                    };
                    let sort_details = serde_json::json!({
                        "order": order,
                        "value": point,
                        "distance": details.distance(),
                    });
                    details_map.insert(sort, sort_details);
                    order += 1;
                }
                ScoreDetails::Vector(s) => {
                    let similarity = s.similarity.as_ref();

                    let details = serde_json::json!({
                        "order": order,
                        "similarity": similarity,
                    });
                    details_map.insert("vectorSort".into(), details);
                    order += 1;
                }
                ScoreDetails::Skipped => {
                    details_map
                        .insert("skipped".to_string(), serde_json::json!({ "order": order }));
                    order += 1;
                }
                ScoreDetails::Pin { position } => {
                    let pin_details = serde_json::json!({
                        "order": order,
                        "position": position,
                    });
                    details_map.insert("pin".into(), pin_details);
                    order += 1;
                }
            }
        }
        details_map
    }
}

/// The strategy to compute scores.
///
/// It makes sense to pass down this strategy to the internals of the search, because
/// some optimizations (today, mainly skipping ranking rules for universes of a single document)
/// are not correct to do when computing the scores.
///
/// This strategy could feasibly be extended to differentiate between the normalized score and the
/// detailed scores, but it is not useful today as the normalized score is *derived from* the
/// detailed scores.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
pub enum ScoringStrategy {
    /// Don't compute scores
    #[default]
    Skip,
    /// Compute detailed scores
    Detailed,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct Words {
    pub matching_words: u32,
    pub max_matching_words: u32,
}

impl Words {
    pub fn rank(&self) -> Rank {
        Rank { rank: self.matching_words, max_rank: self.max_matching_words }
    }

    pub(crate) fn from_rank(rank: Rank) -> Self {
        Self { matching_words: rank.rank, max_matching_words: rank.max_rank }
    }
}

/// Structure that is super similar to [`Words`], but whose semantics is a bit distinct.
///
/// In exactness, the number of matching words can actually be 0 with a non-zero score,
/// if no words from the query appear exactly in the document.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct ExactWords {
    pub matching_words: u32,
    pub max_matching_words: u32,
}

impl ExactWords {
    pub fn rank(&self) -> Rank {
        // 0 matching words means last rank (1)
        Rank { rank: self.matching_words + 1, max_rank: self.max_matching_words + 1 }
    }

    pub(crate) fn from_rank(rank: Rank) -> Self {
        // last rank (1) means that 0 words from the query appear exactly in the document.
        // first rank (max_rank) means that (max_rank - 1) words from the query appear exactly in the document.
        Self {
            matching_words: rank.rank.saturating_sub(1),
            max_matching_words: rank.max_rank.saturating_sub(1),
        }
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct Typo {
    pub typo_count: u32,
    pub max_typo_count: u32,
}

impl Typo {
    pub fn rank(&self) -> Rank {
        Rank {
            rank: (self.max_typo_count + 1).saturating_sub(self.typo_count),
            max_rank: (self.max_typo_count + 1),
        }
    }

    // max_rank = max_typo + 1
    // max_typo = max_rank - 1
    //
    // rank = max_typo - typo + 1
    // rank = max_rank - 1 - typo + 1
    // rank + typo = max_rank
    // typo = max_rank - rank
    pub fn from_rank(rank: Rank) -> Typo {
        Typo {
            typo_count: rank.max_rank.saturating_sub(rank.rank),
            max_typo_count: rank.max_rank.saturating_sub(1),
        }
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct Rank {
    /// The ordinal rank, such that `max_rank` is the first rank, and 0 is the last rank.
    ///
    /// The higher the better. Documents with a rank of 0 have a score of 0 and are typically never returned
    /// (they don't match the query).
    pub rank: u32,
    /// The maximum possible rank. Documents with this rank have a score of 1.
    ///
    /// The max rank should not be 0.
    pub max_rank: u32,
}

impl Rank {
    pub fn local_score(self) -> f64 {
        self.rank as f64 / self.max_rank as f64
    }

    pub fn global_score(details: impl Iterator<Item = Self>) -> f64 {
        let mut rank = Rank { rank: 1, max_rank: 1 };
        for inner_rank in details {
            rank = Rank::merge(rank, inner_rank);
        }
        rank.local_score()
    }

    pub fn merge(mut outer: Rank, inner: Rank) -> Rank {
        outer.rank = outer.rank.saturating_sub(1);

        outer.rank *= inner.max_rank;
        outer.max_rank *= inner.max_rank;

        outer.rank += inner.rank;

        outer
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Serialize)]
#[serde(rename_all = "camelCase")]
pub enum ExactAttribute {
    ExactMatch,
    MatchesStart,
    NoExactMatch,
}

impl ExactAttribute {
    pub fn rank(&self) -> Rank {
        let rank = match self {
            ExactAttribute::ExactMatch => 3,
            ExactAttribute::MatchesStart => 2,
            ExactAttribute::NoExactMatch => 1,
        };
        Rank { rank, max_rank: 3 }
    }
}

#[derive(Debug, Clone, PartialEq)]
pub struct Sort {
    pub field_name: String,
    pub ascending: bool,
    pub redacted: bool,
    pub value: serde_json::Value,
}

pub fn compare_sort_values(
    ascending: bool,
    left: &serde_json::Value,
    right: &serde_json::Value,
) -> Ordering {
    use serde_json::Value::*;
    match (left, right) {
        (Null, Null) => Ordering::Equal,
        (Null, _) => Ordering::Less,
        (_, Null) => Ordering::Greater,
        // numbers are always before strings
        (Number(_), String(_)) => Ordering::Greater,
        (String(_), Number(_)) => Ordering::Less,
        (Number(left), Number(right)) => {
            // FIXME: unwrap permitted here?
            let order = left
                .as_f64()
                .unwrap()
                .partial_cmp(&right.as_f64().unwrap())
                .unwrap_or(Ordering::Equal);
            // 12 < 42, and when ascending, we want to see 12 first, so the smallest.
            // Hence, when ascending, smaller is better
            if ascending {
                order.reverse()
            } else {
                order
            }
        }
        (String(left), String(right)) => {
            let order = left.cmp(right);
            // Taking e.g. "a" and "z"
            // "a" < "z", and when ascending, we want to see "a" first, so the smallest.
            // Hence, when ascending, smaller is better
            if ascending {
                order.reverse()
            } else {
                order
            }
        }
        (left, right) => {
            tracing::warn!(%left, %right, "sort values that are neither numbers, strings or null, handling as equal");
            Ordering::Equal
        }
    }
}

impl PartialOrd for Sort {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        if self.ascending != other.ascending {
            return None;
        }
        Some(compare_sort_values(self.ascending, &self.value, &other.value))
    }
}

#[derive(Debug, Clone, Copy, PartialEq)]
pub struct GeoSort {
    pub target_point: [f64; 2],
    pub ascending: bool,
    pub value: Option<[f64; 2]>,
}

impl PartialOrd for GeoSort {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        if self.ascending != other.ascending {
            return None;
        }
        Some(match (self.distance(), other.distance()) {
            (None, None) => Ordering::Equal,
            (None, Some(_)) => Ordering::Less,
            (Some(_), None) => Ordering::Greater,
            (Some(left), Some(right)) => {
                let order = left.partial_cmp(&right)?;
                if self.ascending {
                    // when ascending, the one with the smallest distance has the best score
                    order.reverse()
                } else {
                    order
                }
            }
        })
    }
}

#[derive(Debug, Clone, PartialEq, PartialOrd)]
pub struct Vector {
    pub similarity: Option<f32>,
}

impl GeoSort {
    pub fn distance(&self) -> Option<f64> {
        self.value.map(|value| distance_between_two_points(&self.target_point, &value))
    }
}
