lineprior 0.1.0

use serde::{Deserialize, Serialize};
use std::cmp::Ordering;
use std::collections::HashMap;

/// One recorded step: from `state`, `action` was taken, with `outcome`.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct Observation {
    pub sequence_id: String,
    pub step: u32,
    pub state: String,
    pub action: String,
    pub outcome: Outcome,
    pub score: Option<f64>,
    pub weight: f64,
    pub tags: Vec<String>,
}

/// Result of taking `action` from `state`.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default, Serialize, Deserialize)]
#[serde(rename_all = "lowercase")]
pub enum Outcome {
    Success,
    Failure,
    Draw,
    #[default]
    Unknown,
}

impl Outcome {
    pub fn parse(s: &str) -> Option<Self> {
        match s {
            "success" => Some(Outcome::Success),
            "failure" => Some(Outcome::Failure),
            "draw" => Some(Outcome::Draw),
            "unknown" => Some(Outcome::Unknown),
            _ => None,
        }
    }
}

/// We use k=20 so confidence grows slowly for low-sample actions.
/// This prevents one-off successes from dominating the prior.
pub const DEFAULT_CONFIDENCE_K: f64 = 20.0;

/// A draw is a genuine partial outcome in adversarial games (chess, shogi),
/// not a loss -- we default to crediting it as half a win rather than
/// scoring it identically to a failure.
pub const DEFAULT_DRAW_VALUE: f64 = 0.5;

/// Tuning knobs for [`crate::build::build_prior_book`].
#[derive(Debug, Clone)]
pub struct BuildConfig {
    pub min_count: u64,
    /// Minimum weighted count for an action to appear in the output.
    /// `0.0` means no filtering beyond `min_count`.
    pub min_weighted_count: f64,
    /// Minimum confidence (see [`DEFAULT_CONFIDENCE_K`]) for an action to
    /// appear in the output. `0.0` means no filtering.
    pub min_confidence: f64,
    pub max_step: Option<u32>,
    pub smoothing_alpha: f64,
    pub score_weight: f64,
    pub success_weight: f64,
    pub count_weight: f64,
    pub max_actions_per_state: Option<usize>,
    pub confidence_k: f64,
    /// Success credit given to a `Draw` outcome, between 0.0 (scores like
    /// a failure) and 1.0 (scores like a win).
    pub draw_value: f64,
    /// Keep only observations carrying at least one of these tags.
    /// `None` means no tag filtering.
    pub tag_filter: Option<Vec<String>>,
}

impl Default for BuildConfig {
    fn default() -> Self {
        Self {
            min_count: 1,
            min_weighted_count: 0.0,
            min_confidence: 0.0,
            max_step: None,
            smoothing_alpha: 5.0,
            score_weight: 1.0,
            success_weight: 1.0,
            count_weight: 1.0,
            max_actions_per_state: None,
            confidence_k: DEFAULT_CONFIDENCE_K,
            draw_value: DEFAULT_DRAW_VALUE,
            tag_filter: None,
        }
    }
}

/// One candidate action ranked for a given state.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct PriorAction {
    pub action: String,
    pub count: u64,
    pub weighted_count: f64,
    /// Raw (unsmoothed) rate: successes count as 1.0, draws count as
    /// `BuildConfig::draw_value` (default 0.5), failures as 0.0.
    pub success_rate: Option<f64>,
    pub mean_score: Option<f64>,
    pub prior: f64,
    pub confidence: f64,
}

/// One line of prior-book output: a state and its ranked actions.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct PriorEntry {
    pub state: String,
    pub actions: Vec<PriorAction>,
}

/// In-memory prior book: state -> ranked candidate actions.
#[derive(Debug, Clone, Default)]
pub struct PriorBook {
    pub entries: HashMap<String, Vec<PriorAction>>,
}

/// Deterministic action ordering: descending prior, tie-broken by action
/// string. Shared by build (emit) and query so both agree on ranking.
fn sort_actions(actions: &mut [PriorAction]) {
    actions.sort_by(|a, b| {
        b.prior
            .partial_cmp(&a.prior)
            .unwrap_or(Ordering::Equal)
            .then_with(|| a.action.cmp(&b.action))
    });
}

impl PriorBook {
    /// All entries, states sorted lexicographically and each state's
    /// actions sorted by descending prior. This is the canonical order
    /// used for JSONL output and for query results.
    pub fn entries_sorted(&self) -> Vec<PriorEntry> {
        let mut states: Vec<&String> = self.entries.keys().collect();
        states.sort();
        states
            .into_iter()
            .map(|state| {
                let mut actions = self.entries[state].clone();
                sort_actions(&mut actions);
                PriorEntry {
                    state: state.clone(),
                    actions,
                }
            })
            .collect()
    }

    /// Ranked candidates for `state`. An unseen state yields an empty
    /// vec, never an error and never an invented action.
    pub fn query(&self, state: &str, top_k: Option<usize>) -> Vec<PriorAction> {
        let Some(actions) = self.entries.get(state) else {
            return Vec::new();
        };
        let mut actions = actions.clone();
        sort_actions(&mut actions);
        if let Some(k) = top_k {
            actions.truncate(k);
        }
        actions
    }
}