rsaeb 0.10.1

use super::once::{MatchedRuleCommit, OnceRuleReadiness, OnceStateSet, RuntimeRule};
use super::state::{State, StateMatch};
use crate::error::RuleRuntimeStateError;
use crate::program::{RuleScan, RuleTarget};
use crate::rule::{Rule, RuleAnchorSyntax};

/// Outcome of scanning the rule table for the next applicable rule.
#[derive(Debug)]
pub(crate) enum RuleSearch<'program, 'state, 'once> {
    /// A rule matched and carries the commit permit needed after success.
    Matched(MatchedRuleApplication<'program, 'state, 'once>),
    /// No currently available rule matched the runtime state.
    Stable,
}

/// Outcome of evaluating one executable rule line against the current state.
#[derive(Debug)]
pub(crate) enum RuleAttempt<'program, 'state, 'once> {
    /// The rule matched and carries the commit permit needed after success.
    Matched(MatchedRuleApplication<'program, 'state, 'once>),
    /// The rule was consumed by the attempt but did not apply.
    Missed(RuleAttemptMiss<'program>),
}

/// Reason a consumed executable rule line did not apply.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum RuleMissReason {
    /// The rule is available, but its left side does not match the current state.
    StateMismatch,
    /// The rule is a `(once)` rule that has already committed in this run.
    OnceConsumed,
}

/// Matched rule plus the state range and commit action needed to apply it.
#[derive(Debug)]
pub(crate) struct MatchedRuleApplication<'program, 'state, 'once> {
    /// Parsed rule selected by the matcher.
    rule: &'program Rule,
    /// Once-state side effect to apply only after successful rewrite.
    commit: MatchedRuleCommit<'once>,
    /// Runtime-state range matched by the rule left side.
    state_match: StateMatch<'state>,
}

/// Matched rule after runtime-state match data has been consumed for preparation.
#[derive(Debug)]
pub(crate) struct PreparedMatchedRule<'program, 'once> {
    /// Parsed rule selected by the matcher.
    rule: &'program Rule,
    /// Once-state side effect to apply only after successful rewrite.
    commit: MatchedRuleCommit<'once>,
}

/// Non-applying rule consumed by a rule-attempt step.
#[derive(Debug, Clone, Copy)]
pub(crate) struct RuleAttemptMiss<'program> {
    /// Parsed rule selected as the attempted rule line.
    rule: &'program Rule,
    /// Reason the attempted rule did not apply.
    reason: RuleMissReason,
}

/// Rule candidate before a linear commit permit has been reserved.
struct MatchedRuleCandidate<'program, 'state> {
    /// Parsed rule selected as a candidate.
    rule: &'program Rule,
    /// Runtime-state range matched by the rule left side.
    state_match: StateMatch<'state>,
}

/// Rule view after all runtime side effects have committed.
#[derive(Debug, Clone, Copy)]
pub(crate) struct CommittedRule<'program> {
    /// Parsed rule whose runtime side effects committed.
    rule: &'program Rule,
}

impl<'program> RuleAttemptMiss<'program> {
    /// Captures a consumed non-applying rule line.
    const fn new(rule: &'program Rule, reason: RuleMissReason) -> Self {
        Self { rule, reason }
    }

    /// Parsed rule selected as the attempted rule line.
    pub(crate) const fn rule(self) -> &'program Rule {
        self.rule
    }

    /// Reason the attempted rule did not apply.
    pub(crate) const fn reason(self) -> RuleMissReason {
        self.reason
    }
}

impl<'program, 'state> MatchedRuleCandidate<'program, 'state> {
    /// Captures a rule match before once-state commit is permitted.
    const fn new(rule: &'program Rule, state_match: StateMatch<'state>) -> Self {
        Self { rule, state_match }
    }

    /// Attaches the linear commit action to the matched candidate.
    const fn into_application<'once>(
        self,
        commit: MatchedRuleCommit<'once>,
    ) -> MatchedRuleApplication<'program, 'state, 'once> {
        MatchedRuleApplication::new(self.rule, self.state_match, commit)
    }
}

impl<'program, 'state, 'once> MatchedRuleApplication<'program, 'state, 'once> {
    /// Captures the complete data needed to apply a matched rule.
    const fn new(
        rule: &'program Rule,
        state_match: StateMatch<'state>,
        commit: MatchedRuleCommit<'once>,
    ) -> Self {
        Self {
            rule,
            commit,
            state_match,
        }
    }

    /// Splits the state-match witness from the rule commit witness.
    pub(crate) fn into_prepare_parts(
        self,
    ) -> (StateMatch<'state>, PreparedMatchedRule<'program, 'once>) {
        (
            self.state_match,
            PreparedMatchedRule {
                rule: self.rule,
                commit: self.commit,
            },
        )
    }
}

impl<'program> PreparedMatchedRule<'program, '_> {
    /// Parsed rule selected by the matcher.
    pub(crate) const fn rule(&self) -> &'program Rule {
        self.rule
    }

    /// Commits the matched rule's deferred side effects.
    pub(crate) fn commit(self) -> CommittedRule<'program> {
        self.commit.commit();
        CommittedRule { rule: self.rule }
    }
}

impl<'program> CommittedRule<'program> {
    /// Parsed rule whose runtime side effects committed.
    pub(crate) const fn rule(self) -> &'program Rule {
        self.rule
    }
}

/// Finds the first currently available rule that matches `state`.
///
/// # Errors
///
/// Returns `RuleRuntimeStateError` if parsed rule metadata and per-run
/// once-state slots no longer align.
pub(crate) fn find_next_match<'program, 'state, 'once>(
    rules: RuleScan<'program>,
    once_states: &'once mut OnceStateSet,
    state: &'state State,
) -> Result<RuleSearch<'program, 'state, 'once>, RuleRuntimeStateError> {
    for runtime_rule in once_states.runtime_rules_mut(rules) {
        let runtime_rule = runtime_rule?;
        let rule = runtime_rule.rule();
        let Some(candidate) = matched_candidate_for_rule(rule, state) else {
            continue;
        };

        match runtime_rule.readiness() {
            OnceRuleReadiness::Available(commit) => {
                return Ok(RuleSearch::Matched(candidate.into_application(commit)));
            }
            OnceRuleReadiness::Consumed => {}
        }
    }

    Ok(RuleSearch::Stable)
}

/// Evaluates exactly one parsed rule line against the current runtime state.
pub(crate) fn attempt_rule<'program, 'state, 'once>(
    runtime_rule: RuntimeRule<'program, 'once>,
    state: &'state State,
) -> RuleAttempt<'program, 'state, 'once> {
    let rule = runtime_rule.rule();
    let commit = match runtime_rule.readiness() {
        OnceRuleReadiness::Available(commit) => commit,
        OnceRuleReadiness::Consumed => {
            return RuleAttempt::Missed(RuleAttemptMiss::new(rule, RuleMissReason::OnceConsumed));
        }
    };

    let Some(candidate) = matched_candidate_for_rule(rule, state) else {
        return RuleAttempt::Missed(RuleAttemptMiss::new(rule, RuleMissReason::StateMismatch));
    };

    RuleAttempt::Matched(candidate.into_application(commit))
}

/// Pairs a rule-attempt target with aligned runtime state.
///
/// # Errors
///
/// Returns `RuleRuntimeStateError` if the targeted parsed rule refers to a
/// missing per-run once-state slot.
pub(crate) fn runtime_rule_for_target<'program, 'once>(
    once_states: &'once mut OnceStateSet,
    target: RuleTarget<'program>,
) -> Result<RuntimeRule<'program, 'once>, RuleRuntimeStateError> {
    once_states.runtime_rule_mut(target.rule())
}

/// Builds a committed-rule candidate for a single parsed rule.
fn matched_candidate_for_rule<'program, 'state>(
    rule: &'program Rule,
    state: &'state State,
) -> Option<MatchedRuleCandidate<'program, 'state>> {
    let state_match = find_match(state, rule)?;
    Some(MatchedRuleCandidate::new(rule, state_match))
}

/// Finds this rule's match span in the current state.
fn find_match<'state>(state: &'state State, rule: &Rule) -> Option<StateMatch<'state>> {
    match rule.anchor() {
        RuleAnchorSyntax::Anywhere => state.find_payload(rule.lhs()),
        RuleAnchorSyntax::Start => state.starts_with_payload(rule.lhs()),
        RuleAnchorSyntax::End => state.ends_with_payload(rule.lhs()),
    }
}