crtx-retrieval 0.1.1

//! Deterministic contradiction-resolution scaffold for retrieval.
//!
//! This module is intentionally read-only. Store and context-pack wiring can
//! adapt durable memory rows into these inputs later.

use std::collections::HashSet;

use cortex_core::{
    compose_policy_outcomes, CoreError, CoreResult, PolicyContribution, PolicyDecision,
    PolicyOutcome,
};

/// High-level result of attempting to resolve a conflict set.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ResolutionState {
    /// A single candidate is safe to consume as the resolved memory.
    Resolved,
    /// Multiple hypotheses must be surfaced because no safe winner exists.
    MultiHypothesis,
    /// Proof, claim-slot, or precedence evidence is insufficient.
    Unknown,
}

/// Coarse authority level supplied by the caller.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
pub enum AuthorityLevel {
    /// Low authority — observed or unverified.
    Low,
    /// Medium authority — partially verified.
    Medium,
    /// High authority — fully verified or operator-grade.
    High,
}

/// Authority proof closure hint for a candidate memory.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum ProofClosureHint {
    /// All proof axes required by the caller passed.
    FullChainVerified,
    /// At least one proof axis is intentionally unavailable or development-grade.
    Partial,
    /// Proof state has not been established.
    Unknown,
    /// A proof axis failed with a named edge.
    Broken {
        /// Name of the proof axis that failed.
        edge: String,
    },
}

impl ProofClosureHint {
    fn is_full_chain_verified(&self) -> bool {
        matches!(self, Self::FullChainVerified)
    }
}

/// Authority and proof hints attached to a memory candidate.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct AuthorityProofHint {
    /// Caller-provided authority level.
    pub authority: AuthorityLevel,
    /// Caller-provided proof closure result.
    pub proof: ProofClosureHint,
}

impl AuthorityProofHint {
    /// Returns true when a candidate has high authority and full proof closure.
    #[must_use]
    pub fn is_high_authority_verified(&self) -> bool {
        self.authority == AuthorityLevel::High && self.proof.is_full_chain_verified()
    }
}

/// Memory-shaped input for a caller-supplied contradiction set.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct ConflictingMemoryInput {
    /// Durable memory identifier.
    pub memory_id: String,
    /// Stable belief-slot key when known.
    pub claim_key: Option<String>,
    /// Memory claim text.
    pub claim: String,
    /// Authority and proof hints for this memory.
    pub authority: AuthorityProofHint,
    /// Memory IDs this input is known to conflict with.
    pub conflicts_with: Vec<String>,
}

impl ConflictingMemoryInput {
    /// Creates a memory input with no explicit `conflicts_with` edges.
    #[must_use]
    pub fn new(
        memory_id: impl Into<String>,
        claim_key: Option<impl Into<String>>,
        claim: impl Into<String>,
        authority: AuthorityProofHint,
    ) -> Self {
        Self {
            memory_id: memory_id.into(),
            claim_key: claim_key.map(Into::into),
            claim: claim.into(),
            authority,
            conflicts_with: Vec::new(),
        }
    }

    /// Adds explicit conflict edges.
    #[must_use]
    pub fn with_conflicts(mut self, conflicts_with: Vec<String>) -> Self {
        self.conflicts_with = conflicts_with;
        self
    }
}

/// Explicit evidence that one candidate supersedes the others for this conflict set.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct PrecedenceEvidence {
    /// Winning memory ID.
    pub winner_memory_id: String,
    /// Memory IDs explicitly superseded by `winner_memory_id`.
    pub loser_memory_ids: Vec<String>,
    /// Human- or policy-readable resolution reason.
    pub reason: String,
    /// Proof closure for the precedence evidence itself.
    pub proof: ProofClosureHint,
}

/// Machine-readable reason emitted by the resolver.
#[allow(missing_docs)]
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum ResolutionReason {
    /// No candidate inputs were provided.
    NoInputs,
    /// Exactly one candidate was present; no conflict to resolve.
    SingleCandidate,
    /// All candidates share the same claim text.
    DuplicateClaim,
    /// An explicit precedence record nominated the winner.
    ExplicitPrecedence { winner_memory_id: String },
    /// Multiple candidates have conflicting claims.
    ConflictingClaims,
    /// A candidate is missing a required claim key.
    MissingClaimKey { memory_id: String },
    /// A candidate has only partial proof closure.
    PartialProof { memory_id: String },
    /// A candidate has unknown proof state.
    UnknownProof { memory_id: String },
    /// A candidate has a broken proof axis.
    BrokenProof { memory_id: String, edge: String },
    /// High-authority verified conflict requires explicit precedence before resolution.
    HighAuthorityVerifiedConflictRequiresPrecedence,
    /// Precedence evidence does not cover all losers.
    IncompletePrecedence {
        winner_memory_id: String,
        missing_loser_ids: Vec<String>,
    },
    /// Multiple candidates could claim precedence; winner is ambiguous.
    AmbiguousPrecedence { winner_memory_ids: Vec<String> },
}

impl ResolutionReason {
    const fn policy_rule_id(&self) -> &'static str {
        match self {
            Self::NoInputs => "retrieval.resolve.no_inputs",
            Self::SingleCandidate => "retrieval.resolve.single_candidate",
            Self::DuplicateClaim => "retrieval.resolve.duplicate_claim",
            Self::ExplicitPrecedence { .. } => "retrieval.resolve.explicit_precedence",
            Self::ConflictingClaims => "retrieval.resolve.conflicting_claims",
            Self::MissingClaimKey { .. } => "retrieval.resolve.missing_claim_key",
            Self::PartialProof { .. } => "retrieval.resolve.partial_proof",
            Self::UnknownProof { .. } => "retrieval.resolve.unknown_proof",
            Self::BrokenProof { .. } => "retrieval.resolve.broken_proof",
            Self::HighAuthorityVerifiedConflictRequiresPrecedence => {
                "retrieval.resolve.high_authority_conflict_requires_precedence"
            }
            Self::IncompletePrecedence { .. } => "retrieval.resolve.incomplete_precedence",
            Self::AmbiguousPrecedence { .. } => "retrieval.resolve.ambiguous_precedence",
        }
    }

    const fn policy_outcome(&self, state: ResolutionState) -> PolicyOutcome {
        match self {
            Self::SingleCandidate | Self::DuplicateClaim | Self::ExplicitPrecedence { .. }
                if matches!(state, ResolutionState::Resolved) =>
            {
                PolicyOutcome::Allow
            }
            Self::BrokenProof { .. } => PolicyOutcome::Reject,
            _ => PolicyOutcome::Quarantine,
        }
    }

    const fn policy_reason(&self) -> &'static str {
        match self {
            Self::NoInputs => "retrieval conflict resolver received no inputs",
            Self::SingleCandidate => "single candidate can be consumed",
            Self::DuplicateClaim => "duplicate claims resolved by deterministic authority ordering",
            Self::ExplicitPrecedence { .. } => "explicit full-chain precedence resolved conflict",
            Self::ConflictingClaims => "conflicting claims require multi-hypothesis handling",
            Self::MissingClaimKey { .. } => "candidate is missing claim-key evidence",
            Self::PartialProof { .. } => "candidate proof is partial",
            Self::UnknownProof { .. } => "candidate proof is unknown",
            Self::BrokenProof { .. } => "candidate proof is broken",
            Self::HighAuthorityVerifiedConflictRequiresPrecedence => {
                "high-authority verified conflict requires explicit precedence"
            }
            Self::IncompletePrecedence { .. } => "precedence evidence does not cover all losers",
            Self::AmbiguousPrecedence { .. } => "multiple precedence winners remain ambiguous",
        }
    }
}

/// Resolver output consumed by later retrieval/context-pack wiring.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct ResolverOutput {
    /// Resolution state.
    pub state: ResolutionState,
    /// Selected candidate when `state == Resolved`.
    pub selected: Option<ConflictingMemoryInput>,
    /// Candidate hypotheses that must be surfaced to callers.
    pub hypotheses: Vec<ConflictingMemoryInput>,
    /// Reasons supporting the state.
    pub reasons: Vec<ResolutionReason>,
}

impl ResolverOutput {
    /// Derive the ADR 0026 policy decision for this resolver output.
    #[must_use]
    pub fn policy_decision(&self) -> PolicyDecision {
        if self.reasons.is_empty() {
            return compose_policy_outcomes(
                vec![PolicyContribution::new(
                    "retrieval.resolve.no_reason",
                    PolicyOutcome::Quarantine,
                    "resolver returned no reason and cannot be treated as clean authority",
                )
                .expect("static policy contribution is valid")],
                None,
            );
        }

        let contributions = self
            .reasons
            .iter()
            .map(|reason| {
                PolicyContribution::new(
                    reason.policy_rule_id(),
                    reason.policy_outcome(self.state),
                    reason.policy_reason(),
                )
                .expect("static policy contribution is valid")
            })
            .collect();
        compose_policy_outcomes(contributions, None)
    }

    /// Fail closed before a resolver output is consumed as a default,
    /// canonical retrieval result.
    ///
    /// Multi-hypothesis and unknown outputs may still be rendered explicitly,
    /// but they must not silently act as resolved support for promotion,
    /// active-memory updates, or default context-pack inclusion.
    pub fn require_default_use_allowed(&self) -> CoreResult<()> {
        let policy = self.policy_decision();
        match policy.final_outcome {
            PolicyOutcome::Reject | PolicyOutcome::Quarantine => {
                Err(CoreError::Validation(format!(
                    "retrieval resolver default use blocked by policy outcome {:?}",
                    policy.final_outcome
                )))
            }
            PolicyOutcome::Allow | PolicyOutcome::Warn | PolicyOutcome::BreakGlass => Ok(()),
        }
    }
}

/// Resolves a caller-supplied contradiction set without mutating memory.
#[must_use]
pub fn resolve_conflicts(
    inputs: &[ConflictingMemoryInput],
    precedence: &[PrecedenceEvidence],
) -> ResolverOutput {
    let candidates = sorted_candidates(inputs);
    if candidates.is_empty() {
        return ResolverOutput {
            state: ResolutionState::Unknown,
            selected: None,
            hypotheses: Vec::new(),
            reasons: vec![ResolutionReason::NoInputs],
        };
    }

    let mut reasons = proof_reasons(&candidates);
    reasons.extend(missing_claim_key_reasons(&candidates));
    if !reasons.is_empty() {
        return ResolverOutput {
            state: ResolutionState::Unknown,
            selected: None,
            hypotheses: candidates,
            reasons,
        };
    }

    if candidates.len() == 1 {
        return ResolverOutput {
            state: ResolutionState::Resolved,
            selected: candidates.first().cloned(),
            hypotheses: candidates,
            reasons: vec![ResolutionReason::SingleCandidate],
        };
    }

    if !has_conflict(&candidates) {
        let selected = strongest_candidate(&candidates);
        return ResolverOutput {
            state: ResolutionState::Resolved,
            selected: Some(selected),
            hypotheses: candidates,
            reasons: vec![ResolutionReason::DuplicateClaim],
        };
    }

    match valid_precedence_winner(&candidates, precedence) {
        PrecedenceMatch::One(winner) => ResolverOutput {
            state: ResolutionState::Resolved,
            selected: Some(winner.clone()),
            hypotheses: vec![winner.clone()],
            reasons: vec![ResolutionReason::ExplicitPrecedence {
                winner_memory_id: winner.memory_id,
            }],
        },
        PrecedenceMatch::Many(winner_memory_ids) => ResolverOutput {
            state: ResolutionState::MultiHypothesis,
            selected: None,
            hypotheses: candidates,
            reasons: vec![ResolutionReason::AmbiguousPrecedence { winner_memory_ids }],
        },
        PrecedenceMatch::Incomplete {
            winner_memory_id,
            missing_loser_ids,
        } => ResolverOutput {
            state: ResolutionState::MultiHypothesis,
            selected: None,
            hypotheses: candidates,
            reasons: vec![ResolutionReason::IncompletePrecedence {
                winner_memory_id,
                missing_loser_ids,
            }],
        },
        PrecedenceMatch::None => unresolved_conflict(candidates),
    }
}

fn unresolved_conflict(candidates: Vec<ConflictingMemoryInput>) -> ResolverOutput {
    let mut reasons = vec![ResolutionReason::ConflictingClaims];
    if high_authority_verified_conflict(&candidates) {
        reasons.push(ResolutionReason::HighAuthorityVerifiedConflictRequiresPrecedence);
    }

    ResolverOutput {
        state: ResolutionState::MultiHypothesis,
        selected: None,
        hypotheses: candidates,
        reasons,
    }
}

fn proof_reasons(candidates: &[ConflictingMemoryInput]) -> Vec<ResolutionReason> {
    let mut reasons = Vec::new();
    for candidate in candidates {
        match &candidate.authority.proof {
            ProofClosureHint::FullChainVerified => {}
            ProofClosureHint::Partial => reasons.push(ResolutionReason::PartialProof {
                memory_id: candidate.memory_id.clone(),
            }),
            ProofClosureHint::Unknown => reasons.push(ResolutionReason::UnknownProof {
                memory_id: candidate.memory_id.clone(),
            }),
            ProofClosureHint::Broken { edge } => reasons.push(ResolutionReason::BrokenProof {
                memory_id: candidate.memory_id.clone(),
                edge: edge.clone(),
            }),
        }
    }
    reasons
}

fn missing_claim_key_reasons(candidates: &[ConflictingMemoryInput]) -> Vec<ResolutionReason> {
    candidates
        .iter()
        .filter(|candidate| {
            candidate
                .claim_key
                .as_ref()
                .is_none_or(|claim_key| claim_key.trim().is_empty())
        })
        .map(|candidate| ResolutionReason::MissingClaimKey {
            memory_id: candidate.memory_id.clone(),
        })
        .collect()
}

fn has_conflict(candidates: &[ConflictingMemoryInput]) -> bool {
    let claims: HashSet<_> = candidates
        .iter()
        .map(|candidate| normalize_claim(&candidate.claim))
        .collect();
    if claims.len() > 1 {
        return true;
    }

    let ids: HashSet<_> = candidates
        .iter()
        .map(|candidate| candidate.memory_id.as_str())
        .collect();
    candidates.iter().any(|candidate| {
        candidate
            .conflicts_with
            .iter()
            .any(|conflict_id| ids.contains(conflict_id.as_str()))
    })
}

fn high_authority_verified_conflict(candidates: &[ConflictingMemoryInput]) -> bool {
    candidates
        .iter()
        .filter(|candidate| candidate.authority.is_high_authority_verified())
        .take(2)
        .count()
        > 1
}

fn strongest_candidate(candidates: &[ConflictingMemoryInput]) -> ConflictingMemoryInput {
    let mut sorted = candidates.to_vec();
    sorted.sort_by(|left, right| {
        right
            .authority
            .authority
            .cmp(&left.authority.authority)
            .then_with(|| left.memory_id.cmp(&right.memory_id))
    });
    sorted
        .into_iter()
        .next()
        .expect("strongest_candidate requires at least one candidate")
}

fn sorted_candidates(inputs: &[ConflictingMemoryInput]) -> Vec<ConflictingMemoryInput> {
    let mut candidates = inputs.to_vec();
    candidates.sort_by(|left, right| left.memory_id.cmp(&right.memory_id));
    candidates
}

fn normalize_claim(claim: &str) -> String {
    claim
        .split_whitespace()
        .collect::<Vec<_>>()
        .join(" ")
        .to_ascii_lowercase()
}

enum PrecedenceMatch {
    One(ConflictingMemoryInput),
    Many(Vec<String>),
    Incomplete {
        winner_memory_id: String,
        missing_loser_ids: Vec<String>,
    },
    None,
}

fn valid_precedence_winner(
    candidates: &[ConflictingMemoryInput],
    precedence: &[PrecedenceEvidence],
) -> PrecedenceMatch {
    let candidate_ids: HashSet<_> = candidates
        .iter()
        .map(|candidate| candidate.memory_id.as_str())
        .collect();
    let mut complete_winners = Vec::new();
    let mut first_incomplete = None;

    for evidence in precedence
        .iter()
        .filter(|evidence| evidence.proof.is_full_chain_verified())
        .filter(|evidence| candidate_ids.contains(evidence.winner_memory_id.as_str()))
    {
        let loser_ids: HashSet<_> = evidence
            .loser_memory_ids
            .iter()
            .map(String::as_str)
            .collect();
        let mut missing_loser_ids: Vec<_> = candidate_ids
            .iter()
            .copied()
            .filter(|candidate_id| *candidate_id != evidence.winner_memory_id)
            .filter(|candidate_id| !loser_ids.contains(candidate_id))
            .map(str::to_string)
            .collect();
        missing_loser_ids.sort();

        if missing_loser_ids.is_empty() {
            complete_winners.push(evidence.winner_memory_id.clone());
        } else if first_incomplete.is_none() {
            first_incomplete = Some(PrecedenceMatch::Incomplete {
                winner_memory_id: evidence.winner_memory_id.clone(),
                missing_loser_ids,
            });
        }
    }

    complete_winners.sort();
    complete_winners.dedup();
    match complete_winners.len() {
        0 => first_incomplete.unwrap_or(PrecedenceMatch::None),
        1 => {
            let winner_id = &complete_winners[0];
            let winner = candidates
                .iter()
                .find(|candidate| &candidate.memory_id == winner_id)
                .expect("complete winner came from candidate IDs")
                .clone();
            PrecedenceMatch::One(winner)
        }
        _ => PrecedenceMatch::Many(complete_winners),
    }
}

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

    fn verified_high(memory_id: &str, claim: &str) -> ConflictingMemoryInput {
        ConflictingMemoryInput::new(
            memory_id,
            Some("slot/runtime"),
            claim,
            AuthorityProofHint {
                authority: AuthorityLevel::High,
                proof: ProofClosureHint::FullChainVerified,
            },
        )
    }

    #[test]
    fn conflicting_verified_memories_enter_multi_hypothesis() {
        let left = verified_high("mem_a", "Use replay adapter version 1");
        let right = verified_high("mem_b", "Use replay adapter version 2");

        let output = resolve_conflicts(&[left, right], &[]);

        assert_eq!(output.state, ResolutionState::MultiHypothesis);
        assert_eq!(
            output.policy_decision().final_outcome,
            PolicyOutcome::Quarantine
        );
        assert_eq!(output.selected, None);
        assert_eq!(output.hypotheses.len(), 2);
        assert!(output
            .reasons
            .contains(&ResolutionReason::HighAuthorityVerifiedConflictRequiresPrecedence));
    }

    #[test]
    fn unknown_proof_propagates_unknown() {
        let input = ConflictingMemoryInput::new(
            "mem_unknown",
            Some("slot/runtime"),
            "Use replay adapter version 1",
            AuthorityProofHint {
                authority: AuthorityLevel::High,
                proof: ProofClosureHint::Unknown,
            },
        );

        let output = resolve_conflicts(&[input], &[]);

        assert_eq!(output.state, ResolutionState::Unknown);
        assert_eq!(
            output.policy_decision().final_outcome,
            PolicyOutcome::Quarantine
        );
        assert_eq!(output.selected, None);
        assert!(output.reasons.contains(&ResolutionReason::UnknownProof {
            memory_id: "mem_unknown".into()
        }));
    }

    #[test]
    fn explicit_full_chain_precedence_resolves_conflict() {
        let left = verified_high("mem_a", "Use replay adapter version 1");
        let right = verified_high("mem_b", "Use replay adapter version 2");
        let precedence = PrecedenceEvidence {
            winner_memory_id: "mem_b".into(),
            loser_memory_ids: vec!["mem_a".into()],
            reason: "operator-attested supersession".into(),
            proof: ProofClosureHint::FullChainVerified,
        };

        let output = resolve_conflicts(&[left, right], &[precedence]);

        assert_eq!(output.state, ResolutionState::Resolved);
        assert_eq!(output.policy_decision().final_outcome, PolicyOutcome::Allow);
        assert_eq!(
            output
                .selected
                .as_ref()
                .map(|candidate| candidate.memory_id.as_str()),
            Some("mem_b")
        );
        assert_eq!(
            output.reasons,
            [ResolutionReason::ExplicitPrecedence {
                winner_memory_id: "mem_b".into()
            }]
        );
        output
            .require_default_use_allowed()
            .expect("resolved output is default-usable");
    }

    #[test]
    fn broken_proof_maps_to_policy_reject() {
        let input = ConflictingMemoryInput::new(
            "mem_broken",
            Some("slot/runtime"),
            "Use replay adapter version 1",
            AuthorityProofHint {
                authority: AuthorityLevel::High,
                proof: ProofClosureHint::Broken {
                    edge: "event:missing_hash".into(),
                },
            },
        );

        let output = resolve_conflicts(&[input], &[]);
        let policy = output.policy_decision();

        assert_eq!(output.state, ResolutionState::Unknown);
        assert_eq!(policy.final_outcome, PolicyOutcome::Reject);
        assert_eq!(
            policy.contributing[0].rule_id.as_str(),
            "retrieval.resolve.broken_proof"
        );
    }

    #[test]
    fn unresolved_conflict_fails_closed_for_default_use() {
        let left = verified_high("mem_a", "Use replay adapter version 1");
        let right = verified_high("mem_b", "Use replay adapter version 2");

        let output = resolve_conflicts(&[left, right], &[]);
        let err = output
            .require_default_use_allowed()
            .expect_err("multi-hypothesis output must not be default-usable");

        assert!(
            err.to_string().contains("Quarantine"),
            "default-use failure should expose the policy outcome: {err}"
        );
    }

    #[test]
    fn broken_proof_fails_closed_for_default_use() {
        let input = ConflictingMemoryInput::new(
            "mem_broken",
            Some("slot/runtime"),
            "Use replay adapter version 1",
            AuthorityProofHint {
                authority: AuthorityLevel::High,
                proof: ProofClosureHint::Broken {
                    edge: "event:missing_hash".into(),
                },
            },
        );

        let output = resolve_conflicts(&[input], &[]);
        let err = output
            .require_default_use_allowed()
            .expect_err("broken proof must not be default-usable");

        assert!(
            err.to_string().contains("Reject"),
            "default-use failure should expose the policy outcome: {err}"
        );
    }
}