//! Phase 5 — dry-run audit mode 🚦 (impl plan §5).
//!
//! **This phase adds no capability. Its entire purpose is to be wrong loudly
//! and safely.** It runs phases 2–4 against the *live* graph on every graph
//! event and reports what they conclude. It creates no links, loads no modules,
//! and changes no routing — the only thing it produces is a line of JSON.
//!
//! Why this is the gate the plan marks 🚦: the defects that matter here are
//! graph-*reasoning* defects. The 57 phase-2 fixture tests prove the engine
//! matches my model of PipeWire; only a live run proves my model matches
//! PipeWire. A wrong answer at this phase costs a log line. The same wrong
//! answer in phase 6 costs an echo — the sharer's own voice, copied back into
//! the share, which is the failure this whole design exists to prevent.
//!
//! ## The one structural requirement (§5.1)
//!
//! Every emitted record carries the **complete candidate universe partitioned
//! into exact eligible and excluded sets**, with a stable reason code on each
//! excluded row — never a spot check on named nodes. Checking only the nodes a
//! row names constrains nothing about the rest, and it lets the degenerate
//! "exclude everything" implementation pass: that build is silent, produces no
//! echo, and satisfies any assertion phrased purely as *this must be excluded*.
//! Asserting the eligible half of each row is what fails it. That requirement is
//! also the plan's answer to open question O7 (over-exclusion needs no separate
//! gate — it is subsumed by this one).
//!
//! ## What is deliberately *not* here
//!
//! - **No link creation, and no code path that could reach one.** The auditor
//!   consumes a [`Projection`] and returns a record. It has no handle to
//!   anything mutable.
//! - **No stdout.** Records go to stderr as JSON Lines
//!   ([`sink`]) because peerspeak parses pixelpass's stdout event stream
//!   (`screenshare/mod.rs:92`); a stray line there corrupts it.
//! - **No `--aec` CLI flag.** That surface is phase 7's mode selector. The audit
//!   takes its AEC identity from `PIXELPASS_AUDIO_AUDIT_AEC` through the
//!   *same* [`parse_aec_arg`] the real flag will use, so the parser and the
//!   validator are both exercised without committing to a public interface
//!   before it is designed.
//!
//! ## Fan-out gating vs. taint (read before interpreting a record)
//!
//! Two independent things can exclude a candidate and the record keeps them
//! distinguishable:
//!
//! - The **taint engine** (phase 2) excludes individual nodes with its own
//!   reason codes — `peerspeak-owned`, `aec-identity`, `tainted-upstream`, …
//! - The **AEC validator** (phase 4) can forbid fan-out *entirely*, regardless
//!   of taint, whenever the configured identity is unvalidated, failed or
//!   revoked. Silence over echo.
//!
//! When the gate is shut, a candidate the engine would have called eligible is
//! reported excluded with an audit-level reason ([`GateReason`]); a candidate
//! the engine excluded on its own keeps *its* reason, because that names the
//! mechanism that actually applies to it. `fan_out_permitted` on the record
//! carries the gate state, so the two cases are always tellable apart.
//!
//! **Consequence for the §5.1 matrix:** every row whose point is the
//! eligible/excluded partition must run with `PIXELPASS_AUDIO_AUDIT_AEC=off`
//! (state `NotConfigured`, gate open). Row 12 — the AEC lifecycle row — is the
//! one that runs with a real `pulse-module:<idx>`, and the gate slamming shut is
//! precisely what it asserts.

#![allow(dead_code)] // Trigger paths are wired by `sink` + `run`; rows are read by tests.

pub mod metrics;
pub mod run;
pub mod sink;

#[cfg(test)]
mod tests;

use serde::Serialize;

use crate::host::aec::{AecConfig, AecState, AecValidator};
use crate::host::observer::{EventKind, Millis, Projection, Readiness};
use crate::host::taint::snapshot::Serial;
use crate::host::taint::{Decisions, Eligibility, ExclusionCtx, StickyState, evaluate};

/// How long the AEC validator may sit in `Validating` after the graph first
/// reports ready before failing closed. Generous relative to the observer's own
/// 2 s readiness budget: in the audit a `Failed` is a diagnostic, and timing out
/// early would report an absent module that was merely slow to appear.
pub const AEC_VALIDATION_TIMEOUT_MILLIS: Millis = 5_000;

/// Everything the auditor needs beyond the live graph.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct AuditConfig {
    /// The AEC identity to validate, as parsed from
    /// `PIXELPASS_AUDIO_AUDIT_AEC`. Defaults to [`AecConfig::Off`] — an audit
    /// run is not a share, so "there is no echo canceller in play" is the
    /// honest default, and it is what leaves the fan-out gate open for the
    /// partition rows.
    pub aec: AecConfig,
    pub aec_timeout: Millis,
}

impl Default for AuditConfig {
    fn default() -> Self {
        Self {
            aec: AecConfig::Off,
            aec_timeout: AEC_VALIDATION_TIMEOUT_MILLIS,
        }
    }
}

/// An audit-level exclusion: the AEC validator has shut the fan-out gate. These
/// codes are disjoint from the taint engine's
/// [`Reason::code`](crate::host::taint::Reason::code) values, so a reader never
/// has to know which layer produced a code to interpret it.
// The shared `Aec` prefix is the point: `GateReason::Validating` and
// `AecState::Validating` would be one careless glob import away from being
// confused, and these three are the *audit's* view of that machine, not the
// machine itself.
#[allow(clippy::enum_variant_names)]
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum GateReason {
    /// The configured AEC identity has not been seen yet. Not an error — the
    /// module may still be loading — but no fan-out happens meanwhile.
    AecValidating,
    /// The deadline passed with the identity never observed.
    AecFailed,
    /// The whole identity disappeared mid-run: every node bearing the index is
    /// gone (v3.4 §5.3).
    AecRevoked,
}

impl GateReason {
    pub fn code(self) -> &'static str {
        match self {
            Self::AecValidating => "aec-validating",
            Self::AecFailed => "aec-failed",
            Self::AecRevoked => "aec-revoked",
        }
    }

    /// The gate reason implied by a validator state, or `None` when fan-out is
    /// permitted. Mirrors [`AecValidator::fan_out_permitted`] — kept as one
    /// `match` over the same enum so the two cannot drift: every state that
    /// permits fan-out maps to `None` and every state that forbids it maps to a
    /// code.
    pub fn from_state(state: AecState) -> Option<Self> {
        match state {
            AecState::NotConfigured | AecState::Validated => None,
            AecState::Validating => Some(Self::AecValidating),
            AecState::Failed => Some(Self::AecFailed),
            AecState::Revoked => Some(Self::AecRevoked),
        }
    }
}

/// Stable string for an [`AecState`], for the record's `aec_state` field.
///
/// Defined here rather than on [`AecState`] to keep the merged phase-4 module
/// untouched by a reporting concern.
fn aec_state_code(state: AecState) -> &'static str {
    match state {
        AecState::NotConfigured => "not-configured",
        AecState::Validating => "validating",
        AecState::Validated => "validated",
        AecState::Failed => "failed",
        AecState::Revoked => "revoked",
    }
}

/// Stable string for the observer's readiness epoch.
fn readiness_code(readiness: Readiness) -> &'static str {
    match readiness {
        Readiness::Waiting => "waiting",
        Readiness::Complete => "complete",
        Readiness::TimedOut => "timed-out",
    }
}

/// One candidate node's effective answer. `reason` is `None` exactly when
/// `eligible` is true.
#[derive(Clone, Debug, PartialEq, Eq, Serialize)]
pub struct AuditRow {
    pub serial: u64,
    pub name: Option<String>,
    pub eligible: bool,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub reason: Option<&'static str>,
    /// The exclusion was carried over from a previous snapshot rather than
    /// derived from the current topology (phase-2 stickiness).
    pub sticky: bool,
}

/// A tainted node of *any* media role, not just fan-out candidates. Candidates
/// already appear in [`AuditBody::candidates`]; this is the diagnostic view —
/// when a candidate's exclusion is a surprise, the taint that reached it is the
/// next question, and it usually sits on a node that is not itself a candidate.
#[derive(Clone, Debug, PartialEq, Eq, Serialize)]
pub struct TaintRow {
    pub serial: u64,
    pub name: Option<String>,
    pub reason: &'static str,
    pub sticky: bool,
}

/// The decision content of one recompute — everything except which recompute it
/// was. Split out from [`AuditRecord`] so "did anything actually change?" is a
/// derived `==` rather than a hand-maintained field comparison that a later
/// field addition could silently fall out of.
#[derive(Clone, Debug, PartialEq, Eq, Serialize)]
pub struct AuditBody {
    /// The observer's dynamic readiness. False ⇒ every candidate is excluded
    /// `graph-not-ready`; no decision from a partial graph is a decision.
    pub graph_ready: bool,
    /// The sticky readiness epoch, which distinguishes the three ways
    /// `graph_ready` can be false (see [`Projection::readiness`]).
    pub epoch: &'static str,
    pub aec_state: &'static str,
    /// The index handed to the taint engine — `Some` only while `Validated`.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub aec_module_id: Option<u64>,
    /// Whether the AEC validator permits fan-out at all right now.
    pub fan_out_permitted: bool,
    /// The audit-level reason fan-out is forbidden, when it is.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub gate_reason: Option<&'static str>,
    /// **The complete candidate universe**, ascending by serial — every
    /// `Stream/Output/Audio` node in the snapshot, partitioned. §5.1's exact
    /// partition is `candidates`, not a subset of it.
    pub candidates: Vec<AuditRow>,
    pub eligible_count: usize,
    pub excluded_count: usize,
    /// Taint across all node roles, ascending by serial.
    pub taint: Vec<TaintRow>,
}

impl AuditBody {
    /// Serials of eligible candidates, ascending — the half of the partition an
    /// exclude-everything build fails.
    pub fn eligible(&self) -> Vec<u64> {
        self.candidates
            .iter()
            .filter(|row| row.eligible)
            .map(|row| row.serial)
            .collect()
    }

    /// `(serial, reason code)` for excluded candidates, ascending.
    pub fn excluded(&self) -> Vec<(u64, &'static str)> {
        self.candidates
            .iter()
            .filter(|row| !row.eligible)
            .map(|row| (row.serial, row.reason.unwrap_or("?")))
            .collect()
    }

    /// The eligible candidate with this name, if any. Convenience for the
    /// matrix rows, which name nodes rather than serials.
    pub fn row_named(&self, name: &str) -> Option<&AuditRow> {
        self.candidates
            .iter()
            .find(|row| row.name.as_deref() == Some(name))
    }
}

/// One recompute, as emitted.
#[derive(Clone, Debug, PartialEq, Eq, Serialize)]
pub struct AuditRecord {
    /// Monotonic per-run counter over *every* recompute, emitted or suppressed,
    /// so a gap in the emitted sequence is visibly a suppression rather than a
    /// lost line.
    pub seq: u64,
    pub trigger: &'static str,
    /// Observer-clock milliseconds at which this recompute ran.
    pub at_ms: Millis,
    #[serde(flatten)]
    pub body: AuditBody,
}

/// What one [`Auditor::observe`] produced.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct AuditOutcome {
    pub record: AuditRecord,
    /// Whether the record should be written. See [`Auditor::observe`].
    pub emit: bool,
}

/// The dry-run auditor: phases 2–4 folded together over a live projection.
///
/// Read-only by construction — it borrows a [`Projection`] and owns only the
/// state phases 2 and 4 thread explicitly ([`StickyState`], [`AecValidator`]).
/// There is no field here through which a link could be created.
#[derive(Clone, Debug)]
pub struct Auditor {
    validator: AecValidator,
    sticky: StickyState,
    seq: u64,
    /// The body of the last record actually written, for change suppression.
    last_emitted: Option<AuditBody>,
}

impl Auditor {
    pub fn new(config: AuditConfig) -> Self {
        Self {
            validator: AecValidator::new(config.aec, config.aec_timeout),
            sticky: StickyState::default(),
            seq: 0,
            last_emitted: None,
        }
    }

    pub fn aec_state(&self) -> AecState {
        self.validator.state()
    }

    pub fn sticky(&self) -> &StickyState {
        &self.sticky
    }

    /// Fold one projection into the audit.
    ///
    /// **Called once per applied registry event — never on a coalesced batch.**
    /// That is not a performance preference, it is the phase-4 integration
    /// contract (`aec/mod.rs`, the `Validated` arm): revocation is detected by
    /// observing the *empty gap* between a module unload and the next reload,
    /// and module indices are reused verbatim (v3.4 §5.2 correction 3). Coalesce
    /// across that gap and a fresh module silently inherits a dead module's
    /// validated identity. [`sink`] is what upholds this, by running the
    /// recompute inline on the observer thread rather than polling
    /// [`RegistryObserverHandle::latest`](crate::host::observer::adapter::RegistryObserverHandle::latest),
    /// which coalesces by nature.
    ///
    /// `emit` is true for every graph-triggered recompute, and for a
    /// tick-triggered one only when the decision content changed. Ticks arrive
    /// at a constant 4 Hz purely to drive the AEC deadline; emitting an
    /// identical record four times a second would bury the graph events the
    /// audit exists to show. `seq` still advances on suppressed records, so
    /// nothing about the run is silently unaccounted for.
    pub fn observe(
        &mut self,
        projection: &Projection,
        kind: EventKind,
        now: Millis,
    ) -> AuditOutcome {
        self.seq += 1;

        // Phase 4 first: its verdict is an *input* to phase 2 via
        // `ExclusionCtx::aec_module_id`, so observing the graph in the other
        // order would evaluate taint against the previous recompute's identity.
        self.validator
            .observe(&projection.snapshot, projection.graph_ready, now);
        let aec_state = self.validator.state();
        let gate_reason = GateReason::from_state(aec_state);

        let ctx = ExclusionCtx {
            aec_module_id: self.validator.validated_module_id(),
            pipewire_pulse_pid: projection.pipewire_pulse_pid,
            // The audit creates nothing, so it owns nothing. Another host's
            // capture sink is still caught — by the `pixelpass_capture_*` name
            // prefix (v3.4 §6.2), which is what §5.1 row 7 exercises — so an
            // empty set costs the matrix nothing.
            pixelpass_owned: Default::default(),
            graph_ready: projection.graph_ready,
        };

        let (decisions, sticky) = evaluate(&projection.snapshot, &ctx, &self.sticky);
        self.sticky = sticky;

        let body = build_body(
            projection,
            &decisions,
            aec_state,
            self.validator.validated_module_id(),
            gate_reason,
        );

        let emit = kind == EventKind::Graph || self.last_emitted.as_ref() != Some(&body);
        if emit {
            self.last_emitted = Some(body.clone());
        }

        AuditOutcome {
            record: AuditRecord {
                seq: self.seq,
                trigger: kind.code(),
                at_ms: now,
                body,
            },
            emit,
        }
    }
}

fn build_body(
    projection: &Projection,
    decisions: &Decisions,
    aec_state: AecState,
    aec_module_id: Option<u64>,
    gate_reason: Option<GateReason>,
) -> AuditBody {
    let candidates: Vec<AuditRow> = decisions
        .candidates
        .values()
        .map(|decision| {
            // The engine's own reason wins when it has one: it names the
            // mechanism that actually excluded *this* node, which is what the
            // §5.1 rows assert. The gate reason applies only to candidates the
            // engine would have passed — otherwise a shut gate would erase every
            // reason code in the record and the matrix would stop constraining
            // the engine at all.
            let (eligible, reason, sticky) = match decision.eligibility {
                Eligibility::NotEligible { reason, sticky } => (false, Some(reason.code()), sticky),
                Eligibility::Eligible => match gate_reason {
                    Some(gate) => (false, Some(gate.code()), false),
                    None => (true, None, false),
                },
            };
            AuditRow {
                serial: decision.serial.0,
                name: decision.name.clone(),
                eligible,
                reason,
                sticky,
            }
        })
        .collect();

    let eligible_count = candidates.iter().filter(|row| row.eligible).count();

    let taint: Vec<TaintRow> = decisions
        .taint
        .iter()
        .map(|(&serial, entry)| TaintRow {
            serial: serial.0,
            name: node_name(projection, serial),
            reason: entry.reason.code(),
            sticky: entry.sticky,
        })
        .collect();

    AuditBody {
        graph_ready: projection.graph_ready,
        epoch: readiness_code(projection.readiness),
        aec_state: aec_state_code(aec_state),
        aec_module_id,
        fan_out_permitted: gate_reason.is_none(),
        gate_reason: gate_reason.map(GateReason::code),
        excluded_count: candidates.len() - eligible_count,
        eligible_count,
        candidates,
        taint,
    }
}

fn node_name(projection: &Projection, serial: Serial) -> Option<String> {
    projection
        .snapshot
        .node(serial)
        .and_then(|node| node.name.clone())
}