behavior-contracts 0.2.2

//! plan — execution-plan.md reference implementation.
//!
//! run_plan(plan, ops, exec): execute stage groups sequentially, interpret
//! null-binding skip, Skip propagation, and Error Policy Kind (fail/retry/continue)
//! to produce a deterministic result tree. Node execution is delegated to `exec`.
//!
//! Bounded parallel stage execution (bc#23, execution-plan.md §4.1):
//! [`run_plan_parallel`] additionally dispatches the members of a stage on scoped
//! worker threads, bounded by `plan.concurrency`, while COMMITTING interpretation
//! (Skip / Policy Kind / Failure) in ascending index order — the observed result
//! (tree / executed / skipped / failure code+message) is byte-identical to
//! [`run_plan`]. It requires `exec: Fn + Sync` (callable from multiple threads),
//! which is why it is a separate, additive entry point: [`run_plan`] keeps the
//! `FnMut` seam (and stays sequential — a conforming §4.1 fallback) so existing
//! consumers, including [`crate::behavior::run_behavior`]'s stateful exec closure,
//! are untouched.

use crate::value::Value;

#[derive(Debug, Clone)]
pub struct ExecutionPlanSpec {
    pub groups: Vec<Vec<usize>>,
    pub concurrency: i64,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum PolicyKind {
    Fail,
    Retry,
    Continue,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum RelationKind {
    Single,
    Connection,
}

#[derive(Debug, Clone)]
pub struct OpSpec {
    pub id: String,
    pub parent: Option<usize>,
    pub bind_field: Option<String>,
    pub relation_kind: Option<RelationKind>,
    /// Raw policy string from the vector (validated at run time so unknown
    /// policies fail closed with UNKNOWN_POLICY rather than at parse time).
    pub policy: Option<String>,
}

/// consumer-supplied node execution outcome (mock).
#[derive(Debug, Clone)]
pub enum ExecOutcome {
    Ok(Value),
    Error(String),
}

#[derive(Debug, Clone)]
enum OpState {
    Ok(Value),
    Skipped,
    // Failed is never stored: fail policy raises immediately.
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum PlanFailureCode {
    OpFailed,
    UnknownPolicy,
    InvalidPlan,
}

impl PlanFailureCode {
    pub fn as_str(self) -> &'static str {
        match self {
            PlanFailureCode::OpFailed => "OP_FAILED",
            PlanFailureCode::UnknownPolicy => "UNKNOWN_POLICY",
            PlanFailureCode::InvalidPlan => "INVALID_PLAN",
        }
    }
}

#[derive(Debug, Clone)]
pub struct PlanFailure {
    pub code: PlanFailureCode,
    pub message: String,
}

impl std::fmt::Display for PlanFailure {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{}: {}", self.code.as_str(), self.message)
    }
}
impl std::error::Error for PlanFailure {}

fn fail<T>(code: PlanFailureCode, message: impl Into<String>) -> Result<T, PlanFailure> {
    Err(PlanFailure {
        code,
        message: message.into(),
    })
}

#[derive(Debug)]
pub struct RunResult {
    states: Vec<Option<OpState>>,
    pub executed: Vec<String>,
    pub skipped: Vec<String>,
    ops_ref: Vec<(String, Option<RelationKind>)>,
}

impl RunResult {
    /// Build the observed result tree (opId → value; Skip → unproduced form).
    pub fn final_tree(&self) -> Vec<(String, Value)> {
        let mut tree = Vec::new();
        for (i, st) in self.states.iter().enumerate() {
            match st {
                Some(OpState::Ok(v)) => tree.push((self.ops_ref[i].0.clone(), v.clone())),
                Some(OpState::Skipped) => tree.push((
                    self.ops_ref[i].0.clone(),
                    unproduced_value(self.ops_ref[i].1),
                )),
                None => {}
            }
        }
        tree
    }
}

fn unproduced_value(kind: Option<RelationKind>) -> Value {
    if kind == Some(RelationKind::Connection) {
        Value::Obj(vec![
            ("items".into(), Value::Arr(vec![])),
            ("cursor".into(), Value::Null),
        ])
    } else {
        Value::Null
    }
}

fn parse_policy(raw: &Option<String>) -> Result<PolicyKind, PlanFailure> {
    match raw.as_deref() {
        None | Some("fail") => Ok(PolicyKind::Fail),
        Some("retry") => Ok(PolicyKind::Retry),
        Some("continue") => Ok(PolicyKind::Continue),
        Some(other) => fail(
            PlanFailureCode::UnknownPolicy,
            format!("unknown policy kind: {other}"),
        ),
    }
}

/// Run the plan. `exec(op, bound_value)` returns the node outcome (mock).
pub fn run_plan<F>(
    plan: Option<&ExecutionPlanSpec>,
    ops: &[OpSpec],
    mut exec: F,
) -> Result<RunResult, PlanFailure>
where
    F: FnMut(&OpSpec, Option<&Value>) -> ExecOutcome,
{
    let n = ops.len();
    let mut states: Vec<Option<OpState>> = vec![None; n];
    let mut executed_idx: Vec<usize> = Vec::new();
    let mut skipped_idx: Vec<usize> = Vec::new();

    let stages: Vec<Vec<usize>> = match plan {
        Some(p) => p.groups.clone(),
        None => (0..n).map(|i| vec![i]).collect(),
    };

    validate_coverage(&stages, n)?;

    for stage in &stages {
        let mut ordered = stage.clone();
        ordered.sort_unstable(); // determinism: concurrency does not change results
        for &i in &ordered {
            let st = run_op(
                i,
                &ops[i],
                &states,
                &mut exec,
                &mut executed_idx,
                &mut skipped_idx,
            )?;
            states[i] = Some(st);
        }
    }

    executed_idx.sort_unstable();
    skipped_idx.sort_unstable();

    Ok(RunResult {
        executed: executed_idx.iter().map(|&i| ops[i].id.clone()).collect(),
        skipped: skipped_idx.iter().map(|&i| ops[i].id.clone()).collect(),
        ops_ref: ops
            .iter()
            .map(|o| (o.id.clone(), o.relation_kind))
            .collect(),
        states,
    })
}

/// Bounded parallel variant of [`run_plan`] (bc#23).
///
/// Deterministic commit protocol (execution-plan.md §4.1), per stage:
/// 1. preflight (ascending index): policy validation, skip decision, and bindField
///    binding are derived from the settled prior-stage states (stage members are
///    mutually independent — §1).
/// 2. dispatch (ascending index, bounded): exec of runnable members runs on scoped
///    worker threads, at most `plan.concurrency` in flight.
/// 3. commit (ascending index): outcomes are interpreted in declaration order, so
///    the failure identity (code + message) matches [`run_plan`] exactly.
///
/// The only observable difference from [`run_plan`] is speculative dispatch: when a
/// member's interpretation fails, later members of the same stage may already have
/// been executed (same allowance as graphddb's historical thread-overlap).
///
/// A consumer shipping a plan with `concurrency > 1` declares that `exec` may be
/// invoked from that many threads concurrently (ship `concurrency: 1` otherwise —
/// that, single-member stages, and intra-stage parent/child dependencies all fall
/// back to sequential dispatch with unchanged results).
pub fn run_plan_parallel<F>(
    plan: Option<&ExecutionPlanSpec>,
    ops: &[OpSpec],
    exec: F,
) -> Result<RunResult, PlanFailure>
where
    F: Fn(&OpSpec, Option<&Value>) -> ExecOutcome + Sync,
{
    let n = ops.len();
    let mut states: Vec<Option<OpState>> = vec![None; n];
    let mut executed_idx: Vec<usize> = Vec::new();
    let mut skipped_idx: Vec<usize> = Vec::new();

    let stages: Vec<Vec<usize>> = match plan {
        Some(p) => p.groups.clone(),
        None => (0..n).map(|i| vec![i]).collect(),
    };
    let concurrency = plan.map(|p| p.concurrency).unwrap_or(1);

    validate_coverage(&stages, n)?;

    for stage in &stages {
        let mut ordered = stage.clone();
        ordered.sort_unstable();

        let has_intra_deps = ordered
            .iter()
            .any(|&i| matches!(ops[i].parent, Some(p) if ordered.contains(&p)));

        if concurrency <= 1 || ordered.len() <= 1 || has_intra_deps {
            // Sequential fallback (§4.1) — identical per-op flow to run_plan.
            for &i in &ordered {
                let st = run_op(
                    i,
                    &ops[i],
                    &states,
                    &mut |op: &OpSpec, b: Option<&Value>| exec(op, b),
                    &mut executed_idx,
                    &mut skipped_idx,
                )?;
                states[i] = Some(st);
            }
            continue;
        }

        // ── parallel path ────────────────────────────────────────────────────
        let pres: Vec<Preflight> = ordered
            .iter()
            .map(|&i| preflight_op(&ops[i], &states))
            .collect();

        // Jobs = runnable members in declaration order; a shared cursor hands them
        // out in that order to at most `concurrency` scoped worker threads.
        let jobs: Vec<usize> = (0..ordered.len())
            .filter(|&k| matches!(pres[k], Preflight::Exec { .. }))
            .collect();
        let workers = (concurrency.max(1) as usize).min(jobs.len());
        let cursor = std::sync::atomic::AtomicUsize::new(0);
        let slots: Vec<std::sync::Mutex<Option<ExecOutcome>>> = (0..ordered.len())
            .map(|_| std::sync::Mutex::new(None))
            .collect();

        std::thread::scope(|scope| {
            for _ in 0..workers {
                scope.spawn(|| loop {
                    let j = cursor.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
                    if j >= jobs.len() {
                        break;
                    }
                    let k = jobs[j];
                    let i = ordered[k];
                    let bound = match &pres[k] {
                        Preflight::Exec { bound, .. } => bound.as_ref(),
                        _ => unreachable!(),
                    };
                    let outcome = exec(&ops[i], bound);
                    *slots[k].lock().unwrap() = Some(outcome);
                });
            }
        }); // worker panics propagate here (like sequential exec panics)

        // Commit (ascending index): declaration-order interpretation.
        for (k, &i) in ordered.iter().enumerate() {
            match &pres[k] {
                Preflight::InvalidPolicy(msg) => {
                    return fail(PlanFailureCode::UnknownPolicy, msg.clone())
                }
                Preflight::Skip => {
                    skipped_idx.push(i);
                    states[i] = Some(OpState::Skipped);
                }
                Preflight::Exec { policy, .. } => {
                    let outcome = slots[k]
                        .lock()
                        .unwrap()
                        .take()
                        .expect("dispatched op must have an outcome");
                    let st = interpret_outcome(
                        i,
                        &ops[i],
                        *policy,
                        outcome,
                        &mut executed_idx,
                        &mut skipped_idx,
                    )?;
                    states[i] = Some(st);
                }
            }
        }
    }

    executed_idx.sort_unstable();
    skipped_idx.sort_unstable();

    Ok(RunResult {
        executed: executed_idx.iter().map(|&i| ops[i].id.clone()).collect(),
        skipped: skipped_idx.iter().map(|&i| ops[i].id.clone()).collect(),
        ops_ref: ops
            .iter()
            .map(|o| (o.id.clone(), o.relation_kind))
            .collect(),
        states,
    })
}

/// Pure pre-exec decision for one op (policy validation → skip decision →
/// bindField binding), shared by the sequential and parallel paths. The order
/// mirrors the sequential run_op exactly: the policy check precedes the skip
/// decision (UNKNOWN_POLICY fires even for ops that would be skipped).
enum Preflight {
    InvalidPolicy(String),
    Skip,
    Exec {
        policy: PolicyKind,
        bound: Option<Value>,
    },
}

fn preflight_op(op: &OpSpec, states: &[Option<OpState>]) -> Preflight {
    let policy = match parse_policy(&op.policy) {
        Ok(p) => p,
        Err(e) => return Preflight::InvalidPolicy(e.message), // fail-closed on unknown
    };

    let mut bound_value: Option<Value> = None;
    if let Some(pidx) = op.parent {
        match states.get(pidx).and_then(|s| s.as_ref()) {
            Some(OpState::Ok(pv)) => {
                if let Some(field) = &op.bind_field {
                    let bound = pv.obj_get(field);
                    match bound {
                        None | Some(Value::Null) => return Preflight::Skip,
                        Some(b) => bound_value = Some(b.clone()),
                    }
                }
            }
            _ => {
                // parent skipped / failed / not produced → skip (chain)
                return Preflight::Skip;
            }
        }
    }
    Preflight::Exec {
        policy,
        bound: bound_value,
    }
}

/// Post-exec interpretation (executed bookkeeping → Policy Kind), shared by both
/// paths so failure messages stay identical.
fn interpret_outcome(
    i: usize,
    op: &OpSpec,
    policy: PolicyKind,
    outcome: ExecOutcome,
    executed_idx: &mut Vec<usize>,
    skipped_idx: &mut Vec<usize>,
) -> Result<OpState, PlanFailure> {
    executed_idx.push(i);

    match outcome {
        ExecOutcome::Ok(v) => Ok(OpState::Ok(v)),
        ExecOutcome::Error(e) => match policy {
            PolicyKind::Fail => fail(
                PlanFailureCode::OpFailed,
                format!("operation '{}' failed under 'fail' policy: {e}", op.id),
            ),
            PolicyKind::Retry => fail(
                PlanFailureCode::OpFailed,
                format!(
                    "operation '{}' failed under 'retry' policy (exhausted): {e}",
                    op.id
                ),
            ),
            PolicyKind::Continue => {
                // failed op produces no Port → treat as unproduced/skip downstream.
                skipped_idx.push(i);
                executed_idx.pop(); // ran but produced no Port
                Ok(OpState::Skipped)
            }
        },
    }
}

fn run_op<F>(
    i: usize,
    op: &OpSpec,
    states: &[Option<OpState>],
    exec: &mut F,
    executed_idx: &mut Vec<usize>,
    skipped_idx: &mut Vec<usize>,
) -> Result<OpState, PlanFailure>
where
    F: FnMut(&OpSpec, Option<&Value>) -> ExecOutcome,
{
    let (policy, bound_value) = match preflight_op(op, states) {
        Preflight::InvalidPolicy(msg) => return fail(PlanFailureCode::UnknownPolicy, msg),
        Preflight::Skip => {
            skipped_idx.push(i);
            return Ok(OpState::Skipped);
        }
        Preflight::Exec { policy, bound } => (policy, bound),
    };

    let outcome = exec(op, bound_value.as_ref());
    interpret_outcome(i, op, policy, outcome, executed_idx, skipped_idx)
}

fn validate_coverage(stages: &[Vec<usize>], n: usize) -> Result<(), PlanFailure> {
    let mut seen = std::collections::HashSet::new();
    for stage in stages {
        for &i in stage {
            if i >= n {
                return fail(
                    PlanFailureCode::InvalidPlan,
                    format!("stage index {i} out of range [0,{n})"),
                );
            }
            if !seen.insert(i) {
                return fail(
                    PlanFailureCode::InvalidPlan,
                    format!("operation {i} appears in more than one stage"),
                );
            }
        }
    }
    if seen.len() != n {
        return fail(
            PlanFailureCode::InvalidPlan,
            format!(
                "plan does not cover all {n} operations (covered {})",
                seen.len()
            ),
        );
    }
    Ok(())
}