//! DAG shape builders — every operation as a template over the shared
//! node primitives — plus submit-time cycle validation (petgraph is
//! confined to this validation; the runtime store stays the plain
//! `Vec<Node>` + `deps`).
//!
//! ```text
//! rebuild(a):        Prebuild(a) → StopForUpdate(a) → Swap(a) →(any) Reconcile(a)
//! graceful-stop(a):  [wanted=Offline]  Signal(a) → Drain(a) → Reconcile(a)
//! restart(a):        StopForUpdate(a) → Reconcile(a)      (wanted unchanged)
//! start(a):          [wanted=Up]       Reconcile(a)
//! stop(a):           [wanted=Offline]  Reconcile(a)
//! spawn(a):          [wanted=Up]  Create(a) → WriteDropin(a) → Reconcile(a)
//! perm-change(a):    WritePermFile(a) → «rebuild subgraph»
//! meta-update(inp):  MetaLock(inp) → «fan-out rebuild(a) per affected a»
//! startup sweep:     MetaLock(hyperhive, non-fatal) → «fan-out rebuild(stale a)»
//! ```

use anyhow::{Result, bail};

use super::model::{DagSpec, Dep, DepWhen, NodeKind, NodeSpec, PermPayload, Source, Template};
use crate::coordinator::TransientKind;

/// After-ok edge on the previous node — the common chain link.
fn after_ok(on: u32) -> Vec<Dep> {
    vec![Dep {
        on,
        when: DepWhen::AfterOk,
    }]
}

/// The rebuild node chain. `Reconcile` deps on `Swap` with `AfterAny`:
/// it must run even when the profile swap failed, so a previously-up
/// agent comes back on its old config (today's recovery-start). This
/// is the only `AfterAny` edge in v1.
fn rebuild_nodes(relock: bool, base: u32) -> Vec<NodeSpec> {
    vec![
        NodeSpec {
            kind: NodeKind::Prebuild { relock },
            deps: if base == 0 {
                Vec::new()
            } else {
                after_ok(base - 1)
            },
        },
        NodeSpec {
            kind: NodeKind::StopForUpdate,
            deps: after_ok(base),
        },
        NodeSpec {
            kind: NodeKind::Swap,
            deps: after_ok(base + 1),
        },
        NodeSpec {
            kind: NodeKind::Reconcile,
            deps: vec![Dep {
                on: base + 2,
                when: DepWhen::AfterAny,
            }],
        },
    ]
}

/// One uniform rebuild shape — no `was_running` branch. `StopForUpdate`
/// noops when already down; the tail `Reconcile` auto-noops the start
/// when `wanted = Offline` (a rebuild of a deliberately-stopped agent
/// leaves it stopped). `relock = false` only for meta-update cascade
/// children.
pub fn rebuild(
    agent: &str,
    source: Source,
    reason: String,
    parent_id: Option<u64>,
    relock: bool,
) -> DagSpec {
    DagSpec {
        template: Template::Rebuild,
        agent: agent.to_owned(),
        source,
        reason,
        parent_id,
        approval_id: None,
        inputs: Vec::new(),
        perm_payload: None,
        transient: Some(TransientKind::Rebuilding),
        nodes: rebuild_nodes(relock, 0),
    }
}

/// Approval-driven deploy (`ApplyCommit` / `MergeConfigPr`): the whole
/// two-phase pipeline stays one opaque node in v1 (design doc §9) —
/// wire-visible as a `rebuild` card like today.
pub fn approval_deploy(agent: &str, approval_id: i64, reason: String) -> DagSpec {
    DagSpec {
        template: Template::Rebuild,
        agent: agent.to_owned(),
        source: Source::Approval,
        reason,
        parent_id: None,
        approval_id: Some(approval_id),
        inputs: Vec::new(),
        perm_payload: None,
        transient: Some(TransientKind::Rebuilding),
        nodes: vec![NodeSpec {
            kind: NodeKind::ApprovalDeploy,
            deps: Vec::new(),
        }],
    }
}

/// Graceful stop: cheap `Signal` fires immediately (no build slot), the
/// `Drain` awaits the harness checkpoint (bounded), and the tail
/// `Reconcile` performs the actual container stop — the caller sets
/// `wanted = Offline` at submit time. A whole-hive graceful stop
/// therefore signals every agent up front and overlaps every drain,
/// replacing the old detached-watcher thread structurally.
pub fn graceful_stop(agent: &str, source: Source, reason: String) -> DagSpec {
    DagSpec {
        template: Template::GracefulStop,
        agent: agent.to_owned(),
        source,
        reason,
        parent_id: None,
        approval_id: None,
        inputs: Vec::new(),
        perm_payload: None,
        transient: Some(TransientKind::Stopping),
        nodes: vec![
            NodeSpec {
                kind: NodeKind::Signal,
                deps: Vec::new(),
            },
            NodeSpec {
                kind: NodeKind::Drain,
                deps: after_ok(0),
            },
            NodeSpec {
                kind: NodeKind::Reconcile,
                deps: after_ok(1),
            },
        ],
    }
}

/// Restart: mechanical stop, then converge back to `wanted`
/// (unchanged) — a stop + start for a wanted-up agent.
pub fn restart(agent: &str, source: Source, reason: String) -> DagSpec {
    DagSpec {
        template: Template::Restart,
        agent: agent.to_owned(),
        source,
        reason,
        parent_id: None,
        approval_id: None,
        inputs: Vec::new(),
        perm_payload: None,
        transient: Some(TransientKind::Restarting),
        nodes: vec![
            NodeSpec {
                kind: NodeKind::StopForUpdate,
                deps: Vec::new(),
            },
            NodeSpec {
                kind: NodeKind::Reconcile,
                deps: after_ok(0),
            },
        ],
    }
}

/// Single-`Reconcile` DAG: `Start` / `Stop` (caller writes `wanted`
/// first) and the boot-time `Reconcile` converge (wanted untouched).
pub fn reconcile_only(
    template: Template,
    agent: &str,
    source: Source,
    reason: String,
    transient: Option<TransientKind>,
) -> DagSpec {
    DagSpec {
        template,
        agent: agent.to_owned(),
        source,
        reason,
        parent_id: None,
        approval_id: None,
        inputs: Vec::new(),
        perm_payload: None,
        transient,
        nodes: vec![NodeSpec {
            kind: NodeKind::Reconcile,
            deps: Vec::new(),
        }],
    }
}

/// First-deploy spawn (approval-driven): pre-start provisioning +
/// `nixos-container create`, drop-in write, then `Reconcile` starts the
/// container (`wanted = Up` written at approve time).
pub fn spawn(agent: &str, approval_id: i64, reason: String) -> DagSpec {
    DagSpec {
        template: Template::Spawn,
        agent: agent.to_owned(),
        source: Source::Approval,
        reason,
        parent_id: None,
        approval_id: Some(approval_id),
        inputs: Vec::new(),
        perm_payload: None,
        transient: Some(TransientKind::Spawning),
        nodes: vec![
            NodeSpec {
                kind: NodeKind::Create,
                deps: Vec::new(),
            },
            NodeSpec {
                kind: NodeKind::WriteDropin,
                deps: after_ok(0),
            },
            NodeSpec {
                kind: NodeKind::Reconcile,
                deps: after_ok(1),
            },
        ],
    }
}

/// Perm change: commit the JSON file(s), then the rebuild subgraph so
/// the updated `HIVE_TOOL_GROUPS` / `HIVE_CAPABILITIES` env var takes
/// effect in the container.
pub fn perm_change(agent: &str, source: Source, reason: String, payload: PermPayload) -> DagSpec {
    let mut nodes = vec![NodeSpec {
        kind: NodeKind::WritePermFile,
        deps: Vec::new(),
    }];
    nodes.extend(rebuild_nodes(true, 1));
    DagSpec {
        template: Template::PermChange,
        agent: agent.to_owned(),
        source,
        reason,
        parent_id: None,
        approval_id: None,
        inputs: Vec::new(),
        perm_payload: Some(payload),
        transient: Some(TransientKind::Rebuilding),
        nodes,
    }
}

/// Meta-input lock bump. Child `Rebuild` DAGs fan out on completion —
/// appended *after* the bump lands so their prebuilds run against the
/// post-bump lock (and so a failed bump simply fans out nothing,
/// replacing the old pre-enqueue + `cancel_children` dance).
pub fn meta_update(
    inputs: Vec<String>,
    source: Source,
    reason: String,
    approval_id: Option<i64>,
) -> DagSpec {
    DagSpec {
        template: Template::MetaUpdate,
        agent: "hyperhive".to_owned(),
        source,
        reason,
        parent_id: None,
        approval_id,
        inputs,
        perm_payload: None,
        transient: None,
        nodes: vec![NodeSpec {
            kind: NodeKind::MetaLock {
                sweep: false,
                fanout: None,
            },
            deps: Vec::new(),
        }],
    }
}

/// Boot-time sweep parent: bump meta's hyperhive input (non-fatal),
/// then fan out `Rebuild` children for the precomputed stale agent
/// list (topology-sorted by the caller).
pub fn startup_sweep(reason: String, stale_agents: Vec<String>) -> DagSpec {
    DagSpec {
        template: Template::StartupSweep,
        agent: "hyperhive".to_owned(),
        source: Source::AutoUpdate,
        reason,
        parent_id: None,
        approval_id: None,
        inputs: Vec::new(),
        perm_payload: None,
        transient: None,
        nodes: vec![NodeSpec {
            kind: NodeKind::MetaLock {
                sweep: true,
                fanout: Some(stale_agents),
            },
            deps: Vec::new(),
        }],
    }
}

/// Validate a spec before it enters the queue: node ids are dense
/// (index = id), deps reference existing nodes, and the dep graph is
/// acyclic (petgraph `toposort`). Rejecting cycles here fixes the old
/// queue's documented "circular dep silently deadlocks forever" caveat.
pub fn validate(spec: &DagSpec) -> Result<()> {
    if spec.nodes.is_empty() {
        bail!("dag spec {:?} has no nodes", spec.template);
    }
    let n = spec.nodes.len();
    let mut graph = petgraph::graph::DiGraph::<u32, ()>::new();
    let idx: Vec<_> = (0..n)
        .map(|i| graph.add_node(u32::try_from(i).unwrap_or(u32::MAX)))
        .collect();
    for (i, node) in spec.nodes.iter().enumerate() {
        for dep in &node.deps {
            let Some(&dep_idx) = idx.get(dep.on as usize) else {
                bail!(
                    "dag spec {:?} node {i} depends on unknown node {}",
                    spec.template,
                    dep.on
                );
            };
            graph.add_edge(dep_idx, idx[i], ());
        }
    }
    if petgraph::algo::toposort(&graph, None).is_err() {
        bail!("dag spec {:?} contains a dependency cycle", spec.template);
    }
    Ok(())
}