//! Agent **live-state** — the volatile, "what is each agent doing right now"
//! projection (programme live-state, lot LS1).
//!
//! Unlike the conversation log (an append-only journal) this is a **keyed,
//! last-writer-wins** snapshot: there is exactly **one** [`LiveEntry`] per
//! [`AgentId`], replaced in place on every update. There is deliberately **no
//! append API** — stacking duplicate rows per agent is an architectural
//! anti-pattern here (it would turn a live snapshot back into a journal). The
//! only mutations are [`LiveState::upsert`] (keyed replace-or-insert) and
//! [`LiveState::prune`] (TTL + cardinality bound).
//!
//! The type is **pure** (zero I/O). Persistence is the job of the
//! [`crate::ports::LiveStateStore`] port, implemented by infrastructure in a
//! later lot.

use serde::{Deserialize, Serialize};

use crate::error::DomainError;
use crate::ids::AgentId;
use crate::mailbox::TicketId;

/// Soft bound (in characters) applied to free-text fields (`intent`,
/// `progress`): values longer than this are **truncated**, not rejected. Aligned
/// with the workstate UI task preview (`TASK_PREVIEW_MAX_CHARS`, ≈160 chars) so
/// the live state and its rendering agree on excerpt length.
pub const FIELD_PREVIEW_MAX_CHARS: usize = 160;

/// Hard anti-dump threshold (in **bytes**) for any single free-text field. A
/// value above this is **rejected** with [`DomainError::Invariant`] rather than
/// silently truncated: the soft bound trims ordinary over-long lines, while this
/// guards against a caller dumping long content (file bodies, logs) into the
/// live state. Distinct semantics: soft = truncate, hard = reject.
pub const FIELD_MAX_BYTES: usize = 2 * 1024;

/// `progress` marker stamped on an orphan row reconciled at restart (see
/// [`LiveState::reconcile_orphans`]): it records *why* a `Working`/`Waiting`/
/// `Blocked` row was downgraded to `Idle` — its session was not running when the
/// project reopened. Well under both field bounds.
pub const STALE_AT_RESTART_MARKER: &str = "(stale — session not running at restart)";

/// What an agent is doing right now, at a glance.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub enum WorkStatus {
    /// No active task — available.
    Idle,
    /// Actively working on its current `intent`.
    Working,
    /// Stuck / cannot proceed (e.g. needs a decision or input).
    Blocked,
    /// Suspended awaiting an external event (e.g. a delegation reply).
    Waiting,
    /// Current task finished.
    Done,
}

impl WorkStatus {
    /// Parses a status label (case-insensitive) into a [`WorkStatus`].
    ///
    /// Accepts exactly the five canonical labels (`idle`, `working`, `blocked`,
    /// `waiting`, `done`), ignoring surrounding whitespace and ASCII case. Returns
    /// `None` for anything else, so the caller can raise a typed error rather than
    /// guess a default.
    #[must_use]
    pub fn parse(raw: &str) -> Option<Self> {
        match raw.trim().to_ascii_lowercase().as_str() {
            "idle" => Some(Self::Idle),
            "working" => Some(Self::Working),
            "blocked" => Some(Self::Blocked),
            "waiting" => Some(Self::Waiting),
            "done" => Some(Self::Done),
            _ => None,
        }
    }

    /// The canonical, human-readable label of this status (the inverse of
    /// [`WorkStatus::parse`]): `idle`, `working`, `blocked`, `waiting` or `done`.
    #[must_use]
    pub fn label(self) -> &'static str {
        match self {
            Self::Idle => "idle",
            Self::Working => "working",
            Self::Blocked => "blocked",
            Self::Waiting => "waiting",
            Self::Done => "done",
        }
    }
}

/// A single agent's live-state row. One per [`AgentId`] in a [`LiveState`].
///
/// Construct via [`LiveEntry::new`], which enforces the field invariants
/// (soft-truncation of `intent`/`progress`, hard rejection of oversize input).
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct LiveEntry {
    /// The agent this row describes (the keyed identity for last-writer-wins).
    pub agent_id: AgentId,
    /// The ticket the agent is currently handling, if any.
    pub ticket: Option<TicketId>,
    /// Short human-readable description of the current intent (soft-bounded).
    pub intent: String,
    /// Coarse status at a glance.
    pub status: WorkStatus,
    /// Optional finer-grained progress note (soft-bounded).
    pub progress: Option<String>,
    /// The ticket of the most recent delegation this agent issued, if any.
    pub last_delegation: Option<TicketId>,
    /// Wall-clock update time in epoch milliseconds (drives `prune` ordering).
    pub updated_at_ms: u64,
}

impl LiveEntry {
    /// Builds a validated live-state entry.
    ///
    /// `intent` and `progress` are bounded: each is **rejected** if it exceeds
    /// the hard [`FIELD_MAX_BYTES`] anti-dump threshold, otherwise **truncated**
    /// to [`FIELD_PREVIEW_MAX_CHARS`] characters (never mid-codepoint).
    ///
    /// # Errors
    /// [`DomainError::Invariant`] if `intent` or `progress` exceeds
    /// [`FIELD_MAX_BYTES`] bytes.
    pub fn new(
        agent_id: AgentId,
        ticket: Option<TicketId>,
        intent: impl Into<String>,
        status: WorkStatus,
        progress: Option<String>,
        last_delegation: Option<TicketId>,
        updated_at_ms: u64,
    ) -> Result<Self, DomainError> {
        let intent = bound_text("intent", intent.into())?;
        let progress = progress.map(|p| bound_text("progress", p)).transpose()?;
        Ok(Self {
            agent_id,
            ticket,
            intent,
            status,
            progress,
            last_delegation,
            updated_at_ms,
        })
    }
}

/// Enforces the field bounds: reject above the hard byte threshold, otherwise
/// truncate to the soft character bound (char-boundary safe).
fn bound_text(field: &'static str, value: String) -> Result<String, DomainError> {
    if value.len() > FIELD_MAX_BYTES {
        return Err(DomainError::Invariant(format!(
            "live-state field `{field}` exceeds the max size of {FIELD_MAX_BYTES} bytes ({} bytes)",
            value.len()
        )));
    }
    if value.chars().count() <= FIELD_PREVIEW_MAX_CHARS {
        Ok(value)
    } else {
        Ok(value.chars().take(FIELD_PREVIEW_MAX_CHARS).collect())
    }
}

/// The live-state snapshot: one [`LiveEntry`] per agent, keyed last-writer-wins.
///
/// There is **no append API by design** (anti-journal invariant): the only
/// mutations are [`LiveState::upsert`] and [`LiveState::prune`].
#[derive(Debug, Clone, Default, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct LiveState {
    /// The current rows, at most one per [`AgentId`].
    pub entries: Vec<LiveEntry>,
}

impl LiveState {
    /// Inserts or **replaces** the row for `entry.agent_id` (last-writer-wins).
    ///
    /// Never produces a duplicate row for an agent: if an entry with the same
    /// `agent_id` already exists it is overwritten in place; otherwise the entry
    /// is appended as a new key. (This is *keyed* upsert, not an append of
    /// duplicates — see the type-level anti-journal invariant.)
    pub fn upsert(&mut self, entry: LiveEntry) {
        if let Some(slot) = self
            .entries
            .iter_mut()
            .find(|e| e.agent_id == entry.agent_id)
        {
            *slot = entry;
        } else {
            self.entries.push(entry);
        }
    }

    /// Computes the **reconciliation** of orphan rows at restart: rows whose
    /// status implies a live session (`Working`/`Waiting`/`Blocked`) but whose
    /// agent is **not** currently live according to `is_live`.
    ///
    /// At reboot a crash never runs `close_project`, so `live-state.json` can keep
    /// "ghost" rows for agents whose sessions are dead. This pure transform returns
    /// the **rewritten** rows to upsert (it does **not** mutate `self`): each orphan
    /// is downgraded to [`WorkStatus::Idle`], keeping its `intent` (trace), clearing
    /// the now-dead `ticket` and `last_delegation`, stamping a `progress` stale
    /// marker and a fresh `updated_at_ms = now_ms` (last-writer-wins).
    ///
    /// Rows that are already `Idle`/`Done`, or whose agent is still live, are
    /// **never** touched and are absent from the result. The caller persists each
    /// returned entry through the keyed [`upsert`](LiveState::upsert) (best-effort).
    #[must_use]
    pub fn reconcile_orphans(
        &self,
        is_live: impl Fn(&AgentId) -> bool,
        now_ms: u64,
    ) -> Vec<LiveEntry> {
        self.entries
            .iter()
            .filter(|e| {
                matches!(
                    e.status,
                    WorkStatus::Working | WorkStatus::Waiting | WorkStatus::Blocked
                ) && !is_live(&e.agent_id)
            })
            .map(|e| LiveEntry {
                agent_id: e.agent_id,
                ticket: None,
                intent: e.intent.clone(),
                status: WorkStatus::Idle,
                progress: Some(STALE_AT_RESTART_MARKER.to_owned()),
                last_delegation: None,
                updated_at_ms: now_ms,
            })
            .collect()
    }

    /// Drops entries older than `ttl_ms` relative to `now_ms`, then bounds the
    /// result to `max_n`, keeping the most recently updated rows.
    ///
    /// Age is `now_ms.saturating_sub(updated_at_ms)`; a row is kept while its
    /// age is `<= ttl_ms`. After the TTL sweep, if more than `max_n` rows remain
    /// they are ordered by `updated_at_ms` (most recent first, stable on ties)
    /// and truncated to `max_n`.
    pub fn prune(&mut self, now_ms: u64, ttl_ms: u64, max_n: usize) {
        self.entries
            .retain(|e| now_ms.saturating_sub(e.updated_at_ms) <= ttl_ms);
        if self.entries.len() > max_n {
            self.entries
                .sort_by(|a, b| b.updated_at_ms.cmp(&a.updated_at_ms));
            self.entries.truncate(max_n);
        }
    }
}

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

    fn aid(n: u128) -> AgentId {
        AgentId::from_uuid(uuid::Uuid::from_u128(n))
    }

    fn tid(n: u128) -> TicketId {
        TicketId::from_uuid(uuid::Uuid::from_u128(n))
    }

    #[test]
    fn work_status_parse_is_case_insensitive_and_rejects_unknown() {
        assert_eq!(WorkStatus::parse("idle"), Some(WorkStatus::Idle));
        assert_eq!(WorkStatus::parse("  Working "), Some(WorkStatus::Working));
        assert_eq!(WorkStatus::parse("BLOCKED"), Some(WorkStatus::Blocked));
        assert_eq!(WorkStatus::parse("waiting"), Some(WorkStatus::Waiting));
        assert_eq!(WorkStatus::parse("Done"), Some(WorkStatus::Done));
        assert_eq!(WorkStatus::parse("busy"), None);
        assert_eq!(WorkStatus::parse(""), None);
    }

    #[test]
    fn work_status_label_round_trips_through_parse() {
        for status in [
            WorkStatus::Idle,
            WorkStatus::Working,
            WorkStatus::Blocked,
            WorkStatus::Waiting,
            WorkStatus::Done,
        ] {
            assert_eq!(WorkStatus::parse(status.label()), Some(status));
        }
    }

    #[test]
    fn new_truncates_intent_and_progress_at_soft_bound() {
        let long = "x".repeat(FIELD_PREVIEW_MAX_CHARS + 50);
        let entry = LiveEntry::new(
            aid(1),
            None,
            long.clone(),
            WorkStatus::Working,
            Some(long.clone()),
            None,
            10,
        )
        .expect("under the hard threshold ⇒ accepted, just truncated");

        assert_eq!(entry.intent.chars().count(), FIELD_PREVIEW_MAX_CHARS);
        assert_eq!(
            entry.progress.as_deref().map(|p| p.chars().count()),
            Some(FIELD_PREVIEW_MAX_CHARS)
        );
    }

    #[test]
    fn new_keeps_short_text_verbatim() {
        let entry =
            LiveEntry::new(aid(1), None, "ship it", WorkStatus::Done, None, None, 5).unwrap();
        assert_eq!(entry.intent, "ship it");
        assert!(entry.progress.is_none());
    }

    #[test]
    fn new_rejects_intent_over_hard_byte_threshold() {
        let huge = "x".repeat(FIELD_MAX_BYTES + 1);
        let err = LiveEntry::new(aid(1), None, huge, WorkStatus::Working, None, None, 0)
            .expect_err("oversize intent must be rejected, not truncated");
        assert!(matches!(err, DomainError::Invariant(_)));
    }

    #[test]
    fn new_rejects_progress_over_hard_byte_threshold() {
        let huge = "y".repeat(FIELD_MAX_BYTES + 1);
        let err = LiveEntry::new(aid(1), None, "ok", WorkStatus::Working, Some(huge), None, 0)
            .expect_err("oversize progress must be rejected, not truncated");
        assert!(matches!(err, DomainError::Invariant(_)));
    }

    #[test]
    fn upsert_is_last_writer_wins_per_agent_no_duplicates() {
        let mut state = LiveState::default();
        state.upsert(
            LiveEntry::new(aid(1), None, "first", WorkStatus::Working, None, None, 1).unwrap(),
        );
        state.upsert(
            LiveEntry::new(
                aid(1),
                Some(tid(9)),
                "second",
                WorkStatus::Blocked,
                None,
                None,
                2,
            )
            .unwrap(),
        );

        // A second upsert for the same agent replaces, never appends.
        assert_eq!(state.entries.len(), 1, "same agent ⇒ exactly one row");
        let row = &state.entries[0];
        assert_eq!(row.intent, "second");
        assert_eq!(row.status, WorkStatus::Blocked);
        assert_eq!(row.ticket, Some(tid(9)));
    }

    #[test]
    fn upsert_distinct_agents_coexist() {
        let mut state = LiveState::default();
        state
            .upsert(LiveEntry::new(aid(1), None, "a", WorkStatus::Working, None, None, 1).unwrap());
        state.upsert(LiveEntry::new(aid(2), None, "b", WorkStatus::Idle, None, None, 1).unwrap());
        assert_eq!(state.entries.len(), 2, "distinct agents ⇒ distinct rows");
    }

    #[test]
    fn prune_drops_entries_older_than_ttl() {
        let mut state = LiveState::default();
        state.upsert(
            LiveEntry::new(aid(1), None, "stale", WorkStatus::Idle, None, None, 100).unwrap(),
        );
        state.upsert(
            LiveEntry::new(aid(2), None, "fresh", WorkStatus::Working, None, None, 900).unwrap(),
        );

        // now=1000, ttl=200 ⇒ age(aid1)=900 > 200 dropped; age(aid2)=100 kept.
        state.prune(1000, 200, 100);

        assert_eq!(state.entries.len(), 1);
        assert_eq!(state.entries[0].agent_id, aid(2));
    }

    #[test]
    fn prune_bounds_to_max_n_keeping_most_recent() {
        let mut state = LiveState::default();
        for n in 1..=5u128 {
            state.upsert(
                LiveEntry::new(
                    aid(n),
                    None,
                    "x",
                    WorkStatus::Working,
                    None,
                    None,
                    n as u64 * 10,
                )
                .unwrap(),
            );
        }

        // All within TTL; bound to 2 ⇒ keep the two highest updated_at_ms (40,50).
        state.prune(60, 1_000, 2);

        assert_eq!(state.entries.len(), 2);
        let kept: Vec<u64> = state.entries.iter().map(|e| e.updated_at_ms).collect();
        assert_eq!(kept, vec![50, 40], "most recent first, oldest dropped");
    }

    #[test]
    fn reconcile_orphans_downgrades_dead_active_rows_and_rewrites_fields() {
        let mut state = LiveState::default();
        // An orphan: Working but its agent is not live.
        state.upsert(
            LiveEntry::new(
                aid(1),
                Some(tid(7)),
                "implementing lot 2",
                WorkStatus::Working,
                Some("half done".to_owned()),
                Some(tid(8)),
                100,
            )
            .unwrap(),
        );

        // Nothing is live ⇒ aid(1) is an orphan.
        let rewritten = state.reconcile_orphans(|_| false, 999);

        assert_eq!(rewritten.len(), 1, "the single active-but-dead row is an orphan");
        let row = &rewritten[0];
        assert_eq!(row.agent_id, aid(1));
        assert_eq!(row.status, WorkStatus::Idle, "downgraded to idle");
        assert_eq!(row.intent, "implementing lot 2", "intent kept as trace");
        assert_eq!(row.ticket, None, "dead ticket cleared");
        assert_eq!(row.last_delegation, None, "dead delegation cleared");
        assert_eq!(row.progress.as_deref(), Some(STALE_AT_RESTART_MARKER));
        assert_eq!(row.updated_at_ms, 999, "stamped with the fresh now");
    }

    #[test]
    fn reconcile_orphans_covers_working_waiting_blocked_only() {
        let mut state = LiveState::default();
        state.upsert(
            LiveEntry::new(aid(1), None, "w", WorkStatus::Working, None, None, 1).unwrap(),
        );
        state.upsert(
            LiveEntry::new(aid(2), None, "a", WorkStatus::Waiting, None, None, 1).unwrap(),
        );
        state.upsert(
            LiveEntry::new(aid(3), None, "b", WorkStatus::Blocked, None, None, 1).unwrap(),
        );
        // idle/done are never orphans, even when the agent is dead.
        state.upsert(LiveEntry::new(aid(4), None, "i", WorkStatus::Idle, None, None, 1).unwrap());
        state.upsert(LiveEntry::new(aid(5), None, "d", WorkStatus::Done, None, None, 1).unwrap());

        let rewritten = state.reconcile_orphans(|_| false, 50);

        let mut ids: Vec<AgentId> = rewritten.iter().map(|e| e.agent_id).collect();
        ids.sort();
        assert_eq!(
            ids,
            vec![aid(1), aid(2), aid(3)],
            "only working/waiting/blocked rows are reconciled; idle/done untouched"
        );
    }

    #[test]
    fn reconcile_orphans_spares_live_agents() {
        let mut state = LiveState::default();
        state.upsert(
            LiveEntry::new(aid(1), None, "alive", WorkStatus::Working, None, None, 1).unwrap(),
        );
        state.upsert(
            LiveEntry::new(aid(2), None, "dead", WorkStatus::Working, None, None, 1).unwrap(),
        );

        // aid(1) is still live ⇒ spared; only aid(2) is reconciled.
        let rewritten = state.reconcile_orphans(|a| *a == aid(1), 50);

        assert_eq!(rewritten.len(), 1);
        assert_eq!(rewritten[0].agent_id, aid(2), "only the dead agent is reconciled");
    }

    #[test]
    fn reconcile_orphans_does_not_mutate_self() {
        let mut state = LiveState::default();
        state.upsert(
            LiveEntry::new(aid(1), Some(tid(1)), "x", WorkStatus::Working, None, None, 1).unwrap(),
        );
        let before = state.clone();

        let _ = state.reconcile_orphans(|_| false, 999);

        assert_eq!(state, before, "reconcile_orphans is a pure read (returns rows to upsert)");
    }

    #[test]
    fn serde_round_trip_is_camel_case() {
        let mut state = LiveState::default();
        state.upsert(
            LiveEntry::new(
                aid(7),
                Some(tid(3)),
                "review PR",
                WorkStatus::Waiting,
                Some("waiting on QA".to_owned()),
                Some(tid(4)),
                1234,
            )
            .unwrap(),
        );

        let json = serde_json::to_string(&state).unwrap();
        // Field names are camelCase…
        assert!(json.contains("\"agentId\""));
        assert!(json.contains("\"lastDelegation\""));
        assert!(json.contains("\"updatedAtMs\""));
        // …and the enum variant is camelCase too.
        assert!(json.contains("\"waiting\""));

        let back: LiveState = serde_json::from_str(&json).unwrap();
        assert_eq!(back, state, "round-trip is lossless");
    }
}