//! TransitionFired subscriber that snapshots token cost into the CostRollup register
//! on terminal pipeline stage transitions.
//!
//! When a story reaches Done, Archived, Abandoned, Superseded, or Rejected,
//! this subscriber reads the accumulated token records from disk, aggregates
//! them by agent, and writes the result into
//! [`crate::service::agents::cost_rollup`] so that status renderers and the
//! cost command can read from the register instead of re-walking the JSONL file.

use std::path::{Path, PathBuf};

use crate::pipeline_state::Stage;
use crate::slog;
use crate::slog_warn;

/// Spawn a background task that maintains the CostRollup register.
///
/// On every terminal stage transition (Done, Archived, Abandoned, Superseded,
/// Rejected), reads the token records for that story and writes an aggregated
/// [`crate::service::agents::cost_rollup::CostRollup`] to the global register.
pub(crate) fn spawn_cost_rollup_subscriber(project_root: PathBuf) {
    let mut rx = crate::pipeline_state::subscribe_transitions();
    tokio::spawn(async move {
        loop {
            match rx.recv().await {
                Ok(fired) => {
                    on_terminal_transition(&project_root, &fired).await;
                }
                Err(tokio::sync::broadcast::error::RecvError::Lagged(n)) => {
                    slog_warn!(
                        "[cost-rollup-sub] Subscriber lagged, skipped {n} event(s). \
                         Some story cost rollups may be stale until next terminal transition."
                    );
                }
                Err(tokio::sync::broadcast::error::RecvError::Closed) => break,
            }
        }
    });
}

/// Returns `true` if `stage` is a terminal pipeline stage.
///
/// Terminal stages are those from which no further work is expected:
/// Done, Archived, Abandoned, Superseded, Rejected.
/// MergeFailure variants are NOT terminal — stories can recover from them.
fn is_terminal(stage: &Stage) -> bool {
    matches!(
        stage,
        Stage::Done { .. }
            | Stage::Archived { .. }
            | Stage::Abandoned { .. }
            | Stage::Superseded { .. }
            | Stage::Rejected { .. }
    )
}

/// Snapshot the cost data for `fired.story_id` into the register when
/// `fired.after` is a terminal stage.
pub(crate) async fn on_terminal_transition(
    project_root: &Path,
    fired: &crate::pipeline_state::TransitionFired,
) {
    if !is_terminal(&fired.after) {
        return;
    }

    let story_id = &fired.story_id.0;
    let records = match crate::agents::token_usage::read_all(project_root) {
        Ok(r) => r,
        Err(e) => {
            slog_warn!("[cost-rollup-sub] Failed to read token records for '{story_id}': {e}");
            return;
        }
    };

    let summary = crate::service::agents::token::aggregate_for_story(&records, story_id);

    crate::service::agents::cost_rollup::set_rollup(
        project_root,
        story_id,
        crate::service::agents::cost_rollup::CostRollup {
            story_id: story_id.clone(),
            total_cost_usd: summary.total_cost_usd,
            agents: summary.agents,
            recorded_at: fired.at,
        },
    );

    slog!(
        "[cost-rollup-sub] Rolled up cost for '{}': ${:.4}",
        story_id,
        summary.total_cost_usd
    );
}

// ── Tests ─────────────────────────────────────────────────────────────────────

#[cfg(test)]
mod tests {
    use super::*;
    use crate::agents::TokenUsage;
    use crate::agents::token_usage::TokenUsageRecord;
    use crate::pipeline_state::{BranchName, PipelineEvent, Stage, StoryId, TransitionFired};
    use chrono::Utc;
    use std::num::NonZeroU32;

    fn make_record(story_id: &str, agent: &str, cost: f64) -> TokenUsageRecord {
        TokenUsageRecord {
            story_id: story_id.to_string(),
            agent_name: agent.to_string(),
            timestamp: Utc::now().to_rfc3339(),
            model: None,
            usage: TokenUsage {
                input_tokens: 100,
                output_tokens: 50,
                cache_creation_input_tokens: 0,
                cache_read_input_tokens: 0,
                total_cost_usd: cost,
            },
        }
    }

    fn write_records(root: &std::path::Path, records: &[TokenUsageRecord]) {
        for r in records {
            crate::agents::token_usage::append_record(root, r).unwrap();
        }
    }

    fn fired_done(story_id: &str) -> TransitionFired {
        TransitionFired {
            story_id: StoryId(story_id.to_string()),
            before: Stage::Merge {
                feature_branch: BranchName("feature/test".to_string()),
                commits_ahead: NonZeroU32::new(1).unwrap(),
                claim: None,
            },
            after: Stage::Done {
                merged_at: Utc::now(),
                merge_commit: crate::pipeline_state::GitSha("abc123".to_string()),
            },
            event: PipelineEvent::MergeSucceeded {
                merge_commit: crate::pipeline_state::GitSha("abc123".to_string()),
            },
            at: Utc::now(),
        }
    }

    fn fired_abandoned(story_id: &str) -> TransitionFired {
        TransitionFired {
            story_id: StoryId(story_id.to_string()),
            before: Stage::Coding { claim: None },
            after: Stage::Abandoned { ts: Utc::now() },
            event: PipelineEvent::Abandon,
            at: Utc::now(),
        }
    }

    fn fired_coding(story_id: &str) -> TransitionFired {
        TransitionFired {
            story_id: StoryId(story_id.to_string()),
            before: Stage::Backlog,
            after: Stage::Coding { claim: None },
            event: PipelineEvent::DepsMet,
            at: Utc::now(),
        }
    }

    // ── AC1: subscriber writes the register on terminal transitions ──────────

    #[tokio::test]
    async fn done_transition_writes_rollup() {
        let tmp = tempfile::tempdir().unwrap();
        let story_id = "1017_sub_done";

        write_records(
            tmp.path(),
            &[
                make_record(story_id, "coder-1", 1.50),
                make_record(story_id, "qa-1", 0.50),
            ],
        );

        let fired = fired_done(story_id);
        on_terminal_transition(tmp.path(), &fired).await;

        let rollup = crate::service::agents::cost_rollup::get_rollup(tmp.path(), story_id)
            .expect("rollup must exist after Done transition");
        assert!(
            (rollup.total_cost_usd - 2.0).abs() < f64::EPSILON,
            "total must be sum of all agents: {}",
            rollup.total_cost_usd
        );
        assert_eq!(rollup.agents.len(), 2, "must have 2 agent entries");
    }

    // ── AC4: multiple agents produce correct breakdown ────────────────────────

    #[tokio::test]
    async fn multiple_agents_correct_breakdown() {
        let tmp = tempfile::tempdir().unwrap();
        let story_id = "1017_sub_multi";

        write_records(
            tmp.path(),
            &[
                make_record(story_id, "coder-1", 1.00),
                make_record(story_id, "coder-1", 0.50), // second run
                make_record(story_id, "qa-1", 0.75),
                make_record(story_id, "mergemaster", 0.25),
                // Different story — must not leak into rollup
                make_record("9999_other_story", "coder-1", 99.0),
            ],
        );

        on_terminal_transition(tmp.path(), &fired_done(story_id)).await;

        let rollup = crate::service::agents::cost_rollup::get_rollup(tmp.path(), story_id)
            .expect("rollup must exist");

        // Total: 1.00 + 0.50 + 0.75 + 0.25 = 2.50
        assert!(
            (rollup.total_cost_usd - 2.50).abs() < f64::EPSILON,
            "total must be 2.50, got {}",
            rollup.total_cost_usd
        );

        // coder-1 should be aggregated: 1.00 + 0.50 = 1.50
        let coder = rollup
            .agents
            .iter()
            .find(|a| a.agent_name == "coder-1")
            .expect("coder-1 must be in agents");
        assert!(
            (coder.total_cost_usd - 1.50).abs() < f64::EPSILON,
            "coder-1 cost must be 1.50, got {}",
            coder.total_cost_usd
        );

        // Other story must NOT appear in this rollup
        assert!(
            rollup.agents.iter().all(|a| a.agent_name != "9999_other"),
            "other story's agent must not leak into rollup"
        );
    }

    // ── Non-terminal transitions are ignored ──────────────────────────────────

    #[tokio::test]
    async fn non_terminal_transition_does_not_write_rollup() {
        let tmp = tempfile::tempdir().unwrap();
        let story_id = "1017_sub_nonterminal";

        write_records(tmp.path(), &[make_record(story_id, "coder-1", 5.0)]);

        // Coding transition — not terminal
        on_terminal_transition(tmp.path(), &fired_coding(story_id)).await;

        assert!(
            crate::service::agents::cost_rollup::get_rollup(tmp.path(), story_id).is_none(),
            "non-terminal transition must not write rollup"
        );
    }

    // ── Abandoned transition is also terminal ─────────────────────────────────

    #[tokio::test]
    async fn abandoned_transition_writes_rollup() {
        let tmp = tempfile::tempdir().unwrap();
        let story_id = "1017_sub_abandoned";

        write_records(tmp.path(), &[make_record(story_id, "coder-1", 0.30)]);
        on_terminal_transition(tmp.path(), &fired_abandoned(story_id)).await;

        let rollup = crate::service::agents::cost_rollup::get_rollup(tmp.path(), story_id)
            .expect("rollup must exist after Abandoned transition");
        assert!(
            (rollup.total_cost_usd - 0.30).abs() < f64::EPSILON,
            "abandoned story cost must be 0.30, got {}",
            rollup.total_cost_usd
        );
    }

    // ── Story with no records gets a zero rollup ──────────────────────────────

    #[tokio::test]
    async fn zero_cost_story_gets_empty_rollup() {
        let tmp = tempfile::tempdir().unwrap();
        let story_id = "1017_sub_zero";

        // No records written for this story
        on_terminal_transition(tmp.path(), &fired_done(story_id)).await;

        let rollup = crate::service::agents::cost_rollup::get_rollup(tmp.path(), story_id)
            .expect("rollup must be written even for zero-cost story");
        assert_eq!(rollup.total_cost_usd, 0.0);
        assert!(rollup.agents.is_empty());
    }

    // ── Via broadcast subscriber ──────────────────────────────────────────────

    #[tokio::test]
    async fn broadcast_subscriber_reacts_to_terminal_transition() {
        crate::crdt_state::init_for_test();
        crate::db::ensure_content_store();

        let tmp = tempfile::tempdir().unwrap();
        let story_id = "1017_sub_broadcast";

        crate::db::write_item_with_content(
            story_id,
            "2_current",
            "---\nname: Test\n---\n",
            crate::db::ItemMeta::named("Test"),
        );

        write_records(tmp.path(), &[make_record(story_id, "coder-1", 1.23)]);

        spawn_cost_rollup_subscriber(tmp.path().to_path_buf());

        crate::agents::lifecycle::abandon_story(story_id).expect("abandon must succeed");

        // Give the subscriber task time to process.
        tokio::time::sleep(std::time::Duration::from_millis(200)).await;

        let rollup = crate::service::agents::cost_rollup::get_rollup(tmp.path(), story_id)
            .expect("rollup must be written via broadcast subscriber");
        assert!(
            (rollup.total_cost_usd - 1.23).abs() < f64::EPSILON,
            "rollup cost must match records: {}",
            rollup.total_cost_usd
        );
    }
}