//! Auto-assign: scan pipeline stages and dispatch free agents to unassigned stories.

use crate::config::ProjectConfig;
use crate::slog;
use crate::slog_error;
use crate::slog_warn;
use crate::worktree;
use std::path::Path;

use super::super::super::PipelineStage;
use super::super::AgentPool;
use super::scan::{
    count_active_agents_for_stage, find_free_agent_for_stage, is_agent_free,
    is_story_assigned_for_stage, scan_stage_items,
};
use super::story_checks::{
    has_merge_failure, has_review_hold, is_story_blocked, read_story_front_matter_agent,
};

impl AgentPool {
    pub async fn auto_assign_available_work(&self, project_root: &Path) {
        let config = match ProjectConfig::load(project_root) {
            Ok(c) => c,
            Err(e) => {
                slog_warn!("[auto-assign] Failed to load project config: {e}");
                return;
            }
        };

        // Process each active pipeline stage in order.
        let stages: [(&str, PipelineStage); 3] = [
            ("2_current", PipelineStage::Coder),
            ("3_qa", PipelineStage::Qa),
            ("4_merge", PipelineStage::Mergemaster),
        ];

        for (stage_dir, stage) in &stages {
            let items = scan_stage_items(project_root, stage_dir);
            if items.is_empty() {
                continue;
            }

            for story_id in &items {
                // Items marked with review_hold (e.g. spikes after QA passes) stay
                // in their current stage for human review — don't auto-assign agents.
                if has_review_hold(project_root, stage_dir, story_id) {
                    continue;
                }

                // Skip blocked stories (retry limit exceeded).
                if is_story_blocked(project_root, stage_dir, story_id) {
                    continue;
                }

                // Skip stories in 4_merge/ that already have a reported merge failure.
                // These need human intervention — auto-assigning a new mergemaster
                // would just waste tokens on the same broken merge.
                if *stage == PipelineStage::Mergemaster
                    && has_merge_failure(project_root, stage_dir, story_id)
                {
                    continue;
                }

                // AC6: Detect empty-diff stories in 4_merge/ before starting a
                // mergemaster. If the worktree has no commits on the feature branch,
                // write a merge_failure and block the story immediately.
                if *stage == PipelineStage::Mergemaster
                    && let Some(wt_path) = worktree::find_worktree_path(project_root, story_id)
                    && !crate::agents::gates::worktree_has_committed_work(&wt_path)
                {
                    slog_warn!(
                        "[auto-assign] Story '{story_id}' in 4_merge/ has no commits \
                         on feature branch. Writing merge_failure and blocking."
                    );
                    let story_path = project_root
                        .join(".huskies/work")
                        .join(stage_dir)
                        .join(format!("{story_id}.md"));
                    let empty_diff_reason = "Feature branch has no code changes — the coder agent \
                         did not produce any commits.";
                    let _ = crate::io::story_metadata::write_merge_failure(
                        &story_path,
                        empty_diff_reason,
                    );
                    let _ = crate::io::story_metadata::write_blocked(&story_path);
                    let _ = self.watcher_tx.send(crate::io::watcher::WatcherEvent::StoryBlocked {
                        story_id: story_id.to_string(),
                        reason: empty_diff_reason.to_string(),
                    });
                    continue;
                }

                // Re-acquire the lock on each iteration to see state changes
                // from previous start_agent calls in the same pass.
                let preferred_agent =
                    read_story_front_matter_agent(project_root, stage_dir, story_id);

                // Check max_coders limit for the Coder stage before agent selection.
                // If the pool is full, all remaining items in this stage wait.
                if *stage == PipelineStage::Coder
                    && let Some(max) = config.max_coders
                {
                    let agents_lock = match self.agents.lock() {
                        Ok(a) => a,
                        Err(e) => {
                            slog_error!("[auto-assign] Failed to lock agents: {e}");
                            break;
                        }
                    };
                    let active = count_active_agents_for_stage(&config, &agents_lock, stage);
                    if active >= max {
                        slog!(
                            "[auto-assign] Coder pool full ({active}/{max}); remaining items in {stage_dir}/ will wait."
                        );
                        break;
                    }
                }

                // Outcome: (already_assigned, chosen_agent, preferred_busy, stage_mismatch)
                // preferred_busy=true means the story has a specific agent requested but it is
                // currently occupied — the story should wait rather than fall back.
                // stage_mismatch=true means the preferred agent's stage doesn't match the
                // pipeline stage, so we fell back to a generic stage agent.
                let (already_assigned, free_agent, preferred_busy, stage_mismatch) = {
                    let agents = match self.agents.lock() {
                        Ok(a) => a,
                        Err(e) => {
                            slog_error!("[auto-assign] Failed to lock agents: {e}");
                            break;
                        }
                    };
                    let assigned = is_story_assigned_for_stage(&config, &agents, story_id, stage);
                    if assigned {
                        (true, None, false, false)
                    } else if let Some(ref pref) = preferred_agent {
                        // Story has a front-matter agent preference.
                        // Verify the preferred agent's stage matches the current
                        // pipeline stage — a coder shouldn't be assigned to QA.
                        let pref_stage_matches = config
                            .find_agent(pref)
                            .map(|cfg| super::super::super::agent_config_stage(cfg) == *stage)
                            .unwrap_or(false);
                        if !pref_stage_matches {
                            // Stage mismatch — fall back to any free agent for this stage.
                            let free = find_free_agent_for_stage(&config, &agents, stage)
                                .map(|s| s.to_string());
                            (false, free, false, true)
                        } else if is_agent_free(&agents, pref) {
                            (false, Some(pref.clone()), false, false)
                        } else {
                            (false, None, true, false)
                        }
                    } else {
                        let free = find_free_agent_for_stage(&config, &agents, stage)
                            .map(|s| s.to_string());
                        (false, free, false, false)
                    }
                };

                if already_assigned {
                    // Story already has an active agent — skip silently.
                    continue;
                }

                if preferred_busy {
                    // The story requests a specific agent that is currently busy.
                    // Do not fall back to a different agent; let this story wait.
                    slog!(
                        "[auto-assign] Preferred agent '{}' busy for '{story_id}'; story will wait.",
                        preferred_agent.as_deref().unwrap_or("?")
                    );
                    continue;
                }

                if stage_mismatch {
                    slog!(
                        "[auto-assign] Preferred agent '{}' stage mismatch for '{story_id}' in {stage_dir}/; falling back to stage-appropriate agent.",
                        preferred_agent.as_deref().unwrap_or("?")
                    );
                }

                match free_agent {
                    Some(agent_name) => {
                        slog!(
                            "[auto-assign] Assigning '{agent_name}' to '{story_id}' in {stage_dir}/"
                        );
                        if let Err(e) = self
                            .start_agent(project_root, story_id, Some(&agent_name), None)
                            .await
                        {
                            slog!(
                                "[auto-assign] Failed to start '{agent_name}' for '{story_id}': {e}"
                            );
                        }
                    }
                    None => {
                        // No free agents of this type — stop scanning this stage.
                        slog!(
                            "[auto-assign] All {:?} agents busy; remaining items in {stage_dir}/ will wait.",
                            stage
                        );
                        break;
                    }
                }
            }
        }
    }
}

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

#[cfg(test)]
mod tests {
    use super::super::super::AgentPool;
    use crate::agents::AgentStatus;
    use crate::io::watcher::WatcherEvent;
    use tokio::sync::broadcast;

    /// Story 203: auto_assign_available_work must detect a story in 2_current/
    /// with no active agent and start an agent for it.
    #[tokio::test]
    async fn auto_assign_picks_up_story_queued_in_current() {
        let tmp = tempfile::tempdir().unwrap();
        let sk = tmp.path().join(".huskies");
        let current = sk.join("work/2_current");
        std::fs::create_dir_all(&current).unwrap();
        std::fs::write(
            sk.join("project.toml"),
            "[[agent]]\nname = \"coder-1\"\nstage = \"coder\"\n",
        )
        .unwrap();
        // Place the story in 2_current/ (simulating the "queued" state).
        std::fs::write(current.join("story-3.md"), "---\nname: Story 3\n---\n").unwrap();

        let pool = AgentPool::new_test(3001);
        // No agents are running — coder-1 is free.

        // auto_assign will try to call start_agent, which will attempt to create
        // a worktree (will fail without a git repo) — that is fine. We only need
        // to verify the agent is registered as Pending before the background
        // task eventually fails.
        pool.auto_assign_available_work(tmp.path()).await;

        let agents = pool.agents.lock().unwrap();
        let has_pending = agents.values().any(|a| {
            a.agent_name == "coder-1"
                && matches!(a.status, AgentStatus::Pending | AgentStatus::Running)
        });
        assert!(
            has_pending,
            "auto_assign should have started coder-1 for story-3, but pool is empty"
        );
    }

    /// Story 265: auto_assign_available_work must skip spikes in 3_qa/ that
    /// have review_hold: true set in their front matter.
    #[tokio::test]
    async fn auto_assign_skips_spikes_with_review_hold() {
        let tmp = tempfile::tempdir().unwrap();
        let root = tmp.path();

        // Create project.toml with a QA agent.
        let sk = root.join(".huskies");
        std::fs::create_dir_all(&sk).unwrap();
        std::fs::write(
            sk.join("project.toml"),
            "[[agents]]\nname = \"qa\"\nrole = \"qa\"\nmodel = \"test\"\nprompt = \"test\"\n",
        )
        .unwrap();

        // Put a spike in 3_qa/ with review_hold: true.
        let qa_dir = root.join(".huskies/work/3_qa");
        std::fs::create_dir_all(&qa_dir).unwrap();
        std::fs::write(
            qa_dir.join("20_spike_test.md"),
            "---\nname: Test Spike\nreview_hold: true\n---\n# Spike\n",
        )
        .unwrap();

        let (watcher_tx, _) = broadcast::channel::<WatcherEvent>(4);
        let pool = AgentPool::new(3001, watcher_tx);

        pool.auto_assign_available_work(root).await;

        // No agent should have been started for the spike.
        let agents = pool.agents.lock().unwrap();
        assert!(
            agents.is_empty(),
            "No agents should be assigned to a spike with review_hold"
        );
    }

    // ── Story 279: auto-assign respects agent stage from front matter ──────────

    /// When a story in 3_qa/ has `agent: coder-1` in its front matter but
    /// coder-1 is a coder-stage agent, auto-assign must NOT assign coder-1.
    /// Instead it should fall back to a free QA-stage agent.
    #[tokio::test]
    async fn auto_assign_ignores_coder_preference_when_story_is_in_qa_stage() {
        let tmp = tempfile::tempdir().unwrap();
        let sk = tmp.path().join(".huskies");
        let qa_dir = sk.join("work/3_qa");
        std::fs::create_dir_all(&qa_dir).unwrap();
        std::fs::write(
            sk.join("project.toml"),
            "[[agent]]\nname = \"coder-1\"\nstage = \"coder\"\n\n\
             [[agent]]\nname = \"qa-1\"\nstage = \"qa\"\n",
        )
        .unwrap();
        // Story in 3_qa/ with a preferred coder-stage agent.
        std::fs::write(
            qa_dir.join("story-qa1.md"),
            "---\nname: QA Story\nagent: coder-1\n---\n",
        )
        .unwrap();

        let pool = AgentPool::new_test(3001);

        pool.auto_assign_available_work(tmp.path()).await;

        let agents = pool.agents.lock().unwrap();
        // coder-1 must NOT have been assigned (wrong stage for 3_qa/).
        let coder_assigned = agents.values().any(|a| {
            a.agent_name == "coder-1"
                && matches!(a.status, AgentStatus::Pending | AgentStatus::Running)
        });
        assert!(
            !coder_assigned,
            "coder-1 should not be assigned to a QA-stage story"
        );
        // qa-1 should have been assigned instead.
        let qa_assigned = agents.values().any(|a| {
            a.agent_name == "qa-1"
                && matches!(a.status, AgentStatus::Pending | AgentStatus::Running)
        });
        assert!(
            qa_assigned,
            "qa-1 should be assigned as fallback for the QA-stage story"
        );
    }

    /// When a story in 2_current/ has `agent: coder-1` in its front matter and
    /// coder-1 is a coder-stage agent, auto-assign must respect the preference
    /// and assign coder-1 (not fall back to some other coder).
    #[tokio::test]
    async fn auto_assign_respects_coder_preference_when_story_is_in_current_stage() {
        let tmp = tempfile::tempdir().unwrap();
        let sk = tmp.path().join(".huskies");
        let current_dir = sk.join("work/2_current");
        std::fs::create_dir_all(&current_dir).unwrap();
        std::fs::write(
            sk.join("project.toml"),
            "[[agent]]\nname = \"coder-1\"\nstage = \"coder\"\n\n\
             [[agent]]\nname = \"coder-2\"\nstage = \"coder\"\n",
        )
        .unwrap();
        // Story in 2_current/ with a preferred coder-1 agent.
        std::fs::write(
            current_dir.join("story-pref.md"),
            "---\nname: Coder Story\nagent: coder-1\n---\n",
        )
        .unwrap();

        let pool = AgentPool::new_test(3001);

        pool.auto_assign_available_work(tmp.path()).await;

        let agents = pool.agents.lock().unwrap();
        // coder-1 should have been picked (it matches the stage and is preferred).
        let coder1_assigned = agents.values().any(|a| {
            a.agent_name == "coder-1"
                && matches!(a.status, AgentStatus::Pending | AgentStatus::Running)
        });
        assert!(
            coder1_assigned,
            "coder-1 should be assigned when it matches the stage and is preferred"
        );
        // coder-2 must NOT be assigned (not preferred).
        let coder2_assigned = agents.values().any(|a| {
            a.agent_name == "coder-2"
                && matches!(a.status, AgentStatus::Pending | AgentStatus::Running)
        });
        assert!(
            !coder2_assigned,
            "coder-2 should not be assigned when coder-1 is explicitly preferred"
        );
    }

    /// When the preferred agent's stage mismatches and no other agent of the
    /// correct stage is available, auto-assign must not start any agent for that
    /// story (no panic, no error).
    #[tokio::test]
    async fn auto_assign_stage_mismatch_with_no_fallback_starts_no_agent() {
        let tmp = tempfile::tempdir().unwrap();
        let sk = tmp.path().join(".huskies");
        let qa_dir = sk.join("work/3_qa");
        std::fs::create_dir_all(&qa_dir).unwrap();
        // Only a coder agent is configured — no QA agent exists.
        std::fs::write(
            sk.join("project.toml"),
            "[[agent]]\nname = \"coder-1\"\nstage = \"coder\"\n",
        )
        .unwrap();
        // Story in 3_qa/ requests coder-1 (wrong stage) and no QA agent exists.
        std::fs::write(
            qa_dir.join("story-noqa.md"),
            "---\nname: QA Story No Agent\nagent: coder-1\n---\n",
        )
        .unwrap();

        let pool = AgentPool::new_test(3001);

        // Must not panic.
        pool.auto_assign_available_work(tmp.path()).await;

        let agents = pool.agents.lock().unwrap();
        assert!(
            agents.is_empty(),
            "No agent should be started when no stage-appropriate agent is available"
        );
    }

    /// Two concurrent auto_assign_available_work calls must not assign the same
    /// agent to two stories simultaneously.  After both complete, at most one
    /// Pending/Running entry must exist per agent name.
    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
    async fn toctou_concurrent_auto_assign_no_duplicate_agent_assignments() {
        use std::fs;
        use std::sync::Arc;

        let tmp = tempfile::tempdir().unwrap();
        let root = tmp.path().to_path_buf();

        let sk_dir = root.join(".huskies");
        // Two stories waiting in 2_current, one coder agent.
        fs::create_dir_all(sk_dir.join("work/2_current")).unwrap();
        fs::write(
            sk_dir.join("project.toml"),
            "[[agent]]\nname = \"coder-1\"\n",
        )
        .unwrap();
        fs::write(
            sk_dir.join("work/2_current/86_story_foo.md"),
            "---\nname: Foo\n---\n",
        )
        .unwrap();
        fs::write(
            sk_dir.join("work/2_current/130_story_bar.md"),
            "---\nname: Bar\n---\n",
        )
        .unwrap();

        let pool = Arc::new(AgentPool::new_test(3099));

        // Run two concurrent auto_assign calls.
        let pool1 = pool.clone();
        let root1 = root.clone();
        let t1 = tokio::spawn(async move { pool1.auto_assign_available_work(&root1).await });

        let pool2 = pool.clone();
        let root2 = root.clone();
        let t2 = tokio::spawn(async move { pool2.auto_assign_available_work(&root2).await });

        let _ = tokio::join!(t1, t2);

        // At most one Pending/Running entry should exist for coder-1.
        let agents = pool.agents.lock().unwrap();
        let active_coder_count = agents
            .values()
            .filter(|a| {
                a.agent_name == "coder-1"
                    && matches!(a.status, AgentStatus::Pending | AgentStatus::Running)
            })
            .count();

        assert!(
            active_coder_count <= 1,
            "coder-1 must not be assigned to more than one story simultaneously; \
             found {active_coder_count} active entries"
        );
    }
}