//! Workflow engine: interprets `ScriptPrimitive` values (agent, parallel,
//! pipeline, phase) by spawning subagents, collecting results, and
//! managing concurrency.
//!
//! Key design points:
//! - `Parallel` branches run concurrently (capped by semaphore) — this is
//!   the main advantage over single-turn chat.
//! - `Pipeline` branches run sequentially so each stage sees findings from
//!   the previous one.
//! - `run_workflow_tracked` accepts a `LiveState` callback that receives
//!   real-time agent status updates for the TUI panel.
//! - Findings (inter-agent notes) are scoped per invocation via an
//!   `Arc<Mutex<Vec<String>>>` threaded through `execute_primitive` and
//!   `spawn_single_agent` rather than a global static, preventing data
//!   leaks between concurrent workflow runs.

use std::collections::HashMap;
use std::sync::{Arc, Mutex};
use std::time::Duration;
use serde::{Deserialize, Serialize};
use super::script::{ScriptPrimitive, WorkflowScript};

/// The lifecycle state of an agent within a workflow run.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
pub enum AgentState {
    Idle,
    Running,
    Completed,
    Failed,
}

/// Timestamped status of one workflow agent.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct AgentStatus {
    pub state: AgentState,
    pub started_at: Option<i64>,
    pub completed_at: Option<i64>,
    pub error: Option<String>,
}

/// A single agent tracked within a workflow run.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct WorkflowAgent {
    pub id: String,
    pub name: String,
    pub status: AgentStatus,
}

/// Orchestrator for running workflow scripts: holds agent roster and a
/// shared finding accumulator visible to all pipeline stages.
#[derive(Debug, Clone)]
pub struct WorkflowEngine {
    pub agents: Vec<WorkflowAgent>,
    pub findings: Vec<String>,
}

impl WorkflowEngine {
    /// Create an empty workflow engine with no agents or findings.
    pub fn new() -> Self {
        WorkflowEngine {
            agents: Vec::new(),
            findings: Vec::new(),
        }
    }
}

/// Shared live state used by `run_workflow_tracked` to push real-time
/// agent status updates into the TUI's `WorkflowEngine`.
///
/// The closure receives `(agent_id, new_status)` and should update the
/// corresponding agent in `AppStateRest::workflow_engine`.
pub type LiveStateFn = Arc<dyn Fn(String, AgentStatus) + Send + Sync>;

/// Spawn a single synchronous subagent with the given prompt, passing it
/// any findings from earlier sibling agents. Updates live state before and
/// after to reflect Running → Completed/Failed transitions.
///
/// Flow: push agent as `Running` → build SubagentContext with prompt +
/// findings preamble, linking the `workflow_findings` Arc so the subagent's
/// `note_finding` tool pushes into the same vec → call `run_subagent`
/// (draining the event channel into a consumer so events are not blocked)
/// → push `Completed` or `Failed`.
///
/// Why: the `workflow_findings` Arc is shared by all agents within the same
/// `execute_primitive` scope, so pipeline stages can pass data between each
/// other while different workflow invocations remain isolated.
///
/// When `timeout_ms` is `Some`, the subagent is killed (abandoned on a
/// separate thread) if it does not complete within the deadline, preventing
/// a stuck stage from blocking the entire pipeline forever.
///
/// Return: the agent's text output, or an error on failure.
fn spawn_single_agent(
    agent_id: &str,
    agent_name: &str,
    prompt: &str,
    findings_snapshot: Vec<String>,
    findings: &Arc<Mutex<Vec<String>>>,
    live: Option<&LiveStateFn>,
    session_dir: &std::path::Path,
    workspaces: &[std::path::PathBuf],
    timeout_ms: Option<u64>,
) -> anyhow::Result<String> {
    use crate::app::subagent::context::build_subagent_context;
    use crate::app::subagent::engine::run_subagent;
    use crate::app::subagent::spawn::AgentDefinition;

    let started_at = chrono::Utc::now().timestamp_millis();

    // Notify UI: this agent is now running
    if let Some(f) = live {
        f(agent_id.to_string(), AgentStatus {
            state: AgentState::Running,
            started_at: Some(started_at),
            completed_at: None,
            error: None,
        });
    }

    let def = AgentDefinition::new(agent_name.to_string(), "coder".to_string())
        .with_max_steps(50);
    let mut ctx = build_subagent_context(def);
    ctx.session_dir = session_dir.to_path_buf();
    ctx.workspaces = workspaces.to_vec();

    let findings_section = if findings_snapshot.is_empty() {
        String::new()
    } else {
        format!(
            "\n\nFindings from sibling agents in this workflow run:\n{}",
            findings_snapshot
                .iter()
                .enumerate()
                .map(|(i, f)| format!("{}. {}", i + 1, f))
                .collect::<Vec<_>>()
                .join("\n")
        )
    };

    ctx.system_prompt = format!("{}{}", prompt, findings_section);
    // Link the shared findings Arc so note_finding calls within this
    // subagent write into the same vec visible to sibling agents.
    ctx.workflow_findings = Some(findings.clone());

    // Create an mpsc channel and drain events in a background thread so
    // run_subagent's blocking_send never blocks (previously the _rx was
    // dropped immediately, which would cause blocking_send to panic/fail
    // on a closed channel).
    let (tx, rx) = tokio::sync::mpsc::channel(64);
    let _drain_thread = std::thread::spawn(move || {
        // Drain all events so run_subagent's blocking_send never blocks.
        // Individual SubagentEvent items are not surfaced to the TUI —
        // the live state callbacks above handle coarse-grained Running /
        // Completed / Failed status. ToolCall / ToolResult / StepCompleted
        // events are traced at debug level for observability.
        use crate::app::subagent::event::SubagentEvent;
        let mut rx = rx;
        while let Some(event) = rx.blocking_recv() {
            match &event {
                SubagentEvent::ToolCall { _tool, _args } => {
                    tracing::debug!("[subagent] tool call: {}", _tool);
                }
                SubagentEvent::ToolResult { _tool, .. } => {
                    tracing::debug!("[subagent] tool result: {}", _tool);
                }
                SubagentEvent::StepCompleted { _step, .. } => {
                    tracing::trace!("[subagent] step {} completed", _step);
                }
                SubagentEvent::StepFailed { _step, _error } => {
                    tracing::warn!("[subagent] step {} failed: {}", _step, _error);
                }
                SubagentEvent::Completed { .. } => {
                    tracing::debug!("[subagent] completed");
                }
            }
        }
    });

    // Enforce timeout by running subagent on a separate thread and
    // waiting with a deadline. If the deadline expires, the thread is
    // abandoned (Rust threads cannot be forcibly killed, but we proceed
    // without waiting for it — the drain thread will drop when tx is
    // dropped on thread exit).
        let result = if let Some(timeout) = timeout_ms {
            let (done_tx, done_rx) = std::sync::mpsc::channel::<anyhow::Result<String>>();
            let timeout_ctx = ctx;
            let timeout_tx = tx;
            std::thread::spawn(move || {
                let _ = done_tx.send(run_subagent(timeout_ctx, timeout_tx));
            });
            match done_rx.recv_timeout(Duration::from_millis(timeout)) {
                Ok(r) => r,
                Err(_) => Err(anyhow::anyhow!(
                    "subagent '{}' timed out after {}ms",
                    agent_name, timeout,
                )),
            }
        } else {
            run_subagent(ctx, tx)
        };

    let completed_at = chrono::Utc::now().timestamp_millis();

    // Notify UI: agent completed or failed
    if let Some(f) = live {
        match &result {
            Ok(_) => f(agent_id.to_string(), AgentStatus {
                state: AgentState::Completed,
                started_at: Some(started_at),
                completed_at: Some(completed_at),
                error: None,
            }),
            Err(e) => f(agent_id.to_string(), AgentStatus {
                state: AgentState::Failed,
                started_at: Some(started_at),
                completed_at: Some(completed_at),
                error: Some(e.to_string()),
            }),
        }
    }

    result
}

type ParallelResult = (usize, anyhow::Result<Vec<String>>);

/// Recursively execute a `ScriptPrimitive` tree, respecting an overall
/// concurrency cap for parallel branches.
///
/// Flow: match the primitive →
///   `Agent` → `spawn_single_agent`
///   `Parallel` → spawn threads up to `concurrency_cap` (semaphore-gated),
///               collect results in submission order
///   `Pipeline` → execute stages sequentially; findings flow between stages
///   `Phase` → recurse (pass-through wrapper)
///
/// Why: `Parallel` uses OS threads + a semaphore so the main async event
/// loop remains responsive. `Pipeline` is sequential so each stage sees
/// findings deposited by the previous one. Findings are scoped to an
/// `Arc<Mutex<Vec<String>>>` rather than a global static, so concurrent
/// workflow runs are isolated from each other.
///
/// `timeout_ms` propagates to individual agents so that no single agent
/// can block the entire workflow beyond the configured deadline.
///
/// Return: a `Vec<String>` of all agent outputs (or error strings) in
/// the order they were submitted.
pub fn execute_primitive(
    primitive: &ScriptPrimitive,
    args: &HashMap<String, String>,
    concurrency_cap: usize,
    continue_on_error: bool,
    live: Option<&LiveStateFn>,
    session_dir: &std::path::Path,
    workspaces: &[std::path::PathBuf],
    findings: &Arc<Mutex<Vec<String>>>,
    timeout_ms: Option<u64>,
) -> anyhow::Result<Vec<String>> {
    match primitive {
        ScriptPrimitive::Agent(prompt) => {
            let resolved = resolve_template(prompt, args);
            let findings_snapshot = findings.lock().map(|f| f.clone()).unwrap_or_default();
            let agent_id = uuid::Uuid::new_v4().to_string();
            let agent_name = resolved.chars().take(40).collect::<String>();
            match spawn_single_agent(&agent_id, &agent_name, &resolved, findings_snapshot, findings, live, session_dir, workspaces, timeout_ms) {
                Ok(text) => Ok(vec![text]),
                Err(e) => {
                    if continue_on_error {
                        Ok(vec![format!("agent error: {}", e)])
                    } else {
                        Err(e)
                    }
                }
            }
        }

        ScriptPrimitive::Parallel(scripts) => {
            // All branches run concurrently, capped by semaphore.
            // This is the primary advantage over single-turn chat: multiple
            // independent subagents work simultaneously.
            // Each branch shares the same `findings` Arc so note_finding
            // calls within any branch are visible to all other branches.
            let semaphore = Arc::new(Semaphore::new(concurrency_cap.max(1)));
            let results: Arc<Mutex<Vec<ParallelResult>>> =
                Arc::new(Mutex::new(Vec::new()));

            let handles: Vec<_> = scripts
                .iter()
                .enumerate()
                .map(|(idx, script)| {
                    let script = script.clone();
                    let args = args.clone();
                    let sem = Arc::clone(&semaphore);
                    let results = Arc::clone(&results);
                    let cap = concurrency_cap;
                    let live_clone = live.cloned();
                    let session_dir = session_dir.to_path_buf();
                    let workspaces = workspaces.to_vec();
                    let findings = Arc::clone(findings);
                    let to = timeout_ms;

                    std::thread::spawn(move || {
                        let _permit = sem.acquire();
                        let result = execute_primitive(
                            &script, &args, cap, continue_on_error,
                            live_clone.as_ref(),
                            &session_dir,
                            &workspaces,
                            &findings,
                            to,
                        );
                        if let Ok(mut locked) = results.lock() {
                            locked.push((idx, result));
                        }
                    })
                })
                .collect();

            for handle in handles {
                let _ = handle.join();
            }

            let mut locked = results.lock().map_err(|_| anyhow::anyhow!("parallel results lock poisoned"))?;
            locked.sort_by_key(|(idx, _)| *idx);
            let mut all = Vec::new();
            for (_, res) in locked.drain(..) {
                match res {
                    Ok(outputs) => all.extend(outputs),
                    Err(e) => all.push(format!("agent error: {}", e)),
                }
            }
            Ok(all)
        }

        ScriptPrimitive::Pipeline(scripts) => {
            // Sequential: each stage runs only after the previous completes.
            //
            // Why: parallel execution defeats the purpose of a pipeline whose
            // stages are supposed to build on each other's output. Findings
            // written by stage N are visible to stage N+1 through the shared
            // `findings` Arc (same isolation scope as parent).
            let mut all = Vec::new();
            for (idx, script) in scripts.iter().enumerate() {
                match execute_primitive(script, args, concurrency_cap, continue_on_error, live, session_dir, workspaces, findings, timeout_ms) {
                    Ok(outputs) => all.extend(outputs),
                    Err(e) => {
                        if continue_on_error {
                            all.push(format!("pipeline stage {} error: {}", idx, e));
                        } else {
                            return Err(e);
                        }
                    }
                }
            }
            Ok(all)
        }

        ScriptPrimitive::Phase { name: _name, script } => {
            execute_primitive(script, args, concurrency_cap, continue_on_error, live, session_dir, workspaces, findings, timeout_ms)
        }
    }
}

/// Run a `WorkflowScript` with the given template arguments and produce a
/// summary string. Uses no live-state callback.
///
/// Return: a human-readable summary string.
pub fn run_workflow(
    script: &WorkflowScript,
    args: &HashMap<String, String>,
    session_dir: &std::path::Path,
    workspaces: &[std::path::PathBuf],
) -> anyhow::Result<String> {
    run_workflow_tracked(script, args, None, session_dir, workspaces)
}

/// Run a `WorkflowScript` with real-time live-state callbacks so the TUI
/// panel updates as each agent transitions between Idle/Running/Done/Failed.
///
/// Flow: create an empty findings Arc (scoped to this invocation) → cap
/// concurrency to 8 → call `execute_primitive` with the live callback and
/// findings → format results.
///
/// Why: findings are scoped to an `Arc<Mutex<Vec<String>>>` rather than a
/// global static, so concurrent `run_workflow_tracked` calls from different
/// spawn_agents invocations remain fully isolated.
///
/// Return: a human-readable summary string.
pub fn run_workflow_tracked(
    script: &WorkflowScript,
    args: &HashMap<String, String>,
    live: Option<LiveStateFn>,
    session_dir: &std::path::Path,
    workspaces: &[std::path::PathBuf],
) -> anyhow::Result<String> {
    let concurrency_cap = if script.options.max_concurrency > 0 {
        script.options.max_concurrency.min(10) // allow up to 10 parallel agents
    } else {
        10
    };

    let live_ref = live.as_ref();
    let findings = Arc::new(Mutex::new(Vec::new()));
    let results = execute_primitive(
        &script.script, args, concurrency_cap,
        script.options.continue_on_error, live_ref,
        session_dir, workspaces, &findings,
        script.options.timeout_ms,
    )?;

    let summary = if results.is_empty() {
        "workflow completed with no output".to_string()
    } else {
        format!(
            "workflow '{}' completed. {} agent result(s):\n{}",
            script.name,
            results.len(),
            results
                .iter()
                .enumerate()
                .map(|(i, r)| format!("[{}] {}", i + 1, r.lines().next().unwrap_or(r)))
                .collect::<Vec<_>>()
                .join("\n")
        )
    };

    Ok(summary)
}

/// Simple template engine: replace `{{key}}` placeholders with values
/// from `args`.
///
/// Why: a structured template engine is unnecessary for the limited
/// use-case; this is intentionally simple and safe.
fn resolve_template(template: &str, args: &HashMap<String, String>) -> String {
    let mut result = template.to_string();
    for (key, value) in args {
        result = result.replace(&format!("{{{{{}}}}}", key), value);
    }
    result
}

/// A counting semaphore built from a `Mutex` + `Condvar`.
///
/// Used by `execute_primitive` to cap concurrent parallel branches.
///
/// Panic-safety: if a thread panics while holding a permit, the Mutex
/// becomes poisoned. Both `acquire` and the `Drop` implementation recover
/// from poisoned mutexes by discarding the poison, ensuring the semaphore
/// remains usable after a thread panic.
struct Semaphore {
    count: Mutex<usize>,
    condvar: std::sync::Condvar,
}

impl Semaphore {
    fn new(count: usize) -> Self {
        Semaphore {
            count: Mutex::new(count),
            condvar: std::sync::Condvar::new(),
        }
    }

    fn acquire(&self) -> SemaphoreGuard<'_> {
        let mut count = self.count.lock().unwrap_or_else(|e| {
            tracing::warn!("[semaphore] mutex poisoned in acquire, recovering");
            e.into_inner()
        });
        while *count == 0 {
            count = self.condvar.wait(count).unwrap_or_else(|e| {
                tracing::warn!("[semaphore] mutex poisoned in wait, recovering");
                e.into_inner()
            });
        }
        *count -= 1;
        SemaphoreGuard { sem: self }
    }
}

struct SemaphoreGuard<'a> {
    sem: &'a Semaphore,
}

impl<'a> Drop for SemaphoreGuard<'a> {
    fn drop(&mut self) {
        let mut count = self.sem.count.lock().unwrap_or_else(|e| {
            tracing::warn!("[semaphore] mutex poisoned in drop, recovering");
            e.into_inner()
        });
        *count += 1;
        self.sem.condvar.notify_one();
    }
}