use std::collections::{HashMap, HashSet};

use crate::error::YamlWorkflowError;
use crate::schema::{WorkflowSpec, YamlStep};

/// Validate a parsed workflow spec.
pub fn validate(spec: &WorkflowSpec) -> Result<(), YamlWorkflowError> {
    if spec.steps.is_empty() {
        return Err(YamlWorkflowError::Validation(
            "Workflow must have at least one step".to_string(),
        ));
    }

    let mut seen_names = HashSet::new();
    validate_steps(&spec.steps, &mut seen_names)?;

    // Validate workflow-level error behavior.
    if let Some(ref eb) = spec.error_behavior {
        validate_error_behavior_type(&eb.behavior_type)?;
    }

    Ok(())
}

/// Validate multiple workflow specs from a multi-workflow file.
/// Checks cross-workflow references and cycles in addition to per-workflow validation.
pub fn validate_multi(specs: &[WorkflowSpec]) -> Result<(), YamlWorkflowError> {
    // Validate each workflow individually.
    for spec in specs {
        validate(spec)?;
    }

    // Check for duplicate workflow IDs.
    let mut seen_ids = HashSet::new();
    for spec in specs {
        if !seen_ids.insert(&spec.id) {
            return Err(YamlWorkflowError::Validation(format!(
                "Duplicate workflow ID: '{}'",
                spec.id
            )));
        }
    }

    // Validate cross-workflow references and detect cycles.
    validate_workflow_references(specs)?;

    Ok(())
}

/// Validate that workflow step references point to known workflows
/// and detect circular dependencies.
fn validate_workflow_references(specs: &[WorkflowSpec]) -> Result<(), YamlWorkflowError> {
    let known_ids: HashSet<&str> = specs.iter().map(|s| s.id.as_str()).collect();

    // Build a dependency graph: workflow_id -> set of referenced workflow_ids.
    let mut deps: HashMap<&str, HashSet<&str>> = HashMap::new();

    for spec in specs {
        let mut spec_deps = HashSet::new();
        collect_workflow_refs(&spec.steps, &mut spec_deps);
        deps.insert(spec.id.as_str(), spec_deps);
    }

    // Detect cycles using DFS with coloring.
    detect_cycles(&known_ids, &deps)?;

    Ok(())
}

/// Collect all workflow IDs referenced by `type: workflow` steps.
fn collect_workflow_refs<'a>(steps: &'a [YamlStep], refs: &mut HashSet<&'a str>) {
    for step in steps {
        if step.step_type.as_deref() == Some("workflow")
            && let Some(ref config) = step.config
            && let Some(ref wf_id) = config.child_workflow
        {
            refs.insert(wf_id.as_str());
        }
        if let Some(ref children) = step.parallel {
            collect_workflow_refs(children, refs);
        }
        if let Some(ref hook) = step.on_success {
            collect_workflow_refs(std::slice::from_ref(hook.as_ref()), refs);
        }
        if let Some(ref hook) = step.on_failure {
            collect_workflow_refs(std::slice::from_ref(hook.as_ref()), refs);
        }
        if let Some(ref hook) = step.ensure {
            collect_workflow_refs(std::slice::from_ref(hook.as_ref()), refs);
        }
    }
}

/// Detect circular references in the workflow dependency graph.
fn detect_cycles(
    known_ids: &HashSet<&str>,
    deps: &HashMap<&str, HashSet<&str>>,
) -> Result<(), YamlWorkflowError> {
    #[derive(Clone, Copy, PartialEq)]
    enum Color {
        White,
        Gray,
        Black,
    }

    let mut colors: HashMap<&str, Color> = known_ids.iter().map(|id| (*id, Color::White)).collect();

    fn dfs<'a>(
        node: &'a str,
        deps: &HashMap<&str, HashSet<&'a str>>,
        colors: &mut HashMap<&'a str, Color>,
        path: &mut Vec<&'a str>,
    ) -> Result<(), YamlWorkflowError> {
        colors.insert(node, Color::Gray);
        path.push(node);

        if let Some(neighbors) = deps.get(node) {
            for &neighbor in neighbors {
                match colors.get(neighbor) {
                    Some(Color::Gray) => {
                        // Found a cycle. Build the cycle path for the error message.
                        let cycle_start = path.iter().position(|&n| n == neighbor).unwrap();
                        let cycle: Vec<&str> = path[cycle_start..].to_vec();
                        return Err(YamlWorkflowError::Validation(format!(
                            "Circular workflow reference detected: {} -> {}",
                            cycle.join(" -> "),
                            neighbor
                        )));
                    }
                    Some(Color::White) | None => {
                        // Only recurse into nodes that are in our known set.
                        if colors.contains_key(neighbor) {
                            dfs(neighbor, deps, colors, path)?;
                        }
                    }
                    Some(Color::Black) => {
                        // Already fully processed, skip.
                    }
                }
            }
        }

        path.pop();
        colors.insert(node, Color::Black);
        Ok(())
    }

    let nodes: Vec<&str> = known_ids.iter().copied().collect();
    for node in nodes {
        if colors.get(node) == Some(&Color::White) {
            let mut path = Vec::new();
            dfs(node, deps, &mut colors, &mut path)?;
        }
    }

    Ok(())
}

fn validate_steps(
    steps: &[YamlStep],
    seen_names: &mut HashSet<String>,
) -> Result<(), YamlWorkflowError> {
    for step in steps {
        // Check for duplicate names.
        if !seen_names.insert(step.name.clone()) {
            return Err(YamlWorkflowError::Validation(format!(
                "Duplicate step name: '{}'",
                step.name
            )));
        }

        // A step must have either (type + config) or parallel, but not both.
        let has_type = step.step_type.is_some();
        let has_parallel = step.parallel.is_some();

        if !has_type && !has_parallel {
            return Err(YamlWorkflowError::Validation(format!(
                "Step '{}' must have either 'type' + 'config' or 'parallel'",
                step.name
            )));
        }

        if has_type && has_parallel {
            return Err(YamlWorkflowError::Validation(format!(
                "Step '{}' cannot have both 'type' and 'parallel'",
                step.name
            )));
        }

        // Shell steps must have config.run or config.file.
        if let Some(ref step_type) = step.step_type
            && step_type == "shell"
        {
            let config = step.config.as_ref().ok_or_else(|| {
                YamlWorkflowError::Validation(format!(
                    "Shell step '{}' must have a 'config' section",
                    step.name
                ))
            })?;
            if config.run.is_none() && config.file.is_none() {
                return Err(YamlWorkflowError::Validation(format!(
                    "Shell step '{}' must have 'config.run' or 'config.file'",
                    step.name
                )));
            }
        }

        // Deno steps must have config with script or file.
        if let Some(ref step_type) = step.step_type
            && step_type == "deno"
        {
            let config = step.config.as_ref().ok_or_else(|| {
                YamlWorkflowError::Validation(format!(
                    "Deno step '{}' must have a 'config' section",
                    step.name
                ))
            })?;
            if config.script.is_none() && config.file.is_none() {
                return Err(YamlWorkflowError::Validation(format!(
                    "Deno step '{}' must have 'config.script' or 'config.file'",
                    step.name
                )));
            }
        }

        // BuildKit steps must have config with dockerfile and context.
        if let Some(ref step_type) = step.step_type
            && step_type == "buildkit"
        {
            let config = step.config.as_ref().ok_or_else(|| {
                YamlWorkflowError::Validation(format!(
                    "BuildKit step '{}' must have a 'config' section",
                    step.name
                ))
            })?;
            if config.dockerfile.is_none() {
                return Err(YamlWorkflowError::Validation(format!(
                    "BuildKit step '{}' must have 'config.dockerfile'",
                    step.name
                )));
            }
            if config.context.is_none() {
                return Err(YamlWorkflowError::Validation(format!(
                    "BuildKit step '{}' must have 'config.context'",
                    step.name
                )));
            }
            if config.push.unwrap_or(false) && config.tags.is_empty() {
                return Err(YamlWorkflowError::Validation(format!(
                    "BuildKit step '{}' has push=true but no tags specified",
                    step.name
                )));
            }
        }

        // Containerd steps must have config with image and exactly one of run or command.
        if let Some(ref step_type) = step.step_type
            && step_type == "containerd"
        {
            let config = step.config.as_ref().ok_or_else(|| {
                YamlWorkflowError::Validation(format!(
                    "Containerd step '{}' must have a 'config' section",
                    step.name
                ))
            })?;
            if config.image.is_none() {
                return Err(YamlWorkflowError::Validation(format!(
                    "Containerd step '{}' must have 'config.image'",
                    step.name
                )));
            }
            let has_run = config.run.is_some();
            let has_command = config.command.is_some();
            if !has_run && !has_command {
                return Err(YamlWorkflowError::Validation(format!(
                    "Containerd step '{}' must have 'config.run' or 'config.command'",
                    step.name
                )));
            }
            if has_run && has_command {
                return Err(YamlWorkflowError::Validation(format!(
                    "Containerd step '{}' cannot have both 'config.run' and 'config.command'",
                    step.name
                )));
            }
            if let Some(ref network) = config.network {
                match network.as_str() {
                    "none" | "host" | "bridge" => {}
                    other => {
                        return Err(YamlWorkflowError::Validation(format!(
                            "Containerd step '{}' has invalid network '{}'. Must be none, host, or bridge",
                            step.name, other
                        )));
                    }
                }
            }
            if let Some(ref pull) = config.pull {
                match pull.as_str() {
                    "always" | "if-not-present" | "never" => {}
                    other => {
                        return Err(YamlWorkflowError::Validation(format!(
                            "Containerd step '{}' has invalid pull policy '{}'. Must be always, if-not-present, or never",
                            step.name, other
                        )));
                    }
                }
            }
        }

        // Workflow steps must have config.workflow.
        if let Some(ref step_type) = step.step_type
            && step_type == "workflow"
        {
            let config = step.config.as_ref().ok_or_else(|| {
                YamlWorkflowError::Validation(format!(
                    "Workflow step '{}' must have a 'config' section",
                    step.name
                ))
            })?;
            if config.child_workflow.is_none() {
                return Err(YamlWorkflowError::Validation(format!(
                    "Workflow step '{}' must have 'config.workflow'",
                    step.name
                )));
            }
        }

        // Validate step-level error behavior.
        if let Some(ref eb) = step.error_behavior {
            validate_error_behavior_type(&eb.behavior_type)?;
        }

        // Validate parallel children.
        if let Some(ref children) = step.parallel {
            validate_steps(children, seen_names)?;
        }

        // Validate hook steps.
        if let Some(ref hook) = step.on_success {
            validate_steps(std::slice::from_ref(hook.as_ref()), seen_names)?;
        }
        if let Some(ref hook) = step.on_failure {
            validate_steps(std::slice::from_ref(hook.as_ref()), seen_names)?;
        }
        if let Some(ref hook) = step.ensure {
            validate_steps(std::slice::from_ref(hook.as_ref()), seen_names)?;
        }
    }
    Ok(())
}

fn validate_error_behavior_type(behavior_type: &str) -> Result<(), YamlWorkflowError> {
    match behavior_type {
        "retry" | "suspend" | "terminate" | "compensate" => Ok(()),
        other => Err(YamlWorkflowError::Validation(format!(
            "Invalid error behavior type: '{}'. Must be retry, suspend, terminate, or compensate",
            other
        ))),
    }
}