use std::io::ErrorKind;
use std::path::Path;
use std::path::PathBuf;
use std::sync::Arc;

use arc_swap::ArcSwap;

use crate::config_loader::ConfigLayerStack;
use crate::config_loader::ConfigLayerStackOrdering;
use crate::is_dangerous_command::command_might_be_dangerous;
use crate::is_safe_command::is_known_safe_command;
use codex_execpolicy::AmendError;
use codex_execpolicy::Decision;
use codex_execpolicy::Error as ExecPolicyRuleError;
use codex_execpolicy::Evaluation;
use codex_execpolicy::Policy;
use codex_execpolicy::PolicyParser;
use codex_execpolicy::RuleMatch;
use codex_execpolicy::blocking_append_allow_prefix_rule;
use codex_protocol::approvals::ExecPolicyAmendment;
use codex_protocol::protocol::AskForApproval;
use codex_protocol::protocol::SandboxPolicy;
use thiserror::Error;
use tokio::fs;
use tokio::task::spawn_blocking;

use crate::bash::parse_shell_lc_plain_commands;
use crate::features::Feature;
use crate::features::Features;
use crate::sandboxing::SandboxPermissions;
use crate::tools::sandboxing::ExecApprovalRequirement;
use shlex::try_join as shlex_try_join;

const PROMPT_CONFLICT_REASON: &str =
    "approval required by policy, but AskForApproval is set to Never";
const RULES_DIR_NAME: &str = "rules";
const RULE_EXTENSION: &str = "rules";
const DEFAULT_POLICY_FILE: &str = "default.rules";

fn is_policy_match(rule_match: &RuleMatch) -> bool {
    match rule_match {
        RuleMatch::PrefixRuleMatch { .. } => true,
        RuleMatch::HeuristicsRuleMatch { .. } => false,
    }
}

#[derive(Debug, Error)]
pub enum ExecPolicyError {
    #[error("failed to read rules files from {dir}: {source}")]
    ReadDir {
        dir: PathBuf,
        source: std::io::Error,
    },

    #[error("failed to read rules file {path}: {source}")]
    ReadFile {
        path: PathBuf,
        source: std::io::Error,
    },

    #[error("failed to parse rules file {path}: {source}")]
    ParsePolicy {
        path: String,
        source: codex_execpolicy::Error,
    },
}

#[derive(Debug, Error)]
pub enum ExecPolicyUpdateError {
    #[error("failed to update rules file {path}: {source}")]
    AppendRule { path: PathBuf, source: AmendError },

    #[error("failed to join blocking rules update task: {source}")]
    JoinBlockingTask { source: tokio::task::JoinError },

    #[error("failed to update in-memory rules: {source}")]
    AddRule {
        #[from]
        source: ExecPolicyRuleError,
    },

    #[error("cannot append rule because rules feature is disabled")]
    FeatureDisabled,
}

pub(crate) struct ExecPolicyManager {
    policy: ArcSwap<Policy>,
}

pub(crate) struct ExecApprovalRequest<'a> {
    pub(crate) features: &'a Features,
    pub(crate) command: &'a [String],
    pub(crate) approval_policy: AskForApproval,
    pub(crate) sandbox_policy: &'a SandboxPolicy,
    pub(crate) sandbox_permissions: SandboxPermissions,
    pub(crate) prefix_rule: Option<Vec<String>>,
}

impl ExecPolicyManager {
    pub(crate) fn new(policy: Arc<Policy>) -> Self {
        Self {
            policy: ArcSwap::from(policy),
        }
    }

    pub(crate) async fn load(
        features: &Features,
        config_stack: &ConfigLayerStack,
    ) -> Result<Self, ExecPolicyError> {
        let (policy, warning) =
            load_exec_policy_for_features_with_warning(features, config_stack).await?;
        if let Some(err) = warning.as_ref() {
            tracing::warn!("failed to parse rules: {err}");
        }
        Ok(Self::new(Arc::new(policy)))
    }

    pub(crate) fn current(&self) -> Arc<Policy> {
        self.policy.load_full()
    }

    pub(crate) async fn create_exec_approval_requirement_for_command(
        &self,
        req: ExecApprovalRequest<'_>,
    ) -> ExecApprovalRequirement {
        let ExecApprovalRequest {
            features,
            command,
            approval_policy,
            sandbox_policy,
            sandbox_permissions,
            prefix_rule,
        } = req;
        let exec_policy = self.current();
        let commands =
            parse_shell_lc_plain_commands(command).unwrap_or_else(|| vec![command.to_vec()]);
        let exec_policy_fallback = |cmd: &[String]| {
            render_decision_for_unmatched_command(
                approval_policy,
                sandbox_policy,
                cmd,
                sandbox_permissions,
            )
        };
        let evaluation = exec_policy.check_multiple(commands.iter(), &exec_policy_fallback);

        let requested_amendment = derive_requested_execpolicy_amendment(
            features,
            prefix_rule.as_ref(),
            &evaluation.matched_rules,
        );

        match evaluation.decision {
            Decision::Forbidden => ExecApprovalRequirement::Forbidden {
                reason: derive_forbidden_reason(command, &evaluation),
            },
            Decision::Prompt => {
                if matches!(approval_policy, AskForApproval::Never) {
                    ExecApprovalRequirement::Forbidden {
                        reason: PROMPT_CONFLICT_REASON.to_string(),
                    }
                } else {
                    ExecApprovalRequirement::NeedsApproval {
                        reason: derive_prompt_reason(command, &evaluation),
                        proposed_execpolicy_amendment: if features.enabled(Feature::ExecPolicy) {
                            requested_amendment.or_else(|| {
                                try_derive_execpolicy_amendment_for_prompt_rules(
                                    &evaluation.matched_rules,
                                )
                            })
                        } else {
                            None
                        },
                    }
                }
            }
            Decision::Allow => ExecApprovalRequirement::Skip {
                // Bypass sandbox if execpolicy allows the command
                bypass_sandbox: evaluation.matched_rules.iter().any(|rule_match| {
                    is_policy_match(rule_match) && rule_match.decision() == Decision::Allow
                }),
                proposed_execpolicy_amendment: if features.enabled(Feature::ExecPolicy) {
                    try_derive_execpolicy_amendment_for_allow_rules(&evaluation.matched_rules)
                } else {
                    None
                },
            },
        }
    }

    pub(crate) async fn append_amendment_and_update(
        &self,
        codex_home: &Path,
        amendment: &ExecPolicyAmendment,
    ) -> Result<(), ExecPolicyUpdateError> {
        let policy_path = default_policy_path(codex_home);
        let prefix = amendment.command.clone();
        spawn_blocking({
            let policy_path = policy_path.clone();
            let prefix = prefix.clone();
            move || blocking_append_allow_prefix_rule(&policy_path, &prefix)
        })
        .await
        .map_err(|source| ExecPolicyUpdateError::JoinBlockingTask { source })?
        .map_err(|source| ExecPolicyUpdateError::AppendRule {
            path: policy_path,
            source,
        })?;

        let mut updated_policy = self.current().as_ref().clone();
        updated_policy.add_prefix_rule(&prefix, Decision::Allow)?;
        self.policy.store(Arc::new(updated_policy));
        Ok(())
    }
}

impl Default for ExecPolicyManager {
    fn default() -> Self {
        Self::new(Arc::new(Policy::empty()))
    }
}

pub async fn check_execpolicy_for_warnings(
    features: &Features,
    config_stack: &ConfigLayerStack,
) -> Result<Option<ExecPolicyError>, ExecPolicyError> {
    let (_, warning) = load_exec_policy_for_features_with_warning(features, config_stack).await?;
    Ok(warning)
}

async fn load_exec_policy_for_features_with_warning(
    features: &Features,
    config_stack: &ConfigLayerStack,
) -> Result<(Policy, Option<ExecPolicyError>), ExecPolicyError> {
    if !features.enabled(Feature::ExecPolicy) {
        return Ok((Policy::empty(), None));
    }

    match load_exec_policy(config_stack).await {
        Ok(policy) => Ok((policy, None)),
        Err(err @ ExecPolicyError::ParsePolicy { .. }) => Ok((Policy::empty(), Some(err))),
        Err(err) => Err(err),
    }
}

pub async fn load_exec_policy(config_stack: &ConfigLayerStack) -> Result<Policy, ExecPolicyError> {
    // Iterate the layers in increasing order of precedence, adding the *.rules
    // from each layer, so that higher-precedence layers can override
    // rules defined in lower-precedence ones.
    let mut policy_paths = Vec::new();
    // Include disabled project layers so .codex/rules still applies when
    // project config.toml is trust-disabled.
    for layer in config_stack.get_layers(ConfigLayerStackOrdering::LowestPrecedenceFirst, true) {
        if let Some(config_folder) = layer.config_folder() {
            #[expect(clippy::expect_used)]
            let policy_dir = config_folder.join(RULES_DIR_NAME).expect("safe join");
            let layer_policy_paths = collect_policy_files(&policy_dir).await?;
            policy_paths.extend(layer_policy_paths);
        }
    }

    let mut parser = PolicyParser::new();
    for policy_path in &policy_paths {
        let contents =
            fs::read_to_string(policy_path)
                .await
                .map_err(|source| ExecPolicyError::ReadFile {
                    path: policy_path.clone(),
                    source,
                })?;
        let identifier = policy_path.to_string_lossy().to_string();
        parser
            .parse(&identifier, &contents)
            .map_err(|source| ExecPolicyError::ParsePolicy {
                path: identifier,
                source,
            })?;
    }

    let policy = parser.build();
    tracing::debug!("loaded rules from {} files", policy_paths.len());

    Ok(policy)
}

/// If a command is not matched by any execpolicy rule, derive a [`Decision`].
pub fn render_decision_for_unmatched_command(
    approval_policy: AskForApproval,
    sandbox_policy: &SandboxPolicy,
    command: &[String],
    sandbox_permissions: SandboxPermissions,
) -> Decision {
    if is_known_safe_command(command) {
        return Decision::Allow;
    }

    // On Windows, ReadOnly sandbox is not a real sandbox, so special-case it
    // here.
    let runtime_sandbox_provides_safety =
        cfg!(windows) && matches!(sandbox_policy, SandboxPolicy::ReadOnly);

    // If the command is flagged as dangerous or we have no sandbox protection,
    // we should never allow it to run without user approval.
    //
    // We prefer to prompt the user rather than outright forbid the command,
    // but if the user has explicitly disabled prompts, we must
    // forbid the command.
    if command_might_be_dangerous(command) || runtime_sandbox_provides_safety {
        return if matches!(approval_policy, AskForApproval::Never) {
            Decision::Forbidden
        } else {
            Decision::Prompt
        };
    }

    match approval_policy {
        AskForApproval::Never | AskForApproval::OnFailure => {
            // We allow the command to run, relying on the sandbox for
            // protection.
            Decision::Allow
        }
        AskForApproval::UnlessTrusted => {
            // We already checked `is_known_safe_command(command)` and it
            // returned false, so we must prompt.
            Decision::Prompt
        }
        AskForApproval::OnRequest => {
            match sandbox_policy {
                SandboxPolicy::DangerFullAccess | SandboxPolicy::ExternalSandbox { .. } => {
                    // The user has indicated we should "just run" commands
                    // in their unrestricted environment, so we do so since the
                    // command has not been flagged as dangerous.
                    Decision::Allow
                }
                SandboxPolicy::ReadOnly | SandboxPolicy::WorkspaceWrite { .. } => {
                    // In restricted sandboxes (ReadOnly/WorkspaceWrite), do not prompt for
                    // non‑escalated, non‑dangerous commands — let the sandbox enforce
                    // restrictions (e.g., block network/write) without a user prompt.
                    if sandbox_permissions.requires_escalated_permissions() {
                        Decision::Prompt
                    } else {
                        Decision::Allow
                    }
                }
            }
        }
    }
}

fn default_policy_path(codex_home: &Path) -> PathBuf {
    codex_home.join(RULES_DIR_NAME).join(DEFAULT_POLICY_FILE)
}

/// Derive a proposed execpolicy amendment when a command requires user approval
/// - If any execpolicy rule prompts, return None, because an amendment would not skip that policy requirement.
/// - Otherwise return the first heuristics Prompt.
/// - Examples:
/// - execpolicy: empty. Command: `["python"]`. Heuristics prompt -> `Some(vec!["python"])`.
/// - execpolicy: empty. Command: `["bash", "-c", "cd /some/folder && prog1 --option1 arg1 && prog2 --option2 arg2"]`.
///   Parsed commands include `cd /some/folder`, `prog1 --option1 arg1`, and `prog2 --option2 arg2`. If heuristics allow `cd` but prompt
///   on `prog1`, we return `Some(vec!["prog1", "--option1", "arg1"])`.
/// - execpolicy: contains a `prompt for prefix ["prog2"]` rule. For the same command as above,
///   we return `None` because an execpolicy prompt still applies even if we amend execpolicy to allow ["prog1", "--option1", "arg1"].
fn try_derive_execpolicy_amendment_for_prompt_rules(
    matched_rules: &[RuleMatch],
) -> Option<ExecPolicyAmendment> {
    if matched_rules
        .iter()
        .any(|rule_match| is_policy_match(rule_match) && rule_match.decision() == Decision::Prompt)
    {
        return None;
    }

    matched_rules
        .iter()
        .find_map(|rule_match| match rule_match {
            RuleMatch::HeuristicsRuleMatch {
                command,
                decision: Decision::Prompt,
            } => Some(ExecPolicyAmendment::from(command.clone())),
            _ => None,
        })
}

/// - Note: we only use this amendment when the command fails to run in sandbox and codex prompts the user to run outside the sandbox
/// - The purpose of this amendment is to bypass sandbox for similar commands in the future
/// - If any execpolicy rule matches, return None, because we would already be running command outside the sandbox
fn try_derive_execpolicy_amendment_for_allow_rules(
    matched_rules: &[RuleMatch],
) -> Option<ExecPolicyAmendment> {
    if matched_rules.iter().any(is_policy_match) {
        return None;
    }

    matched_rules
        .iter()
        .find_map(|rule_match| match rule_match {
            RuleMatch::HeuristicsRuleMatch {
                command,
                decision: Decision::Allow,
            } => Some(ExecPolicyAmendment::from(command.clone())),
            _ => None,
        })
}

fn derive_requested_execpolicy_amendment(
    features: &Features,
    prefix_rule: Option<&Vec<String>>,
    matched_rules: &[RuleMatch],
) -> Option<ExecPolicyAmendment> {
    if !features.enabled(Feature::ExecPolicy) {
        return None;
    }

    let prefix_rule = prefix_rule?;
    if prefix_rule.is_empty() {
        return None;
    }

    if matched_rules
        .iter()
        .any(|rule_match| is_policy_match(rule_match) && rule_match.decision() == Decision::Prompt)
    {
        return None;
    }

    Some(ExecPolicyAmendment::new(prefix_rule.clone()))
}

/// Only return a reason when a policy rule drove the prompt decision.
fn derive_prompt_reason(command_args: &[String], evaluation: &Evaluation) -> Option<String> {
    let command = render_shlex_command(command_args);

    let most_specific_prompt = evaluation
        .matched_rules
        .iter()
        .filter_map(|rule_match| match rule_match {
            RuleMatch::PrefixRuleMatch {
                matched_prefix,
                decision: Decision::Prompt,
                justification,
                ..
            } => Some((matched_prefix.len(), justification.as_deref())),
            _ => None,
        })
        .max_by_key(|(matched_prefix_len, _)| *matched_prefix_len);

    match most_specific_prompt {
        Some((_matched_prefix_len, Some(justification))) => {
            Some(format!("`{command}` requires approval: {justification}"))
        }
        Some((_matched_prefix_len, None)) => {
            Some(format!("`{command}` requires approval by policy"))
        }
        None => None,
    }
}

fn render_shlex_command(args: &[String]) -> String {
    shlex_try_join(args.iter().map(String::as_str)).unwrap_or_else(|_| args.join(" "))
}

/// Derive a string explaining why the command was forbidden. If `justification`
/// is set by the user, this can contain instructions with recommended
/// alternatives, for example.
fn derive_forbidden_reason(command_args: &[String], evaluation: &Evaluation) -> String {
    let command = render_shlex_command(command_args);

    let most_specific_forbidden = evaluation
        .matched_rules
        .iter()
        .filter_map(|rule_match| match rule_match {
            RuleMatch::PrefixRuleMatch {
                matched_prefix,
                decision: Decision::Forbidden,
                justification,
                ..
            } => Some((matched_prefix, justification.as_deref())),
            _ => None,
        })
        .max_by_key(|(matched_prefix, _)| matched_prefix.len());

    match most_specific_forbidden {
        Some((_matched_prefix, Some(justification))) => {
            format!("`{command}` rejected: {justification}")
        }
        Some((matched_prefix, None)) => {
            let prefix = render_shlex_command(matched_prefix);
            format!("`{command}` rejected: policy forbids commands starting with `{prefix}`")
        }
        None => format!("`{command}` rejected: blocked by policy"),
    }
}

async fn collect_policy_files(dir: impl AsRef<Path>) -> Result<Vec<PathBuf>, ExecPolicyError> {
    let dir = dir.as_ref();
    let mut read_dir = match fs::read_dir(dir).await {
        Ok(read_dir) => read_dir,
        Err(err) if err.kind() == ErrorKind::NotFound => return Ok(Vec::new()),
        Err(source) => {
            return Err(ExecPolicyError::ReadDir {
                dir: dir.to_path_buf(),
                source,
            });
        }
    };

    let mut policy_paths = Vec::new();
    while let Some(entry) =
        read_dir
            .next_entry()
            .await
            .map_err(|source| ExecPolicyError::ReadDir {
                dir: dir.to_path_buf(),
                source,
            })?
    {
        let path = entry.path();
        let file_type = entry
            .file_type()
            .await
            .map_err(|source| ExecPolicyError::ReadDir {
                dir: dir.to_path_buf(),
                source,
            })?;

        if path
            .extension()
            .and_then(|ext| ext.to_str())
            .is_some_and(|ext| ext == RULE_EXTENSION)
            && file_type.is_file()
        {
            policy_paths.push(path);
        }
    }

    policy_paths.sort();

    tracing::debug!(
        "loaded {} .rules files in {}",
        policy_paths.len(),
        dir.display()
    );
    Ok(policy_paths)
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::config_loader::ConfigLayerEntry;
    use crate::config_loader::ConfigLayerStack;
    use crate::config_loader::ConfigRequirements;
    use crate::config_loader::ConfigRequirementsToml;
    use crate::features::Feature;
    use crate::features::Features;
    use codex_app_server_protocol::ConfigLayerSource;
    use codex_protocol::protocol::AskForApproval;
    use codex_protocol::protocol::SandboxPolicy;
    use codex_utils_absolute_path::AbsolutePathBuf;
    use pretty_assertions::assert_eq;
    use std::fs;
    use std::path::Path;
    use std::sync::Arc;
    use tempfile::tempdir;
    use toml::Value as TomlValue;

    fn config_stack_for_dot_codex_folder(dot_codex_folder: &Path) -> ConfigLayerStack {
        let dot_codex_folder = AbsolutePathBuf::from_absolute_path(dot_codex_folder)
            .expect("absolute dot_codex_folder");
        let layer = ConfigLayerEntry::new(
            ConfigLayerSource::Project { dot_codex_folder },
            TomlValue::Table(Default::default()),
        );
        ConfigLayerStack::new(
            vec![layer],
            ConfigRequirements::default(),
            ConfigRequirementsToml::default(),
        )
        .expect("ConfigLayerStack")
    }

    #[tokio::test]
    async fn returns_empty_policy_when_feature_disabled() {
        let mut features = Features::with_defaults();
        features.disable(Feature::ExecPolicy);
        let temp_dir = tempdir().expect("create temp dir");
        let config_stack = config_stack_for_dot_codex_folder(temp_dir.path());

        let manager = ExecPolicyManager::load(&features, &config_stack)
            .await
            .expect("manager result");
        let policy = manager.current();

        let commands = [vec!["rm".to_string()]];
        assert_eq!(
            Evaluation {
                decision: Decision::Allow,
                matched_rules: vec![RuleMatch::HeuristicsRuleMatch {
                    command: vec!["rm".to_string()],
                    decision: Decision::Allow
                }],
            },
            policy.check_multiple(commands.iter(), &|_| Decision::Allow)
        );
        assert!(!temp_dir.path().join(RULES_DIR_NAME).exists());
    }

    #[tokio::test]
    async fn collect_policy_files_returns_empty_when_dir_missing() {
        let temp_dir = tempdir().expect("create temp dir");

        let policy_dir = temp_dir.path().join(RULES_DIR_NAME);
        let files = collect_policy_files(&policy_dir)
            .await
            .expect("collect policy files");

        assert!(files.is_empty());
    }

    #[tokio::test]
    async fn loads_policies_from_policy_subdirectory() {
        let temp_dir = tempdir().expect("create temp dir");
        let config_stack = config_stack_for_dot_codex_folder(temp_dir.path());
        let policy_dir = temp_dir.path().join(RULES_DIR_NAME);
        fs::create_dir_all(&policy_dir).expect("create policy dir");
        fs::write(
            policy_dir.join("deny.rules"),
            r#"prefix_rule(pattern=["rm"], decision="forbidden")"#,
        )
        .expect("write policy file");

        let policy = load_exec_policy(&config_stack)
            .await
            .expect("policy result");
        let command = [vec!["rm".to_string()]];
        assert_eq!(
            Evaluation {
                decision: Decision::Forbidden,
                matched_rules: vec![RuleMatch::PrefixRuleMatch {
                    matched_prefix: vec!["rm".to_string()],
                    decision: Decision::Forbidden,
                    justification: None,
                }],
            },
            policy.check_multiple(command.iter(), &|_| Decision::Allow)
        );
    }

    #[tokio::test]
    async fn ignores_policies_outside_policy_dir() {
        let temp_dir = tempdir().expect("create temp dir");
        let config_stack = config_stack_for_dot_codex_folder(temp_dir.path());
        fs::write(
            temp_dir.path().join("root.rules"),
            r#"prefix_rule(pattern=["ls"], decision="prompt")"#,
        )
        .expect("write policy file");

        let policy = load_exec_policy(&config_stack)
            .await
            .expect("policy result");
        let command = [vec!["ls".to_string()]];
        assert_eq!(
            Evaluation {
                decision: Decision::Allow,
                matched_rules: vec![RuleMatch::HeuristicsRuleMatch {
                    command: vec!["ls".to_string()],
                    decision: Decision::Allow
                }],
            },
            policy.check_multiple(command.iter(), &|_| Decision::Allow)
        );
    }

    #[tokio::test]
    async fn loads_rules_from_disabled_project_layers() -> anyhow::Result<()> {
        let project_dir = tempdir()?;
        let policy_dir = project_dir.path().join(RULES_DIR_NAME);
        fs::create_dir_all(&policy_dir)?;
        fs::write(
            policy_dir.join("disabled.rules"),
            r#"prefix_rule(pattern=["ls"], decision="forbidden")"#,
        )?;

        let project_dot_codex_folder = AbsolutePathBuf::from_absolute_path(project_dir.path())?;
        let layers = vec![ConfigLayerEntry::new_disabled(
            ConfigLayerSource::Project {
                dot_codex_folder: project_dot_codex_folder,
            },
            TomlValue::Table(Default::default()),
            "trust disabled",
        )];
        let config_stack = ConfigLayerStack::new(
            layers,
            ConfigRequirements::default(),
            ConfigRequirementsToml::default(),
        )?;

        let policy = load_exec_policy(&config_stack).await?;

        assert_eq!(
            Evaluation {
                decision: Decision::Forbidden,
                matched_rules: vec![RuleMatch::PrefixRuleMatch {
                    matched_prefix: vec!["ls".to_string()],
                    decision: Decision::Forbidden,
                    justification: None,
                }],
            },
            policy.check_multiple([vec!["ls".to_string()]].iter(), &|_| Decision::Allow)
        );

        Ok(())
    }

    #[tokio::test]
    async fn loads_policies_from_multiple_config_layers() -> anyhow::Result<()> {
        let user_dir = tempdir()?;
        let project_dir = tempdir()?;

        let user_policy_dir = user_dir.path().join(RULES_DIR_NAME);
        fs::create_dir_all(&user_policy_dir)?;
        fs::write(
            user_policy_dir.join("user.rules"),
            r#"prefix_rule(pattern=["rm"], decision="forbidden")"#,
        )?;

        let project_policy_dir = project_dir.path().join(RULES_DIR_NAME);
        fs::create_dir_all(&project_policy_dir)?;
        fs::write(
            project_policy_dir.join("project.rules"),
            r#"prefix_rule(pattern=["ls"], decision="prompt")"#,
        )?;

        let user_config_toml =
            AbsolutePathBuf::from_absolute_path(user_dir.path().join("config.toml"))?;
        let project_dot_codex_folder = AbsolutePathBuf::from_absolute_path(project_dir.path())?;
        let layers = vec![
            ConfigLayerEntry::new(
                ConfigLayerSource::User {
                    file: user_config_toml,
                },
                TomlValue::Table(Default::default()),
            ),
            ConfigLayerEntry::new(
                ConfigLayerSource::Project {
                    dot_codex_folder: project_dot_codex_folder,
                },
                TomlValue::Table(Default::default()),
            ),
        ];
        let config_stack = ConfigLayerStack::new(
            layers,
            ConfigRequirements::default(),
            ConfigRequirementsToml::default(),
        )?;

        let policy = load_exec_policy(&config_stack).await?;

        assert_eq!(
            Evaluation {
                decision: Decision::Forbidden,
                matched_rules: vec![RuleMatch::PrefixRuleMatch {
                    matched_prefix: vec!["rm".to_string()],
                    decision: Decision::Forbidden,
                    justification: None,
                }],
            },
            policy.check_multiple([vec!["rm".to_string()]].iter(), &|_| Decision::Allow)
        );
        assert_eq!(
            Evaluation {
                decision: Decision::Prompt,
                matched_rules: vec![RuleMatch::PrefixRuleMatch {
                    matched_prefix: vec!["ls".to_string()],
                    decision: Decision::Prompt,
                    justification: None,
                }],
            },
            policy.check_multiple([vec!["ls".to_string()]].iter(), &|_| Decision::Allow)
        );
        Ok(())
    }

    #[tokio::test]
    async fn evaluates_bash_lc_inner_commands() {
        let policy_src = r#"
prefix_rule(pattern=["rm"], decision="forbidden")
"#;
        let mut parser = PolicyParser::new();
        parser
            .parse("test.rules", policy_src)
            .expect("parse policy");
        let policy = Arc::new(parser.build());

        let forbidden_script = vec![
            "bash".to_string(),
            "-lc".to_string(),
            "rm -rf /some/important/folder".to_string(),
        ];

        let manager = ExecPolicyManager::new(policy);
        let requirement = manager
            .create_exec_approval_requirement_for_command(ExecApprovalRequest {
                features: &Features::with_defaults(),
                command: &forbidden_script,
                approval_policy: AskForApproval::OnRequest,
                sandbox_policy: &SandboxPolicy::DangerFullAccess,
                sandbox_permissions: SandboxPermissions::UseDefault,
                prefix_rule: None,
            })
            .await;

        assert_eq!(
            requirement,
            ExecApprovalRequirement::Forbidden {
                reason: "`bash -lc 'rm -rf /some/important/folder'` rejected: policy forbids commands starting with `rm`".to_string()
            }
        );
    }

    #[tokio::test]
    async fn justification_is_included_in_forbidden_exec_approval_requirement() {
        let policy_src = r#"
prefix_rule(
    pattern=["rm"],
    decision="forbidden",
    justification="destructive command",
)
"#;
        let mut parser = PolicyParser::new();
        parser
            .parse("test.rules", policy_src)
            .expect("parse policy");
        let policy = Arc::new(parser.build());

        let manager = ExecPolicyManager::new(policy);
        let requirement = manager
            .create_exec_approval_requirement_for_command(ExecApprovalRequest {
                features: &Features::with_defaults(),
                command: &[
                    "rm".to_string(),
                    "-rf".to_string(),
                    "/some/important/folder".to_string(),
                ],
                approval_policy: AskForApproval::OnRequest,
                sandbox_policy: &SandboxPolicy::DangerFullAccess,
                sandbox_permissions: SandboxPermissions::UseDefault,
                prefix_rule: None,
            })
            .await;

        assert_eq!(
            requirement,
            ExecApprovalRequirement::Forbidden {
                reason: "`rm -rf /some/important/folder` rejected: destructive command".to_string()
            }
        );
    }

    #[tokio::test]
    async fn exec_approval_requirement_prefers_execpolicy_match() {
        let policy_src = r#"prefix_rule(pattern=["rm"], decision="prompt")"#;
        let mut parser = PolicyParser::new();
        parser
            .parse("test.rules", policy_src)
            .expect("parse policy");
        let policy = Arc::new(parser.build());
        let command = vec!["rm".to_string()];

        let manager = ExecPolicyManager::new(policy);
        let requirement = manager
            .create_exec_approval_requirement_for_command(ExecApprovalRequest {
                features: &Features::with_defaults(),
                command: &command,
                approval_policy: AskForApproval::OnRequest,
                sandbox_policy: &SandboxPolicy::DangerFullAccess,
                sandbox_permissions: SandboxPermissions::UseDefault,
                prefix_rule: None,
            })
            .await;

        assert_eq!(
            requirement,
            ExecApprovalRequirement::NeedsApproval {
                reason: Some("`rm` requires approval by policy".to_string()),
                proposed_execpolicy_amendment: None,
            }
        );
    }

    #[tokio::test]
    async fn exec_approval_requirement_respects_approval_policy() {
        let policy_src = r#"prefix_rule(pattern=["rm"], decision="prompt")"#;
        let mut parser = PolicyParser::new();
        parser
            .parse("test.rules", policy_src)
            .expect("parse policy");
        let policy = Arc::new(parser.build());
        let command = vec!["rm".to_string()];

        let manager = ExecPolicyManager::new(policy);
        let requirement = manager
            .create_exec_approval_requirement_for_command(ExecApprovalRequest {
                features: &Features::with_defaults(),
                command: &command,
                approval_policy: AskForApproval::Never,
                sandbox_policy: &SandboxPolicy::DangerFullAccess,
                sandbox_permissions: SandboxPermissions::UseDefault,
                prefix_rule: None,
            })
            .await;

        assert_eq!(
            requirement,
            ExecApprovalRequirement::Forbidden {
                reason: PROMPT_CONFLICT_REASON.to_string()
            }
        );
    }

    #[tokio::test]
    async fn exec_approval_requirement_falls_back_to_heuristics() {
        let command = vec!["cargo".to_string(), "build".to_string()];

        let manager = ExecPolicyManager::default();
        let requirement = manager
            .create_exec_approval_requirement_for_command(ExecApprovalRequest {
                features: &Features::with_defaults(),
                command: &command,
                approval_policy: AskForApproval::UnlessTrusted,
                sandbox_policy: &SandboxPolicy::ReadOnly,
                sandbox_permissions: SandboxPermissions::UseDefault,
                prefix_rule: None,
            })
            .await;

        assert_eq!(
            requirement,
            ExecApprovalRequirement::NeedsApproval {
                reason: None,
                proposed_execpolicy_amendment: Some(ExecPolicyAmendment::new(command))
            }
        );
    }

    #[tokio::test]
    async fn request_rule_uses_prefix_rule() {
        let command = vec![
            "cargo".to_string(),
            "install".to_string(),
            "cargo-insta".to_string(),
        ];
        let manager = ExecPolicyManager::default();
        let mut features = Features::with_defaults();
        features.enable(Feature::RequestRule);

        let requirement = manager
            .create_exec_approval_requirement_for_command(ExecApprovalRequest {
                features: &features,
                command: &command,
                approval_policy: AskForApproval::OnRequest,
                sandbox_policy: &SandboxPolicy::ReadOnly,
                sandbox_permissions: SandboxPermissions::RequireEscalated,
                prefix_rule: Some(vec!["cargo".to_string(), "install".to_string()]),
            })
            .await;

        assert_eq!(
            requirement,
            ExecApprovalRequirement::NeedsApproval {
                reason: None,
                proposed_execpolicy_amendment: Some(ExecPolicyAmendment::new(vec![
                    "cargo".to_string(),
                    "install".to_string(),
                ])),
            }
        );
    }

    #[tokio::test]
    async fn heuristics_apply_when_other_commands_match_policy() {
        let policy_src = r#"prefix_rule(pattern=["apple"], decision="allow")"#;
        let mut parser = PolicyParser::new();
        parser
            .parse("test.rules", policy_src)
            .expect("parse policy");
        let policy = Arc::new(parser.build());
        let command = vec![
            "bash".to_string(),
            "-lc".to_string(),
            "apple | orange".to_string(),
        ];

        assert_eq!(
            ExecPolicyManager::new(policy)
                .create_exec_approval_requirement_for_command(ExecApprovalRequest {
                    features: &Features::with_defaults(),
                    command: &command,
                    approval_policy: AskForApproval::UnlessTrusted,
                    sandbox_policy: &SandboxPolicy::DangerFullAccess,
                    sandbox_permissions: SandboxPermissions::UseDefault,
                    prefix_rule: None,
                })
                .await,
            ExecApprovalRequirement::NeedsApproval {
                reason: None,
                proposed_execpolicy_amendment: Some(ExecPolicyAmendment::new(vec![
                    "orange".to_string()
                ]))
            }
        );
    }

    #[tokio::test]
    async fn append_execpolicy_amendment_updates_policy_and_file() {
        let codex_home = tempdir().expect("create temp dir");
        let prefix = vec!["echo".to_string(), "hello".to_string()];
        let manager = ExecPolicyManager::default();

        manager
            .append_amendment_and_update(codex_home.path(), &ExecPolicyAmendment::from(prefix))
            .await
            .expect("update policy");
        let updated_policy = manager.current();

        let evaluation = updated_policy.check(
            &["echo".to_string(), "hello".to_string(), "world".to_string()],
            &|_| Decision::Allow,
        );
        assert!(matches!(
            evaluation,
            Evaluation {
                decision: Decision::Allow,
                ..
            }
        ));

        let contents = fs::read_to_string(default_policy_path(codex_home.path()))
            .expect("policy file should have been created");
        assert_eq!(
            contents,
            r#"prefix_rule(pattern=["echo", "hello"], decision="allow")
"#
        );
    }

    #[tokio::test]
    async fn append_execpolicy_amendment_rejects_empty_prefix() {
        let codex_home = tempdir().expect("create temp dir");
        let manager = ExecPolicyManager::default();

        let result = manager
            .append_amendment_and_update(codex_home.path(), &ExecPolicyAmendment::from(vec![]))
            .await;

        assert!(matches!(
            result,
            Err(ExecPolicyUpdateError::AppendRule {
                source: AmendError::EmptyPrefix,
                ..
            })
        ));
    }

    #[tokio::test]
    async fn proposed_execpolicy_amendment_is_present_for_single_command_without_policy_match() {
        let command = vec!["cargo".to_string(), "build".to_string()];

        let manager = ExecPolicyManager::default();
        let requirement = manager
            .create_exec_approval_requirement_for_command(ExecApprovalRequest {
                features: &Features::with_defaults(),
                command: &command,
                approval_policy: AskForApproval::UnlessTrusted,
                sandbox_policy: &SandboxPolicy::ReadOnly,
                sandbox_permissions: SandboxPermissions::UseDefault,
                prefix_rule: None,
            })
            .await;

        assert_eq!(
            requirement,
            ExecApprovalRequirement::NeedsApproval {
                reason: None,
                proposed_execpolicy_amendment: Some(ExecPolicyAmendment::new(command))
            }
        );
    }

    #[tokio::test]
    async fn proposed_execpolicy_amendment_is_disabled_when_execpolicy_feature_disabled() {
        let command = vec!["cargo".to_string(), "build".to_string()];

        let mut features = Features::with_defaults();
        features.disable(Feature::ExecPolicy);

        let manager = ExecPolicyManager::default();
        let requirement = manager
            .create_exec_approval_requirement_for_command(ExecApprovalRequest {
                features: &features,
                command: &command,
                approval_policy: AskForApproval::UnlessTrusted,
                sandbox_policy: &SandboxPolicy::ReadOnly,
                sandbox_permissions: SandboxPermissions::UseDefault,
                prefix_rule: None,
            })
            .await;

        assert_eq!(
            requirement,
            ExecApprovalRequirement::NeedsApproval {
                reason: None,
                proposed_execpolicy_amendment: None,
            }
        );
    }

    #[tokio::test]
    async fn proposed_execpolicy_amendment_is_omitted_when_policy_prompts() {
        let policy_src = r#"prefix_rule(pattern=["rm"], decision="prompt")"#;
        let mut parser = PolicyParser::new();
        parser
            .parse("test.rules", policy_src)
            .expect("parse policy");
        let policy = Arc::new(parser.build());
        let command = vec!["rm".to_string()];

        let manager = ExecPolicyManager::new(policy);
        let requirement = manager
            .create_exec_approval_requirement_for_command(ExecApprovalRequest {
                features: &Features::with_defaults(),
                command: &command,
                approval_policy: AskForApproval::OnRequest,
                sandbox_policy: &SandboxPolicy::DangerFullAccess,
                sandbox_permissions: SandboxPermissions::UseDefault,
                prefix_rule: None,
            })
            .await;

        assert_eq!(
            requirement,
            ExecApprovalRequirement::NeedsApproval {
                reason: Some("`rm` requires approval by policy".to_string()),
                proposed_execpolicy_amendment: None,
            }
        );
    }

    #[tokio::test]
    async fn proposed_execpolicy_amendment_is_present_for_multi_command_scripts() {
        let command = vec![
            "bash".to_string(),
            "-lc".to_string(),
            "cargo build && echo ok".to_string(),
        ];
        let manager = ExecPolicyManager::default();
        let requirement = manager
            .create_exec_approval_requirement_for_command(ExecApprovalRequest {
                features: &Features::with_defaults(),
                command: &command,
                approval_policy: AskForApproval::UnlessTrusted,
                sandbox_policy: &SandboxPolicy::ReadOnly,
                sandbox_permissions: SandboxPermissions::UseDefault,
                prefix_rule: None,
            })
            .await;

        assert_eq!(
            requirement,
            ExecApprovalRequirement::NeedsApproval {
                reason: None,
                proposed_execpolicy_amendment: Some(ExecPolicyAmendment::new(vec![
                    "cargo".to_string(),
                    "build".to_string()
                ])),
            }
        );
    }

    #[tokio::test]
    async fn proposed_execpolicy_amendment_uses_first_no_match_in_multi_command_scripts() {
        let policy_src = r#"prefix_rule(pattern=["cat"], decision="allow")"#;
        let mut parser = PolicyParser::new();
        parser
            .parse("test.rules", policy_src)
            .expect("parse policy");
        let policy = Arc::new(parser.build());

        let command = vec![
            "bash".to_string(),
            "-lc".to_string(),
            "cat && apple".to_string(),
        ];

        assert_eq!(
            ExecPolicyManager::new(policy)
                .create_exec_approval_requirement_for_command(ExecApprovalRequest {
                    features: &Features::with_defaults(),
                    command: &command,
                    approval_policy: AskForApproval::UnlessTrusted,
                    sandbox_policy: &SandboxPolicy::ReadOnly,
                    sandbox_permissions: SandboxPermissions::UseDefault,
                    prefix_rule: None,
                })
                .await,
            ExecApprovalRequirement::NeedsApproval {
                reason: None,
                proposed_execpolicy_amendment: Some(ExecPolicyAmendment::new(vec![
                    "apple".to_string()
                ])),
            }
        );
    }

    #[tokio::test]
    async fn proposed_execpolicy_amendment_is_present_when_heuristics_allow() {
        let command = vec!["echo".to_string(), "safe".to_string()];

        let manager = ExecPolicyManager::default();
        let requirement = manager
            .create_exec_approval_requirement_for_command(ExecApprovalRequest {
                features: &Features::with_defaults(),
                command: &command,
                approval_policy: AskForApproval::OnRequest,
                sandbox_policy: &SandboxPolicy::ReadOnly,
                sandbox_permissions: SandboxPermissions::UseDefault,
                prefix_rule: None,
            })
            .await;

        assert_eq!(
            requirement,
            ExecApprovalRequirement::Skip {
                bypass_sandbox: false,
                proposed_execpolicy_amendment: Some(ExecPolicyAmendment::new(command)),
            }
        );
    }

    #[tokio::test]
    async fn proposed_execpolicy_amendment_is_suppressed_when_policy_matches_allow() {
        let policy_src = r#"prefix_rule(pattern=["echo"], decision="allow")"#;
        let mut parser = PolicyParser::new();
        parser
            .parse("test.rules", policy_src)
            .expect("parse policy");
        let policy = Arc::new(parser.build());
        let command = vec!["echo".to_string(), "safe".to_string()];

        let manager = ExecPolicyManager::new(policy);
        let requirement = manager
            .create_exec_approval_requirement_for_command(ExecApprovalRequest {
                features: &Features::with_defaults(),
                command: &command,
                approval_policy: AskForApproval::OnRequest,
                sandbox_policy: &SandboxPolicy::ReadOnly,
                sandbox_permissions: SandboxPermissions::UseDefault,
                prefix_rule: None,
            })
            .await;

        assert_eq!(
            requirement,
            ExecApprovalRequirement::Skip {
                bypass_sandbox: true,
                proposed_execpolicy_amendment: None,
            }
        );
    }

    fn vec_str(items: &[&str]) -> Vec<String> {
        items.iter().map(std::string::ToString::to_string).collect()
    }

    /// Note this test behaves differently on Windows because it exercises an
    /// `if cfg!(windows)` code path in render_decision_for_unmatched_command().
    #[tokio::test]
    async fn verify_approval_requirement_for_unsafe_powershell_command() {
        // `brew install powershell` to run this test on a Mac!
        // Note `pwsh` is required to parse a PowerShell command to see if it
        // is safe.
        if which::which("pwsh").is_err() {
            return;
        }

        let policy = ExecPolicyManager::new(Arc::new(Policy::empty()));
        let features = Features::with_defaults();
        let permissions = SandboxPermissions::UseDefault;

        // This command should not be run without user approval unless there is
        // a proper sandbox in place to ensure safety.
        let sneaky_command = vec_str(&["pwsh", "-Command", "echo hi @(calc)"]);
        let expected_amendment = Some(ExecPolicyAmendment::new(vec_str(&[
            "pwsh",
            "-Command",
            "echo hi @(calc)",
        ])));
        let (pwsh_approval_reason, expected_req) = if cfg!(windows) {
            (
                r#"On Windows, SandboxPolicy::ReadOnly should be assumed to mean
                that no sandbox is present, so anything that is not "provably
                safe" should require approval."#,
                ExecApprovalRequirement::NeedsApproval {
                    reason: None,
                    proposed_execpolicy_amendment: expected_amendment.clone(),
                },
            )
        } else {
            (
                "On non-Windows, rely on the read-only sandbox to prevent harm.",
                ExecApprovalRequirement::Skip {
                    bypass_sandbox: false,
                    proposed_execpolicy_amendment: expected_amendment.clone(),
                },
            )
        };
        assert_eq!(
            expected_req,
            policy
                .create_exec_approval_requirement_for_command(ExecApprovalRequest {
                    features: &features,
                    command: &sneaky_command,
                    approval_policy: AskForApproval::OnRequest,
                    sandbox_policy: &SandboxPolicy::ReadOnly,
                    sandbox_permissions: permissions,
                    prefix_rule: None,
                })
                .await,
            "{pwsh_approval_reason}"
        );

        // This is flagged as a dangerous command on all platforms.
        let dangerous_command = vec_str(&["rm", "-rf", "/important/data"]);
        assert_eq!(
            ExecApprovalRequirement::NeedsApproval {
                reason: None,
                proposed_execpolicy_amendment: Some(ExecPolicyAmendment::new(vec_str(&[
                    "rm",
                    "-rf",
                    "/important/data",
                ]))),
            },
            policy
                .create_exec_approval_requirement_for_command(ExecApprovalRequest {
                    features: &features,
                    command: &dangerous_command,
                    approval_policy: AskForApproval::OnRequest,
                    sandbox_policy: &SandboxPolicy::ReadOnly,
                    sandbox_permissions: permissions,
                    prefix_rule: None,
                })
                .await,
            r#"On all platforms, a forbidden command should require approval
            (unless AskForApproval::Never is specified)."#
        );

        // A dangerous command should be forbidden if the user has specified
        // AskForApproval::Never.
        assert_eq!(
            ExecApprovalRequirement::Forbidden {
                reason: "`rm -rf /important/data` rejected: blocked by policy".to_string(),
            },
            policy
                .create_exec_approval_requirement_for_command(ExecApprovalRequest {
                    features: &features,
                    command: &dangerous_command,
                    approval_policy: AskForApproval::Never,
                    sandbox_policy: &SandboxPolicy::ReadOnly,
                    sandbox_permissions: permissions,
                    prefix_rule: None,
                })
                .await,
            r#"On all platforms, a forbidden command should require approval
            (unless AskForApproval::Never is specified)."#
        );
    }
}
