use crate::config::types::EnvironmentVariablePattern;
use crate::config::types::ShellEnvironmentPolicy;
use crate::config::types::ShellEnvironmentPolicyInherit;
use codex_protocol::ThreadId;
use std::collections::HashMap;
use std::collections::HashSet;

pub const CODEX_THREAD_ID_ENV_VAR: &str = "CODEX_THREAD_ID";

/// Construct an environment map based on the rules in the specified policy. The
/// resulting map can be passed directly to `Command::envs()` after calling
/// `env_clear()` to ensure no unintended variables are leaked to the spawned
/// process.
///
/// The derivation follows the algorithm documented in the struct-level comment
/// for [`ShellEnvironmentPolicy`].
///
/// `CODEX_THREAD_ID` is injected when a thread id is provided, even when
/// `include_only` is set.
pub fn create_env(
    policy: &ShellEnvironmentPolicy,
    thread_id: Option<ThreadId>,
) -> HashMap<String, String> {
    populate_env(std::env::vars(), policy, thread_id)
}

fn populate_env<I>(
    vars: I,
    policy: &ShellEnvironmentPolicy,
    thread_id: Option<ThreadId>,
) -> HashMap<String, String>
where
    I: IntoIterator<Item = (String, String)>,
{
    // Step 1 – determine the starting set of variables based on the
    // `inherit` strategy.
    let mut env_map: HashMap<String, String> = match policy.inherit {
        ShellEnvironmentPolicyInherit::All => vars.into_iter().collect(),
        ShellEnvironmentPolicyInherit::None => HashMap::new(),
        ShellEnvironmentPolicyInherit::Core => {
            const CORE_VARS: &[&str] = &[
                "HOME", "LOGNAME", "PATH", "SHELL", "USER", "USERNAME", "TMPDIR", "TEMP", "TMP",
            ];
            let allow: HashSet<&str> = CORE_VARS.iter().copied().collect();
            let is_core_var = |name: &str| {
                if cfg!(target_os = "windows") {
                    CORE_VARS
                        .iter()
                        .any(|allowed| allowed.eq_ignore_ascii_case(name))
                } else {
                    allow.contains(name)
                }
            };
            vars.into_iter().filter(|(k, _)| is_core_var(k)).collect()
        }
    };

    // Internal helper – does `name` match **any** pattern in `patterns`?
    let matches_any = |name: &str, patterns: &[EnvironmentVariablePattern]| -> bool {
        patterns.iter().any(|pattern| pattern.matches(name))
    };

    // Step 2 – Apply the default exclude if not disabled.
    if !policy.ignore_default_excludes {
        let default_excludes = vec![
            EnvironmentVariablePattern::new_case_insensitive("*KEY*"),
            EnvironmentVariablePattern::new_case_insensitive("*SECRET*"),
            EnvironmentVariablePattern::new_case_insensitive("*TOKEN*"),
        ];
        env_map.retain(|k, _| !matches_any(k, &default_excludes));
    }

    // Step 3 – Apply custom excludes.
    if !policy.exclude.is_empty() {
        env_map.retain(|k, _| !matches_any(k, &policy.exclude));
    }

    // Step 4 – Apply user-provided overrides.
    for (key, val) in &policy.r#set {
        env_map.insert(key.clone(), val.clone());
    }

    // Step 5 – If include_only is non-empty, keep *only* the matching vars.
    if !policy.include_only.is_empty() {
        env_map.retain(|k, _| matches_any(k, &policy.include_only));
    }

    // Step 6 – Populate the thread ID environment variable when provided.
    if let Some(thread_id) = thread_id {
        env_map.insert(CODEX_THREAD_ID_ENV_VAR.to_string(), thread_id.to_string());
    }

    env_map
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::config::types::ShellEnvironmentPolicyInherit;
    use maplit::hashmap;

    fn make_vars(pairs: &[(&str, &str)]) -> Vec<(String, String)> {
        pairs
            .iter()
            .map(|(k, v)| (k.to_string(), v.to_string()))
            .collect()
    }

    #[test]
    fn test_core_inherit_defaults_keep_sensitive_vars() {
        let vars = make_vars(&[
            ("PATH", "/usr/bin"),
            ("HOME", "/home/user"),
            ("API_KEY", "secret"),
            ("SECRET_TOKEN", "t"),
        ]);

        let policy = ShellEnvironmentPolicy::default(); // inherit All, default excludes ignored
        let thread_id = ThreadId::new();
        let result = populate_env(vars, &policy, Some(thread_id));

        let mut expected: HashMap<String, String> = hashmap! {
            "PATH".to_string() => "/usr/bin".to_string(),
            "HOME".to_string() => "/home/user".to_string(),
            "API_KEY".to_string() => "secret".to_string(),
            "SECRET_TOKEN".to_string() => "t".to_string(),
        };
        expected.insert(CODEX_THREAD_ID_ENV_VAR.to_string(), thread_id.to_string());

        assert_eq!(result, expected);
    }

    #[test]
    fn test_core_inherit_with_default_excludes_enabled() {
        let vars = make_vars(&[
            ("PATH", "/usr/bin"),
            ("HOME", "/home/user"),
            ("API_KEY", "secret"),
            ("SECRET_TOKEN", "t"),
        ]);

        let policy = ShellEnvironmentPolicy {
            ignore_default_excludes: false, // apply KEY/SECRET/TOKEN filter
            ..Default::default()
        };
        let thread_id = ThreadId::new();
        let result = populate_env(vars, &policy, Some(thread_id));

        let mut expected: HashMap<String, String> = hashmap! {
            "PATH".to_string() => "/usr/bin".to_string(),
            "HOME".to_string() => "/home/user".to_string(),
        };
        expected.insert(CODEX_THREAD_ID_ENV_VAR.to_string(), thread_id.to_string());

        assert_eq!(result, expected);
    }

    #[test]
    fn test_include_only() {
        let vars = make_vars(&[("PATH", "/usr/bin"), ("FOO", "bar")]);

        let policy = ShellEnvironmentPolicy {
            // skip default excludes so nothing is removed prematurely
            ignore_default_excludes: true,
            include_only: vec![EnvironmentVariablePattern::new_case_insensitive("*PATH")],
            ..Default::default()
        };

        let thread_id = ThreadId::new();
        let result = populate_env(vars, &policy, Some(thread_id));

        let mut expected: HashMap<String, String> = hashmap! {
            "PATH".to_string() => "/usr/bin".to_string(),
        };
        expected.insert(CODEX_THREAD_ID_ENV_VAR.to_string(), thread_id.to_string());

        assert_eq!(result, expected);
    }

    #[test]
    fn test_set_overrides() {
        let vars = make_vars(&[("PATH", "/usr/bin")]);

        let mut policy = ShellEnvironmentPolicy {
            ignore_default_excludes: true,
            ..Default::default()
        };
        policy.r#set.insert("NEW_VAR".to_string(), "42".to_string());

        let thread_id = ThreadId::new();
        let result = populate_env(vars, &policy, Some(thread_id));

        let mut expected: HashMap<String, String> = hashmap! {
            "PATH".to_string() => "/usr/bin".to_string(),
            "NEW_VAR".to_string() => "42".to_string(),
        };
        expected.insert(CODEX_THREAD_ID_ENV_VAR.to_string(), thread_id.to_string());

        assert_eq!(result, expected);
    }

    #[test]
    fn populate_env_inserts_thread_id() {
        let vars = make_vars(&[("PATH", "/usr/bin")]);
        let policy = ShellEnvironmentPolicy::default();
        let thread_id = ThreadId::new();
        let result = populate_env(vars, &policy, Some(thread_id));

        let mut expected: HashMap<String, String> = hashmap! {
            "PATH".to_string() => "/usr/bin".to_string(),
        };
        expected.insert(CODEX_THREAD_ID_ENV_VAR.to_string(), thread_id.to_string());

        assert_eq!(result, expected);
    }

    #[test]
    fn populate_env_omits_thread_id_when_missing() {
        let vars = make_vars(&[("PATH", "/usr/bin")]);
        let policy = ShellEnvironmentPolicy::default();
        let result = populate_env(vars, &policy, None);

        let expected: HashMap<String, String> = hashmap! {
            "PATH".to_string() => "/usr/bin".to_string(),
        };

        assert_eq!(result, expected);
    }

    #[test]
    fn test_inherit_all() {
        let vars = make_vars(&[("PATH", "/usr/bin"), ("FOO", "bar")]);

        let policy = ShellEnvironmentPolicy {
            inherit: ShellEnvironmentPolicyInherit::All,
            ignore_default_excludes: true, // keep everything
            ..Default::default()
        };

        let thread_id = ThreadId::new();
        let result = populate_env(vars.clone(), &policy, Some(thread_id));
        let mut expected: HashMap<String, String> = vars.into_iter().collect();
        expected.insert(CODEX_THREAD_ID_ENV_VAR.to_string(), thread_id.to_string());
        assert_eq!(result, expected);
    }

    #[test]
    fn test_inherit_all_with_default_excludes() {
        let vars = make_vars(&[("PATH", "/usr/bin"), ("API_KEY", "secret")]);

        let policy = ShellEnvironmentPolicy {
            inherit: ShellEnvironmentPolicyInherit::All,
            ignore_default_excludes: false,
            ..Default::default()
        };

        let thread_id = ThreadId::new();
        let result = populate_env(vars, &policy, Some(thread_id));
        let mut expected: HashMap<String, String> = hashmap! {
            "PATH".to_string() => "/usr/bin".to_string(),
        };
        expected.insert(CODEX_THREAD_ID_ENV_VAR.to_string(), thread_id.to_string());
        assert_eq!(result, expected);
    }

    #[test]
    #[cfg(target_os = "windows")]
    fn test_core_inherit_respects_case_insensitive_names_on_windows() {
        let vars = make_vars(&[
            ("Path", "C:\\Windows\\System32"),
            ("TEMP", "C:\\Temp"),
            ("FOO", "bar"),
        ]);

        let policy = ShellEnvironmentPolicy {
            inherit: ShellEnvironmentPolicyInherit::Core,
            ignore_default_excludes: true,
            ..Default::default()
        };

        let thread_id = ThreadId::new();
        let result = populate_env(vars, &policy, Some(thread_id));
        let mut expected: HashMap<String, String> = hashmap! {
            "Path".to_string() => "C:\\Windows\\System32".to_string(),
            "TEMP".to_string() => "C:\\Temp".to_string(),
        };
        expected.insert(CODEX_THREAD_ID_ENV_VAR.to_string(), thread_id.to_string());

        assert_eq!(result, expected);
    }

    #[test]
    fn test_inherit_none() {
        let vars = make_vars(&[("PATH", "/usr/bin"), ("HOME", "/home")]);

        let mut policy = ShellEnvironmentPolicy {
            inherit: ShellEnvironmentPolicyInherit::None,
            ignore_default_excludes: true,
            ..Default::default()
        };
        policy
            .r#set
            .insert("ONLY_VAR".to_string(), "yes".to_string());

        let thread_id = ThreadId::new();
        let result = populate_env(vars, &policy, Some(thread_id));
        let mut expected: HashMap<String, String> = hashmap! {
            "ONLY_VAR".to_string() => "yes".to_string(),
        };
        expected.insert(CODEX_THREAD_ID_ENV_VAR.to_string(), thread_id.to_string());
        assert_eq!(result, expected);
    }
}