//! On-disk persistence for recovery codes. One file per user under
//! `cfg.recovery_dir`, mode 0600, root-owned.
//!
//! File format (two lines, UTF-8, trailing LFs):
//!     <expires_unix>\n<argon2id-PHC-string>\n
//! Picked over JSON so the C PAM module can parse it without linking json-c.

#![allow(dead_code)] // wired through AppState in Task 5.

use crate::recovery::{hash_code, verify_code};
use std::fs;
use std::os::unix::fs::PermissionsExt;
use std::path::PathBuf;
use std::time::{SystemTime, UNIX_EPOCH};
use thiserror::Error;

#[derive(Debug, Error)]
pub(crate) enum RecoveryStoreError {
    #[error("io: {0}")]
    Io(#[from] std::io::Error),
    #[error("invalid username: {0:?}")]
    InvalidUser(String),
    #[error("malformed recovery file for {0:?}")]
    Malformed(String),
    #[error("hash error: {0}")]
    Hash(String),
    #[error("system clock before unix epoch")]
    Clock,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub(crate) struct RecoveryEntry {
    pub user: String,
    pub expires_unix: u64,
}

pub(crate) struct RecoveryStore {
    dir: PathBuf,
}

impl RecoveryStore {
    pub fn new(dir: PathBuf) -> Self {
        Self { dir }
    }

    fn user_path(&self, user: &str) -> Result<PathBuf, RecoveryStoreError> {
        super::safe_user::join_user_segment(&self.dir, user).map_err(|e| match e {
            super::safe_user::SegmentError::Invalid(s) => RecoveryStoreError::InvalidUser(s),
        })
    }

    /// Generate, hash, and persist a fresh code for `user`. The file is
    /// written atomically (temp + rename) so a concurrent reader never sees
    /// a half-written file. Mode is set to 0600 before rename. Returns the
    /// plaintext code so the caller can show it to the admin once.
    pub fn issue(&self, user: &str, ttl_secs: u64) -> Result<String, RecoveryStoreError> {
        fs::create_dir_all(&self.dir)?;
        // Tighten directory mode so a non-root snoop can't list users.
        fs::set_permissions(&self.dir, fs::Permissions::from_mode(0o700))?;

        let path = self.user_path(user)?;
        let code = crate::recovery::generate_code();
        let phc = hash_code(&code).map_err(|e| RecoveryStoreError::Hash(e.to_string()))?;
        let expires = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .map_err(|_| RecoveryStoreError::Clock)?
            .as_secs()
            .saturating_add(ttl_secs);

        let body = format!("{expires}\n{phc}\n");
        let tmp = path.with_extension("tmp");
        fs::write(&tmp, body.as_bytes())?;
        fs::set_permissions(&tmp, fs::Permissions::from_mode(0o600))?;
        fs::rename(&tmp, &path)?;
        Ok(code)
    }

    /// List all users with a recovery code on file (expired or not). Sorted
    /// alphabetically for stable display.
    pub fn list(&self) -> Result<Vec<RecoveryEntry>, RecoveryStoreError> {
        let mut out = Vec::new();
        let rd = match fs::read_dir(&self.dir) {
            Ok(r) => r,
            Err(e) if e.kind() == std::io::ErrorKind::NotFound => return Ok(out),
            Err(e) => return Err(e.into()),
        };
        for entry in rd {
            let entry = entry?;
            if !entry.file_type()?.is_file() {
                continue;
            }
            let user = entry.file_name().to_string_lossy().to_string();
            // Skip atomic-rename leftovers.
            if user.ends_with(".tmp") {
                continue;
            }
            if let Ok(e) = self.entry_for(&user) {
                out.push(e);
            }
        }
        out.sort_by(|a, b| a.user.cmp(&b.user));
        Ok(out)
    }

    pub fn entry_for(&self, user: &str) -> Result<RecoveryEntry, RecoveryStoreError> {
        let path = self.user_path(user)?;
        let body = fs::read_to_string(&path)?;
        let mut lines = body.lines();
        let expires: u64 = lines
            .next()
            .ok_or_else(|| RecoveryStoreError::Malformed(user.to_string()))?
            .parse()
            .map_err(|_| RecoveryStoreError::Malformed(user.to_string()))?;
        Ok(RecoveryEntry {
            user: user.to_string(),
            expires_unix: expires,
        })
    }

    /// Delete the recovery file for `user`. Returns true if a file was
    /// removed, false if there was nothing there.
    pub fn revoke(&self, user: &str) -> Result<bool, RecoveryStoreError> {
        let path = self.user_path(user)?;
        match fs::remove_file(path) {
            Ok(()) => Ok(true),
            Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(false),
            Err(e) => Err(e.into()),
        }
    }

    /// Verify a candidate code for `user`. On match: deletes the recovery
    /// file (one-shot semantics) and returns Ok(true). On expired: deletes
    /// the file as a side-effect cleanup and returns Ok(false).
    pub fn verify_and_consume(
        &self,
        user: &str,
        candidate: &str,
    ) -> Result<bool, RecoveryStoreError> {
        let path = self.user_path(user)?;
        let body = match fs::read_to_string(&path) {
            Ok(s) => s,
            Err(e) if e.kind() == std::io::ErrorKind::NotFound => return Ok(false),
            Err(e) => return Err(e.into()),
        };
        let mut lines = body.lines();
        let expires: u64 = lines
            .next()
            .ok_or_else(|| RecoveryStoreError::Malformed(user.to_string()))?
            .parse()
            .map_err(|_| RecoveryStoreError::Malformed(user.to_string()))?;
        let phc = lines
            .next()
            .ok_or_else(|| RecoveryStoreError::Malformed(user.to_string()))?;

        let now = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .map_err(|_| RecoveryStoreError::Clock)?
            .as_secs();
        if now > expires {
            let _ = fs::remove_file(&path);
            return Ok(false);
        }

        let ok =
            verify_code(candidate, phc).map_err(|e| RecoveryStoreError::Hash(e.to_string()))?;
        if ok {
            let _ = fs::remove_file(&path);
        }
        Ok(ok)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use tempfile::tempdir;

    fn store() -> (tempfile::TempDir, RecoveryStore) {
        let d = tempdir().unwrap();
        let s = RecoveryStore::new(d.path().to_path_buf());
        (d, s)
    }

    #[test]
    fn issue_then_verify_consumes_file() {
        let (_d, s) = store();
        let code = s.issue("alice", 600).unwrap();
        assert!(s.entry_for("alice").is_ok());
        assert!(s.verify_and_consume("alice", &code).unwrap());
        assert!(matches!(
            s.entry_for("alice"),
            Err(RecoveryStoreError::Io(_))
        ));
    }

    #[test]
    fn verify_with_wrong_code_does_not_consume() {
        let (_d, s) = store();
        s.issue("alice", 600).unwrap();
        assert!(!s.verify_and_consume("alice", "00000000").unwrap());
        assert!(s.entry_for("alice").is_ok());
    }

    #[test]
    fn expired_entry_is_treated_as_absent_and_cleaned_up() {
        let (_d, s) = store();
        s.issue("alice", 0).unwrap();
        std::thread::sleep(std::time::Duration::from_millis(1100));
        assert!(!s.verify_and_consume("alice", "anything").unwrap());
        assert!(matches!(
            s.entry_for("alice"),
            Err(RecoveryStoreError::Io(_))
        ));
    }

    #[test]
    fn revoke_returns_false_on_missing_user() {
        let (_d, s) = store();
        assert!(!s.revoke("ghost").unwrap());
    }

    #[test]
    fn list_sorts_users_alphabetically() {
        let (_d, s) = store();
        s.issue("charlie", 600).unwrap();
        s.issue("alice", 600).unwrap();
        s.issue("bob", 600).unwrap();
        let users: Vec<_> = s.list().unwrap().into_iter().map(|e| e.user).collect();
        assert_eq!(users, vec!["alice", "bob", "charlie"]);
    }

    #[test]
    fn rejects_traversal_usernames() {
        let (_d, s) = store();
        for evil in ["", ".", "..", "a/b", "x\0y"] {
            assert!(s.issue(evil, 600).is_err());
        }
    }

    #[test]
    fn issue_writes_file_with_mode_0600() {
        let (_d, s) = store();
        s.issue("alice", 600).unwrap();
        let path = s.user_path("alice").unwrap();
        let mode = fs::metadata(&path).unwrap().permissions().mode() & 0o777;
        assert_eq!(mode, 0o600);
    }
}