//! SMB Share Snapshot Manager (MS-SMB2 §2.2.31 / MS-FSCC §2.3.7)
//!
//! Implements FSCTL_SRV_SNAPSHOT_CREATE/READ/WRITE/DELETE operations
//! for Windows VSS (Volume Shadow Copy Service) support.

use std::collections::HashMap;
use std::sync::{Arc, RwLock};
use std::time::SystemTime;

use crate::ntstatus;

/// Snapshot entry stored in SnapshotManager
#[derive(Debug, Clone)]
pub struct SnapshotEntry {
    /// Unique snapshot ID (GMT token format: @GMT-YYYY.MM.DD-HH.MM.SS)
    pub snapshot_id: String,
    /// Share name this snapshot belongs to
    pub share_name: String,
    /// Creation timestamp
    pub created_at: SystemTime,
    /// Snapshot state
    pub state: SnapshotState,
    /// Snapshot metadata (JSON)
    pub metadata: Option<String>,
}

/// Snapshot state enum
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum SnapshotState {
    Created,
    Active,
    Deleting,
    Deleted,
}

/// SMB Snapshot request types
#[derive(Debug, Clone)]
pub enum SnapshotRequest {
    Create {
        share_name: String,
        snapshot_name: Option<String>,
    },
    Read {
        share_name: String,
        snapshot_id: String,
    },
    Write {
        share_name: String,
        snapshot_id: String,
        data: Vec<u8>,
    },
    Delete {
        share_name: String,
        snapshot_id: String,
    },
}

/// SMB Snapshot response types
#[derive(Debug, Clone)]
pub enum SnapshotResponse {
    Create {
        snapshot_id: String,
        created_at: SystemTime,
    },
    Read {
        snapshot_id: String,
        data: Vec<u8>,
    },
    Write {
        bytes_written: u32,
    },
    Delete {
        success: bool,
    },
    List {
        snapshots: Vec<SnapshotEntry>,
    },
}

/// Snapshot manager - manages share snapshots
pub struct SnapshotManager {
    /// Snapshots indexed by (share_name, snapshot_id)
    snapshots: RwLock<HashMap<(String, String), SnapshotEntry>>,
}

impl SnapshotManager {
    pub fn new() -> Self {
        Self {
            snapshots: RwLock::new(HashMap::new()),
        }
    }

    /// Create a new snapshot for a share
    pub fn create_snapshot(
        &self,
        share_name: &str,
        snapshot_name: Option<&str>,
    ) -> Result<SnapshotEntry, u32> {
        let now = SystemTime::now();
        let snapshot_id = match snapshot_name {
            Some(name) => name.to_string(),
            None => Self::gmt_token_from_time(now),
        };

        let entry = SnapshotEntry {
            snapshot_id: snapshot_id.clone(),
            share_name: share_name.to_string(),
            created_at: now,
            state: SnapshotState::Active,
            metadata: None,
        };

        self.snapshots
            .write()
            .unwrap()
            .insert((share_name.to_string(), snapshot_id.clone()), entry.clone());

        Ok(entry)
    }

    /// Read snapshot metadata
    pub fn read_snapshot(
        &self,
        share_name: &str,
        snapshot_id: &str,
    ) -> Result<SnapshotEntry, u32> {
        self.snapshots
            .read()
            .unwrap()
            .get(&(share_name.to_string(), snapshot_id.to_string()))
            .cloned()
            .ok_or(ntstatus::STATUS_OBJECT_NAME_NOT_FOUND)
    }

    /// Delete a snapshot
    pub fn delete_snapshot(
        &self,
        share_name: &str,
        snapshot_id: &str,
    ) -> Result<(), u32> {
        let mut snapshots = self.snapshots.write().unwrap();
        
        let entry = snapshots
            .get_mut(&(share_name.to_string(), snapshot_id.to_string()))
            .ok_or(ntstatus::STATUS_OBJECT_NAME_NOT_FOUND)?;

        if entry.state == SnapshotState::Deleting {
            return Err(ntstatus::STATUS_SNAPSHOT_OPERATION_IN_PROGRESS);
        }

        entry.state = SnapshotState::Deleted;
        snapshots.remove(&(share_name.to_string(), snapshot_id.to_string()));

        Ok(())
    }

    /// List all snapshots for a share
    pub fn list_snapshots(&self, share_name: &str) -> Vec<SnapshotEntry> {
        self.snapshots
            .read()
            .unwrap()
            .iter()
            .filter(|((s, _), _)| s == share_name)
            .map(|(_, entry)| entry.clone())
            .collect()
    }

    /// Convert SystemTime to GMT token format (@GMT-YYYY.MM.DD-HH.MM.SS)
    pub fn gmt_token_from_time(time: SystemTime) -> String {
        use std::time::UNIX_EPOCH;
        
        let duration = time
            .duration_since(UNIX_EPOCH)
            .unwrap_or(std::time::Duration::ZERO);
        
        let total_secs = duration.as_secs();
        let hours = total_secs / 3600;
        let minutes = (total_secs % 3600) / 60;
        let seconds = total_secs % 60;
        
        // Simplified: use days since epoch (not calendar date)
        let days = hours / 24;
        let year = 1970 + days / 365;
        let remaining_days = days % 365;
        let month = remaining_days / 30 + 1;
        let day = remaining_days % 30 + 1;
        let hour = hours % 24;
        
        format!(
            "@GMT-{:04}.{:02}.{:02}-{:02}.{:02}.{:02}",
            year, month, day, hour, minutes, seconds
        )
    }

    /// Parse GMT token to SystemTime
    pub fn time_from_gmt_token(token: &str) -> Option<SystemTime> {
        use std::time::UNIX_EPOCH;
        
        if !token.starts_with("@GMT-") {
            return None;
        }

        let parts: Vec<&str> = token[5..].split('-').collect();
        if parts.len() != 2 {
            return None;
        }

        let date_parts: Vec<&str> = parts[0].split('.').collect();
        let time_parts: Vec<&str> = parts[1].split('.').collect();

        if date_parts.len() != 3 || time_parts.len() != 3 {
            return None;
        }

        let year: u64 = date_parts[0].parse().ok()?;
        let month: u64 = date_parts[1].parse().ok()?;
        let day: u64 = date_parts[2].parse().ok()?;
        let hour: u64 = time_parts[0].parse().ok()?;
        let minute: u64 = time_parts[1].parse().ok()?;
        let second: u64 = time_parts[2].parse().ok()?;

        // Simplified calculation (not calendar-aware)
        let days_since_epoch = (year - 1970) * 365 + month * 30 + day;
        let total_secs = days_since_epoch * 86400 + hour * 3600 + minute * 60 + second;

        Some(UNIX_EPOCH + std::time::Duration::from_secs(total_secs))
    }
}

impl Default for SnapshotManager {
    fn default() -> Self {
        Self::new()
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::time::UNIX_EPOCH;

    #[test]
    fn test_create_snapshot() {
        let manager = SnapshotManager::new();
        let entry = manager.create_snapshot("test_share", Some("snapshot1")).unwrap();
        
        assert_eq!(entry.share_name, "test_share");
        assert_eq!(entry.snapshot_id, "snapshot1");
        assert_eq!(entry.state, SnapshotState::Active);
    }

    #[test]
    fn test_read_snapshot() {
        let manager = SnapshotManager::new();
        manager.create_snapshot("test_share", Some("snapshot1")).unwrap();
        
        let entry = manager.read_snapshot("test_share", "snapshot1").unwrap();
        assert_eq!(entry.snapshot_id, "snapshot1");
    }

    #[test]
    fn test_delete_snapshot() {
        let manager = SnapshotManager::new();
        manager.create_snapshot("test_share", Some("snapshot1")).unwrap();
        
        manager.delete_snapshot("test_share", "snapshot1").unwrap();
        
        assert!(manager.read_snapshot("test_share", "snapshot1").is_err());
    }

    #[test]
    fn test_list_snapshots() {
        let manager = SnapshotManager::new();
        manager.create_snapshot("share1", Some("snap1")).unwrap();
        manager.create_snapshot("share1", Some("snap2")).unwrap();
        manager.create_snapshot("share2", Some("snap3")).unwrap();
        
        let snapshots = manager.list_snapshots("share1");
        assert_eq!(snapshots.len(), 2);
    }

    #[test]
    fn test_gmt_token_format() {
        let time = UNIX_EPOCH + std::time::Duration::from_secs(1609459200); // 2021-01-01 00:00:00
        let token = SnapshotManager::gmt_token_from_time(time);
        
        assert!(token.starts_with("@GMT-"));
        assert!(token.contains("2021"));
    }

    #[test]
    fn test_gmt_token_parse() {
        let token = "@GMT-2021.01.01-00.00.00";
        let time = SnapshotManager::time_from_gmt_token(token).unwrap();
        
        let token2 = SnapshotManager::gmt_token_from_time(time);
        assert!(token2.starts_with("@GMT-"));
    }
}