use argon2::{Algorithm, Argon2, Params, Version};
use rand::RngCore;
use serde::{Deserialize, Serialize};
use sha2::{Digest, Sha256, Sha384};
use std::fs;
use subtle::ConstantTimeEq;
use tauri::Manager;

use crate::database;

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Profile {
    pub id: String,
    pub name: String,
    pub color: String,
    pub pin_hash: Option<String>,
    pub db_filename: String,
    pub created_at: String,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ProfilesConfig {
    pub active_profile_id: String,
    pub profiles: Vec<Profile>,
}

fn get_profiles_path(app: &tauri::AppHandle) -> Result<std::path::PathBuf, String> {
    let app_dir = app
        .path()
        .app_data_dir()
        .map_err(|e| format!("Cannot get app data dir: {}", e))?;
    Ok(app_dir.join("profiles.json"))
}

fn make_default_config() -> ProfilesConfig {
    let now = chrono_now();
    let default_id = "default".to_string();
    ProfilesConfig {
        active_profile_id: default_id.clone(),
        profiles: vec![Profile {
            id: default_id,
            name: "Default".to_string(),
            color: "#4A90A4".to_string(),
            pin_hash: None,
            db_filename: "simpl_resultat.db".to_string(),
            created_at: now,
        }],
    }
}

fn chrono_now() -> String {
    // Simple ISO-ish timestamp without pulling in chrono crate
    let dur = std::time::SystemTime::now()
        .duration_since(std::time::UNIX_EPOCH)
        .unwrap_or_default();
    let secs = dur.as_secs();
    // Return as unix timestamp string — frontend can format it
    secs.to_string()
}

#[tauri::command]
pub fn load_profiles(app: tauri::AppHandle) -> Result<ProfilesConfig, String> {
    let path = get_profiles_path(&app)?;

    if !path.exists() {
        let config = make_default_config();
        let json =
            serde_json::to_string_pretty(&config).map_err(|e| format!("JSON error: {}", e))?;

        // Ensure parent dir exists
        if let Some(parent) = path.parent() {
            fs::create_dir_all(parent)
                .map_err(|e| format!("Cannot create app data dir: {}", e))?;
        }

        fs::write(&path, json).map_err(|e| format!("Cannot write profiles.json: {}", e))?;
        return Ok(config);
    }

    let content =
        fs::read_to_string(&path).map_err(|e| format!("Cannot read profiles.json: {}", e))?;
    let config: ProfilesConfig =
        serde_json::from_str(&content).map_err(|e| format!("Invalid profiles.json: {}", e))?;
    Ok(config)
}

#[tauri::command]
pub fn save_profiles(app: tauri::AppHandle, config: ProfilesConfig) -> Result<(), String> {
    let path = get_profiles_path(&app)?;
    let json =
        serde_json::to_string_pretty(&config).map_err(|e| format!("JSON error: {}", e))?;
    fs::write(&path, json).map_err(|e| format!("Cannot write profiles.json: {}", e))
}

#[tauri::command]
pub fn delete_profile_db(app: tauri::AppHandle, db_filename: String) -> Result<(), String> {
    if db_filename == "simpl_resultat.db" {
        return Err("Cannot delete the default profile database".to_string());
    }

    let app_dir = app
        .path()
        .app_data_dir()
        .map_err(|e| format!("Cannot get app data dir: {}", e))?;
    let db_path = app_dir.join(&db_filename);

    if db_path.exists() {
        fs::remove_file(&db_path)
            .map_err(|e| format!("Cannot delete database file: {}", e))?;
    }

    Ok(())
}

#[tauri::command]
pub fn get_new_profile_init_sql() -> Result<Vec<String>, String> {
    Ok(vec![
        database::CONSOLIDATED_SCHEMA.to_string(),
        database::SEED_CATEGORIES.to_string(),
    ])
}

// Argon2id parameters for PIN hashing (same as export_import_commands.rs)
const ARGON2_M_COST: u32 = 65536; // 64 MiB
const ARGON2_T_COST: u32 = 3;
const ARGON2_P_COST: u32 = 1;
const ARGON2_OUTPUT_LEN: usize = 32;
const ARGON2_SALT_LEN: usize = 16;

fn argon2_hash(pin: &str, salt: &[u8]) -> Result<Vec<u8>, String> {
    let params = Params::new(ARGON2_M_COST, ARGON2_T_COST, ARGON2_P_COST, Some(ARGON2_OUTPUT_LEN))
        .map_err(|e| format!("Argon2 params error: {}", e))?;
    let argon2 = Argon2::new(Algorithm::Argon2id, Version::V0x13, params);
    let mut hash = vec![0u8; ARGON2_OUTPUT_LEN];
    argon2
        .hash_password_into(pin.as_bytes(), salt, &mut hash)
        .map_err(|e| format!("Argon2 hash error: {}", e))?;
    Ok(hash)
}

#[tauri::command]
pub fn hash_pin(pin: String) -> Result<String, String> {
    let mut salt = [0u8; ARGON2_SALT_LEN];
    rand::rngs::OsRng.fill_bytes(&mut salt);
    let salt_hex = hex_encode(&salt);

    let hash = argon2_hash(&pin, &salt)?;
    let hash_hex = hex_encode(&hash);

    // Store as "argon2id:salt:hash" to distinguish from legacy SHA-256 "salt:hash"
    Ok(format!("argon2id:{}:{}", salt_hex, hash_hex))
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct VerifyPinResult {
    pub valid: bool,
    /// New Argon2id hash when a legacy SHA-256 PIN was successfully verified and re-hashed
    pub rehashed: Option<String>,
}

#[tauri::command]
pub fn verify_pin(pin: String, stored_hash: String) -> Result<VerifyPinResult, String> {
    // Argon2id format: "argon2id:salt_hex:hash_hex"
    if let Some(rest) = stored_hash.strip_prefix("argon2id:") {
        let parts: Vec<&str> = rest.split(':').collect();
        if parts.len() != 2 {
            return Err("Invalid Argon2id hash format".to_string());
        }
        let salt = hex_decode(parts[0])?;
        let expected_hash = hex_decode(parts[1])?;

        let computed = argon2_hash(&pin, &salt)?;

        let valid = computed.ct_eq(&expected_hash).into();
        return Ok(VerifyPinResult { valid, rehashed: None });
    }

    // Legacy SHA-256 format: "salt_hex:hash_hex"
    let parts: Vec<&str> = stored_hash.split(':').collect();
    if parts.len() != 2 {
        return Err("Invalid stored hash format".to_string());
    }
    let salt_hex = parts[0];
    let expected_hash = hex_decode(parts[1])?;

    let mut hasher = Sha256::new();
    hasher.update(salt_hex.as_bytes());
    hasher.update(pin.as_bytes());
    let result = hasher.finalize();

    let valid: bool = result.as_slice().ct_eq(&expected_hash).into();

    if valid {
        // Re-hash with Argon2id so this legacy PIN is upgraded
        let new_hash = hash_pin(pin)?;
        Ok(VerifyPinResult { valid: true, rehashed: Some(new_hash) })
    } else {
        Ok(VerifyPinResult { valid: false, rehashed: None })
    }
}

fn hex_encode(bytes: &[u8]) -> String {
    bytes.iter().map(|b| format!("{:02x}", b)).collect()
}

fn hex_decode(hex: &str) -> Result<Vec<u8>, String> {
    if hex.len() % 2 != 0 {
        return Err("Invalid hex string length".to_string());
    }
    (0..hex.len())
        .step_by(2)
        .map(|i| {
            u8::from_str_radix(&hex[i..i + 2], 16)
                .map_err(|e| format!("Invalid hex character: {}", e))
        })
        .collect()
}

/// Repair migration checksums for a profile database.
/// Updates stored checksums to match current migration SQL, avoiding re-application
/// of destructive migrations (e.g., migration 2 which DELETEs categories/keywords).
#[tauri::command]
pub fn repair_migrations(app: tauri::AppHandle, db_filename: String) -> Result<bool, String> {
    let app_dir = app
        .path()
        .app_data_dir()
        .map_err(|e| format!("Cannot get app data dir: {}", e))?;
    let db_path = app_dir.join(&db_filename);

    if !db_path.exists() {
        return Ok(false);
    }

    let conn = rusqlite::Connection::open(&db_path)
        .map_err(|e| format!("Cannot open database: {}", e))?;

    let table_exists: bool = conn
        .query_row(
            "SELECT COUNT(*) > 0 FROM sqlite_master WHERE type='table' AND name='_sqlx_migrations'",
            [],
            |row| row.get(0),
        )
        .unwrap_or(false);

    if !table_exists {
        return Ok(false);
    }

    // Current migration SQL — must match the vec in lib.rs
    let migrations: &[(i64, &str)] = &[
        (1, database::SCHEMA),
        (2, database::SEED_CATEGORIES),
    ];

    let mut repaired = false;
    for (version, sql) in migrations {
        let expected_checksum = Sha384::digest(sql.as_bytes()).to_vec();

        // Check if this migration exists with a different checksum
        let needs_repair: bool = conn
            .query_row(
                "SELECT COUNT(*) > 0 FROM _sqlx_migrations WHERE version = ?1 AND checksum != ?2",
                rusqlite::params![version, expected_checksum],
                |row| row.get(0),
            )
            .unwrap_or(false);

        if needs_repair {
            conn.execute(
                "UPDATE _sqlx_migrations SET checksum = ?1 WHERE version = ?2",
                rusqlite::params![expected_checksum, version],
            )
            .map_err(|e| format!("Cannot repair migration {}: {}", version, e))?;
            repaired = true;
        }
    }

    Ok(repaired)
}

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

    #[test]
    fn test_hash_pin_produces_argon2id_format() {
        let hash = hash_pin("1234".to_string()).unwrap();
        assert!(hash.starts_with("argon2id:"), "Hash should start with 'argon2id:' prefix");
        let parts: Vec<&str> = hash.split(':').collect();
        assert_eq!(parts.len(), 3, "Hash should have 3 parts: prefix:salt:hash");
        assert_eq!(parts[1].len(), ARGON2_SALT_LEN * 2, "Salt should be {} hex chars", ARGON2_SALT_LEN * 2);
        assert_eq!(parts[2].len(), ARGON2_OUTPUT_LEN * 2, "Hash should be {} hex chars", ARGON2_OUTPUT_LEN * 2);
    }

    #[test]
    fn test_hash_pin_different_salts() {
        let h1 = hash_pin("1234".to_string()).unwrap();
        let h2 = hash_pin("1234".to_string()).unwrap();
        assert_ne!(h1, h2, "Two hashes of the same PIN should use different salts");
    }

    #[test]
    fn test_verify_argon2id_pin_correct() {
        let hash = hash_pin("5678".to_string()).unwrap();
        let result = verify_pin("5678".to_string(), hash).unwrap();
        assert!(result.valid, "Correct PIN should verify");
        assert!(result.rehashed.is_none(), "Argon2id PIN should not be rehashed");
    }

    #[test]
    fn test_verify_argon2id_pin_wrong() {
        let hash = hash_pin("5678".to_string()).unwrap();
        let result = verify_pin("0000".to_string(), hash).unwrap();
        assert!(!result.valid, "Wrong PIN should not verify");
        assert!(result.rehashed.is_none());
    }

    #[test]
    fn test_verify_legacy_sha256_correct_and_rehash() {
        // Create a legacy SHA-256 hash: "salt_hex:sha256(salt_hex + pin)"
        let salt_hex = "abcdef0123456789";
        let mut hasher = Sha256::new();
        hasher.update(salt_hex.as_bytes());
        hasher.update(b"4321");
        let hash_bytes = hasher.finalize();
        let hash_hex = hex_encode(&hash_bytes);
        let stored = format!("{}:{}", salt_hex, hash_hex);

        let result = verify_pin("4321".to_string(), stored).unwrap();
        assert!(result.valid, "Correct legacy PIN should verify");
        assert!(result.rehashed.is_some(), "Legacy PIN should be rehashed to Argon2id");

        // Verify the rehashed value is a valid Argon2id hash
        let new_hash = result.rehashed.unwrap();
        assert!(new_hash.starts_with("argon2id:"));

        // Verify the rehashed value works for future verification
        let result2 = verify_pin("4321".to_string(), new_hash).unwrap();
        assert!(result2.valid, "Rehashed PIN should verify");
        assert!(result2.rehashed.is_none(), "Already Argon2id, no rehash needed");
    }

    #[test]
    fn test_verify_legacy_sha256_wrong() {
        let salt_hex = "abcdef0123456789";
        let mut hasher = Sha256::new();
        hasher.update(salt_hex.as_bytes());
        hasher.update(b"4321");
        let hash_bytes = hasher.finalize();
        let hash_hex = hex_encode(&hash_bytes);
        let stored = format!("{}:{}", salt_hex, hash_hex);

        let result = verify_pin("9999".to_string(), stored).unwrap();
        assert!(!result.valid, "Wrong legacy PIN should not verify");
        assert!(result.rehashed.is_none(), "Failed verification should not rehash");
    }

    #[test]
    fn test_verify_invalid_format() {
        let result = verify_pin("1234".to_string(), "invalid".to_string());
        assert!(result.is_err(), "Single-part hash should fail");

        let result = verify_pin("1234".to_string(), "argon2id:bad".to_string());
        assert!(result.is_err(), "Argon2id with wrong part count should fail");
    }

    #[test]
    fn test_hex_roundtrip() {
        let original = vec![0u8, 127, 255, 1, 16];
        let encoded = hex_encode(&original);
        let decoded = hex_decode(&encoded).unwrap();
        assert_eq!(original, decoded);
    }
}