use base64::engine::general_purpose::STANDARD_NO_PAD as BASE64;
use base64::Engine;
use ed25519_dalek::{Signature, VerifyingKey};
use serde::{Deserialize, Serialize};
use std::path::PathBuf;
use std::time::{SystemTime, UNIX_EPOCH};

pub const TALKEDIT_PUBLIC_KEY: [u8; 32] = [123, 66, 135, 187, 184, 19, 205, 192, 129, 94, 91, 138, 123, 3, 72, 52, 229, 8, 245, 226, 187, 218, 67, 131, 38, 214, 239, 203, 206, 7, 132, 176];

pub const TRIAL_DURATION_SECS: u64 = 7 * 86400;

#[derive(Debug, Serialize, Deserialize, Clone)]
pub struct LicensePayload {
    pub license_id: String,
    pub customer_email: String,
    pub tier: String,
    pub features: Vec<String>,
    pub issued_at: u64,
    pub expires_at: u64,
    pub max_activations: u32,
}

#[derive(Debug, Serialize, Deserialize, Clone)]
pub struct TrialState {
    pub started_at: u64,
}

/// On-disk format with integrity seed to deter tampering.
#[derive(Debug, Serialize, Deserialize)]
struct TrialFile {
    started_at: u64,
    seed: u64,
}

#[derive(Debug, Serialize, Deserialize)]
#[serde(tag = "tag")]
pub enum AppStatus {
    Licensed { license: LicensePayload },
    Trial { days_remaining: u32, started_at: u64 },
    Expired,
}

#[derive(Debug)]
pub enum LicenseError {
    InvalidFormat,
    InvalidSignature,
    Expired,
    DecodeError(String),
    CryptoError(String),
}

impl std::fmt::Display for LicenseError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::InvalidFormat => write!(f, "Invalid license key format"),
            Self::InvalidSignature => write!(f, "License signature is invalid"),
            Self::Expired => write!(f, "License has expired"),
            Self::DecodeError(e) => write!(f, "License decode error: {e}"),
            Self::CryptoError(e) => write!(f, "Crypto error: {e}"),
        }
    }
}

// --- License key verification ---

pub fn verify_license_key(license_key: &str) -> Result<LicensePayload, LicenseError> {
    let stripped = license_key
        .strip_prefix("talkedit_v1_")
        .ok_or(LicenseError::InvalidFormat)?;

    let dot_pos = stripped.rfind('.').ok_or(LicenseError::InvalidFormat)?;
    let payload_b64 = &stripped[..dot_pos];
    let sig_b64 = &stripped[dot_pos + 1..];

    if payload_b64.is_empty() || sig_b64.is_empty() {
        return Err(LicenseError::InvalidFormat);
    }

    let payload_bytes = BASE64
        .decode(payload_b64)
        .map_err(|e| LicenseError::DecodeError(e.to_string()))?;
    let sig_bytes = BASE64
        .decode(sig_b64)
        .map_err(|e| LicenseError::DecodeError(e.to_string()))?;

    let verifying_key = VerifyingKey::from_bytes(&TALKEDIT_PUBLIC_KEY)
        .map_err(|e| LicenseError::CryptoError(e.to_string()))?;
    let signature = Signature::from_slice(&sig_bytes)
        .map_err(|e| LicenseError::DecodeError(e.to_string()))?;

    verifying_key
        .verify_strict(&payload_bytes, &signature)
        .map_err(|_| LicenseError::InvalidSignature)?;

    let payload: LicensePayload = serde_json::from_slice(&payload_bytes)
        .map_err(|e| LicenseError::DecodeError(e.to_string()))?;

    let now = now_secs();
    if now > payload.expires_at {
        return Err(LicenseError::Expired);
    }

    Ok(payload)
}

// --- License file I/O ---

fn now_secs() -> u64 {
    SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .unwrap_or_default()
        .as_secs()
}

pub fn license_file_path(app_data_dir: &PathBuf) -> PathBuf {
    app_data_dir.join("license.key")
}

pub fn trial_file_path(app_data_dir: &PathBuf) -> PathBuf {
    app_data_dir.join("trial.json")
}

pub fn trial_sentinel_path(app_data_dir: &PathBuf) -> PathBuf {
    app_data_dir.join(".trial_lock")
}

// Simple integrity check constant — not crypto-grade, but deters casual editing.
const TRIAL_SEED: u64 = 0x9F3A_2E7D_C1B8_5604;

pub fn get_or_start_trial(app_data_dir: &PathBuf) -> TrialState {
    let path = trial_file_path(app_data_dir);
    let sentinel = trial_sentinel_path(app_data_dir);
    let now = now_secs();

    // If sentinel exists but trial was deleted, refuse to create a new one.
    let sentinel_exists = sentinel.exists();

    if let Ok(content) = std::fs::read_to_string(&path) {
        if let Ok(wrapped) = serde_json::from_str::<TrialFile>(&content) {
            // Verify integrity
            if (wrapped.started_at ^ TRIAL_SEED) == wrapped.seed {
                return TrialState { started_at: wrapped.started_at };
            }
        }
    }

    if sentinel_exists {
        // Trial was tampered with — return an expired trial
        return TrialState { started_at: 0 };
    }

    // Start new trial
    let trial = TrialState { started_at: now };
    if let Some(parent) = path.parent() {
        let _ = std::fs::create_dir_all(parent);
    }
    let _ = std::fs::write(&sentinel, "1");
    let _ = std::fs::write(
        &path,
        serde_json::to_string(&TrialFile {
            started_at: trial.started_at,
            seed: trial.started_at ^ TRIAL_SEED,
        })
        .unwrap(),
    );
    trial
}

pub fn load_cached_license(app_data_dir: &PathBuf) -> Result<LicensePayload, LicenseError> {
    let path = license_file_path(app_data_dir);
    let content = std::fs::read_to_string(&path).map_err(|_| LicenseError::InvalidFormat)?;
    verify_license_key(content.trim())
}

pub fn cache_license(app_data_dir: &PathBuf, license_key: &str) -> Result<(), LicenseError> {
    let path = license_file_path(app_data_dir);
    if let Some(parent) = path.parent() {
        std::fs::create_dir_all(parent)
            .map_err(|e| LicenseError::DecodeError(e.to_string()))?;
    }
    std::fs::write(&path, license_key)
        .map_err(|e| LicenseError::DecodeError(e.to_string()))
}

pub fn remove_license(app_data_dir: &PathBuf) {
    let path = license_file_path(app_data_dir);
    let _ = std::fs::remove_file(&path);
}

// --- Trial logic ---

pub fn get_trial_info(trial: &TrialState) -> (u64, u64, bool) {
    let now = now_secs();
    let elapsed = now.saturating_sub(trial.started_at);
    let remaining = TRIAL_DURATION_SECS.saturating_sub(elapsed);
    let days_remaining = remaining / 86400;
    let is_active = remaining > 0;
    (days_remaining, remaining, is_active)
}

/// Check if trial is still valid and return remaining days.
pub fn get_trial_days_remaining(trial: &TrialState) -> Option<u32> {
    let (days, _, active) = get_trial_info(trial);
    if active {
        Some(days as u32)
    } else {
        None
    }
}

pub fn clear_trial(app_data_dir: &PathBuf) {
    let _ = std::fs::remove_file(trial_file_path(app_data_dir));
    let _ = std::fs::remove_file(trial_sentinel_path(app_data_dir));
}

/// Get the overall app status: Licensed > Trial > Expired.
pub fn get_app_status(app_data_dir: &PathBuf) -> AppStatus {
    // 1. Check for valid license
    if let Ok(license) = load_cached_license(app_data_dir) {
        return AppStatus::Licensed { license };
    }

    // 2. Check for active trial
    let trial = get_or_start_trial(app_data_dir);
    if let Some(days) = get_trial_days_remaining(&trial) {
        return AppStatus::Trial {
            days_remaining: days,
            started_at: trial.started_at,
        };
    }

    // 3. Everything expired
    AppStatus::Expired
}

pub fn has_feature(payload: &LicensePayload, feature: &str) -> bool {
    payload.features.iter().any(|f| f == feature)
}

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

    const TEST_KEY: &str = "talkedit_v1_eyJsaWNlbnNlX2lkIjoidGVzdF8wMDEiLCJjdXN0b21lcl9lbWFpbCI6InRlc3RAZXhhbXBsZS5jb20iLCJ0aWVyIjoicHJvIiwiZmVhdHVyZXMiOlsiYnVuZGxlZF9kZXBzIiwiYXV0b191cGRhdGVzIiwiYmdfcmVtb3ZhbCJdLCJpc3N1ZWRfYXQiOjE3NzgwMDAwMDAsImV4cGlyZXNfYXQiOjE4MDk1MzYwMDAsIm1heF9hY3RpdmF0aW9ucyI6M30.vnT0xa8GqINY5ZvU5cCulmlwiS6IUr+Ln5yVzgY+KmGfAlfhiiOpQIsFNiwaG0rb8qk5//7CWFDe6kQdEFnnBw";

    #[test]
    fn test_verify_valid_license() {
        let result = verify_license_key(TEST_KEY);
        assert!(result.is_ok(), "Expected OK, got: {:?}", result);
        let payload = result.unwrap();
        assert_eq!(payload.customer_email, "test@example.com");
        assert_eq!(payload.tier, "pro");
        assert!(payload.features.contains(&"bg_removal".to_string()));
    }

    #[test]
    fn test_verify_invalid_signature() {
        let dot = TEST_KEY.rfind('.').unwrap();
        let prefix = &TEST_KEY[..dot + 1];
        let bad_sig = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
        let tampered = format!("{prefix}{bad_sig}");
        let result = verify_license_key(&tampered);
        assert!(matches!(result, Err(LicenseError::InvalidSignature)));
    }

    #[test]
    fn test_verify_bad_format() {
        let result = verify_license_key("not-a-license-key");
        assert!(matches!(result, Err(LicenseError::InvalidFormat)));
    }

    #[test]
    fn test_has_feature() {
        let payload = verify_license_key(TEST_KEY).unwrap();
        assert!(has_feature(&payload, "bg_removal"));
        assert!(!has_feature(&payload, "nonexistent_feature"));
    }

    #[test]
    fn test_trial_dates() {
        let trial = TrialState { started_at: now_secs() };
        let days = get_trial_days_remaining(&trial);
        assert!(days.is_some());
        assert_eq!(days.unwrap(), 7);
    }

    #[test]
    fn test_expired_trial() {
        let trial = TrialState { started_at: 0 }; // epoch = 1970, definitely expired
        let days = get_trial_days_remaining(&trial);
        assert!(days.is_none());
    }
}