use once_cell::sync::Lazy;
use regex::Regex;

static PHONE_REGEX: Lazy<Regex> = Lazy::new(|| Regex::new(r"^[6-9]\d{9}$").unwrap());

static EMAIL_REGEX: Lazy<Regex> =
    Lazy::new(|| Regex::new(r"^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$").unwrap());

static PINCODE_REGEX: Lazy<Regex> = Lazy::new(|| Regex::new(r"^[1-9]\d{5}$").unwrap());

pub fn validate_email(email: &str) -> Result<(), ValidationError> {
    if email.is_empty() {
        return Err(ValidationError::new("Email cannot be empty"));
    }
    if email.len() > 255 {
        return Err(ValidationError::new("Email too long"));
    }
    if !EMAIL_REGEX.is_match(email) {
        return Err(ValidationError::new("Invalid email format"));
    }
    Ok(())
}

pub fn validate_pincode(pincode: &str) -> Result<(), ValidationError> {
    if pincode.is_empty() {
        return Err(ValidationError::new("Pincode cannot be empty"));
    }
    if !PINCODE_REGEX.is_match(pincode) {
        return Err(ValidationError::new(
            "Invalid Indian pincode format (6 digits starting with 1-9)",
        ));
    }
    Ok(())
}

pub fn validate_price(price: f64) -> Result<(), ValidationError> {
    if price <= 0.0 {
        return Err(ValidationError::new("Price must be greater than 0"));
    }
    if price > 1_000_000.0 {
        return Err(ValidationError::new("Price exceeds maximum allowed value"));
    }
    if price.is_nan() || price.is_infinite() {
        return Err(ValidationError::new("Invalid price value"));
    }
    Ok(())
}

pub fn validate_product_name(name: &str) -> Result<(), ValidationError> {
    if name.trim().is_empty() {
        return Err(ValidationError::new("Product name cannot be empty"));
    }
    if name.len() > 200 {
        return Err(ValidationError::new(
            "Product name too long (max 200 characters)",
        ));
    }
    Ok(())
}

pub fn validate_weight(weight: f64) -> Result<(), ValidationError> {
    if weight < 0.0 {
        return Err(ValidationError::new("Weight cannot be negative"));
    }
    if weight > 100_000.0 {
        // 100kg limit for social checkout
        return Err(ValidationError::new(
            "Weight exceeds maximum allowed value (100kg)",
        ));
    }
    if weight.is_nan() || weight.is_infinite() {
        return Err(ValidationError::new("Invalid weight value"));
    }
    Ok(())
}

pub fn sanitize_string(input: &str) -> String {
    input
        .trim()
        .chars()
        .filter(|c| !c.is_control())
        .take(1000)
        .collect()
}

pub fn normalize_phone(phone: &str) -> Result<String, ValidationError> {
    if phone.is_empty() {
        return Err(ValidationError::new("Phone cannot be empty"));
    }

    let digits: String = phone.chars().filter(|c| c.is_ascii_digit()).collect();
    let normalized = match digits.len() {
        10 => digits,
        11 if digits.starts_with('0') => digits[1..].to_string(),
        12 if digits.starts_with("91") => digits[2..].to_string(),
        _ => return Err(ValidationError::new("Invalid Indian phone number format")),
    };

    if !PHONE_REGEX.is_match(&normalized) {
        return Err(ValidationError::new("Invalid Indian phone number format"));
    }

    Ok(normalized)
}

pub fn validate_base64_payload(data: &str, max_bytes: usize) -> Result<Vec<u8>, ValidationError> {
    if data.is_empty() {
        return Err(ValidationError::new("Base64 payload cannot be empty"));
    }

    let raw_data = if let Some(pos) = data.find(',') {
        &data[pos + 1..]
    } else {
        data
    };

    use base64::{engine::general_purpose, Engine as _};
    match general_purpose::STANDARD.decode(raw_data) {
        Ok(bytes) => {
            if bytes.len() > max_bytes {
                return Err(ValidationError::new(&format!(
                    "Payload exceeds maximum size of {} bytes",
                    max_bytes
                )));
            }
            Ok(bytes)
        }
        Err(_) => Err(ValidationError::new("Invalid Base64 encoding")),
    }
}

pub fn sanitize_filename(filename: &str) -> String {
    let sanitized: String = filename
        .replace("..", "")
        .chars()
        .filter(|c| c.is_alphanumeric() || *c == '.' || *c == '-' || *c == '_')
        .collect();

    if sanitized.starts_with('.') || sanitized.is_empty() {
        return "unnamed".to_string();
    }

    sanitized.chars().take(255).collect()
}

#[derive(Debug, Clone)]
pub struct ValidationError {
    pub message: String,
}

impl ValidationError {
    pub fn new(msg: &str) -> Self {
        Self {
            message: msg.to_string(),
        }
    }
}

impl std::fmt::Display for ValidationError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{}", self.message)
    }
}

impl std::error::Error for ValidationError {}