use time::{Date, OffsetDateTime};

use crate::errors::AuthError;

pub fn validate_email(raw: &str) -> Result<String, AuthError> {
    let email = raw.trim().to_lowercase();
    if email.len() < 3 || email.len() > 254 {
        return Err(AuthError::BadRequest("invalid email address".to_string()));
    }
    if email.chars().any(|c| c.is_whitespace()) {
        return Err(AuthError::BadRequest("invalid email address".to_string()));
    }
    let Some(at) = email.find('@') else {
        return Err(AuthError::BadRequest("invalid email address".to_string()));
    };
    if at == 0 || at == email.len() - 1 || !email[at + 1..].contains('.') {
        return Err(AuthError::BadRequest("invalid email address".to_string()));
    }
    Ok(email)
}

pub fn validate_username(name: &str) -> Result<String, AuthError> {
    if name.is_empty() || name.len() > 64 {
        return Err(AuthError::BadRequest(
            "username must be between 1 and 64 characters".to_string(),
        ));
    }
    if !name
        .chars()
        .all(|c| c.is_ascii_alphanumeric() || matches!(c, '_' | '.' | '-'))
    {
        return Err(AuthError::BadRequest(
            "username may only contain letters, digits, underscores, dots and dashes".to_string(),
        ));
    }
    Ok(name.to_string())
}

pub fn derive_username(email: &str, explicit: Option<&str>) -> Result<String, AuthError> {
    match explicit {
        Some(name) => validate_username(name),
        None => {
            let local_part = email.split('@').next().unwrap_or_default();
            let base = local_part.split('+').next().unwrap_or_default();
            validate_username(base)
        }
    }
}

pub fn validate_age(date_of_birth: Option<Date>, min_age: u8) -> Result<(), AuthError> {
    let Some(dob) = date_of_birth else {
        return Err(AuthError::BadRequest(
            "date of birth is required".to_string(),
        ));
    };
    let today = OffsetDateTime::now_utc().date();
    let mut age = today.year() - dob.year();
    if (today.month(), today.day()) < (dob.month(), dob.day()) {
        age -= 1;
    }
    if age < min_age as i32 {
        return Err(AuthError::BadRequest(format!(
            "you must be at least {min_age} years old"
        )));
    }
    Ok(())
}