use chrono::{Datelike, NaiveDate, Utc};

use crate::errors::{AuthError, AuthResult};

pub const MAX_USERNAME_LEN: usize = 64;
pub const MAX_DISPLAY_NAME_LEN: usize = 64;
pub const MIN_EMAIL_LEN: usize = 3;
pub const MAX_EMAIL_LEN: usize = 254;

pub fn validate_email(raw: &str) -> AuthResult<String> {
    let email = raw.trim().to_lowercase();
    if email.len() < MIN_EMAIL_LEN || email.len() > MAX_EMAIL_LEN {
        return Err(AuthError::InvalidEmail);
    }
    if email.chars().any(char::is_whitespace) {
        return Err(AuthError::InvalidEmail);
    }
    let mut parts = email.split('@');
    let (Some(local), Some(domain), None) = (parts.next(), parts.next(), parts.next()) else {
        return Err(AuthError::InvalidEmail);
    };
    if !valid_local_part(local) || !valid_domain(domain) {
        return Err(AuthError::InvalidEmail);
    }
    Ok(email)
}

/// 本地部分：不允许空、首尾点与连续点，字符限于 RFC 5321 的常用集合。
fn valid_local_part(local: &str) -> bool {
    const MAX_LOCAL_LEN: usize = 64;
    if local.is_empty() || local.len() > MAX_LOCAL_LEN {
        return false;
    }
    if local.starts_with('.') || local.ends_with('.') || local.contains("..") {
        return false;
    }
    local.chars().all(|c| {
        c.is_ascii_alphanumeric()
            || matches!(
                c,
                '.' | '!'
                    | '#'
                    | '$'
                    | '%'
                    | '&'
                    | '\''
                    | '*'
                    | '+'
                    | '-'
                    | '/'
                    | '='
                    | '?'
                    | '^'
                    | '_'
                    | '`'
                    | '{'
                    | '|'
                    | '}'
                    | '~'
            )
    })
}

/// 域名：至少两段、每段非空且不以连字符开头/结尾，顶级域纯字母且至少两位。
fn valid_domain(domain: &str) -> bool {
    const MAX_LABEL_LEN: usize = 63;
    let labels: Vec<&str> = domain.split('.').collect();
    if labels.len() < 2 {
        return false;
    }
    for label in &labels {
        if label.is_empty() || label.len() > MAX_LABEL_LEN {
            return false;
        }
        if label.starts_with('-') || label.ends_with('-') {
            return false;
        }
        if !label.chars().all(|c| c.is_ascii_alphanumeric() || c == '-') {
            return false;
        }
    }
    let Some(tld) = labels.last() else {
        return false;
    };
    tld.len() >= 2 && tld.chars().all(|c| c.is_ascii_alphabetic())
}

pub fn validate_username(name: &str) -> AuthResult<String> {
    let name = name.trim();
    if name.is_empty() || name.len() > MAX_USERNAME_LEN {
        return Err(AuthError::InvalidUsername);
    }
    if !name
        .chars()
        .all(|c| c.is_ascii_alphanumeric() || matches!(c, '_' | '.' | '-'))
    {
        return Err(AuthError::InvalidUsername);
    }
    Ok(name.to_string())
}

pub fn validate_display_name(name: &str) -> AuthResult<String> {
    let name = name.trim();
    if name.is_empty() || name.chars().count() > MAX_DISPLAY_NAME_LEN {
        return Err(AuthError::InvalidDisplayname);
    }
    Ok(name.to_string())
}

pub fn validate_age(date_of_birth: Option<NaiveDate>, min_age: u8) -> AuthResult<NaiveDate> {
    let Some(birth) = date_of_birth else {
        return Err(AuthError::InvalidBirthDate);
    };
    let today = Utc::now().date_naive();
    if birth > today {
        return Err(AuthError::InvalidBirthDate);
    }
    let mut age = today.year() - birth.year();
    if (today.month(), today.day()) < (birth.month(), birth.day()) {
        age -= 1;
    }
    if age < min_age as i32 {
        return Err(AuthError::UnderMinimumAge {
            min_age: min_age as u32,
        });
    }
    Ok(birth)
}