use std::collections::HashMap;

use actix_web::http::{header::HeaderMap, Method, Uri};
use chrono::{DateTime, Duration, TimeZone, Utc};
use regex::Regex;
use rsa::RsaPublicKey;

use mitra_utils::crypto_rsa::verify_rsa_sha256_signature;

const SIGNATURE_PARAMETER_RE: &str = r#"^(?P<key>[a-zA-Z]+)="(?P<value>.+)"$"#;

const SIGNATURE_EXPIRES_IN: i64 = 12; // 12 hours

#[derive(thiserror::Error, Debug)]
pub enum HttpSignatureVerificationError {
    #[error("missing signature header")]
    NoSignature,

    #[error("{0}")]
    HeaderError(&'static str),

    #[error("{0}")]
    ParseError(&'static str),

    #[error("invalid encoding")]
    InvalidEncoding(#[from] base64::DecodeError),

    #[error("invalid signature")]
    InvalidSignature,
}

type VerificationError = HttpSignatureVerificationError;

pub struct HttpSignatureData {
    pub key_id: String,
    pub message: String,   // reconstructed message
    pub signature: String, // base64-encoded signature
    pub expires_at: DateTime<Utc>,
}

pub fn parse_http_signature(
    request_method: &Method,
    request_uri: &Uri,
    request_headers: &HeaderMap,
) -> Result<HttpSignatureData, VerificationError> {
    let signature_header = request_headers
        .get("signature")
        .ok_or(VerificationError::NoSignature)?
        .to_str()
        .map_err(|_| VerificationError::HeaderError("invalid signature header"))?;

    let signature_parameter_re = Regex::new(SIGNATURE_PARAMETER_RE).unwrap();
    let mut signature_parameters = HashMap::new();
    for item in signature_header.split(',') {
        let caps = signature_parameter_re
            .captures(item)
            .ok_or(VerificationError::HeaderError("invalid signature header"))?;
        let key = caps["key"].to_string();
        let value = caps["value"].to_string();
        signature_parameters.insert(key, value);
    }

    let key_id = signature_parameters
        .get("keyId")
        .ok_or(VerificationError::ParseError("keyId parameter is missing"))?
        .to_owned();
    let headers_parameter = signature_parameters
        .get("headers")
        .ok_or(VerificationError::ParseError(
            "headers parameter is missing",
        ))?
        .to_owned();
    let signature = signature_parameters
        .get("signature")
        .ok_or(VerificationError::ParseError("signature is missing"))?
        .to_owned();
    let created_at = if let Some(created_at) = signature_parameters.get("created") {
        let create_at_timestamp = created_at
            .parse()
            .map_err(|_| VerificationError::ParseError("invalid timestamp"))?;
        Utc.timestamp_opt(create_at_timestamp, 0)
            .single()
            .ok_or(VerificationError::ParseError("invalid timestamp"))?
    } else {
        let date_str = request_headers
            .get("date")
            .ok_or(VerificationError::ParseError("missing date"))?
            .to_str()
            .map_err(|_| VerificationError::ParseError("invalid date header"))?;
        let date = DateTime::parse_from_rfc2822(date_str)
            .map_err(|_| VerificationError::ParseError("invalid date"))?;
        date.with_timezone(&Utc)
    };
    let expires_at = if let Some(expires_at) = signature_parameters.get("expires") {
        let expires_at_timestamp = expires_at
            .parse()
            .map_err(|_| VerificationError::ParseError("invalid timestamp"))?;
        Utc.timestamp_opt(expires_at_timestamp, 0)
            .single()
            .ok_or(VerificationError::ParseError("invalid timestamp"))?
    } else {
        created_at + Duration::hours(SIGNATURE_EXPIRES_IN)
    };

    let mut message_parts = vec![];
    for header in headers_parameter.split(' ') {
        let message_part = if header == "(request-target)" {
            format!(
                "(request-target): {} {}",
                request_method.as_str().to_lowercase(),
                request_uri.path(),
            )
        } else if header == "(created)" {
            let created =
                signature_parameters
                    .get("created")
                    .ok_or(VerificationError::ParseError(
                        "created parameter is missing",
                    ))?;
            format!("(created): {}", created)
        } else if header == "(expires)" {
            let expires =
                signature_parameters
                    .get("expires")
                    .ok_or(VerificationError::ParseError(
                        "expires parameter is missing",
                    ))?;
            format!("(expires): {}", expires)
        } else {
            let header_value = request_headers
                .get(header)
                .ok_or(VerificationError::HeaderError("missing header"))?
                .to_str()
                .map_err(|_| VerificationError::HeaderError("invalid header value"))?;
            format!("{}: {}", header, header_value)
        };
        message_parts.push(message_part);
    }
    let message = message_parts.join("\n");

    let signature_data = HttpSignatureData {
        key_id,
        message,
        signature,
        expires_at,
    };
    Ok(signature_data)
}

pub fn verify_http_signature(
    signature_data: &HttpSignatureData,
    signer_key: &RsaPublicKey,
) -> Result<(), VerificationError> {
    if signature_data.expires_at < Utc::now() {
        log::warn!("signature has expired");
    };
    let signature = base64::decode(&signature_data.signature)?;
    let is_valid_signature =
        verify_rsa_sha256_signature(signer_key, &signature_data.message, &signature);
    if !is_valid_signature {
        return Err(VerificationError::InvalidSignature);
    };
    Ok(())
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::http_signatures::create::create_http_signature;
    use actix_web::http::{
        header,
        header::{HeaderMap, HeaderName, HeaderValue},
        Uri,
    };
    use mitra_utils::crypto_rsa::generate_weak_rsa_key;

    #[test]
    fn test_parse_signature() {
        let request_method = Method::POST;
        let request_uri = "/user/123/inbox".parse::<Uri>().unwrap();
        let date = "20 Oct 2022 20:00:00 GMT";
        let mut request_headers = HeaderMap::new();
        request_headers.insert(header::HOST, HeaderValue::from_static("example.com"));
        request_headers.insert(
            HeaderName::from_static("date"),
            HeaderValue::from_str(&date).unwrap(),
        );
        let signature_header = concat!(
            r#"keyId="https://myserver.org/actor#main-key","#,
            r#"headers="(request-target) host date","#,
            r#"signature="test""#,
        );
        request_headers.insert(
            HeaderName::from_static("signature"),
            HeaderValue::from_static(signature_header),
        );

        let signature_data =
            parse_http_signature(&request_method, &request_uri, &request_headers).unwrap();
        assert_eq!(signature_data.key_id, "https://myserver.org/actor#main-key");
        assert_eq!(
            signature_data.message,
            "(request-target): post /user/123/inbox\nhost: example.com\ndate: 20 Oct 2022 20:00:00 GMT",
        );
        assert_eq!(signature_data.signature, "test");
        assert!(signature_data.expires_at < Utc::now());
    }

    #[test]
    fn test_create_and_verify_signature() {
        let request_method = Method::POST;
        let request_url = "https://example.org/inbox";
        let request_body = "{}";
        let signer_key = generate_weak_rsa_key().unwrap();
        let signer_key_id = "https://myserver.org/actor#main-key";
        let signed_headers = create_http_signature(
            request_method.clone(),
            request_url,
            request_body,
            &signer_key,
            signer_key_id,
        )
        .unwrap();

        let request_url = request_url.parse::<Uri>().unwrap();
        let mut request_headers = HeaderMap::new();
        request_headers.append(
            HeaderName::from_static("host"),
            HeaderValue::from_str(&signed_headers.host).unwrap(),
        );
        request_headers.append(
            HeaderName::from_static("signature"),
            HeaderValue::from_str(&signed_headers.signature).unwrap(),
        );
        request_headers.append(
            HeaderName::from_static("date"),
            HeaderValue::from_str(&signed_headers.date).unwrap(),
        );
        request_headers.append(
            HeaderName::from_static("digest"),
            HeaderValue::from_str(&signed_headers.digest.unwrap()).unwrap(),
        );
        let signature_data =
            parse_http_signature(&request_method, &request_url, &request_headers).unwrap();

        let signer_public_key = RsaPublicKey::from(signer_key);
        let result = verify_http_signature(&signature_data, &signer_public_key);
        assert_eq!(result.is_ok(), true);
    }
}