#![deny(missing_docs)]

//! # HTTP Signature Normaliztion
//! _An HTTP Signatures library that leaves the signing to you_
//!
//! - [crates.io](https://crates.io/crates/http-signature-normalization)
//! - [docs.rs](https://docs.rs/http-signature-normalization)
//! - [Join the discussion on Matrix](https://matrix.to/#/!IRQaBCMWKbpBWKjQgx:asonix.dog?via=asonix.dog)
//!
//! Http Signature Normalization is a minimal-dependency crate for producing HTTP Signatures with user-provided signing and verification. The API is simple; there's a series of steps for creation and verification with types that ensure reasonable usage.
//!
//! ```rust
//! use chrono::Duration;
//! use http_signature_normalization::Config;
//! use std::collections::BTreeMap;
//!
//! fn main() -> Result<(), Box<dyn std::error::Error>> {
//!     let config = Config {
//!         expires_after: Duration::seconds(5),
//!     };
//!
//!     let headers = BTreeMap::new();
//!
//!     let signature_header_value = config
//!         .begin_sign("GET", "/foo?bar=baz", headers)
//!         .sign("my-key-id".to_owned(), |signing_string| {
//!             // sign the string here
//!             Ok(signing_string.to_owned()) as Result<_, Box<dyn std::error::Error>>
//!         })?
//!         .signature_header();
//!
//!     let mut headers = BTreeMap::new();
//!     headers.insert("Signature".to_owned(), signature_header_value);
//!
//!     let verified = config
//!         .begin_verify("GET", "/foo?bar=baz", headers)?
//!         .verify(|sig, signing_string| {
//!             // Verify the signature here
//!             sig == signing_string
//!         });
//!
//!     assert!(verified);
//!     Ok(())
//! }
//! ```

use chrono::{DateTime, Duration, Utc};
use std::{collections::BTreeMap, error::Error, fmt};

pub mod create;
pub mod verify;

use self::{
    create::Unsigned,
    verify::{ParseSignatureError, ParsedHeader, Unverified, ValidateError},
};

const REQUEST_TARGET: &'static str = "(request-target)";
const CREATED: &'static str = "(created)";
const EXPIRES: &'static str = "(expires)";

const KEY_ID_FIELD: &'static str = "keyId";
const ALGORITHM_FIELD: &'static str = "algorithm";
const ALGORITHM_VALUE: &'static str = "hs2019";
const CREATED_FIELD: &'static str = "created";
const EXPIRES_FIELD: &'static str = "expires";
const HEADERS_FIELD: &'static str = "headers";
const SIGNATURE_FIELD: &'static str = "signature";

#[derive(Clone, Debug)]
/// Configuration for signing and verifying signatures
///
/// Currently, the only configuration provided is how long a signature should be considered valid
/// before it expires.
pub struct Config {
    /// How long a singature is valid
    pub expires_after: Duration,
}

#[derive(Debug)]
/// Error preparing a header for validation
///
/// This could be due to a missing header, and unparsable header, or an expired header
pub enum PrepareVerifyError {
    /// Error validating the header
    Validate(ValidateError),
    /// Error parsing the header
    Parse(ParseSignatureError),
}

impl Config {
    /// Perform the neccessary operations to produce an [`Unsigned`] type, which can be used to
    /// sign the header
    pub fn begin_sign(
        &self,
        method: &str,
        path_and_query: &str,
        headers: BTreeMap<String, String>,
    ) -> Unsigned {
        let mut headers = headers
            .into_iter()
            .map(|(k, v)| (k.to_lowercase(), v))
            .collect();
        let sig_headers = build_headers_list(&headers);

        let created = Utc::now();
        let expires = created + self.expires_after;

        let signing_string = build_signing_string(
            method,
            path_and_query,
            Some(created),
            Some(expires),
            &sig_headers,
            &mut headers,
        );

        Unsigned {
            signing_string,
            sig_headers,
            created,
            expires,
        }
    }

    /// Perform the neccessary operations to produce and [`Unerified`] type, which can be used to
    /// verify the header
    pub fn begin_verify(
        &self,
        method: &str,
        path_and_query: &str,
        headers: BTreeMap<String, String>,
    ) -> Result<Unverified, PrepareVerifyError> {
        let mut headers: BTreeMap<String, String> = headers
            .into_iter()
            .map(|(k, v)| (k.to_lowercase().to_owned(), v))
            .collect();

        let header = headers
            .remove("authorization")
            .or_else(|| headers.remove("signature"))
            .ok_or(ValidateError::Missing)?;

        let parsed_header: ParsedHeader = header.parse()?;
        let unvalidated = parsed_header.into_unvalidated(method, path_and_query, &mut headers);

        Ok(unvalidated.validate(self.expires_after)?)
    }
}

fn build_headers_list(btm: &BTreeMap<String, String>) -> Vec<String> {
    let http_header_keys: Vec<String> = btm.keys().cloned().collect();

    let mut sig_headers = vec![
        REQUEST_TARGET.to_owned(),
        CREATED.to_owned(),
        EXPIRES.to_owned(),
    ];

    sig_headers.extend(http_header_keys);

    sig_headers
}

fn build_signing_string(
    method: &str,
    path_and_query: &str,
    created: Option<DateTime<Utc>>,
    expires: Option<DateTime<Utc>>,
    sig_headers: &[String],
    btm: &mut BTreeMap<String, String>,
) -> String {
    let request_target = format!("{} {}", method.to_string().to_lowercase(), path_and_query);

    btm.insert(REQUEST_TARGET.to_owned(), request_target.clone());
    if let Some(created) = created {
        btm.insert(CREATED.to_owned(), created.timestamp().to_string());
    }
    if let Some(expires) = expires {
        btm.insert(EXPIRES.to_owned(), expires.timestamp().to_string());
    }

    let signing_string = sig_headers
        .iter()
        .filter_map(|h| btm.remove(h).map(|v| format!("{}: {}", h, v)))
        .collect::<Vec<_>>()
        .join("\n");

    signing_string
}

impl fmt::Display for PrepareVerifyError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match *self {
            PrepareVerifyError::Validate(ref e) => fmt::Display::fmt(e, f),
            PrepareVerifyError::Parse(ref e) => fmt::Display::fmt(e, f),
        }
    }
}

impl Error for PrepareVerifyError {
    fn description(&self) -> &str {
        match *self {
            PrepareVerifyError::Validate(ref e) => e.description(),
            PrepareVerifyError::Parse(ref e) => e.description(),
        }
    }

    fn source(&self) -> Option<&(dyn Error + 'static)> {
        match *self {
            PrepareVerifyError::Validate(ref e) => Some(e),
            PrepareVerifyError::Parse(ref e) => Some(e),
        }
    }
}

impl From<ValidateError> for PrepareVerifyError {
    fn from(v: ValidateError) -> Self {
        PrepareVerifyError::Validate(v)
    }
}

impl From<ParseSignatureError> for PrepareVerifyError {
    fn from(p: ParseSignatureError) -> Self {
        PrepareVerifyError::Parse(p)
    }
}

impl Default for Config {
    fn default() -> Self {
        Config {
            expires_after: Duration::seconds(10),
        }
    }
}

#[cfg(test)]
mod tests {
    use super::Config;
    use std::collections::BTreeMap;

    fn prepare_headers() -> BTreeMap<String, String> {
        let mut headers = BTreeMap::new();
        headers.insert(
            "Content-Type".to_owned(),
            "application/activity+json".to_owned(),
        );
        headers
    }

    #[test]
    fn round_trip_authorization() {
        let headers = prepare_headers();
        let config = Config::default();

        let authorization_header = config
            .begin_sign("GET", "/foo?bar=baz", headers)
            .sign("hi".to_owned(), |s| {
                Ok(s.to_owned()) as Result<_, std::io::Error>
            })
            .unwrap()
            .authorization_header();

        let mut headers = prepare_headers();
        headers.insert("Authorization".to_owned(), authorization_header);

        let verified = config
            .begin_verify("GET", "/foo?bar=baz", headers)
            .unwrap()
            .verify(|sig, signing_string| sig == signing_string);

        assert!(verified);
    }

    #[test]
    fn round_trip_signature() {
        let headers = prepare_headers();
        let config = Config::default();

        let signature_header = config
            .begin_sign("GET", "/foo?bar=baz", headers)
            .sign("hi".to_owned(), |s| {
                Ok(s.to_owned()) as Result<_, std::io::Error>
            })
            .unwrap()
            .signature_header();

        let mut headers = prepare_headers();
        headers.insert("Signature".to_owned(), signature_header);

        let verified = config
            .begin_verify("GET", "/foo?bar=baz", headers)
            .unwrap()
            .verify(|sig, signing_string| sig == signing_string);

        assert!(verified);
    }
}