use chrono::{DateTime, TimeZone, Utc};
use http::{
    header::{HeaderMap, ToStrError},
    method::Method,
    uri::PathAndQuery,
};
use std::{collections::HashMap, error::Error, fmt, str::FromStr};

use crate::{
    build_headers_list, build_signing_string, ALGORITHM_FIELD, CREATED, CREATED_FIELD,
    EXPIRES_FIELD, HEADERS_FIELD, KEY_ID_FIELD, SIGNATURE_FIELD,
};

pub struct Unvalidated {
    pub(crate) key_id: String,
    pub(crate) signature: String,
    pub(crate) algorithm: Option<Algorithm>,
    pub(crate) created: Option<DateTime<Utc>>,
    pub(crate) expires: Option<DateTime<Utc>>,
    pub(crate) parsed_at: DateTime<Utc>,
    pub(crate) signing_string: String,
}

pub struct ParsedHeader {
    signature: String,
    key_id: String,
    headers: Vec<String>,
    algorithm: Option<Algorithm>,
    created: Option<DateTime<Utc>>,
    expires: Option<DateTime<Utc>>,
    parsed_at: DateTime<Utc>,
}

#[derive(Clone, Copy, Debug)]
pub enum DeprecatedAlgorithm {
    HmacSha1,
    HmacSha256,
    HmacSha384,
    HmacSha512,
    RsaSha1,
    RsaSha256,
    RsaSha384,
    RsaSha512,
    EcdsaSha1,
    EcdsaSha256,
    EcdsaSha384,
    EcdsaSha512,
}

#[derive(Clone, Debug)]
pub enum Algorithm {
    Hs2019,
    Deprecated(DeprecatedAlgorithm),
    Unknown(String),
}

#[derive(Clone, Debug)]
pub enum ValidateError {
    Expired,
    Decode,
}

#[derive(Clone, Debug)]
pub struct ParseSignatureError(&'static str);

impl Unvalidated {
    pub fn key_id(&self) -> &str {
        &self.key_id
    }

    pub fn algorithm(&self) -> Option<&Algorithm> {
        self.algorithm.as_ref()
    }
}

impl ParsedHeader {
    pub fn to_unvalidated(
        self,
        method: Method,
        path_and_query: &PathAndQuery,
        headers: &HeaderMap,
    ) -> Result<Unvalidated, ToStrError> {
        let (_, mut btm) = build_headers_list(headers)?;

        let signing_string = build_signing_string(
            method,
            path_and_query,
            self.created,
            self.expires,
            &self.headers,
            &mut btm,
        );

        Ok(Unvalidated {
            key_id: self.key_id,
            signature: self.signature,
            parsed_at: self.parsed_at,
            algorithm: self.algorithm,
            created: self.created,
            expires: self.expires,
            signing_string,
        })
    }
}

impl FromStr for ParsedHeader {
    type Err = ParseSignatureError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let s = s.trim_start_matches("Signature").trim();
        let mut hm: HashMap<String, String> = s
            .split(',')
            .filter_map(|part| {
                let mut i = part.splitn(2, "=");

                if let Some(key) = i.next() {
                    if let Some(value) = i.next() {
                        return Some((key.to_owned(), value.to_owned()));
                    }
                }
                None
            })
            .collect();

        Ok(ParsedHeader {
            signature: hm
                .remove(SIGNATURE_FIELD)
                .ok_or(ParseSignatureError(SIGNATURE_FIELD))?,
            key_id: hm
                .remove(KEY_ID_FIELD)
                .ok_or(ParseSignatureError(KEY_ID_FIELD))?,
            headers: hm
                .remove(HEADERS_FIELD)
                .map(|h| h.split_whitespace().map(|s| s.to_owned()).collect())
                .unwrap_or_else(|| vec![CREATED.to_owned()]),
            algorithm: hm.remove(ALGORITHM_FIELD).map(Algorithm::from),
            created: parse_time(&mut hm, CREATED_FIELD)?,
            expires: parse_time(&mut hm, EXPIRES_FIELD)?,
            parsed_at: Utc::now(),
        })
    }
}

fn parse_time(
    hm: &mut HashMap<String, String>,
    key: &'static str,
) -> Result<Option<DateTime<Utc>>, ParseSignatureError> {
    let r = hm.remove(key).map(|s| {
        Utc.datetime_from_str(&s, "%s")
            .map_err(|_| ParseSignatureError(key))
    });

    match r {
        Some(Ok(t)) => Ok(Some(t)),
        Some(Err(e)) => Err(e),
        None => Ok(None),
    }
}

impl From<DeprecatedAlgorithm> for Algorithm {
    fn from(d: DeprecatedAlgorithm) -> Algorithm {
        Algorithm::Deprecated(d)
    }
}

impl From<String> for Algorithm {
    fn from(s: String) -> Self {
        Algorithm::from(s.as_str())
    }
}

impl From<&str> for Algorithm {
    fn from(s: &str) -> Self {
        match s {
            "hmac-sha1" => DeprecatedAlgorithm::HmacSha1.into(),
            "hmac-sha256" => DeprecatedAlgorithm::HmacSha256.into(),
            "hmac-sha384" => DeprecatedAlgorithm::HmacSha384.into(),
            "hmac-sha512" => DeprecatedAlgorithm::HmacSha512.into(),
            "rsa-sha1" => DeprecatedAlgorithm::RsaSha1.into(),
            "rsa-sha256" => DeprecatedAlgorithm::RsaSha256.into(),
            "rsa-sha384" => DeprecatedAlgorithm::RsaSha384.into(),
            "rsa-sha512" => DeprecatedAlgorithm::RsaSha512.into(),
            "ecdsa-sha1" => DeprecatedAlgorithm::EcdsaSha1.into(),
            "ecdsa-sha256" => DeprecatedAlgorithm::EcdsaSha256.into(),
            "ecdsa-sha384" => DeprecatedAlgorithm::EcdsaSha384.into(),
            "ecdsa-sha512" => DeprecatedAlgorithm::EcdsaSha512.into(),
            "hs2019" => Algorithm::Hs2019,
            other => Algorithm::Unknown(other.into()),
        }
    }
}

impl fmt::Display for ValidateError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match *self {
            ValidateError::Expired => write!(f, "Http Signature is expired"),
            ValidateError::Decode => write!(f, "Http Signature could not be decoded"),
        }
    }
}

impl fmt::Display for ParseSignatureError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "Error when parsing {} from Http Signature", self.0)
    }
}

impl Error for ValidateError {
    fn description(&self) -> &'static str {
        match *self {
            ValidateError::Expired => "Http Signature is expired",
            ValidateError::Decode => "Http Signature could not be decoded",
        }
    }
}

impl Error for ParseSignatureError {
    fn description(&self) -> &'static str {
        "There was an error parsing the Http Signature"
    }
}