use std::collections::BTreeMap;
use std::fs::File;
use std::io::{self, Read};

use sha2::{Digest, Sha256};

use crate::config::OAuthConfig;

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct OAuthTokenSet {
    pub access_token: String,
    pub refresh_token: Option<String>,
    pub expires_at: Option<u64>,
    pub scopes: Vec<String>,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct PkceCodePair {
    pub verifier: String,
    pub challenge: String,
    pub challenge_method: PkceChallengeMethod,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum PkceChallengeMethod {
    S256,
}

impl PkceChallengeMethod {
    #[must_use]
    pub const fn as_str(self) -> &'static str {
        match self {
            Self::S256 => "S256",
        }
    }
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct OAuthAuthorizationRequest {
    pub authorize_url: String,
    pub client_id: String,
    pub redirect_uri: String,
    pub scopes: Vec<String>,
    pub state: String,
    pub code_challenge: String,
    pub code_challenge_method: PkceChallengeMethod,
    pub extra_params: BTreeMap<String, String>,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct OAuthTokenExchangeRequest {
    pub grant_type: &'static str,
    pub code: String,
    pub redirect_uri: String,
    pub client_id: String,
    pub code_verifier: String,
    pub state: String,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct OAuthRefreshRequest {
    pub grant_type: &'static str,
    pub refresh_token: String,
    pub client_id: String,
    pub scopes: Vec<String>,
}

impl OAuthAuthorizationRequest {
    #[must_use]
    pub fn from_config(
        config: &OAuthConfig,
        redirect_uri: impl Into<String>,
        state: impl Into<String>,
        pkce: &PkceCodePair,
    ) -> Self {
        Self {
            authorize_url: config.authorize_url.clone(),
            client_id: config.client_id.clone(),
            redirect_uri: redirect_uri.into(),
            scopes: config.scopes.clone(),
            state: state.into(),
            code_challenge: pkce.challenge.clone(),
            code_challenge_method: pkce.challenge_method,
            extra_params: BTreeMap::new(),
        }
    }

    #[must_use]
    pub fn with_extra_param(mut self, key: impl Into<String>, value: impl Into<String>) -> Self {
        self.extra_params.insert(key.into(), value.into());
        self
    }

    #[must_use]
    pub fn build_url(&self) -> String {
        let mut params = vec![
            ("response_type", "code".to_string()),
            ("client_id", self.client_id.clone()),
            ("redirect_uri", self.redirect_uri.clone()),
            ("scope", self.scopes.join(" ")),
            ("state", self.state.clone()),
            ("code_challenge", self.code_challenge.clone()),
            (
                "code_challenge_method",
                self.code_challenge_method.as_str().to_string(),
            ),
        ];
        params.extend(
            self.extra_params
                .iter()
                .map(|(key, value)| (key.as_str(), value.clone())),
        );
        let query = params
            .into_iter()
            .map(|(key, value)| format!("{}={}", percent_encode(key), percent_encode(&value)))
            .collect::<Vec<_>>()
            .join("&");
        format!(
            "{}{}{}",
            self.authorize_url,
            if self.authorize_url.contains('?') {
                '&'
            } else {
                '?'
            },
            query
        )
    }
}

impl OAuthTokenExchangeRequest {
    #[must_use]
    pub fn from_config(
        config: &OAuthConfig,
        code: impl Into<String>,
        state: impl Into<String>,
        verifier: impl Into<String>,
        redirect_uri: impl Into<String>,
    ) -> Self {
        let _ = config;
        Self {
            grant_type: "authorization_code",
            code: code.into(),
            redirect_uri: redirect_uri.into(),
            client_id: config.client_id.clone(),
            code_verifier: verifier.into(),
            state: state.into(),
        }
    }

    #[must_use]
    pub fn form_params(&self) -> BTreeMap<&str, String> {
        BTreeMap::from([
            ("grant_type", self.grant_type.to_string()),
            ("code", self.code.clone()),
            ("redirect_uri", self.redirect_uri.clone()),
            ("client_id", self.client_id.clone()),
            ("code_verifier", self.code_verifier.clone()),
            ("state", self.state.clone()),
        ])
    }
}

impl OAuthRefreshRequest {
    #[must_use]
    pub fn from_config(
        config: &OAuthConfig,
        refresh_token: impl Into<String>,
        scopes: Option<Vec<String>>,
    ) -> Self {
        Self {
            grant_type: "refresh_token",
            refresh_token: refresh_token.into(),
            client_id: config.client_id.clone(),
            scopes: scopes.unwrap_or_else(|| config.scopes.clone()),
        }
    }

    #[must_use]
    pub fn form_params(&self) -> BTreeMap<&str, String> {
        BTreeMap::from([
            ("grant_type", self.grant_type.to_string()),
            ("refresh_token", self.refresh_token.clone()),
            ("client_id", self.client_id.clone()),
            ("scope", self.scopes.join(" ")),
        ])
    }
}

pub fn generate_pkce_pair() -> io::Result<PkceCodePair> {
    let verifier = generate_random_token(32)?;
    Ok(PkceCodePair {
        challenge: code_challenge_s256(&verifier),
        verifier,
        challenge_method: PkceChallengeMethod::S256,
    })
}

pub fn generate_state() -> io::Result<String> {
    generate_random_token(32)
}

#[must_use]
pub fn code_challenge_s256(verifier: &str) -> String {
    let digest = Sha256::digest(verifier.as_bytes());
    base64url_encode(&digest)
}

#[must_use]
pub fn loopback_redirect_uri(port: u16) -> String {
    format!("http://localhost:{port}/callback")
}

fn generate_random_token(bytes: usize) -> io::Result<String> {
    let mut buffer = vec![0_u8; bytes];
    File::open("/dev/urandom")?.read_exact(&mut buffer)?;
    Ok(base64url_encode(&buffer))
}

fn base64url_encode(bytes: &[u8]) -> String {
    const TABLE: &[u8; 64] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
    let mut output = String::new();
    let mut index = 0;
    while index + 3 <= bytes.len() {
        let block = (u32::from(bytes[index]) << 16)
            | (u32::from(bytes[index + 1]) << 8)
            | u32::from(bytes[index + 2]);
        output.push(TABLE[((block >> 18) & 0x3F) as usize] as char);
        output.push(TABLE[((block >> 12) & 0x3F) as usize] as char);
        output.push(TABLE[((block >> 6) & 0x3F) as usize] as char);
        output.push(TABLE[(block & 0x3F) as usize] as char);
        index += 3;
    }
    match bytes.len().saturating_sub(index) {
        1 => {
            let block = u32::from(bytes[index]) << 16;
            output.push(TABLE[((block >> 18) & 0x3F) as usize] as char);
            output.push(TABLE[((block >> 12) & 0x3F) as usize] as char);
        }
        2 => {
            let block = (u32::from(bytes[index]) << 16) | (u32::from(bytes[index + 1]) << 8);
            output.push(TABLE[((block >> 18) & 0x3F) as usize] as char);
            output.push(TABLE[((block >> 12) & 0x3F) as usize] as char);
            output.push(TABLE[((block >> 6) & 0x3F) as usize] as char);
        }
        _ => {}
    }
    output
}

fn percent_encode(value: &str) -> String {
    let mut encoded = String::new();
    for byte in value.bytes() {
        match byte {
            b'A'..=b'Z' | b'a'..=b'z' | b'0'..=b'9' | b'-' | b'_' | b'.' | b'~' => {
                encoded.push(char::from(byte));
            }
            _ => {
                use std::fmt::Write as _;
                let _ = write!(&mut encoded, "%{byte:02X}");
            }
        }
    }
    encoded
}

#[cfg(test)]
mod tests {
    use super::{
        code_challenge_s256, generate_pkce_pair, generate_state, loopback_redirect_uri,
        OAuthAuthorizationRequest, OAuthConfig, OAuthRefreshRequest, OAuthTokenExchangeRequest,
    };

    fn sample_config() -> OAuthConfig {
        OAuthConfig {
            client_id: "runtime-client".to_string(),
            authorize_url: "https://console.test/oauth/authorize".to_string(),
            token_url: "https://console.test/oauth/token".to_string(),
            callback_port: Some(4545),
            manual_redirect_url: Some("https://console.test/oauth/callback".to_string()),
            scopes: vec!["org:read".to_string(), "user:write".to_string()],
        }
    }

    #[test]
    fn s256_challenge_matches_expected_vector() {
        assert_eq!(
            code_challenge_s256("dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk"),
            "E9Melhoa2OwvFrEMTJguCHaoeK1t8URWbuGJSstw-cM"
        );
    }

    #[test]
    fn generates_pkce_pair_and_state() {
        let pair = generate_pkce_pair().expect("pkce pair");
        let state = generate_state().expect("state");
        assert!(!pair.verifier.is_empty());
        assert!(!pair.challenge.is_empty());
        assert!(!state.is_empty());
    }

    #[test]
    fn builds_authorize_url_and_form_requests() {
        let config = sample_config();
        let pair = generate_pkce_pair().expect("pkce");
        let url = OAuthAuthorizationRequest::from_config(
            &config,
            loopback_redirect_uri(4545),
            "state-123",
            &pair,
        )
        .with_extra_param("login_hint", "user@example.com")
        .build_url();
        assert!(url.starts_with("https://console.test/oauth/authorize?"));
        assert!(url.contains("response_type=code"));
        assert!(url.contains("client_id=runtime-client"));
        assert!(url.contains("scope=org%3Aread%20user%3Awrite"));
        assert!(url.contains("login_hint=user%40example.com"));

        let exchange = OAuthTokenExchangeRequest::from_config(
            &config,
            "auth-code",
            "state-123",
            pair.verifier,
            loopback_redirect_uri(4545),
        );
        assert_eq!(
            exchange.form_params().get("grant_type").map(String::as_str),
            Some("authorization_code")
        );

        let refresh = OAuthRefreshRequest::from_config(&config, "refresh-token", None);
        assert_eq!(
            refresh.form_params().get("scope").map(String::as_str),
            Some("org:read user:write")
        );
    }
}