use std::sync::Arc;

use axum::extract::State;
use axum::http::header::CONTENT_TYPE;
use axum::http::{HeaderMap, StatusCode};
use axum::response::IntoResponse;
use axum::Json;
use base64::Engine;
use chrono::{DateTime, Utc};
use serde::{Deserialize, Serialize};
use serde_json::Value;

use crate::email;
use crate::serve::AppState;

#[derive(Serialize)]
pub struct Question {
    id: i64,
    question: String,
    answer: String,
    created_at: String,
    answered_at: String,
}

#[derive(Serialize)]
pub struct QuestionStats {
    asked: i64,
    answered: i64,
}

const SITE_URL: &str = "https://jetpham.com";

fn xml_escape(text: &str) -> String {
    text.replace('&', "&")
        .replace('<', "&lt;")
        .replace('>', "&gt;")
        .replace('"', "&quot;")
        .replace('\'', "&apos;")
}

fn rss_pub_date(timestamp: &str) -> String {
    DateTime::parse_from_rfc3339(timestamp)
        .map(|dt| dt.to_rfc2822())
        .unwrap_or_else(|_| Utc::now().to_rfc2822())
}

pub async fn get_questions(
    State(state): State<Arc<AppState>>,
) -> Result<Json<Vec<Question>>, StatusCode> {
    let db = state
        .db
        .lock()
        .map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?;
    let mut stmt = db
        .prepare(
            "SELECT id, question, answer, created_at, answered_at \
             FROM questions WHERE answer IS NOT NULL \
             ORDER BY answered_at DESC",
        )
        .map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?;

    let questions = stmt
        .query_map([], |row| {
            Ok(Question {
                id: row.get(0)?,
                question: row.get(1)?,
                answer: row.get(2)?,
                created_at: row.get(3)?,
                answered_at: row.get(4)?,
            })
        })
        .map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?
        .collect::<Result<Vec<_>, _>>()
        .map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?;

    Ok(Json(questions))
}

pub async fn get_question_stats(
    State(state): State<Arc<AppState>>,
) -> Result<Json<QuestionStats>, StatusCode> {
    let db = state
        .db
        .lock()
        .map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?;

    let asked: i64 = db
        .query_row("SELECT COUNT(*) FROM questions", [], |row| row.get(0))
        .map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?;

    let answered: i64 = db
        .query_row(
            "SELECT COUNT(*) FROM questions WHERE answer IS NOT NULL",
            [],
            |row| row.get(0),
        )
        .map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?;

    Ok(Json(QuestionStats { asked, answered }))
}

pub async fn get_question_rss(
    State(state): State<Arc<AppState>>,
) -> Result<impl IntoResponse, StatusCode> {
    let db = state
        .db
        .lock()
        .map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?;
    let mut stmt = db
        .prepare(
            "SELECT id, question, answer, created_at, answered_at \
             FROM questions WHERE answer IS NOT NULL \
             ORDER BY answered_at DESC",
        )
        .map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?;

    let questions = stmt
        .query_map([], |row| {
            Ok(Question {
                id: row.get(0)?,
                question: row.get(1)?,
                answer: row.get(2)?,
                created_at: row.get(3)?,
                answered_at: row.get(4)?,
            })
        })
        .map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?
        .collect::<Result<Vec<_>, _>>()
        .map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?;

    let items = questions
        .into_iter()
        .map(|question| {
            let guid = format!("{SITE_URL}/qa#question-{}", question.id);
            let description = format!(
                "Question: {}\n\nAnswer: {}",
                question.question, question.answer
            );

            format!(
                "<item><title>{}</title><link>{}</link><guid>{}</guid><pubDate>{}</pubDate><description>{}</description></item>",
                xml_escape(&question.question),
                xml_escape(&guid),
                xml_escape(&guid),
                xml_escape(&rss_pub_date(&question.answered_at)),
                xml_escape(&description),
            )
        })
        .collect::<Vec<_>>()
        .join("");

    let xml = format!(
        "<?xml version=\"1.0\" encoding=\"UTF-8\"?><rss version=\"2.0\"><channel><title>Jet Pham Q+A</title><link>{SITE_URL}/qa</link><description>Answered questions from Jet Pham&apos;s site</description><language>en-us</language>{items}</channel></rss>"
    );

    Ok(([(CONTENT_TYPE, "application/rss+xml; charset=utf-8")], xml))
}

#[derive(Deserialize)]
pub struct SubmitQuestion {
    question: String,
}

pub async fn post_question(
    State(state): State<Arc<AppState>>,
    headers: HeaderMap,
    Json(body): Json<SubmitQuestion>,
) -> Result<StatusCode, (StatusCode, String)> {
    if body.question.is_empty() || body.question.len() > 200 {
        return Err((
            StatusCode::BAD_REQUEST,
            "Question must be 1-200 characters".to_string(),
        ));
    }

    let ip = headers
        .get("x-forwarded-for")
        .and_then(|v| v.to_str().ok())
        .and_then(|s| s.split(',').next())
        .map(|s| s.trim().to_string())
        .unwrap_or_else(|| "unknown".to_string());

    if !state.rate_limiter.check(&ip) {
        return Err((
            StatusCode::TOO_MANY_REQUESTS,
            "Too many questions. Try again later.".to_string(),
        ));
    }

    let id: i64 = {
        let db = state
            .db
            .lock()
            .map_err(|_| (StatusCode::INTERNAL_SERVER_ERROR, "db error".to_string()))?;
        db.execute(
            "INSERT INTO questions (question) VALUES (?1)",
            rusqlite::params![body.question],
        )
        .map_err(|_| {
            (
                StatusCode::INTERNAL_SERVER_ERROR,
                "insert error".to_string(),
            )
        })?;
        db.last_insert_rowid()
    };

    let notify_email = state.notify_email.clone();
    let mail_domain = state.mail_domain.clone();
    let qa_reply_domain = state.qa_reply_domain.clone();
    let question_text = body.question.clone();
    tokio::task::spawn_blocking(move || {
        if let Err(e) = email::send_notification(
            id,
            &question_text,
            &notify_email,
            &mail_domain,
            &qa_reply_domain,
        ) {
            eprintln!("Failed to send notification: {e}");
        }
    });

    Ok(StatusCode::CREATED)
}

// --- MTA Hook webhook types ---

#[derive(Deserialize)]
pub struct MtaHookPayload {
    #[serde(default)]
    pub messages: Vec<MtaHookMessage>,
    #[serde(default)]
    pub envelope: Envelope,
    #[serde(default)]
    pub message: MtaHookBody,
}

#[derive(Deserialize)]
pub struct MtaHookMessage {
    #[serde(default)]
    pub envelope: Envelope,
    #[serde(default)]
    pub message: MtaHookBody,
    #[serde(default)]
    pub contents: String,
}

#[derive(Deserialize, Default)]
pub struct Envelope {
    #[serde(default)]
    pub to: Vec<Recipient>,
}

#[derive(Deserialize)]
#[serde(untagged)]
pub enum Recipient {
    Address(String),
    WithAddress { address: String },
}

impl Default for Recipient {
    fn default() -> Self {
        Self::Address(String::new())
    }
}

impl Recipient {
    fn address(&self) -> &str {
        match self {
            Self::Address(address) => address,
            Self::WithAddress { address } => address,
        }
    }
}

#[derive(Deserialize, Default)]
pub struct MtaHookBody {
    #[serde(default)]
    pub subject: Option<String>,
    #[serde(default)]
    pub headers: MessageHeaders,
    #[serde(default)]
    pub contents: String,
}

#[derive(Deserialize, Default)]
pub struct MessageHeaders {
    #[serde(default)]
    pub subject: Option<String>,
}

#[derive(Serialize)]
pub struct MtaHookResponse {
    pub action: &'static str,
}

fn webhook_secret_matches(headers: &HeaderMap, expected_secret: &str) -> bool {
    let expected_secret = expected_secret.trim();
    let header_secret = headers
        .get("X-Webhook-Secret")
        .and_then(|v| v.to_str().ok())
        .unwrap_or("")
        .trim();
    if header_secret == expected_secret {
        return true;
    }

    let auth_header = match headers.get(axum::http::header::AUTHORIZATION) {
        Some(value) => value,
        None => return false,
    };
    let auth_header = match auth_header.to_str() {
        Ok(value) => value,
        Err(_) => return false,
    };
    let encoded = match auth_header.strip_prefix("Basic ") {
        Some(value) => value,
        None => return false,
    };
    let decoded = match base64::engine::general_purpose::STANDARD.decode(encoded) {
        Ok(value) => value,
        Err(_) => return false,
    };
    let credentials = match std::str::from_utf8(&decoded) {
        Ok(value) => value,
        Err(_) => return false,
    };
    let (_, password) = match credentials.split_once(':') {
        Some(parts) => parts,
        None => return false,
    };

    password.trim() == expected_secret
}

fn webhook_secret_debug(headers: &HeaderMap) -> String {
    let header_secret = headers
        .get("X-Webhook-Secret")
        .and_then(|v| v.to_str().ok())
        .unwrap_or("");

    let auth = headers
        .get(axum::http::header::AUTHORIZATION)
        .and_then(|v| v.to_str().ok())
        .unwrap_or("");

    let decoded = auth
        .strip_prefix("Basic ")
        .and_then(|encoded| base64::engine::general_purpose::STANDARD.decode(encoded).ok())
        .and_then(|bytes| String::from_utf8(bytes).ok())
        .unwrap_or_default();

    format!(
        "x-webhook-secret={header_secret:?}; authorization={auth:?}; basic-decoded={decoded:?}"
    )
}

fn extract_qa_reply(payload: &MtaHookPayload, expected_domain: &str) -> Option<(i64, String)> {
    if !payload.messages.is_empty() {
        for message in &payload.messages {
            if let Some(reply) = extract_qa_reply_from_message(
                &message.envelope.to,
                expected_domain,
                message.message.subject.as_deref().or(message.message.headers.subject.as_deref()),
                if message.message.contents.is_empty() {
                    &message.contents
                } else {
                    &message.message.contents
                },
            ) {
                return Some(reply);
            }
        }
        return None;
    }

    extract_qa_reply_from_message(
        &payload.envelope.to,
        expected_domain,
        payload
            .message
            .subject
            .as_deref()
            .or(payload.message.headers.subject.as_deref()),
        &payload.message.contents,
    )
}

fn value_at_path<'a>(value: &'a Value, path: &[&str]) -> Option<&'a Value> {
    let mut current = value;
    for key in path {
        current = current.get(*key)?;
    }
    Some(current)
}

fn string_from_value(value: &Value) -> Option<String> {
    match value {
        Value::String(s) => Some(s.clone()),
        Value::Object(map) => map
            .get("address")
            .or_else(|| map.get("email"))
            .or_else(|| map.get("value"))
            .and_then(|v| v.as_str())
            .map(ToOwned::to_owned),
        _ => None,
    }
}

fn recipients_from_value(value: Option<&Value>) -> Vec<Recipient> {
    let Some(value) = value else {
        return Vec::new();
    };

    match value {
        Value::Array(values) => values
            .iter()
            .filter_map(|v| string_from_value(v).map(Recipient::Address))
            .collect(),
        _ => string_from_value(value)
            .map(Recipient::Address)
            .into_iter()
            .collect(),
    }
}

fn string_at_paths(value: &Value, paths: &[&[&str]]) -> Option<String> {
    paths.iter().find_map(|path| {
        value_at_path(value, path)
            .and_then(|v| v.as_str())
            .map(ToOwned::to_owned)
    })
}

fn subject_from_headers_value(value: Option<&Value>) -> Option<String> {
    let headers = value?.as_array()?;
    headers.iter().find_map(|header| {
        let parts = header.as_array()?;
        let name = parts.first()?.as_str()?.trim();
        if !name.eq_ignore_ascii_case("Subject") {
            return None;
        }
        parts
            .get(1)?
            .as_str()
            .map(|s| s.trim().to_string())
    })
}

fn extract_qa_reply_from_value(payload: &Value, expected_domain: &str) -> Option<(i64, String)> {
    if let Some(messages) = payload.get("messages").and_then(Value::as_array) {
        for message in messages {
            if let Some(reply) = extract_qa_reply_from_message(
                &recipients_from_value(value_at_path(message, &["envelope", "to"])),
                expected_domain,
                string_at_paths(
                    message,
                    &[
                        &["message", "subject"],
                        &["message", "headers", "subject"],
                        &["headers", "subject"],
                    ],
                )
                .or_else(|| subject_from_headers_value(value_at_path(message, &["message", "headers"])))
                .as_deref(),
                &string_at_paths(message, &[&["message", "contents"], &["contents"], &["raw_message"]])
                    .unwrap_or_default(),
            ) {
                return Some(reply);
            }
        }
    }

    extract_qa_reply_from_message(
        &recipients_from_value(value_at_path(payload, &["envelope", "to"])),
        expected_domain,
        string_at_paths(
            payload,
            &[
                &["message", "subject"],
                &["message", "headers", "subject"],
                &["headers", "subject"],
            ],
        )
        .or_else(|| subject_from_headers_value(value_at_path(payload, &["message", "headers"])))
        .as_deref(),
        &string_at_paths(payload, &[&["message", "contents"], &["contents"], &["raw_message"]])
            .unwrap_or_default(),
    )
}

fn extract_qa_reply_from_message(
    recipients: &[Recipient],
    expected_domain: &str,
    subject: Option<&str>,
    contents: &str,
) -> Option<(i64, String)> {
    let _qa_recipient = recipients.iter().find(|recipient| {
        let address = recipient.address();
        let Some((local, domain)) = address.rsplit_once('@') else {
            return false;
        };

        local.eq_ignore_ascii_case("qa") && domain.eq_ignore_ascii_case(expected_domain)
    })?;

    let subject = subject.map(ToOwned::to_owned).or_else(|| {
        contents
            .replace("\r\n", "\n")
            .lines()
            .find_map(|line| line.strip_prefix("Subject: ").map(ToOwned::to_owned))
    })?;
    let id = email::extract_id_from_subject(&subject).ok()?;
    let body = email::extract_plain_text_body(contents);
    if body.is_empty() {
        return None;
    }

    Some((id, body))
}

pub async fn webhook(
    State(state): State<Arc<AppState>>,
    headers: HeaderMap,
    body: String,
) -> Result<Json<MtaHookResponse>, (StatusCode, String)> {
    if !webhook_secret_matches(&headers, &state.webhook_secret) {
        eprintln!(
            "Rejected webhook: invalid secret; expected_len={}; {}",
            state.webhook_secret.len(),
            webhook_secret_debug(&headers)
        );
        return Err((StatusCode::UNAUTHORIZED, "invalid secret".to_string()));
    }

    let payload_value: Value = match serde_json::from_str(&body) {
        Ok(payload) => payload,
        Err(err) => {
            eprintln!("Rejected webhook: invalid JSON payload: {err}; body={body}");
            return Ok(Json(MtaHookResponse { action: "accept" }));
        }
    };

    let parsed_reply = serde_json::from_value::<MtaHookPayload>(payload_value.clone())
        .ok()
        .and_then(|payload| extract_qa_reply(&payload, &state.qa_reply_domain))
        .or_else(|| extract_qa_reply_from_value(&payload_value, &state.qa_reply_domain));

    if let Some((id, body)) = parsed_reply {
        let db = state
            .db
            .lock()
            .map_err(|_| (StatusCode::INTERNAL_SERVER_ERROR, "db error".to_string()))?;
        db.execute(
            "UPDATE questions SET answer = ?1, answered_at = strftime('%Y-%m-%dT%H:%M:%SZ', 'now') \
             WHERE id = ?2 AND answer IS NULL",
            rusqlite::params![body, id],
        )
        .map_err(|_| (StatusCode::INTERNAL_SERVER_ERROR, "update error".to_string()))?;

        eprintln!("Stored Q&A reply for question #{id}");
        return Ok(Json(MtaHookResponse { action: "discard" }));
    }

    eprintln!("Q&A webhook accepted payload without matched reply: {payload_value}");
    Ok(Json(MtaHookResponse { action: "accept" }))
}

#[cfg(test)]
mod tests {
    use axum::http::HeaderMap;
    use serde_json::Value;

    use super::{extract_qa_reply, extract_qa_reply_from_value, webhook_secret_matches, MtaHookPayload};

    #[test]
    fn extracts_reply_from_current_stalwart_payload() {
        let payload: MtaHookPayload = serde_json::from_str(
            r#"{
                "envelope": {
                    "to": [
                        {
                            "address": "qa@extremist.software"
                        }
                    ]
                },
                "message": {
                    "subject": "Re: 42 - hello",
                    "contents": "This is the answer.\n\nOn earlier mail wrote:\n> quoted"
                }
            }"#,
        )
        .unwrap();

        assert_eq!(
            extract_qa_reply(&payload, "extremist.software"),
            Some((42, "This is the answer.".to_string()))
        );
    }

    #[test]
    fn extracts_reply_from_legacy_batch_payload() {
        let payload: MtaHookPayload = serde_json::from_str(
            r#"{
                "messages": [
                    {
                        "envelope": {
                            "to": ["qa@extremist.software"]
                        },
                        "message": {
                            "subject": "Re: 7 - legacy"
                        },
                        "contents": "Legacy answer"
                    }
                ]
            }"#,
        )
        .unwrap();

        assert_eq!(
            extract_qa_reply(&payload, "extremist.software"),
            Some((7, "Legacy answer".to_string()))
        );
    }

    #[test]
    fn accepts_header_secret() {
        let mut headers = HeaderMap::new();
        headers.insert("X-Webhook-Secret", "topsecret".parse().unwrap());

        assert!(webhook_secret_matches(&headers, "topsecret"));
    }

    #[test]
    fn accepts_basic_auth_password() {
        let mut headers = HeaderMap::new();
        headers.insert(
            axum::http::header::AUTHORIZATION,
            "Basic dXNlcjp0b3BzZWNyZXQ=".parse().unwrap(),
        );

        assert!(webhook_secret_matches(&headers, "topsecret"));
    }

    #[test]
    fn extracts_reply_from_value_with_string_recipient() {
        let payload: Value = serde_json::from_str(
            r#"{
                "envelope": {
                    "to": "qa@extremist.software"
                },
                "message": {
                    "headers": {
                        "subject": "Re: 9 - hi"
                    },
                    "contents": "Answer body"
                }
            }"#,
        )
        .unwrap();

        assert_eq!(
            extract_qa_reply_from_value(&payload, "extremist.software"),
            Some((9, "Answer body".to_string()))
        );
    }

    #[test]
    fn extracts_reply_from_value_with_header_pairs() {
        let payload: Value = serde_json::from_str(
            r#"{
                "envelope": {
                    "to": [{"address":"qa@extremist.software"}]
                },
                "message": {
                    "headers": [
                        ["From", " jet@extremist.software\r\n"],
                        ["Subject", " Re: 11 - hi\r\n"]
                    ],
                    "contents": "Answer from header pairs"
                }
            }"#,
        )
        .unwrap();

        assert_eq!(
            extract_qa_reply_from_value(&payload, "extremist.software"),
            Some((11, "Answer from header pairs".to_string()))
        );
    }
}