perfect-postcode/server-rs/src/routes/rightmove.rs

use std::sync::Arc;

use axum::extract::{Query, State};
use axum::http::StatusCode;
use axum::response::Redirect;
use reqwest::Url;
use serde::Deserialize;
use serde_json::Value;
use tracing::warn;

use crate::state::SharedState;
use crate::utils::normalize_postcode;

const RIGHTMOVE_TYPEAHEAD_URL: &str = "https://los.rightmove.co.uk/typeahead";
const RIGHTMOVE_HOST: &str = "www.rightmove.co.uk";
const RIGHTMOVE_FIND_PATH: &str = "/property-for-sale/find.html";

#[derive(Deserialize)]
pub struct RightmoveRedirectParams {
    postcode: String,
    target: String,
}

#[derive(Deserialize)]
struct RightmoveTypeaheadResponse {
    #[serde(default)]
    matches: Vec<RightmoveTypeaheadMatch>,
}

#[derive(Deserialize)]
struct RightmoveTypeaheadMatch {
    id: Value,
    #[serde(rename = "type")]
    match_type: String,
    #[serde(default, rename = "displayName")]
    display_name: String,
}

pub async fn get_rightmove_redirect(
    State(shared): State<Arc<SharedState>>,
    Query(params): Query<RightmoveRedirectParams>,
) -> Result<Redirect, (StatusCode, String)> {
    if !looks_like_full_uk_postcode(&params.postcode) {
        return Err((
            StatusCode::BAD_REQUEST,
            "'postcode' must be a full UK postcode".to_string(),
        ));
    }

    let postcode = normalize_postcode(&params.postcode);
    let mut target = parse_rightmove_target(&params.target)?;
    let state = shared.load_state();

    match fetch_exact_postcode_location_identifier(&state.http_client, &postcode).await {
        Some(location_identifier) => {
            apply_exact_postcode_location(&mut target, &postcode, &location_identifier);
        }
        None => warn!(
            postcode,
            "Could not resolve exact Rightmove postcode location"
        ),
    }

    Ok(Redirect::temporary(target.as_str()))
}

async fn fetch_exact_postcode_location_identifier(
    client: &reqwest::Client,
    postcode: &str,
) -> Option<String> {
    let url = format!(
        "{}?query={}&limit=5",
        RIGHTMOVE_TYPEAHEAD_URL,
        urlencoding::encode(postcode)
    );

    let response = client
        .get(url)
        .send()
        .await
        .map_err(|err| warn!(postcode, "Rightmove typeahead request failed: {err}"))
        .ok()?;

    if !response.status().is_success() {
        warn!(
            postcode,
            status = %response.status(),
            "Rightmove typeahead returned an error"
        );
        return None;
    }

    let typeahead: RightmoveTypeaheadResponse = response
        .json()
        .await
        .map_err(|err| {
            warn!(
                postcode,
                "Failed to parse Rightmove typeahead response: {err}"
            )
        })
        .ok()?;

    typeahead.matches.iter().find_map(|item| {
        if !item.match_type.eq_ignore_ascii_case("POSTCODE") {
            return None;
        }
        if compact_postcode(&item.display_name) != compact_postcode(postcode) {
            return None;
        }
        rightmove_id_to_string(&item.id).map(|id| format!("POSTCODE^{id}"))
    })
}

fn parse_rightmove_target(target: &str) -> Result<Url, (StatusCode, String)> {
    let url = Url::parse(target).map_err(|_| {
        (
            StatusCode::BAD_REQUEST,
            "'target' must be a valid Rightmove URL".to_string(),
        )
    })?;

    if url.scheme() != "https"
        || url.host_str() != Some(RIGHTMOVE_HOST)
        || url.path() != RIGHTMOVE_FIND_PATH
    {
        return Err((
            StatusCode::BAD_REQUEST,
            "'target' must be a Rightmove property search URL".to_string(),
        ));
    }

    Ok(url)
}

fn apply_exact_postcode_location(url: &mut Url, postcode: &str, location_identifier: &str) {
    let mut pairs: Vec<(String, String)> = url
        .query_pairs()
        .filter(|(key, _)| {
            key != "searchLocation"
                && key != "useLocationIdentifier"
                && key != "locationIdentifier"
                && key != "radius"
        })
        .map(|(key, value)| (key.into_owned(), value.into_owned()))
        .collect();

    pairs.push(("searchLocation".to_string(), postcode.to_string()));
    pairs.push(("useLocationIdentifier".to_string(), "true".to_string()));
    pairs.push((
        "locationIdentifier".to_string(),
        location_identifier.to_string(),
    ));
    pairs.push(("radius".to_string(), "0.0".to_string()));

    let mut query = url.query_pairs_mut();
    query.clear();
    for (key, value) in pairs {
        query.append_pair(&key, &value);
    }
}

fn rightmove_id_to_string(value: &Value) -> Option<String> {
    match value {
        Value::String(id) if !id.trim().is_empty() => Some(id.clone()),
        Value::Number(id) => Some(id.to_string()),
        _ => None,
    }
}

fn compact_postcode(postcode: &str) -> String {
    postcode
        .chars()
        .filter(|ch| !ch.is_whitespace())
        .map(|ch| ch.to_ascii_uppercase())
        .collect()
}

fn looks_like_full_uk_postcode(postcode: &str) -> bool {
    let compact = compact_postcode(postcode);
    let bytes = compact.as_bytes();
    if !(5..=7).contains(&bytes.len()) {
        return false;
    }

    let outward_len = bytes.len() - 3;
    bytes[0].is_ascii_alphabetic()
        && bytes[..outward_len]
            .iter()
            .all(|byte| byte.is_ascii_alphanumeric())
        && bytes[outward_len].is_ascii_digit()
        && bytes[outward_len + 1].is_ascii_alphabetic()
        && bytes[outward_len + 2].is_ascii_alphabetic()
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn rewrites_rightmove_url_to_exact_postcode_location() {
        let mut url = Url::parse(
            "https://www.rightmove.co.uk/property-for-sale/find.html?searchLocation=SW1A+1AA&useLocationIdentifier=true&locationIdentifier=OUTCODE%5E2506&radius=0.25&minPrice=100000",
        )
        .unwrap();

        apply_exact_postcode_location(&mut url, "SW1A 1AA", "POSTCODE^837246");

        let pairs: std::collections::HashMap<_, _> = url.query_pairs().into_owned().collect();
        assert_eq!(pairs.get("searchLocation").unwrap(), "SW1A 1AA");
        assert_eq!(pairs.get("useLocationIdentifier").unwrap(), "true");
        assert_eq!(pairs.get("locationIdentifier").unwrap(), "POSTCODE^837246");
        assert_eq!(pairs.get("radius").unwrap(), "0.0");
        assert_eq!(pairs.get("minPrice").unwrap(), "100000");
    }

    #[test]
    fn rejects_non_rightmove_redirect_targets() {
        assert!(parse_rightmove_target("https://example.com/property-for-sale/find.html").is_err());
        assert!(
            parse_rightmove_target("http://www.rightmove.co.uk/property-for-sale/find.html")
                .is_err()
        );
        assert!(
            parse_rightmove_target("https://www.rightmove.co.uk/property-to-rent/find.html")
                .is_err()
        );
    }

    #[test]
    fn validates_full_postcode_shape() {
        assert!(looks_like_full_uk_postcode("SW1A 1AA"));
        assert!(looks_like_full_uk_postcode("e16an"));
        assert!(!looks_like_full_uk_postcode("SW1A"));
        assert!(!looks_like_full_uk_postcode("not a postcode"));
    }
}