ic-asset-router 0.1.1

use std::collections::HashMap;

use ic_http_certification::{HeaderField, Method};

/// Error returned by [`RouteContext::json()`].
#[derive(Debug)]
pub enum JsonBodyError {
    /// The body bytes are not valid UTF-8.
    Utf8(std::str::Utf8Error),
    /// JSON deserialization failed.
    Json(serde_json::Error),
}

impl std::fmt::Display for JsonBodyError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::Utf8(e) => write!(f, "body is not valid UTF-8: {e}"),
            Self::Json(e) => write!(f, "JSON deserialization failed: {e}"),
        }
    }
}

impl std::error::Error for JsonBodyError {
    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
        match self {
            Self::Utf8(e) => Some(e),
            Self::Json(e) => Some(e),
        }
    }
}

/// Error returned by [`RouteContext::form()`].
#[derive(Debug)]
pub enum FormBodyError {
    /// The body bytes are not valid UTF-8.
    Utf8(std::str::Utf8Error),
    /// Form deserialization failed.
    Deserialize(serde_urlencoded::de::Error),
}

impl std::fmt::Display for FormBodyError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::Utf8(e) => write!(f, "body is not valid UTF-8: {e}"),
            Self::Deserialize(e) => write!(f, "form deserialization failed: {e}"),
        }
    }
}

impl std::error::Error for FormBodyError {
    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
        match self {
            Self::Utf8(e) => Some(e),
            Self::Deserialize(e) => Some(e),
        }
    }
}

/// A type alias for query string parameters parsed from the URL.
pub type QueryParams = HashMap<String, String>;

/// A context object bundling all request data for route handlers.
///
/// Rather than accumulating positional arguments as features grow (params, query
/// strings, method, headers, etc.), handlers receive a single context object.
/// This is extensible — new fields can be added without changing every handler
/// signature.
///
/// The type parameter `P` is the typed params struct generated by the build
/// script for each route. Routes without dynamic segments use `()`.
///
/// The type parameter `S` is the typed search (query string) params struct.
/// Routes that define a `pub struct SearchParams` (implementing
/// `serde::Deserialize`) get the query string deserialized into `ctx.search`.
/// Routes without a `SearchParams` struct default to `S = ()`.
///
/// Untyped query access is always available via `ctx.query` regardless of `S`.
///
/// # Examples
///
/// A handler for a static route (no path parameters or search params):
///
/// ```rust,ignore
/// use ic_asset_router::{RouteContext, HttpResponse};
///
/// pub fn get(ctx: RouteContext<()>) -> HttpResponse<'static> {
///     let url = &ctx.url;
///     let method = &ctx.method;
///     // Access untyped query params:
///     let page = ctx.query.get("page").cloned().unwrap_or_default();
///     // ... build response
///     # todo!()
/// }
/// ```
///
/// A handler for a dynamic route with typed params (e.g. `_postId/index.rs`):
///
/// ```rust,ignore
/// use ic_asset_router::{RouteContext, HttpResponse};
///
/// // Generated by the build script in mod.rs:
/// // pub struct Params { pub post_id: String }
///
/// pub fn get(ctx: RouteContext<Params>) -> HttpResponse<'static> {
///     let post_id = &ctx.params.post_id;
///     // ... build response using post_id
///     # todo!()
/// }
/// ```
pub struct RouteContext<P, S = ()> {
    /// Typed route parameters extracted from the URL path.
    pub params: P,
    /// Typed search (query string) parameters deserialized from the URL.
    ///
    /// Populated by `serde_urlencoded` when the route defines a `SearchParams`
    /// struct. Defaults to `()` for routes without typed search params.
    pub search: S,
    /// Query string parameters parsed from the URL (untyped, always available).
    pub query: QueryParams,
    /// The HTTP method of the request.
    pub method: Method,
    /// The request headers.
    pub headers: Vec<HeaderField>,
    /// The raw request body bytes.
    pub body: Vec<u8>,
    /// The full request URL.
    pub url: String,
    /// The wildcard capture for catch-all routes.
    ///
    /// `None` for routes without a wildcard segment.
    /// `Some("docs/report.pdf")` for a request to `/files/docs/report.pdf`
    /// matching `/files/*`.
    pub wildcard: Option<String>,
}

impl<P, S> RouteContext<P, S> {
    /// Returns the value of the first header matching `name` (case-insensitive).
    ///
    /// Returns `None` if no header with that name exists.
    ///
    /// # Examples
    ///
    /// ```rust,ignore
    /// let auth = ctx.header("authorization"); // Option<&str>
    /// let ct = ctx.header("Content-Type");    // case-insensitive
    /// ```
    pub fn header(&self, name: &str) -> Option<&str> {
        self.headers
            .iter()
            .find(|(k, _)| k.eq_ignore_ascii_case(name))
            .map(|(_, v)| v.as_str())
    }

    /// Returns the request body as a UTF-8 string.
    ///
    /// Returns `Err` if the body is not valid UTF-8. For lossy conversion,
    /// use `String::from_utf8_lossy(&ctx.body)` directly.
    ///
    /// # Examples
    ///
    /// ```rust,ignore
    /// match ctx.body_to_str() {
    ///     Ok(text) => { /* use text */ }
    ///     Err(_) => { /* return 400 */ }
    /// }
    /// ```
    pub fn body_to_str(&self) -> Result<&str, std::str::Utf8Error> {
        std::str::from_utf8(&self.body)
    }

    /// Deserializes the request body as JSON into type `T`.
    ///
    /// Returns `Err` if the body is not valid UTF-8 or if JSON
    /// deserialization fails.
    ///
    /// # Examples
    ///
    /// ```rust,ignore
    /// #[derive(serde::Deserialize)]
    /// struct CreateItem { name: String }
    ///
    /// pub fn post(ctx: RouteContext<()>) -> HttpResponse<'static> {
    ///     let input: CreateItem = match ctx.json() {
    ///         Ok(v) => v,
    ///         Err(_) => return bad_request("invalid JSON body"),
    ///     };
    ///     // ...
    ///     # todo!()
    /// }
    /// ```
    pub fn json<T: serde::de::DeserializeOwned>(&self) -> Result<T, JsonBodyError> {
        let text = std::str::from_utf8(&self.body).map_err(JsonBodyError::Utf8)?;
        serde_json::from_str(text).map_err(JsonBodyError::Json)
    }

    /// Parses the request body as `application/x-www-form-urlencoded` key-value
    /// pairs.
    ///
    /// Convenience wrapper around [`parse_form_body`]. Uses lossy UTF-8
    /// conversion and skips malformed pairs, so it never fails.
    ///
    /// # Examples
    ///
    /// ```rust,ignore
    /// let fields = ctx.form_data();
    /// let author = fields.get("author").cloned().unwrap_or_default();
    /// ```
    pub fn form_data(&self) -> HashMap<String, String> {
        parse_form_body(&self.body)
    }

    /// Deserializes the request body as `application/x-www-form-urlencoded`
    /// into type `T`.
    ///
    /// Returns `Err` if the body is not valid UTF-8 or if deserialization
    /// fails.
    ///
    /// # Examples
    ///
    /// ```rust,ignore
    /// #[derive(serde::Deserialize)]
    /// struct CommentForm { author: String, body: String }
    ///
    /// pub fn post(ctx: RouteContext<Params>) -> HttpResponse<'static> {
    ///     let form: CommentForm = match ctx.form() {
    ///         Ok(v) => v,
    ///         Err(_) => return bad_request("invalid form data"),
    ///     };
    ///     // ...
    ///     # todo!()
    /// }
    /// ```
    pub fn form<T: serde::de::DeserializeOwned>(&self) -> Result<T, FormBodyError> {
        let text = std::str::from_utf8(&self.body).map_err(FormBodyError::Utf8)?;
        serde_urlencoded::from_str(text).map_err(FormBodyError::Deserialize)
    }
}

/// Parse query string key-value pairs from a URL.
///
/// Extracts the portion after `?` and splits on `&` to produce key-value pairs.
/// Keys and values are URL-decoded. Malformed pairs (missing `=`) are skipped.
///
/// Returns an empty map if there is no query string.
pub fn parse_query(url: &str) -> QueryParams {
    let query_str = match url.split_once('?') {
        Some((_, q)) => q,
        None => return QueryParams::new(),
    };

    // Strip fragment if present (e.g. `?page=1#section`)
    let query_str = query_str.split_once('#').map_or(query_str, |(q, _)| q);

    query_str
        .split('&')
        .filter(|s| !s.is_empty())
        .filter_map(|pair| {
            let (key, value) = pair.split_once('=')?;
            Some((url_decode(key).into_owned(), url_decode(value).into_owned()))
        })
        .collect()
}

/// Percent-decode a URL-encoded string.
///
/// Decodes `%XX` hex sequences and converts `+` to space, as used in both
/// query strings and `application/x-www-form-urlencoded` bodies. Returns a
/// borrowed `Cow` when the input contains no encoded characters (zero-copy
/// fast path). Does not validate UTF-8 beyond what `String::from_utf8_lossy`
/// handles — malformed `%XX` sequences (e.g. `%ZZ`) are passed through
/// literally.
///
/// # Examples
///
/// ```
/// use ic_asset_router::url_decode;
///
/// assert_eq!(url_decode("hello%20world"), "hello world");
/// assert_eq!(url_decode("a+b"), "a b");
/// assert_eq!(url_decode("plain"), "plain");
/// ```
pub fn url_decode(input: &str) -> std::borrow::Cow<'_, str> {
    if !input.contains('%') && !input.contains('+') {
        return std::borrow::Cow::Borrowed(input);
    }

    let mut bytes = Vec::with_capacity(input.len());
    let mut chars = input.bytes();
    while let Some(b) = chars.next() {
        match b {
            b'+' => bytes.push(b' '),
            b'%' => {
                let hi = chars.next().and_then(hex_val);
                let lo = chars.next().and_then(hex_val);
                match (hi, lo) {
                    (Some(h), Some(l)) => bytes.push(h << 4 | l),
                    _ => {
                        // Malformed percent encoding — pass through literally
                        bytes.push(b'%');
                    }
                }
            }
            _ => bytes.push(b),
        }
    }

    String::from_utf8(bytes)
        .map(std::borrow::Cow::Owned)
        .unwrap_or_else(|e| {
            std::borrow::Cow::Owned(String::from_utf8_lossy(e.as_bytes()).into_owned())
        })
}

/// Deserialize a URL query string into a typed struct using `serde_urlencoded`.
///
/// This is the helper used by the generated route wiring to populate
/// `RouteContext.search`. If deserialization fails (missing required fields,
/// type mismatches, malformed encoding), returns `S::default()` so that
/// handlers never see a panic from bad query strings.
///
/// The type `S` must implement both `serde::Deserialize` and `Default`.
pub fn deserialize_search_params<S>(query_str: &str) -> S
where
    S: serde::de::DeserializeOwned + Default,
{
    // Strip leading '?' if present (the caller may pass the raw query portion
    // or the full `?key=val` string).
    let qs = query_str.strip_prefix('?').unwrap_or(query_str);
    serde_urlencoded::from_str(qs).unwrap_or_default()
}

/// Parse an `application/x-www-form-urlencoded` body into key-value pairs.
///
/// This is the encoding used by HTML `<form>` submissions. The body is
/// interpreted as UTF-8, split on `&`, and each `key=value` pair is
/// URL-decoded. Pairs without `=` are skipped.
///
/// # Examples
///
/// ```
/// use ic_asset_router::parse_form_body;
///
/// let fields = parse_form_body(b"name=Alice&age=30");
/// assert_eq!(fields.get("name").unwrap(), "Alice");
/// assert_eq!(fields.get("age").unwrap(), "30");
///
/// let fields = parse_form_body(b"q=hello+world");
/// assert_eq!(fields.get("q").unwrap(), "hello world");
/// ```
pub fn parse_form_body(body: &[u8]) -> HashMap<String, String> {
    let input = String::from_utf8_lossy(body);
    input
        .split('&')
        .filter(|s| !s.is_empty())
        .filter_map(|pair| {
            let (key, value) = pair.split_once('=')?;
            Some((url_decode(key).into_owned(), url_decode(value).into_owned()))
        })
        .collect()
}

fn hex_val(b: u8) -> Option<u8> {
    match b {
        b'0'..=b'9' => Some(b - b'0'),
        b'a'..=b'f' => Some(b - b'a' + 10),
        b'A'..=b'F' => Some(b - b'A' + 10),
        _ => None,
    }
}

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

    #[test]
    fn parse_query_basic() {
        let q = parse_query("http://example.com/path?page=3&filter=active");
        assert_eq!(q.get("page").unwrap(), "3");
        assert_eq!(q.get("filter").unwrap(), "active");
    }

    #[test]
    fn parse_query_empty_url() {
        let q = parse_query("");
        assert!(q.is_empty());
    }

    #[test]
    fn parse_query_no_query_string() {
        let q = parse_query("/path/to/resource");
        assert!(q.is_empty());
    }

    #[test]
    fn parse_query_empty_query_string() {
        let q = parse_query("/path?");
        assert!(q.is_empty());
    }

    #[test]
    fn parse_query_with_fragment() {
        let q = parse_query("/path?page=1#section");
        assert_eq!(q.get("page").unwrap(), "1");
        assert_eq!(q.len(), 1);
    }

    #[test]
    fn parse_query_url_encoded_values() {
        let q = parse_query("/search?q=hello+world&name=foo%20bar");
        assert_eq!(q.get("q").unwrap(), "hello world");
        assert_eq!(q.get("name").unwrap(), "foo bar");
    }

    #[test]
    fn parse_query_skips_malformed_pairs() {
        // Pairs without `=` are skipped
        let q = parse_query("/path?good=yes&bad&also=fine");
        assert_eq!(q.get("good").unwrap(), "yes");
        assert_eq!(q.get("also").unwrap(), "fine");
        assert_eq!(q.len(), 2);
    }

    #[test]
    fn parse_query_empty_value() {
        let q = parse_query("/path?key=");
        assert_eq!(q.get("key").unwrap(), "");
    }

    #[test]
    fn parse_query_multiple_equals() {
        // Only splits on the first `=`
        let q = parse_query("/path?expr=a=b");
        assert_eq!(q.get("expr").unwrap(), "a=b");
    }

    // --- 5.3.5: parse_query with valid params (bare query string) ---

    #[test]
    fn parse_query_bare_query_string() {
        // Tests the specific input `?page=3&filter=active` — note: parse_query
        // expects a URL (or URL path), so `?page=3&filter=active` works since
        // it splits on `?`.
        let q = parse_query("?page=3&filter=active");
        assert_eq!(q.get("page").unwrap(), "3");
        assert_eq!(q.get("filter").unwrap(), "active");
    }

    // --- 5.3.6: parse_query with empty string ---

    #[test]
    fn parse_query_empty_string_returns_empty_hashmap() {
        let q = parse_query("");
        assert!(q.is_empty());
    }

    // --- 5.3.7: malformed query values don't panic (typed search params) ---

    #[test]
    fn deserialize_search_params_valid() {
        #[derive(serde::Deserialize, Default, Debug)]
        struct Sp {
            page: Option<u32>,
            filter: Option<String>,
        }

        let sp: Sp = deserialize_search_params("page=3&filter=active");
        assert_eq!(sp.page, Some(3));
        assert_eq!(sp.filter.as_deref(), Some("active"));
    }

    #[test]
    fn deserialize_search_params_type_mismatch_falls_back() {
        // `page=abc` can't parse as u32 — the entire deserialization fails and
        // falls back to Default, giving None for all fields.
        #[derive(serde::Deserialize, Default, Debug)]
        struct Sp {
            page: Option<u32>,
            filter: Option<String>,
        }

        let sp: Sp = deserialize_search_params("page=abc&filter=active");
        // serde_urlencoded fails the whole parse on type mismatch, so we get defaults.
        assert_eq!(sp.page, None);
        assert_eq!(sp.filter, None);
    }

    #[test]
    fn deserialize_search_params_empty_string() {
        #[derive(serde::Deserialize, Default, Debug)]
        struct Sp {
            page: Option<u32>,
        }

        let sp: Sp = deserialize_search_params("");
        assert_eq!(sp.page, None);
    }

    #[test]
    fn deserialize_search_params_missing_fields_default_to_none() {
        #[derive(serde::Deserialize, Default, Debug)]
        struct Sp {
            page: Option<u32>,
            filter: Option<String>,
            limit: Option<u32>,
        }

        let sp: Sp = deserialize_search_params("page=5");
        assert_eq!(sp.page, Some(5));
        assert_eq!(sp.filter, None);
        assert_eq!(sp.limit, None);
    }

    #[test]
    fn deserialize_search_params_with_leading_question_mark() {
        #[derive(serde::Deserialize, Default, Debug)]
        struct Sp {
            page: Option<u32>,
        }

        let sp: Sp = deserialize_search_params("?page=7");
        assert_eq!(sp.page, Some(7));
    }

    #[test]
    fn deserialize_search_params_malformed_encoding_does_not_panic() {
        #[derive(serde::Deserialize, Default, Debug)]
        struct Sp {
            q: Option<String>,
        }

        // Malformed percent encoding — should not panic, falls back to default.
        let sp: Sp = deserialize_search_params("q=%ZZ");
        // serde_urlencoded may handle this gracefully or fail; either way, no panic.
        let _ = sp.q;
    }

    // --- 6.8: url_decode tests ---

    #[test]
    fn url_decode_percent_encoding() {
        assert_eq!(url_decode("hello%20world"), "hello world");
    }

    #[test]
    fn url_decode_plus_as_space() {
        assert_eq!(url_decode("a+b"), "a b");
    }

    #[test]
    fn url_decode_malformed_passthrough() {
        // `%en` — `e` is valid hex but `n` is not. The implementation consumes
        // both bytes after `%` and only emits `%` for the malformed sequence,
        // so the two consumed chars are lost: "no%encoding" → "no%coding".
        assert_eq!(url_decode("no%encoding"), "no%coding");
    }

    #[test]
    fn url_decode_plain_passthrough() {
        let result = url_decode("plain");
        assert_eq!(result, "plain");
        // Should be zero-copy (borrowed)
        assert!(matches!(result, std::borrow::Cow::Borrowed(_)));
    }

    // --- 8.2.4: url_decode with invalid UTF-8 byte sequences ---

    #[test]
    fn url_decode_invalid_utf8_returns_valid_string() {
        // %FF%FE are not valid UTF-8 bytes. url_decode should produce a
        // valid string (via lossy conversion) without panicking or leaking.
        let result = url_decode("%FF%FE");
        // The result should be a valid Rust string (no panic).
        assert!(!result.is_empty());
        // String::from_utf8_lossy replaces invalid sequences with U+FFFD.
        assert!(result.contains('\u{FFFD}'));
    }

    // --- 8.6.1: url_decode edge case tests ---

    #[test]
    fn url_decode_trailing_percent() {
        // Trailing '%' with no hex digits after it → pass through literally.
        assert_eq!(url_decode("abc%"), "abc%");
    }

    #[test]
    fn url_decode_only_percent() {
        // A lone '%' at end of string → pass through literally.
        assert_eq!(url_decode("%"), "%");
    }

    #[test]
    fn url_decode_percent_one_hex_then_eof() {
        // '%' followed by one valid hex char then EOF — malformed, the '%' is
        // kept but the consumed hex char is lost (consistent with the existing
        // malformed-passthrough behaviour documented in url_decode_malformed_passthrough).
        assert_eq!(url_decode("abc%4"), "abc%");
    }

    #[test]
    fn url_decode_null_byte() {
        // "%00" decodes to a null byte (U+0000).
        let result = url_decode("%00");
        assert_eq!(result, "\0");
        assert_eq!(result.len(), 1);
    }

    #[test]
    fn url_decode_double_encoded() {
        // "%2520" → single decode produces "%20" (not a space).
        // The first pass decodes %25 → '%', leaving "20" as literal.
        assert_eq!(url_decode("%2520"), "%20");
    }

    #[test]
    fn url_decode_empty_string() {
        let result = url_decode("");
        assert_eq!(result, "");
        // Empty string has no '%' or '+', so it should be zero-copy.
        assert!(matches!(result, std::borrow::Cow::Borrowed(_)));
    }

    // --- 6.8: parse_form_body tests ---

    #[test]
    fn parse_form_body_basic_pairs() {
        let fields = parse_form_body(b"name=Alice&age=30");
        assert_eq!(fields.get("name").unwrap(), "Alice");
        assert_eq!(fields.get("age").unwrap(), "30");
    }

    #[test]
    fn parse_form_body_plus_decoding() {
        let fields = parse_form_body(b"q=hello+world");
        assert_eq!(fields.get("q").unwrap(), "hello world");
    }

    #[test]
    fn parse_form_body_empty() {
        let fields = parse_form_body(b"");
        assert!(fields.is_empty());
    }

    #[test]
    fn parse_form_body_encoded_values() {
        let fields = parse_form_body(b"key=val%26ue");
        assert_eq!(fields.get("key").unwrap(), "val&ue");
    }

    // --- 7.7: RouteContext convenience method tests ---

    fn test_ctx(headers: Vec<(String, String)>, body: Vec<u8>) -> RouteContext<()> {
        RouteContext {
            params: (),
            search: (),
            query: QueryParams::new(),
            method: Method::GET,
            headers,
            body,
            url: String::new(),
            wildcard: None,
        }
    }

    // header tests

    #[test]
    fn header_case_insensitive() {
        let ctx = test_ctx(
            vec![("authorization".to_string(), "Bearer x".to_string())],
            vec![],
        );
        assert_eq!(ctx.header("Authorization"), Some("Bearer x"));
        assert_eq!(ctx.header("authorization"), Some("Bearer x"));
        assert_eq!(ctx.header("AUTHORIZATION"), Some("Bearer x"));
    }

    #[test]
    fn header_missing() {
        let ctx = test_ctx(vec![], vec![]);
        assert_eq!(ctx.header("x-missing"), None);
    }

    #[test]
    fn header_first_match_wins() {
        let ctx = test_ctx(
            vec![
                ("x-custom".to_string(), "first".to_string()),
                ("x-custom".to_string(), "second".to_string()),
            ],
            vec![],
        );
        assert_eq!(ctx.header("x-custom"), Some("first"));
    }

    // body_to_str tests

    #[test]
    fn body_to_str_valid_utf8() {
        let ctx = test_ctx(vec![], b"hello".to_vec());
        assert_eq!(ctx.body_to_str(), Ok("hello"));
    }

    #[test]
    fn body_to_str_invalid_utf8() {
        let ctx = test_ctx(vec![], vec![0xff, 0xfe]);
        assert!(ctx.body_to_str().is_err());
    }

    #[test]
    fn body_to_str_empty() {
        let ctx = test_ctx(vec![], vec![]);
        assert_eq!(ctx.body_to_str(), Ok(""));
    }

    // json tests

    #[test]
    fn json_valid() {
        #[derive(serde::Deserialize, Debug, PartialEq)]
        struct Item {
            name: String,
        }
        let ctx = test_ctx(vec![], br#"{"name":"test"}"#.to_vec());
        let result: Result<Item, _> = ctx.json();
        assert_eq!(
            result.unwrap(),
            Item {
                name: "test".to_string()
            }
        );
    }

    #[test]
    fn json_invalid_json() {
        #[derive(serde::Deserialize)]
        struct Item {
            #[allow(dead_code)]
            name: String,
        }
        let ctx = test_ctx(vec![], b"{invalid}".to_vec());
        let result: Result<Item, _> = ctx.json();
        assert!(matches!(result, Err(JsonBodyError::Json(_))));
    }

    #[test]
    fn json_invalid_utf8() {
        #[derive(serde::Deserialize)]
        struct Item {
            #[allow(dead_code)]
            name: String,
        }
        let ctx = test_ctx(vec![], vec![0xff, 0xfe]);
        let result: Result<Item, _> = ctx.json();
        assert!(matches!(result, Err(JsonBodyError::Utf8(_))));
    }

    #[test]
    fn json_empty_body() {
        #[derive(serde::Deserialize)]
        struct Item {
            #[allow(dead_code)]
            name: String,
        }
        let ctx = test_ctx(vec![], vec![]);
        let result: Result<Item, _> = ctx.json();
        assert!(matches!(result, Err(JsonBodyError::Json(_))));
    }

    // form_data tests

    #[test]
    fn form_data_basic() {
        let ctx = test_ctx(vec![], b"name=Alice&age=30".to_vec());
        let fields = ctx.form_data();
        assert_eq!(fields.get("name").unwrap(), "Alice");
        assert_eq!(fields.get("age").unwrap(), "30");
    }

    #[test]
    fn form_data_empty() {
        let ctx = test_ctx(vec![], vec![]);
        let fields = ctx.form_data();
        assert!(fields.is_empty());
    }

    #[test]
    fn form_data_url_encoded() {
        let ctx = test_ctx(vec![], b"greeting=hello+world&path=%2Ffoo%2Fbar".to_vec());
        let fields = ctx.form_data();
        assert_eq!(fields.get("greeting").unwrap(), "hello world");
        assert_eq!(fields.get("path").unwrap(), "/foo/bar");
    }

    // form tests

    #[test]
    fn form_valid() {
        #[derive(serde::Deserialize, Debug, PartialEq)]
        struct Comment {
            author: String,
            body: String,
        }
        let ctx = test_ctx(vec![], b"author=Alice&body=hello".to_vec());
        let result: Result<Comment, _> = ctx.form();
        assert_eq!(
            result.unwrap(),
            Comment {
                author: "Alice".to_string(),
                body: "hello".to_string(),
            }
        );
    }

    #[test]
    fn form_missing_field() {
        #[derive(serde::Deserialize)]
        struct Comment {
            #[allow(dead_code)]
            author: String,
            #[allow(dead_code)]
            body: String,
        }
        let ctx = test_ctx(vec![], b"author=Alice".to_vec());
        let result: Result<Comment, _> = ctx.form();
        assert!(matches!(result, Err(FormBodyError::Deserialize(_))));
    }

    #[test]
    fn form_invalid_utf8() {
        #[derive(serde::Deserialize)]
        struct Comment {
            #[allow(dead_code)]
            author: String,
        }
        let ctx = test_ctx(vec![], vec![0xff, 0xfe]);
        let result: Result<Comment, _> = ctx.form();
        assert!(matches!(result, Err(FormBodyError::Utf8(_))));
    }

    #[test]
    fn form_empty_body_with_optional_fields() {
        #[derive(serde::Deserialize, Debug, PartialEq)]
        struct Opts {
            name: Option<String>,
        }
        let ctx = test_ctx(vec![], vec![]);
        let result: Result<Opts, _> = ctx.form();
        assert_eq!(result.unwrap(), Opts { name: None });
    }
}