use std::cell::RefCell;
use std::iter::Peekable;
use std::str::Chars;
use std::sync::Arc;

use pyo3::intern;
use pyo3::prelude::*;
use pyo3::types::{PyDict, PyList};

use ahash::AHashSet;
use pyo3::IntoPyObjectExt;
use url::{ParseError, SyntaxViolation, Url};

use crate::build_tools::LazyLock;
use crate::build_tools::schema_or_config;
use crate::build_tools::{is_strict, py_schema_err};
use crate::errors::{ErrorType, ErrorTypeDefaults, ValError, ValResult};
use crate::input::Input;
use crate::input::ValidationMatch;
use crate::input::downcast_python_input;
use crate::tools::SchemaDict;
use crate::url::{PyMultiHostUrl, PyUrl, scheme_is_special};
use crate::validators::literal::expected_name;
use crate::validators::literal::expected_repr;

use super::Exactness;
use super::{BuildValidator, CombinedValidator, DefinitionsBuilder, ValidationState, Validator};

type AllowedSchemes = Option<(AHashSet<String>, String)>;

#[derive(Debug, Clone)]
pub struct UrlValidator {
    strict: bool,
    max_length: Option<usize>,
    allowed_schemes: AllowedSchemes,
    host_required: bool,
    default_host: Option<String>,
    default_port: Option<u16>,
    default_path: Option<String>,
    name: String,
    preserve_empty_path: bool,
}

static SIMPLE_URL_VALIDATOR: LazyLock<Arc<CombinedValidator>> = LazyLock::new(|| {
    Arc::new(CombinedValidator::Url(UrlValidator {
        strict: false,
        max_length: None,
        allowed_schemes: None,
        host_required: false,
        default_host: None,
        default_port: None,
        default_path: None,
        name: "url".to_string(),
        preserve_empty_path: false,
    }))
});

static SIMPLE_URL_VALIDATOR_STRICT: LazyLock<Arc<CombinedValidator>> = LazyLock::new(|| {
    Arc::new(CombinedValidator::Url(UrlValidator {
        strict: true,
        max_length: None,
        allowed_schemes: None,
        host_required: false,
        default_host: None,
        default_port: None,
        default_path: None,
        name: "url".to_string(),
        preserve_empty_path: false,
    }))
});

static SIMPLE_URL_VALIDATOR_PRESERVE_EMPTY_PATH: LazyLock<Arc<CombinedValidator>> = LazyLock::new(|| {
    Arc::new(CombinedValidator::Url(UrlValidator {
        strict: false,
        max_length: None,
        allowed_schemes: None,
        host_required: false,
        default_host: None,
        default_port: None,
        default_path: None,
        name: "url".to_string(),
        preserve_empty_path: true,
    }))
});

static SIMPLE_URL_VALIDATOR_STRICT_PRESERVE_EMPTY_PATH: LazyLock<Arc<CombinedValidator>> = LazyLock::new(|| {
    Arc::new(CombinedValidator::Url(UrlValidator {
        strict: true,
        max_length: None,
        allowed_schemes: None,
        host_required: false,
        default_host: None,
        default_port: None,
        default_path: None,
        name: "url".to_string(),
        preserve_empty_path: true,
    }))
});

fn get_preserve_empty_path(schema: &Bound<'_, PyDict>, config: Option<&Bound<'_, PyDict>>) -> PyResult<bool> {
    schema_or_config(
        schema,
        config,
        intern!(schema.py(), "preserve_empty_path"),
        intern!(schema.py(), "url_preserve_empty_path"),
    )
    .map(|v| v.unwrap_or(false))
}

impl BuildValidator for UrlValidator {
    const EXPECTED_TYPE: &'static str = "url";

    fn build(
        schema: &Bound<'_, PyDict>,
        config: Option<&Bound<'_, PyDict>>,
        _definitions: &mut DefinitionsBuilder<Arc<CombinedValidator>>,
    ) -> PyResult<Arc<CombinedValidator>> {
        let (allowed_schemes, name) = get_allowed_schemes(schema, Self::EXPECTED_TYPE)?;

        let validator = Self {
            strict: is_strict(schema, config)?,
            max_length: schema.get_as(intern!(schema.py(), "max_length"))?,
            host_required: schema.get_as(intern!(schema.py(), "host_required"))?.unwrap_or(false),
            default_host: schema.get_as(intern!(schema.py(), "default_host"))?,
            default_port: schema.get_as(intern!(schema.py(), "default_port"))?,
            default_path: schema.get_as(intern!(schema.py(), "default_path"))?,
            allowed_schemes,
            name,
            preserve_empty_path: get_preserve_empty_path(schema, config)?,
        };

        // if no defaults, the prebuilt simple validator will do
        if validator.max_length.is_none()
            && validator.allowed_schemes.is_none()
            && !validator.host_required
            && validator.default_host.is_none()
            && validator.default_port.is_none()
            && validator.default_path.is_none()
        {
            return Ok(UrlValidator::get_simple(validator.strict, validator.preserve_empty_path).clone());
        }

        Ok(CombinedValidator::Url(validator).into())
    }
}

impl_py_gc_traverse!(UrlValidator {});

impl Validator for UrlValidator {
    fn validate<'py>(
        &self,
        py: Python<'py>,
        input: &(impl Input<'py> + ?Sized),
        state: &mut ValidationState<'_, 'py>,
    ) -> ValResult<Py<PyAny>> {
        let mut either_url = self.get_url(py, input, state.strict_or(self.strict))?;

        if let Some((ref allowed_schemes, ref expected_schemes_repr)) = self.allowed_schemes
            && !allowed_schemes.contains(either_url.url().scheme())
        {
            let expected_schemes = expected_schemes_repr.clone();
            return Err(ValError::new(
                ErrorType::UrlScheme {
                    expected_schemes,
                    context: None,
                },
                input,
            ));
        }

        match check_sub_defaults(
            &mut either_url,
            self.host_required,
            self.default_host.as_ref(),
            self.default_port,
            self.default_path.as_ref(),
        ) {
            Ok(()) => {
                // Lax rather than strict to preserve V2.4 semantic that str wins over url in union
                state.floor_exactness(Exactness::Lax);
                Ok(either_url.into_py_any(py)?)
            }
            Err(error_type) => Err(ValError::new(error_type, input)),
        }
    }

    fn get_name(&self) -> &str {
        &self.name
    }
}

impl UrlValidator {
    pub(crate) fn get_simple(strict: bool, preserve_empty_path: bool) -> &'static Arc<CombinedValidator> {
        match (strict, preserve_empty_path) {
            (false, false) => &SIMPLE_URL_VALIDATOR,
            (true, false) => &SIMPLE_URL_VALIDATOR_STRICT,
            (false, true) => &SIMPLE_URL_VALIDATOR_PRESERVE_EMPTY_PATH,
            (true, true) => &SIMPLE_URL_VALIDATOR_STRICT_PRESERVE_EMPTY_PATH,
        }
    }

    fn get_url<'py>(
        &self,
        py: Python<'py>,
        input: &(impl Input<'py> + ?Sized),
        strict: bool,
    ) -> ValResult<EitherUrl<'py>> {
        if let Some(py_url) = downcast_python_input::<PyUrl>(input) {
            // we don't need to worry about whether the url was parsed in strict mode before,
            // even if it was, any syntax errors would have been fixed by the first validation
            self.check_length(input, py_url.get().__str__(py))?;
            return Ok(EitherUrl::Py(py_url.clone()));
        }

        let either_str_owned;
        let url_str = if let Some(multi_host_url) = downcast_python_input::<PyMultiHostUrl>(input) {
            multi_host_url.get().__str__(py)
        } else if let Ok(either_str) = input.validate_str(strict, false).map(ValidationMatch::into_inner) {
            either_str_owned = either_str; // to extend the lifetime outside the if let
            either_str_owned.as_cow()?
        } else {
            return Err(ValError::new(ErrorTypeDefaults::UrlType, input));
        };

        let url_str = url_str.as_ref();
        self.check_length(input, url_str)?;
        let url = parse_url(url_str, input, strict)?;
        let path_is_empty = need_to_preserve_empty_path(&url, url_str, self.preserve_empty_path);
        Ok(EitherUrl::Rust(PyUrl::new(url, path_is_empty)))
    }

    fn check_length<'py>(&self, input: &(impl Input<'py> + ?Sized), url_str: &str) -> ValResult<()> {
        if let Some(max_length) = self.max_length
            && url_str.len() > max_length
        {
            return Err(ValError::new(
                ErrorType::UrlTooLong {
                    max_length,
                    context: None,
                },
                input,
            ));
        }
        Ok(())
    }
}

enum EitherUrl<'py> {
    Py(Bound<'py, PyUrl>),
    Rust(PyUrl),
}

impl<'py> IntoPyObject<'py> for EitherUrl<'py> {
    type Target = PyUrl;
    type Output = Bound<'py, PyUrl>;
    type Error = PyErr;

    fn into_pyobject(self, py: Python<'py>) -> PyResult<Self::Output> {
        match self {
            EitherUrl::Py(py_url) => Ok(py_url),
            EitherUrl::Rust(rust_url) => Bound::new(py, rust_url),
        }
    }
}

impl CopyFromPyUrl for EitherUrl<'_> {
    fn url(&self) -> &Url {
        match self {
            EitherUrl::Py(py_url) => py_url.get().url(),
            EitherUrl::Rust(rust_url) => rust_url.url(),
        }
    }

    fn url_mut(&mut self) -> &mut Url {
        if let EitherUrl::Py(py_url) = self {
            *self = EitherUrl::Rust(py_url.get().clone());
        }
        match self {
            EitherUrl::Py(_) => unreachable!(),
            EitherUrl::Rust(rust_url) => rust_url.url_mut(),
        }
    }
}

#[derive(Debug, Clone)]
pub struct MultiHostUrlValidator {
    strict: bool,
    max_length: Option<usize>,
    allowed_schemes: AllowedSchemes,
    host_required: bool,
    default_host: Option<String>,
    default_port: Option<u16>,
    default_path: Option<String>,
    name: String,
    preserve_empty_path: bool,
}

static SIMPLE_MULTI_HOST_URL_VALIDATOR: LazyLock<Arc<CombinedValidator>> = LazyLock::new(|| {
    Arc::new(CombinedValidator::MultiHostUrl(MultiHostUrlValidator {
        strict: false,
        max_length: None,
        allowed_schemes: None,
        host_required: false,
        default_host: None,
        default_port: None,
        default_path: None,
        name: "multi-host-url".to_string(),
        preserve_empty_path: false,
    }))
});

static SIMPLE_MULTI_HOST_URL_VALIDATOR_STRICT: LazyLock<Arc<CombinedValidator>> = LazyLock::new(|| {
    Arc::new(CombinedValidator::MultiHostUrl(MultiHostUrlValidator {
        strict: true,
        max_length: None,
        allowed_schemes: None,
        host_required: false,
        default_host: None,
        default_port: None,
        default_path: None,
        name: "multi-host-url".to_string(),
        preserve_empty_path: false,
    }))
});

static SIMPLE_MULTI_HOST_URL_VALIDATOR_PRESERVE_EMPTY_PATH: LazyLock<Arc<CombinedValidator>> = LazyLock::new(|| {
    Arc::new(CombinedValidator::MultiHostUrl(MultiHostUrlValidator {
        strict: false,
        max_length: None,
        allowed_schemes: None,
        host_required: false,
        default_host: None,
        default_port: None,
        default_path: None,
        name: "multi-host-url".to_string(),
        preserve_empty_path: true,
    }))
});

static SIMPLE_MULTI_HOST_URL_VALIDATOR_STRICT_PRESERVE_EMPTY_PATH: LazyLock<Arc<CombinedValidator>> =
    LazyLock::new(|| {
        Arc::new(CombinedValidator::MultiHostUrl(MultiHostUrlValidator {
            strict: true,
            max_length: None,
            allowed_schemes: None,
            host_required: false,
            default_host: None,
            default_port: None,
            default_path: None,
            name: "multi-host-url".to_string(),
            preserve_empty_path: true,
        }))
    });

impl BuildValidator for MultiHostUrlValidator {
    const EXPECTED_TYPE: &'static str = "multi-host-url";

    fn build(
        schema: &Bound<'_, PyDict>,
        config: Option<&Bound<'_, PyDict>>,
        _definitions: &mut DefinitionsBuilder<Arc<CombinedValidator>>,
    ) -> PyResult<Arc<CombinedValidator>> {
        let (allowed_schemes, name) = get_allowed_schemes(schema, Self::EXPECTED_TYPE)?;

        let default_host: Option<String> = schema.get_as(intern!(schema.py(), "default_host"))?;
        if let Some(ref default_host) = default_host
            && default_host.contains(',')
        {
            return py_schema_err!("default_host cannot contain a comma, see pydantic-core#326");
        }

        let validator = Self {
            strict: is_strict(schema, config)?,
            max_length: schema.get_as(intern!(schema.py(), "max_length"))?,
            allowed_schemes,
            host_required: schema.get_as(intern!(schema.py(), "host_required"))?.unwrap_or(false),
            default_host,
            default_port: schema.get_as(intern!(schema.py(), "default_port"))?,
            default_path: schema.get_as(intern!(schema.py(), "default_path"))?,
            name,
            preserve_empty_path: get_preserve_empty_path(schema, config)?,
        };

        if validator.max_length.is_none()
            && validator.allowed_schemes.is_none()
            && !validator.host_required
            && validator.default_host.is_none()
            && validator.default_port.is_none()
            && validator.default_path.is_none()
        {
            return Ok(MultiHostUrlValidator::get_simple(validator.strict, validator.preserve_empty_path).clone());
        }

        Ok(CombinedValidator::MultiHostUrl(validator).into())
    }
}

impl_py_gc_traverse!(MultiHostUrlValidator {});

impl Validator for MultiHostUrlValidator {
    fn validate<'py>(
        &self,
        py: Python<'py>,
        input: &(impl Input<'py> + ?Sized),
        state: &mut ValidationState<'_, 'py>,
    ) -> ValResult<Py<PyAny>> {
        let mut multi_url = self.get_url(py, input, state.strict_or(self.strict))?;

        if let Some((ref allowed_schemes, ref expected_schemes_repr)) = self.allowed_schemes
            && !allowed_schemes.contains(multi_url.url().scheme())
        {
            let expected_schemes = expected_schemes_repr.clone();
            return Err(ValError::new(
                ErrorType::UrlScheme {
                    expected_schemes,
                    context: None,
                },
                input,
            ));
        }
        match check_sub_defaults(
            &mut multi_url,
            self.host_required,
            self.default_host.as_ref(),
            self.default_port,
            self.default_path.as_ref(),
        ) {
            Ok(()) => {
                // Lax rather than strict to preserve V2.4 semantic that str wins over url in union
                state.floor_exactness(Exactness::Lax);
                Ok(multi_url.into_py_any(py)?)
            }
            Err(error_type) => Err(ValError::new(error_type, input)),
        }
    }

    fn get_name(&self) -> &str {
        &self.name
    }
}

impl MultiHostUrlValidator {
    pub(crate) fn get_simple(strict: bool, preserve_empty_path: bool) -> &'static Arc<CombinedValidator> {
        match (strict, preserve_empty_path) {
            (false, false) => &SIMPLE_MULTI_HOST_URL_VALIDATOR,
            (true, false) => &SIMPLE_MULTI_HOST_URL_VALIDATOR_STRICT,
            (false, true) => &SIMPLE_MULTI_HOST_URL_VALIDATOR_PRESERVE_EMPTY_PATH,
            (true, true) => &SIMPLE_MULTI_HOST_URL_VALIDATOR_STRICT_PRESERVE_EMPTY_PATH,
        }
    }

    fn get_url<'py>(
        &self,
        py: Python<'py>,
        input: &(impl Input<'py> + ?Sized),
        strict: bool,
    ) -> ValResult<EitherMultiHostUrl<'py>> {
        // we don't need to worry about whether the url was parsed in strict mode before,
        // even if it was, any syntax errors would have been fixed by the first validation
        if let Some(multi_url) = downcast_python_input::<PyMultiHostUrl>(input) {
            self.check_length(input, || multi_url.get().__str__(py).len())?;
            Ok(EitherMultiHostUrl::Py(multi_url.clone()))
        } else if let Some(py_url) = downcast_python_input::<PyUrl>(input) {
            self.check_length(input, || py_url.get().__str__(py).len())?;
            Ok(EitherMultiHostUrl::Rust(PyMultiHostUrl::new(
                py_url.get().clone(),
                None,
            )))
        } else if let Ok(either_str) = input.validate_str(strict, false).map(ValidationMatch::into_inner) {
            let cow = either_str.as_cow()?;
            let url_str = cow.as_ref();

            self.check_length(input, || url_str.len())?;

            parse_multihost_url(url_str, input, strict, self.preserve_empty_path).map(EitherMultiHostUrl::Rust)
        } else {
            Err(ValError::new(ErrorTypeDefaults::UrlType, input))
        }
    }

    fn check_length<'py, F>(&self, input: &(impl Input<'py> + ?Sized), func: F) -> ValResult<()>
    where
        F: FnOnce() -> usize,
    {
        if let Some(max_length) = self.max_length
            && func() > max_length
        {
            return Err(ValError::new(
                ErrorType::UrlTooLong {
                    max_length,
                    context: None,
                },
                input,
            ));
        }
        Ok(())
    }
}

enum EitherMultiHostUrl<'py> {
    Py(Bound<'py, PyMultiHostUrl>),
    Rust(PyMultiHostUrl),
}

impl<'py> IntoPyObject<'py> for EitherMultiHostUrl<'py> {
    type Target = PyMultiHostUrl;
    type Output = Bound<'py, PyMultiHostUrl>;
    type Error = PyErr;

    fn into_pyobject(self, py: Python<'py>) -> PyResult<Self::Output> {
        match self {
            EitherMultiHostUrl::Py(py_multi_url) => Ok(py_multi_url),
            EitherMultiHostUrl::Rust(rust_multi_url) => Bound::new(py, rust_multi_url),
        }
    }
}

impl CopyFromPyUrl for EitherMultiHostUrl<'_> {
    fn url(&self) -> &Url {
        match self {
            EitherMultiHostUrl::Py(py_multi_url) => py_multi_url.get().lib_url(),
            EitherMultiHostUrl::Rust(rust_multi_url) => rust_multi_url.lib_url(),
        }
    }

    fn url_mut(&mut self) -> &mut Url {
        if let EitherMultiHostUrl::Py(py_multi_url) = self {
            *self = EitherMultiHostUrl::Rust(py_multi_url.get().clone());
        }
        match self {
            EitherMultiHostUrl::Py(_) => unreachable!(),
            EitherMultiHostUrl::Rust(rust_multi_url) => rust_multi_url.mut_lib_url(),
        }
    }
}

fn parse_multihost_url<'py>(
    url_str: &str,
    input: &(impl Input<'py> + ?Sized),
    strict: bool,
    preserve_empty_path: bool,
) -> ValResult<PyMultiHostUrl> {
    macro_rules! parsing_err {
        ($parse_error:expr) => {
            Err(ValError::new(
                ErrorType::UrlParsing {
                    error: $parse_error.to_string(),
                    context: None,
                },
                input,
            ))
        };
    }

    if url_str.is_empty() {
        return parsing_err!(EMPTY_INPUT);
    }

    let mut chars = PositionedPeekable::new(url_str);
    // consume whitespace, taken from `with_log`
    // https://github.com/servo/rust-url/blob/v2.3.1/url/src/parser.rs#L213-L226
    loop {
        let peek = chars.peek();
        if let Some(c) = peek {
            match c {
                '\t' | '\n' | '\r' => (),
                c if c <= &' ' => (),
                _ => break,
            }
            chars.next();
        } else {
            break;
        }
    }

    // consume the url scheme, some logic from `parse_scheme`
    // https://github.com/servo/rust-url/blob/v2.3.1/url/src/parser.rs#L387-L411
    let scheme_start = chars.position;
    let scheme_end = loop {
        match chars.next() {
            Some('a'..='z' | 'A'..='Z' | '0'..='9' | '+' | '-' | '.') => continue,
            Some(':') => {
                // require the scheme to be non-empty
                let scheme_end = chars.position - ':'.len_utf8();
                if scheme_end > scheme_start {
                    break scheme_end;
                }
            }
            _ => {}
        }
        return parsing_err!(ParseError::RelativeUrlWithoutBase);
    };
    let scheme = url_str[scheme_start..scheme_end].to_ascii_lowercase();

    // consume the double slash, or any number of slashes, including backslashes, taken from `parse_with_scheme`
    // https://github.com/servo/rust-url/blob/v2.3.1/url/src/parser.rs#L413-L456
    loop {
        let peek = chars.peek();
        match peek {
            Some(&'/' | &'\\') => {
                chars.next();
            }
            _ => break,
        }
    }
    let prefix = &url_str[..chars.position];

    // process host and port, splitting based on `,`, some logic taken from `parse_host`
    // https://github.com/servo/rust-url/blob/v2.3.1/url/src/parser.rs#L971-L1026
    let mut hosts: Vec<&str> = Vec::with_capacity(3);
    let mut start = chars.position;
    while let Some(c) = chars.next() {
        match c {
            '\\' if scheme_is_special(&scheme) => break,
            '/' | '?' | '#' => break,
            ',' => {
                // minus 1 because we know that the last char was a `,` with length 1
                let end = chars.position - ','.len_utf8();
                if start == end {
                    return parsing_err!(ParseError::EmptyHost);
                }
                hosts.push(&url_str[start..end]);
                start = chars.position;
            }
            _ => (),
        }
    }
    // with just one host, for consistent behaviour, we parse the URL the same as with multiple hosts

    let reconstructed_url = format!("{prefix}{}", &url_str[start..]);
    let ref_url = parse_url(&reconstructed_url, input, strict)?;
    let path_is_empty = need_to_preserve_empty_path(&ref_url, &reconstructed_url, preserve_empty_path);

    let ref_url = PyUrl::new(ref_url, path_is_empty);

    if hosts.is_empty() {
        // if there's no one host (e.g. no `,`), we allow it to be empty to allow for default hosts
        Ok(PyMultiHostUrl::new(ref_url, None))
    } else {
        // with more than one host, none of them can be empty
        if !ref_url.url().has_host() {
            return parsing_err!(ParseError::EmptyHost);
        }
        let extra_urls: Vec<Url> = hosts
            .iter()
            .map(|host| {
                let reconstructed_url = format!("{prefix}{host}");
                parse_url(&reconstructed_url, input, strict)
            })
            .collect::<ValResult<_>>()?;

        if extra_urls.iter().any(|url| !url.has_host()) {
            return parsing_err!(ParseError::EmptyHost);
        }

        Ok(PyMultiHostUrl::new(ref_url, Some(extra_urls)))
    }
}

fn parse_url<'py>(url_str: &str, input: &(impl Input<'py> + ?Sized), strict: bool) -> ValResult<Url> {
    if url_str.is_empty() {
        return Err(ValError::new(
            ErrorType::UrlParsing {
                error: EMPTY_INPUT.into(),
                context: None,
            },
            input,
        ));
    }

    // we could build a vec of syntax violations and return them all, but that seems like overkill
    // and unlike other parser style validators
    let vios = RefCell::new(None);

    let url = Url::options()
        // if we're in strict mode, we collect considering a syntax violation as an error
        .syntax_violation_callback(strict.then_some(&|v| {
            match v {
                // telling users offer about credentials in URLs doesn't really make sense in this context
                SyntaxViolation::EmbeddedCredentials => (),
                _ => *vios.borrow_mut() = Some(v),
            }
        }))
        .parse(url_str)
        .map_err(|e| {
            ValError::new(
                ErrorType::UrlParsing {
                    error: e.to_string(),
                    context: None,
                },
                input,
            )
        })?;

    if let Some(vio) = vios.into_inner() {
        return Err(ValError::new(
            ErrorType::UrlSyntaxViolation {
                error: vio.description().into(),
                context: None,
            },
            input,
        ));
    }

    Ok(url)
}

/// Check if the path got normalized to `/` and the original string had an empty path
fn need_to_preserve_empty_path(url: &Url, url_str: &str, preserve_empty_path: bool) -> bool {
    if !preserve_empty_path {
        return false;
    }

    if url.path() != "/" {
        // was definitely not the case
        return false;
    }

    if !scheme_is_special(url.scheme()) {
        // non-special schemes don't normalize the path
        return false;
    }

    // find the scheme marker in the original input
    let (_, input_without_scheme) = url_str.split_once(':').expect("url has a scheme");

    // strip any leading / (which would be part of the authority marker), URL will normalize any
    // number of them even if there should only be two
    let input_without_scheme = input_without_scheme.trim_start_matches('/');

    // Now find the start of the path, which is either the first /, ?, or #, or the end of the
    // string
    for c in input_without_scheme.chars() {
        match c {
            '/' => return false,      // found the start of the path, and it's not empty
            '?' | '#' => return true, // found the start of the query or fragment, so path is empty
            _ => (),
        }
    }

    // reached the end of the string without finding a path, so it's empty
    true
}

/// check host_required and substitute `default_host`, `default_port` & `default_path` if they aren't set
fn check_sub_defaults(
    url: &mut impl CopyFromPyUrl,
    host_required: bool,
    default_host: Option<&String>,
    default_port: Option<u16>,
    default_path: Option<&String>,
) -> Result<(), ErrorType> {
    let map_parse_err = |e: ParseError| ErrorType::UrlParsing {
        error: e.to_string(),
        context: None,
    };

    if !url.url().has_host() {
        if let Some(default_host) = default_host {
            url.url_mut().set_host(Some(default_host)).map_err(map_parse_err)?;
        } else if host_required {
            return Err(ErrorType::UrlParsing {
                error: ParseError::EmptyHost.to_string(),
                context: None,
            });
        }
    }
    if let Some(default_port) = default_port
        && url.url().port().is_none()
    {
        url.url_mut()
            .set_port(Some(default_port))
            .map_err(|()| map_parse_err(ParseError::EmptyHost))?;
    }
    if let Some(default_path) = default_path {
        let path = url.url().path();
        if path.is_empty() || path == "/" {
            url.url_mut().set_path(default_path);
        }
    }
    Ok(())
}

/// Abstraction to create a new Url only when necessary if the existing Url is a PyUrl
/// and needs to be updated with new defaults
trait CopyFromPyUrl {
    fn url(&self) -> &Url;
    fn url_mut(&mut self) -> &mut Url;
}

fn get_allowed_schemes(schema: &Bound<'_, PyDict>, name: &'static str) -> PyResult<(AllowedSchemes, String)> {
    match schema.get_as::<Bound<'_, PyList>>(intern!(schema.py(), "allowed_schemes"))? {
        Some(list) => {
            if list.is_empty() {
                return py_schema_err!("`allowed_schemes` should have length > 0");
            }

            let mut expected: AHashSet<String> = AHashSet::new();
            let mut repr_args = Vec::new();
            for item in list {
                let str = item.extract()?;
                repr_args.push(item.repr()?);
                expected.insert(str);
            }
            let repr = expected_repr(&repr_args)?;
            let name = expected_name(&repr_args, name)?;
            Ok((Some((expected, repr)), name))
        }
        None => Ok((None, name.to_string())),
    }
}

#[cfg_attr(debug_assertions, derive(Debug))]
struct PositionedPeekable<'a> {
    peekable: Peekable<Chars<'a>>,
    position: usize,
}

impl<'a> PositionedPeekable<'a> {
    fn new(input: &'a str) -> Self {
        Self {
            peekable: input.chars().peekable(),
            position: 0,
        }
    }

    fn next(&mut self) -> Option<char> {
        let c = self.peekable.next();
        if let Some(c) = c {
            self.position += c.len_utf8();
        }
        c
    }

    fn peek(&mut self) -> Option<&char> {
        self.peekable.peek()
    }
}

const EMPTY_INPUT: &str = "input is empty";
