//! Declarative HTTP redirects with listener-aware hostname ownership.
//! Redirects never open an upstream connection and are resolved before proxy routes.
use anyhow::{ensure, Context, Result};
use http::{header::HeaderValue, uri::Authority, StatusCode, Uri};
use serde::{Deserialize, Serialize};
use std::str::FromStr;
use url::{Position, Url};

fn yes() -> bool {
    true
}
fn root() -> String {
    "/".into()
}
fn default_status() -> u16 {
    308
}

#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum SourceScheme {
    #[default]
    Any,
    Http,
    Https,
}
impl SourceScheme {
    fn matches(self, tls: bool) -> bool {
        matches!(self, Self::Any)
            || matches!((self, tls), (Self::Http, false) | (Self::Https, true))
    }
}

#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum MatchType {
    #[default]
    Prefix,
    Exact,
}

#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum TargetType {
    #[default]
    Url,
    Host,
    Path,
}

#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum TargetScheme {
    #[default]
    Preserve,
    Http,
    Https,
}

#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum PathMode {
    #[default]
    Append,
    StripPrefix,
    Replace,
}

#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum QueryMode {
    #[default]
    Preserve,
    Drop,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(default, deny_unknown_fields)]
pub struct Rule {
    pub id: String,
    pub enabled: bool,
    pub source_scheme: SourceScheme,
    pub match_type: MatchType,
    pub path_prefix: String,
    pub target_type: TargetType,
    /// Absolute http(s) URL, authority (`example.com[:port]`) or absolute path,
    /// according to `target_type`.
    pub target: String,
    /// Used only by `target_type=host`.
    pub target_scheme: TargetScheme,
    pub path_mode: PathMode,
    pub query_mode: QueryMode,
    pub status_code: u16,
    /// 0 emits `Cache-Control: no-store`; otherwise public max-age, up to one year.
    pub cache_seconds: u32,
}
impl Default for Rule {
    fn default() -> Self {
        Self {
            id: "root".into(),
            enabled: true,
            source_scheme: SourceScheme::Any,
            match_type: MatchType::Prefix,
            path_prefix: root(),
            target_type: TargetType::Url,
            target: "https://example.com/".into(),
            target_scheme: TargetScheme::Preserve,
            path_mode: PathMode::Append,
            query_mode: QueryMode::Preserve,
            status_code: default_status(),
            cache_seconds: 0,
        }
    }
}

#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(deny_unknown_fields)]
pub struct Host {
    pub id: String,
    #[serde(default)]
    pub name: String,
    #[serde(default = "yes")]
    pub enabled: bool,
    #[serde(default = "yes")]
    pub http2_enabled: bool,
    #[serde(default = "yes")]
    pub http3_enabled: bool,
    pub frontend: crate::vhost::Frontend,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub certificate_id: Option<String>,
    #[serde(default)]
    pub rules: Vec<Rule>,
}
impl Host {
    pub fn validate(&mut self) -> Result<()> {
        ensure!(crate::config::valid_id(&self.id), "invalid redirect id");
        if self.name.is_empty() {
            self.name = self.id.clone();
        }
        self.name = self.name.trim().to_owned();
        ensure!(
            !self.name.is_empty()
                && self.name.len() <= 96
                && !self.name.chars().any(char::is_control),
            "redirect name must be 1..96 bytes without controls"
        );
        ensure!(
            !self.frontend.hosts.is_empty(),
            "redirect requires at least one hostname"
        );
        let mut hosts = std::collections::HashSet::new();
        for host in &mut self.frontend.hosts {
            *host = crate::config::normalize_host_pattern(host)?;
            ensure!(hosts.insert(host.clone()), "duplicate redirect hostname");
        }
        ensure!(
            !self.frontend.listener_ids.is_empty() && self.frontend.listener_ids.len() <= 16,
            "redirect requires 1..16 named listeners"
        );
        if self.rules.is_empty() {
            self.rules.push(Rule::default());
        }
        ensure!(self.rules.len() <= 64, "at most 64 rules per redirect host");
        let mut ids = std::collections::HashSet::new();
        let mut bindings: Vec<(String, SourceScheme, MatchType)> = Vec::new();
        for rule in &mut self.rules {
            ensure!(
                crate::config::valid_id(&rule.id) && ids.insert(rule.id.clone()),
                "invalid/duplicate redirect rule id"
            );
            normalize_prefix(&mut rule.path_prefix)?;
            ensure!(
                matches!(rule.status_code, 301 | 302 | 303 | 307 | 308),
                "redirect status_code must be 301, 302, 303, 307 or 308"
            );
            ensure!(
                rule.cache_seconds <= 31_536_000,
                "redirect cache_seconds must be <= 31536000"
            );
            validate_target(rule)?;
            for (path, scheme, kind) in &bindings {
                if path == &rule.path_prefix
                    && *kind == rule.match_type
                    && schemes_overlap(*scheme, rule.source_scheme)
                {
                    anyhow::bail!("overlapping redirect rules for {}", rule.path_prefix);
                }
            }
            bindings.push((
                rule.path_prefix.clone(),
                rule.source_scheme,
                rule.match_type,
            ));
            if rule.target_type == TargetType::Path
                && rule.path_mode == PathMode::Replace
                && rule.target == rule.path_prefix
            {
                anyhow::bail!(
                    "redirect rule {} is an unconditional self-redirect",
                    rule.id
                );
            }
        }
        Ok(())
    }
}

fn schemes_overlap(a: SourceScheme, b: SourceScheme) -> bool {
    a == SourceScheme::Any || b == SourceScheme::Any || a == b
}

fn normalize_prefix(prefix: &mut String) -> Result<()> {
    ensure!(
        prefix.starts_with('/')
            && prefix.len() <= 512
            && !prefix.contains('?')
            && !prefix.contains('#')
            && !prefix.bytes().any(|b| b <= 32 || b == 127),
        "invalid redirect path prefix"
    );
    if prefix.len() > 1 {
        *prefix = prefix.trim_end_matches('/').to_owned();
    }
    *prefix = crate::acl::routing_path(prefix)?;
    Ok(())
}

fn validate_path(value: &str) -> Result<()> {
    ensure!(
        value.starts_with('/')
            && value.len() <= 2048
            && !value.contains('?')
            && !value.contains('#')
            && !value.bytes().any(|b| b <= 32 || b == 127),
        "redirect path target must be an absolute path without query or fragment"
    );
    crate::acl::routing_path(value)?;
    Ok(())
}

fn validate_target(rule: &Rule) -> Result<()> {
    ensure!(
        !rule.target.is_empty() && rule.target.len() <= 2048,
        "redirect target must be 1..2048 bytes"
    );
    match rule.target_type {
        TargetType::Url => {
            let url = Url::parse(&rule.target).context("invalid redirect URL")?;
            ensure!(
                matches!(url.scheme(), "http" | "https"),
                "redirect URL scheme must be http or https"
            );
            ensure!(url.host_str().is_some(), "redirect URL requires a host");
            ensure!(
                url.username().is_empty() && url.password().is_none(),
                "redirect URL must not contain credentials"
            );
        }
        TargetType::Host => {
            ensure!(
                !rule.target.contains('@'),
                "redirect host must not contain credentials"
            );
            let authority =
                Authority::from_str(&rule.target).context("invalid redirect host/port")?;
            crate::config::request_host(authority.as_str())
                .context("invalid redirect host/port")?;
        }
        TargetType::Path => validate_path(&rule.target)?,
    }
    Ok(())
}

#[derive(Debug, Clone)]
enum CompiledTarget {
    Url {
        prefix: String,
        base_path: String,
        query: Option<String>,
        fragment: Option<String>,
    },
    Host {
        authority: String,
        scheme: TargetScheme,
    },
    Path {
        base_path: String,
    },
}

#[derive(Debug, Clone)]
pub struct CompiledRule {
    pub id: String,
    pub source_scheme: SourceScheme,
    pub match_type: MatchType,
    pub path_prefix: String,
    target: CompiledTarget,
    pub path_mode: PathMode,
    pub query_mode: QueryMode,
    pub status_code: u16,
    pub cache_seconds: u32,
}

#[derive(Debug, Clone)]
pub struct CompiledHost {
    pub id: String,
    pub bindings: Vec<crate::vhost::Listener>,
    pub http2_enabled: bool,
    pub http3_enabled: bool,
    pub rules: Vec<CompiledRule>,
}

pub fn compile(host: &Host, listeners: &crate::settings::Listeners) -> Result<CompiledHost> {
    let bindings = host.frontend.resolved(listeners)?;
    let mut rules = Vec::new();
    for rule in host.rules.iter().filter(|rule| rule.enabled) {
        let target = match rule.target_type {
            TargetType::Url => {
                let url = Url::parse(&rule.target)?;
                CompiledTarget::Url {
                    prefix: url[..Position::BeforePath].to_owned(),
                    base_path: url.path().to_owned(),
                    query: url.query().map(str::to_owned),
                    fragment: url.fragment().map(str::to_owned),
                }
            }
            TargetType::Host => CompiledTarget::Host {
                authority: Authority::from_str(&rule.target)?.to_string(),
                scheme: rule.target_scheme,
            },
            TargetType::Path => CompiledTarget::Path {
                base_path: rule.target.clone(),
            },
        };
        rules.push(CompiledRule {
            id: rule.id.clone(),
            source_scheme: rule.source_scheme,
            match_type: rule.match_type,
            path_prefix: rule.path_prefix.clone(),
            target,
            path_mode: rule.path_mode,
            query_mode: rule.query_mode,
            status_code: rule.status_code,
            cache_seconds: rule.cache_seconds,
        });
    }
    rules.sort_by(|a, b| {
        b.path_prefix.len().cmp(&a.path_prefix.len()).then_with(|| {
            match (a.match_type, b.match_type) {
                (MatchType::Exact, MatchType::Prefix) => std::cmp::Ordering::Less,
                (MatchType::Prefix, MatchType::Exact) => std::cmp::Ordering::Greater,
                _ => std::cmp::Ordering::Equal,
            }
        })
    });
    Ok(CompiledHost {
        id: host.id.clone(),
        bindings,
        http2_enabled: host.http2_enabled,
        http3_enabled: host.http3_enabled,
        rules,
    })
}

impl CompiledRule {
    pub fn matches(&self, path: &str, tls: bool) -> bool {
        self.source_scheme.matches(tls)
            && match self.match_type {
                MatchType::Exact => path == self.path_prefix,
                MatchType::Prefix => crate::config::prefix_matches(&self.path_prefix, path),
            }
    }

    pub fn response(
        &self,
        request_host: &str,
        tls: bool,
        uri: &Uri,
    ) -> Option<axum::response::Response> {
        use axum::response::IntoResponse;
        let location = self.location(request_host, tls, uri)?;
        let status = StatusCode::from_u16(self.status_code).ok()?;
        let mut response = status.into_response();
        response
            .headers_mut()
            .insert(http::header::LOCATION, location);
        let cache = if self.cache_seconds == 0 {
            HeaderValue::from_static("no-store")
        } else {
            HeaderValue::from_str(&format!("public, max-age={}", self.cache_seconds)).ok()?
        };
        response
            .headers_mut()
            .insert(http::header::CACHE_CONTROL, cache);
        Some(response)
    }

    pub fn location(&self, request_host: &str, tls: bool, uri: &Uri) -> Option<HeaderValue> {
        let request_path = uri.path();
        let suffix = match self.path_mode {
            PathMode::Replace => "",
            PathMode::Append => request_path,
            PathMode::StripPrefix => request_path.strip_prefix(&self.path_prefix).unwrap_or(""),
        };
        let (prefix, base_path, static_query, fragment) = match &self.target {
            CompiledTarget::Url {
                prefix,
                base_path,
                query,
                fragment,
            } => (
                prefix.clone(),
                base_path.clone(),
                query.clone(),
                fragment.clone(),
            ),
            CompiledTarget::Host { authority, scheme } => {
                let scheme = match scheme {
                    TargetScheme::Preserve => {
                        if tls {
                            "https"
                        } else {
                            "http"
                        }
                    }
                    TargetScheme::Http => "http",
                    TargetScheme::Https => "https",
                };
                (format!("{scheme}://{authority}"), "/".into(), None, None)
            }
            CompiledTarget::Path { base_path } => {
                let scheme = if tls { "https" } else { "http" };
                (
                    format!("{scheme}://{request_host}"),
                    base_path.clone(),
                    None,
                    None,
                )
            }
        };
        let path = match self.path_mode {
            PathMode::Replace => base_path,
            PathMode::Append | PathMode::StripPrefix => join_paths(&base_path, suffix),
        };
        let mut value = format!("{prefix}{path}");
        let source_query = if self.query_mode == QueryMode::Preserve {
            uri.query()
        } else {
            None
        };
        match (static_query.as_deref(), source_query) {
            (Some(a), Some(b)) if !a.is_empty() && !b.is_empty() => {
                value.push_str(&format!("?{a}&{b}"))
            }
            (Some(a), _) if !a.is_empty() => value.push_str(&format!("?{a}")),
            (_, Some(b)) if !b.is_empty() => value.push_str(&format!("?{b}")),
            _ => {}
        }
        if let Some(fragment) = fragment.filter(|value| !value.is_empty()) {
            value.push('#');
            value.push_str(&fragment);
        }
        HeaderValue::from_str(&value).ok()
    }
}

fn join_paths(base: &str, suffix: &str) -> String {
    if suffix.is_empty() || suffix == "/" {
        return if base.is_empty() {
            "/".into()
        } else {
            base.into()
        };
    }
    let base = if base.is_empty() { "/" } else { base };
    if base == "/" {
        format!("/{}", suffix.trim_start_matches('/'))
    } else {
        format!(
            "{}/{}",
            base.trim_end_matches('/'),
            suffix.trim_start_matches('/')
        )
    }
}

#[cfg(test)]
include!("redirect/tests.rs");