use hemplate_core::ast::build_ast;
use hemplate_core::surface::{
    extract_surface, AttributeOrigin, ControlKind, ScopeId, ScopeKind, SurfaceAttribute,
    SurfaceDocument, SurfaceNodeKind,
};
use slhx_core::{EFFECT_BATCH_ABI_VERSION, RUNTIME_ABI_VERSION, SURFACE_SCHEMA_VERSION};
use std::collections::{BTreeMap, BTreeSet};
use std::io;
use std::path::{Path, PathBuf};
use std::sync::Arc;

#[derive(Clone, Debug)]
pub struct AppBuilder {
    out_dir: Option<PathBuf>,
    template_dir: PathBuf,
}

impl AppBuilder {
    pub fn out_dir(mut self, out_dir: impl Into<PathBuf>) -> Self {
        self.out_dir = Some(out_dir.into());
        self
    }

    pub fn template_dir(mut self, template_dir: impl Into<PathBuf>) -> Self {
        self.template_dir = template_dir.into();
        self
    }

    pub fn run(self) -> io::Result<()> {
        println!("cargo:rerun-if-changed={}", self.template_dir.display());

        let out_dir = self
            .out_dir
            .or_else(|| std::env::var_os("OUT_DIR").map(PathBuf::from));

        let Some(out_dir) = out_dir else {
            return Ok(());
        };

        std::fs::create_dir_all(&out_dir)?;

        let mut resources = Resources::default();
        for path in collect_heml(&self.template_dir)? {
            let source = std::fs::read_to_string(&path)?;
            let doc = build_ast(Arc::new(source)).map_err(|err| parse_error(&path, err))?;
            let Some(doc) = doc else {
                continue;
            };
            let surface = extract_surface(&doc);
            resources.add_surface(&self.template_dir, &path, &surface)?;
        }
        for path in collect_stylesheets(&self.template_dir)? {
            let source = std::fs::read_to_string(&path)?;
            resources.add_stylesheet(&self.template_dir, &path, &source)?;
        }

        std::fs::write(out_dir.join("slhx.generated.rs"), resources.generated_rs())?;
        std::fs::write(out_dir.join("slhx.syms"), resources.syms())?;
        Ok(())
    }
}

pub fn app() -> AppBuilder {
    AppBuilder {
        out_dir: None,
        template_dir: PathBuf::from("templates"),
    }
}

#[derive(Default)]
struct Resources {
    slots: BTreeMap<String, Resource>,
    handles: BTreeMap<String, Resource>,
    handle_forms: BTreeMap<String, String>,
    handle_params: BTreeMap<String, BTreeSet<String>>,
    forms: BTreeMap<String, FormResource>,
    atoms: BTreeMap<String, Resource>,
    classes: BTreeMap<String, ClassToken>,
}

#[derive(Clone, Debug)]
struct Resource {
    symbol: String,
    ident: String,
    component: String,
    keyed: bool,
    id: u32,
}

#[derive(Clone, Debug)]
struct FormResource {
    resource: Resource,
    controls: Vec<GeneratedControl>,
}

#[derive(Clone, Debug)]
struct GeneratedControl {
    name: String,
    kind: ControlKind,
    required: bool,
}

#[derive(Clone, Debug)]
struct ClassToken {
    symbol: String,
    ident: String,
    component: String,
    token: String,
}

impl Resources {
    fn add_surface(&mut self, root: &Path, path: &Path, surface: &SurfaceDocument) -> io::Result<()> {
        let component = component_ident(root, path)?;
        for node in &surface.nodes {
            let SurfaceNodeKind::Element { tag } = &node.kind else {
                continue;
            };

            if let Some(class_attr) = static_attr(&node.attrs, "class") {
                for token in class_tokens(&class_attr) {
                    let canonical = canonical_symbol(root, path, token);
                    self.insert_class(canonical, token.to_owned(), component.clone())?;
                }
            }

            if let Some(name) = static_attr(&node.attrs, "data-slhx-slot") {
                reject_unkeyed_loop(surface, node.scope, path, "slot", &name)?;
                let keyed = is_inside_keyed_for(surface, node.scope);
                let canonical = canonical_symbol(root, path, &name);
                self.insert_slot(canonical, name, component.clone(), keyed)?;
            }

            if let Some(name) = static_attr(&node.attrs, "data-slhx-atom") {
                reject_unkeyed_loop(surface, node.scope, path, "atom", &name)?;
                let canonical = canonical_symbol(root, path, &name);
                self.insert_atom(canonical, name, component.clone())?;
            }

            if let Some(name) = static_attr(&node.attrs, "data-slhx-handle") {
                reject_unkeyed_loop(surface, node.scope, path, "handle", &name)?;
                let canonical = canonical_symbol(root, path, &name);
                self.insert_handle(canonical, name.clone(), component.clone())?;
                self.insert_handle_params(&name, &node.attrs)?;

                if tag == "form" {
                    let form_name = static_attr(&node.attrs, "data-slhx-form").unwrap_or_else(|| name.clone());
                    let controls = surface
                        .forms
                        .iter()
                        .find(|form| form.node == node.id)
                        .map(|form| {
                            form.controls
                                .iter()
                                .map(|control| GeneratedControl {
                                    name: control.name.clone(),
                                    kind: control.kind.clone(),
                                    required: control.required,
                                })
                                .collect()
                        })
                        .unwrap_or_default();
                    self.insert_form(canonical_symbol(root, path, &form_name), form_name.clone(), component.clone(), controls)?;
                    if let (Some(handle_ident), Some(form_ident)) = (rust_ident(&name), rust_ident(&form_name)) {
                        self.handle_forms.insert(handle_ident, form_ident);
                    }
                }
            }
        }
        Ok(())
    }

    fn insert_slot(&mut self, symbol: String, name: String, component: String, keyed: bool) -> io::Result<()> {
        insert_resource(&mut self.slots, "slot", symbol, name, component, keyed)
    }

    fn insert_handle(&mut self, symbol: String, name: String, component: String) -> io::Result<()> {
        insert_resource(&mut self.handles, "handle", symbol, name, component, false)
    }

    fn insert_atom(&mut self, symbol: String, name: String, component: String) -> io::Result<()> {
        insert_resource(&mut self.atoms, "atom", symbol, name, component, false)
    }

    fn insert_class(&mut self, symbol: String, token: String, component: String) -> io::Result<()> {
        let ident = class_ident(&token).ok_or_else(|| {
            io::Error::new(
                io::ErrorKind::InvalidData,
                format!("invalid CSS class `{token}`; expected an ASCII class token usable from Rust"),
            )
        })?;
        let class = ClassToken { symbol, ident, component, token };
        if let Some(existing) = self.classes.values().find(|existing| {
            existing.ident == class.ident && existing.token != class.token
        }) {
            return Err(io::Error::new(
                io::ErrorKind::InvalidData,
                format!(
                    "duplicate generated class identifier `{}` for CSS classes `{}` and `{}`",
                    class.ident, existing.token, class.token
                ),
            ));
        }
        match self.classes.get(&class.symbol) {
            Some(existing) if existing.token != class.token => Err(io::Error::new(
                io::ErrorKind::InvalidData,
                format!("conflicting CSS class token for `{}`", existing.symbol),
            )),
            Some(_) => Ok(()),
            None => {
                self.classes.insert(class.symbol.clone(), class);
                Ok(())
            }
        }
    }

    fn insert_handle_params(&mut self, handle: &str, attrs: &[SurfaceAttribute]) -> io::Result<()> {
        let Some(handle_ident) = rust_ident(handle) else {
            return Ok(());
        };
        for attr in attrs {
            if !is_handle_param_attr(attr) {
                continue;
            }
            let Some(param) = data_param_ident(&attr.name) else {
                return Err(io::Error::new(
                    io::ErrorKind::InvalidData,
                    format!("invalid handler param attribute `{}`; expected data-* name usable from Rust", attr.name),
                ));
            };
            self.handle_params.entry(handle_ident.clone()).or_default().insert(param);
        }
        Ok(())
    }

    fn insert_form(
        &mut self,
        symbol: String,
        name: String,
        component: String,
        controls: Vec<GeneratedControl>,
    ) -> io::Result<()> {
        let resource = make_resource("form", symbol, name, component, false)?;
        match self.forms.get(&resource.ident) {
            Some(existing) if existing.resource.symbol != resource.symbol => Err(io::Error::new(
                io::ErrorKind::InvalidData,
                format!(
                    "duplicate generated identifier `{}` for `{}` and `{}`",
                    resource.ident, existing.resource.symbol, resource.symbol
                ),
            )),
            Some(_) => Ok(()),
            None => {
                self.forms.insert(resource.ident.clone(), FormResource { resource, controls });
                Ok(())
            }
        }
    }

    fn add_stylesheet(&mut self, root: &Path, path: &Path, source: &str) -> io::Result<()> {
        let component = component_ident(root, path)?;
        for token in stylesheet_class_tokens(source) {
            let canonical = canonical_symbol(root, path, token);
            self.insert_class(canonical, token.to_owned(), component.clone())?;
        }
        Ok(())
    }

    fn generated_rs(&self) -> String {
        let mut out = String::new();
        out.push_str("// @generated by slhx-build. Do not edit.\n");
        out.push_str(&format!(
            "pub const BUILD_FINGERPRINT: ::slhx::BuildFingerprint = ::slhx::BuildFingerprint::from_parts(&[{}]);\n\n",
            self.fingerprint_parts()
                .into_iter()
                .map(|part| part.to_string())
                .collect::<Vec<_>>()
                .join(", ")
        ));

        // req: build/001
        self.push_resource_modules(&mut out, None, 0);
        self.push_lowering_api(&mut out, None, 0);

        for component in self.component_names() {
            out.push_str("\n#[allow(non_upper_case_globals)]\n");
            out.push_str(&format!("pub mod {component} {{\n"));
            self.push_resource_modules(&mut out, Some(&component), 1);
            self.push_lowering_api(&mut out, Some(&component), 1);
            out.push_str("}\n");
        }

        self.push_lowering_helpers(&mut out);
        out
    }

    fn push_resource_modules(&self, out: &mut String, component: Option<&str>, indent: usize) {
        let pad = "    ".repeat(indent);
        let inner = "    ".repeat(indent + 1);
        let mut handle_ids = Vec::new();

        out.push_str(&format!("{pad}#[allow(non_upper_case_globals)]\n{pad}pub mod slots {{\n"));
        for res in self.slots.values().filter(|res| component_matches(res, component)) {
            if res.keyed {
                out.push_str(&format!(
                    "{inner}pub const {}: ::slhx::KeyedSlot<::std::string::String, ::std::string::String> = ::slhx::KeyedSlot::new({});\n",
                    res.ident, res.id
                ));
            } else {
                out.push_str(&format!(
                    "{inner}pub const {}: ::slhx::Slot<::std::string::String> = ::slhx::Slot::new({});\n",
                    res.ident, res.id
                ));
            }
        }
        out.push_str(&format!("{pad}}}\n\n"));

        out.push_str(&format!("{pad}#[allow(non_upper_case_globals)]\n{pad}pub mod handles {{\n"));
        for res in self.handles.values().filter(|res| component_matches(res, component)) {
            handle_ids.push(res.id);
            let input = if self.handle_forms.contains_key(&res.ident) {
                "::slhx::Form<::std::string::String>"
            } else {
                "()"
            };
            out.push_str(&format!(
                "{inner}pub const {}: ::slhx::Handle<{input}> = ::slhx::Handle::new({});\n",
                res.ident, res.id
            ));
        }
        out.push_str(&format!(
            "{inner}pub const ALL_IDS: &[u32] = &[{}];\n",
            handle_ids
                .into_iter()
                .map(|id| id.to_string())
                .collect::<Vec<_>>()
                .join(", ")
        ));
        out.push_str(&format!("{pad}}}\n\n"));

        out.push_str(&format!("{pad}#[allow(non_upper_case_globals)]\n{pad}pub mod atoms {{\n"));
        for res in self.atoms.values().filter(|res| component_matches(res, component)) {
            out.push_str(&format!(
                "{inner}pub const {}: ::slhx::Atom<::std::string::String> = ::slhx::Atom::new({});\n",
                res.ident, res.id
            ));
        }
        out.push_str(&format!("{pad}}}\n\n"));

        out.push_str(&format!("{pad}#[allow(non_upper_case_globals)]\n{pad}pub mod classes {{\n"));
        let mut emitted_classes = BTreeSet::new();
        for class in self.classes.values().filter(|class| class_matches(class, component)) {
            if !emitted_classes.insert(class.ident.as_str()) {
                continue;
            }
            out.push_str(&format!(
                "{inner}pub const {}: ::slhx::CssClass = ::slhx::CssClass::new({});\n",
                class.ident,
                rust_str(&class.token)
            ));
        }
        out.push_str(&format!("{pad}}}\n\n"));

        out.push_str(&format!("{pad}#[allow(non_upper_case_globals)]\n{pad}pub mod forms {{\n"));
        for form in self.forms.values().filter(|form| component_matches(&form.resource, component)) {
            let res = &form.resource;
            out.push_str(&format!(
                "{inner}pub const {}: ::slhx::Form<::std::string::String> = ::slhx::Form::new({});\n",
                res.ident, res.id
            ));
            out.push_str(&format!(
                "{inner}pub const {}_CONTRACT: ::slhx::FormContract = ::slhx::FormContract {{ fields: &{}_FIELDS }};\n",
                res.ident.to_ascii_uppercase(), res.ident.to_ascii_uppercase()
            ));
            out.push_str(&format!(
                "{inner}pub const {}_FIELDS: &[::slhx::FormField] = &[\n",
                res.ident.to_ascii_uppercase()
            ));
            for control in &form.controls {
                out.push_str(&format!(
                    "{inner}    ::slhx::FormField {{ name: {}, kind: {}, required: {} }},\n",
                    rust_str(&control.name),
                    form_control_kind_expr(&control.kind),
                    control.required
                ));
            }
            out.push_str(&format!("{inner}];\n"));
        }
        out.push_str(&format!("{pad}}}\n"));
    }

    fn push_lowering_api(&self, out: &mut String, component: Option<&str>, indent: usize) {
        let pad = "    ".repeat(indent);
        let table_name = match component {
            Some(component) => format!("__SLHX_LOWERING_TABLE_{}", component.to_ascii_uppercase()),
            None => "__SLHX_LOWERING_TABLE".to_string(),
        };
        out.push_str(&format!("\n{pad}pub fn lower_html(html: impl ::std::convert::AsRef<str>) -> ::std::string::String {{\n"));
        out.push_str(&format!("{pad}    "));
        if component.is_some() {
            out.push_str("super::");
        }
        out.push_str(&format!("__slhx_lower_html(html.as_ref(), &{table_name})\n"));
        out.push_str(&format!("{pad}}}\n\n"));
        self.push_lowering_table(out, component, indent, &table_name);
    }

    fn push_lowering_table(&self, out: &mut String, component: Option<&str>, indent: usize, name: &str) {
        let pad = "    ".repeat(indent);
        out.push_str(&format!("{pad}const {name}: &[(&str, &str, u32)] = &[\n"));
        for res in self.slots.values().filter(|res| component_matches(res, component)) {
            out.push_str(&format!("{pad}    (\"data-slhx-slot\", {}, {}),\n", rust_str(&res.ident), res.id));
        }
        for res in self.handles.values().filter(|res| component_matches(res, component)) {
            out.push_str(&format!("{pad}    (\"data-slhx-handle\", {}, {}),\n", rust_str(&res.ident), res.id));
        }
        for form in self.forms.values().filter(|form| component_matches(&form.resource, component)) {
            let res = &form.resource;
            out.push_str(&format!("{pad}    (\"data-slhx-form\", {}, {}),\n", rust_str(&res.ident), res.id));
        }
        for res in self.atoms.values().filter(|res| component_matches(res, component)) {
            out.push_str(&format!("{pad}    (\"data-slhx-atom\", {}, {}),\n", rust_str(&res.ident), res.id));
        }
        out.push_str(&format!("{pad}];\n"));
    }

    fn push_lowering_helpers(&self, out: &mut String) {
        out.push_str(r#"
fn __slhx_lower_html(html: &str, table: &[(&str, &str, u32)]) -> ::std::string::String {
    let mut out = html.to_owned();
    for (attr, name, id) in table {
        let runtime_attr = match *attr {
            "data-slhx-slot" => "data-sid",
            "data-slhx-handle" => "data-hid",
            "data-slhx-form" => "data-fid",
            "data-slhx-atom" => "data-aid",
            _ => continue,
        };
        out = __slhx_replace_attr(out, attr, name, runtime_attr, *id);
    }
    out = __slhx_lower_static_attr(out, "data-slhx-key", "data-key");
    __slhx_inject_handle_inputs(out)
}

fn __slhx_replace_attr(mut html: ::std::string::String, attr: &str, name: &str, runtime_attr: &str, id: u32) -> ::std::string::String {
    let replacement = if runtime_attr == "value" {
        ::std::format!("{attr}=\"{name}\" {runtime_attr}=\"{id}\"")
    } else {
        ::std::format!("{runtime_attr}=\"{id}\"")
    };
    let double = ::std::format!("{attr}=\"{name}\"");
    html = html.replace(&double, &replacement);
    let single_replacement = replacement.replace('"', "'");
    let single = ::std::format!("{attr}='{name}'");
    html.replace(&single, &single_replacement)
}

fn __slhx_lower_static_attr(mut html: ::std::string::String, attr: &str, runtime_attr: &str) -> ::std::string::String {
    html = html.replace(&::std::format!("{attr}=\""), &::std::format!("{runtime_attr}=\""));
    html.replace(&::std::format!("{attr}='"), &::std::format!("{runtime_attr}='"))
}

fn __slhx_inject_handle_inputs(html: ::std::string::String) -> ::std::string::String {
    let mut out = ::std::string::String::with_capacity(html.len());
    let mut rest = html.as_str();
    while let Some(start) = rest.find("<form") {
        out.push_str(&rest[..start]);
        rest = &rest[start..];
        let Some(open_end) = rest.find('>') else {
            out.push_str(rest);
            return out;
        };
        let opening = &rest[..=open_end];
        out.push_str(opening);
        rest = &rest[open_end + 1..];

        let Some(handle_id) = __slhx_attr(opening, "data-hid") else {
            continue;
        };
        let form_body_end = rest.find("</form>").unwrap_or(rest.len());
        let form_body = &rest[..form_body_end];
        if !__slhx_has_handle_input(form_body) {
            out.push_str(&::std::format!("<input type=\"hidden\" name=\"__h\" value=\"{}\">", handle_id));
        }
    }
    out.push_str(rest);
    out
}

fn __slhx_has_handle_input(html: &str) -> bool {
    html.contains("name=\"__h\"") || html.contains("name='__h'")
}

fn __slhx_attr(tag: &str, attr: &str) -> Option<::std::string::String> {
    let attr_at = tag.find(attr)?;
    let after_attr = &tag[attr_at + attr.len()..];
    let after_equals = after_attr.trim_start().strip_prefix('=')?.trim_start();
    let quote = after_equals.chars().next()?;
    if quote != '\"' && quote != '\'' {
        return None;
    }
    let value = &after_equals[quote.len_utf8()..];
    let end = value.find(quote)?;
    Some(value[..end].to_owned())
}
"#);
    }

    fn component_names(&self) -> Vec<String> {
        let mut components = Vec::new();
        for component in self
            .slots
            .values()
            .map(|res| &res.component)
            .chain(self.handles.values().map(|res| &res.component))
            .chain(self.atoms.values().map(|res| &res.component))
            .chain(self.forms.values().map(|form| &form.resource.component))
            .chain(self.classes.values().map(|class| &class.component))
        {
            if !components.contains(component) {
                components.push(component.clone());
            }
        }
        components.sort();
        components
    }

    fn syms(&self) -> String {
        let mut out = String::from("slhx-syms-v1\n");
        for res in self.slots.values() {
            out.push_str(&format!("slot\t{}\t{}\t{}\n", res.symbol, res.ident, res.id));
        }
        for res in self.handles.values() {
            out.push_str(&format!("handle\t{}\t{}\t{}\n", res.symbol, res.ident, res.id));
        }
        for form in self.forms.values() {
            let res = &form.resource;
            out.push_str(&format!("form\t{}\t{}\t{}\n", res.symbol, res.ident, res.id));
        }
        for (handle_ident, form_ident) in &self.handle_forms {
            out.push_str(&format!("handle_form\t{handle_ident}\t{form_ident}\n"));
        }
        for (handle_ident, params) in &self.handle_params {
            for param in params {
                out.push_str(&format!("handle_param\t{handle_ident}\t{param}\n"));
            }
        }
        for res in self.atoms.values() {
            out.push_str(&format!("atom\t{}\t{}\t{}\n", res.symbol, res.ident, res.id));
        }
        for class in self.classes.values() {
            out.push_str(&format!("class\t{}\t{}\t{}\n", class.symbol, class.ident, class.token));
        }
        out
    }

    fn fingerprint_parts(&self) -> Vec<u32> {
        let mut parts = vec![
            SURFACE_SCHEMA_VERSION,
            EFFECT_BATCH_ABI_VERSION,
            RUNTIME_ABI_VERSION,
        ];

        for res in self.slots.values() {
            parts.push(0);
            parts.push(res.id);
        }
        for res in self.handles.values() {
            parts.push(1);
            parts.push(res.id);
        }
        for res in self.atoms.values() {
            parts.push(3);
            parts.push(res.id);
        }
        for form in self.forms.values() {
            parts.push(2);
            parts.push(form.resource.id);
            parts.push(form.controls.len() as u32);
            for control in &form.controls {
                parts.push(stable_id("form-field", &control.name));
                parts.push(control.required as u32);
            }
        }

        parts
    }
}

fn insert_resource(
    map: &mut BTreeMap<String, Resource>,
    kind: &str,
    symbol: String,
    name: String,
    component: String,
    keyed: bool,
) -> io::Result<()> {
    let resource = make_resource(kind, symbol, name, component, keyed)?;
    match map.get(&resource.ident) {
        Some(existing) if existing.symbol != resource.symbol => Err(io::Error::new(
            io::ErrorKind::InvalidData,
            format!(
                "duplicate generated identifier `{}` for `{}` and `{}`",
                resource.ident, existing.symbol, resource.symbol
            ),
        )),
        Some(_) => Ok(()),
        None => {
            map.insert(resource.ident.clone(), resource);
            Ok(())
        }
    }
}

fn make_resource(
    kind: &str,
    symbol: String,
    name: String,
    component: String,
    keyed: bool,
) -> io::Result<Resource> {
    let ident = rust_ident(&name).ok_or_else(|| {
        io::Error::new(
            io::ErrorKind::InvalidData,
            format!("invalid slhx {kind} name `{name}`; expected a Rust identifier"),
        )
    })?;
    let id = stable_id(kind, &symbol);
    Ok(Resource {
        symbol,
        ident,
        component,
        keyed,
        id,
    })
}

fn collect_heml(root: &Path) -> io::Result<Vec<PathBuf>> {
    let mut paths = Vec::new();
    if !root.exists() {
        return Ok(paths);
    }
    collect_heml_into(root, &mut paths)?;
    paths.sort();
    Ok(paths)
}

fn collect_heml_into(dir: &Path, paths: &mut Vec<PathBuf>) -> io::Result<()> {
    for entry in std::fs::read_dir(dir)? {
        let entry = entry?;
        let path = entry.path();
        if path.is_dir() {
            collect_heml_into(&path, paths)?;
        } else if path.extension().and_then(|ext| ext.to_str()) == Some("heml") {
            paths.push(path);
        }
    }
    Ok(())
}

fn collect_stylesheets(root: &Path) -> io::Result<Vec<PathBuf>> {
    let mut paths = Vec::new();
    if !root.exists() {
        return Ok(paths);
    }
    collect_stylesheets_into(root, &mut paths)?;
    paths.sort();
    Ok(paths)
}

fn collect_stylesheets_into(dir: &Path, paths: &mut Vec<PathBuf>) -> io::Result<()> {
    for entry in std::fs::read_dir(dir)? {
        let entry = entry?;
        let path = entry.path();
        if path.is_dir() {
            collect_stylesheets_into(&path, paths)?;
        } else if matches!(path.extension().and_then(|ext| ext.to_str()), Some("css" | "scss")) {
            paths.push(path);
        }
    }
    Ok(())
}

fn static_attr(attrs: &[SurfaceAttribute], name: &str) -> Option<String> {
    attrs
        .iter()
        .find(|attr| attr.origin == AttributeOrigin::Static && attr.name == name)
        .and_then(|attr| attr.value.clone())
}

fn component_matches(res: &Resource, component: Option<&str>) -> bool {
    match component {
        Some(component) => res.component == component,
        None => true,
    }
}

fn class_matches(class: &ClassToken, component: Option<&str>) -> bool {
    match component {
        Some(component) => class.component == component,
        None => true,
    }
}

fn class_tokens(value: &str) -> impl Iterator<Item = &str> {
    value.split_ascii_whitespace().filter(|token| !token.is_empty())
}

fn stylesheet_class_tokens(source: &str) -> Vec<&str> {
    let bytes = source.as_bytes();
    let mut tokens = Vec::new();
    let mut i = 0;
    while i < bytes.len() {
        if bytes[i] != b'.' {
            i += 1;
            continue;
        }
        let prev = i.checked_sub(1).map(|idx| bytes[idx]);
        if prev.is_some_and(|ch| ch == b'-' || ch == b'_' || ch.is_ascii_alphanumeric())
            && !preceded_by_class_in_compound(bytes, i)
        {
            i += 1;
            continue;
        }
        let start = i + 1;
        if start >= bytes.len() || !is_class_start(bytes[start]) {
            i += 1;
            continue;
        }
        let mut end = start + 1;
        while end < bytes.len() && is_class_continue(bytes[end]) {
            end += 1;
        }
        if let Ok(token) = std::str::from_utf8(&bytes[start..end]) {
            tokens.push(token);
        }
        i = end;
    }
    tokens.sort_unstable();
    tokens.dedup();
    tokens
}

fn preceded_by_class_in_compound(bytes: &[u8], dot: usize) -> bool {
    let mut i = dot;
    while let Some(prev) = i.checked_sub(1) {
        let byte = bytes[prev];
        if byte == b'.' {
            return true;
        }
        if matches!(byte, b' ' | b'\n' | b'\r' | b'\t' | b',' | b'{' | b'}' | b'>' | b'+' | b'~' | b'(' | b')') {
            return false;
        }
        i = prev;
    }
    false
}

fn is_class_start(byte: u8) -> bool {
    byte == b'_' || byte == b'-' || byte.is_ascii_alphabetic()
}

fn is_class_continue(byte: u8) -> bool {
    is_class_start(byte) || byte.is_ascii_digit()
}

fn class_ident(token: &str) -> Option<String> {
    let mut ident = String::with_capacity(token.len());
    for ch in token.chars() {
        match ch {
            '-' => ident.push('_'),
            '_' => ident.push('_'),
            ch if ch.is_ascii_alphanumeric() => ident.push(ch),
            _ => return None,
        }
    }
    rust_ident(&ident)
}

fn is_handle_param_attr(attr: &SurfaceAttribute) -> bool {
    matches!(attr.origin, AttributeOrigin::Static | AttributeOrigin::Dynamic)
        && attr.name.starts_with("data-")
        && !attr.name.starts_with("data-slhx-")
}

fn data_param_ident(name: &str) -> Option<String> {
    let data_name = name.strip_prefix("data-")?;
    rust_ident(&data_name.replace('-', "_"))
}

fn is_inside_keyed_for(surface: &SurfaceDocument, mut scope: ScopeId) -> bool {
    loop {
        let Some(current) = surface.scopes.get(scope.0 as usize) else {
            return false;
        };
        if matches!(current.kind, ScopeKind::For { key_expr: Some(_), .. }) {
            return true;
        }
        let Some(parent) = current.parent else {
            return false;
        };
        scope = parent;
    }
}

fn reject_unkeyed_loop(
    surface: &SurfaceDocument,
    mut scope: ScopeId,
    path: &Path,
    kind: &str,
    name: &str,
) -> io::Result<()> {
    loop {
        let Some(current) = surface.scopes.get(scope.0 as usize) else {
            return Ok(());
        };
        if matches!(current.kind, ScopeKind::For { key_expr: None, .. }) {
            return Err(io::Error::new(
                io::ErrorKind::InvalidData,
                format!(
                    "{}: data-slhx-{kind}=\"{name}\" is inside an h-for without h-key; add h-key=\"item.id\" to the loop",
                    path.display()
                ),
            ));
        }
        let Some(parent) = current.parent else {
            return Ok(());
        };
        scope = parent;
    }
}

fn canonical_symbol(root: &Path, path: &Path, name: &str) -> String {
    let rel = path.strip_prefix(root).unwrap_or(path);
    format!("{}::{name}", rel.to_string_lossy().replace('\\', "/"))
}

fn component_ident(root: &Path, path: &Path) -> io::Result<String> {
    let rel = path.strip_prefix(root).unwrap_or(path);
    let stem = rel
        .file_stem()
        .and_then(|stem| stem.to_str())
        .ok_or_else(|| io::Error::new(io::ErrorKind::InvalidData, format!("invalid template path `{}`", path.display())))?;
    rust_ident(stem).ok_or_else(|| {
        io::Error::new(
            io::ErrorKind::InvalidData,
            format!("invalid template name `{stem}`; expected a Rust module identifier"),
        )
    })
}

fn rust_ident(name: &str) -> Option<String> {
    let mut chars = name.chars();
    let first = chars.next()?;
    if !(first == '_' || first.is_ascii_alphabetic()) {
        return None;
    }
    if chars.clone().any(|ch| !(ch == '_' || ch.is_ascii_alphanumeric())) {
        return None;
    }
    Some(name.to_string())
}

fn stable_id(kind: &str, symbol: &str) -> u32 {
    let mut hash = 0x811c9dc5u32;
    for byte in kind.bytes().chain([b':']).chain(symbol.bytes()) {
        hash ^= byte as u32;
        hash = hash.wrapping_mul(0x01000193);
    }
    hash
}

fn form_control_kind_expr(kind: &ControlKind) -> String {
    match kind {
        ControlKind::Text => "::slhx::FormControlKind::Text".to_string(),
        ControlKind::Number { min, max, step } => format!(
            "::slhx::FormControlKind::Number {{ min: {}, max: {}, step: {} }}",
            rust_str_opt(min.as_deref()),
            rust_str_opt(max.as_deref()),
            rust_str_opt(step.as_deref())
        ),
        ControlKind::Checkbox => "::slhx::FormControlKind::Checkbox".to_string(),
        ControlKind::Radio => "::slhx::FormControlKind::Radio".to_string(),
        ControlKind::Select { multiple } => {
            format!("::slhx::FormControlKind::Select {{ multiple: {multiple} }}")
        }
        ControlKind::TextArea => "::slhx::FormControlKind::TextArea".to_string(),
        ControlKind::File => "::slhx::FormControlKind::File".to_string(),
        ControlKind::Hidden => "::slhx::FormControlKind::Hidden".to_string(),
        ControlKind::Submit => "::slhx::FormControlKind::Submit".to_string(),
        ControlKind::Other { tag, input_type } => format!(
            "::slhx::FormControlKind::Other {{ tag: {}, input_type: {} }}",
            rust_str(tag),
            rust_str_opt(input_type.as_deref())
        ),
    }
}

fn rust_str(value: &str) -> String {
    format!("{value:?}")
}

fn rust_str_opt(value: Option<&str>) -> String {
    match value {
        Some(value) => format!("Some({})", rust_str(value)),
        None => "None".to_string(),
    }
}

fn parse_error(path: &Path, err: impl std::fmt::Display) -> io::Error {
    io::Error::new(
        io::ErrorKind::InvalidData,
        format!("failed to parse {}: {err}", path.display()),
    )
}

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

    #[test]
    fn emits_generated_resources_from_heml() {
        // req: codegen/003
        let base = test_dir("slhx-build-test");
        let templates = base.join("templates");
        let out = base.join("out");
        let _ = std::fs::remove_dir_all(&base);
        std::fs::create_dir_all(&templates).unwrap();
        std::fs::write(
            templates.join("todo.heml"),
            r#"<form data-slhx-handle="create" data-slhx-form="new_todo"><input name="title"></form><button data-slhx-handle="delete" data-todo-id="7">Delete</button><ul data-slhx-slot="todos"></ul><section data-slhx-atom="filter"></section>"#,
        )
        .unwrap();

        app().template_dir(&templates).out_dir(&out).run().unwrap();

        let generated = std::fs::read_to_string(out.join("slhx.generated.rs")).unwrap();
        assert!(generated.contains("pub mod slots"));
        assert!(generated.contains("pub const todos"));
        assert!(generated.contains("pub mod handles"));
        assert!(generated.contains("pub const create: ::slhx::Handle<::slhx::Form<::std::string::String>>"));
        assert!(generated.contains("pub mod forms"));
        assert!(generated.contains("pub mod atoms"));
        assert!(generated.contains("pub const filter"));
        assert!(generated.contains("pub const new_todo"));
        assert!(generated.contains("pub mod todo"));
        assert!(generated.contains("pub const ALL_IDS"));
        assert!(generated.contains("pub fn lower_html"));
        assert!(generated.contains("data-slhx-slot"));
        assert!(generated.contains("data-slhx-form"));
        assert!(generated.contains("data-sid"));
        assert!(generated.contains("data-fid"));
        assert!(generated.contains("__slhx_inject_handle_inputs"));

        let syms = std::fs::read_to_string(out.join("slhx.syms")).unwrap();
        assert!(syms.contains("atom\t"));
        assert!(syms.contains("\tfilter\t"));
        assert!(syms.contains("handle_form\tcreate\tnew_todo\n"));
        assert!(syms.contains("handle_param\tdelete\ttodo_id\n"));

        let _ = std::fs::remove_dir_all(&base);
    }

    #[test]
    fn emits_checked_css_class_tokens_from_templates_and_stylesheets() {
        // req: style/001, req: codegen/001
        let base = test_dir("slhx-build-classes-test");
        let templates = base.join("templates");
        let out = base.join("out");
        let _ = std::fs::remove_dir_all(&base);
        std::fs::create_dir_all(&templates).unwrap();
        std::fs::write(
            templates.join("card.heml"),
            r#"<article class="card is-active" data-slhx-slot="card_body"></article>"#,
        )
        .unwrap();
        std::fs::write(
            templates.join("card.css"),
            r#".card { padding: 1rem; }
.is-active:hover, .drag-handle { cursor: grab; }
.work-card.is-selected { outline: 1px solid currentColor; }
"#,
        )
        .unwrap();
        std::fs::write(
            templates.join("panel.scss"),
            r#".panel-shell { &.is-open { display: block; } }"#,
        )
        .unwrap();

        app().template_dir(&templates).out_dir(&out).run().unwrap();

        let generated = std::fs::read_to_string(out.join("slhx.generated.rs")).unwrap();
        assert!(generated.contains("pub mod classes"));
        assert!(generated.contains("pub const card: ::slhx::CssClass = ::slhx::CssClass::new(\"card\")"));
        assert!(generated.contains("pub const is_active: ::slhx::CssClass = ::slhx::CssClass::new(\"is-active\")"));
        assert!(generated.contains("pub const drag_handle: ::slhx::CssClass = ::slhx::CssClass::new(\"drag-handle\")"));
        assert!(generated.contains("pub const work_card: ::slhx::CssClass = ::slhx::CssClass::new(\"work-card\")"));
        assert!(generated.contains("pub const is_selected: ::slhx::CssClass = ::slhx::CssClass::new(\"is-selected\")"));
        assert!(generated.contains("pub mod card"));
        assert!(generated.contains("pub mod panel"));

        let syms = std::fs::read_to_string(out.join("slhx.syms")).unwrap();
        assert!(syms.contains("class\t"));
        assert!(syms.contains("\tdrag_handle\tdrag-handle"));

        let source = format!(
            r###"
#![allow(dead_code)]
mod slhx {{
    #[derive(Clone, Copy)] pub struct BuildFingerprint;
    impl BuildFingerprint {{ pub const fn from_parts(_: &[u32]) -> Self {{ Self }} }}
    #[derive(Clone, Copy)] pub struct Slot<T>(::std::marker::PhantomData<T>);
    impl<T> Slot<T> {{ pub const fn new(_: u32) -> Self {{ Self(::std::marker::PhantomData) }} }}
    #[derive(Clone, Copy)] pub struct KeyedSlot<K, T>(::std::marker::PhantomData<(K, T)>);
    impl<K, T> KeyedSlot<K, T> {{ pub const fn new(_: u32) -> Self {{ Self(::std::marker::PhantomData) }} }}
    #[derive(Clone, Copy)] pub struct Handle<T>(::std::marker::PhantomData<T>);
    impl<T> Handle<T> {{ pub const fn new(_: u32) -> Self {{ Self(::std::marker::PhantomData) }} }}
    #[derive(Clone, Copy)] pub struct Atom<T>(::std::marker::PhantomData<T>);
    impl<T> Atom<T> {{ pub const fn new(_: u32) -> Self {{ Self(::std::marker::PhantomData) }} }}
    #[derive(Clone, Copy)] pub struct Form<T>(::std::marker::PhantomData<T>);
    impl<T> Form<T> {{ pub const fn new(_: u32) -> Self {{ Self(::std::marker::PhantomData) }} }}
    #[derive(Clone, Copy)] pub struct CssClass(&'static str);
    impl CssClass {{ pub const fn new(name: &'static str) -> Self {{ Self(name) }} pub const fn as_str(self) -> &'static str {{ self.0 }} }}
    pub struct FormContract {{ pub fields: &'static [FormField] }}
    pub struct FormField {{ pub name: &'static str, pub kind: FormControlKind, pub required: bool }}
    pub enum FormControlKind {{ Text, Number {{ min: Option<&'static str>, max: Option<&'static str>, step: Option<&'static str> }}, Checkbox, Radio, Select {{ multiple: bool }}, TextArea, File, Hidden, Submit, Other {{ tag: &'static str, input_type: Option<&'static str> }} }}
}}
{generated}
fn main() {{
    assert_eq!(classes::drag_handle.as_str(), "drag-handle");
    assert_eq!(card::classes::is_active.as_str(), "is-active");
    assert_eq!(panel::classes::panel_shell.as_str(), "panel-shell");
}}
"###,
        );
        let source_path = base.join("classes.rs");
        let bin_path = base.join("classes-bin");
        std::fs::write(&source_path, source).unwrap();
        let status = std::process::Command::new("rustc")
            .arg(&source_path)
            .arg("-o")
            .arg(&bin_path)
            .status()
            .unwrap();
        assert!(status.success());
        let status = std::process::Command::new(&bin_path).status().unwrap();
        assert!(status.success());

        let _ = std::fs::remove_dir_all(&base);
    }

    #[test]
    fn rejects_slhx_resources_inside_unkeyed_for() {
        let base = test_dir("slhx-build-unkeyed-for-test");
        let templates = base.join("templates");
        let out = base.join("out");
        let _ = std::fs::remove_dir_all(&base);
        std::fs::create_dir_all(&templates).unwrap();
        std::fs::write(
            templates.join("todo.heml"),
            r#"<template h-for="todo in &self.todos"><li data-slhx-slot="todo_row">{+ todo.title +}</li></template>"#,
        )
        .unwrap();

        let err = app().template_dir(&templates).out_dir(&out).run().unwrap_err();
        assert!(err.to_string().contains("inside an h-for without h-key"));
        assert!(err.to_string().contains("data-slhx-slot=\"todo_row\""));

        let _ = std::fs::remove_dir_all(&base);
    }

    #[test]
    fn generated_lowering_injects_progressive_form_handle_and_key() {
        // req: form/002, req: wire/001
        let base = test_dir("slhx-build-lowering-test");
        let templates = base.join("templates");
        let out = base.join("out");
        let _ = std::fs::remove_dir_all(&base);
        std::fs::create_dir_all(&templates).unwrap();
        std::fs::write(
            templates.join("todo.heml"),
            r#"<form data-slhx-handle="create"><input name="title"></form><li data-slhx-slot="row" data-slhx-key="7"></li>"#,
        )
        .unwrap();

        app().template_dir(&templates).out_dir(&out).run().unwrap();
        let generated = std::fs::read_to_string(out.join("slhx.generated.rs")).unwrap();
        assert!(generated.contains("fn __slhx_lower_html"));
        let source = format!(
            r###"
#![allow(dead_code)]
mod slhx {{
    #[derive(Clone, Copy)] pub struct BuildFingerprint;
    impl BuildFingerprint {{ pub const fn from_parts(_: &[u32]) -> Self {{ Self }} }}
    #[derive(Clone, Copy)] pub struct Slot<T>(::std::marker::PhantomData<T>);
    impl<T> Slot<T> {{ pub const fn new(_: u32) -> Self {{ Self(::std::marker::PhantomData) }} }}
    #[derive(Clone, Copy)] pub struct KeyedSlot<K, T>(::std::marker::PhantomData<(K, T)>);
    impl<K, T> KeyedSlot<K, T> {{ pub const fn new(_: u32) -> Self {{ Self(::std::marker::PhantomData) }} }}
    #[derive(Clone, Copy)] pub struct Handle<T>(::std::marker::PhantomData<T>);
    impl<T> Handle<T> {{ pub const fn new(_: u32) -> Self {{ Self(::std::marker::PhantomData) }} }}
    #[derive(Clone, Copy)] pub struct Atom<T>(::std::marker::PhantomData<T>);
    impl<T> Atom<T> {{ pub const fn new(_: u32) -> Self {{ Self(::std::marker::PhantomData) }} }}
    #[derive(Clone, Copy)] pub struct Form<T>(::std::marker::PhantomData<T>);
    impl<T> Form<T> {{ pub const fn new(_: u32) -> Self {{ Self(::std::marker::PhantomData) }} }}
    pub struct FormContract {{ pub fields: &'static [FormField] }}
    pub struct FormField {{ pub name: &'static str, pub kind: FormControlKind, pub required: bool }}
    pub enum FormControlKind {{ Text, Number {{ min: Option<&'static str>, max: Option<&'static str>, step: Option<&'static str> }}, Checkbox, Radio, Select {{ multiple: bool }}, TextArea, File, Hidden, Submit, Other {{ tag: &'static str, input_type: Option<&'static str> }} }}
}}
{generated}
fn main() {{
    let html = lower_html(r#"<form data-slhx-handle="create"><input name="title"></form><li data-slhx-slot="row" data-slhx-key="7"></li>"#);
    assert!(html.contains(r#"data-hid="#));
    assert!(html.contains(r#"name="__h""#));
    assert!(html.contains(r#"data-key="7""#));
    assert!(!html.contains("data-slhx-key"));
}}
"###,
        );
        let source_path = base.join("lowering.rs");
        let bin_path = base.join("lowering-bin");
        std::fs::write(&source_path, source).unwrap();
        let status = std::process::Command::new("rustc")
            .arg(&source_path)
            .arg("-o")
            .arg(&bin_path)
            .status()
            .unwrap();
        assert!(status.success());
        let status = std::process::Command::new(&bin_path).status().unwrap();
        assert!(status.success());

        let _ = std::fs::remove_dir_all(&base);
    }

    fn test_dir(prefix: &str) -> PathBuf {
        std::env::temp_dir().join(format!("{prefix}-{}", std::process::id()))
    }
}