use syn::Item;

use crate::pattern_analyzer::{AnalyzeItem, AnalyzePattern};

/// Match `#[chain]` functions, extract the generated internal struct name.
///
/// `#[chain] fn handle_greet(...)` → `__internal_chain_handle_greet`
///
/// Covered forms:
/// - `#[chain] fn handle(args: EntryType) -> Next { ... }`
/// - `#[chain] fn handle(args: EntryType, res: &mut Res) -> Next { ... }`
/// - async version
pub struct ChainPattern;

impl AnalyzePattern for ChainPattern {
    fn contains(&self, content: &str) -> bool {
        content.contains("chain]")
    }

    fn analyze(&self, content: &str) -> Vec<AnalyzeItem> {
        let Ok(syntax) = syn::parse_file(content) else {
            return Vec::new();
        };

        let mut items = Vec::new();

        for item in &syntax.items {
            collect_from_item(item, "", &mut items);
        }

        items
    }
}

fn internal_name(fn_name: &str) -> String {
    format!("__internal_chain_{fn_name}")
}

fn collect_from_item(item: &Item, current_mod: &str, items: &mut Vec<AnalyzeItem>) {
    match item {
        Item::Fn(f) if has_attr(&f.attrs, "chain") => {
            let fn_name = f.sig.ident.to_string();
            items.push(AnalyzeItem {
                module: current_mod.to_string(),
                item_name: internal_name(&fn_name),
            });
        }
        Item::Mod(item_mod) => {
            if let Some((_, nested)) = &item_mod.content {
                let mod_name = &item_mod.ident.to_string();
                let nested_mod = if current_mod.is_empty() {
                    mod_name.clone()
                } else {
                    format!("{current_mod}::{mod_name}")
                };
                for n in nested {
                    collect_from_item(n, &nested_mod, items);
                }
            }
        }
        _ => {}
    }
}

fn has_attr(attrs: &[syn::Attribute], name: &str) -> bool {
    attrs.iter().any(|a| {
        a.path()
            .segments
            .last()
            .is_some_and(|s| s.ident == name)
    })
}