// Unique-tail function name resolution
// Extracted from execute_legacy_call to keep handlers lean

use std::collections::HashMap;

use super::MirFunction;

/// Resolve function name using unique-tail matching algorithm.
///
/// Resolution strategy:
/// 1. Fast path: exact match on raw name
/// 2. Normalize with arity: "base/N"
/// 3. Unique-tail matching: find candidates ending with ".method/N"
/// 4. Same-box preference: prioritize functions in the same box as current_function
///
/// Returns resolved function name, or None if resolution fails.
pub(super) fn resolve_function_name(
    raw: &str,
    arity: usize,
    functions: &HashMap<String, MirFunction>,
    current_function: Option<&str>,
) -> Option<String> {
    // Fast path: exact match
    if functions.contains_key(raw) {
        return Some(raw.to_string());
    }

    // Robust normalization for names like "Box.method/Arity" or just "method"
    let (base, ar_from_raw) = if let Some((b, a)) = raw.rsplit_once('/') {
        (b.to_string(), a.parse::<usize>().ok())
    } else {
        (raw.to_string(), None)
    };
    let want_arity = ar_from_raw.unwrap_or(arity);

    // Try exact canonical form: "base/arity"
    let exact = format!("{}/{}", base, want_arity);
    if functions.contains_key(&exact) {
        return Some(exact);
    }

    // Split base into optional box and method name
    let (maybe_box, method) = if let Some((bx, m)) = base.split_once('.') {
        (Some(bx.to_string()), m.to_string())
    } else {
        (None, base.clone())
    };

    // Collect candidates that end with ".method/arity"
    let mut cands: Vec<String> = Vec::new();
    let tail = format!(".{}{}", method, format!("/{}", want_arity));
    for k in functions.keys() {
        if k.ends_with(&tail) {
            if let Some(ref bx) = maybe_box {
                if k.starts_with(&format!("{}.", bx)) {
                    cands.push(k.clone());
                }
            } else {
                cands.push(k.clone());
            }
        }
    }

    if cands.len() > 1 {
        // Prefer same-box candidate based on current function's box
        if let Some(cur) = current_function {
            let cur_box = cur.split('.').next().unwrap_or("");
            let scoped: Vec<String> = cands
                .iter()
                .filter(|k| k.starts_with(&format!("{}.", cur_box)))
                .cloned()
                .collect();
            if scoped.len() == 1 {
                cands = scoped;
            }
        }
    }

    match cands.len() {
        0 => None,
        1 => Some(cands.into_iter().next().unwrap()),
        _ => {
            // Multiple candidates: sort and pick first (deterministic fallback)
            let mut c = cands;
            c.sort();
            Some(c.into_iter().next().unwrap())
        }
    }
}