neo-decompiler 0.10.1

use super::braces::{find_matching_brace, find_overflow_block_end};
use super::model::OverflowCollapse;
use super::parse::parse_let_assignment;
use super::scan::next_code_line;

/// Known type-boundary constants that start an overflow check sequence.
const OVERFLOW_BOUNDS: &[&str] = &[
    "-2147483648",
    "0",
    "-9223372036854775808",
    "2147483647",
    "4294967295",
    "9223372036854775807",
    "18446744073709551615",
];

/// Try to match the overflow-check pattern starting at `idx`.
pub(super) fn try_match_overflow(statements: &[String], idx: usize) -> Option<OverflowCollapse> {
    let line0 = statements[idx].trim();
    if line0.is_empty() || line0.starts_with("//") {
        return None;
    }
    let (result_var, expr) = parse_let_assignment(line0)?;

    let dup_idx = next_code_line(statements, idx + 1)?;
    let line1 = statements[dup_idx].trim();
    let (dup_var, dup_rhs) = parse_let_assignment(line1)?;
    if dup_rhs != result_var {
        return None;
    }

    let bound_idx = next_code_line(statements, dup_idx + 1)?;
    let line2 = statements[bound_idx].trim();
    let (_bound_var, bound_val) = parse_let_assignment(line2)?;
    if !OVERFLOW_BOUNDS.contains(&bound_val.as_str()) {
        return None;
    }

    let if_idx = next_code_line(statements, bound_idx + 1)?;
    let line3 = statements[if_idx].trim();
    if !line3.starts_with("if ") || !line3.ends_with('{') {
        return None;
    }
    if !line3.contains(&format!("{dup_var} <"))
        && !line3.contains(&format!("{dup_var} =="))
        && !line3.contains(&format!("{dup_var} >"))
    {
        return None;
    }

    let if_block_end = find_matching_brace(statements, if_idx)?;
    let first_body = ((if_idx + 1)..statements.len())
        .find(|&i| {
            let t = statements[i].trim();
            !t.is_empty() && !t.starts_with("//")
        })
        .map(|i| statements[i].trim().to_string());

    let is_checked = first_body
        .as_deref()
        .is_some_and(|s| s.starts_with("throw("));

    let (blank_end, else_unwrap) = if is_checked {
        let unwrap = next_code_line(statements, if_block_end + 1).and_then(|next| {
            let trimmed = statements[next].trim();
            if trimmed == "else {" || trimmed == "} else {" {
                let else_end = find_matching_brace(statements, next)?;
                Some((next, else_end))
            } else {
                None
            }
        });
        (if_block_end, unwrap)
    } else {
        (find_overflow_block_end(statements, if_idx)?, None)
    };

    Some(OverflowCollapse {
        op_line: idx,
        expr,
        result_var,
        blank_start: idx + 1,
        blank_end,
        is_checked,
        else_unwrap,
    })
}