use clippy_utils::diagnostics::span_lint;
use clippy_utils::source::SpanRangeExt;
use rustc_hir as hir;
use rustc_hir::intravisit::FnKind;
use rustc_lint::{LateContext, LintContext};
use rustc_span::Span;

use super::TOO_MANY_LINES;

pub(super) fn check_fn(
    cx: &LateContext<'_>,
    kind: FnKind<'_>,
    span: Span,
    body: &hir::Body<'_>,
    too_many_lines_threshold: u64,
) {
    // Closures must be contained in a parent body, which will be checked for `too_many_lines`.
    // Don't check closures for `too_many_lines` to avoid duplicated lints.
    if matches!(kind, FnKind::Closure) || span.in_external_macro(cx.sess().source_map()) {
        return;
    }

    let mut line_count: u64 = 0;
    let too_many = body.value.span.check_source_text(cx, |src| {
        let mut in_comment = false;
        let mut code_in_line;

        let function_lines = if matches!(body.value.kind, hir::ExprKind::Block(..))
            && src.as_bytes().first().copied() == Some(b'{')
            && src.as_bytes().last().copied() == Some(b'}')
        {
            // Removing the braces from the enclosing block
            &src[1..src.len() - 1]
        } else {
            src
        }
        .trim() // Remove leading and trailing blank lines
        .lines();

        for mut line in function_lines {
            code_in_line = false;
            loop {
                line = line.trim_start();
                if line.is_empty() {
                    break;
                }
                if in_comment {
                    if let Some(i) = line.find("*/") {
                        line = &line[i + 2..];
                        in_comment = false;
                        continue;
                    }
                } else {
                    let multi_idx = line.find("/*").unwrap_or(line.len());
                    let single_idx = line.find("//").unwrap_or(line.len());
                    code_in_line |= multi_idx > 0 && single_idx > 0;
                    // Implies multi_idx is below line.len()
                    if multi_idx < single_idx {
                        line = &line[multi_idx + 2..];
                        in_comment = true;
                        continue;
                    }
                }
                break;
            }
            if code_in_line {
                line_count += 1;
            }
        }
        line_count > too_many_lines_threshold
    });

    if too_many {
        span_lint(
            cx,
            TOO_MANY_LINES,
            span,
            format!("this function has too many lines ({line_count}/{too_many_lines_threshold})"),
        );
    }
}
