//! History window selection and context-size error detection.

use crate::llm::Entry;

pub fn is_too_large(error: &str) -> bool {
    let Some((status, body)) = error
        .strip_prefix("HTTP ")
        .and_then(|error| error.split_once(':'))
    else {
        return false;
    };
    if !matches!(status.split_whitespace().next(), Some("400" | "413")) {
        return false;
    }
    let body = body.to_ascii_lowercase();
    body.contains("context_length_exceeded")
        || body.contains("maximum context length")
        || body.contains("context length exceeded")
        || body.contains("too large")
        || (body.contains("too long")
            && ["context", "input", "prompt"]
                .iter()
                .any(|term| body.contains(term)))
}

pub fn next_turn_start(history: &[Entry], from: usize, current: usize) -> Option<usize> {
    let end = current.min(history.len().checked_sub(1)?);
    (from..=end).find(|&index| matches!(&history[index], Entry::User { .. }))
}

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

    #[test]
    fn detects_context_size_errors_only_for_http_400_or_413() {
        assert!(is_too_large("HTTP 400: context_length_exceeded"));
        assert!(is_too_large("HTTP 413: prompt is too long"));
        assert!(is_too_large("HTTP 400: maximum context length"));
        assert!(is_too_large("HTTP 400: request is too large"));
        assert!(!is_too_large("HTTP 500: prompt is too long"));
        assert!(!is_too_large("HTTP 400: invalid token"));
    }

    #[test]
    fn history_skip_advances_by_whole_user_turns() {
        let history = vec![
            Entry::User {
                text: "first".into(),
            },
            Entry::ToolCall {
                id: "a".into(),
                name: "tool".into(),
                arguments: "{}".into(),
            },
            Entry::ToolResult {
                id: "a".into(),
                output: "done".into(),
            },
            Entry::User {
                text: "second".into(),
            },
            Entry::ToolCall {
                id: "b".into(),
                name: "tool".into(),
                arguments: "{}".into(),
            },
            Entry::ToolResult {
                id: "b".into(),
                output: "done".into(),
            },
            Entry::User {
                text: "current".into(),
            },
        ];
        assert_eq!(next_turn_start(&history, 0, 6), Some(0));
        assert_eq!(next_turn_start(&history, 1, 6), Some(3));
        assert_eq!(next_turn_start(&history, 4, 6), Some(6));
        assert_eq!(next_turn_start(&history, usize::MAX, 6).unwrap_or(6), 6);
    }
}