use std::future::Future;
use std::time::Duration;

use crate::agent::request::AgentRequest;
use crate::error::{AiError, AiResult};

pub fn build_input_string(request: &AgentRequest) -> String {
    let mut input = String::new();

    if !request.context.is_empty() {
        input.push_str("<retrieved_context>\n");
        for chunk in &request.context {
            let source = chunk.source.as_deref().unwrap_or("unknown");
            let score = chunk
                .score
                .map(|s| format!("{s:.4}"))
                .unwrap_or_else(|| "n/a".to_string());
            input.push_str(&format!(
                "\n<chunk id=\"{}\" source=\"{}\" score=\"{}\">\n{}\n</chunk>\n",
                chunk.id, source, score, chunk.content
            ));
        }
        input.push_str("</retrieved_context>\n\n");
    }

    for message in &request.messages {
        match message {
            super::request::AgentMessage::User(content) => {
                input.push_str(&format!("User: {content}\n"));
            }
            super::request::AgentMessage::Assistant(content) => {
                input.push_str(&format!("Assistant: {content}\n"));
            }
        }
    }

    input.push_str(&format!("User: {}", request.input));

    input
}

pub fn estimate_tokens(text: &str) -> u64 {
    if text.is_empty() {
        return 0;
    }
    (text.chars().count() as f64 / 2.5).ceil() as u64
}

pub fn check_token_budget(
    estimated_input_tokens: u64,
    accumulated_output_chars: usize,
    limit: i64,
) -> bool {
    let output_estimate = (accumulated_output_chars as f64 / 2.5).ceil() as u64;
    estimated_input_tokens + output_estimate > limit as u64
}

pub async fn with_retry<F, Fut, T>(
    max_attempts: usize,
    base_delay_ms: u64,
    f: F,
) -> AiResult<T>
where
    F: Fn() -> Fut,
    Fut: Future<Output = AiResult<T>>,
{
    let mut last_error: Option<AiError> = None;
    for attempt in 0..max_attempts {
        match f().await {
            Ok(result) => return Ok(result),
            Err(e) if is_retryable(&e) && attempt + 1 < max_attempts => {
                let delay = Duration::from_millis(base_delay_ms * 2u64.pow(attempt as u32));
                tracing::warn!(
                    error = %e,
                    attempt = attempt + 1,
                    max_attempts,
                    delay_ms = delay.as_millis(),
                    "retrying after transient error"
                );
                tokio::time::sleep(delay).await;
                last_error = Some(e);
            }
            Err(e) => return Err(e),
        }
    }
    Err(AiError::ModelRetriesExhausted {
        attempts: max_attempts,
        last_error: last_error
            .map(|e| e.to_string())
            .unwrap_or_else(|| "unknown".to_string()),
    })
}

fn is_retryable(error: &AiError) -> bool {
    matches!(
        error,
        AiError::Api(_) | AiError::Response(_) | AiError::ModelRetriesExhausted { .. }
    )
}

pub fn tool_result_content_to_string(
    content: &rig::one_or_many::OneOrMany<rig::completion::message::ToolResultContent>,
) -> String {
    use rig::completion::message::ToolResultContent;
    content
        .iter()
        .filter_map(|item| match item {
            ToolResultContent::Text(t) => Some(t.text.clone()),
            _ => None,
        })
        .collect::<Vec<_>>()
        .join("\n")
}