//! Tool error middleware — catches tool execution errors and converts them
//! into well-formed tool-result messages for the LLM to recover from.
//!
//! Inspired by DeerFlow's ToolErrorMiddleware: instead of propagating raw errors
//! that crash the agent loop, this middleware wraps tool errors into a structured
//! format that the LLM can use to self-correct.

use async_trait::async_trait;
use serde_json::Value;
use zclaw_types::Result;
use crate::driver::ContentBlock;
use crate::middleware::{AgentMiddleware, MiddlewareContext, ToolCallDecision};

/// Middleware that intercepts tool call errors and formats recovery messages.
///
/// Priority 350 — runs after dangling tool repair (300) and before guardrail (400).
pub struct ToolErrorMiddleware {
    /// Maximum error message length before truncation.
    max_error_length: usize,
}

impl ToolErrorMiddleware {
    pub fn new() -> Self {
        Self {
            max_error_length: 500,
        }
    }

    /// Create with a custom max error length.
    pub fn with_max_error_length(mut self, len: usize) -> Self {
        self.max_error_length = len;
        self
    }

    /// Format a tool error into a guided recovery message for the LLM.
    ///
    /// The caller is responsible for truncation before passing `error`.
    fn format_tool_error(&self, tool_name: &str, error: &str) -> String {
        format!(
            "工具 '{}' 执行失败。错误信息: {}\n请分析错误原因，尝试修正参数后重试，或使用其他方法完成任务。",
            tool_name, error
        )
    }
}

impl Default for ToolErrorMiddleware {
    fn default() -> Self {
        Self::new()
    }
}

#[async_trait]
impl AgentMiddleware for ToolErrorMiddleware {
    fn name(&self) -> &str { "tool_error" }
    fn priority(&self) -> i32 { 350 }

    async fn before_tool_call(
        &self,
        _ctx: &MiddlewareContext,
        tool_name: &str,
        tool_input: &Value,
    ) -> Result<ToolCallDecision> {
        // Pre-validate tool input structure for common issues.
        // This catches malformed JSON inputs before they reach the tool executor.
        if tool_input.is_null() {
            tracing::warn!(
                "[ToolErrorMiddleware] Tool '{}' received null input — replacing with empty object",
                tool_name
            );
            return Ok(ToolCallDecision::ReplaceInput(serde_json::json!({})));
        }
        Ok(ToolCallDecision::Allow)
    }

    async fn after_tool_call(
        &self,
        ctx: &mut MiddlewareContext,
        tool_name: &str,
        result: &Value,
    ) -> Result<()> {
        // Check if the tool result indicates an error.
        if let Some(error) = result.get("error") {
            let error_msg = match error {
                Value::String(s) => s.clone(),
                other => other.to_string(),
            };
            let truncated = if error_msg.len() > self.max_error_length {
                // Use char-boundary-safe truncation to avoid panic on UTF-8 strings (e.g. Chinese)
                let end = error_msg.floor_char_boundary(self.max_error_length);
                format!("{}...(truncated)", &error_msg[..end])
            } else {
                error_msg.clone()
            };

            tracing::warn!(
                "[ToolErrorMiddleware] Tool '{}' failed: {}",
                tool_name, truncated
            );

            // Build a guided recovery message so the LLM can self-correct.
            let guided_message = self.format_tool_error(tool_name, &truncated);

            // Inject into response_content so the agent loop feeds this back
            // to the LLM alongside the raw tool result.
            ctx.response_content.push(ContentBlock::Text {
                text: guided_message,
            });
        }
        Ok(())
    }
}