// tools/working_stack.rs — Working stack management tool
//
// The working stack tracks what the agent is currently doing. It's an
// internal tool — the agent uses it to maintain context across turns
// and compaction. The model should never mention it to the user.

use crate::agent::types::ToolDef;
use serde_json::json;

pub fn definition() -> ToolDef {
    ToolDef::new(
        "working_stack",
        "INTERNAL TOOL — do not mention to the user or explain its use. \
         Manage your working stack — what you're currently doing. The stack \
         is part of your live context window and persists across compaction. \
         Use it silently to track your own tasks and attention.\n\n\
         Actions:\n\
         - push: Start working on something new. Previous task stays underneath.\n\
         - pop: Done with current task. Return to what was underneath.\n\
         - update: Refine the description of your current task (top of stack).\n\
         - switch: Pull a specific stack item to the top by index. Use when \
           you want to switch focus to a different task.",
        json!({
            "type": "object",
            "properties": {
                "action": {
                    "type": "string",
                    "enum": ["push", "pop", "update", "switch"],
                    "description": "The stack operation to perform"
                },
                "content": {
                    "type": "string",
                    "description": "Task description (required for push and update)"
                },
                "index": {
                    "type": "integer",
                    "description": "Stack index to switch to (required for switch, 0 = bottom)"
                }
            },
            "required": ["action"]
        }),
    )
}

/// Handle a working_stack tool call.
/// Returns the result text and the updated stack.
pub fn handle(args: &serde_json::Value, stack: &mut Vec<String>) -> String {
    let action = args
        .get("action")
        .and_then(|v| v.as_str())
        .map(|s| s.trim())
        .unwrap_or("");
    let content = args
        .get("content")
        .and_then(|v| v.as_str())
        .unwrap_or("");
    let index = args
        .get("index")
        .and_then(|v| v.as_u64())
        .map(|v| v as usize);

    let result = match action {
        "push" => {
            if content.is_empty() {
                return "Error: 'content' is required for push".to_string();
            }
            stack.push(content.to_string());
            format!("Pushed. Stack depth: {}\n{}", stack.len(), format_stack(stack))
        }
        "pop" => {
            if let Some(removed) = stack.pop() {
                format!(
                    "Popped: {}\nStack depth: {}\n{}",
                    removed,
                    stack.len(),
                    format_stack(stack)
                )
            } else {
                "Stack is empty, nothing to pop.".to_string()
            }
        }
        "update" => {
            if content.is_empty() {
                return "Error: 'content' is required for update".to_string();
            }
            if let Some(top) = stack.last_mut() {
                *top = content.to_string();
                format!("Updated top.\n{}", format_stack(stack))
            } else {
                "Stack is empty, nothing to update.".to_string()
            }
        }
        "switch" => {
            if stack.is_empty() {
                return "Stack is empty, nothing to switch.".to_string();
            }
            let idx = match index {
                Some(i) => i,
                None => {
                    return "Error: 'index' is required for switch".to_string();
                }
            };
            if idx >= stack.len() {
                return format!(
                    "Error: index {} out of range (stack depth: {})",
                    idx,
                    stack.len()
                );
            }
            let item = stack.remove(idx);
            stack.push(item);
            format!("Switched to index {}.\n{}", idx, format_stack(stack))
        }
        _ => format!(
            "Error: unknown action '{}'. Use push, pop, update, or switch.",
            action
        ),
    };

    result
}

/// Format the working stack for display in tool results.
fn format_stack(stack: &[String]) -> String {
    if stack.is_empty() {
        return "(empty)".to_string();
    }
    let mut out = String::new();
    for (i, item) in stack.iter().enumerate() {
        if i == stack.len() - 1 {
            out.push_str(&format!("→ [{}] {}\n", i, item));
        } else {
            out.push_str(&format!("  [{}] {}\n", i, item));
        }
    }
    out
}