//! Workspace directory-tree generation for subagent system prompts.
//!
//! Build an ASCII tree of the workspace directory structure so the LLM
//! can see the file layout — this is the same tree shown to the main
//! agent and gives subagents the same project-awareness.
//!
//! Flow: for each workspace root, walk using `ignore::WalkBuilder`
//! (respecting `.gitignore` and hidden files) → prefix `[DIR]` for
//! directories → truncate after 1000 entries to keep the prompt
//! reasonably sized.

use std::fmt::Write;
use tracing;

/// Build an ASCII tree of the workspace directory structure for the
/// system prompt, so the LLM can see the file layout.
///
/// Flow: for each root, walk using `ignore::WalkBuilder` (respecting
/// `.gitignore` and hidden files) → prefix `[DIR]` for directories →
/// truncate after 1000 entries to keep the system prompt under control.
///
/// The tree is appended to the subagent's system prompt so the LLM can
/// reference file paths without having seen them in conversation.
///
/// Return: a multi-line string containing the ASCII tree, or an empty
/// string preamble + entries if no roots are provided.
pub(crate) fn generate_workspace_tree(roots: &[std::path::PathBuf]) -> String {
    tracing::debug!("[subagent] generating workspace tree for {} root(s)", roots.len());

    let mut out = String::new();
    out.push_str("Current Workspace Directory Structure:\n");

    for root in roots {
        // Print the root path as a section header.
        writeln!(out, "Root: {}", root.display()).unwrap();

        // Walk the directory tree using ignore::WalkBuilder, which respects
        // .gitignore rules and hidden files by default.
        let walker = ignore::WalkBuilder::new(root)
            .hidden(true)
            .git_ignore(true)
            .build();

        let mut count = 0;
        for entry in walker.flatten() {
            let path = entry.path();
            if let Ok(rel) = path.strip_prefix(root) {
                // Skip the root entry itself (empty relative path).
                if rel.as_os_str().is_empty() {
                    continue;
                }
                // Prefix directories with [DIR] for visual clarity.
                let is_dir = entry.file_type().is_some_and(|ft| ft.is_dir());
                let prefix = if is_dir { "[DIR] " } else { "      " };
                writeln!(out, "  {}{}", prefix, rel.display()).unwrap();
                count += 1;
                // Hard cap at 1000 entries to avoid blowing up the prompt.
                if count > 1000 {
                    tracing::info!("[subagent] workspace tree truncated at 1000 entries for '{}'", root.display());
                    out.push_str("  ... (truncated)\n");
                    break;
                }
            }
        }
    }

    tracing::debug!("[subagent] workspace tree generated ({} entries across {} roots)", out.lines().count(), roots.len());
    out
}