use crate::core::cache::SessionCache;
use crate::core::heatmap;
use crate::core::tokens::count_tokens;
use crate::tools::CrpMode;
use crate::tools::ctx_read;

pub fn handle(cache: &mut SessionCache, paths: &[String], mode: &str, crp_mode: CrpMode) -> String {
    handle_with_task(cache, paths, mode, crp_mode, None)
}

pub fn handle_with_task(
    cache: &mut SessionCache,
    paths: &[String],
    mode: &str,
    crp_mode: CrpMode,
    task: Option<&str>,
) -> String {
    handle_with_task_fresh(cache, paths, mode, false, crp_mode, task)
}

const DEFAULT_MAX_MULTI_READ_BYTES: usize = 512 * 1024;

fn max_multi_read_bytes() -> usize {
    std::env::var("LCTX_MAX_MULTI_READ_BYTES")
        .ok()
        .and_then(|v| v.parse().ok())
        .unwrap_or(DEFAULT_MAX_MULTI_READ_BYTES)
}

pub fn handle_with_task_fresh(
    cache: &mut SessionCache,
    paths: &[String],
    mode: &str,
    fresh: bool,
    crp_mode: CrpMode,
    task: Option<&str>,
) -> String {
    let n = paths.len();
    if n == 0 {
        return "Read 0 files | 0 tokens saved".to_string();
    }

    let max_bytes = max_multi_read_bytes();
    let mut sections: Vec<String> = Vec::with_capacity(n);
    let mut total_saved: usize = 0;
    let mut total_original: usize = 0;
    let mut accumulated_bytes: usize = 0;
    let mut files_read = 0usize;
    let mut truncated = false;

    for path in paths {
        let effective_mode = if ctx_read::is_instruction_file(path) {
            "full"
        } else {
            mode
        };
        let chunk = if fresh {
            ctx_read::handle_fresh_with_task(cache, path, effective_mode, crp_mode, task)
        } else {
            ctx_read::handle_with_task(cache, path, effective_mode, crp_mode, task)
        };
        let original = cache.get(path).map_or(0, |e| e.original_tokens);
        let sent = count_tokens(&chunk);
        heatmap::record_file_access(path, original, original.saturating_sub(sent));
        // Verified ledger (#685): model-correct counts. The default O200kBase model
        // reuses the o200k counts above (same BPE + cache key → zero extra work); a
        // resolved Claude/Gemini/Llama model re-tokenizes the raw source (from the
        // cache) and the sent chunk so savings match the provider's billing units.
        {
            use crate::core::savings_ledger as ledger;
            let (lbase, lsaved) =
                if ledger::ledger_family() == crate::core::tokens::TokenizerFamily::O200kBase {
                    (original, original.saturating_sub(sent))
                } else if let Some(raw) = cache
                    .get(path)
                    .and_then(crate::core::cache::CacheEntry::content)
                {
                    let lo = ledger::count_for_ledger(&raw);
                    (lo, lo.saturating_sub(ledger::count_for_ledger(&chunk)))
                } else {
                    (original, original.saturating_sub(sent))
                };
            ledger::record_read_event(lbase, lsaved);
        }
        total_original = total_original.saturating_add(original);
        total_saved = total_saved.saturating_add(original.saturating_sub(sent));

        let chunk_bytes = chunk.len();
        if accumulated_bytes > 0 && accumulated_bytes + chunk_bytes > max_bytes {
            truncated = true;
            break;
        }
        accumulated_bytes += chunk_bytes;
        sections.push(chunk);
        files_read += 1;
    }

    let body = sections.join("\n---\n");
    let summary = if truncated {
        let skipped = n - files_read;
        format!(
            "Read {files_read}/{n} files | {total_saved} tokens saved\n\
             ⚠ Output capped at {max_bytes} bytes (LCTX_MAX_MULTI_READ_BYTES). \
             {skipped} file(s) skipped. Use individual ctx_read calls for remaining files."
        )
    } else {
        format!("Read {n} files | {total_saved} tokens saved")
    };
    format!("{body}\n---\n{summary}")
}
