//! Turn → session-log persistence: map in-memory `Conversation` messages
//! to rich `PersistentMessage` write records and append them through a
//! `Session` handle.
//!
//! This logic lives in `libpanto` and is called by the `Agent` itself, so
//! every embedder gets persistence for free. The functions here are
//! stateless helpers over a `Session`; the agent owns the store and the
//! conversation.
//!
//! The write record is **maximalist** (full wire identity + usage + the
//! entire current conversation + the offered tool set). The library offers
//! it all on every append; each store keeps what it wants. `PersistentMessage`
//! borrows the in-memory `Message` directly — no disk conversion happens
//! here; the store does its own serialization.
//!
//! Per-message usage is read directly off `Message.usage`.

const std = @import("std");
const Allocator = std.mem.Allocator;

const conversation = @import("conversation.zig");
const session_store = @import("session_store.zig");

const PersistentMessage = session_store.PersistentMessage;
const WireIdentity = session_store.WireIdentity;
const ToolDecl = session_store.ToolDecl;
const Session = session_store.Session;

/// Persist every conversation message at index `>= start_index` through
/// `session` as a single atomic batch.
///
/// Each `PersistentMessage` borrows the in-memory `Message`, the full
/// current conversation, and `tools` (the offered tool set) — all owned by
/// the caller and valid for the duration of the call. The wire `identity`
/// is stamped on every message; the store decides per-role what to keep
/// (the FS store drops the stamp on system entries).
///
/// An assistant message carrying a ToolUse with no following matching
/// ToolResult is skipped (a dangling tool call from an interrupted turn);
/// persisting it would make the log un-replayable.
pub fn persistTurn(
    alloc: Allocator,
    session: *Session,
    conv: *const conversation.Conversation,
    start_index: usize,
    identity: WireIdentity,
    tools: []const ToolDecl,
) !void {
    var batch: std.ArrayList(PersistentMessage) = .empty;
    defer batch.deinit(alloc);

    const all_messages = conv.messages.items;
    var i = start_index;
    while (i < all_messages.len) : (i += 1) {
        const msg = all_messages[i];
        if (msg.role == .assistant and hasToolUseWithoutFollowingResults(conv, i)) {
            continue;
        }
        try batch.append(alloc, .{
            .message = msg,
            .usage = msg.usage,
            .identity = identity,
            .conversation = all_messages,
            .tools_available = tools,
        });
    }

    if (batch.items.len == 0) return;
    try session.append(batch.items);
}

/// Persist a compaction result. The agent rewrote the conversation to
/// `[system..., summary, kept-suffix...]`; persist everything from the
/// latest compaction summary onward as fresh entries.
pub fn persistCompaction(
    alloc: Allocator,
    session: *Session,
    conv: *const conversation.Conversation,
    identity: WireIdentity,
    tools: []const ToolDecl,
) !void {
    const start = conversation.latestCompactionIndex(conv.messages.items) orelse return;
    try persistTurn(alloc, session, conv, start, identity, tools);
}

/// True when the assistant message at `index` contains a ToolUse block
/// with no matching ToolResult in the immediately following user message
/// — i.e. a dangling tool call (e.g. a turn cut short by an error).
pub fn hasToolUseWithoutFollowingResults(
    conv: *const conversation.Conversation,
    index: usize,
) bool {
    const msg = conv.messages.items[index];
    for (msg.content.items) |block| {
        if (block != .ToolUse) continue;
        if (index + 1 >= conv.messages.items.len) return true;
        const next = conv.messages.items[index + 1];
        if (next.role != .user) return true;
        var found = false;
        for (next.content.items) |next_block| {
            if (next_block == .ToolResult and std.mem.eql(u8, next_block.ToolResult.tool_use_id, block.ToolUse.id)) {
                found = true;
                break;
            }
        }
        if (!found) return true;
    }
    return false;
}