//! The TUI application loop (plan §2/§9): wires the libpanto pull `Stream`
//! into component state and drives the differential render engine.
//!
//! This module is the NEW app/chat loop that `main.zig` shrinks to wiring
//! around. It owns:
//!   - a `Terminal` (raw mode + bracketed paste + SIGWINCH/restore),
//!   - a `tui_engine.Engine` driving a LIST of components,
//!   - the transcript (heap-allocated user/assistant/status components that
//!     persist for the engine to borrow),
//!   - a pinned `InputBox` (focused) and `Footer` (fps element),
//!   - the libpanto stream pump that routes each `Event` to component state.
//!
//! ## No "active component" invariant (plan §6)
//!
//! Streaming state is keyed by libpanto BLOCK INDEX (and tool call identity),
//! never a single mutable "current component" pointer. `TurnRouter` holds a
//! `block_index -> *transcript entry` map, so when parallel tool calls or
//! interleaved blocks arrive later (P2), each delta lands on the right
//! component without restructuring. P1 only spawns the minimal component set
//! (user/assistant/input/footer + minimal status lines), but the routing
//! structure is already parallel-safe.
//!
//! ## Streaming -> component state (plan §8)
//!
//! There is no per-delta render method. The pump consumes the pull `Stream`
//! and, for each event, MUTATES component state and calls
//! `scheduler.requestRender()`. The engine's append fast path
//! (`firstLineChanged` near the tail via the render cache + the line-diff
//! backstop) repaints only the dirty tail. stdout is never written directly.
//!
//! ## Thinking / tool deltas in P1 (deferred display, non-crashing)
//!
//! P1's minimal component set is user/assistant/input/footer. There is no
//! dedicated thinking or collapsible tool-use component yet (P2). To avoid
//! crashing on those blocks while keeping the loop honest:
//!   - a Thinking block streams its deltas into a DIM status line (one
//!     `AssistantText`-style component styled dim), and
//!   - a ToolUse block renders a single dim `tool: <name>` status line
//!     (name resolved at `tool_details` / `block_complete`).
//! The full thinking component and the collapsible tool-use component are
//! deferred to P2; this is the documented minimal stand-in.

const std = @import("std");
const posix = std.posix;
const panto = @import("panto");

const terminal_mod = @import("tui_terminal.zig");
const engine_mod = @import("tui_engine.zig");
const components = @import("tui_components.zig");
const input_mod = @import("tui_input.zig");
const theme = @import("tui_theme.zig");
const component = @import("tui_component.zig");
const command = @import("command.zig");

const Terminal = terminal_mod.Terminal;
const Engine = engine_mod.Engine;
const Scheduler = engine_mod.Scheduler;
const Clock = engine_mod.Clock;
const AssistantText = components.AssistantText;
const UserText = components.UserText;
const InputBox = components.InputBox;
const Footer = components.Footer;
const Component = component.Component;

const Event = panto.Event;

// ===========================================================================
// IoClock — the real monotonic clock for the engine's scheduler
// ===========================================================================

/// Wraps `std.Io`'s monotonic (`.awake`) clock as an engine `Clock`. The
/// engine stays Io-agnostic; this is the app-side adapter that supplies real
/// time. Store one by value and pass `clock()` into the engine/`App`.
pub const IoClock = struct {
    io: std.Io,

    pub fn init(io: std.Io) IoClock {
        return .{ .io = io };
    }

    fn nowFn(ptr: *anyopaque) i128 {
        const self: *IoClock = @ptrCast(@alignCast(ptr));
        return @intCast(std.Io.Clock.now(.awake, self.io).nanoseconds);
    }

    pub fn clock(self: *IoClock) Clock {
        return .{ .ptr = self, .nowFn = nowFn };
    }
};

// ===========================================================================
// Transcript
// ===========================================================================

/// A heap-allocated transcript entry. The engine borrows each entry's
/// `comp()`; the entry must outlive its time in the engine's list, so the
/// transcript owns the boxes on the heap and frees them on `deinit`.
///
/// `StatusText` reuses `AssistantText` but is styled by the caller via a
/// leading style escape baked into the text (we keep it as a plain
/// AssistantText for P1 and prefix a dim/style run in the seeded text).
const Entry = union(enum) {
    user: *UserText,
    /// Assistant message body (streaming text block).
    assistant: *AssistantText,
    /// A dim status/thinking/tool/retry line (minimal P1 stand-in; not a full
    /// component — see module docs).
    status: *AssistantText,

    fn comp(self: Entry) Component {
        return switch (self) {
            .user => |p| p.comp(),
            .assistant => |p| p.comp(),
            .status => |p| p.comp(),
        };
    }

    fn deinit(self: Entry, alloc: std.mem.Allocator) void {
        switch (self) {
            .user => |p| {
                p.deinit();
                alloc.destroy(p);
            },
            .assistant => |p| {
                p.deinit();
                alloc.destroy(p);
            },
            .status => |p| {
                p.deinit();
                alloc.destroy(p);
            },
        }
    }
};

// ===========================================================================
// App
// ===========================================================================

pub const App = struct {
    alloc: std.mem.Allocator,
    engine: *Engine,
    scheduler: Scheduler,
    clock: Clock,

    /// Owned transcript entries (boxes the engine borrows). Top-to-bottom.
    transcript: std.ArrayList(Entry) = .empty,

    /// Pinned, persistent components. Owned here (by value); the engine
    /// borrows their `comp()`.
    input_box: *InputBox,
    footer: *Footer,

    /// Per-turn block routing. Cleared at each turn boundary.
    router: TurnRouter,

    /// Optional sink flusher. The real terminal's engine writer is a buffered
    /// file writer that must be flushed after each frame for output to reach
    /// the tty; tests inject an in-memory writer and leave this null.
    flush_ctx: ?*anyopaque = null,
    flush_fn: ?*const fn (ctx: *anyopaque) void = null,

    /// Whether the input box currently participates in the engine list. It is
    /// removed during an in-flight turn (so streaming output appends below the
    /// transcript) and re-added when the turn completes. P1 keeps it simple:
    /// input + footer are always present and pinned at the bottom.
    pub fn init(
        alloc: std.mem.Allocator,
        engine: *Engine,
        clock: Clock,
        input_box: *InputBox,
        footer: *Footer,
    ) App {
        return .{
            .alloc = alloc,
            .engine = engine,
            .scheduler = Scheduler.init(8 * std.time.ns_per_ms),
            .clock = clock,
            .input_box = input_box,
            .footer = footer,
            .router = TurnRouter.init(alloc),
        };
    }

    pub fn deinit(self: *App) void {
        for (self.transcript.items) |e| e.deinit(self.alloc);
        self.transcript.deinit(self.alloc);
        self.router.deinit();
    }

    /// Install a sink flusher (the buffered terminal file writer). Called once
    /// during real-terminal bring-up; tests leave it unset.
    pub fn setFlusher(self: *App, ctx: *anyopaque, f: *const fn (ctx: *anyopaque) void) void {
        self.flush_ctx = ctx;
        self.flush_fn = f;
    }

    fn flushSink(self: *App) void {
        if (self.flush_fn) |f| f(self.flush_ctx.?);
    }

    // -- transcript spawning ------------------------------------------------

    /// Append a fresh transcript entry and register it with the engine,
    /// keeping the pinned input box + footer at the very bottom. Returns the
    /// new entry (still owned by the transcript).
    fn pushEntry(self: *App, entry: Entry) !void {
        try self.transcript.append(self.alloc, entry);
        try self.rebuildEngineList();
    }

    /// Rebuild the engine's component list: all transcript entries top-to-
    /// bottom, then the pinned input box, then the footer. Called whenever the
    /// transcript layout changes (a layout change forces a full redraw inside
    /// the engine, which is correct here).
    fn rebuildEngineList(self: *App) !void {
        // Clear and re-add. `removeComponent` is O(n) per call, so clear by
        // re-initializing the slot list via repeated pops is awkward; instead
        // remove the pinned components, then append the new entry, then re-add
        // the pinned ones. To keep it simple and correct we drain & rebuild.
        while (self.engine.componentCount() > 0) {
            const first = self.engine.slots.items[0].comp;
            _ = self.engine.removeComponent(first);
        }
        for (self.transcript.items) |e| try self.engine.addComponent(e.comp());
        try self.engine.addComponent(self.input_box.comp());
        try self.engine.addComponent(self.footer.comp());
    }

    /// Spawn a new assistant-text entry for the given block index and return
    /// it. Keyed by index in the router so deltas route without an "active
    /// component" pointer.
    fn spawnAssistant(self: *App) !*AssistantText {
        const box = try self.alloc.create(AssistantText);
        box.* = AssistantText.init(self.alloc);
        try self.pushEntry(.{ .assistant = box });
        return box;
    }

    /// Spawn a dim status line seeded with `text`. Used for thinking blocks,
    /// tool-call status, retry notices, command output, and errors. Returns
    /// the box so streaming callers (thinking) can append more.
    fn spawnStatus(self: *App, text: []const u8) !*AssistantText {
        const box = try self.alloc.create(AssistantText);
        box.* = AssistantText.init(self.alloc);
        // Seed with a dim run so the status reads as chrome, not assistant
        // prose. The component renders plain assistant style, so we bake the
        // dim escape into the text itself (a documented P1 minimal stand-in
        // for a real status component).
        const dim = theme.default.fg(.dim);
        const seeded = try std.fmt.allocPrint(self.alloc, "{s}{s}{s}", .{ dim.open(), text, dim.close() });
        defer self.alloc.free(seeded);
        try box.setText(seeded);
        try self.pushEntry(.{ .status = box });
        return box;
    }

    /// Spawn a user-message entry seeded with `text`.
    fn spawnUser(self: *App, text: []const u8) !void {
        const box = try self.alloc.create(UserText);
        box.* = UserText.init(self.alloc);
        try box.setText(text);
        try self.pushEntry(.{ .user = box });
    }

    // -- the render pump ----------------------------------------------------

    /// Render a frame if one is pending, feeding the footer the measured
    /// render time. Returns true if a frame was drawn.
    pub fn maybeRender(self: *App) !bool {
        const now = self.clock.now();
        if (!self.scheduler.shouldRenderNow(now)) return false;
        const start = self.clock.now();
        try self.engine.render();
        self.flushSink();
        const end = self.clock.now();
        const ms = @as(f64, @floatFromInt(end - start)) / @as(f64, std.time.ns_per_ms);
        // Feed the footer the last frame's render time. This dirties the
        // footer for NEXT frame; we don't recursively render here (the next
        // pending frame picks it up), keeping the fps readout one frame
        // behind, which is acceptable for the perf-validation surface.
        self.footer.setFrameTime(ms);
        self.scheduler.noteRendered(self.clock.now());
        return true;
    }

    /// Force a render now (e.g. after a turn boundary or resize), bypassing
    /// the coalescing window.
    pub fn renderNow(self: *App) !void {
        self.scheduler.requestRender();
        const start = self.clock.now();
        try self.engine.render();
        self.flushSink();
        const end = self.clock.now();
        const ms = @as(f64, @floatFromInt(end - start)) / @as(f64, std.time.ns_per_ms);
        self.footer.setFrameTime(ms);
        self.scheduler.noteRendered(self.clock.now());
    }

    // -- event routing ------------------------------------------------------

    /// Route one libpanto `Event` to component state (plan §8). NEVER writes
    /// to stdout; mutates components and requests a render. Keyed by block
    /// index via `router` so there is no "active component" pointer.
    pub fn routeEvent(self: *App, ev: Event) !void {
        switch (ev) {
            .message_start => {},
            .block_start => |b| {
                switch (b.block_type) {
                    .Text => {
                        const box = try self.spawnAssistant();
                        try self.router.put(b.index, .{ .assistant = box });
                    },
                    .Thinking => {
                        // Minimal P1 stand-in: a dim streaming status line.
                        const box = try self.spawnStatus("[thinking] ");
                        try self.router.put(b.index, .{ .thinking = box });
                    },
                    .ToolUse => {
                        // Minimal P1 stand-in: a dim one-line tool status. The
                        // name is unknown at start (streamed); fill it in at
                        // tool_details / block_complete.
                        const box = try self.spawnStatus("tool: …");
                        try self.router.put(b.index, .{ .tool = box });
                    },
                    .ToolResult => {},
                }
                self.scheduler.requestRender();
            },
            .tool_details => |d| {
                if (self.router.get(d.index)) |ref| switch (ref) {
                    .tool => |box| {
                        const dim = theme.default.fg(.dim);
                        const line = try std.fmt.allocPrint(self.alloc, "{s}tool: {s}{s}", .{ dim.open(), d.name, dim.close() });
                        defer self.alloc.free(line);
                        try box.setText(line);
                        self.scheduler.requestRender();
                    },
                    else => {},
                };
            },
            .content_delta => |d| {
                if (self.router.get(d.index)) |ref| switch (ref) {
                    .assistant => |box| {
                        try box.appendDelta(d.delta);
                        self.scheduler.requestRender();
                    },
                    .thinking => |box| {
                        // Append thinking deltas (still dim — the seed kept the
                        // dim run open; we append raw text, which renders plain
                        // assistant style. Acceptable P1 stand-in).
                        try box.appendDelta(d.delta);
                        self.scheduler.requestRender();
                    },
                    // Tool args stream as deltas too; P1 doesn't display the
                    // streamed JSON args (deferred to the P2 tool component).
                    .tool => {},
                };
            },
            .block_complete => |b| {
                switch (b.block) {
                    .ToolUse => |tu| {
                        if (self.router.get(b.index)) |ref| switch (ref) {
                            .tool => |box| {
                                const dim = theme.default.fg(.dim);
                                const line = try std.fmt.allocPrint(self.alloc, "{s}tool: {s}{s}", .{ dim.open(), tu.name, dim.close() });
                                defer self.alloc.free(line);
                                try box.setText(line);
                                self.scheduler.requestRender();
                            },
                            else => {},
                        };
                    },
                    else => {},
                }
            },
            .message_complete => {},
            .provider_retry => |info| {
                // Preserve the existing dim retry messaging meaning as a status
                // line in the transcript.
                if (info.compaction) {
                    _ = try self.spawnStatus("context overflow: compacting and retrying");
                } else {
                    const secs = @as(f64, @floatFromInt(info.delay_ms)) / 1000.0;
                    const msg = try std.fmt.allocPrint(
                        self.alloc,
                        "provider unavailable ({s}): retrying in {d:.1}s (attempt {d}/{d})",
                        .{ @errorName(info.err), secs, info.attempt + 1, info.max_attempts },
                    );
                    defer self.alloc.free(msg);
                    _ = try self.spawnStatus(msg);
                }
                self.scheduler.requestRender();
            },
            .tool_dispatch_start, .tool_dispatch_complete, .turn_complete => {},
        }
    }

    /// Reset per-turn routing state. The transcript entries persist (they are
    /// the chat history); only the block-index map is cleared.
    pub fn beginTurn(self: *App) void {
        self.router.reset();
    }

    /// Surface a turn error as a dim status line in the transcript.
    pub fn routeError(self: *App, err: anyerror) !void {
        const msg = try std.fmt.allocPrint(self.alloc, "[error: {s}]", .{@errorName(err)});
        defer self.alloc.free(msg);
        _ = try self.spawnStatus(msg);
        self.scheduler.requestRender();
    }
};

// ===========================================================================
// TurnRouter — block-index -> component map (no "active component")
// ===========================================================================

/// A reference to the transcript component a libpanto block is streaming into.
/// Keyed by block index in `TurnRouter`. This is the structure that makes the
/// loop parallel-tool-call ready: each block index has its own sink, so there
/// is never a single mutable "current" component.
pub const BlockRef = union(enum) {
    assistant: *AssistantText,
    /// Thinking block (dim status stand-in for P1).
    thinking: *AssistantText,
    /// Tool-use block (one-line status stand-in for P1).
    tool: *AssistantText,
};

pub const TurnRouter = struct {
    map: std.AutoHashMap(usize, BlockRef),

    pub fn init(alloc: std.mem.Allocator) TurnRouter {
        return .{ .map = std.AutoHashMap(usize, BlockRef).init(alloc) };
    }

    pub fn deinit(self: *TurnRouter) void {
        self.map.deinit();
    }

    pub fn reset(self: *TurnRouter) void {
        self.map.clearRetainingCapacity();
    }

    pub fn put(self: *TurnRouter, index: usize, ref: BlockRef) !void {
        try self.map.put(index, ref);
    }

    pub fn get(self: *TurnRouter, index: usize) ?BlockRef {
        return self.map.get(index);
    }
};

// ===========================================================================
// Driving the loop (real terminal)
// ===========================================================================

/// Inputs the loop needs from `main.zig` (kept as a struct so the wiring stays
/// a single call). The agent, command registry, and command context are
/// borrowed for the loop's lifetime.
pub const RunOptions = struct {
    agent: *panto.Agent,
    cmd_registry: *const command.Registry,
    cmd_ctx: *command.Context,
    /// In-memory writer that command handlers write to (their `stdout`). After
    /// each dispatch the captured text is flushed into the transcript as a dim
    /// status line, then cleared. See `runLoop` for the rationale.
    cmd_capture: *std.Io.Writer.Allocating,
    model_label: []const u8,
};

/// Run the interactive chat loop against a real terminal until EOF / Ctrl+D /
/// Ctrl+C. Restores the terminal on every exit path (the `Terminal` installs
/// signal + the caller installs panic restore).
///
/// Loop shape (single-threaded, poll-based):
///   1. Render any pending frame (feeding the footer the frame time).
///   2. Poll the tty for input with a short timeout (so coalesced renders and
///      SIGWINCH are serviced promptly even with no keypress).
///   3. Decode buffered bytes -> keys -> the focused input box.
///   4. On a submitted line: drive a turn (or dispatch a slash command),
///      pumping the stream's events into component state.
pub fn runLoop(app: *App, term: *Terminal, opts: RunOptions) !void {
    // Negotiate bracketed paste (+ opportunistic Kitty). Teardown on exit.
    term.writeAll(input_mod.negotiate_setup);
    defer term.writeAll(input_mod.negotiate_teardown);
    term.hideCursor();
    defer term.showCursor();

    try app.footer.setModel(opts.model_label);
    app.input_box.setFocused(true);
    try app.rebuildEngineList();
    try app.renderNow();

    var read_buf: [4096]u8 = undefined;
    // Retained partial-sequence tail across reads (a CSI/UTF-8 split across
    // read() boundaries).
    var tail: std.ArrayList(u8) = .empty;
    defer tail.deinit(app.alloc);

    while (true) {
        // 1. Service a pending coalesced frame.
        _ = try app.maybeRender();

        // 1b. SIGWINCH -> resize -> full redraw.
        if (term.takeResized()) {
            const size = term.refreshSize();
            app.engine.resize(size.cols, size.rows);
            try app.renderNow();
        }

        // 2. Poll for input (short timeout so renders/resize stay responsive).
        const ready = pollReadable(term.fd, 16) catch true;
        if (!ready) continue;

        const n = posix.read(term.fd, &read_buf) catch |err| switch (err) {
            error.WouldBlock => continue,
            else => return,
        };
        if (n == 0) break; // EOF (Ctrl+D on an empty line closes the tty)

        // 3. Decode. Prepend any retained tail, decode all complete sequences,
        //    retain the unconsumed tail for the next read.
        try tail.appendSlice(app.alloc, read_buf[0..n]);
        const consumed = try handleBytes(app, tail.items, opts);
        // Keep the unconsumed tail.
        const leftover = tail.items.len - consumed;
        std.mem.copyForwards(u8, tail.items[0..leftover], tail.items[consumed..]);
        tail.items.len = leftover;

        // 4. A frame may now be pending (input edited the box / a turn ran).
        _ = try app.maybeRender();
    }
}

/// Decode `bytes` into keys, route control keys (Ctrl+C/Ctrl+D) at the app
/// level, feed the rest to the focused input box, and act on any submitted
/// line. Returns the number of bytes consumed (the unconsumed partial tail is
/// retained by the caller).
fn handleBytes(app: *App, bytes: []const u8, opts: RunOptions) !usize {
    var off: usize = 0;
    while (off < bytes.len) {
        const step = input_mod.decodeOne(bytes[off..]) orelse break; // partial tail
        switch (step.decoded) {
            .key => |k| {
                // App-level control keys.
                if (k.isCtrl('c') or k.isCtrl('d')) {
                    // Clean exit: restore handled by deferred teardown + the
                    // terminal's deinit in main. Signal EOF by closing the loop.
                    return error.UserExit;
                }
                // Feed the key to the focused input box.
                app.input_box.comp().handleInput(bytes[off .. off + step.consumed]);
            },
            .paste => {
                app.input_box.comp().handleInput(bytes[off .. off + step.consumed]);
            },
        }
        off += step.consumed;
        app.scheduler.requestRender();

        // Did the box submit a line?
        if (app.input_box.takeSubmitted()) |line_borrowed| {
            // Copy: the box may reuse its buffer.
            const line = try app.alloc.dupe(u8, line_borrowed);
            defer app.alloc.free(line);
            try handleSubmittedLine(app, line, opts);
        }
    }
    return off;
}

/// Handle a submitted input line: slash command vs. model turn.
fn handleSubmittedLine(app: *App, line: []const u8, opts: RunOptions) !void {
    if (line.len == 0) return;

    if (std.mem.startsWith(u8, line, "/")) {
        // Slash command. Output is captured into `opts.cmd_capture` (the
        // command Context's stdout) and flushed into the transcript as a dim
        // status line — TUI-safe (no raw stdout writes during a frame).
        opts.cmd_capture.clearRetainingCapacity();
        opts.cmd_registry.dispatch(line, opts.cmd_ctx) catch |err| switch (err) {
            command.Error.CommandNotFound => {
                const msg = try std.fmt.allocPrint(app.alloc, "[unknown command: {s}]", .{line});
                defer app.alloc.free(msg);
                _ = try app.spawnStatus(msg);
            },
            else => {
                const msg = try std.fmt.allocPrint(app.alloc, "[command error: {s}]", .{@errorName(err)});
                defer app.alloc.free(msg);
                _ = try app.spawnStatus(msg);
            },
        };
        // Surface any captured command output.
        const captured = opts.cmd_capture.written();
        if (captured.len != 0) {
            _ = try app.spawnStatus(captured);
        }
        try app.renderNow();
        return;
    }

    // Model turn. Echo the user message, then pump the stream into components.
    try app.spawnUser(line);
    app.beginTurn();
    try app.renderNow();

    driveTurn(app, opts.agent, .{ .text = line }) catch |err| {
        try app.routeError(err);
    };
    try app.renderNow();
}

/// Drive one whole turn: open the pull stream, route every event into
/// component state until it terminates, rendering coalesced frames as deltas
/// arrive. The stream is always `deinit`ed (persisting the turn tail) on every
/// exit path — agent persistence is untouched.
fn driveTurn(app: *App, agent: *panto.Agent, message: panto.UserMessage) !void {
    var stream = try agent.run(message);
    defer stream.deinit();
    while (try stream.next()) |ev| {
        try app.routeEvent(ev);
        _ = try app.maybeRender();
    }
}

/// Poll the fd for readability with a millisecond timeout. Returns true when
/// data is available. Uses `poll(2)`.
fn pollReadable(fd: posix.fd_t, timeout_ms: i32) !bool {
    var fds = [_]posix.pollfd{.{ .fd = fd, .events = posix.POLL.IN, .revents = 0 }};
    const n = try posix.poll(&fds, timeout_ms);
    if (n == 0) return false;
    return (fds[0].revents & posix.POLL.IN) != 0;
}

// ===========================================================================
// Tests
// ===========================================================================

const testing = std.testing;

/// A test clock that advances by a fixed step each `now()` call so the
/// scheduler's coalescing logic is deterministic.
const TestClock = struct {
    t: i128 = 0,
    step: i128 = 1,

    fn now(ptr: *anyopaque) i128 {
        const self: *TestClock = @ptrCast(@alignCast(ptr));
        const v = self.t;
        self.t += self.step;
        return v;
    }

    fn clock(self: *TestClock) Clock {
        return .{ .ptr = self, .nowFn = now };
    }
};

/// Build an App backed by an in-memory engine writer (no TTY) for routing
/// tests. Caller owns the returned pieces and must call `teardown`.
const Harness = struct {
    buf: std.Io.Writer.Allocating,
    engine: Engine,
    input_box: InputBox,
    footer: Footer,
    test_clock: TestClock,
    app: App,

    fn make(alloc: std.mem.Allocator) !*Harness {
        const h = try alloc.create(Harness);
        h.buf = std.Io.Writer.Allocating.init(alloc);
        h.engine = Engine.init(alloc, &h.buf.writer, 80, 24, false);
        h.input_box = InputBox.init(alloc);
        h.footer = Footer.init(alloc);
        h.test_clock = .{ .t = 0, .step = 100 };
        h.app = App.init(alloc, &h.engine, h.test_clock.clock(), &h.input_box, &h.footer);
        return h;
    }

    fn teardown(h: *Harness, alloc: std.mem.Allocator) void {
        h.app.deinit();
        h.engine.deinit();
        h.input_box.deinit();
        h.footer.deinit();
        h.buf.deinit();
        alloc.destroy(h);
    }
};

fn delta(index: usize, text: []const u8) Event {
    return .{ .content_delta = .{ .index = index, .delta = text } };
}

test "routeEvent: text block + deltas append to an assistant component" {
    const alloc = testing.allocator;
    const h = try Harness.make(alloc);
    defer h.teardown(alloc);

    try h.app.routeEvent(.{ .block_start = .{ .block_type = .Text, .index = 0 } });
    try h.app.routeEvent(delta(0, "hello"));
    try h.app.routeEvent(delta(0, " world"));

    // One transcript entry (assistant), buffer accumulated both deltas.
    try testing.expectEqual(@as(usize, 1), h.app.transcript.items.len);
    const ref = h.app.router.get(0).?;
    try testing.expectEqualStrings("hello world", ref.assistant.buffer.items);
}

test "routeEvent: two text blocks key by index, no active-component clobber" {
    const alloc = testing.allocator;
    const h = try Harness.make(alloc);
    defer h.teardown(alloc);

    // Two interleaved text blocks (the no-active-component invariant: deltas
    // for index 0 must NOT land on index 1 even after block 1 opened).
    try h.app.routeEvent(.{ .block_start = .{ .block_type = .Text, .index = 0 } });
    try h.app.routeEvent(.{ .block_start = .{ .block_type = .Text, .index = 1 } });
    try h.app.routeEvent(delta(1, "B"));
    try h.app.routeEvent(delta(0, "A"));
    try h.app.routeEvent(delta(0, "A2"));

    try testing.expectEqualStrings("AA2", h.app.router.get(0).?.assistant.buffer.items);
    try testing.expectEqualStrings("B", h.app.router.get(1).?.assistant.buffer.items);
}

test "routeEvent: thinking deltas do not crash and stream to a status line" {
    const alloc = testing.allocator;
    const h = try Harness.make(alloc);
    defer h.teardown(alloc);

    try h.app.routeEvent(.{ .block_start = .{ .block_type = .Thinking, .index = 0 } });
    try h.app.routeEvent(delta(0, "reasoning"));

    const ref = h.app.router.get(0).?;
    try testing.expect(ref == .thinking);
    // The status line buffer contains the seed + appended delta.
    try testing.expect(std.mem.indexOf(u8, ref.thinking.buffer.items, "reasoning") != null);
}

test "routeEvent: tool block renders a minimal tool: <name> status (no crash)" {
    const alloc = testing.allocator;
    const h = try Harness.make(alloc);
    defer h.teardown(alloc);

    try h.app.routeEvent(.{ .block_start = .{ .block_type = .ToolUse, .index = 0 } });
    // Tool args streaming as deltas must be dropped silently, not crash.
    try h.app.routeEvent(delta(0, "{\"path\":"));
    try h.app.routeEvent(.{ .tool_details = .{ .index = 0, .id = "t1", .name = "read" } });

    const ref = h.app.router.get(0).?;
    try testing.expect(ref == .tool);
    try testing.expect(std.mem.indexOf(u8, ref.tool.buffer.items, "tool: read") != null);
}

test "routeEvent: provider_retry adds a dim status line" {
    const alloc = testing.allocator;
    const h = try Harness.make(alloc);
    defer h.teardown(alloc);

    try h.app.routeEvent(.{ .provider_retry = .{
        .err = error.ConnectionResetByPeer,
        .delay_ms = 1500,
        .attempt = 0,
        .max_attempts = 3,
        .compaction = false,
    } });
    try testing.expectEqual(@as(usize, 1), h.app.transcript.items.len);
    const e = h.app.transcript.items[0];
    try testing.expect(e == .status);
    try testing.expect(std.mem.indexOf(u8, e.status.buffer.items, "retrying") != null);
}

test "routeEvent: full event stream renders through the real engine, no stdout" {
    const alloc = testing.allocator;
    const h = try Harness.make(alloc);
    defer h.teardown(alloc);

    // Pin input + footer like the real loop.
    h.app.input_box.setFocused(true);
    try h.app.rebuildEngineList();

    h.app.beginTurn();
    try h.app.routeEvent(.{ .message_start = .assistant });
    try h.app.routeEvent(.{ .block_start = .{ .block_type = .Text, .index = 0 } });
    try h.app.routeEvent(delta(0, "Hi there"));
    try h.app.routeEvent(.{ .turn_complete = {} });

    try h.app.renderNow();
    const out = h.buf.written();
    // The assistant text reached the engine output (not stdout).
    try testing.expect(std.mem.indexOf(u8, out, "Hi there") != null);
}

test "beginTurn clears the block-index map but keeps transcript history" {
    const alloc = testing.allocator;
    const h = try Harness.make(alloc);
    defer h.teardown(alloc);

    try h.app.routeEvent(.{ .block_start = .{ .block_type = .Text, .index = 0 } });
    try h.app.routeEvent(delta(0, "first turn"));
    try testing.expect(h.app.router.get(0) != null);

    h.app.beginTurn();
    // Router cleared...
    try testing.expect(h.app.router.get(0) == null);
    // ...but the transcript entry persists as history.
    try testing.expectEqual(@as(usize, 1), h.app.transcript.items.len);
}

test "maybeRender feeds the footer a frame time and respects coalescing" {
    const alloc = testing.allocator;
    const h = try Harness.make(alloc);
    defer h.teardown(alloc);
    try h.app.rebuildEngineList();

    // No pending frame => no render.
    try testing.expect(!(try h.app.maybeRender()));

    h.app.scheduler.requestRender();
    try testing.expect(try h.app.maybeRender()); // idle => renders
    // Footer received a frame time (>= 0).
    try testing.expect(h.app.footer.frame_ms != null);
}