package agent

import (
	"bufio"
	"context"
	"fmt"
	"io"
	"os/exec"
	"strings"
	"sync"
	"sync/atomic"
	"time"
)

// traecliBlockedArgs are flags hardcoded by the daemon that must not be
// overridden by user-configured custom_args. `acp` and `serve` are the
// protocol subcommand/action; `-y`/`--yolo` is daemon-owned so headless ACP
// always runs in bypass-permissions mode (the official traecli gates non-read
// tools behind a permission prompt otherwise — see
// https://docs.trae.cn/cli_permission-mode). `--print`/`-p` and
// `--output-format` would switch the binary out of ACP into print mode and
// break the daemon↔traecli transport, and `--permission-mode` is owned by the
// daemon via --yolo.
var traecliBlockedArgs = map[string]blockedArgMode{
	"acp":               blockedStandalone,
	"serve":             blockedStandalone,
	"-y":                blockedStandalone,
	"--yolo":            blockedStandalone,
	"-p":                blockedStandalone,
	"--print":           blockedStandalone,
	"--output-format":   blockedWithValue,
	"--permission-mode": blockedWithValue,
}

// traecliBackend implements Backend by spawning `traecli acp serve --yolo` and
// communicating via the standard ACP (Agent Client Protocol) JSON-RPC 2.0
// transport over stdin/stdout.
//
// This targets ByteDance's official TRAE CLI (the `traecli` binary documented
// at https://docs.trae.cn/cli — NOT the open-source bytedance/trae-agent
// `trae-cli`, which has no ACP transport). traecli is ACP-native: it advertises
// `loadSession: true` and `mcpCapabilities: {http, sse}` from `initialize`,
// returns its model catalog from `session/new`, and supports `session/load`
// (resume), `session/set_model`, and `session/prompt`. That lets the existing
// Hermes/Kimi/Kiro/Qoder ACP client (hermesClient) drive it with only
// provider-specific launch args and tool-name normalization.
//
// The `initialize` capabilities above were captured from the real traecli
// v0.120.42 binary; the streaming gate mirrors the other ACP backends so
// history replay flushed during session setup does not corrupt the streamed
// output.
type traecliBackend struct {
	cfg Config
}

var traecliReaderDrainGrace = 2 * time.Second

// traecliMessageStream serializes sends and the final close so a late stdout
// reader (traecli may keep the process and its pipes open briefly after
// session/prompt returns) cannot send on a closed channel. Mirrors qoder.
type traecliMessageStream struct {
	ch     chan Message
	mu     sync.Mutex
	closed bool
}

func newTraecliMessageStream(size int) *traecliMessageStream {
	return &traecliMessageStream{ch: make(chan Message, size)}
}

func (s *traecliMessageStream) send(msg Message) {
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.closed {
		return
	}
	trySend(s.ch, msg)
}

func (s *traecliMessageStream) close() {
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.closed {
		return
	}
	s.closed = true
	close(s.ch)
}

func (b *traecliBackend) Execute(ctx context.Context, prompt string, opts ExecOptions) (*Session, error) {
	execPath := b.cfg.ExecutablePath
	if execPath == "" {
		execPath = "traecli"
	}
	if _, err := exec.LookPath(execPath); err != nil {
		return nil, fmt.Errorf("traecli executable not found at %q: %w", execPath, err)
	}

	// Translate the agent's mcp_config (Claude-style object of objects) into
	// the array shape ACP session/new and session/load expect. Fail closed on
	// malformed JSON so the launch surfaces the real error instead of silently
	// dropping every MCP server.
	mcpServers, err := buildACPMcpServers(opts.McpConfig, b.cfg.Logger)
	if err != nil {
		return nil, fmt.Errorf("traecli: invalid mcp_config: %w", err)
	}

	timeout := opts.Timeout
	runCtx, cancel := runContext(ctx, timeout)

	traecliArgs := append(
		[]string{"acp", "serve", "--yolo"},
		filterCustomArgs(opts.CustomArgs, traecliBlockedArgs, b.cfg.Logger)...,
	)
	cmd := exec.CommandContext(runCtx, execPath, traecliArgs...)
	hideAgentWindow(cmd)
	b.cfg.Logger.Info("agent command", "exec", execPath, "args", traecliArgs)
	if opts.Cwd != "" {
		cmd.Dir = opts.Cwd
	}
	cmd.Env = buildEnv(b.cfg.Env)

	stdout, err := cmd.StdoutPipe()
	if err != nil {
		cancel()
		return nil, fmt.Errorf("traecli stdout pipe: %w", err)
	}
	stdin, err := cmd.StdinPipe()
	if err != nil {
		cancel()
		return nil, fmt.Errorf("traecli stdin pipe: %w", err)
	}
	// StderrPipe + an explicit copier give us a join point (`stderrDone`) that
	// fires before the failure-promotion decision; see the matching comment in
	// hermes.go for why the io.MultiWriter form races with stopReason=end_turn
	// under load.
	providerErr := newACPProviderErrorSniffer("traecli")
	stderr, err := cmd.StderrPipe()
	if err != nil {
		cancel()
		return nil, fmt.Errorf("traecli stderr pipe: %w", err)
	}

	if err := cmd.Start(); err != nil {
		cancel()
		return nil, fmt.Errorf("start traecli: %w", err)
	}

	stderrSink := io.MultiWriter(newLogWriter(b.cfg.Logger, "[traecli:stderr] "), providerErr)
	stderrDone := make(chan struct{})
	go func() {
		defer close(stderrDone)
		_, _ = io.Copy(stderrSink, stderr)
	}()

	b.cfg.Logger.Info("traecli acp started", "pid", cmd.Process.Pid, "cwd", opts.Cwd)

	msgStream := newTraecliMessageStream(256)
	resCh := make(chan Result, 1)

	var outputMu sync.Mutex
	var output strings.Builder
	var streamingCurrentTurn atomic.Bool

	promptDone := make(chan hermesPromptResult, 1)

	c := &hermesClient{
		cfg:          b.cfg,
		stdin:        stdin,
		pending:      make(map[int]*pendingRPC),
		pendingTools: make(map[string]*pendingToolCall),
		acceptNotification: func(string) bool {
			return streamingCurrentTurn.Load()
		},
		onMessage: func(msg Message) {
			if !streamingCurrentTurn.Load() {
				return
			}
			if msg.Type == MessageToolUse {
				msg.Tool = kimiToolNameFromTitle(msg.Tool)
			}
			if msg.Type == MessageText {
				outputMu.Lock()
				output.WriteString(msg.Content)
				outputMu.Unlock()
			}
			msgStream.send(msg)
		},
		onPromptDone: func(result hermesPromptResult) {
			if !streamingCurrentTurn.Load() {
				return
			}
			select {
			case promptDone <- result:
			default:
			}
		},
	}

	readerDone := make(chan struct{})
	go func() {
		defer close(readerDone)
		scanner := bufio.NewScanner(stdout)
		scanner.Buffer(make([]byte, 0, 1024*1024), 10*1024*1024)
		for scanner.Scan() {
			line := strings.TrimSpace(scanner.Text())
			if line == "" {
				continue
			}
			c.handleLine(line)
		}
		c.closeAllPending(fmt.Errorf("traecli process exited"))
	}()

	go func() {
		defer cancel()
		defer msgStream.close()
		defer close(resCh)
		defer func() {
			stdin.Close()
			_ = cmd.Wait()
		}()

		startTime := time.Now()
		finalStatus := "completed"
		var finalError string
		var sessionID string
		effectiveModel := strings.TrimSpace(opts.Model)

		initResult, err := c.request(runCtx, "initialize", map[string]any{
			"protocolVersion": 1,
			"clientInfo": map[string]any{
				"name":    "multica-agent-sdk",
				"version": "0.2.0",
			},
			"clientCapabilities": map[string]any{},
		})
		if err != nil {
			finalStatus = "failed"
			finalError = fmt.Sprintf("traecli initialize failed: %v", err)
			resCh <- Result{Status: finalStatus, Error: finalError, DurationMs: time.Since(startTime).Milliseconds()}
			return
		}

		// Drop MCP entries whose remote transport the runtime didn't advertise
		// (traecli advertises mcpCapabilities {http, sse}). See hermes.go for
		// why sending an unsupported transport tanks the whole session/new.
		mcpServers = filterACPMcpServersByCapability(mcpServers, extractACPMcpCapabilities(initResult), "traecli", b.cfg.Logger)

		cwd := opts.Cwd
		if cwd == "" {
			cwd = "."
		}

		if opts.ResumeSessionID != "" {
			// traecli advertises loadSession:true, so resume goes through the
			// standard ACP session/load (same as Kiro).
			result, err := c.request(runCtx, "session/load", map[string]any{
				"cwd":        cwd,
				"sessionId":  opts.ResumeSessionID,
				"mcpServers": mcpServers,
			})
			if err != nil {
				finalStatus = "failed"
				finalError = fmt.Sprintf("traecli session/load failed: %v", err)
				resCh <- Result{Status: finalStatus, Error: finalError, DurationMs: time.Since(startTime).Milliseconds()}
				return
			}
			var changed bool
			sessionID, changed = resolveResumedSessionID(opts.ResumeSessionID, result)
			if changed {
				b.cfg.Logger.Warn("agent returned a different session id on resume — original was likely lost; continuing with the new id",
					"backend", "traecli",
					"requested", opts.ResumeSessionID,
					"actual", sessionID,
				)
			}
			if effectiveModel == "" {
				effectiveModel = extractACPCurrentModelID(result)
			}
		} else {
			result, err := c.request(runCtx, "session/new", map[string]any{
				"cwd":        cwd,
				"mcpServers": mcpServers,
			})
			if err != nil {
				finalStatus = "failed"
				finalError = fmt.Sprintf("traecli session/new failed: %v", err)
				resCh <- Result{Status: finalStatus, Error: finalError, DurationMs: time.Since(startTime).Milliseconds()}
				return
			}
			sessionID = extractACPSessionID(result)
			if sessionID == "" {
				finalStatus = "failed"
				finalError = "traecli session/new returned no session ID"
				resCh <- Result{Status: finalStatus, Error: finalError, DurationMs: time.Since(startTime).Milliseconds()}
				return
			}
			if effectiveModel == "" {
				effectiveModel = extractACPCurrentModelID(result)
			}
		}

		c.sessionID = sessionID
		b.cfg.Logger.Info("traecli session created", "session_id", sessionID)

		if opts.Model != "" {
			if _, err := c.request(runCtx, "session/set_model", map[string]any{
				"sessionId": sessionID,
				"modelId":   opts.Model,
			}); err != nil {
				b.cfg.Logger.Warn("traecli set_session_model failed", "error", err, "requested_model", opts.Model)
				finalStatus = "failed"
				finalError = fmt.Sprintf("traecli could not switch to model %q: %v", opts.Model, err)
				if opts.ResumeSessionID != "" && isACPSessionNotFound(err) {
					b.cfg.Logger.Warn("resumed session not found at set_model time; clearing session id so the daemon retries fresh",
						"backend", "traecli",
						"session_id", sessionID,
					)
					sessionID = ""
				}
				resCh <- Result{
					Status:     finalStatus,
					Error:      finalError,
					DurationMs: time.Since(startTime).Milliseconds(),
					SessionID:  sessionID,
				}
				return
			}
			b.cfg.Logger.Info("traecli session model set", "model", opts.Model)
		}

		userText := prompt
		if opts.SystemPrompt != "" {
			userText = opts.SystemPrompt + "\n\n---\n\n" + prompt
		}

		streamingCurrentTurn.Store(true)
		_, err = c.request(runCtx, "session/prompt", map[string]any{
			"sessionId": sessionID,
			"prompt": []map[string]any{
				{"type": "text", "text": userText},
			},
		})
		if err != nil {
			if runCtx.Err() == context.DeadlineExceeded {
				finalStatus = "timeout"
				finalError = fmt.Sprintf("traecli timed out after %s", timeout)
			} else if runCtx.Err() == context.Canceled {
				finalStatus = "aborted"
				finalError = "execution cancelled"
			} else {
				finalStatus = "failed"
				finalError = fmt.Sprintf("traecli session/prompt failed: %v", err)
				if opts.ResumeSessionID != "" && isACPSessionNotFound(err) {
					b.cfg.Logger.Warn("resumed session not found at prompt time; clearing session id so the daemon retries fresh",
						"backend", "traecli",
						"session_id", sessionID,
					)
					sessionID = ""
				}
			}
		} else {
			select {
			case pr := <-promptDone:
				if pr.stopReason == "cancelled" {
					finalStatus = "aborted"
					finalError = "traecli cancelled the prompt"
				}
				c.usageMu.Lock()
				c.usage.InputTokens += pr.usage.InputTokens
				c.usage.OutputTokens += pr.usage.OutputTokens
				c.usage.CacheReadTokens += pr.usage.CacheReadTokens
				c.usageMu.Unlock()
			default:
			}
		}

		duration := time.Since(startTime)
		b.cfg.Logger.Info("traecli finished", "pid", cmd.Process.Pid, "status", finalStatus, "duration", duration.Round(time.Millisecond).String())

		stdin.Close()
		cancel()

		// traecli ACP may keep the process — and the stdout/stderr pipes — open
		// briefly after session/prompt returns. The prompt response is already
		// terminal, so bound the drain: wait for the stdout reader and the
		// stderr copier, but no longer than the grace window (CommandContext
		// cancellation tears the process down). Draining stderr is what makes
		// the provider-error promotion below see a terminal marker.
		drainCtx, drainCancel := context.WithTimeout(context.Background(), traecliReaderDrainGrace)
		select {
		case <-readerDone:
		case <-drainCtx.Done():
		}
		select {
		case <-stderrDone:
		case <-drainCtx.Done():
		}
		drainCancel()
		// Flip the gate before the defer closes msgStream; a late reader that
		// already passed the gate is serialized by traecliMessageStream so the
		// late send is dropped instead of panicking.
		streamingCurrentTurn.Store(false)

		outputMu.Lock()
		finalOutput := output.String()
		outputMu.Unlock()

		// Promote completed→failed when stderr or the agent text stream show a
		// terminal upstream-LLM failure (HTTP 4xx / rate-limit / expired token).
		// Mirrors hermes/kimi/kiro/qoder.
		finalStatus, finalError = promoteACPResultOnProviderError(finalStatus, finalError, finalOutput, providerErr)

		c.usageMu.Lock()
		u := c.usage
		c.usageMu.Unlock()

		var usageMap map[string]TokenUsage
		if u.InputTokens > 0 || u.OutputTokens > 0 || u.CacheReadTokens > 0 || u.CacheWriteTokens > 0 {
			model := effectiveModel
			if model == "" {
				model = "unknown"
			}
			usageMap = map[string]TokenUsage{model: u}
		}

		resCh <- Result{
			Status:     finalStatus,
			Output:     finalOutput,
			Error:      finalError,
			DurationMs: duration.Milliseconds(),
			SessionID:  sessionID,
			Usage:      usageMap,
		}
	}()

	return &Session{Messages: msgStream.ch, Result: resCh}, nil
}