Plexum-gemini-provider/internal/runner/runner.go

// Package runner forks the `gemini` CLI per Plexum turn and translates
// its JSON output into canonical TurnEvents.
//
// Each Stream call spawns one subprocess:
//
//	gemini --skip-trust --output-format json [--model <m>] [--resume <sid>] -p <prompt>
//
// in the agent's workspace dir. The CLI emits a single JSON blob at
// exit; we parse it, capture session_id (for next-turn --resume), and
// emit synthetic message_start + text_delta + message_end events to
// match Plexum's streaming agentic-loop expectations.
//
// Session continuity: per-workspace UUID stored at
// <workspace>/.plexum-gemini-session, used as --resume on subsequent
// turns. Mirrors the contractor pattern in Plexum-anthropic-provider.
package runner

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"

	"git.hangman-lab.top/hzhang/Plexum-sdk-go/canonical"
	plugin "git.hangman-lab.top/hzhang/Plexum-sdk-go/plugin"
)

// SessionFile is the per-workspace filename storing the captured
// session id between turns.
const SessionFile = ".plexum-gemini-session"

// Run is the ProviderPlugin Stream implementation. It forks gemini,
// waits for completion, and pushes events on the returned channel.
// Channel closes when the subprocess exits (clean or error).
func Run(
	ctx context.Context,
	host plugin.HostAPI,
	agent plugin.AgentContext,
	model string,
	binary string,
	extraArgs []string,
	req canonical.TurnRequest,
) (<-chan canonical.TurnEvent, error) {
	workspace := agent.Workspace
	if workspace == "" {
		return nil, errors.New("gemini: agent workspace required (host must supply AgentContext)")
	}
	if err := os.MkdirAll(workspace, 0o755); err != nil {
		return nil, fmt.Errorf("mkdir workspace: %w", err)
	}

	prompt := extractLastUserText(req.Messages)
	if prompt == "" {
		return nil, errors.New("gemini: no user text in request messages")
	}

	resumeID := loadSessionID(workspace)

	args := []string{"--skip-trust", "--output-format", "json"}
	if model != "" {
		args = append(args, "--model", model)
	}
	if resumeID != "" {
		args = append(args, "--resume", resumeID)
	}
	args = append(args, extraArgs...)
	args = append(args, "-p", prompt)

	host.Log("info", "gemini: spawning CLI", map[string]any{
		"workspace": workspace, "model": model, "resume": resumeID,
		"prompt_len": len(prompt),
	})

	cmd := exec.CommandContext(ctx, binary, args...)
	cmd.Dir = workspace
	cmd.Env = os.Environ()

	var stdoutBuf, stderrBuf bytes.Buffer
	cmd.Stdout = &stdoutBuf
	cmd.Stderr = &stderrBuf
	if err := cmd.Start(); err != nil {
		return nil, fmt.Errorf("gemini: start: %w", err)
	}

	out := make(chan canonical.TurnEvent, 8)
	go func() {
		defer close(out)
		err := cmd.Wait()
		emit := func(ev canonical.TurnEvent) {
			select {
			case out <- ev:
			case <-ctx.Done():
			}
		}
		emit(canonical.TurnEvent{Type: canonical.EventMessageStart})

		// stderr is informational; log it but don't treat as fatal
		// (gemini chatters about Ripgrep etc. on stderr).
		if stderrBuf.Len() > 0 {
			host.Log("debug", "gemini stderr",
				map[string]any{"text": stderrBuf.String()})
		}

		// Parse the JSON output. gemini may prepend a "Ripgrep is not
		// available." line BEFORE the JSON; skip leading non-{ bytes.
		raw := stripPreamble(stdoutBuf.Bytes())
		var resp struct {
			SessionID string `json:"session_id"`
			Response  string `json:"response"`
			Stats     struct {
				Models map[string]struct {
					Tokens struct {
						Input  int `json:"input"`
						Total  int `json:"total"`
						Cached int `json:"cached"`
					} `json:"tokens"`
				} `json:"models"`
			} `json:"stats"`
			Error string `json:"error,omitempty"`
		}
		if perr := json.Unmarshal(raw, &resp); perr != nil {
			// Subprocess may have died before producing JSON.
			msg := stderrBuf.String()
			if err != nil {
				msg = fmt.Sprintf("%s (wait err: %v)", msg, err)
			}
			emit(canonical.TurnEvent{
				Type: canonical.EventError,
				Error: &canonical.ErrorInfo{
					Code:    "gemini_unparsable",
					Message: fmt.Sprintf("gemini output not JSON: %v\nstdout=%q\nstderr=%q",
						perr, truncate(string(raw), 200), truncate(msg, 400)),
				},
			})
			emit(canonical.TurnEvent{
				Type: canonical.EventMessageEnd, StopReason: "error",
			})
			return
		}
		if resp.SessionID != "" {
			saveSessionID(workspace, resp.SessionID, host)
		}
		if resp.Error != "" {
			emit(canonical.TurnEvent{
				Type:  canonical.EventError,
				Error: &canonical.ErrorInfo{Code: "gemini_error", Message: resp.Error},
			})
		}
		if resp.Response != "" {
			emit(canonical.TurnEvent{
				Type: canonical.EventTextDelta, Text: resp.Response,
			})
		}

		var usage canonical.Usage
		for _, m := range resp.Stats.Models {
			usage.InputTokens += m.Tokens.Input
			usage.OutputTokens += m.Tokens.Total - m.Tokens.Input
			usage.CacheReadTokens += m.Tokens.Cached
		}

		stopReason := canonical.StopEndTurn
		if err != nil {
			stopReason = "error"
		}
		emit(canonical.TurnEvent{
			Type: canonical.EventMessageEnd,
			StopReason: stopReason,
			Usage: &usage,
		})
	}()
	return out, nil
}

// ---- helpers ----

func extractLastUserText(msgs []canonical.Message) string {
	for i := len(msgs) - 1; i >= 0; i-- {
		m := msgs[i]
		if m.Role != canonical.RoleUser {
			continue
		}
		var parts []string
		for _, b := range m.Content {
			if t, ok := b.(*canonical.TextBlock); ok {
				parts = append(parts, t.Text)
			}
		}
		if len(parts) > 0 {
			out := parts[0]
			for _, p := range parts[1:] {
				out += "\n" + p
			}
			return out
		}
	}
	return ""
}

func loadSessionID(workspace string) string {
	raw, err := os.ReadFile(filepath.Join(workspace, SessionFile))
	if err != nil {
		return ""
	}
	return string(bytes.TrimSpace(raw))
}

func saveSessionID(workspace, id string, host plugin.HostAPI) {
	path := filepath.Join(workspace, SessionFile)
	if err := os.WriteFile(path, []byte(id), 0o600); err != nil {
		host.Log("warn", "gemini: save session id failed",
			map[string]any{"err": err.Error(), "path": path})
	}
}

// stripPreamble drops any non-`{` bytes before the first `{` so the
// "Ripgrep is not available" line gemini sometimes prepends doesn't
// trip json.Unmarshal.
func stripPreamble(b []byte) []byte {
	i := bytes.IndexByte(b, '{')
	if i <= 0 {
		return b
	}
	return b[i:]
}

func truncate(s string, n int) string {
	if len(s) <= n {
		return s
	}
	return s[:n] + "…"
}