Name package-level code for its feature

[onechat] / agent.go

package main

import (
        "bytes"
        "crypto/rand"
        "encoding/hex"
        "encoding/json"
        "errors"
        "fmt"
        "io"
        "os"
        "path/filepath"
        "strings"
)

const (
        // instructionsFileName is the file of the user's instructions in the
        // directory of an agent.
        instructionsFileName = "instructions.md"

        // agentIDBytes is the number of random bytes of an agent ID.
        agentIDBytes = 16
)

// AgentConfig holds the settings of the config.json of an agent. ID is random,
// made once when the file is made, and never changes. The cache key comes from
// the ID, so a rename keeps the prompt cache and two agents with one name do
// not share a key. Workdir is the directory where the commands of the agent
// run.
type AgentConfig struct {
        Name    string `json:"name"`
        ID      string `json:"id"`
        Model   string `json:"model"`
        Effort  string `json:"effort"`
        Workdir string `json:"workdir"`
}

// Agent is one agent and its directory. The directory holds config.json, the
// user's instructions in instructions.md, the chat, and the usage file.
type Agent struct {
        dir    string
        config AgentConfig
}

// openAgent reads the config.json of the agent in dir. When the file does not
// exist, it makes the directory and writes the file with the defaults and a new
// ID. A missing field of an existing file takes the default, but the ID must be
// there. An unknown field is an error, so a typo does not become a silent
// default.
func openAgent(dir string) (*Agent, error) {
        err := os.MkdirAll(dir, 0o700)
        if err != nil {
                return nil, fmt.Errorf("create agent directory: %w", err)
        }

        path := filepath.Join(dir, "config.json")
        data, err := os.ReadFile(path)
        if errors.Is(err, os.ErrNotExist) {
                return createAgent(dir)
        }

        if err != nil {
                return nil, fmt.Errorf("read agent config: %w", err)
        }

        config, err := defaultAgentConfig()
        if err != nil {
                return nil, err
        }

        decoder := json.NewDecoder(bytes.NewReader(data))
        decoder.DisallowUnknownFields()
        err = decoder.Decode(&config)
        if err == nil && !errors.Is(decoder.Decode(&struct{}{}), io.EOF) {
                err = errors.New("data after the JSON object")
        }

        if err == nil {
                err = config.validate()
        }

        if err != nil {
                return nil, fmt.Errorf("%s: %w", path, err)
        }

        return &Agent{
                dir:    dir,
                config: config,
        }, nil
}

// createAgent writes the config.json of a new agent in dir with the defaults
// and a new ID.
func createAgent(dir string) (*Agent, error) {
        config, err := defaultAgentConfig()
        if err != nil {
                return nil, err
        }

        id := make([]byte, agentIDBytes)
        _, err = rand.Read(id)
        if err != nil {
                return nil, fmt.Errorf("make agent ID: %w", err)
        }

        config.ID = hex.EncodeToString(id)
        data, err := json.MarshalIndent(config, "", "  ")
        if err != nil {
                return nil, fmt.Errorf("encode agent config: %w", err)
        }

        err = writeFileAtomic(filepath.Join(dir, "config.json"), append(data, '\n'))
        if err != nil {
                return nil, fmt.Errorf("write agent config: %w", err)
        }

        return &Agent{
                dir:    dir,
                config: config,
        }, nil
}

// defaultAgentConfig returns the settings of a new agent, without an ID. The
// commands run in the home directory of the user.
func defaultAgentConfig() (AgentConfig, error) {
        home, err := os.UserHomeDir()
        if err != nil {
                return AgentConfig{}, fmt.Errorf("find working directory: %w", err)
        }

        return AgentConfig{
                Name:    "OneChat",
                Model:   "gpt-6.1-sol",
                Effort:  "medium",
                Workdir: home,
        }, nil
}

// validate makes sure that each setting has a valid value.
func (c AgentConfig) validate() error {
        if c.Name == "" || strings.ContainsAny(c.Name, "\r\n") {
                return errors.New("name must be one line of text")
        }

        id, err := hex.DecodeString(c.ID)
        if err != nil || len(id) != agentIDBytes {
                return fmt.Errorf("id must be %d hexadecimal digits", 2*agentIDBytes)
        }

        if c.Model == "" || c.Effort == "" {
                return errors.New("agent needs a model and an effort")
        }

        if !filepath.IsAbs(c.Workdir) {
                return fmt.Errorf("workdir %q is not an absolute path", c.Workdir)
        }

        return nil
}

// CacheKey returns the prompt cache key of every model call of the agent.
func (a *Agent) CacheKey() string {
        return "onechat-" + a.config.ID
}

// Prompt returns the system prompt of the agent with the user's instructions
// from instructions.md. It reads the file on each call, so a change applies at
// the next call. A missing file means no instructions.
func (a *Agent) Prompt() (string, error) {
        data, err := os.ReadFile(filepath.Join(a.dir, instructionsFileName))
        if err != nil && !errors.Is(err, os.ErrNotExist) {
                return "", fmt.Errorf("read instructions: %w", err)
        }

        return prompt(a.config.Name, string(data)), nil
}