package main

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"log"
	"maps"
	"os"
	"path/filepath"
	"slices"
	"strings"
	"sync"
	"time"
)

const (
	// subagentNote is the first message of the log of a subagent.
	subagentNote = "subagent"

	// subagentNoteEffort follows subagentNote when the subagent has its own
	// effort.
	subagentNoteEffort = " at effort "

	// subagentWorkFileName is the file of the names of the running
	// subagents in the directory of an agent.
	subagentWorkFileName = "work.json"
)

// The statuses of the end of a run, in the work event of its report.
const (
	subagentFinished = "finished"
	subagentStopped  = "stopped"
	subagentFailed   = "failed"
)

// errSubagentClosed tells that the runs of the subagents ended with the loop.
var errSubagentClosed = errors.New("the daemon stops, so no subagent starts")

// SubagentRuns runs the subagents of one agent in the background. Each run is a
// goroutine with its own context, which only Stop and Close end. A run is one
// or more request chains. The first request of each chain holds the view of the
// agent at the start of the run, then the state of the turn, then the whole log
// of the subagent. A message of Tell that comes during a chain joins its next
// request after the tool results. One that comes after the final answer starts
// one more chain, which reads the log again. The report of the run goes to
// report: the final answer of each chain, or the error of a failed call. The
// logger gets one line at the end of a run: done, failed with the cause, or
// stopped. Stop ends one run, and its report says that it stopped. At the stop
// of the daemon the runs end with no report.
//
// work.json in the directory of the agent holds the names of the running
// subagents. Each start and each end of a run writes it whole, but Close does
// not, so after a stop of the daemon it names the runs that the stop cut, and
// Resume goes on with them. The logs alone cannot tell this, because a stop
// can cut a run just after its final reply.
//
// Spawn and Tell split the view with the layout of the agent, which has no
// lock. They are tools, so they run in the goroutine of the turns, as each
// split of a turn does.
type SubagentRuns struct {
	agent     *Agent
	memory    *Memory
	subagents *Subagents
	layout    *ViewLayout
	client    ChainClient
	state     func() string
	report    func(name, text, status string)
	note      func(text string) error
	fail      func(err error)
	logger    *log.Logger
	notify    func(Event)

	mutex   sync.Mutex
	running map[string]*SubagentRun
	closed  bool
	workers sync.WaitGroup
}

// Spawn starts one subagent for each task and returns their names at once. It
// waits until the view has no pending summary, and gives the view to each
// subagent. A nil effort is the effort of the agent.
func (r *SubagentRuns) Spawn(ctx context.Context, tasks []string, effort *string) (string, error) {
	if len(tasks) == 0 {
		return "", errors.New("no tasks")
	}

	r.mutex.Lock()

	closed := r.closed
	r.mutex.Unlock()

	if closed {
		return "", errSubagentClosed
	}

	note := subagentNote
	runEffort := r.agent.config.Effort
	if effort != nil && !slices.Contains(promptEfforts, *effort) {
		return "", fmt.Errorf("no effort %q: one of %s", *effort, strings.Join(promptEfforts, ", "))
	}

	if effort != nil && *effort != runEffort {
		note += subagentNoteEffort + *effort
		runEffort = *effort
	}

	err := r.memory.Settle(ctx)
	if err != nil {
		return "", fmt.Errorf("wait for the summaries: %w", err)
	}

	view, err := r.layout.Split(r.memory.ViewLines(nil))
	if err != nil {
		return "", err
	}

	names := make([]string, 0, len(tasks))
	for _, task := range tasks {
		name, err := r.create(ctx, note, task, view, runEffort)
		if err != nil && len(names) > 0 {
			return "", fmt.Errorf("started %s, then: %w", strings.Join(names, ", "), err)
		}

		if err != nil {
			return "", err
		}

		names = append(names, name)
	}

	return "Started " + strings.Join(names, ", ") + ". Each one's report will reach you as a message when it finishes.", nil
}

// Tell sends message to the subagent name. A running subagent reads it between
// its tool calls, and its report answers it. A finished subagent goes on from
// its log with a new run, with the view of now and the effort of its note.
func (r *SubagentRuns) Tell(ctx context.Context, name, message string) (string, error) {
	r.mutex.Lock()

	run, found := r.running[name]
	if found {
		defer r.mutex.Unlock()

		told, err := run.subagent.Append("user", message)
		if err != nil {
			return "", err
		}

		run.pending = append(run.pending, told)

		return "Sent. " + name + " reads it between its tool calls, and its report answers it.", nil
	}

	closed := r.closed
	r.mutex.Unlock()

	if closed {
		return "", errSubagentClosed
	}

	subagent, err := r.subagents.Get(ctx, name)
	if err != nil {
		return "", err
	}

	effort, err := r.effort(subagent)
	if err != nil {
		return "", err
	}

	err = r.memory.Settle(ctx)
	if err != nil {
		return "", fmt.Errorf("wait for the summaries: %w", err)
	}

	view, err := r.layout.Split(r.memory.ViewLines(nil))
	if err != nil {
		return "", err
	}

	_, err = subagent.Append("user", message)
	if err == nil {
		err = subagent.Flush(ctx)
	}

	if err != nil {
		return "", err
	}

	err = r.start(ctx, &SubagentRun{
		subagent: subagent,
		view:     view,
		effort:   effort,
	})
	if err != nil {
		return "", err
	}

	return "Sent. " + name + "'s reply will reach you as a message.", nil
}

// Stop ends the run of the subagent name and tells if it ran. The chat gets the
// note "Stopped by the user: NAME." under the mutex, so the note comes before
// the report of the run.
func (r *SubagentRuns) Stop(name string) (bool, error) {
	r.mutex.Lock()
	defer r.mutex.Unlock()

	run, found := r.running[name]
	if !found {
		return false, nil
	}

	err := r.note("Stopped by the user: " + name + ".")
	if err != nil {
		return true, err
	}

	run.stopped = true
	run.cancel()

	return true, nil
}

// Resume goes on with the runs that a stop of the daemon cut, as work.json
// names them. The chat gets the note "The daemon restarted, cutting NAMES;
// nothing was lost: go on.", and each cut subagent gets the same text as a
// message of Tell. A subagent that cannot go on gets a failed report.
func (r *SubagentRuns) Resume(ctx context.Context) error {
	names, err := r.load()
	if err != nil || len(names) == 0 {
		return err
	}

	text := "The daemon restarted, cutting " + strings.Join(names, ", ") + "; nothing was lost: go on."
	err = r.note(text)
	if err != nil {
		return err
	}

	for _, name := range names {
		_, err = r.Tell(ctx, name, text)
		if err != nil {
			r.logger.Printf("subagent %s lost at restart: %v", name, err)
			r.report(name, subagentReport(name, []string{"failed: " + err.Error()}), subagentFailed)
		}
	}

	// A subagent that cannot go on does not run, so work.json no longer
	// names it, and the next start does not try it again.
	r.mutex.Lock()
	defer r.mutex.Unlock()

	return r.save()
}

// Close ends every run and waits for them. No subagent starts after Close.
func (r *SubagentRuns) Close() {
	r.mutex.Lock()

	r.closed = true
	for _, run := range r.running {
		run.cancel()
	}

	r.mutex.Unlock()

	r.workers.Wait()
}

// create makes a new subagent with its note, its task, and its work directory,
// and starts its run.
func (r *SubagentRuns) create(ctx context.Context, note, task string, view []string, effort string) (string, error) {
	subagent, err := r.subagents.Create(ctx)
	if err != nil {
		return "", err
	}

	for _, message := range [][2]string{{"note", note}, {"user", task}} {
		_, err = subagent.Append(message[0], message[1])
		if err != nil {
			return "", err
		}
	}

	err = subagent.Flush(ctx)
	if err != nil {
		return "", err
	}

	err = os.MkdirAll(subagent.WorkDir(), 0o700)
	if err != nil {
		return "", fmt.Errorf("create work directory: %w", err)
	}

	return subagent.name, r.start(ctx, &SubagentRun{
		subagent: subagent,
		view:     view,
		effort:   effort,
	})
}

// effort returns the effort of subagent from the note at the start of its log:
// the effort of the agent, or the effort that the note names.
func (r *SubagentRuns) effort(subagent *Subagent) (string, error) {
	note, err := subagent.First()
	if err != nil {
		return "", err
	}

	effort, own := strings.CutPrefix(note.Text, subagentNote+subagentNoteEffort)
	switch {
	case note.Kind != "note":
	case own:
		return effort, nil
	case note.Text == subagentNote:
		return r.agent.config.Effort, nil
	}

	return "", fmt.Errorf("the log of %s does not start with a subagent note", subagent.name)
}

// start runs run in the background and logs its start. Its context keeps the
// values of ctx, but only Stop and Close end it.
func (r *SubagentRuns) start(ctx context.Context, run *SubagentRun) error {
	ctx, run.cancel = context.WithCancel(context.WithoutCancel(ctx))

	r.mutex.Lock()

	_, found := r.running[run.subagent.name]
	if r.closed || found {
		r.mutex.Unlock()
		run.cancel()

		if found {
			return fmt.Errorf("%s runs already", run.subagent.name)
		}

		return errSubagentClosed
	}

	r.running[run.subagent.name] = run
	err := r.save()
	if err != nil {
		delete(r.running, run.subagent.name)
		r.mutex.Unlock()
		run.cancel()

		return err
	}

	r.workers.Add(1)
	r.mutex.Unlock()

	run.started = r.subagents.clock()
	r.logger.Printf("subagent %s started", run.subagent.name)
	r.notify(Event{
		Kind: "subagent",
		Text: run.subagent.name,
	})

	go r.run(ctx, run)

	return nil
}

// load reads the names of work.json. A missing file names none.
func (r *SubagentRuns) load() ([]string, error) {
	data, err := os.ReadFile(r.workPath())
	if errors.Is(err, os.ErrNotExist) {
		return nil, nil
	}

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

	var file SubagentWorkFile

	err = json.Unmarshal(data, &file)
	if err != nil {
		return nil, fmt.Errorf("decode running subagents: %w", err)
	}

	return file.Running, nil
}

// save writes the names of the running subagents to work.json. The caller
// holds the mutex.
func (r *SubagentRuns) save() error {
	file := SubagentWorkFile{
		Running: append([]string{}, slices.Sorted(maps.Keys(r.running))...),
	}

	data, err := json.Marshal(file)
	if err != nil {
		return fmt.Errorf("encode running subagents: %w", err)
	}

	err = writeFileAtomic(r.workPath(), append(data, '\n'))
	if err != nil {
		return fmt.Errorf("save running subagents: %w", err)
	}

	return nil
}

func (r *SubagentRuns) workPath() string {
	return filepath.Join(r.agent.dir, subagentWorkFileName)
}

// run runs the chains of run and reports and logs its end with the length of
// the run, unless Close ended it. A chain follows while messages wait after the final answer of the chain before
// it, and no chain failed. A chain that Stop ends gives the reply "stopped".
func (r *SubagentRuns) run(ctx context.Context, run *SubagentRun) {
	defer r.workers.Done()
	defer run.cancel()

	var (
		replies []string
		failure error
	)

	stopped := false
	status := subagentFinished
	for more := true; more; {
		reply, err := r.chain(ctx, run)

		r.mutex.Lock()

		stopped = run.stopped
		switch {
		case err != nil && stopped:
			reply = "stopped"
		case err != nil:
			reply = "failed: " + err.Error()
			status = subagentFailed
			failure = err
		}

		more = err == nil && ctx.Err() == nil && len(run.pending) > 0
		run.pending = nil

		var saveErr error

		if !more {
			delete(r.running, run.subagent.name)

			if !r.closed {
				saveErr = r.save()
			}
		}

		r.mutex.Unlock()

		if saveErr != nil {
			r.fail(saveErr)
		}

		replies = append(replies, reply)
	}

	if ctx.Err() != nil && !stopped {
		return
	}

	if stopped {
		status = subagentStopped
	}

	length := durationText(r.subagents.clock().Sub(run.started))
	switch status {
	case subagentStopped:
		r.logger.Printf("subagent %s stopped after %s", run.subagent.name, length)
	case subagentFailed:
		r.logger.Printf("subagent %s failed after %s: %v", run.subagent.name, length, failure)
	default:
		r.logger.Printf("subagent %s done after %s", run.subagent.name, length)
	}

	r.report(run.subagent.name, subagentReport(run.subagent.name, replies), status)
}

// chain runs one request chain of run and returns its final answer.
func (r *SubagentRuns) chain(ctx context.Context, run *SubagentRun) (string, error) {
	instructions, err := r.agent.SubagentPrompt()
	if err != nil {
		return "", err
	}

	log, err := run.subagent.Show()
	if err != nil {
		return "", err
	}

	input := make([]any, 0, len(run.view)+2)
	for _, text := range run.view {
		input = append(input, modelUserMessage(text))
	}

	input = append(input, modelUserMessage(r.state()), modelUserMessage(log))
	chain := &Chain{
		client: r.client,
		tools: &Toolbox{
			log:       run.subagent,
			chat:      r.memory,
			subagents: r.subagents,
			workdir:   run.subagent.WorkDir(),
		},
		request: ModelRequest{
			Model:        r.agent.config.Model,
			Effort:       run.effort,
			Instructions: instructions,
			Tools:        promptSubagentTools(),
			Agent:        run.subagent.name,
		},
		take: func() []Message {
			return r.take(run)
		},
	}

	return chain.Run(ctx, input)
}

// take returns the messages of Tell that wait for a request of run, and
// removes them.
func (r *SubagentRuns) take(run *SubagentRun) []Message {
	r.mutex.Lock()
	defer r.mutex.Unlock()

	messages := run.pending
	run.pending = nil

	return messages
}

// SubagentRun is one run of a subagent: the view that its requests get, its
// effort, the end of its context, the messages of Tell that wait for a request,
// whether Stop ended it, and the time it started. The mutex of SubagentRuns protects the messages
// and the stop.
type SubagentRun struct {
	subagent *Subagent
	view     []string
	effort   string
	cancel   context.CancelFunc
	pending  []Message
	stopped  bool
	started  time.Time
}

// SubagentWorkFile is the content of work.json.
type SubagentWorkFile struct {
	Running []string `json:"running"`
}

// subagentReport returns the report of the subagent name with its replies: the
// name in brackets, a new line, the replies, and the zoom that gives its whole
// chat.
func subagentReport(name string, replies []string) string {
	return "[" + name + "]\n" + strings.Join(replies, "\n\n") + "\n\nFull chat: zoom(\"" + name + "\")"
}