package main

import (
	"bufio"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log"
	"os"
	"path/filepath"
	"strconv"
	"time"
)

const (
	// probeName is the agent name of a probe run. The cache key comes from
	// it.
	probeName = "Probe"

	// probeCallLimit is the most model calls of a probe run.
	probeCallLimit = 660
)

// probe runs "onechat probe LOG COUNT [BUILDS]". It appends the first COUNT
// messages of LOG, one JSON object {kind, text} per line, to a new chat in
// probe/ in the data directory, and builds its tree with the real compactor.
// Before each user message it waits for the builds, as a turn does. It stops at
// the first failed call, after probeCallLimit calls, or when the used percent
// of a quota window grows by more than buildQuotaLimit points. At the end it
// reports the calls, the time per call, the calls at once, the cached share,
// the quota, the retries, and the line sizes. BUILDS, from 1 to buildMax,
// limits the builds that call the model at once in this run only. The core
// still queues up to buildMax builds. The run holds the lock of the token file,
// so it does not run while the daemon runs.
func probe(ctx context.Context, args []string, out io.Writer) (err error) {
	if len(args) != 2 && len(args) != 3 {
		return errors.New("usage: onechat probe LOG COUNT [BUILDS]")
	}

	count, err := strconv.Atoi(args[1])
	if err != nil {
		return fmt.Errorf("parse probe count: %w", err)
	}

	if count <= 0 {
		return fmt.Errorf("COUNT %q is not a positive number", args[1])
	}

	builds := buildMax
	if len(args) == 3 {
		builds, err = strconv.Atoi(args[2])
		if err != nil {
			return fmt.Errorf("parse probe builds: %w", err)
		}

		if builds < 1 || builds > buildMax {
			return fmt.Errorf("BUILDS %q is not a number from 1 to %d", args[2], buildMax)
		}
	}

	entries, err := probeReadLog(args[0], count)
	if err != nil {
		return fmt.Errorf("read probe input: %w", err)
	}

	dir, err := dataDir()
	if err != nil {
		return fmt.Errorf("find probe data directory: %w", err)
	}

	config, err := loadConfig(dir)
	if err != nil {
		return fmt.Errorf("load probe configuration: %w", err)
	}

	tokens, err := lockTokens(dir)
	if err != nil {
		return fmt.Errorf("lock probe tokens: %w", err)
	}

	defer func() {
		closeErr := tokens.Close()
		if closeErr != nil {
			err = errors.Join(err, fmt.Errorf("close probe token lock: %w", closeErr))
		}
	}()

	address, auth, err := modelEndpoint(config, dir)
	if err != nil {
		return fmt.Errorf("select probe endpoint: %w", err)
	}

	root := filepath.Join(dir, "probe", time.Now().Format("20060102-150405"))
	err = os.MkdirAll(root, 0o700)
	if err != nil {
		return fmt.Errorf("create probe directory: %w", err)
	}

	usagePath := filepath.Join(root, "usage.jsonl")
	client := newModelClient(address, auth, "onechat-"+probeName, usagePath)
	client.LimitCalls(probeCallLimit)

	summarizer := ProbeSlotSummarizer{
		inner: newCompactor(client, probePrompt, config.Compactor),
		slots: make(chan struct{}, builds),
	}

	// The report of the probe counts the failed calls, so the lines of the
	// failed builds are not needed.
	memory, err := openMemory(ctx, root, time.Now, summarizer, log.New(io.Discard, "", 0))
	if err != nil {
		return fmt.Errorf("open probe memory: %w", err)
	}

	_, err = fmt.Fprintf(out, "probe: %d messages into %s with %s at %s effort, %d builds at once\n", len(entries), root, config.Compactor.Model, config.Compactor.Effort, builds)
	if err != nil {
		return fmt.Errorf("write probe header: %w", errors.Join(err, memory.Close()))
	}

	run := BuildRun{
		memory:    memory,
		client:    client,
		usagePath: usagePath,
	}

	appended, stop := run.Run(ctx, entries)
	sizes, err := memory.buildModelLines()
	err = errors.Join(err, memory.Close())
	if err != nil {
		return fmt.Errorf("finish probe memory: %w", err)
	}

	records, err := buildReadUsage(usagePath)
	if err != nil {
		return fmt.Errorf("read probe usage: %w", err)
	}

	err = buildWriteReport(out, appended, stop, records, sizes)
	if err != nil {
		return fmt.Errorf("write probe report: %w", err)
	}

	return nil
}

// ProbeSlotSummarizer lets at most cap(slots) builds call inner at once. A
// build past the limit waits for a slot.
type ProbeSlotSummarizer struct {
	inner Summarizer
	slots chan struct{}
}

// Summarize waits for a slot and builds the node with inner.
func (s ProbeSlotSummarizer) Summarize(ctx context.Context, task Task) (string, error) {
	select {
	case s.slots <- struct{}{}:
	case <-ctx.Done():
		return "", ctx.Err()
	}

	defer func() {
		<-s.slots
	}()

	return s.inner.Summarize(ctx, task)
}

// probeReadLog reads the first count messages of the probe log at path. Source
// dates are ignored because a probe uses its own clock.
func probeReadLog(path string, count int) (entries []DatedMessage, err error) {
	file, err := os.Open(path)
	if err != nil {
		return nil, fmt.Errorf("open probe log: %w", err)
	}

	defer func() {
		closeErr := file.Close()
		if closeErr != nil {
			err = errors.Join(err, fmt.Errorf("close probe log: %w", closeErr))
		}
	}()

	scanner := bufio.NewScanner(file)
	scanner.Buffer(make([]byte, 64*1024), buildLineBytes)

	for len(entries) < count && scanner.Scan() {
		var entry DatedMessage

		err = json.Unmarshal(scanner.Bytes(), &entry)
		if err != nil {
			return nil, fmt.Errorf("probe log line %d: %w", len(entries)+1, err)
		}

		entry.Date = ""
		entries = append(entries, entry)
	}

	err = scanner.Err()
	if err != nil {
		return nil, fmt.Errorf("read probe log: %w", err)
	}

	if len(entries) < count {
		return nil, fmt.Errorf("probe log has %d messages, fewer than %d", len(entries), count)
	}

	return entries, nil
}

// probePrompt returns the system prompt of a probe run: the prompt of the agent
// probeName, without instructions and with a fixed instructions file path.
func probePrompt() (string, error) {
	return prompt(probeName, "/PROBE/instructions.md", ""), nil
}