// Package execlog persists incremental command output for an execution and
// announces it on the event stream.
//
// It exists as its own package because both SSH execution paths need it —
// internal/mcp (the agent's auto-run windows) and internal/httpapi (the
// post-approval actuator). Those two already carry near-identical copies of
// sshExec, and every bug found in this area so far has been a case of the two
// copies drifting apart; one shared sink is the cheap way not to repeat that.
package execlog

import (
	"context"
	"log/slog"
	"sync"
	"time"

	"github.com/dtoro/oikos/internal/db"
	"github.com/dtoro/oikos/internal/db/sqlcgen"
	"github.com/dtoro/oikos/internal/observability"
	"github.com/google/uuid"
)

// eventInterval throttles execution.output events. Chunks are persisted as
// they arrive, but a chatty command (apt, a long build) can produce hundreds
// per second and the SSE broker drops events for slow subscribers — flooding
// it would push out the signal.* and approval.* events that actually need to
// arrive. The event is only a "there is more output" ping; subscribers re-read
// the rows.
const eventInterval = time.Second

// Sink receives output chunks as they arrive from a remote command.
type Sink func(stream string, chunk []byte)

// New returns a Sink that writes chunks to execution_logs and emits a
// throttled execution.output event, plus a Flush to call when the command
// finishes.
//
// The returned Sink is safe for concurrent use: stdout and stderr are written
// from separate goroutines.
func New(ctx context.Context, pool *db.Pool, execID uuid.UUID, correlationID string) (Sink, func()) {
	var (
		mu        sync.Mutex
		seq       int
		lastEvent time.Time
		pending   bool
	)

	emit := func() {
		if err := observability.Event(ctx, sqlcgen.New(pool), "execution.output", &execID,
			"info", "actuator", correlationID, map[string]any{"execution_id": execID.String()}); err != nil {
			slog.Debug("execlog: emit output event", "error", err, "execution_id", execID)
		}
	}

	sink := func(stream string, chunk []byte) {
		if len(chunk) == 0 {
			return
		}
		mu.Lock()
		seq++
		n := seq
		mu.Unlock()

		// A failed log write must never fail the command: this is observability,
		// and the authoritative output still lands in executions.result at the
		// end. Log and carry on.
		if _, err := pool.Exec(ctx,
			`INSERT INTO execution_logs (execution_id, seq, stream, chunk)
			 VALUES ($1, $2, $3, $4)`,
			execID, n, stream, string(chunk)); err != nil {
			slog.Debug("execlog: persist chunk", "error", err, "execution_id", execID)
			return
		}

		mu.Lock()
		due := time.Since(lastEvent) >= eventInterval
		if due {
			lastEvent = time.Now()
			pending = false
		} else {
			pending = true
		}
		mu.Unlock()

		if due {
			emit()
		}
	}

	// Flush emits a final event when output arrived inside the throttle window,
	// so the last few lines of a short command are not left unannounced.
	flush := func() {
		mu.Lock()
		due := pending
		pending = false
		mu.Unlock()
		if due {
			emit()
		}
	}

	return sink, flush
}

// Read returns an execution's persisted output in order.
func Read(ctx context.Context, pool *db.Pool, execID uuid.UUID, limit int) ([]Chunk, error) {
	if limit <= 0 {
		limit = 1000
	}
	rows, err := pool.Query(ctx,
		`SELECT seq, stream, chunk, ts FROM execution_logs
		 WHERE execution_id = $1 ORDER BY seq LIMIT $2`, execID, limit)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var out []Chunk
	for rows.Next() {
		var c Chunk
		if err := rows.Scan(&c.Seq, &c.Stream, &c.Chunk, &c.TS); err != nil {
			return nil, err
		}
		out = append(out, c)
	}
	return out, rows.Err()
}

// Chunk is one persisted slice of command output.
type Chunk struct {
	Seq    int       `json:"seq"`
	Stream string    `json:"stream"`
	Chunk  string    `json:"chunk"`
	TS     time.Time `json:"ts"`
}