package ws

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"log/slog"
	stdhttp "net/http"
	"strings"
	"time"

	"github.com/coder/websocket"

	"gitea.dcglab.co.uk/steve/restic-manager/internal/api"
	"gitea.dcglab.co.uk/steve/restic-manager/internal/auth"
	"gitea.dcglab.co.uk/steve/restic-manager/internal/store"
)

// HandlerDeps is the set of collaborators the agent WS handler needs.
type HandlerDeps struct {
	Hub    *Hub
	Store  *store.Store
	JobHub *JobHub
	// OnHello is called once per successful hello, after the host row
	// has been touched and the conn registered. Used by the HTTP
	// layer to push host_credentials down as a config.update before
	// the agent starts asking for jobs. Optional; nil = no-op.
	OnHello func(ctx context.Context, hostID string, conn *Conn)
}

// AgentHandler is the http.Handler that owns /ws/agent. Agents
// authenticate with `Authorization: Bearer <token>` (issued at
// enrollment) before the WS upgrade.
//
// Lifecycle:
//   1. Bearer token resolves to a Host row.
//   2. Upgrade.
//   3. First message must be `hello`; protocol_version checked here.
//   4. Loop: read messages, dispatch by type. Heartbeats touch the
//      host row; job/log/repo messages forward to the relevant
//      handlers (TODO: lands with P1-18 onward).
//   5. On Read error or context cancel, mark host offline, unregister
//      from the hub.
func AgentHandler(deps HandlerDeps) stdhttp.Handler {
	return stdhttp.HandlerFunc(func(w stdhttp.ResponseWriter, r *stdhttp.Request) {
		host, ok := authenticateAgent(r, deps.Store)
		if !ok {
			stdhttp.Error(w, "unauthorized", stdhttp.StatusUnauthorized)
			return
		}

		conn, err := websocket.Accept(w, r, &websocket.AcceptOptions{
			InsecureSkipVerify: true, // Origin checks are pointless for an agent CLI.
		})
		if err != nil {
			slog.Warn("ws accept failed", "err", err, "host_id", host.ID)
			return
		}

		c := NewConn(host.ID, conn)
		// Keep agents alive across NAT boxes; coder/websocket
		// auto-pings under the hood when configured. The default 60s
		// works fine for a 30s heartbeat cadence.

		runAgentLoop(r.Context(), c, host.ID, deps)
	})
}

// authenticateAgent returns the host that owns the bearer token in
// the request, or (nil, false) if anything is amiss. The same
// "false" path is used for missing header, malformed header, unknown
// token — no information leak about why.
func authenticateAgent(r *stdhttp.Request, st *store.Store) (*store.Host, bool) {
	hdr := r.Header.Get("Authorization")
	const prefix = "Bearer "
	if !strings.HasPrefix(hdr, prefix) {
		return nil, false
	}
	token := strings.TrimPrefix(hdr, prefix)
	if token == "" {
		return nil, false
	}
	h, err := st.LookupHostByAgentToken(r.Context(), auth.HashToken(token))
	if err != nil {
		return nil, false
	}
	return h, true
}

// runAgentLoop is the per-connection driver. Returns when the socket
// is closed for any reason. It owns the hub registration: register on
// hello acceptance, unregister on exit.
func runAgentLoop(ctx context.Context, c *Conn, hostID string, deps HandlerDeps) {
	// Stage 1: hello (with a tight deadline).
	helloCtx, cancel := context.WithTimeout(ctx, 10*time.Second)
	hello, err := c.Read(helloCtx)
	cancel()
	if err != nil {
		slog.Info("ws hello read failed", "host_id", hostID, "err", err)
		_ = c.Close()
		return
	}
	if hello.Type != api.MsgHello {
		c.SendError(ctx, api.ErrBadRequest, "first message must be hello", "")
		return
	}
	var helloPayload api.HelloPayload
	if err := hello.UnmarshalPayload(&helloPayload); err != nil {
		c.SendError(ctx, api.ErrBadRequest, "malformed hello payload", "")
		return
	}
	if helloPayload.ProtocolVersion < api.MinAgentProtocolVersion {
		c.SendError(ctx, api.ErrProtocolTooOld,
			fmt.Sprintf("agent protocol_version %d below minimum %d",
				helloPayload.ProtocolVersion, api.MinAgentProtocolVersion),
			"https://restic-manager.example/docs/upgrade")
		return
	}
	if helloPayload.ProtocolVersion > api.CurrentProtocolVersion {
		// Forward-compat is fine — newer agents talking to older
		// servers should accept their lower version. Just log it.
		slog.Info("ws agent newer than server",
			"host_id", hostID,
			"agent_proto", helloPayload.ProtocolVersion,
			"server_proto", api.CurrentProtocolVersion)
	}

	now := time.Now().UTC()
	if err := deps.Store.MarkHostHello(ctx, hostID,
		helloPayload.AgentVersion, helloPayload.ResticVersion,
		helloPayload.ProtocolVersion, now); err != nil {
		slog.Error("ws mark host hello failed", "host_id", hostID, "err", err)
	}

	deps.Hub.Register(hostID, c)
	defer deps.Hub.Unregister(hostID, c)
	defer func() { _ = c.Close() }()

	slog.Info("ws agent connected",
		"host_id", hostID,
		"agent_version", helloPayload.AgentVersion,
		"protocol_version", helloPayload.ProtocolVersion)

	if deps.OnHello != nil {
		// Run synchronously so the config.update lands before any
		// command.run an operator might race in.
		deps.OnHello(ctx, hostID, c)
	}

	// Stage 2: main read loop.
	for {
		env, err := c.Read(ctx)
		if err != nil {
			if !errors.Is(err, context.Canceled) {
				slog.Info("ws agent read loop ended", "host_id", hostID, "err", err)
			}
			return
		}
		dispatchAgentMessage(ctx, c, hostID, env, deps)
	}
}

// dispatchAgentMessage routes a single envelope to its handler.
func dispatchAgentMessage(ctx context.Context, c *Conn, hostID string, env api.Envelope, deps HandlerDeps) {
	switch env.Type {
	case api.MsgHeartbeat:
		_ = deps.Store.TouchHost(ctx, hostID, time.Now().UTC())

	case api.MsgJobStarted:
		var p api.JobStartedPayload
		_ = env.UnmarshalPayload(&p)
		if err := deps.Store.MarkJobStarted(ctx, p.JobID, p.StartedAt); err != nil {
			slog.Warn("ws: mark job started", "job_id", p.JobID, "err", err)
		}
		if deps.JobHub != nil {
			deps.JobHub.Broadcast(p.JobID, env)
		}

	case api.MsgJobProgress:
		// Progress ticks aren't persisted (1Hz × every job × every
		// path-walk would dwarf the rest of the DB). The live UI
		// subscribes to JobHub and gets them in real time; once a
		// job finishes the final summary lands via job.finished.
		var p api.JobProgressPayload
		_ = env.UnmarshalPayload(&p)
		if deps.JobHub != nil {
			deps.JobHub.Broadcast(p.JobID, env)
		}

	case api.MsgJobFinished:
		var p api.JobFinishedPayload
		_ = env.UnmarshalPayload(&p)
		errMsg := p.Error
		if err := deps.Store.MarkJobFinished(ctx, p.JobID,
			string(p.Status), p.ExitCode, p.Stats, errMsg, p.FinishedAt); err != nil {
			slog.Warn("ws: mark job finished", "job_id", p.JobID, "err", err)
		}
		if deps.JobHub != nil {
			deps.JobHub.Broadcast(p.JobID, env)
		}

	case api.MsgLogStream:
		var p api.LogStreamLine
		_ = env.UnmarshalPayload(&p)
		if err := deps.Store.AppendJobLog(ctx, p.JobID, p.Seq, p.TS,
			string(p.Stream), p.Payload); err != nil {
			slog.Warn("ws: append job log", "job_id", p.JobID, "err", err)
		}
		if deps.JobHub != nil {
			deps.JobHub.Broadcast(p.JobID, env)
		}

	case api.MsgSnapshotsRpt:
		var p api.SnapshotsReportPayload
		if err := env.UnmarshalPayload(&p); err != nil {
			slog.Warn("ws: bad snapshots.report payload", "host_id", hostID, "err", err)
			break
		}
		snaps := make([]store.Snapshot, len(p.Snapshots))
		for i, s := range p.Snapshots {
			snaps[i] = store.Snapshot{
				ID:        s.ID,
				ShortID:   s.ShortID,
				Time:      s.Time,
				Hostname:  s.Hostname,
				Paths:     s.Paths,
				Tags:      s.Tags,
				SizeBytes: s.SizeBytes,
				FileCount: s.FileCount,
			}
		}
		if err := deps.Store.ReplaceHostSnapshots(ctx, hostID, snaps, time.Now().UTC()); err != nil {
			slog.Warn("ws: replace snapshots", "host_id", hostID, "err", err)
		} else {
			slog.Info("ws: snapshots refreshed", "host_id", hostID, "count", len(snaps))
		}

	case api.MsgRepoStats, api.MsgScheduleAck, api.MsgCommandResult:
		// TODO(P2): persist these projections.
		slog.Debug("ws msg not yet handled", "type", env.Type, "host_id", hostID)

	case api.MsgError:
		var ep api.ErrorPayload
		_ = env.UnmarshalPayload(&ep)
		slog.Warn("ws agent reported error", "host_id", hostID,
			"code", string(ep.Code), "message", ep.Message)

	default:
		slog.Warn("ws unknown message type from agent",
			"type", env.Type, "host_id", hostID)
	}
}

// MinHeartbeatInterval is a sanity floor — any agent reporting
// heartbeats more often than this is misbehaving. (Spec says 30s.)
const MinHeartbeatInterval = 5 * time.Second

// suppress unused-import false-positives if json drops out later
var _ = json.Marshal