package api

import (
	"bufio"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"net/http"
	"regexp"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/go-chi/chi/v5"

	"github.com/alexei/tinyforge/internal/store"
)

// Limits and constants for the log endpoints.
const (
	defaultLogTail = 200
	maxLogTail     = 5000
	maxJSONLogBytes = 4 << 20 // 4 MiB cap for non-streaming log responses
	maxLogLineBytes = 1 << 20 // 1 MiB max line length for the bufio.Scanner
	logHeartbeatPeriod = 20 * time.Second
)

// ANSI escape sequence patterns. Stripped from streamed log lines so a
// hostile container cannot inject terminal control sequences (cursor moves,
// hyperlink escapes, screen clears) into operator displays or pasted output.
var (
	ansiCSIPattern = regexp.MustCompile(`\x1b\[[0-9;?]*[ -/]*[@-~]`)
	ansiOSCPattern = regexp.MustCompile(`\x1b\][^\x07\x1b]*(?:\x07|\x1b\\)`)
	ctlBytePattern = regexp.MustCompile(`[\x00-\x08\x0b-\x1a\x1c-\x1f\x7f]`)
)

// listProjectImages handles GET /api/projects/{id}/images.
// Returns all local Docker images matching the project's image reference.
func (s *Server) listProjectImages(w http.ResponseWriter, r *http.Request) {
	id := chi.URLParam(r, "id")

	project, err := s.store.GetProjectByID(id)
	if err != nil {
		if errors.Is(err, store.ErrNotFound) {
			respondNotFound(w, "project")
			return
		}
		slog.Error("failed to get project", "error", err)
		respondError(w, http.StatusInternalServerError, "internal server error")
		return
	}

	if s.docker == nil || project.Image == "" {
		respondJSON(w, http.StatusOK, []any{})
		return
	}

	images, err := s.docker.ListImagesByRef(r.Context(), project.Image)
	if err != nil {
		slog.Warn("list project images", "project", project.Name, "error", err)
		respondJSON(w, http.StatusOK, []any{})
		return
	}

	respondJSON(w, http.StatusOK, images)
}

// streamContainerLogs handles GET /api/projects/{id}/stages/{stage}/instances/{iid}/logs.
// Streams container logs via SSE. {iid} is the container row ID. Ownership is
// verified by joining through workload + stage so an attacker cannot stream
// logs for a foreign container by guessing IDs under the wrong project URL.
func (s *Server) streamContainerLogs(w http.ResponseWriter, r *http.Request) {
	projectID := chi.URLParam(r, "id")
	stageID := chi.URLParam(r, "stage")
	containerRowID := chi.URLParam(r, "iid")

	c, err := s.store.GetContainerByID(containerRowID)
	if err != nil {
		if errors.Is(err, store.ErrNotFound) {
			respondNotFound(w, "container")
			return
		}
		slog.Error("failed to get container", "error", err)
		respondError(w, http.StatusInternalServerError, "internal server error")
		return
	}

	wl, err := s.store.GetWorkloadByID(c.WorkloadID)
	if err != nil {
		respondNotFound(w, "container")
		return
	}
	stage, err := s.store.GetStageByID(stageID)
	if err != nil || stage.ProjectID != projectID {
		respondNotFound(w, "container")
		return
	}
	if wl.Kind != string(store.WorkloadKindProject) || wl.RefID != projectID || c.Role != stage.Name {
		respondNotFound(w, "container")
		return
	}

	if c.ContainerID == "" {
		respondError(w, http.StatusBadRequest, "container row has no docker container bound")
		return
	}

	s.streamLogsForContainer(w, r, c.ContainerID)
}

// streamLogsForContainer streams logs for an arbitrary container ID using the
// shared SSE/JSON dual-mode pattern. Owner-specific handlers (instance, site)
// should validate ownership and then delegate here.
func (s *Server) streamLogsForContainer(w http.ResponseWriter, r *http.Request, containerID string) {
	if s.docker == nil {
		respondError(w, http.StatusServiceUnavailable, "Docker is not available")
		return
	}

	tail := parseTailParam(r.URL.Query().Get("tail"))
	follow := r.URL.Query().Get("follow") == "true"

	// Check if client accepts SSE.
	accept := r.Header.Get("Accept")
	isSSE := strings.Contains(accept, "text/event-stream")

	logReader, err := s.docker.ContainerLogs(r.Context(), containerID, follow && isSSE, tail)
	if err != nil {
		slog.Error("failed to get container logs", "container", containerID, "error", err)
		respondError(w, http.StatusInternalServerError, "failed to get container logs")
		return
	}
	defer logReader.Close()

	if !isSSE {
		// JSON mode: cap the total bytes read so a chatty container with
		// tail=large cannot exhaust server memory.
		scanner := bufio.NewScanner(io.LimitReader(logReader, maxJSONLogBytes))
		scanner.Buffer(make([]byte, 0, 64*1024), maxLogLineBytes)
		var lines []string
		for scanner.Scan() {
			line := sanitizeDockerLogLine(scanner.Text())
			if line != "" {
				lines = append(lines, line)
			}
		}
		if lines == nil {
			lines = []string{}
		}
		respondJSON(w, http.StatusOK, lines)
		return
	}

	// SSE mode: stream lines as they arrive.
	release, ok := acquireSSESlot(w, s.sseGate)
	if !ok {
		return
	}
	defer release()

	flusher, ok := w.(http.Flusher)
	if !ok {
		respondError(w, http.StatusInternalServerError, "streaming not supported")
		return
	}

	w.Header().Set("Content-Type", "text/event-stream")
	w.Header().Set("Cache-Control", "no-cache")
	w.Header().Set("Connection", "keep-alive")

	// Heartbeat keeps the connection warm through proxies that close idle
	// streams. Sent as an SSE comment which the EventSource API ignores.
	heartbeat := time.NewTicker(logHeartbeatPeriod)
	defer heartbeat.Stop()
	heartbeatDone := make(chan struct{})
	defer close(heartbeatDone)
	var hbMu sync.Mutex
	go func() {
		for {
			select {
			case <-heartbeat.C:
				hbMu.Lock()
				_, _ = io.WriteString(w, ": ping\n\n")
				flusher.Flush()
				hbMu.Unlock()
			case <-heartbeatDone:
				return
			case <-r.Context().Done():
				return
			}
		}
	}()

	scanner := bufio.NewScanner(logReader)
	scanner.Buffer(make([]byte, 0, 64*1024), maxLogLineBytes)
	for scanner.Scan() {
		line := sanitizeDockerLogLine(scanner.Text())
		if line == "" {
			continue
		}

		data, _ := json.Marshal(map[string]string{"line": line})
		hbMu.Lock()
		fmt.Fprintf(w, "data: %s\n\n", data)
		flusher.Flush()
		hbMu.Unlock()

		// Check if client disconnected.
		select {
		case <-r.Context().Done():
			return
		default:
		}
	}
}

// parseTailParam validates and clamps the ?tail= query value. Empty/invalid
// inputs fall back to the default; values above the cap are clamped down.
// "all" is rejected — letting the caller request unbounded log history is a
// trivial DoS vector.
func parseTailParam(raw string) string {
	if raw == "" {
		return strconv.Itoa(defaultLogTail)
	}
	n, err := strconv.Atoi(raw)
	if err != nil || n <= 0 {
		return strconv.Itoa(defaultLogTail)
	}
	if n > maxLogTail {
		n = maxLogTail
	}
	return strconv.Itoa(n)
}

// sanitizeDockerLogLine strips the Docker log stream header (8-byte prefix)
// that Docker adds to non-TTY container logs, and removes terminal control
// sequences so a hostile container cannot inject ANSI escapes that hijack an
// operator's terminal when log output is pasted or rendered raw.
func sanitizeDockerLogLine(line string) string {
	// Docker multiplexed stream: first 8 bytes are header (stream type + size).
	// If the line starts with a non-printable byte followed by 0x00 0x00 0x00, strip 8 bytes.
	if len(line) > 8 && (line[0] == 1 || line[0] == 2) && line[1] == 0 && line[2] == 0 && line[3] == 0 {
		line = line[8:]
	}
	line = ansiOSCPattern.ReplaceAllString(line, "")
	line = ansiCSIPattern.ReplaceAllString(line, "")
	line = ctlBytePattern.ReplaceAllString(line, "")
	return line
}

// buildActiveImagesSet returns the set of "image:tag" strings currently used
// by any container, computed in a single DB pass against the normalized
// containers index. Returning an error (rather than swallowing) prevents
// prune logic from treating a transient DB failure as "nothing is active".
func buildActiveImagesSet(st *store.Store, projects []store.Project) (map[string]bool, error) {
	// `projects` is unused now — kept in the signature for back-compat with
	// callers that already happen to have the slice. The image_ref column
	// holds the full "image:tag" string written by the deployer.
	_ = projects
	containers, err := st.ListContainers(store.ContainerFilter{})
	if err != nil {
		return nil, fmt.Errorf("list containers: %w", err)
	}
	active := make(map[string]bool, len(containers))
	for _, c := range containers {
		if c.ImageRef == "" {
			continue
		}
		active[c.ImageRef] = true
	}
	return active, nil
}

// unusedImageStats handles GET /api/docker/unused-images.
// Returns the total size of unused project images and whether the threshold is exceeded.
func (s *Server) unusedImageStats(w http.ResponseWriter, r *http.Request) {
	if s.docker == nil {
		respondJSON(w, http.StatusOK, map[string]any{
			"total_size_mb": 0, "count": 0, "threshold_mb": 0, "exceeded": false,
		})
		return
	}

	settings, err := s.store.GetSettings()
	if err != nil {
		slog.Error("unused images: get settings", "error", err)
		respondError(w, http.StatusInternalServerError, "internal server error")
		return
	}

	projects, err := s.store.GetAllProjects()
	if err != nil {
		slog.Error("unused images: list projects", "error", err)
		respondError(w, http.StatusInternalServerError, "internal server error")
		return
	}

	// Build set of active image refs in one DB pass instead of N×K queries.
	// A flaky read here previously masqueraded as "no images are active",
	// which on the prune endpoint would have deleted *running* images.
	activeImages, err := buildActiveImagesSet(s.store, projects)
	if err != nil {
		slog.Error("unused images: build active set", "error", err)
		respondError(w, http.StatusInternalServerError, "internal server error")
		return
	}

	// Sum unused image sizes.
	ctx := r.Context()
	var totalSize int64
	var count int
	for _, p := range projects {
		if p.Image == "" {
			continue
		}
		images, err := s.docker.ListImagesByRef(ctx, p.Image)
		if err != nil {
			continue
		}
		for _, img := range images {
			if !activeImages[img.Ref] {
				totalSize += img.Size
				count++
			}
		}
	}

	totalMB := totalSize / (1024 * 1024)
	exceeded := settings.ImagePruneThresholdMB > 0 && int(totalMB) >= settings.ImagePruneThresholdMB

	respondJSON(w, http.StatusOK, map[string]any{
		"total_size_mb": totalMB,
		"count":         count,
		"threshold_mb":  settings.ImagePruneThresholdMB,
		"exceeded":      exceeded,
	})
}

// pruneImages handles POST /api/docker/prune-images.
// Only removes images that belong to Tinyforge projects (not all system images).
func (s *Server) pruneImages(w http.ResponseWriter, r *http.Request) {
	if s.docker == nil {
		respondError(w, http.StatusServiceUnavailable, "Docker is not available")
		return
	}

	// Collect all image references from our projects.
	projects, err := s.store.GetAllProjects()
	if err != nil {
		slog.Error("prune: failed to list projects", "error", err)
		respondError(w, http.StatusInternalServerError, "internal server error")
		return
	}

	// Build a set of image refs used by active instances. Bail out on error
	// — silently treating a DB blip as "no active images" would prune
	// images currently in use by running containers.
	activeImages, err := buildActiveImagesSet(s.store, projects)
	if err != nil {
		slog.Error("prune: build active set", "error", err)
		respondError(w, http.StatusInternalServerError, "internal server error")
		return
	}

	// Collect all unique image bases from projects (without tags).
	projectImages := make(map[string]bool)
	for _, p := range projects {
		if p.Image != "" {
			projectImages[p.Image] = true
		}
	}

	if len(projectImages) == 0 {
		respondJSON(w, http.StatusOK, map[string]any{
			"images_removed":     0,
			"space_reclaimed_mb": 0,
			"message":            "No project images to clean up",
		})
		return
	}

	// List all local Docker images and find ones matching our projects but not actively used.
	ctx := r.Context()
	removed := 0
	var reclaimedBytes int64

	for imageBase := range projectImages {
		// List all tags for this image.
		images, err := s.docker.ListImagesByRef(ctx, imageBase)
		if err != nil {
			slog.Warn("prune: list images", "image", imageBase, "error", err)
			continue
		}

		for _, img := range images {
			// Skip images that are actively used by running instances.
			if activeImages[img.Ref] {
				continue
			}

			// Remove unused image.
			if err := s.docker.RemoveImage(ctx, img.ID); err != nil {
				slog.Warn("prune: remove image", "image", img.Ref, "error", err)
				continue
			}
			removed++
			reclaimedBytes += img.Size
			slog.Info("prune: removed image", "ref", img.Ref, "size_mb", img.Size/(1024*1024))
		}
	}

	respondJSON(w, http.StatusOK, map[string]any{
		"images_removed":     removed,
		"space_reclaimed_mb": reclaimedBytes / (1024 * 1024),
	})
}