package oci

import (
	"crypto/rand"
	"errors"
	"fmt"
	"io"
	"net/http"
	"sync"

	"git.wntrmute.dev/kyle/mcr/internal/db"
	"git.wntrmute.dev/kyle/mcr/internal/policy"
	"git.wntrmute.dev/kyle/mcr/internal/storage"
)

// uploadManager tracks in-progress blob writers by UUID.
type uploadManager struct {
	mu      sync.Mutex
	writers map[string]*storage.BlobWriter
}

func newUploadManager() *uploadManager {
	return &uploadManager{writers: make(map[string]*storage.BlobWriter)}
}

func (m *uploadManager) set(uuid string, bw *storage.BlobWriter) {
	m.mu.Lock()
	m.writers[uuid] = bw
	m.mu.Unlock()
}

func (m *uploadManager) get(uuid string) (*storage.BlobWriter, bool) {
	m.mu.Lock()
	bw, ok := m.writers[uuid]
	m.mu.Unlock()
	return bw, ok
}

func (m *uploadManager) remove(uuid string) {
	m.mu.Lock()
	delete(m.writers, uuid)
	m.mu.Unlock()
}

// generateUUID creates a random UUID (v4) string.
func generateUUID() (string, error) {
	var buf [16]byte
	if _, err := rand.Read(buf[:]); err != nil {
		return "", fmt.Errorf("oci: generate uuid: %w", err)
	}
	// Set version 4 and variant bits.
	buf[6] = (buf[6] & 0x0f) | 0x40
	buf[8] = (buf[8] & 0x3f) | 0x80
	return fmt.Sprintf("%08x-%04x-%04x-%04x-%012x",
		buf[0:4], buf[4:6], buf[6:8], buf[8:10], buf[10:16]), nil
}

// handleUploadInitiate handles POST /v2/<name>/blobs/uploads/
func (h *Handler) handleUploadInitiate(w http.ResponseWriter, r *http.Request, repo string) {
	if !h.checkPolicy(w, r, policy.ActionPush, repo) {
		return
	}

	// Create repository if it doesn't exist (implicit creation).
	repoID, err := h.db.GetOrCreateRepository(repo)
	if err != nil {
		writeOCIError(w, "UNKNOWN", http.StatusInternalServerError, "internal error")
		return
	}

	uuid, err := generateUUID()
	if err != nil {
		writeOCIError(w, "UNKNOWN", http.StatusInternalServerError, "internal error")
		return
	}

	// Insert upload row in DB.
	if err := h.db.CreateUpload(uuid, repoID); err != nil {
		writeOCIError(w, "UNKNOWN", http.StatusInternalServerError, "internal error")
		return
	}

	// Create temp file via storage.
	bw, err := h.blobs.StartUpload(uuid)
	if err != nil {
		// Clean up DB row on storage failure.
		_ = h.db.DeleteUpload(uuid)
		writeOCIError(w, "UNKNOWN", http.StatusInternalServerError, "internal error")
		return
	}

	h.uploads.set(uuid, bw)

	w.Header().Set("Location", fmt.Sprintf("/v2/%s/blobs/uploads/%s", repo, uuid))
	w.Header().Set("Docker-Upload-UUID", uuid)
	w.Header().Set("Range", "0-0")
	w.WriteHeader(http.StatusAccepted)
}

// handleUploadChunk handles PATCH /v2/<name>/blobs/uploads/<uuid>
func (h *Handler) handleUploadChunk(w http.ResponseWriter, r *http.Request, repo, uuid string) {
	if !h.checkPolicy(w, r, policy.ActionPush, repo) {
		return
	}

	bw, ok := h.uploads.get(uuid)
	if !ok {
		writeOCIError(w, "BLOB_UPLOAD_UNKNOWN", http.StatusNotFound, "upload not found")
		return
	}

	// Append request body to upload file.
	n, err := io.Copy(bw, r.Body)
	if err != nil {
		writeOCIError(w, "UNKNOWN", http.StatusInternalServerError, "write failed")
		return
	}

	// Update offset in DB.
	newOffset := bw.BytesWritten()
	if err := h.db.UpdateUploadOffset(uuid, newOffset); err != nil {
		writeOCIError(w, "UNKNOWN", http.StatusInternalServerError, "internal error")
		return
	}

	_ = n // bytes written this chunk

	w.Header().Set("Location", fmt.Sprintf("/v2/%s/blobs/uploads/%s", repo, uuid))
	w.Header().Set("Docker-Upload-UUID", uuid)
	w.Header().Set("Range", fmt.Sprintf("0-%d", newOffset))
	w.WriteHeader(http.StatusAccepted)
}

// handleUploadComplete handles PUT /v2/<name>/blobs/uploads/<uuid>?digest=<digest>
func (h *Handler) handleUploadComplete(w http.ResponseWriter, r *http.Request, repo, uuid string) {
	if !h.checkPolicy(w, r, policy.ActionPush, repo) {
		return
	}

	digest := r.URL.Query().Get("digest")
	if digest == "" {
		writeOCIError(w, "DIGEST_INVALID", http.StatusBadRequest, "digest parameter required")
		return
	}

	bw, ok := h.uploads.get(uuid)
	if !ok {
		writeOCIError(w, "BLOB_UPLOAD_UNKNOWN", http.StatusNotFound, "upload not found")
		return
	}

	// If request body is non-empty, append it first (monolithic upload).
	if r.ContentLength != 0 {
		if _, err := io.Copy(bw, r.Body); err != nil {
			writeOCIError(w, "UNKNOWN", http.StatusInternalServerError, "write failed")
			return
		}
	}

	// Commit the blob: verify digest, move to final location.
	size := bw.BytesWritten()
	_, err := bw.Commit(digest)
	if err != nil {
		h.uploads.remove(uuid)
		if errors.Is(err, storage.ErrDigestMismatch) {
			_ = h.db.DeleteUpload(uuid)
			writeOCIError(w, "DIGEST_INVALID", http.StatusBadRequest, "digest mismatch")
			return
		}
		if errors.Is(err, storage.ErrInvalidDigest) {
			_ = h.db.DeleteUpload(uuid)
			writeOCIError(w, "DIGEST_INVALID", http.StatusBadRequest, "invalid digest format")
			return
		}
		writeOCIError(w, "UNKNOWN", http.StatusInternalServerError, "commit failed")
		return
	}

	h.uploads.remove(uuid)

	// Insert blob row (no-op if already exists — content-addressed dedup).
	if err := h.db.InsertBlob(digest, size); err != nil {
		writeOCIError(w, "UNKNOWN", http.StatusInternalServerError, "internal error")
		return
	}

	// Delete upload row.
	_ = h.db.DeleteUpload(uuid)

	h.audit(r, "blob_uploaded", repo, digest)

	w.Header().Set("Location", fmt.Sprintf("/v2/%s/blobs/%s", repo, digest))
	w.Header().Set("Docker-Content-Digest", digest)
	w.WriteHeader(http.StatusCreated)
}

// handleUploadStatus handles GET /v2/<name>/blobs/uploads/<uuid>
func (h *Handler) handleUploadStatus(w http.ResponseWriter, r *http.Request, repo, uuid string) {
	if !h.checkPolicy(w, r, policy.ActionPush, repo) {
		return
	}

	upload, err := h.db.GetUpload(uuid)
	if err != nil {
		if errors.Is(err, db.ErrUploadNotFound) {
			writeOCIError(w, "BLOB_UPLOAD_UNKNOWN", http.StatusNotFound, "upload not found")
			return
		}
		writeOCIError(w, "UNKNOWN", http.StatusInternalServerError, "internal error")
		return
	}

	w.Header().Set("Location", fmt.Sprintf("/v2/%s/blobs/uploads/%s", repo, uuid))
	w.Header().Set("Docker-Upload-UUID", uuid)
	w.Header().Set("Range", fmt.Sprintf("0-%d", upload.ByteOffset))
	w.WriteHeader(http.StatusNoContent)
}

// handleUploadCancel handles DELETE /v2/<name>/blobs/uploads/<uuid>
func (h *Handler) handleUploadCancel(w http.ResponseWriter, r *http.Request, repo, uuid string) {
	if !h.checkPolicy(w, r, policy.ActionPush, repo) {
		return
	}

	bw, ok := h.uploads.get(uuid)
	if ok {
		_ = bw.Cancel()
		h.uploads.remove(uuid)
	}

	if err := h.db.DeleteUpload(uuid); err != nil {
		if errors.Is(err, db.ErrUploadNotFound) {
			writeOCIError(w, "BLOB_UPLOAD_UNKNOWN", http.StatusNotFound, "upload not found")
			return
		}
		writeOCIError(w, "UNKNOWN", http.StatusInternalServerError, "internal error")
		return
	}

	w.WriteHeader(http.StatusNoContent)
}