package oci

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"strconv"

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

func (h *Handler) handleManifestGet(w http.ResponseWriter, r *http.Request, repo, reference string) {
	if !h.checkPolicy(w, r, policy.ActionPull, repo) {
		return
	}

	m, ok := h.resolveManifest(w, repo, reference)
	if !ok {
		return
	}

	h.audit(r, "manifest_pulled", repo, m.Digest)

	w.Header().Set("Content-Type", m.MediaType)
	w.Header().Set("Docker-Content-Digest", m.Digest)
	w.Header().Set("Content-Length", strconv.FormatInt(m.Size, 10))
	w.WriteHeader(http.StatusOK)
	_, _ = w.Write(m.Content)
}

func (h *Handler) handleManifestHead(w http.ResponseWriter, r *http.Request, repo, reference string) {
	if !h.checkPolicy(w, r, policy.ActionPull, repo) {
		return
	}

	m, ok := h.resolveManifest(w, repo, reference)
	if !ok {
		return
	}

	w.Header().Set("Content-Type", m.MediaType)
	w.Header().Set("Docker-Content-Digest", m.Digest)
	w.Header().Set("Content-Length", strconv.FormatInt(m.Size, 10))
	w.WriteHeader(http.StatusOK)
}

// resolveManifest looks up a manifest by tag or digest, writing OCI errors on failure.
func (h *Handler) resolveManifest(w http.ResponseWriter, repo, reference string) (*db.ManifestRow, bool) {
	repoID, err := h.db.GetRepositoryByName(repo)
	if err != nil {
		if errors.Is(err, db.ErrRepoNotFound) {
			writeOCIError(w, "NAME_UNKNOWN", http.StatusNotFound,
				fmt.Sprintf("repository %q not found", repo))
			return nil, false
		}
		h.log.Error("manifest resolve: lookup repository", "error", err, "repo", repo)
		writeOCIError(w, "UNKNOWN", http.StatusInternalServerError, "internal error")
		return nil, false
	}

	var m *db.ManifestRow
	if isDigest(reference) {
		m, err = h.db.GetManifestByDigest(repoID, reference)
	} else {
		m, err = h.db.GetManifestByTag(repoID, reference)
	}
	if err != nil {
		if errors.Is(err, db.ErrManifestNotFound) {
			writeOCIError(w, "MANIFEST_UNKNOWN", http.StatusNotFound,
				fmt.Sprintf("manifest %q not found", reference))
			return nil, false
		}
		h.log.Error("manifest resolve: lookup manifest", "error", err, "repo", repo, "reference", reference)
		writeOCIError(w, "UNKNOWN", http.StatusInternalServerError, "internal error")
		return nil, false
	}

	return m, true
}

// ociManifest is the minimal structure for parsing an OCI image manifest.
type ociManifest struct {
	SchemaVersion int             `json:"schemaVersion"`
	MediaType     string          `json:"mediaType,omitempty"`
	Config        ociDescriptor   `json:"config"`
	Layers        []ociDescriptor `json:"layers"`
}

// ociDescriptor is a content-addressed reference within a manifest.
type ociDescriptor struct {
	MediaType string `json:"mediaType"`
	Digest    string `json:"digest"`
	Size      int64  `json:"size"`
}

// supportedManifestMediaTypes lists the manifest media types MCR accepts.
var supportedManifestMediaTypes = map[string]bool{
	"application/vnd.oci.image.manifest.v1+json":           true,
	"application/vnd.docker.distribution.manifest.v2+json": true,
}

// handleManifestPut handles PUT /v2/<name>/manifests/<reference>
func (h *Handler) handleManifestPut(w http.ResponseWriter, r *http.Request, repo, reference string) {
	if !h.checkPolicy(w, r, policy.ActionPush, repo) {
		return
	}

	// Step 1: Read and parse manifest JSON.
	body, err := io.ReadAll(r.Body)
	if err != nil {
		writeOCIError(w, "MANIFEST_INVALID", http.StatusBadRequest, "failed to read request body")
		return
	}
	if len(body) == 0 {
		writeOCIError(w, "MANIFEST_INVALID", http.StatusBadRequest, "empty manifest")
		return
	}

	var manifest ociManifest
	if err := json.Unmarshal(body, &manifest); err != nil {
		writeOCIError(w, "MANIFEST_INVALID", http.StatusBadRequest, "malformed manifest JSON")
		return
	}
	if manifest.SchemaVersion != 2 {
		writeOCIError(w, "MANIFEST_INVALID", http.StatusBadRequest, "unsupported schema version")
		return
	}

	// Determine media type from Content-Type header, falling back to manifest body.
	mediaType := r.Header.Get("Content-Type")
	if mediaType == "" {
		mediaType = manifest.MediaType
	}
	if mediaType == "" {
		mediaType = "application/vnd.oci.image.manifest.v1+json"
	}
	if !supportedManifestMediaTypes[mediaType] {
		writeOCIError(w, "MANIFEST_INVALID", http.StatusBadRequest,
			fmt.Sprintf("unsupported media type: %s", mediaType))
		return
	}

	// Step 2: Compute SHA-256 digest.
	sum := sha256.Sum256(body)
	computedDigest := "sha256:" + hex.EncodeToString(sum[:])

	// Step 3: If reference is a digest, verify it matches.
	tag := ""
	if isDigest(reference) {
		if reference != computedDigest {
			writeOCIError(w, "DIGEST_INVALID", http.StatusBadRequest,
				fmt.Sprintf("digest mismatch: computed %s, got %s", computedDigest, reference))
			return
		}
	} else {
		tag = reference
	}

	// Step 4: Collect all referenced blob digests.
	var blobDigests []string
	if manifest.Config.Digest != "" {
		blobDigests = append(blobDigests, manifest.Config.Digest)
	}
	for _, layer := range manifest.Layers {
		if layer.Digest != "" {
			blobDigests = append(blobDigests, layer.Digest)
		}
	}

	// Step 5: Verify all referenced blobs exist.
	for _, bd := range blobDigests {
		exists, err := h.db.BlobExists(bd)
		if err != nil {
			h.log.Error("manifest push: check blob exists", "error", err, "repo", repo, "blob_digest", bd)
			writeOCIError(w, "UNKNOWN", http.StatusInternalServerError, "internal error")
			return
		}
		if !exists {
			writeOCIError(w, "MANIFEST_BLOB_UNKNOWN", http.StatusBadRequest,
				fmt.Sprintf("blob %s not found", bd))
			return
		}
	}

	// Step 6: Single transaction — create repo, insert manifest, populate
	// manifest_blobs, upsert tag.
	params := db.PushManifestParams{
		RepoName:    repo,
		Digest:      computedDigest,
		MediaType:   mediaType,
		Content:     body,
		Size:        int64(len(body)),
		Tag:         tag,
		BlobDigests: blobDigests,
	}
	if err := h.db.PushManifest(params); err != nil {
		h.log.Error("manifest push: write to database", "error", err, "repo", repo, "digest", computedDigest, "tag", tag)
		writeOCIError(w, "UNKNOWN", http.StatusInternalServerError, "internal error")
		return
	}

	// Step 7: Audit and respond.
	details := map[string]string{}
	if tag != "" {
		details["tag"] = tag
	}
	if h.auditFn != nil {
		claims := auth.ClaimsFromContext(r.Context())
		actorID := ""
		if claims != nil {
			actorID = claims.Subject
		}
		h.auditFn("manifest_pushed", actorID, repo, computedDigest, r.RemoteAddr, details)
	}

	h.log.Info("manifest pushed", "repo", repo, "digest", computedDigest, "tag", tag, "size", len(body))

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