package submit

import (
	"context"
	"errors"
	"fmt"
	"io"
	"net/http"
	"path"
	"strings"

	"github.com/minio/minio-go/v7"
	"github.com/minio/minio-go/v7/pkg/credentials"
)

// s3Client is the minimal object-store surface S3ContextStore needs. *minio.Client
// satisfies it, and a fake satisfies it in tests — so the store's key derivation
// and not-found handling are unit-verifiable without a live bucket.
type s3Client interface {
	PutObject(ctx context.Context, bucket, object string, reader io.Reader, size int64, opts minio.PutObjectOptions) (minio.UploadInfo, error)
	StatObject(ctx context.Context, bucket, object string, opts minio.StatObjectOptions) (minio.ObjectInfo, error)
}

// S3ContextStore is the object-store-backed build-context blob store: it writes
// each submission's uploaded modpack to {prefix}/{id}/context.tar.gz inside an S3
// bucket. It is the second implemented Blobs backend (alongside LocalContextStore),
// selected by cmd/felis when user_uploads_context is an s3:// base.
//
// The bucket + key prefix are parsed from that same base (parseS3Base), so an
// object written here lands at exactly s3://{bucket}/{prefix}/{id}/context.tar.gz —
// the ref deriveContextRef records and Kaniko's native s3:// --context reads.
// Credentials are static V4 keys resolved by cmd/felis from the environment (the
// setup wizard injects them into felis-api from the felis-uploads-s3 Secret); they
// never touch felis.toml.
//
// Kaniko reading the S3 context at build time needs its own credentials + egress
// on the sandboxed build Job — a separate deployment integration, exactly like the
// LocalContextStore PVC mount. This transport only makes the upload durable at the
// derived location.
type S3ContextStore struct {
	client s3Client
	bucket string
	prefix string // key prefix within the bucket; may be empty
}

// S3StoreConfig is the resolved input for NewS3ContextStore. Base is the s3://
// user_uploads_context (bucket + optional prefix are parsed from it, so the write
// path matches deriveContextRef); Endpoint may carry an http:// or https:// scheme
// (a bare host defaults to TLS); the keys come from the environment.
type S3StoreConfig struct {
	Base      string
	Endpoint  string
	Region    string
	AccessKey string
	SecretKey string
}

// NewS3ContextStore builds a store backed by a real minio client. It fails fast
// when the base is malformed or the credentials are missing, so cmd/felis leaves
// Manager.Blobs nil (upload endpoint → 503) rather than wiring a store that cannot
// authenticate.
func NewS3ContextStore(cfg S3StoreConfig) (*S3ContextStore, error) {
	bucket, prefix, err := parseS3Base(cfg.Base)
	if err != nil {
		return nil, err
	}
	if cfg.AccessKey == "" || cfg.SecretKey == "" {
		return nil, errors.New("submit: s3 store requires credentials")
	}
	host, secure, err := splitS3Endpoint(cfg.Endpoint)
	if err != nil {
		return nil, fmt.Errorf("submit: s3 endpoint: %w", err)
	}
	client, err := minio.New(host, &minio.Options{
		Creds:  credentials.NewStaticV4(cfg.AccessKey, cfg.SecretKey, ""),
		Secure: secure,
		Region: cfg.Region,
	})
	if err != nil {
		return nil, fmt.Errorf("submit: s3 client: %w", err)
	}
	return &S3ContextStore{client: client, bucket: bucket, prefix: prefix}, nil
}

// CheckS3Access verifies the S3 coordinates before they are committed to config:
// it builds a client from the entered endpoint/credentials and probes the bucket.
// It is the install-time preflight that turns a mistyped key, wrong endpoint, or
// missing bucket into an immediate, legible error at the keyboard instead of a 503
// at the first real upload.
func CheckS3Access(ctx context.Context, cfg S3StoreConfig) error {
	store, err := NewS3ContextStore(cfg)
	if err != nil {
		return err
	}
	return checkBucketAccess(ctx, store.client, store.bucket)
}

// checkBucketAccess probes the bucket with the SAME object-level HEAD the upload
// path uses (StatObject on a key that will not exist), not a bucket-level
// HeadBucket. This matters: a least-privilege key scoped to object Put/Get may lack
// s3:ListBucket, so a HeadBucket would falsely reject a key that uploads fine. A
// NoSuchKey/absent result means the endpoint is reachable and the credentials are
// accepted — exactly the runtime dependency Exists() relies on. Split from
// CheckS3Access so the error mapping is unit-testable against a fake.
func checkBucketAccess(ctx context.Context, client s3Client, bucket string) error {
	const probe = "felis-access-probe/does-not-exist"
	if _, err := client.StatObject(ctx, bucket, probe, minio.StatObjectOptions{}); err != nil {
		resp := minio.ToErrorResponse(err)
		switch resp.Code {
		case "NoSuchKey", "NotFound":
			return nil // reachable + authorized; the probe object is simply absent
		case "NoSuchBucket":
			return fmt.Errorf("submit: bucket %q not found", bucket)
		case "AccessDenied", "SignatureDoesNotMatch", "InvalidAccessKeyId":
			return fmt.Errorf("submit: s3 credentials rejected: %w", err)
		default:
			// A bare 404 with no bucket-specific code = object absent in a live bucket.
			if resp.StatusCode == http.StatusNotFound {
				return nil
			}
			return fmt.Errorf("submit: cannot reach s3 (endpoint unreachable or credentials rejected): %w", err)
		}
	}
	return nil // the probe object improbably exists — access clearly works
}

// keyFor derives the object key for a submission, re-validating the id at the
// storage boundary (the same defense-in-depth as LocalContextStore: a validated id
// carries no path separator, so it cannot alter the key layout).
func (s *S3ContextStore) keyFor(id string) (string, error) {
	if !idRE.MatchString(id) {
		return "", fmt.Errorf("submit: invalid submission id %q", id)
	}
	return path.Join(s.prefix, id, contextBlobName), nil
}

// Put streams r to the derived object key. Size is unknown (the Manager hands us a
// size-capped reader), so it is uploaded with size -1 (multipart). PutObject is
// atomic from a reader's perspective — a partial upload never becomes a readable
// object — so a failed or oversize upload never replaces a good context. It
// returns the number of bytes stored.
func (s *S3ContextStore) Put(ctx context.Context, id string, r io.Reader) (int64, error) {
	key, err := s.keyFor(id)
	if err != nil {
		return 0, err
	}
	info, err := s.client.PutObject(ctx, s.bucket, key, r, -1, minio.PutObjectOptions{ContentType: "application/gzip"})
	if err != nil {
		return 0, fmt.Errorf("submit: put context blob: %w", err)
	}
	return info.Size, nil
}

// Exists reports whether a context blob has been stored for id. Approve consults
// it so a submission whose context was never uploaded is refused BEFORE the CAS.
func (s *S3ContextStore) Exists(ctx context.Context, id string) (bool, error) {
	key, err := s.keyFor(id)
	if err != nil {
		return false, err
	}
	if _, err := s.client.StatObject(ctx, s.bucket, key, minio.StatObjectOptions{}); err != nil {
		if isS3NotFound(err) {
			return false, nil
		}
		return false, fmt.Errorf("submit: stat context blob: %w", err)
	}
	return true, nil
}

// isS3NotFound recognizes the "object is absent" outcome across S3
// implementations: a GET-shaped NoSuchKey code or a bare 404 from the HEAD that
// StatObject issues.
func isS3NotFound(err error) bool {
	resp := minio.ToErrorResponse(err)
	return resp.Code == "NoSuchKey" || resp.StatusCode == http.StatusNotFound
}

// splitS3Endpoint separates a configured endpoint into the host[:port] minio.New
// wants and a TLS flag. A bare host defaults to TLS (the safe default); an
// explicit http:// opts out for a plaintext dev store.
func splitS3Endpoint(ep string) (host string, secure bool, err error) {
	ep = strings.TrimSpace(ep)
	switch {
	case ep == "":
		return "", false, errors.New("empty endpoint")
	case strings.HasPrefix(ep, "https://"):
		return strings.Trim(strings.TrimPrefix(ep, "https://"), "/"), true, nil
	case strings.HasPrefix(ep, "http://"):
		return strings.Trim(strings.TrimPrefix(ep, "http://"), "/"), false, nil
	default:
		return strings.Trim(ep, "/"), true, nil
	}
}

// parseS3Base splits an s3://bucket[/prefix] base into its bucket and key prefix.
// It is the single source of truth for how a user_uploads_context s3:// base maps
// onto object storage, kept beside the store so the write path and deriveContextRef
// can never disagree about where the blob lands.
func parseS3Base(base string) (bucket, prefix string, err error) {
	rest := base
	if i := strings.Index(strings.ToLower(rest), "://"); i >= 0 {
		rest = rest[i+3:]
	}
	rest = strings.Trim(rest, "/")
	if rest == "" {
		return "", "", fmt.Errorf("submit: s3 base %q has no bucket", base)
	}
	parts := strings.SplitN(rest, "/", 2)
	bucket = parts[0]
	if len(parts) == 2 {
		prefix = strings.Trim(parts[1], "/")
	}
	return bucket, prefix, nil
}

// Compile-time proof that the object store satisfies the Blobs transport.
var _ Blobs = (*S3ContextStore)(nil)