// file_save persists arbitrary bytes (base64-encoded by the caller)
// against a (scope, name) tuple within the calling skill's namespace.
// Returns the new file_id, the SHA256 content hash, and the size.
//
// Why base64 over raw bytes: the LLM's tool-call wire format is JSON,
// which can't carry arbitrary bytes natively. Base64 round-trips
// cleanly through the schema.
//
// Why hash + size in the response: agents commonly want to dedup
// across runs (same hash = same content) or build a manifest. Reporting
// these inline saves an immediate file_get round-trip just to compute
// them.
//
// Per-file cap: maxFileBytes (constructor arg) enforces an upper bound
// on individual file size. 0 falls back to defaultFileMaxBytes (10 MB).
//
// Per-skill quota (sum across all files): the constructor's QuotaProvider
// arg drives the v4 Phase 4 enforcement. nil disables enforcement
// (useful for tests and admin-only deployments). The check is:
//
//	used := storage.FileUsageBytes(skill)
//	if used + len(new content) > filesMax → quota_exceeded
//
// Note we do NOT subtract a "prior" value here the way kv_set does:
// file_save always inserts a new file row (content-addressable dedup
// is at the blob layer, not the row layer), so every save is additive
// to FileUsageBytes.
package tools

import (
	"context"
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"net/http"
	"strings"
	"time"

	"github.com/google/uuid"

	"gitea.stevedudenhoeffer.com/steve/executus/tool"
)

const defaultFileMaxBytes = 16 * 1024 * 1024 // 10 MiB

type fileSaveArgs struct {
	Scope         string `json:"scope" description:"Storage scope: 'skill' (shared across all callers of this skill), 'user:<your_id>' (per-caller), or 'run:<run_id>' (this run's scratchpad)."`
	Name          string `json:"name" description:"Filename including extension. Used for display only — the file is identified by an opaque file_id."`
	ContentBase64 string `json:"content_base64" description:"Base64-encoded file content."`
	Mime          string `json:"mime,omitempty" description:"Optional MIME type. If omitted, detected from the first 512 bytes of content."`
}

type fileSaveResult struct {
	FileID    string `json:"file_id"`
	Hash      string `json:"hash"`
	SizeBytes int64  `json:"size_bytes"`
}

// NewFileSave constructs the file_save tool.
//
// storage nil → "not configured" at execute time.
// maxFileBytes <= 0 falls back to defaultFileMaxBytes (10 MiB).
// quota nil → per-skill quota check skipped (per-file cap still applies).
//
// Permission: anyone may author; safe for share. Scope check at handler
// entry prevents cross-user writes; per-user buckets are isolated by
// inv.CallerID.
func NewFileSave(storage FileStorage, quota QuotaProvider, maxFileBytes int) tool.Tool {
	if maxFileBytes <= 0 {
		maxFileBytes = defaultFileMaxBytes
	}
	return tool.NewGatedTool[fileSaveArgs](
		"file_save",
		"Save base64-encoded bytes against a (scope, name) tuple. Returns file_id (opaque), SHA256 hash, and size_bytes. Content is dedup'd by hash — multiple file_save calls with identical bytes share storage. NOTE: for files produced inside code_exec, do NOT hand-encode base64 here (it corrupts) — write them to /workspace/ in the code_exec call and use the files_out file_id it returns.",
		tool.Permission{
			AuthoringRequirement: tool.RequirementAnyone,
			OperatesOn:           tool.ScopeCaller,
			SafeForShare:         true,
			Categories:           []string{"storage", "write"},
		},
		func(ctx context.Context, inv tool.Invocation, args fileSaveArgs) (string, error) {
			if storage == nil {
				return "", fmt.Errorf("file_save: not configured")
			}
			if err := ValidateScope(inv, args.Scope, inv.CallerIsAdmin); err != nil {
				return "", fmt.Errorf("file_save: %w", err)
			}
			// root_run is a KV-only scope (v1): file storage partitions
			// by the calling skill, so a root_run file would silently be
			// invisible to siblings AND escape the run-scope sweeper.
			// Reject loudly instead.
			if strings.HasPrefix(args.Scope, "root_run:") {
				return "", fmt.Errorf("file_save: root_run scope is KV-only; save under run:<run_id> and share the file_id via kv_set in the root_run scope")
			}
			if args.Name == "" {
				return "", fmt.Errorf("file_save: name required")
			}
			if args.ContentBase64 == "" {
				return "", fmt.Errorf("file_save: content_base64 required")
			}

			// Decode + cap. Decoding twice (once to count, once to
			// store) would waste cycles; we decode once and check size
			// after.
			content, err := base64.StdEncoding.DecodeString(args.ContentBase64)
			if err != nil {
				return "", fmt.Errorf("file_save: invalid base64: %w", err)
			}
			if len(content) > maxFileBytes {
				return "", fmt.Errorf("file_save: file exceeds max %d bytes (got %d)", maxFileBytes, len(content))
			}

			// Per-skill quota gate (v4 Phase 4). Skipped when quota is nil
			// (tests / admin opt-out) so the per-file cap above is the
			// only line of defence in that mode.
			if quota != nil {
				_, filesMax, err := quota.EffectiveQuota(ctx, inv.SkillID)
				if err != nil {
					return "", fmt.Errorf("file_save: quota lookup: %w", err)
				}
				used, err := storage.FileUsageBytes(ctx, inv.SkillID)
				if err != nil {
					return "", fmt.Errorf("file_save: usage check: %w", err)
				}
				if used+int64(len(content)) > filesMax {
					return "", fmt.Errorf("file_save: quota_exceeded — %d/%d bytes used; ask admin for higher quota", used, filesMax)
				}
			}

			// SHA256 for content-addressable dedup at the storage layer.
			h := sha256.Sum256(content)
			hashHex := hex.EncodeToString(h[:])

			mime := args.Mime
			if mime == "" {
				// http.DetectContentType is documented to read at most
				// the first 512 bytes; passing the full slice is fine.
				mime = http.DetectContentType(content)
			}

			meta := FileDomainMeta{
				ID:          uuid.NewString(),
				SkillID:     inv.SkillID,
				Scope:       args.Scope,
				Name:        args.Name,
				ContentHash: hashHex,
				MimeType:    mime,
				SizeBytes:   int64(len(content)),
				CreatedAt:   time.Now(),
			}

			fileID, err := storage.FileSave(ctx, meta, content)
			if err != nil {
				return "", fmt.Errorf("file_save: %w", err)
			}

			res := fileSaveResult{
				FileID:    fileID,
				Hash:      hashHex,
				SizeBytes: int64(len(content)),
			}
			b, err := json.Marshal(res)
			if err != nil {
				return "", fmt.Errorf("file_save: marshal result: %w", err)
			}
			return string(b), nil
		},
	)
}