// Copyright 2026 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package cloudstoragereadobject

import (
	"context"
	"fmt"
	"net/http"
	"strconv"
	"strings"

	yaml "github.com/goccy/go-yaml"
	"github.com/googleapis/mcp-toolbox/internal/tools"
	"github.com/googleapis/mcp-toolbox/internal/tools/cloudstorage/cloudstoragecommon"
	"github.com/googleapis/mcp-toolbox/internal/util"
	"github.com/googleapis/mcp-toolbox/internal/util/parameters"
)

const resourceType string = "cloud-storage-read-object"

const (
	bucketKey = "bucket"
	objectKey = "object"
	rangeKey  = "range"
)

func init() {
	if !tools.Register(resourceType, newConfig) {
		panic(fmt.Sprintf("tool type %q already registered", resourceType))
	}
}

func newConfig(ctx context.Context, name string, decoder *yaml.Decoder) (tools.ToolConfig, error) {
	actual := Config{ConfigBase: tools.ConfigBase{Name: name}}
	if err := decoder.DecodeContext(ctx, &actual); err != nil {
		return nil, err
	}
	return actual, nil
}

type compatibleSource interface {
	ReadObject(ctx context.Context, bucket, object string, offset, length int64) (map[string]any, error)
}

type Config struct {
	tools.ConfigBase `yaml:",inline"`
	Type             string                 `yaml:"type" validate:"required"`
	Source           string                 `yaml:"source" validate:"required"`
	Annotations      *tools.ToolAnnotations `yaml:"annotations,omitempty"`
	Bucket           *string                `yaml:"bucket,omitempty"`
}

// validate interface
var _ tools.ToolConfig = Config{}

func (cfg Config) ToolConfigType() string {
	return resourceType
}

func (cfg Config) Initialize(context.Context) (tools.Tool, error) {
	if cfg.Description == "" {
		return nil, fmt.Errorf("description is required for tool %q", cfg.Name)
	}
	if cfg.Bucket != nil && *cfg.Bucket == "" {
		return nil, fmt.Errorf("bucket cannot be empty for tool %q", cfg.Name)
	}

	objectParam := parameters.NewStringParameter(objectKey, "Full object name (path) within the bucket, e.g. 'path/to/file.txt'.")
	rangeParam := parameters.NewStringParameter(rangeKey, "Optional HTTP byte range, e.g. 'bytes=0-999' (first 1000 bytes), 'bytes=-500' (last 500 bytes), or 'bytes=500-' (from byte 500 to end). Empty reads the full object.", parameters.WithStringDefault(""))
	allParameters := parameters.Parameters{}
	if cfg.Bucket == nil {
		allParameters = append(allParameters, parameters.NewStringParameter(bucketKey, "Name of the Cloud Storage bucket containing the object."))
	}
	allParameters = append(allParameters, objectParam, rangeParam)

	return Tool{
		BaseTool: tools.NewBaseTool(
			cfg,
			tools.GetAnnotationsOrDefault(cfg.Annotations, tools.NewReadOnlyAnnotations),
			tools.Manifest{Description: cfg.Description, Parameters: allParameters.Manifest(), AuthRequired: cfg.AuthRequired},
			allParameters,
		),
	}, nil
}

// validate interface
var _ tools.Tool = Tool{}

type Tool struct {
	tools.BaseTool[Config]
}

func (t Tool) ToConfig() tools.ToolConfig {
	return t.Cfg
}

func (t Tool) Invoke(ctx context.Context, resourceMgr tools.SourceProvider, params parameters.ParamValues, accessToken tools.AccessToken) (any, util.ToolboxError) {
	source, err := tools.GetCompatibleSource[compatibleSource](resourceMgr, t.Cfg.Source, t.Cfg.Name, t.Cfg.Type)
	if err != nil {
		return nil, util.NewClientServerError("source used is not compatible with the tool", http.StatusInternalServerError, err)
	}

	mapParams := params.AsMap()
	bucket := cloudstoragecommon.ResolveString(t.Cfg.Bucket, mapParams, bucketKey)
	if bucket == "" {
		return nil, util.NewAgentError(fmt.Sprintf("invalid or missing '%s' parameter; expected a non-empty string", bucketKey), nil)
	}
	object, ok := mapParams[objectKey].(string)
	if !ok || object == "" {
		return nil, util.NewAgentError(fmt.Sprintf("invalid or missing '%s' parameter; expected a non-empty string", objectKey), nil)
	}
	rangeSpec, _ := mapParams[rangeKey].(string)

	offset, length, err := parseRange(rangeSpec)
	if err != nil {
		return nil, util.NewAgentError(fmt.Sprintf("invalid '%s' parameter: %v", rangeKey, err), err)
	}

	resp, err := source.ReadObject(ctx, bucket, object, offset, length)
	if err != nil {
		return nil, cloudstoragecommon.ProcessGCSError(err)
	}
	return resp, nil
}

// parseRange converts an HTTP Range header value into (offset, length) args for
// storage.ObjectHandle.NewRangeReader, where length == -1 means "read to end".
// Supported forms:
//
//	""           → (0, -1)       // full object
//	"bytes=0-9"  → (0, 10)       // first 10 bytes
//	"bytes=10-"  → (10, -1)      // from byte 10 to end
//	"bytes=-N"   → (-N, -1)      // last N bytes
func parseRange(rangeSpec string) (offset int64, length int64, err error) {
	if rangeSpec == "" {
		return 0, -1, nil
	}

	spec := strings.TrimSpace(rangeSpec)
	if !strings.HasPrefix(spec, "bytes=") {
		return 0, 0, fmt.Errorf("range %q must start with 'bytes='", rangeSpec)
	}
	spec = strings.TrimPrefix(spec, "bytes=")

	dash := strings.IndexByte(spec, '-')
	if dash < 0 {
		return 0, 0, fmt.Errorf("range %q is missing '-'", rangeSpec)
	}

	startStr := spec[:dash]
	endStr := spec[dash+1:]

	switch {
	case startStr == "" && endStr == "":
		return 0, 0, fmt.Errorf("range %q requires at least one bound", rangeSpec)

	case startStr == "":
		n, parseErr := strconv.ParseInt(endStr, 10, 64)
		if parseErr != nil || n <= 0 {
			return 0, 0, fmt.Errorf("range %q has a bad suffix length", rangeSpec)
		}
		return -n, -1, nil

	case endStr == "":
		start, parseErr := strconv.ParseInt(startStr, 10, 64)
		if parseErr != nil || start < 0 {
			return 0, 0, fmt.Errorf("range %q has a bad start", rangeSpec)
		}
		return start, -1, nil

	default:
		start, parseErr := strconv.ParseInt(startStr, 10, 64)
		if parseErr != nil || start < 0 {
			return 0, 0, fmt.Errorf("range %q has a bad start", rangeSpec)
		}
		end, parseErr := strconv.ParseInt(endStr, 10, 64)
		if parseErr != nil || end < start {
			return 0, 0, fmt.Errorf("range %q has a bad end", rangeSpec)
		}
		return start, end - start + 1, nil
	}
}