// Copyright 2024 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 tools

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

	yaml "github.com/goccy/go-yaml"
	"github.com/googleapis/mcp-toolbox/internal/embeddingmodels"
	"github.com/googleapis/mcp-toolbox/internal/sources"
	"github.com/googleapis/mcp-toolbox/internal/util"
	"github.com/googleapis/mcp-toolbox/internal/util/parameters"
)

// ToolConfigFactory defines the signature for a function that creates and
// decodes a specific tool's configuration. It takes the context, the tool's
// name, and a YAML decoder to parse the config.
type ToolConfigFactory func(ctx context.Context, name string, decoder *yaml.Decoder) (ToolConfig, error)

var toolRegistry = make(map[string]ToolConfigFactory)

// Register allows individual tool packages to register their configuration
// factory function. This is typically called from an init() function in the
// tool's package. It associates a 'type' string with a function that can
// produce the specific ToolConfig type. It returns true if the registration was
// successful, and false if a tool with the same type was already registered.
func Register(resourceType string, factory ToolConfigFactory) bool {
	if _, exists := toolRegistry[resourceType]; exists {
		// Tool with this type already exists, do not overwrite.
		return false
	}
	toolRegistry[resourceType] = factory
	return true
}

var ErrUnknownToolType = fmt.Errorf("unknown tool type")

// DecodeConfig looks up the registered factory for the given type and uses it
// to decode the tool configuration.
func DecodeConfig(ctx context.Context, resourceType string, name string, decoder *yaml.Decoder) (ToolConfig, error) {
	factory, found := toolRegistry[resourceType]
	if !found {
		return nil, fmt.Errorf("%w: %q", ErrUnknownToolType, resourceType)
	}
	toolConfig, err := factory(ctx, name, decoder)
	if err != nil {
		return nil, fmt.Errorf("unable to parse tool %q as type %q: %w", name, resourceType, err)
	}
	return toolConfig, nil
}

type ToolConfig interface {
	ToolConfigType() string
	Initialize(context.Context) (Tool, error)
}

// https://modelcontextprotocol.io/specification/2025-06-18/schema#toolannotations
type ToolAnnotations struct {
	DestructiveHint *bool `json:"destructiveHint,omitempty" yaml:"destructiveHint,omitempty"`
	IdempotentHint  *bool `json:"idempotentHint,omitempty" yaml:"idempotentHint,omitempty"`
	OpenWorldHint   *bool `json:"openWorldHint,omitempty" yaml:"openWorldHint,omitempty"`
	ReadOnlyHint    *bool `json:"readOnlyHint,omitempty" yaml:"readOnlyHint,omitempty"`
}

// NewReadOnlyAnnotations creates default annotations for a read-only tool.
// Use this for tools that only query/fetch data without side effects.
func NewReadOnlyAnnotations() *ToolAnnotations {
	readOnly := true
	return &ToolAnnotations{ReadOnlyHint: &readOnly}
}

// NewDestructiveAnnotations creates default annotations for a destructive tool.
// Use this for tools that create, update, or delete data.
func NewDestructiveAnnotations() *ToolAnnotations {
	readOnly := false
	destructive := true
	return &ToolAnnotations{
		ReadOnlyHint:    &readOnly,
		DestructiveHint: &destructive,
	}
}

// NewWriteAnnotations creates default annotations for a non-destructive write
// tool: ReadOnlyHint is false, DestructiveHint is left unset.
func NewWriteAnnotations() *ToolAnnotations {
	readOnly := false
	return &ToolAnnotations{ReadOnlyHint: &readOnly}
}

// GetAnnotationsOrDefault returns the provided annotations if non-nil,
// otherwise returns the result of calling defaultFn.
func GetAnnotationsOrDefault(annotations *ToolAnnotations, defaultFn func() *ToolAnnotations) *ToolAnnotations {
	if annotations != nil {
		return annotations
	}
	return defaultFn()
}

type AccessToken string

func (token AccessToken) ParseBearerToken() (string, error) {
	headerParts := strings.Split(string(token), " ")
	if len(headerParts) != 2 || strings.ToLower(headerParts[0]) != "bearer" {
		return "", util.NewClientServerError("authorization header must be in the format 'Bearer <token>'", http.StatusUnauthorized, nil)
	}
	return headerParts[1], nil
}

type Tool interface {
	GetName() string
	GetDescription() string
	GetAuthRequired() []string
	GetAnnotations() *ToolAnnotations
	Invoke(context.Context, SourceProvider, parameters.ParamValues, AccessToken) (any, util.ToolboxError)
	EmbedParams(context.Context, parameters.ParamValues, map[string]embeddingmodels.EmbeddingModel) (parameters.ParamValues, error)
	Manifest(map[string]sources.Source) (Manifest, error)
	StaticManifest() Manifest
	Authorized([]string) bool
	RequiresClientAuthorization(SourceProvider) (bool, error)
	ToConfig() ToolConfig
	GetAuthTokenHeaderName(SourceProvider) (string, error)
	GetParameters(map[string]sources.Source) (parameters.Parameters, error)
	GetScopesRequired() []string
}

// SourceProvider defines the minimal view of the server.ResourceManager
// that the Tool package needs.
// This is implemented to prevent import cycles.
type SourceProvider interface {
	GetSource(sourceName string) (sources.Source, bool)
}

// Manifest is the representation of tools sent to Client SDKs.
type Manifest struct {
	Description  string                         `json:"description"`
	Parameters   []parameters.ParameterManifest `json:"parameters"`
	AuthRequired []string                       `json:"authRequired"`
}

// Helper function that returns if a tool invocation request is authorized
func IsAuthorized(authRequiredSources []string, verifiedAuthServices []string) bool {
	if len(authRequiredSources) == 0 {
		// no authorization requirement
		return true
	}
	for _, a := range authRequiredSources {
		if slices.Contains(verifiedAuthServices, a) {
			return true
		}
	}
	return false
}

func GetCompatibleSource[T any](resourceMgr SourceProvider, sourceName, toolName, toolType string) (T, error) {
	var zero T
	s, ok := resourceMgr.GetSource(sourceName)
	if !ok {
		return zero, fmt.Errorf("unable to retrieve source %q for tool %q", sourceName, toolName)
	}
	source, ok := s.(T)
	if !ok {
		return zero, fmt.Errorf("invalid source for %q tool: source %q is not a compatible type", toolType, sourceName)
	}
	return source, nil
}

// GetCompatibleSourceFromMap looks up a source by name from a sources map and
// asserts it to the requested type. It mirrors GetCompatibleSource for callers
// that hold the sources map directly (Manifest/GetParameters) rather than a
// SourceProvider.
func GetCompatibleSourceFromMap[T any](srcs map[string]sources.Source, sourceName, toolName, toolType string) (T, error) {
	var zero T
	s, ok := srcs[sourceName]
	if !ok {
		return zero, fmt.Errorf("unable to retrieve source %q for tool %q", sourceName, toolName)
	}
	source, ok := s.(T)
	if !ok {
		return zero, fmt.Errorf("invalid source for %q tool: source %q is not a compatible type", toolType, sourceName)
	}
	return source, nil
}

// ToolMeta is the read-only view BaseTool needs of any tool's Config. Tools
// satisfy it for free by embedding ConfigBase.
type ToolMeta interface {
	GetName() string
	GetDescription() string
	GetAuthRequired() []string
	GetScopesRequired() []string
}

// ConfigBase owns the YAML fields that every tool's Config shares and that
// BaseTool reads through.
// Description is eagerly defaulted by the tool's Initialize (many prebuilt
// configs omit description: and rely on a canned per-tool string), so
// post-Initialize ConfigBase.Description holds the resolved value.
type ConfigBase struct {
	Name           string   `yaml:"name"           validate:"required"`
	Description    string   `yaml:"description"`
	AuthRequired   []string `yaml:"authRequired"`
	ScopesRequired []string `yaml:"scopesRequired"`
}

func (c ConfigBase) GetName() string             { return c.Name }
func (c ConfigBase) GetDescription() string      { return c.Description }
func (c ConfigBase) GetAuthRequired() []string   { return c.AuthRequired }
func (c ConfigBase) GetScopesRequired() []string { return c.ScopesRequired }

// BaseTool provides default implementations of various methods on the Tool
// interface. Tools embed BaseTool to drop their boilerplate and override
// only methods that need custom behavior.
type BaseTool[T ToolMeta] struct {
	Cfg              T
	annotations      *ToolAnnotations
	metadata         Manifest
	StaticParameters parameters.Parameters
}

// NewBaseTool constructs a BaseTool from a resolved Config (typically the
// per-tool Config after Initialize has filled in defaults), the resolved
// annotations, the precomputed Manifest, and the tool's static parameters.
func NewBaseTool[T ToolMeta](cfg T, annotations *ToolAnnotations, metadata Manifest, staticParameters parameters.Parameters) BaseTool[T] {
	return BaseTool[T]{
		Cfg:              cfg,
		annotations:      annotations,
		metadata:         metadata,
		StaticParameters: staticParameters,
	}
}

func (b BaseTool[T]) GetName() string                  { return b.Cfg.GetName() }
func (b BaseTool[T]) GetDescription() string           { return b.Cfg.GetDescription() }
func (b BaseTool[T]) GetAuthRequired() []string        { return b.Cfg.GetAuthRequired() }
func (b BaseTool[T]) GetScopesRequired() []string      { return b.Cfg.GetScopesRequired() }
func (b BaseTool[T]) GetAnnotations() *ToolAnnotations { return b.annotations }

// Manifest returns the precomputed metadata. It and GetParameters stay trivial
// and never call each other: embedded methods have no virtual dispatch, so a
// BaseTool method calling another would miss a concrete tool's override.
func (b BaseTool[T]) Manifest(_ map[string]sources.Source) (Manifest, error) {
	return b.metadata, nil
}

// StaticManifest returns the manifest baked at Initialize, with no source
// resolution. Dynamic tools override Manifest/GetParameters to refine params
// against a live source, but not this method, so it always reaches the baked
// skeleton — used for offline generation (e.g. skills) where no source exists.
func (b BaseTool[T]) StaticManifest() Manifest {
	return b.metadata
}

func (b BaseTool[T]) GetParameters(_ map[string]sources.Source) (parameters.Parameters, error) {
	return b.StaticParameters, nil
}

func (b BaseTool[T]) Authorized(verifiedAuthServices []string) bool {
	return IsAuthorized(b.Cfg.GetAuthRequired(), verifiedAuthServices)
}

func (b BaseTool[T]) RequiresClientAuthorization(_ SourceProvider) (bool, error) {
	return false, nil
}

func (b BaseTool[T]) GetAuthTokenHeaderName(_ SourceProvider) (string, error) {
	return "Authorization", nil
}

func (b BaseTool[T]) EmbedParams(ctx context.Context, paramValues parameters.ParamValues, embeddingModelsMap map[string]embeddingmodels.EmbeddingModel) (parameters.ParamValues, error) {
	return parameters.EmbedParams(ctx, b.StaticParameters, paramValues, embeddingModelsMap, nil)
}