package mcp

import (
	"context"
	"encoding/json"
	"fmt"

	"git.k6n.net/mats/go-cart-actor/pkg/cart"
	messages "git.k6n.net/mats/go-cart-actor/proto/cart"
)

// tool is one MCP tool: a name, a description, a JSON-Schema for its arguments,
// and the handler that runs it.
type tool struct {
	Name        string                                  `json:"name"`
	Description string                                  `json:"description"`
	InputSchema json.RawMessage                         `json:"inputSchema"`
	invoke      func(args json.RawMessage) (any, error) `json:"-"`
}

func (s *Server) callTool(req *rpcRequest) *rpcResponse {
	var p struct {
		Name      string          `json:"name"`
		Arguments json.RawMessage `json:"arguments"`
	}
	if err := json.Unmarshal(req.Params, &p); err != nil {
		return errorResponse(req.ID, codeInvalidParams, "invalid params")
	}
	var t *tool
	for i := range s.tools {
		if s.tools[i].Name == p.Name {
			t = &s.tools[i]
			break
		}
	}
	if t == nil {
		return errorResponse(req.ID, codeInvalidParams, "unknown tool: "+p.Name)
	}
	out, err := t.invoke(p.Arguments)
	if err != nil {
		return result(req.ID, toolError(err))
	}
	return result(req.ID, toolText(out))
}

func (s *Server) buildTools() []tool {
	return []tool{
		{
			Name:        "get_cart",
			Description: "Get the full state of a cart by its base62 cart id: items, totals, vouchers, promotions, user info, currency, language, checkout status, subscription details, and all applied/pending promotions with progress nudges.",
			InputSchema: object(props{
				"cartId": str("the base62 cart id"),
			}, []string{"cartId"}),
			invoke: func(args json.RawMessage) (any, error) {
				var a struct {
					CartID string `json:"cartId"`
				}
				if err := decode(args, &a); err != nil {
					return nil, err
				}
				id, ok := cart.ParseCartId(a.CartID)
				if !ok {
					return nil, fmt.Errorf("invalid cart id %q", a.CartID)
				}
				g, err := s.applier.Get(context.Background(), uint64(id))
				if err != nil {
					return nil, fmt.Errorf("get cart: %w", err)
				}
				return g, nil
			},
		},
		{
			Name:        "get_cart_items",
			Description: "List all items in a cart with their SKU, name, quantity, unit price, total price, stock, tax rate, markings, custom fields, and optional child/parent relationships.",
			InputSchema: object(props{
				"cartId": str("the base62 cart id"),
			}, []string{"cartId"}),
			invoke: func(args json.RawMessage) (any, error) {
				var a struct {
					CartID string `json:"cartId"`
				}
				if err := decode(args, &a); err != nil {
					return nil, err
				}
				id, ok := cart.ParseCartId(a.CartID)
				if !ok {
					return nil, fmt.Errorf("invalid cart id %q", a.CartID)
				}
				g, err := s.applier.Get(context.Background(), uint64(id))
				if err != nil {
					return nil, fmt.Errorf("get cart: %w", err)
				}
				return map[string]any{"items": g.Items, "count": len(g.Items)}, nil
			},
		},
		{
			Name:        "get_cart_totals",
			Description: "Get price breakdown for a cart: total incVat, total exVat, VAT breakdown by rate, total discount (vouchers + promotions), and per-item totals.",
			InputSchema: object(props{
				"cartId": str("the base62 cart id"),
			}, []string{"cartId"}),
			invoke: func(args json.RawMessage) (any, error) {
				var a struct {
					CartID string `json:"cartId"`
				}
				if err := decode(args, &a); err != nil {
					return nil, err
				}
				id, ok := cart.ParseCartId(a.CartID)
				if !ok {
					return nil, fmt.Errorf("invalid cart id %q", a.CartID)
				}
				g, err := s.applier.Get(context.Background(), uint64(id))
				if err != nil {
					return nil, fmt.Errorf("get cart: %w", err)
				}
				return map[string]any{
					"totalPrice":    g.TotalPrice,
					"totalDiscount": g.TotalDiscount,
					"currency":      g.Currency,
					"language":      g.Language,
					"vouchers":      g.Vouchers,
				}, nil
			},
		},
		{
			Name:        "get_cart_promotions",
			Description: "Get all applied and pending promotions on a cart, including discount amounts and progress nudges (e.g. 'spend 1200 SEK more for free shipping').",
			InputSchema: object(props{
				"cartId": str("the base62 cart id"),
			}, []string{"cartId"}),
			invoke: func(args json.RawMessage) (any, error) {
				var a struct {
					CartID string `json:"cartId"`
				}
				if err := decode(args, &a); err != nil {
					return nil, err
				}
				id, ok := cart.ParseCartId(a.CartID)
				if !ok {
					return nil, fmt.Errorf("invalid cart id %q", a.CartID)
				}
				g, err := s.applier.Get(context.Background(), uint64(id))
				if err != nil {
					return nil, fmt.Errorf("get cart: %w", err)
				}
				return map[string]any{
					"appliedPromotions": g.AppliedPromotions,
					"totalDiscount":     g.TotalDiscount,
				}, nil
			},
		},
		{
			Name:        "get_cart_vouchers",
			Description: "List all vouchers applied to a cart with their codes, values, rules, and whether they are currently active.",
			InputSchema: object(props{
				"cartId": str("the base62 cart id"),
			}, []string{"cartId"}),
			invoke: func(args json.RawMessage) (any, error) {
				var a struct {
					CartID string `json:"cartId"`
				}
				if err := decode(args, &a); err != nil {
					return nil, err
				}
				id, ok := cart.ParseCartId(a.CartID)
				if !ok {
					return nil, fmt.Errorf("invalid cart id %q", a.CartID)
				}
				g, err := s.applier.Get(context.Background(), uint64(id))
				if err != nil {
					return nil, fmt.Errorf("get cart: %w", err)
				}
				return map[string]any{"vouchers": g.Vouchers, "count": len(g.Vouchers)}, nil
			},
		},
		{
			Name:        "update_item_quantity",
			Description: "Change the quantity of a line item in a cart. Use quantity=0 to remove the item. Returns the updated cart state.",
			InputSchema: object(props{
				"cartId":   str("the base62 cart id"),
				"itemId":   integer("the line item id (numeric, e.g. 1, 2, 3)"),
				"quantity": integer("the new quantity (0 removes the item)"),
			}, []string{"cartId", "itemId", "quantity"}),
			invoke: func(args json.RawMessage) (any, error) {
				var a struct {
					CartID   string `json:"cartId"`
					ItemID   int    `json:"itemId"`
					Quantity int32  `json:"quantity"`
				}
				if err := decode(args, &a); err != nil {
					return nil, err
				}
				id, ok := cart.ParseCartId(a.CartID)
				if !ok {
					return nil, fmt.Errorf("invalid cart id %q", a.CartID)
				}
				res, err := s.applier.Apply(context.Background(), uint64(id), &messages.ChangeQuantity{
					Id:       uint32(a.ItemID),
					Quantity: a.Quantity,
				})
				if err != nil {
					return nil, fmt.Errorf("change quantity: %w", err)
				}
				// Check for per-mutation errors.
				for _, m := range res.Mutations {
					if m.Error != nil {
						return nil, m.Error
					}
				}
				return map[string]any{"cartId": a.CartID, "cart": &res.Result}, nil
			},
		},
		{
			Name:        "remove_cart_item",
			Description: "Remove a line item (and its children) from a cart by item id. Returns the updated cart state.",
			InputSchema: object(props{
				"cartId": str("the base62 cart id"),
				"itemId": integer("the line item id to remove (numeric, e.g. 1, 2, 3)"),
			}, []string{"cartId", "itemId"}),
			invoke: func(args json.RawMessage) (any, error) {
				var a struct {
					CartID string `json:"cartId"`
					ItemID int    `json:"itemId"`
				}
				if err := decode(args, &a); err != nil {
					return nil, err
				}
				id, ok := cart.ParseCartId(a.CartID)
				if !ok {
					return nil, fmt.Errorf("invalid cart id %q", a.CartID)
				}
				res, err := s.applier.Apply(context.Background(), uint64(id), &messages.RemoveItem{Id: uint32(a.ItemID)})
				if err != nil {
					return nil, fmt.Errorf("remove item: %w", err)
				}
				for _, m := range res.Mutations {
					if m.Error != nil {
						return nil, m.Error
					}
				}
				return map[string]any{"cartId": a.CartID, "cart": &res.Result}, nil
			},
		},
		{
			Name:        "clear_cart",
			Description: "Remove all items and vouchers from a cart, resetting it to an empty state. The cart id, user id, and currency are preserved. Returns the updated (empty) cart.",
			InputSchema: object(props{
				"cartId": str("the base62 cart id"),
			}, []string{"cartId"}),
			invoke: func(args json.RawMessage) (any, error) {
				var a struct {
					CartID string `json:"cartId"`
				}
				if err := decode(args, &a); err != nil {
					return nil, err
				}
				id, ok := cart.ParseCartId(a.CartID)
				if !ok {
					return nil, fmt.Errorf("invalid cart id %q", a.CartID)
				}
				res, err := s.applier.Apply(context.Background(), uint64(id), &messages.ClearCartRequest{})
				if err != nil {
					return nil, fmt.Errorf("clear cart: %w", err)
				}
				for _, m := range res.Mutations {
					if m.Error != nil {
						return nil, m.Error
					}
				}
				return map[string]any{"cartId": a.CartID, "cart": &res.Result}, nil
			},
		},
		{
			Name:        "apply_voucher",
			Description: "Apply a voucher code to a cart. The voucher value is in öre (e.g. 10000 = 100 kr). Returns the updated cart with the voucher applied.",
			InputSchema: object(props{
				"cartId":      str("the base62 cart id"),
				"code":        str("the voucher code"),
				"value":       integer("the voucher value in öre (e.g. 10000 = 100 kr)"),
				"description": str("optional description of the voucher"),
				"rules":       stringArray("optional list of rule expressions for when the voucher applies"),
			}, []string{"cartId", "code", "value"}),
			invoke: func(args json.RawMessage) (any, error) {
				var a struct {
					CartID      string   `json:"cartId"`
					Code        string   `json:"code"`
					Value       int64    `json:"value"`
					Description string   `json:"description"`
					Rules       []string `json:"rules"`
				}
				if err := decode(args, &a); err != nil {
					return nil, err
				}
				id, ok := cart.ParseCartId(a.CartID)
				if !ok {
					return nil, fmt.Errorf("invalid cart id %q", a.CartID)
				}
				res, err := s.applier.Apply(context.Background(), uint64(id), &messages.AddVoucher{
					Code:         a.Code,
					Value:        a.Value,
					Description:  a.Description,
					VoucherRules: a.Rules,
				})
				if err != nil {
					return nil, fmt.Errorf("apply voucher: %w", err)
				}
				for _, m := range res.Mutations {
					if m.Error != nil {
						return nil, m.Error
					}
				}
				return map[string]any{"cartId": a.CartID, "cart": &res.Result}, nil
			},
		},
		{
			Name:        "remove_voucher",
			Description: "Remove a voucher from a cart by its voucher id. Returns the updated cart.",
			InputSchema: object(props{
				"cartId":    str("the base62 cart id"),
				"voucherId": integer("the voucher id to remove (numeric)"),
			}, []string{"cartId", "voucherId"}),
			invoke: func(args json.RawMessage) (any, error) {
				var a struct {
					CartID    string `json:"cartId"`
					VoucherID int    `json:"voucherId"`
				}
				if err := decode(args, &a); err != nil {
					return nil, err
				}
				id, ok := cart.ParseCartId(a.CartID)
				if !ok {
					return nil, fmt.Errorf("invalid cart id %q", a.CartID)
				}
				res, err := s.applier.Apply(context.Background(), uint64(id), &messages.RemoveVoucher{Id: uint32(a.VoucherID)})
				if err != nil {
					return nil, fmt.Errorf("remove voucher: %w", err)
				}
				for _, m := range res.Mutations {
					if m.Error != nil {
						return nil, m.Error
					}
				}
				return map[string]any{"cartId": a.CartID, "cart": &res.Result}, nil
			},
		},
		{
			Name:        "set_cart_user",
			Description: "Set or update the user ID on a cart, linking it to a customer account. Returns the updated cart.",
			InputSchema: object(props{
				"cartId": str("the base62 cart id"),
				"userId": str("the user/customer id"),
			}, []string{"cartId", "userId"}),
			invoke: func(args json.RawMessage) (any, error) {
				var a struct {
					CartID string `json:"cartId"`
					UserID string `json:"userId"`
				}
				if err := decode(args, &a); err != nil {
					return nil, err
				}
				id, ok := cart.ParseCartId(a.CartID)
				if !ok {
					return nil, fmt.Errorf("invalid cart id %q", a.CartID)
				}
				res, err := s.applier.Apply(context.Background(), uint64(id), &messages.SetUserId{UserId: a.UserID})
				if err != nil {
					return nil, fmt.Errorf("set user: %w", err)
				}
				for _, m := range res.Mutations {
					if m.Error != nil {
						return nil, m.Error
					}
				}
				return map[string]any{"cartId": a.CartID, "cart": &res.Result}, nil
			},
		},
	}
}

// ---- result + schema helpers -----------------------------------------------

func toolText(v any) map[string]any {
	b, err := json.Marshal(v)
	if err != nil {
		return toolError(err)
	}
	return map[string]any{
		"content": []map[string]any{{"type": "text", "text": string(b)}},
	}
}

func toolError(err error) map[string]any {
	return map[string]any{
		"isError": true,
		"content": []map[string]any{{"type": "text", "text": err.Error()}},
	}
}

// decode unmarshals tool arguments, tolerating empty/absent arguments.
func decode(args json.RawMessage, v any) error {
	if len(args) == 0 || string(args) == "null" {
		return nil
	}
	if err := json.Unmarshal(args, v); err != nil {
		return fmt.Errorf("invalid arguments: %w", err)
	}
	return nil
}

type props map[string]json.RawMessage

func object(p props, required []string) json.RawMessage {
	m := map[string]any{
		"type":       "object",
		"properties": p,
	}
	if len(required) > 0 {
		m["required"] = required
	}
	b, _ := json.Marshal(m)
	return b
}

func str(desc string) json.RawMessage       { return scalar("string", desc) }
func integer(d string) json.RawMessage      { return scalar("integer", d) }
func obj(desc string) json.RawMessage       { return scalar("object", desc) }

func scalar(typ, desc string) json.RawMessage {
	b, _ := json.Marshal(map[string]any{"type": typ, "description": desc})
	return b
}

func stringArray(desc string) json.RawMessage {
	b, _ := json.Marshal(map[string]any{
		"type": "array", "description": desc, "items": map[string]string{"type": "string"},
	})
	return b
}