package config

import (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os"
	"strings"
)

// AgentEndpoint is deployment-only Dispatcher configuration. It is not a SaaS
// command field and cannot be supplied by a tenant or a call task.
type AgentEndpoint struct {
	AgentID    string `json:"agent_id"`
	CellID     string `json:"cell_id"`
	Address    string `json:"address"`
	ServerName string `json:"server_name"`
}

// LoadAgentEndpoints reads the Dispatcher-owned endpoint inventory. Strict JSON
// decoding prevents silently accepting misspelled authorization or identity
// fields.
func LoadAgentEndpoints(path string) ([]AgentEndpoint, error) {
	if strings.TrimSpace(path) == "" {
		return nil, nil
	}
	data, err := os.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("read Agent endpoint inventory: %w", err)
	}
	decoder := json.NewDecoder(bytes.NewReader(data))
	decoder.DisallowUnknownFields()
	var endpoints []AgentEndpoint
	if err := decoder.Decode(&endpoints); err != nil {
		return nil, fmt.Errorf("decode Agent endpoint inventory: %w", err)
	}
	var trailing any
	if err := decoder.Decode(&trailing); !errors.Is(err, io.EOF) {
		if err == nil {
			return nil, errors.New("Agent endpoint inventory contains trailing JSON")
		}
		return nil, fmt.Errorf("read Agent endpoint inventory trailer: %w", err)
	}
	if len(endpoints) == 0 {
		return nil, errors.New("Agent endpoint inventory must not be empty")
	}
	seenAgents := make(map[string]struct{}, len(endpoints))
	seenCells := make(map[string]struct{}, len(endpoints))
	for index, endpoint := range endpoints {
		if strings.TrimSpace(endpoint.AgentID) == "" || strings.TrimSpace(endpoint.CellID) == "" || strings.TrimSpace(endpoint.Address) == "" || strings.TrimSpace(endpoint.ServerName) == "" {
			return nil, fmt.Errorf("Agent endpoint %d requires agent_id, cell_id, address, and server_name", index)
		}
		if _, exists := seenAgents[endpoint.AgentID]; exists {
			return nil, fmt.Errorf("duplicate Agent ID %q", endpoint.AgentID)
		}
		if _, exists := seenCells[endpoint.CellID]; exists {
			return nil, fmt.Errorf("duplicate Cell ID %q", endpoint.CellID)
		}
		seenAgents[endpoint.AgentID] = struct{}{}
		seenCells[endpoint.CellID] = struct{}{}
	}
	return endpoints, nil
}