package line

import (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"

	"github.com/TwiN/gatus/v5/alerting/alert"
	"github.com/TwiN/gatus/v5/client"
	"github.com/TwiN/gatus/v5/config/endpoint"
	"gopkg.in/yaml.v3"
)

var (
	ErrChannelAccessTokenNotSet = errors.New("channel-access-token not set")
	ErrUserIDsNotSet            = errors.New("user-ids not set")
	ErrDuplicateGroupOverride   = errors.New("duplicate group override")
)

type Config struct {
	ChannelAccessToken string   `yaml:"channel-access-token"` // Line Messaging API channel access token
	UserIDs            []string `yaml:"user-ids"`             // List of Line user IDs to send messages to
}

func (cfg *Config) Validate() error {
	if len(cfg.ChannelAccessToken) == 0 {
		return ErrChannelAccessTokenNotSet
	}
	if len(cfg.UserIDs) == 0 {
		return ErrUserIDsNotSet
	}
	return nil
}

func (cfg *Config) Merge(override *Config) {
	if len(override.ChannelAccessToken) > 0 {
		cfg.ChannelAccessToken = override.ChannelAccessToken
	}
	if len(override.UserIDs) > 0 {
		cfg.UserIDs = override.UserIDs
	}
}

// AlertProvider is the configuration necessary for sending an alert using Line
type AlertProvider struct {
	DefaultConfig Config `yaml:",inline"`

	// DefaultAlert is the default alert configuration to use for endpoints with an alert of the appropriate type
	DefaultAlert *alert.Alert `yaml:"default-alert,omitempty"`

	// Overrides is a list of Override that may be prioritized over the default configuration
	Overrides []Override `yaml:"overrides,omitempty"`
}

// Override is a case under which the default integration is overridden
type Override struct {
	Group  string `yaml:"group"`
	Config `yaml:",inline"`
}

// Validate the provider's configuration
func (provider *AlertProvider) Validate() error {
	registeredGroups := make(map[string]bool)
	if provider.Overrides != nil {
		for _, override := range provider.Overrides {
			if isAlreadyRegistered := registeredGroups[override.Group]; isAlreadyRegistered || override.Group == "" {
				return ErrDuplicateGroupOverride
			}
			registeredGroups[override.Group] = true
		}
	}
	return provider.DefaultConfig.Validate()
}

// Send an alert using the provider
func (provider *AlertProvider) Send(ep *endpoint.Endpoint, alert *alert.Alert, result *endpoint.Result, resolved bool) error {
	cfg, err := provider.GetConfig(ep.Group, alert)
	if err != nil {
		return err
	}
	for _, userID := range cfg.UserIDs {
		body, err := provider.buildRequestBody(ep, alert, result, resolved, userID)
		if err != nil {
			return err
		}
		buffer := bytes.NewBuffer(body)
		request, err := http.NewRequest(http.MethodPost, "https://api.line.me/v2/bot/message/push", buffer)
		if err != nil {
			return err
		}
		request.Header.Set("Content-Type", "application/json")
		request.Header.Set("Authorization", fmt.Sprintf("Bearer %s", cfg.ChannelAccessToken))
		response, err := client.GetHTTPClient(nil).Do(request)
		if err != nil {
			return err
		}
		if response.StatusCode >= 400 {
			body, _ := io.ReadAll(response.Body)
			response.Body.Close()
			return fmt.Errorf("call to line alert returned status code %d: %s", response.StatusCode, string(body))
		}
		response.Body.Close()
	}
	return nil
}

type Body struct {
	To       string    `json:"to"`
	Messages []Message `json:"messages"`
}

type Message struct {
	Type string `json:"type"`
	Text string `json:"text"`
}

// buildRequestBody builds the request body for the provider
func (provider *AlertProvider) buildRequestBody(ep *endpoint.Endpoint, alert *alert.Alert, result *endpoint.Result, resolved bool, userID string) ([]byte, error) {
	var message string
	if resolved {
		message = fmt.Sprintf("✅ RESOLVED: %s\n\nAlert has been resolved after passing successfully %d time(s) in a row", ep.DisplayName(), alert.SuccessThreshold)
	} else {
		message = fmt.Sprintf("⚠️ ALERT: %s\n\nEndpoint has failed %d time(s) in a row", ep.DisplayName(), alert.FailureThreshold)
	}
	if alertDescription := alert.GetDescription(); len(alertDescription) > 0 {
		message += fmt.Sprintf("\n\nDescription: %s", alertDescription)
	}
	if len(result.ConditionResults) > 0 {
		message += "\n\nCondition Results:"
		for _, conditionResult := range result.ConditionResults {
			var status string
			if conditionResult.Success {
				status = "✅"
			} else {
				status = "❌"
			}
			message += fmt.Sprintf("\n%s %s", status, conditionResult.Condition)
		}
	}
	body := Body{
		To: userID,
		Messages: []Message{
			{
				Type: "text",
				Text: message,
			},
		},
	}
	bodyAsJSON, err := json.Marshal(body)
	if err != nil {
		return nil, err
	}
	return bodyAsJSON, nil
}

// GetDefaultAlert returns the provider's default alert configuration
func (provider *AlertProvider) GetDefaultAlert() *alert.Alert {
	return provider.DefaultAlert
}

// GetConfig returns the configuration for the provider with the overrides applied
func (provider *AlertProvider) GetConfig(group string, alert *alert.Alert) (*Config, error) {
	cfg := provider.DefaultConfig
	// Handle group overrides
	if provider.Overrides != nil {
		for _, override := range provider.Overrides {
			if group == override.Group {
				cfg.Merge(&override.Config)
				break
			}
		}
	}
	// Handle alert overrides
	if len(alert.ProviderOverride) != 0 {
		overrideConfig := Config{}
		if err := yaml.Unmarshal(alert.ProviderOverrideAsBytes(), &overrideConfig); err != nil {
			return nil, err
		}
		cfg.Merge(&overrideConfig)
	}
	// Validate the configuration
	err := cfg.Validate()
	return &cfg, err
}

// ValidateOverrides validates the alert's provider override and, if present, the group override
func (provider *AlertProvider) ValidateOverrides(group string, alert *alert.Alert) error {
	_, err := provider.GetConfig(group, alert)
	return err
}