package main

import (
	"fmt"
	"reflect"
	"strings"

	"github.com/pkg/errors"

	"git.nakama.town/fmartingr/mattermost-plugin-shelfmark/server/shelfmark"
)

// configuration captures the plugin's external configuration as exposed in the Mattermost server
// configuration, as well as values computed from the configuration. Any public fields will be
// deserialized from the Mattermost server configuration in OnConfigurationChange.
type configuration struct {
	// ShelfmarkHost is the base URL of the Shelfmark server (e.g., http://shelfmark:8084).
	ShelfmarkHost string `json:"ShelfmarkHost"`

	// ShelfmarkUsername is the username used to authenticate with the Shelfmark server.
	ShelfmarkUsername string `json:"ShelfmarkUsername"`

	// ShelfmarkPassword is the password used to authenticate with the Shelfmark server.
	ShelfmarkPassword string `json:"ShelfmarkPassword"`

	// TeamID restricts the plugin to a specific team. Empty means all teams.
	TeamID string `json:"TeamID"`

	// ChannelID is the Mattermost channel where book posts will be created.
	ChannelID string `json:"ChannelID"`

	// DefaultLanguage is the ISO language code used when no --language flag is specified.
	// Leave empty for no language filtering.
	DefaultLanguage string `json:"DefaultLanguage"`

	// PostTemplate is a Go text/template string used to format the book post message.
	PostTemplate string `json:"PostTemplate"`
}

// Clone shallow copies the configuration.
func (c *configuration) Clone() *configuration {
	clone := *c
	return &clone
}

// IsValid checks that required configuration fields are set.
func (c *configuration) IsValid() error {
	host := strings.TrimSpace(c.ShelfmarkHost)
	if host == "" {
		return fmt.Errorf("shelfmark server URL must be configured")
	}

	if !strings.HasPrefix(host, "http://") && !strings.HasPrefix(host, "https://") {
		return fmt.Errorf("shelfmark server URL must start with http:// or https://")
	}

	if strings.TrimSpace(c.ChannelID) == "" {
		return fmt.Errorf("channel ID must be configured")
	}

	return nil
}

// validateShelfmarkHost checks that the Shelfmark server URL is configured.
func (c *configuration) validateShelfmarkHost() error {
	host := strings.TrimSpace(c.ShelfmarkHost)
	if host == "" {
		return fmt.Errorf("shelfmark server URL must be configured")
	}

	if !strings.HasPrefix(host, "http://") && !strings.HasPrefix(host, "https://") {
		return fmt.Errorf("shelfmark server URL must start with http:// or https://")
	}

	return nil
}

// testShelfmarkConnection verifies connectivity to the Shelfmark server using
// the saved configuration.
func (c *configuration) testShelfmarkConnection() error {
	if err := c.validateShelfmarkHost(); err != nil {
		return err
	}

	host, username, password := c.shelfmarkCredentials()
	client := shelfmark.NewClient(host, username, password)
	if err := client.TestConnection(); err != nil {
		return fmt.Errorf("%s: %w", T("en", MsgShelfmarkUnreachable), err)
	}

	return nil
}

// shelfmarkCredentials returns the trimmed Shelfmark connection credentials.
func (c *configuration) shelfmarkCredentials() (host, username, password string) {
	return strings.TrimSpace(c.ShelfmarkHost),
		strings.TrimSpace(c.ShelfmarkUsername),
		strings.TrimSpace(c.ShelfmarkPassword)
}

// getTeamID returns the configured team ID restriction, trimmed.
// Returns empty string if no team restriction is set.
func (c *configuration) getTeamID() string {
	return strings.TrimSpace(c.TeamID)
}

// getDefaultLanguage returns the configured default language, trimmed.
// Returns empty string if no default is set (meaning no language filtering).
func (c *configuration) getDefaultLanguage() string {
	return strings.TrimSpace(c.DefaultLanguage)
}

// getPostTemplate returns the configured post template or the default.
func (c *configuration) getPostTemplate() string {
	if strings.TrimSpace(c.PostTemplate) == "" {
		return "### {{.Title}}"
	}
	return c.PostTemplate
}

// validateConfiguration performs full validation of the configuration, including
// verifying that the configured channel exists and that the Shelfmark server is reachable.
func (p *Plugin) validateConfiguration(config *configuration) error {
	if err := config.IsValid(); err != nil {
		return err
	}

	// Verify the channel exists in Mattermost.
	if _, appErr := p.API.GetChannel(config.ChannelID); appErr != nil {
		return fmt.Errorf("%s: %s", T("en", MsgChannelNotFound), appErr.Error())
	}

	// Verify the Shelfmark server is reachable.
	host, username, password := config.shelfmarkCredentials()
	client := shelfmark.NewClient(host, username, password)
	if err := client.Ping(); err != nil {
		return fmt.Errorf("%s: %w", T("en", MsgShelfmarkUnreachable), err)
	}

	return nil
}

// getConfiguration retrieves the active configuration under lock, making it safe to use
// concurrently. The active configuration may change underneath the client of this method, but
// the struct returned by this API call is considered immutable.
func (p *Plugin) getConfiguration() *configuration {
	p.configurationLock.RLock()
	defer p.configurationLock.RUnlock()

	if p.configuration == nil {
		return &configuration{}
	}

	return p.configuration
}

// setConfiguration replaces the active configuration under lock.
//
// Do not call setConfiguration while holding the configurationLock, as sync.Mutex is not
// reentrant. In particular, avoid using the plugin API entirely, as this may in turn trigger a
// hook back into the plugin. If that hook attempts to acquire this lock, a deadlock may occur.
//
// This method panics if setConfiguration is called with the existing configuration. This almost
// certainly means that the configuration was modified without being cloned and may result in
// an unsafe access.
func (p *Plugin) setConfiguration(configuration *configuration) {
	p.configurationLock.Lock()
	defer p.configurationLock.Unlock()

	if configuration != nil && p.configuration == configuration {
		if reflect.ValueOf(*configuration).NumField() == 0 {
			return
		}

		panic("setConfiguration called with the existing configuration")
	}

	p.configuration = configuration
}

// OnConfigurationChange is invoked when configuration changes may have been made.
func (p *Plugin) OnConfigurationChange() error {
	configuration := new(configuration)

	// Load the public configuration fields from the Mattermost server configuration.
	if err := p.API.LoadPluginConfiguration(configuration); err != nil {
		return errors.Wrap(err, "failed to load plugin configuration")
	}

	p.setConfiguration(configuration)

	// Warn if the new configuration is invalid (but don't block — Mattermost
	// calls OnConfigurationChange before OnActivate, so partial config is expected).
	if err := p.validateConfiguration(configuration); err != nil {
		if p.API != nil {
			p.API.LogWarn("Plugin configuration is invalid", "error", err.Error())
		}
	}

	// Notify the plugin that configuration has changed so it can update clients.
	p.onConfigurationChanged()

	return nil
}