package functions

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

	cloudevents "github.com/cloudevents/sdk-go/v2"
	"github.com/google/uuid"
)

const (
	DefaultInvokeSource      = "/boson/fn"
	DefaultInvokeType        = "boson.fn"
	DefaultInvokeContentType = "application/json"
	DefaultInvokeData        = `{"message":"Hello World"}`
	DefaultInvokeFormat      = "http"
)

// InvokeMesage is the message used by the convenience method Invoke to provide
// a simple way to trigger the execution of a function during development.
type InvokeMessage struct {
	ID          string
	Source      string
	Type        string
	ContentType string
	Data        string
	Format      string //optional override for function-defined message format
}

// NewInvokeMessage creates a new InvokeMessage with fields populated
func NewInvokeMessage() InvokeMessage {
	return InvokeMessage{
		ID:          uuid.NewString(),
		Source:      DefaultInvokeSource,
		Type:        DefaultInvokeType,
		ContentType: DefaultInvokeContentType,
		Data:        DefaultInvokeData,
		// Format override not set by default: value from function being preferred.
	}
}

// invoke the function instance in the target environment with the
// invocation message.  Returned is metadata (such as HTTP headers or
// CloudEvent fields) and a stringified version of the payload.
func invoke(ctx context.Context, c *Client, f Function, target string, m InvokeMessage, verbose bool) (metadata map[string][]string, body string, err error) {

	// Get the first available route from 'local', 'remote', a named environment
	// or treat target
	route, err := invocationRoute(ctx, c, f, target) // choose instance to invoke
	if err != nil {
		return
	}

	// Format" either 'http' or 'cloudevent'
	// TODO: discuss if providing a Format on Message should a) update the
	// function to use the new format if none is defined already (backwards
	// compatibility fix) or b) always update the function, even if it was already
	// set. Once decided, codify in a test.
	format := DefaultInvokeFormat

	if verbose {
		fmt.Printf("Invoking '%v' function at %v\n", f.Invoke, route)
	}

	if f.Invoke != "" {
		// Prefer the format set during function creation if defined.
		format = f.Invoke
	}
	if m.Format != "" {
		// Use the override specified on the message if provided
		format = m.Format
		if verbose {
			fmt.Printf("Invoking '%v' function using '%v' format\n", f.Invoke, m.Format)
		}
	}

	switch format {
	case "http":
		return sendPost(ctx, route, m, c.transport, verbose)
	case "cloudevent":
		// CouldEvents return a string which always includes a fairly verbose
		// summation of fields, so metadata is not applicable
		meta := make(map[string][]string)
		body, err = sendEvent(ctx, route, m, c.transport, verbose)
		return meta, body, err
	default:
		err = fmt.Errorf("format '%v' not supported", format)
		return
	}
}

// invocationRoute returns a route to the named target instance of a func:
// 'local': local environment; locally running function (error if not running)
// 'remote': remote environment; first available instance (error if none)
// '<environment>': A valid alternate target which contains instances.
// '<url>': An explicit URL
// ”: Default if no target is passed is to first use local, then remote.
//
//	errors if neither are available.
func invocationRoute(ctx context.Context, c *Client, f Function, target string) (string, error) {
	// TODO: this function has code-smell;  will de-smellify it in next pass.
	if target == EnvironmentLocal {
		instance, err := c.Instances().Get(ctx, f, target)
		if err != nil {
			if errors.Is(err, ErrEnvironmentNotFound) {
				return "", errors.New("not running locally")
			}
			return "", err
		}
		return instance.Route, nil

	} else if target == EnvironmentRemote {
		instance, err := c.Instances().Get(ctx, f, target)
		if err != nil {
			if errors.Is(err, ErrEnvironmentNotFound) {
				return "", errors.New("not running in remote")
			}
			return "", err
		}
		return instance.Route, nil

	} else if target == "" { // target blank, check local first then remote.
		instance, err := c.Instances().Get(ctx, f, EnvironmentLocal)
		if err != nil && !errors.Is(err, ErrNotRunning) {
			return "", err // unexpected errors are anything other than ErrNotRunning
		}
		if err == nil {
			return instance.Route, nil // found instance in local environment
		}
		instance, err = c.Instances().Get(ctx, f, EnvironmentRemote)
		if errors.Is(err, ErrNotRunning) {
			return "", errors.New("not running locally or in the remote")
		}
		if err != nil {
			return "", err // unexpected error
		}
		return instance.Route, nil
	} else { // treat an unrecognized target as an ad-hoc verbatim endpoint
		return target, nil
	}
}

// sendEvent to the route populated with data in the invoke message.
func sendEvent(ctx context.Context, route string, m InvokeMessage, t http.RoundTripper, verbose bool) (resp string, err error) {
	event := cloudevents.NewEvent()
	event.SetID(m.ID)
	event.SetSource(m.Source)
	event.SetType(m.Type)
	if m.ContentType == "application/json" {
		var d interface{}
		err = json.Unmarshal([]byte(m.Data), &d)
		if err != nil {
			return
		}
		err = event.SetData(m.ContentType, d)
		if err != nil {
			return
		}
	} else if err = event.SetData(m.ContentType, m.Data); err != nil {
		return
	}

	c, err := cloudevents.NewClientHTTP(
		cloudevents.WithTarget(route),
		cloudevents.WithRoundTripper(t))
	if err != nil {
		return
	}

	if verbose {
		fmt.Printf("Sending event\n%v", event)
		// note event's stringification already includes a trailing linebreak.
	}

	evt, result := c.Request(cloudevents.ContextWithTarget(ctx, route), event)
	if cloudevents.IsUndelivered(result) {
		err = fmt.Errorf("unable to invoke: %v", result)
	} else if evt != nil { // Check for nil in case no event is returned
		resp = evt.String()
	}

	return
}

// sendPost to the route populated with data in the invoke message.
func sendPost(ctx context.Context, route string, m InvokeMessage, t http.RoundTripper, verbose bool) (map[string][]string, string, error) {
	client := http.Client{
		Transport: t,
		Timeout:   time.Minute,
	}
	values := url.Values{
		"ID":          {m.ID},
		"Source":      {m.Source},
		"Type":        {m.Type},
		"ContentType": {m.ContentType},
		"Data":        {m.Data},
	}
	if verbose {
		fmt.Println("Sending values")
		for k, v := range values {
			fmt.Printf("  %v: %v\n", k, v[0]) // NOTE len==1 value slices assumed
		}
	}

	req, err := http.NewRequestWithContext(ctx, "POST", route, bytes.NewBufferString(m.Data))
	if err != nil {
		return nil, "", fmt.Errorf("failure to create request: %w", err)
	}
	req.Header.Add("Content-Type", m.ContentType)

	resp, err := client.Do(req)
	if err != nil {
		return nil, "", err
	}

	defer resp.Body.Close()
	if resp.StatusCode > 299 {
		return nil, "", fmt.Errorf("failure invoking '%v' (HTTP %v)", route, resp.StatusCode)
	}
	b, err := io.ReadAll(resp.Body)
	return resp.Header, string(b), err
}