package ynab

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"os"
	"time"
)

// Reference: https://api.ynab.com/

const apiBaseURL = "https://api.ynab.com/v1/budgets/"

// A client is the structure that will be used to consume the API
// endpoints. It holds the login credentials, http client/transport,
// rate limit information, and the login session timer.
type Client struct {
	bearerToken string
	BudgetID    string
	httpClient  *http.Client
	transport   *http.Transport
	loc         *time.Location
}

// Send an HTTP GET request, and return the processed response
func (c *Client) get(endpoint string, out interface{}, query url.Values) error {
	req, err := http.NewRequest("GET", apiBaseURL+c.BudgetID+endpoint+"?"+query.Encode(), nil)
	if err != nil {
		return fmt.Errorf("failed to create new GET request: %v", err)
	}
	req.Header.Add("Authorization", fmt.Sprintf("Bearer %s", c.bearerToken))

	res, err := c.httpClient.Do(req)
	if err != nil {
		return fmt.Errorf("http GET request failed: %v", err)
	}

	err = c.processResponse(res, out)
	if err != nil {
		return fmt.Errorf("failed to process response: %v", err)
	}
	return nil
}

// Format the message body, send an HTTP POST request, and return the processed response
func (c *Client) post(endpoint string, out interface{}, body interface{}) error {
	// Attempt to marshall the body as JSON
	json, err := json.Marshal(body)
	if err != nil {
		return fmt.Errorf("failed to marshal body to json: %v", err)
	}

	req, err := http.NewRequest("POST", apiBaseURL+c.BudgetID+endpoint, bytes.NewBuffer(json))
	if err != nil {
		return fmt.Errorf("failed to create new POST request: %v", err)
	}
	req.Header.Add("Authorization", fmt.Sprintf("Bearer %s", c.bearerToken))
	req.Header.Add("Content-Type", "application/json")

	res, err := c.httpClient.Do(req)
	if err != nil {
		return fmt.Errorf("http POST request failed: %v", err)
	}

	err = c.processResponse(res, out)
	if err != nil {
		return fmt.Errorf("failed to process response: %v", err)
	}
	return nil
}

// Format the message body, send an HTTP POST request, and return the processed response
func (c *Client) put(endpoint string, out interface{}, body interface{}) error {
	// Attempt to marshall the body as JSON
	json, err := json.Marshal(body)
	if err != nil {
		return fmt.Errorf("failed to marshal body to json: %v", err)
	}

	req, err := http.NewRequest("PUT", apiBaseURL+c.BudgetID+endpoint, bytes.NewBuffer(json))
	if err != nil {
		return fmt.Errorf("failed to create new POST request: %v", err)
	}
	req.Header.Add("Authorization", fmt.Sprintf("Bearer %s", c.bearerToken))
	req.Header.Add("Content-Type", "application/json")

	res, err := c.httpClient.Do(req)
	if err != nil {
		return fmt.Errorf("http POST request failed: %v", err)
	}

	err = c.processResponse(res, out)
	if err != nil {
		return fmt.Errorf("failed to process response: %v", err)
	}
	return nil
}

// processResponse takes the body of an HTTP response, and either returns
// the error code, or unmarshalls the JSON response, extracts
// rate limit info, and places it into the object
// output parameter. This function closes the response body after reading it.
func (c *Client) processResponse(res *http.Response, out interface{}) error {
	body, err := io.ReadAll(res.Body)
	res.Body.Close()
	if err != nil {
		return fmt.Errorf("failed to read response body: %v", err)
	}

	if res.StatusCode != 200 && res.StatusCode != 201 {
		return fmt.Errorf("unexpected http status code '%d': %v", res.StatusCode, err)
	}

	err = json.Unmarshal(body, out)
	if err != nil {
		return fmt.Errorf("failed to unmarshal response body: %v", err)
	}
	return nil
}

// NewClient is the factory function for clients - takes a bearer token
func NewClient(budgetID, bearerToken string) (*Client, error) {
	transport := &http.Transport{
		ResponseHeaderTimeout: 5 * time.Second,
	}

	client := &http.Client{
		Transport: transport,
	}

	loc, err := time.LoadLocation(os.Getenv("TZ"))
	if err != nil {
		return nil, fmt.Errorf("failed to load timezone location '%s': %v", os.Getenv("TZ"), err)
	}

	// Create a new client
	c := &Client{
		BudgetID:    budgetID,
		bearerToken: bearerToken,
		httpClient:  client,
		transport:   transport,
		loc:         loc,
	}
	return c, nil
}