package glance

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"html/template"
	"io"
	"log/slog"
	"math"
	"net/http"
	"regexp"
	"sort"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/tidwall/gjson"
)

var customAPIWidgetTemplate = mustParseTemplate("custom-api.html", "widget-base.html")

// Needs to be exported for the YAML unmarshaler to work
type CustomAPIRequest struct {
	URL                string               `yaml:"url"`
	AllowInsecure      bool                 `yaml:"allow-insecure"`
	Headers            map[string]string    `yaml:"headers"`
	Parameters         queryParametersField `yaml:"parameters"`
	Method             string               `yaml:"method"`
	BodyType           string               `yaml:"body-type"`
	Body               any                  `yaml:"body"`
	SkipJSONValidation bool                 `yaml:"skip-json-validation"`
	bodyReader         io.ReadSeeker        `yaml:"-"`
	httpRequest        *http.Request        `yaml:"-"`
}

type customAPIWidget struct {
	widgetBase        `yaml:",inline"`
	*CustomAPIRequest `yaml:",inline"`             // the primary request
	Subrequests       map[string]*CustomAPIRequest `yaml:"subrequests"`
	Template          string                       `yaml:"template"`
	Frameless         bool                         `yaml:"frameless"`
	compiledTemplate  *template.Template           `yaml:"-"`
	CompiledHTML      template.HTML                `yaml:"-"`
}

func (widget *customAPIWidget) initialize() error {
	widget.withTitle("Custom API").withCacheDuration(1 * time.Hour)

	if err := widget.CustomAPIRequest.initialize(); err != nil {
		return fmt.Errorf("initializing primary request: %v", err)
	}

	for key := range widget.Subrequests {
		if err := widget.Subrequests[key].initialize(); err != nil {
			return fmt.Errorf("initializing subrequest %q: %v", key, err)
		}
	}

	if widget.Template == "" {
		return errors.New("template is required")
	}

	compiledTemplate, err := template.New("").Funcs(customAPITemplateFuncs).Parse(widget.Template)
	if err != nil {
		return fmt.Errorf("parsing template: %w", err)
	}

	widget.compiledTemplate = compiledTemplate

	return nil
}

func (widget *customAPIWidget) update(ctx context.Context) {
	compiledHTML, err := fetchAndParseCustomAPI(widget.CustomAPIRequest, widget.Subrequests, widget.compiledTemplate)
	if !widget.canContinueUpdateAfterHandlingErr(err) {
		return
	}

	widget.CompiledHTML = compiledHTML
}

func (widget *customAPIWidget) Render() template.HTML {
	return widget.renderTemplate(widget, customAPIWidgetTemplate)
}

func (req *CustomAPIRequest) initialize() error {
	if req.URL == "" {
		return errors.New("URL is required")
	}

	if req.Body != nil {
		if req.Method == "" {
			req.Method = http.MethodPost
		}

		if req.BodyType == "" {
			req.BodyType = "json"
		}

		if req.BodyType != "json" && req.BodyType != "string" {
			return errors.New("invalid body type, must be either 'json' or 'string'")
		}

		switch req.BodyType {
		case "json":
			encoded, err := json.Marshal(req.Body)
			if err != nil {
				return fmt.Errorf("marshaling body: %v", err)
			}

			req.bodyReader = bytes.NewReader(encoded)
		case "string":
			bodyAsString, ok := req.Body.(string)
			if !ok {
				return errors.New("body must be a string when body-type is 'string'")
			}

			req.bodyReader = strings.NewReader(bodyAsString)
		}

	} else if req.Method == "" {
		req.Method = http.MethodGet
	}

	httpReq, err := http.NewRequest(strings.ToUpper(req.Method), req.URL, req.bodyReader)
	if err != nil {
		return err
	}

	if len(req.Parameters) > 0 {
		httpReq.URL.RawQuery = req.Parameters.toQueryString()
	}

	if req.BodyType == "json" {
		httpReq.Header.Set("Content-Type", "application/json")
	}

	for key, value := range req.Headers {
		httpReq.Header.Add(key, value)
	}

	req.httpRequest = httpReq

	return nil
}

type customAPIResponseData struct {
	JSON     decoratedGJSONResult
	Response *http.Response
}

type customAPITemplateData struct {
	*customAPIResponseData
	subrequests map[string]*customAPIResponseData
}

func (data *customAPITemplateData) JSONLines() []decoratedGJSONResult {
	result := make([]decoratedGJSONResult, 0, 5)

	gjson.ForEachLine(data.JSON.Raw, func(line gjson.Result) bool {
		result = append(result, decoratedGJSONResult{line})
		return true
	})

	return result
}

func (data *customAPITemplateData) Subrequest(key string) *customAPIResponseData {
	req, exists := data.subrequests[key]
	if !exists {
		// We have to panic here since there's nothing sensible we can return and the
		// lack of an error would cause requested data to return zero values which
		// would be confusing from the user's perspective. Go's template module
		// handles recovering from panics and will return the panic message as an
		// error during template execution.
		panic(fmt.Sprintf("subrequest with key %q has not been defined", key))
	}

	return req
}

func fetchCustomAPIRequest(ctx context.Context, req *CustomAPIRequest) (*customAPIResponseData, error) {
	if req.bodyReader != nil {
		req.bodyReader.Seek(0, io.SeekStart)
	}

	client := ternary(req.AllowInsecure, defaultInsecureHTTPClient, defaultHTTPClient)
	resp, err := client.Do(req.httpRequest.WithContext(ctx))
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	bodyBytes, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, err
	}

	body := strings.TrimSpace(string(bodyBytes))

	if !req.SkipJSONValidation && body != "" && !gjson.Valid(body) {
		if 200 <= resp.StatusCode && resp.StatusCode < 300 {
			truncatedBody, isTruncated := limitStringLength(body, 100)
			if isTruncated {
				truncatedBody += "... <truncated>"
			}

			slog.Error("Invalid response JSON in custom API widget", "url", req.httpRequest.URL.String(), "body", truncatedBody)
			return nil, errors.New("invalid response JSON")
		}

		return nil, errors.New(fmt.Sprintf("%d %s", resp.StatusCode, http.StatusText(resp.StatusCode)))

	}

	data := &customAPIResponseData{
		JSON:     decoratedGJSONResult{gjson.Parse(body)},
		Response: resp,
	}

	return data, nil
}

func fetchAndParseCustomAPI(
	primaryReq *CustomAPIRequest,
	subReqs map[string]*CustomAPIRequest,
	tmpl *template.Template,
) (template.HTML, error) {
	var primaryData *customAPIResponseData
	subData := make(map[string]*customAPIResponseData, len(subReqs))
	var err error

	if len(subReqs) == 0 {
		// If there are no subrequests, we can fetch the primary request in a much simpler way
		primaryData, err = fetchCustomAPIRequest(context.Background(), primaryReq)
	} else {
		// If there are subrequests, we need to fetch them concurrently
		// and cancel all requests if any of them fail. There's probably
		// a more elegant way to do this, but this works for now.
		ctx, cancel := context.WithCancel(context.Background())
		defer cancel()

		var wg sync.WaitGroup
		var mu sync.Mutex // protects subData and err

		wg.Add(1)
		go func() {
			defer wg.Done()
			var localErr error
			primaryData, localErr = fetchCustomAPIRequest(ctx, primaryReq)
			mu.Lock()
			if localErr != nil && err == nil {
				err = localErr
				cancel()
			}
			mu.Unlock()
		}()

		for key, req := range subReqs {
			wg.Add(1)
			go func() {
				defer wg.Done()
				var localErr error
				var data *customAPIResponseData
				data, localErr = fetchCustomAPIRequest(ctx, req)
				mu.Lock()
				if localErr == nil {
					subData[key] = data
				} else if err == nil {
					err = localErr
					cancel()
				}
				mu.Unlock()
			}()
		}

		wg.Wait()
	}

	emptyBody := template.HTML("")

	if err != nil {
		return emptyBody, err
	}

	data := customAPITemplateData{
		customAPIResponseData: primaryData,
		subrequests:           subData,
	}

	var templateBuffer bytes.Buffer
	err = tmpl.Execute(&templateBuffer, &data)
	if err != nil {
		return emptyBody, err
	}

	return template.HTML(templateBuffer.String()), nil
}

type decoratedGJSONResult struct {
	gjson.Result
}

func gJsonResultArrayToDecoratedResultArray(results []gjson.Result) []decoratedGJSONResult {
	decoratedResults := make([]decoratedGJSONResult, len(results))

	for i, result := range results {
		decoratedResults[i] = decoratedGJSONResult{result}
	}

	return decoratedResults
}

func (r *decoratedGJSONResult) Exists(key string) bool {
	return r.Result.Get(key).Exists()
}

func (r *decoratedGJSONResult) Array(key string) []decoratedGJSONResult {
	if key == "" {
		return gJsonResultArrayToDecoratedResultArray(r.Result.Array())
	}

	return gJsonResultArrayToDecoratedResultArray(r.Result.Get(key).Array())
}

func (r *decoratedGJSONResult) String(key string) string {
	if key == "" {
		return r.Result.String()
	}

	return r.Result.Get(key).String()
}

func (r *decoratedGJSONResult) Int(key string) int {
	if key == "" {
		return int(r.Result.Int())
	}

	return int(r.Result.Get(key).Int())
}

func (r *decoratedGJSONResult) Float(key string) float64 {
	if key == "" {
		return r.Result.Float()
	}

	return r.Result.Get(key).Float()
}

func (r *decoratedGJSONResult) Bool(key string) bool {
	if key == "" {
		return r.Result.Bool()
	}

	return r.Result.Get(key).Bool()
}

func (r *decoratedGJSONResult) Get(key string) *decoratedGJSONResult {
	return &decoratedGJSONResult{r.Result.Get(key)}
}

func customAPIDoMathOp[T int | float64](a, b T, op string) T {
	switch op {
	case "add":
		return a + b
	case "sub":
		return a - b
	case "mul":
		return a * b
	case "div":
		if b == 0 {
			return 0
		}
		return a / b
	}
	return 0
}

var customAPITemplateFuncs = func() template.FuncMap {
	var regexpCacheMu sync.Mutex
	var regexpCache = make(map[string]*regexp.Regexp)

	getCachedRegexp := func(pattern string) *regexp.Regexp {
		regexpCacheMu.Lock()
		defer regexpCacheMu.Unlock()

		regex, exists := regexpCache[pattern]
		if !exists {
			regex = regexp.MustCompile(pattern)
			regexpCache[pattern] = regex
		}

		return regex
	}

	doMathOpWithAny := func(a, b any, op string) any {
		switch at := a.(type) {
		case int:
			switch bt := b.(type) {
			case int:
				return customAPIDoMathOp(at, bt, op)
			case float64:
				return customAPIDoMathOp(float64(at), bt, op)
			default:
				return math.NaN()
			}
		case float64:
			switch bt := b.(type) {
			case int:
				return customAPIDoMathOp(at, float64(bt), op)
			case float64:
				return customAPIDoMathOp(at, bt, op)
			default:
				return math.NaN()
			}
		default:
			return math.NaN()
		}
	}

	funcs := template.FuncMap{
		"toFloat": func(a int) float64 {
			return float64(a)
		},
		"toInt": func(a float64) int {
			return int(a)
		},
		"add": func(a, b any) any {
			return doMathOpWithAny(a, b, "add")
		},
		"sub": func(a, b any) any {
			return doMathOpWithAny(a, b, "sub")
		},
		"mul": func(a, b any) any {
			return doMathOpWithAny(a, b, "mul")
		},
		"div": func(a, b any) any {
			return doMathOpWithAny(a, b, "div")
		},
		"now": func() time.Time {
			return time.Now()
		},
		"offsetNow": func(offset string) time.Time {
			d, err := time.ParseDuration(offset)
			if err != nil {
				return time.Now()
			}
			return time.Now().Add(d)
		},
		"duration": func(str string) time.Duration {
			d, err := time.ParseDuration(str)
			if err != nil {
				return 0
			}

			return d
		},
		"parseTime": func(layout, value string) time.Time {
			return customAPIFuncParseTimeInLocation(layout, value, time.UTC)
		},
		"parseLocalTime": func(layout, value string) time.Time {
			return customAPIFuncParseTimeInLocation(layout, value, time.Local)
		},
		"toRelativeTime": dynamicRelativeTimeAttrs,
		"parseRelativeTime": func(layout, value string) template.HTMLAttr {
			// Shorthand to do both of the above with a single function call
			return dynamicRelativeTimeAttrs(customAPIFuncParseTimeInLocation(layout, value, time.UTC))
		},
		// The reason we flip the parameter order is so that you can chain multiple calls together like this:
		// {{ .JSON.String "foo" | trimPrefix "bar" | doSomethingElse }}
		// instead of doing this:
		// {{ trimPrefix (.JSON.String "foo") "bar" | doSomethingElse }}
		// since the piped value gets passed as the last argument to the function.
		"trimPrefix": func(prefix, s string) string {
			return strings.TrimPrefix(s, prefix)
		},
		"trimSuffix": func(suffix, s string) string {
			return strings.TrimSuffix(s, suffix)
		},
		"trimSpace": strings.TrimSpace,
		"replaceAll": func(old, new, s string) string {
			return strings.ReplaceAll(s, old, new)
		},
		"replaceMatches": func(pattern, replacement, s string) string {
			if s == "" {
				return ""
			}

			return getCachedRegexp(pattern).ReplaceAllString(s, replacement)
		},
		"findMatch": func(pattern, s string) string {
			if s == "" {
				return ""
			}

			return getCachedRegexp(pattern).FindString(s)
		},
		"findSubmatch": func(pattern, s string) string {
			if s == "" {
				return ""
			}

			regex := getCachedRegexp(pattern)
			return itemAtIndexOrDefault(regex.FindStringSubmatch(s), 1, "")
		},
		"sortByString": func(key, order string, results []decoratedGJSONResult) []decoratedGJSONResult {
			sort.Slice(results, func(a, b int) bool {
				if order == "asc" {
					return results[a].String(key) < results[b].String(key)
				}

				return results[a].String(key) > results[b].String(key)
			})

			return results
		},
		"sortByInt": func(key, order string, results []decoratedGJSONResult) []decoratedGJSONResult {
			sort.Slice(results, func(a, b int) bool {
				if order == "asc" {
					return results[a].Int(key) < results[b].Int(key)
				}

				return results[a].Int(key) > results[b].Int(key)
			})

			return results
		},
		"sortByFloat": func(key, order string, results []decoratedGJSONResult) []decoratedGJSONResult {
			sort.Slice(results, func(a, b int) bool {
				if order == "asc" {
					return results[a].Float(key) < results[b].Float(key)
				}

				return results[a].Float(key) > results[b].Float(key)
			})

			return results
		},
		"sortByTime": func(key, layout, order string, results []decoratedGJSONResult) []decoratedGJSONResult {
			sort.Slice(results, func(a, b int) bool {
				timeA := customAPIFuncParseTimeInLocation(layout, results[a].String(key), time.UTC)
				timeB := customAPIFuncParseTimeInLocation(layout, results[b].String(key), time.UTC)

				if order == "asc" {
					return timeA.Before(timeB)
				}

				return timeA.After(timeB)
			})

			return results
		},
		"concat": func(items ...string) string {
			return strings.Join(items, "")
		},
		"unique": func(key string, results []decoratedGJSONResult) []decoratedGJSONResult {
			seen := make(map[string]struct{})
			out := make([]decoratedGJSONResult, 0, len(results))
			for _, result := range results {
				val := result.String(key)
				if _, ok := seen[val]; !ok {
					seen[val] = struct{}{}
					out = append(out, result)
				}
			}
			return out
		},
	}

	for key, value := range globalTemplateFunctions {
		if _, exists := funcs[key]; !exists {
			funcs[key] = value
		}
	}

	return funcs
}()

func customAPIFuncParseTimeInLocation(layout, value string, loc *time.Location) time.Time {
	switch strings.ToLower(layout) {
	case "unix":
		asInt, err := strconv.ParseInt(value, 10, 64)
		if err != nil {
			return time.Unix(0, 0)
		}

		return time.Unix(asInt, 0)
	case "rfc3339":
		layout = time.RFC3339
	case "rfc3339nano":
		layout = time.RFC3339Nano
	case "datetime":
		layout = time.DateTime
	case "dateonly":
		layout = time.DateOnly
	}

	parsed, err := time.ParseInLocation(layout, value, loc)
	if err != nil {
		return time.Unix(0, 0)
	}

	return parsed
}