package main

import (
	"bufio"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"
)

type namedURLs []string

func (n *namedURLs) String() string { return strings.Join(*n, ",") }
func (n *namedURLs) Set(value string) error {
	if !strings.Contains(value, "=") {
		return fmt.Errorf("URL must use name=https://host/path")
	}
	*n = append(*n, value)
	return nil
}

type metricSnapshot struct {
	Timestamp time.Time `json:"timestamp"`
	Name      string    `json:"name"`
	URL       string    `json:"url"`
	Status    int       `json:"status"`
	Duration  int64     `json:"duration_ms"`
	Body      string    `json:"body,omitempty"`
	Error     string    `json:"error,omitempty"`
}

func runCollector(ctx context.Context, sources namedURLs, output string, interval, duration time.Duration) error {
	if len(sources) == 0 {
		return fmt.Errorf("at least one --url name=url is required")
	}
	if interval <= 0 || duration <= 0 {
		return fmt.Errorf("interval and duration must be positive")
	}
	if dir := filepath.Dir(output); dir != "." {
		if err := os.MkdirAll(dir, 0o750); err != nil {
			return err
		}
	}
	file, err := os.OpenFile(output, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0o600)
	if err != nil {
		return err
	}
	defer file.Close()
	writer := bufio.NewWriterSize(file, 256<<10)
	defer writer.Flush()
	client := &http.Client{Timeout: 10 * time.Second}
	deadline := time.Now().Add(duration)
	for {
		snapshots := collectOnce(ctx, client, sources)
		for _, snapshot := range snapshots {
			raw, _ := json.Marshal(snapshot)
			if _, err = writer.Write(append(raw, '\n')); err != nil {
				return err
			}
		}
		if err = writer.Flush(); err != nil {
			return err
		}
		if time.Now().Add(interval).After(deadline) {
			return nil
		}
		if err = waitContext(ctx, interval); err != nil {
			return err
		}
	}
}

func collectOnce(ctx context.Context, client *http.Client, sources namedURLs) []metricSnapshot {
	out := make([]metricSnapshot, len(sources))
	var wg sync.WaitGroup
	for i, source := range sources {
		i, source := i, source
		wg.Add(1)
		go func() {
			defer wg.Done()
			parts := strings.SplitN(source, "=", 2)
			snapshot := metricSnapshot{Timestamp: time.Now().UTC(), Name: parts[0], URL: parts[1]}
			started := time.Now()
			req, err := http.NewRequestWithContext(ctx, http.MethodGet, parts[1], nil)
			if err == nil {
				var response *http.Response
				response, err = client.Do(req)
				if err == nil {
					snapshot.Status = response.StatusCode
					raw, readErr := io.ReadAll(io.LimitReader(response.Body, 16<<20))
					_ = response.Body.Close()
					if readErr != nil {
						err = readErr
					} else {
						snapshot.Body = string(raw)
					}
				}
			}
			snapshot.Duration = time.Since(started).Milliseconds()
			if err != nil {
				snapshot.Error = err.Error()
			}
			out[i] = snapshot
		}()
	}
	wg.Wait()
	return out
}