package main

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"time"

	amqp "github.com/rabbitmq/amqp091-go"
)

type capturedMsg struct {
	idx      int
	delivery amqp.Delivery
}

type scanOptions struct {
	queue   string
	search  string
	maxBody int
	timeout time.Duration
	out     io.Writer // message payloads
	diag    io.Writer // queue stats + scan summary; kept off stdout so --json pipes cleanly
	jsonOut bool
	full    bool // include envelope (exchange, routing-key, headers, ...) in human output
}

func scanQueue(ctx context.Context, url string, opts scanOptions) error {
	if opts.out == nil {
		opts.out = io.Discard
	}
	if opts.diag == nil {
		opts.diag = io.Discard
	}
	if opts.timeout == 0 {
		opts.timeout = 30 * time.Second
	}

	conn, err := amqp.DialConfig(url, amqp.Config{
		Heartbeat: 10 * time.Second,
		Locale:    "en_US",
		Dial:      amqp.DefaultDial(opts.timeout),
	})
	if err != nil {
		return fmt.Errorf("connect: %w", err)
	}
	defer conn.Close()

	ch, q, err := inspectQueue(conn, opts.queue)
	if err != nil {
		return err
	}
	defer ch.Close()

	depth := q.Messages
	fmt.Fprintf(opts.diag, "queue %q depth=%d consumers=%d\n", q.Name, depth, q.Consumers)
	if depth == 0 {
		return nil
	}

	captured := make([]capturedMsg, 0, depth)

	// Failsafe: requeue in reverse order on any exit path. Channel close also
	// auto-requeues but explicit reverse-order nacks preserve queue ordering.
	defer func() {
		for i := len(captured) - 1; i >= 0; i-- {
			_ = ch.Nack(captured[i].delivery.DeliveryTag, false, true)
		}
	}()

	for i := 0; i < depth; i++ {
		if err := ctx.Err(); err != nil {
			return err
		}
		msg, ok, err := ch.Get(opts.queue, false)
		if err != nil {
			return fmt.Errorf("basic.get #%d: %w", i, err)
		}
		if !ok {
			break
		}
		captured = append(captured, capturedMsg{idx: i, delivery: msg})
	}

	needle := []byte(opts.search)
	matches := 0
	for _, c := range captured {
		if opts.search != "" && !bytes.Contains(c.delivery.Body, needle) {
			continue
		}
		matches++
		switch {
		case opts.jsonOut && opts.full:
			printJSONFull(opts.out, c.idx, c.delivery)
		case opts.jsonOut:
			printJSONBody(opts.out, c.delivery)
		case opts.full:
			printFull(opts.out, c.idx, c.delivery, opts.maxBody, opts.search)
		default:
			printBodyOnly(opts.out, opts.diag, c.idx, c.delivery, opts.maxBody, opts.search)
		}
	}

	if opts.search != "" {
		fmt.Fprintf(opts.diag, "scanned=%d matched=%d\n", len(captured), matches)
	} else {
		fmt.Fprintf(opts.diag, "scanned=%d\n", len(captured))
	}
	return nil
}

func inspectQueue(conn *amqp.Connection, name string) (*amqp.Channel, amqp.Queue, error) {
	ch, err := conn.Channel()
	if err != nil {
		return nil, amqp.Queue{}, fmt.Errorf("channel: %w", err)
	}
	if q, err := ch.QueueDeclarePassive(name, true, false, false, false, nil); err == nil {
		return ch, q, nil
	}
	ch.Close()
	ch, err = conn.Channel()
	if err != nil {
		return nil, amqp.Queue{}, fmt.Errorf("channel: %w", err)
	}
	q, err := ch.QueueDeclarePassive(name, false, false, false, false, nil)
	if err != nil {
		ch.Close()
		return nil, amqp.Queue{}, fmt.Errorf("queue inspect: %w", err)
	}
	return ch, q, nil
}

// formatBody pretty-prints JSON bodies and decodes Unicode escapes; non-JSON
// bodies are returned as-is.
func formatBody(body []byte) []byte {
	trimmed := bytes.TrimSpace(body)
	if len(trimmed) == 0 || (trimmed[0] != '{' && trimmed[0] != '[') {
		return body
	}
	var v any
	if err := json.Unmarshal(trimmed, &v); err != nil {
		return body
	}
	pretty, err := json.MarshalIndent(v, "", "  ")
	if err != nil {
		return body
	}
	return pretty
}

func truncate(b []byte, max int) (out []byte, truncated bool) {
	if max <= 0 || len(b) <= max {
		return b, false
	}
	return b[:max], true
}

// printBodyOnly writes the message body to `w` (stdout-bound) and a per-message
// marker to `diag` (stderr-bound) so `rb-search ... | jq` sees a clean stream
// of JSON bodies while a human still sees which delivery is which.
func printBodyOnly(w io.Writer, diag io.Writer, idx int, d amqp.Delivery, maxBody int, search string) {
	fmt.Fprintf(diag, "--- #%d tag=%d rk=%s ---\n", idx, d.DeliveryTag, d.RoutingKey)
	body := formatBody(d.Body)
	body, truncated := truncate(body, maxBody)
	w.Write(highlight(body, search))
	if truncated {
		fmt.Fprintf(w, "\n... (truncated, use --max-body=0 for full)")
	}
	if len(body) == 0 || body[len(body)-1] != '\n' {
		fmt.Fprintln(w)
	}
}

func printFull(w io.Writer, idx int, d amqp.Delivery, maxBody int, search string) {
	fmt.Fprintf(w, "=== #%d tag=%d exchange=%q routing-key=%q\n", idx, d.DeliveryTag, d.Exchange, d.RoutingKey)
	if d.ContentType != "" || d.ContentEncoding != "" {
		fmt.Fprintf(w, "    content-type=%s content-encoding=%s\n", d.ContentType, d.ContentEncoding)
	}
	if d.MessageId != "" || d.CorrelationId != "" {
		fmt.Fprintf(w, "    message-id=%s correlation-id=%s\n", d.MessageId, d.CorrelationId)
	}
	if !d.Timestamp.IsZero() {
		fmt.Fprintf(w, "    timestamp=%s\n", d.Timestamp.Format(time.RFC3339))
	}
	if len(d.Headers) > 0 {
		hb, _ := json.Marshal(headersToMap(d.Headers))
		fmt.Fprintf(w, "    headers=%s\n", hb)
	}

	body := formatBody(d.Body)
	body, truncated := truncate(body, maxBody)
	fmt.Fprintf(w, "    body(%d bytes):\n", len(d.Body))
	w.Write(indent(highlight(body, search), "      "))
	if truncated {
		fmt.Fprintf(w, "\n      ... (truncated, use --max-body=0 for full)")
	}
	fmt.Fprintln(w)
}

// printJSONBody emits just the message body as a single JSON value per line:
// if the body is already valid JSON, it is passed through compactly; otherwise
// it is encoded as a JSON string so the stdout stream stays parseable.
func printJSONBody(w io.Writer, d amqp.Delivery) {
	trimmed := bytes.TrimSpace(d.Body)
	if len(trimmed) > 0 && (trimmed[0] == '{' || trimmed[0] == '[') && json.Valid(trimmed) {
		var compact bytes.Buffer
		if err := json.Compact(&compact, trimmed); err == nil {
			compact.WriteByte('\n')
			w.Write(compact.Bytes())
			return
		}
	}
	_ = json.NewEncoder(w).Encode(string(d.Body))
}

func printJSONFull(w io.Writer, idx int, d amqp.Delivery) {
	row := map[string]any{
		"idx":              idx,
		"delivery_tag":     d.DeliveryTag,
		"exchange":         d.Exchange,
		"routing_key":      d.RoutingKey,
		"content_type":     d.ContentType,
		"content_encoding": d.ContentEncoding,
		"message_id":       d.MessageId,
		"correlation_id":   d.CorrelationId,
		"headers":          headersToMap(d.Headers),
		"body":             bodyAsJSONValue(d.Body),
	}
	if !d.Timestamp.IsZero() {
		row["timestamp"] = d.Timestamp.Format(time.RFC3339)
	}
	_ = json.NewEncoder(w).Encode(row)
}

// bodyAsJSONValue returns the body parsed as a JSON object/array when possible
// so `--json --full` consumers can drill into it with `jq .body.foo` without a
// separate `fromjson`. Falls back to the body as a string for non-JSON payloads.
func bodyAsJSONValue(body []byte) any {
	trimmed := bytes.TrimSpace(body)
	if len(trimmed) > 0 && (trimmed[0] == '{' || trimmed[0] == '[') {
		var v any
		if err := json.Unmarshal(trimmed, &v); err == nil {
			return v
		}
	}
	return string(body)
}

func headersToMap(h amqp.Table) map[string]any {
	if h == nil {
		return nil
	}
	out := make(map[string]any, len(h))
	for k, v := range h {
		out[k] = normalizeAMQPValue(v)
	}
	return out
}

func normalizeAMQPValue(v any) any {
	switch x := v.(type) {
	case []byte:
		return string(x)
	case amqp.Table:
		return headersToMap(x)
	case []any:
		out := make([]any, len(x))
		for i, e := range x {
			out[i] = normalizeAMQPValue(e)
		}
		return out
	default:
		return v
	}
}

func indent(b []byte, prefix string) []byte {
	if len(b) == 0 {
		return []byte(prefix)
	}
	var buf bytes.Buffer
	buf.WriteString(prefix)
	for i, line := range bytes.Split(b, []byte{'\n'}) {
		if i > 0 {
			buf.WriteByte('\n')
			buf.WriteString(prefix)
		}
		buf.Write(line)
	}
	return buf.Bytes()
}

func highlight(body []byte, search string) []byte {
	if search == "" {
		return body
	}
	if !bytes.Contains(body, []byte(search)) {
		return body
	}
	const on, off = "\x1b[7m", "\x1b[0m"
	parts := bytes.Split(body, []byte(search))
	var buf bytes.Buffer
	for i, p := range parts {
		buf.Write(p)
		if i < len(parts)-1 {
			buf.WriteString(on)
			buf.WriteString(search)
			buf.WriteString(off)
		}
	}
	return buf.Bytes()
}