package proxy

import (
	"bufio"
	"context"
	"io"
	"net/http"
	"time"

	"github.com/gin-gonic/gin"
	"github.com/rs/zerolog/log"
	"github.com/tidwall/gjson"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/metric"

	"github.com/fujin/anthropic-proxy/internal/auth"
	"github.com/fujin/anthropic-proxy/internal/logging"
	"github.com/fujin/anthropic-proxy/internal/ratelimit"
	"github.com/fujin/anthropic-proxy/internal/telemetry"
)

// requestInfo bundles common request context passed to logging/telemetry helpers.
type requestInfo struct {
	model        string
	stream       bool
	cred         *auth.Credential
	body         []byte
	originalBody []byte
}

func HandleMessages(pool *auth.Pool, profile *SniffedProfile, getSanitizer func() *Sanitizer, tracker *ratelimit.Tracker) gin.HandlerFunc {
	upstream := NewUpstreamClient(profile)

	return func(c *gin.Context) {
		body, err := io.ReadAll(c.Request.Body)
		if err != nil {
			c.JSON(http.StatusBadRequest, gin.H{"error": "failed to read request body"})
			return
		}

		originalBody := make([]byte, len(body))
		copy(originalBody, body)

		log.Info().
			Str("method", c.Request.Method).
			Str("path", c.Request.URL.Path).
			Int("body_size", len(body)).
			Str("model", gjson.GetBytes(body, "model").String()).
			Msg("incoming request")

		san := getSanitizer()
		body = san.SanitizeRequest(body)

		cred, err := pool.Pick()
		if err != nil {
			c.JSON(http.StatusServiceUnavailable, gin.H{"error": err.Error()})
			return
		}

		isStream := gjson.GetBytes(body, "stream").Bool()

		if isStream {
			handleStream(c, upstream, san, pool, cred, body, originalBody, tracker)
		} else {
			handleNonStream(c, upstream, san, pool, cred, body, originalBody, tracker)
		}
	}
}

func handleNonStream(c *gin.Context, upstream *UpstreamClient, san *Sanitizer, pool *auth.Pool, cred *auth.Credential, body []byte, originalBody []byte, tracker *ratelimit.Tracker) {
	startTime := time.Now()
	model := gjson.GetBytes(body, "model").String()
	ctx := c.Request.Context()
	ri := requestInfo{model: model, stream: false, cred: cred, body: body, originalBody: originalBody}

	telemetry.RequestBodySize.Record(ctx, int64(len(body)),
		metric.WithAttributes(attribute.String("model", model), attribute.Bool("stream", false)))

	respBody, headers, statusCode, err := upstream.Execute(ctx, cred, body)
	latencyMs := float64(time.Since(startTime).Milliseconds())

	if err != nil {
		recordConnectionError(ctx, err, ri, latencyMs)
		c.JSON(http.StatusBadGateway, gin.H{"error": "upstream request failed"})
		return
	}

	recordRequestMetrics(ctx, ri, statusCode, latencyMs)

	if statusCode >= 400 {
		pool.MarkFailure(cred, statusCode)
		telemetry.CredentialCooldowns.Add(ctx, 1,
			metric.WithAttributes(attribute.Int("status_code", statusCode)))
		recordUpstreamError(ctx, statusCode, respBody, headers.Get("X-Request-Id"), latencyMs, ri, c.Request.Header)
	} else {
		pool.MarkSuccess(cred)
		respBody = san.DesanitizeResponse(respBody)

		inputTokens := gjson.GetBytes(respBody, "usage.input_tokens").Int()
		outputTokens := gjson.GetBytes(respBody, "usage.output_tokens").Int()
		recordTokenUsage(ctx, model, cred, inputTokens, outputTokens)
		if tracker != nil {
			tracker.UpdateFromHeaders(headers)
		}

		log.Info().
			Int("status", statusCode).
			Float64("latency_ms", latencyMs).
			Str("model", model).
			Int64("input_tokens", inputTokens).
			Int64("output_tokens", outputTokens).
			Msg("request completed")
	}

	for _, h := range []string{"Content-Type", "X-Request-Id"} {
		if v := headers.Get(h); v != "" {
			c.Header(h, v)
		}
	}

	c.Data(statusCode, headers.Get("Content-Type"), respBody)
}

func handleStream(c *gin.Context, upstream *UpstreamClient, san *Sanitizer, pool *auth.Pool, cred *auth.Credential, body []byte, originalBody []byte, tracker *ratelimit.Tracker) {
	startTime := time.Now()
	model := gjson.GetBytes(body, "model").String()
	ctx := c.Request.Context()
	ri := requestInfo{model: model, stream: true, cred: cred, body: body, originalBody: originalBody}

	telemetry.StreamRequests.Add(ctx, 1, metric.WithAttributes(attribute.String("model", model)))
	telemetry.RequestBodySize.Record(ctx, int64(len(body)),
		metric.WithAttributes(attribute.String("model", model), attribute.Bool("stream", true)))

	resp, err := upstream.ExecuteStream(ctx, cred, body)
	if err != nil {
		latencyMs := float64(time.Since(startTime).Milliseconds())
		recordConnectionError(ctx, err, ri, latencyMs)
		c.JSON(http.StatusBadGateway, gin.H{"error": "upstream stream request failed"})
		return
	}
	defer resp.Body.Close()

	if resp.StatusCode >= 400 {
		pool.MarkFailure(cred, resp.StatusCode)
		telemetry.CredentialCooldowns.Add(ctx, 1,
			metric.WithAttributes(attribute.Int("status_code", resp.StatusCode)))
		respBody, _ := io.ReadAll(resp.Body)
		latencyMs := float64(time.Since(startTime).Milliseconds())
		recordRequestMetrics(ctx, ri, resp.StatusCode, latencyMs)
		recordUpstreamError(ctx, resp.StatusCode, respBody, resp.Header.Get("X-Request-Id"), latencyMs, ri, c.Request.Header)

		c.Data(resp.StatusCode, resp.Header.Get("Content-Type"), respBody)
		return
	}

	pool.MarkSuccess(cred)

	c.Header("Content-Type", "text/event-stream")
	c.Header("Cache-Control", "no-cache")
	c.Header("Connection", "keep-alive")
	c.Status(http.StatusOK)

	flusher, ok := c.Writer.(http.Flusher)
	if !ok {
		log.Error().Msg("response writer does not support flushing")
		c.JSON(http.StatusInternalServerError, gin.H{"error": "streaming not supported"})
		return
	}

	var inputTokens, outputTokens int64
	scanner := bufio.NewScanner(resp.Body)
	scanner.Buffer(make([]byte, 0, 64*1024), 1024*1024)
	for scanner.Scan() {
		line := san.DesanitizeStreamEvent(scanner.Text())
		c.Writer.WriteString(line + "\n")
		flusher.Flush()

		if len(line) > 5 && line[:5] == "data:" {
			data := line[5:]
			eventType := gjson.Get(data, "type").String()
			switch eventType {
			case "message_start":
				inputTokens = gjson.Get(data, "message.usage.input_tokens").Int()
			case "message_delta":
				outputTokens = gjson.Get(data, "usage.output_tokens").Int()
			}
		}
	}

	latencyMs := float64(time.Since(startTime).Milliseconds())
	recordRequestMetrics(ctx, ri, http.StatusOK, latencyMs)

	if inputTokens > 0 || outputTokens > 0 {
		recordTokenUsage(ctx, model, cred, inputTokens, outputTokens)
		if tracker != nil {
			tracker.UpdateFromHeaders(resp.Header)
		}
	}

	log.Info().
		Float64("latency_ms", latencyMs).
		Str("model", model).
		Bool("stream", true).
		Int64("input_tokens", inputTokens).
		Int64("output_tokens", outputTokens).
		Msg("stream completed")

	if err := scanner.Err(); err != nil {
		log.Error().Err(err).Msg("stream scan error")
	}
}

// recordConnectionError logs and records metrics for upstream connection failures.
func recordConnectionError(ctx context.Context, err error, ri requestInfo, latencyMs float64) {
	log.Error().
		Err(err).
		Str("credential", ri.cred.Email).
		Str("model", ri.model).
		Bool("stream", ri.stream).
		Str("request_body_original", string(ri.originalBody)).
		Str("request_body_sanitized", string(ri.body)).
		Int("request_body_size", len(ri.body)).
		Float64("latency_ms", latencyMs).
		Msg("upstream connection error")

	telemetry.UpstreamErrors.Add(ctx, 1,
		metric.WithAttributes(
			attribute.String("error_type", "connection"),
			attribute.String("credential", ri.cred.Email),
			attribute.Int("status_code", http.StatusBadGateway),
		))
	recordRequestMetrics(ctx, ri, http.StatusBadGateway, latencyMs)
}

// recordUpstreamError logs and records metrics for upstream HTTP error responses.
func recordUpstreamError(ctx context.Context, statusCode int, respBody []byte, requestID string, latencyMs float64, ri requestInfo, requestHeaders http.Header) {
	errorType := gjson.GetBytes(respBody, "error.type").String()
	errorMessage := gjson.GetBytes(respBody, "error.message").String()
	log.Error().
		Int("status", statusCode).
		Str("error_type", errorType).
		Str("error_message", errorMessage).
		Str("response_body", string(respBody)).
		Str("request_id", requestID).
		Float64("latency_ms", latencyMs).
		Str("credential", ri.cred.Email).
		Str("model", ri.model).
		Bool("stream", ri.stream).
		Str("request_body_original", string(ri.originalBody)).
		Str("request_body_sanitized", string(ri.body)).
		Int("request_body_size", len(ri.body)).
		Str("request_headers", logging.RedactHeaders(requestHeaders)).
		Msg("upstream error")

	telemetry.UpstreamErrors.Add(ctx, 1,
		metric.WithAttributes(
			attribute.Int("status_code", statusCode),
			attribute.String("error_type", errorType),
			attribute.String("credential", ri.cred.Email),
		))
}

// recordRequestMetrics records the request counter and duration histogram.
func recordRequestMetrics(ctx context.Context, ri requestInfo, statusCode int, latencyMs float64) {
	attrs := []attribute.KeyValue{
		attribute.String("model", ri.model),
		attribute.Bool("stream", ri.stream),
		attribute.Int("status_code", statusCode),
	}
	telemetry.RequestCounter.Add(ctx, 1, metric.WithAttributes(attrs...))
	telemetry.RequestDuration.Record(ctx, latencyMs, metric.WithAttributes(attrs...))
}

// recordTokenUsage records token consumption metrics.
func recordTokenUsage(ctx context.Context, model string, cred *auth.Credential, inputTokens, outputTokens int64) {
	tokenAttrs := metric.WithAttributes(
		attribute.String("model", model),
		attribute.String("credential", cred.Email),
	)
	telemetry.TokensInput.Add(ctx, inputTokens, tokenAttrs)
	telemetry.TokensOutput.Add(ctx, outputTokens, tokenAttrs)
}