// ABOUTME: HTTP handlers for the metrics receiver service using Fuego framework.
// ABOUTME: Provides endpoints for receiving and querying metrics with automatic OpenAPI generation.
package receiver

import (
	"crypto/subtle"
	"encoding/json"
	"errors"
	"fmt"
	"log/slog"
	"net/http"
	"strings"
	"time"

	"github.com/go-fuego/fuego"
)

// Handler handles HTTP requests for the metrics receiver
type Handler struct {
	store     *Store
	logger    *slog.Logger
	readToken string // Pre-shared token for read endpoint authentication
	hmacKey   string // Separate key for HMAC-based push token generation/validation
	tokenTTL  time.Duration
}

// NewHandler creates a new HTTP handler with the given store.
// readToken authenticates read endpoints and the token generation endpoint.
// hmacKey is the secret used to derive scoped push tokens.
// tokenTTL specifies how long push tokens are valid (0 uses DefaultTokenTTL).
func NewHandler(store *Store, logger *slog.Logger, readToken, hmacKey string, tokenTTL time.Duration) *Handler {
	if tokenTTL == 0 {
		tokenTTL = DefaultTokenTTL
	}
	return &Handler{store: store, logger: logger, readToken: readToken, hmacKey: hmacKey, tokenTTL: tokenTTL}
}

// Common errors
var (
	ErrUnauthorized   = errors.New("authorization required")
	ErrInvalidToken   = errors.New("invalid token")
	ErrInvalidFormat  = errors.New("invalid authorization format")
	ErrMissingHMACKey = errors.New("token generation requires a configured HMAC key")
	ErrMissingFields  = errors.New("organization, repository, workflow, and job are required")
	ErrMissingRunID   = errors.New("run_id is required")
	ErrInvalidParams  = errors.New("org, repo, workflow and job are required")
	ErrNoMetrics      = errors.New("no metrics found for this workflow/job")
	ErrInvalidPercent = errors.New("invalid cpu_percentile: must be one of peak, p99, p95, p75, p50, avg")
)

// HealthResponse is the response for the health endpoint
type HealthResponse struct {
	Status string `json:"status"`
}

// MetricCreatedResponse is the response when a metric is successfully created
type MetricCreatedResponse struct {
	ID     uint   `json:"id"`
	Status string `json:"status"`
}

// GetMetricsRequest contains path parameters for getting metrics
type GetMetricsRequest struct {
	Org      string `path:"org"`
	Repo     string `path:"repo"`
	Workflow string `path:"workflow"`
	Job      string `path:"job"`
}

// GetSizingRequest contains path and query parameters for sizing endpoint
type GetSizingRequest struct {
	Org           string `path:"org"`
	Repo          string `path:"repo"`
	Workflow      string `path:"workflow"`
	Job           string `path:"job"`
	Runs          int    `query:"runs" default:"5" validate:"min=1,max=100" description:"Number of recent runs to analyze"`
	Buffer        int    `query:"buffer" default:"20" validate:"min=0,max=100" description:"Buffer percentage to add"`
	CPUPercentile string `query:"cpu_percentile" default:"p95" description:"CPU percentile to use (peak, p99, p95, p75, p50, avg)"`
}

// RegisterRoutes registers all HTTP routes on the Fuego server
func (h *Handler) RegisterRoutes(s *fuego.Server) {
	// Health endpoint (no auth)
	fuego.Get(s, "/health", h.Health)

	// API group with authentication
	api := fuego.Group(s, "/api/v1")

	// Token generation (requires read token)
	fuego.Post(api, "/token", h.GenerateToken, fuego.OptionMiddleware(h.requireReadToken))

	// Metrics endpoints
	fuego.Post(api, "/metrics", h.ReceiveMetrics) // Uses push token validated in handler
	fuego.Get(api, "/metrics/repo/{org}/{repo}/{workflow}/{job}", h.GetMetricsByWorkflowJob, fuego.OptionMiddleware(h.requireReadToken))

	// Sizing endpoint
	fuego.Get(api, "/sizing/repo/{org}/{repo}/{workflow}/{job}", h.GetSizing, fuego.OptionMiddleware(h.requireReadToken))
}

// requireReadToken is middleware that validates the read token
func (h *Handler) requireReadToken(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if h.readToken == "" {
			h.logger.Warn("no read-token configured, rejecting request", slog.String("path", r.URL.Path))
			http.Error(w, "authorization required", http.StatusUnauthorized)
			return
		}

		authHeader := r.Header.Get("Authorization")
		if authHeader == "" {
			h.logger.Warn("missing authorization header", slog.String("path", r.URL.Path))
			http.Error(w, "authorization required", http.StatusUnauthorized)
			return
		}

		const bearerPrefix = "Bearer "
		if !strings.HasPrefix(authHeader, bearerPrefix) {
			h.logger.Warn("invalid authorization format", slog.String("path", r.URL.Path))
			http.Error(w, "invalid authorization format", http.StatusUnauthorized)
			return
		}

		token := strings.TrimPrefix(authHeader, bearerPrefix)
		if subtle.ConstantTimeCompare([]byte(token), []byte(h.readToken)) != 1 {
			h.logger.Warn("invalid token", slog.String("path", r.URL.Path))
			http.Error(w, "invalid token", http.StatusUnauthorized)
			return
		}

		next.ServeHTTP(w, r)
	})
}

// validatePushToken checks push authentication via scoped HMAC token
func (h *Handler) validatePushToken(r *http.Request, exec ExecutionContext) error {
	if h.hmacKey == "" {
		h.logger.Warn("no HMAC key configured, rejecting push", slog.String("path", r.URL.Path))
		return ErrUnauthorized
	}

	authHeader := r.Header.Get("Authorization")
	if authHeader == "" {
		h.logger.Warn("missing push authorization", slog.String("path", r.URL.Path))
		return ErrUnauthorized
	}

	const bearerPrefix = "Bearer "
	if !strings.HasPrefix(authHeader, bearerPrefix) {
		h.logger.Warn("invalid push authorization format", slog.String("path", r.URL.Path))
		return ErrInvalidFormat
	}

	token := strings.TrimPrefix(authHeader, bearerPrefix)
	if !ValidateToken(h.hmacKey, token, exec.Organization, exec.Repository, exec.Workflow, exec.Job, h.tokenTTL) {
		h.logger.Warn("invalid push token", slog.String("path", r.URL.Path))
		return ErrInvalidToken
	}

	return nil
}

// Health returns the service health status
func (h *Handler) Health(c fuego.ContextNoBody) (HealthResponse, error) {
	return HealthResponse{Status: "ok"}, nil
}

// GenerateToken generates a scoped HMAC push token for a workflow/job
func (h *Handler) GenerateToken(c fuego.ContextWithBody[TokenRequest]) (TokenResponse, error) {
	if h.hmacKey == "" {
		return TokenResponse{}, fuego.BadRequestError{Detail: ErrMissingHMACKey.Error()}
	}

	req, err := c.Body()
	if err != nil {
		return TokenResponse{}, fuego.BadRequestError{Detail: "invalid JSON body"}
	}

	if req.Organization == "" || req.Repository == "" || req.Workflow == "" || req.Job == "" {
		return TokenResponse{}, fuego.BadRequestError{Detail: ErrMissingFields.Error()}
	}

	token := GenerateToken(h.hmacKey, req.Organization, req.Repository, req.Workflow, req.Job)
	return TokenResponse{Token: token}, nil
}

// ReceiveMetrics receives and stores metrics from a collector
func (h *Handler) ReceiveMetrics(c fuego.ContextNoBody) (MetricCreatedResponse, error) {
	var payload MetricsPayload
	if err := json.NewDecoder(c.Request().Body).Decode(&payload); err != nil {
		h.logger.Error("failed to decode payload", slog.String("error", err.Error()))
		return MetricCreatedResponse{}, fuego.BadRequestError{Detail: "invalid JSON payload"}
	}

	if payload.Execution.RunID == "" {
		return MetricCreatedResponse{}, fuego.BadRequestError{Detail: ErrMissingRunID.Error()}
	}

	// Validate push token
	if err := h.validatePushToken(c.Request(), payload.Execution); err != nil {
		return MetricCreatedResponse{}, fuego.UnauthorizedError{Detail: err.Error()}
	}

	id, err := h.store.SaveMetric(&payload)
	if err != nil {
		h.logger.Error("failed to save metric", slog.String("error", err.Error()))
		return MetricCreatedResponse{}, fuego.InternalServerError{Detail: "failed to save metric"}
	}

	h.logger.Info("metric saved",
		slog.Uint64("id", uint64(id)),
		slog.String("run_id", payload.Execution.RunID),
		slog.String("repository", payload.Execution.Repository),
	)

	c.SetStatus(http.StatusCreated)
	return MetricCreatedResponse{ID: id, Status: "created"}, nil
}

// GetMetricsByWorkflowJob retrieves all metrics for a specific workflow/job
func (h *Handler) GetMetricsByWorkflowJob(c fuego.ContextNoBody) ([]MetricResponse, error) {
	org := c.PathParam("org")
	repo := c.PathParam("repo")
	workflow := c.PathParam("workflow")
	job := c.PathParam("job")

	if org == "" || repo == "" || workflow == "" || job == "" {
		return nil, fuego.BadRequestError{Detail: ErrInvalidParams.Error()}
	}

	metrics, err := h.store.GetMetricsByWorkflowJob(org, repo, workflow, job)
	if err != nil {
		h.logger.Error("failed to get metrics", slog.String("error", err.Error()))
		return nil, fuego.InternalServerError{Detail: "failed to get metrics"}
	}

	// Convert to response type with Payload as JSON object
	response := make([]MetricResponse, len(metrics))
	for i, m := range metrics {
		response[i] = m.ToResponse()
	}

	return response, nil
}

// GetSizing computes Kubernetes resource sizing recommendations
func (h *Handler) GetSizing(c fuego.ContextNoBody) (SizingResponse, error) {
	org := c.PathParam("org")
	repo := c.PathParam("repo")
	workflow := c.PathParam("workflow")
	job := c.PathParam("job")

	if org == "" || repo == "" || workflow == "" || job == "" {
		return SizingResponse{}, fuego.BadRequestError{Detail: ErrInvalidParams.Error()}
	}

	// Parse query parameters with defaults
	runs := parseIntQueryParamFromContext(c, "runs", 5, 1, 100)
	buffer := parseIntQueryParamFromContext(c, "buffer", 20, 0, 100)
	cpuPercentile := c.QueryParam("cpu_percentile")
	if cpuPercentile == "" {
		cpuPercentile = "p95"
	}
	if !IsValidPercentile(cpuPercentile) {
		return SizingResponse{}, fuego.BadRequestError{Detail: ErrInvalidPercent.Error()}
	}

	metrics, err := h.store.GetRecentMetricsByWorkflowJob(org, repo, workflow, job, runs)
	if err != nil {
		h.logger.Error("failed to get metrics", slog.String("error", err.Error()))
		return SizingResponse{}, fuego.InternalServerError{Detail: "failed to get metrics"}
	}

	if len(metrics) == 0 {
		return SizingResponse{}, fuego.NotFoundError{Detail: ErrNoMetrics.Error()}
	}

	response, err := computeSizing(metrics, buffer, cpuPercentile)
	if err != nil {
		h.logger.Error("failed to compute sizing", slog.String("error", err.Error()))
		return SizingResponse{}, fuego.InternalServerError{Detail: "failed to compute sizing"}
	}

	return *response, nil
}

// parseIntQueryParamFromContext parses an integer query parameter with default, min, and max values
func parseIntQueryParamFromContext(c fuego.ContextNoBody, name string, defaultVal, minVal, maxVal int) int {
	strVal := c.QueryParam(name)
	if strVal == "" {
		return defaultVal
	}
	var val int
	if _, err := fmt.Sscanf(strVal, "%d", &val); err != nil {
		return defaultVal
	}
	if val < minVal {
		return minVal
	}
	if val > maxVal {
		return maxVal
	}
	return val
}