package middleware

import (
	"strconv"
	"strings"

	"github.com/gin-gonic/gin"
)

// CacheHeadersConfig defines cache-control rules per path prefix
type CacheHeadersConfig struct {
	Rules []CacheRule
}

// CacheRule maps a URL path prefix to cache headers
type CacheRule struct {
	PathPrefix string
	MaxAge     int    // seconds
	Directive  string // e.g. "public", "private", "no-cache"
	Immutable  bool
}

// DefaultCacheHeadersConfig returns production-ready cache header rules
// Reference: ORIGIN_PERFORMANCE_TARGETS.md §8.4
func DefaultCacheHeadersConfig() CacheHeadersConfig {
	return CacheHeadersConfig{
		Rules: []CacheRule{
			// Static assets (JS, CSS, fonts) — immutable with content hash
			{PathPrefix: "/static/", MaxAge: 31536000, Directive: "public", Immutable: true},
			{PathPrefix: "/assets/", MaxAge: 31536000, Directive: "public", Immutable: true},
			// Audio files — CDN cached for 7 days
			{PathPrefix: "/audio/", MaxAge: 604800, Directive: "public"},
			// HLS segments — short cache (live content changes)
			{PathPrefix: "/hls/", MaxAge: 60, Directive: "public"},
			// Images (covers, avatars) — CDN cached for 30 days
			{PathPrefix: "/images/", MaxAge: 2592000, Directive: "public"},
			{PathPrefix: "/uploads/", MaxAge: 86400, Directive: "public"},
			// API responses — no caching by default (handled by ResponseCache middleware)
			{PathPrefix: "/api/", MaxAge: 0, Directive: "no-cache"},
		},
	}
}

// CacheHeaders returns a middleware that sets appropriate Cache-Control headers
// based on the request path. This enables CDN and browser caching.
func CacheHeaders(cfg CacheHeadersConfig) gin.HandlerFunc {
	return func(c *gin.Context) {
		path := c.Request.URL.Path

		for _, rule := range cfg.Rules {
			if strings.HasPrefix(path, rule.PathPrefix) {
				setCacheHeaders(c, rule)
				break
			}
		}

		c.Next()
	}
}

func setCacheHeaders(c *gin.Context, rule CacheRule) {
	if rule.MaxAge == 0 && rule.Directive == "no-cache" {
		c.Header("Cache-Control", "no-cache, no-store, must-revalidate")
		c.Header("Pragma", "no-cache")
		return
	}

	var parts []string
	if rule.Directive != "" {
		parts = append(parts, rule.Directive)
	}
	if rule.MaxAge > 0 {
		parts = append(parts, "max-age="+strconv.Itoa(rule.MaxAge))
	}
	if rule.Immutable {
		parts = append(parts, "immutable")
	}

	if len(parts) > 0 {
		c.Header("Cache-Control", strings.Join(parts, ", "))
	}
}