package middleware

import (
    "net/http"
    "path/filepath"
    "strings"

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

// AssetCacheControl sets optimal Cache-Control headers for static assets served by this server.
// It only affects GET requests for well-known static prefixes and does not override
// cache headers explicitly set by handlers downstream (they can still modify after c.Next if needed).
func AssetCacheControl() gin.HandlerFunc {
    return func(c *gin.Context) {
        // Only apply to GET requests
        if c.Request.Method == http.MethodGet {
            p := c.Request.URL.Path
            lower := strings.ToLower(p)
            switch {
            // Specific: YouTube channel static cache can be cached longer (content changes infrequently)
            case strings.HasPrefix(lower, "/cache/prefetch/") && strings.HasSuffix(lower, "youtube_channel.json"):
                c.Header("Cache-Control", "public, max-age=3600") // 1 hour
            case strings.HasPrefix(lower, "/dist/"):
                // Fingerprinted build assets should be cached for a year and immutable
                c.Header("Cache-Control", "public, max-age=31536000, immutable")
            case strings.HasPrefix(lower, "/uploads/"):
                // User uploads: cache for a week; allow clients to revalidate if replaced
                // Heuristic: if file name appears fingerprinted (e.g., .<hash>.ext), use longer cache
                base := filepath.Base(lower)
                if looksFingerprinted(base) {
                    c.Header("Cache-Control", "public, max-age=31536000, immutable")
                } else {
                    c.Header("Cache-Control", "public, max-age=604800") // 7 days
                }
            case strings.HasPrefix(lower, "/cache/"):
                // Prefetched JSON and other generated cache files: short to medium cache
                c.Header("Cache-Control", "public, max-age=300") // 5 minutes
            }
        }
        c.Next()
    }
}

// looksFingerprinted checks if a filename contains a long hex-like segment before the extension
// e.g. logo.7eacd9f0bfa04928a9b6936140168f58.png
func looksFingerprinted(name string) bool {
    dot := strings.LastIndexByte(name, '.')
    if dot <= 0 || dot >= len(name)-1 {
        return false
    }
    core := name[:dot]
    // Find final segment after last dot/underscore/hyphen in core
    lastSep := strings.LastIndexAny(core, "._-")
    if lastSep < 0 || lastSep+1 >= len(core) {
        return false
    }
    seg := core[lastSep+1:]
    if len(seg) < 16 { // require at least 16 chars to treat as a hash
        return false
    }
    // hex-like check
    for i := 0; i < len(seg); i++ {
        ch := seg[i]
        if !((ch >= '0' && ch <= '9') || (ch >= 'a' && ch <= 'f')) {
            return false
        }
    }
    return true
}