// Package config defines the pages-server configuration: its shape, defaults,
// and validation. Loading (and the flag > env > file > default precedence) lives
// in load.go.
package config

import (
	"encoding"
	"fmt"
	"net"
	"net/netip"
	"net/url"
	"os"
	"path/filepath"
	"regexp"
	"strings"
	"time"
)

// ProjectNamePattern constrains project names. It is deliberately strict: the
// name becomes a "~name" entry inside $WEBROOT, so anything that could contain
// a path separator, a "..", or a leading dot must be impossible by construction.
var ProjectNamePattern = regexp.MustCompile(`^[a-z0-9][a-z0-9._-]{0,62}$`)

// AssembleMode selects how deployment directories are built from the CAS.
type AssembleMode string

const (
	// AssembleAuto probes for hardlink support at startup and falls back to copy.
	AssembleAuto AssembleMode = "auto"
	// AssembleHardlink requires hardlinks and fails loudly if unavailable.
	AssembleHardlink AssembleMode = "hardlink"
	// AssembleCopy always copies. Correct but uses disk proportional to content.
	AssembleCopy AssembleMode = "copy"
	// AssembleNone skips on-disk assembly entirely; content is served straight
	// from the CAS and $WEBROOT symlinks are not maintained.
	AssembleNone AssembleMode = "none"
)

func (m AssembleMode) valid() bool {
	switch m {
	case AssembleAuto, AssembleHardlink, AssembleCopy, AssembleNone:
		return true
	}
	return false
}

// Duration wraps time.Duration so it can be written as "15m" in TOML.
type Duration time.Duration

var _ encoding.TextUnmarshaler = (*Duration)(nil)

func (d *Duration) UnmarshalText(text []byte) error {
	v, err := time.ParseDuration(string(text))
	if err != nil {
		return err
	}
	*d = Duration(v)
	return nil
}

// Set implements flag.Value, so the same type backs both the TOML field and the
// command-line flag.
func (d *Duration) Set(s string) error { return d.UnmarshalText([]byte(s)) }

func (d Duration) MarshalText() ([]byte, error) { return []byte(d.String()), nil }
func (d Duration) String() string               { return time.Duration(d).String() }
func (d Duration) D() time.Duration             { return time.Duration(d) }

// Limits bounds what a single deployment may push. Per-project overrides live
// in the projects table; these are the server-wide ceilings.
type Limits struct {
	MaxFileBytes         int64 `toml:"max_file_bytes"`
	MaxManifestFiles     int   `toml:"max_manifest_files"`
	MaxConcurrentUploads int   `toml:"max_concurrent_uploads"`
	MaxManifestBytes     int64 `toml:"max_manifest_bytes"`
	MaxJSONBytes         int64 `toml:"max_json_bytes"`
}

// Config is the fully resolved server configuration.
type Config struct {
	DataDir string `toml:"data_dir"`
	Webroot string `toml:"webroot"`

	Listen    string `toml:"listen"`     // public static-content listener
	APIListen string `toml:"api_listen"` // management API listener

	// SiteURL is the public origin the static listener is reachable at, as seen
	// from outside — behind a reverse proxy that is a name the server itself
	// never learns. It exists only so API responses can tell a CI job where its
	// deployment landed; nothing about serving depends on it, so leaving it
	// empty simply omits the url field.
	SiteURL string `toml:"site_url"`

	TrustedProxyCIDRs []string     `toml:"trusted_proxy_cidrs"`
	AssembleMode      AssembleMode `toml:"assemble_mode"`

	LogLevel  string `toml:"log_level"`
	LogFormat string `toml:"log_format"`

	GCInterval        Duration `toml:"gc_interval"`
	ReconcileInterval Duration `toml:"reconcile_interval"`
	ShutdownGrace     Duration `toml:"shutdown_grace"`

	// ReadHeaderTimeout and ReadTimeout guard both listeners. There is
	// deliberately no WriteTimeout: a global write deadline on the static
	// listener would kill legitimate large downloads over slow links.
	ReadHeaderTimeout Duration `toml:"read_header_timeout"`
	ReadTimeout       Duration `toml:"read_timeout"`
	IdleTimeout       Duration `toml:"idle_timeout"`

	Limits Limits `toml:"limits"`

	// trustedNets is the parsed form of TrustedProxyCIDRs, filled by Validate.
	trustedNets []netip.Prefix
}

// Default returns the baseline configuration. Every other layer (file, env,
// flags) is applied on top of this.
func Default() Config {
	return Config{
		DataDir:           "/var/lib/pages-server",
		Webroot:           "/srv/www",
		Listen:            ":8080",
		APIListen:         "127.0.0.1:8081",
		TrustedProxyCIDRs: []string{"127.0.0.1/32", "::1/128"},
		AssembleMode:      AssembleAuto,
		LogLevel:          "info",
		LogFormat:         "json",
		GCInterval:        Duration(15 * time.Minute),
		ReconcileInterval: Duration(5 * time.Minute),
		ShutdownGrace:     Duration(30 * time.Second),
		ReadHeaderTimeout: Duration(10 * time.Second),
		ReadTimeout:       Duration(5 * time.Minute),
		IdleTimeout:       Duration(120 * time.Second),
		Limits: Limits{
			MaxFileBytes:         256 << 20, // 256 MiB
			MaxManifestFiles:     50000,
			MaxConcurrentUploads: 32,
			MaxManifestBytes:     64 << 20, // 64 MiB of manifest JSON
			MaxJSONBytes:         1 << 20,  // 1 MiB for ordinary API bodies
		},
	}
}

// DBPath is the SQLite database file.
func (c *Config) DBPath() string { return filepath.Join(c.DataDir, "pages.db") }

// CASDir holds content-addressed blobs.
func (c *Config) CASDir() string { return filepath.Join(c.DataDir, "cas") }

// DeploymentsDir holds assembled deployment trees.
func (c *Config) DeploymentsDir() string { return filepath.Join(c.DataDir, "deployments") }

// BootstrapTokenPath is where the first-run admin token is written.
func (c *Config) BootstrapTokenPath() string { return filepath.Join(c.DataDir, "bootstrap-token") }

// TrustedProxies returns the parsed trusted-proxy prefixes. Only requests whose
// direct peer falls inside one of these may have their X-Forwarded-For honoured.
func (c *Config) TrustedProxies() []netip.Prefix { return c.trustedNets }

// Validate checks the configuration and normalises it in place. It performs no
// I/O beyond stat-ing the configured directories' parents, so it is safe to run
// from --check-config without binding ports.
func (c *Config) Validate() error {
	if c.DataDir == "" {
		return fmt.Errorf("data_dir is required")
	}
	abs, err := filepath.Abs(c.DataDir)
	if err != nil {
		return fmt.Errorf("data_dir: %w", err)
	}
	c.DataDir = filepath.Clean(abs)

	if c.AssembleMode != AssembleNone {
		if c.Webroot == "" {
			return fmt.Errorf("webroot is required unless assemble_mode is %q", AssembleNone)
		}
		abs, err = filepath.Abs(c.Webroot)
		if err != nil {
			return fmt.Errorf("webroot: %w", err)
		}
		c.Webroot = filepath.Clean(abs)

		// $WEBROOT must not sit inside $DATA_DIR (or vice versa): the reconciler
		// removes stale "~name" symlinks from the webroot, and the GC removes
		// trees from the data dir. Overlapping them makes each capable of
		// deleting the other's state.
		if c.Webroot == c.DataDir {
			return fmt.Errorf("webroot and data_dir must differ (both %q)", c.DataDir)
		}
		if isUnder(c.Webroot, c.DataDir) || isUnder(c.DataDir, c.Webroot) {
			return fmt.Errorf("webroot %q and data_dir %q must not be nested", c.Webroot, c.DataDir)
		}
	}

	if !c.AssembleMode.valid() {
		return fmt.Errorf("assemble_mode: want auto|hardlink|copy|none, got %q", c.AssembleMode)
	}

	for _, spec := range []struct{ name, addr string }{
		{"listen", c.Listen},
		{"api_listen", c.APIListen},
	} {
		if spec.addr == "" {
			return fmt.Errorf("%s is required", spec.name)
		}
		if _, _, err := net.SplitHostPort(spec.addr); err != nil {
			return fmt.Errorf("%s %q: %w", spec.name, spec.addr, err)
		}
	}
	if c.Listen == c.APIListen {
		return fmt.Errorf("listen and api_listen must differ (both %q); "+
			"the management API must not share an origin with served content", c.Listen)
	}

	if c.SiteURL != "" {
		// Stored without the trailing slash so api.SiteURL can append one and
		// get exactly one back.
		c.SiteURL = strings.TrimRight(c.SiteURL, "/")
		u, err := url.Parse(c.SiteURL)
		if err != nil {
			return fmt.Errorf("site_url %q: %w", c.SiteURL, err)
		}
		if u.Scheme != "http" && u.Scheme != "https" {
			return fmt.Errorf("site_url %q must be an absolute http:// or https:// URL", c.SiteURL)
		}
		if u.Host == "" {
			return fmt.Errorf("site_url %q is missing a host", c.SiteURL)
		}
		if u.RawQuery != "" || u.Fragment != "" {
			return fmt.Errorf("site_url %q must not carry a query or fragment", c.SiteURL)
		}
	}

	c.trustedNets = c.trustedNets[:0]
	for _, s := range c.TrustedProxyCIDRs {
		p, err := netip.ParsePrefix(strings.TrimSpace(s))
		if err != nil {
			return fmt.Errorf("trusted_proxy_cidrs %q: %w", s, err)
		}
		c.trustedNets = append(c.trustedNets, p)
	}

	switch c.LogLevel {
	case "debug", "info", "warn", "error":
	default:
		return fmt.Errorf("log_level: want debug|info|warn|error, got %q", c.LogLevel)
	}
	switch c.LogFormat {
	case "json", "text":
	default:
		return fmt.Errorf("log_format: want json|text, got %q", c.LogFormat)
	}

	for _, spec := range []struct {
		name string
		d    Duration
	}{
		{"gc_interval", c.GCInterval},
		{"reconcile_interval", c.ReconcileInterval},
		{"shutdown_grace", c.ShutdownGrace},
		{"read_header_timeout", c.ReadHeaderTimeout},
		{"read_timeout", c.ReadTimeout},
		{"idle_timeout", c.IdleTimeout},
	} {
		if spec.d <= 0 {
			return fmt.Errorf("%s must be positive, got %s", spec.name, spec.d)
		}
	}

	if c.Limits.MaxFileBytes <= 0 {
		return fmt.Errorf("limits.max_file_bytes must be positive")
	}
	if c.Limits.MaxManifestFiles <= 0 {
		return fmt.Errorf("limits.max_manifest_files must be positive")
	}
	if c.Limits.MaxConcurrentUploads <= 0 {
		return fmt.Errorf("limits.max_concurrent_uploads must be positive")
	}
	if c.Limits.MaxManifestBytes <= 0 {
		return fmt.Errorf("limits.max_manifest_bytes must be positive")
	}
	if c.Limits.MaxJSONBytes <= 0 {
		return fmt.Errorf("limits.max_json_bytes must be positive")
	}
	return nil
}

// EnsureDirs creates the data directory layout. Separated from Validate so
// --check-config stays read-only.
func (c *Config) EnsureDirs() error {
	dirs := []string{c.DataDir, c.CASDir(), filepath.Join(c.CASDir(), "tmp"), c.DeploymentsDir()}
	if c.AssembleMode != AssembleNone {
		dirs = append(dirs, c.Webroot)
	}
	for _, d := range dirs {
		if err := os.MkdirAll(d, 0o755); err != nil {
			return fmt.Errorf("create %s: %w", d, err)
		}
	}
	return nil
}

// isUnder reports whether path is lexically inside base.
func isUnder(path, base string) bool {
	rel, err := filepath.Rel(base, path)
	if err != nil {
		return false
	}
	return rel != ".." && !strings.HasPrefix(rel, ".."+string(filepath.Separator))
}