// Package config loads and validates the backend's runtime configuration.
//
// Configuration comes from the process environment. A .env file in the
// repository root is read first as a convenience for local development, and
// never overrides a variable that is already set — so an explicit
// `DATABASE_PASSWORD=… go run ./cmd/api` always wins over the file.
//
// Nothing here has a credential baked in. Load fails loudly rather than
// falling back to a default host, database or user, because a silent default
// is how a development process ends up pointed at the wrong database.
package config

import (
	"fmt"
	"net/netip"
	"net/url"
	"os"
	"strconv"
	"strings"
	"time"
)

// The default model per tier, and the endpoint they are valid on.
//
// THESE THREE AND defaultBaseURL ARE ONE DECISION, not four. A model id is only
// meaningful against the service that serves it, so a Groq id with an OpenAI
// base URL is not a partial configuration — it is a broken one that starts
// cleanly and fails every run at request time. They changed together when the
// Anthropic path was removed and they have to keep changing together.
//
// Unlike the old single default, the tiers are no longer the same model: the
// point of a tier is that `fast` costs less than `deep`, and one id for all
// three made the distinction free and therefore meaningless.
const (
	defaultBaseURL       = "https://api.groq.com/openai/v1"
	defaultFastModel     = "openai/gpt-oss-20b"
	defaultBalancedModel = "openai/gpt-oss-120b"
	defaultDeepModel     = "openai/gpt-oss-120b"
)

// DefaultModels returns the model ids a deployment gets when MODEL_FAST,
// MODEL_BALANCED and MODEL_DEEP are all unset.
//
// Exported so the live suite can ask the provider whether it still serves them.
// It reads these rather than repeating the list because a second copy is the
// first thing that drifts, and drift is the exact failure that check defends
// against: these ids are retired on the provider's schedule, not this repo's.
func DefaultModels() (fast, balanced, deep string) {
	return defaultFastModel, defaultBalancedModel, defaultDeepModel
}

// Config is the whole of the Phase 1 configuration surface.
type Config struct {
	AppEnv    string
	Log       LogConfig
	HTTP      HTTPConfig
	DB        DBConfig
	Seed      SeedConfig
	Agents    AgentsConfig
	Model     ModelConfig
	Knowledge KnowledgeConfig
	OAuth     OAuthConfig
}

// OAuthConfig is the MCP surface's OAuth 2.1 identity.
//
// EMPTY IS THE DEFAULT AND IT MEANS "OFF". A deployment that sets neither
// OAUTH_ISSUER nor MCP_RESOURCE does not serve OAuth or MCP at all, and that is
// the correct default for every deployment that exists today — the routes are
// simply not registered, exactly as routeRuns is skipped without a model
// credential.
//
// NO PRODUCTION DOMAIN IS HARDCODED. Both values are URLs the operator supplies,
// because the issuer identifies the deployment and a default would be one
// deployment's identity baked into every other one.
//
// Issuer and Resource look similar and are not the same thing: the ISSUER
// identifies the authorization server ("who minted this token"), the RESOURCE
// identifies what the token is good for ("which MCP server may spend it"). A
// token's audience is checked against Resource. Conflating them is how a token
// for one service becomes spendable at another.
type OAuthConfig struct {
	// Issuer is the authorization server's base URL, e.g.
	// https://api.example.com. No trailing slash.
	Issuer string

	// Resource is the canonical MCP endpoint URI, e.g.
	// https://api.example.com/mcp. This becomes an issued token's audience.
	Resource string

	// LoginPath is where the authorization endpoint sends somebody who is not
	// signed in. A same-origin path, never an absolute URL — an absolute one
	// would be an open redirect waiting for a misconfiguration.
	LoginPath string
}

// Enabled reports whether this deployment serves OAuth and MCP.
func (c OAuthConfig) Enabled() bool { return c.Issuer != "" && c.Resource != "" }

// KnowledgeConfig routes the retrieval layer's embedding provider.
//
// The chat provider does not serve embeddings, so the dense half of hybrid
// retrieval needs its own provider and credential — this is a separate choice
// from MODEL_*, and pointing one of them somewhere new does not move the other.
//
// An empty key is legitimate: this service boots and serves without one, and
// retrieval degrades to keyword-only rather than failing — reported on every
// result, never silently. What is NOT legitimate is production running on the
// lexical stand-in, which is why that is a separate, deliberate opt-in rather
// than something an empty key falls back to.
type KnowledgeConfig struct {
	// EmbedProvider names which embedder to use: "voyage", "ollama",
	// "lexical", or "" to pick from what is configured.
	//
	// Explicit beats inferred here. The three differ in a way that is invisible
	// from the outside — all of them return vectors and retrieval works with
	// any of them — so a deployment silently running the stand-in would look
	// exactly like one running a real model, right up until somebody phrased a
	// question differently. Naming the provider makes the choice reviewable.
	EmbedProvider string

	// EmbedAPIKey is the hosted provider's credential (Voyage).
	EmbedAPIKey string

	// EmbedBaseURL is where a local model answers. Ollama's default is
	// http://localhost:11434.
	EmbedBaseURL string

	EmbedModel string
	EmbedDims  int

	// UseLexicalEmbedder swaps in the deterministic stand-in. Development only:
	// it is not semantic, and a corpus indexed with it retrieves on word overlap
	// alone. Load() refuses it outside development rather than trusting the
	// operator to have read the comment.
	//
	// Kept alongside EmbedProvider for the deployments that already set it.
	UseLexicalEmbedder bool
}

// ModelConfig routes an agent spec's reasoning tier to a model.
//
// A spec declares `reasoning: fast | balanced | deep`, never a model id, so the
// mapping is a deployment decision and changes without editing a definition.
// All three default to the same model: the tiers differ by *effort*, which the
// gateway owns, and a deployment that wants a cheaper model on the fast tier
// says so explicitly rather than inheriting a downgrade nobody chose.
//
// The API key may legitimately be empty outside production. This service has to
// boot without model credentials — migrations, seeding and every endpoint that
// is not an agent run work fine without one — so the failure belongs at the
// first model call, as a structured gateway.not_configured a run can end with,
// not at startup as a refusal to boot.
type ModelConfig struct {
	// Provider names the wire protocol. "openai" is the only one, and empty
	// means it; "anthropic" is refused at startup rather than ignored, because
	// a deployment still carrying it has not been told the path was removed.
	//
	// "openai" is not only OpenAI. Groq, Gemini's compatibility endpoint,
	// OpenRouter, Together, vLLM and a local Ollama all serve that same shape,
	// and BaseURL is what chooses between them — which is why one wire protocol
	// is not the same thing as one vendor.
	Provider string

	APIKey string

	// BaseURL points the provider at a specific service. Empty means the
	// default in defaultBaseURL, which the default model ids belong to.
	BaseURL string

	Fast            string
	Balanced        string
	Deep            string
	MaxOutputTokens int

	// ReasoningEffort opts into sending the tier's effort level on the
	// OpenAI-compatible wire. Off by default: reasoning models accept the
	// field and most others reject the entire request rather than ignoring it.
	ReasoningEffort bool
}

// SeedConfig locates the demo fixture. The file is generated from the frontend
// repository, so it lives beside the migrations rather than inside the Go
// module: regenerating it must not require rebuilding the binary.
type SeedConfig struct {
	FixturePath string
}

// AgentsConfig locates the curated agent specs that ship with the deployment.
//
// The same directory `importagents` publishes from — Dockerfile.api copies
// `agents/` to /app/agents beside the binary, and the importer's own `-dir`
// default is the same path. Pointing both at one directory is what makes the
// protected set and the published set the same set: an agent is built-in
// because the product ships its spec, not because a column says so.
//
// A missing directory is not a boot failure. This service runs in development
// checkouts and test binaries whose working directory has no `agents/`, and
// refusing to start over a protection list would take the API down to defend
// rows that deployment never created. The consequence is stated where it is
// loaded: the protected set is empty, and that is logged.
type AgentsConfig struct {
	CuratedPath string
}

type LogConfig struct {
	Level string
}

type HTTPConfig struct {
	Host            string
	Port            int
	ReadTimeout     time.Duration
	WriteTimeout    time.Duration
	IdleTimeout     time.Duration
	ShutdownTimeout time.Duration

	// CookieSameSite is the SameSite attribute on the session cookie:
	// "lax" (default), "none" or "strict".
	//
	// This exists because CORS is only half of what a cross-origin browser call
	// needs, and the other half is easy to miss. SameSite is judged on SITE
	// (registrable domain), not origin:
	//
	//   app.krow.com → api.krow.com    SAME site. Lax sends the cookie. ✓
	//   krow.vercel.app → api.krow.com CROSS site. Lax does NOT send it. ✗
	//   localhost:5173 → 127.0.0.1:8080  CROSS site — different hosts. ✗
	//
	// So a deployment whose frontend is on an unrelated domain gets a perfect
	// set of CORS headers and still no session, because the browser never
	// attaches the cookie. "none" is the only value that survives that, and it
	// requires Secure, which means HTTPS.
	//
	// Default stays "lax": it is the safe value, it is correct for the
	// same-site and same-origin deployments this is normally run as, and it
	// gives CSRF protection that "none" gives up.
	CookieSameSite string

	// CORSOrigins is the exact set of browser origins allowed to call the API.
	//
	// It exists for one reason: in local development the Vite dev server is an
	// origin of its own (http://localhost:5173) and the API is another
	// (http://127.0.0.1:8080), so every fetch from the frontend is
	// cross-origin. Empty means CORS is off and the API answers only
	// same-origin callers, which is the correct posture everywhere the
	// frontend is served from the same host as the API.
	//
	// Origins are matched exactly and echoed back one at a time. There is no
	// wildcard and no pattern: "*" would let any page on the internet read
	// this API, and once authentication exists that becomes a real hole rather
	// than a theoretical one.
	CORSOrigins []string

	// TrustedProxies are the networks a forwarded client address may be
	// believed from. Empty by default, and empty means "believe nothing".
	//
	// WHY THIS EXISTS
	//
	// Several limits on this API are keyed by the caller's network address:
	// failed logins, OAuth registration, and OAuth authorization before the
	// caller has signed in. Behind a reverse proxy every request arrives from
	// the proxy, so RemoteAddr is one constant value and those per-address
	// budgets silently become one budget for the entire deployment. The
	// symptom is users rate-limiting each other — one person retrying a
	// connector exhausts everybody's allowance.
	//
	// WHY IT IS NOT SIMPLY "READ X-FORWARDED-FOR"
	//
	// That header is client-supplied. A caller reaching the API directly can
	// invent one and mint a fresh budget per request, which is strictly worse
	// than sharing a bucket: it removes the limit entirely. The header is
	// meaningful only when the immediate peer is a proxy that is known to
	// rewrite it, which is what this list names.
	//
	// WHY THE DEFAULT IS EMPTY
	//
	// So that a missing or misspelt setting cannot open the spoofing hole. An
	// unconfigured deployment behaves exactly as it did before this setting
	// existed: RemoteAddr, and X-Forwarded-For ignored. The failure mode of
	// forgetting to set it is the old shared bucket, which is an availability
	// problem an operator will notice, rather than an unmetered endpoint which
	// they will not.
	//
	// Entries are CIDR blocks or bare addresses (a bare address is treated as
	// a single-host block). Both families are accepted. Set it to the network
	// the load balancer or ingress talks to the API from — see
	// .env.example and infrastructure/.env.docker.example.
	TrustedProxies []netip.Prefix
}

type DBConfig struct {
	Host             string
	Port             int
	Name             string
	User             string
	Password         string
	Schema           string
	SSLMode          string
	MaxOpenConns     int32
	MinIdleConns     int32
	ConnMaxLifetime  time.Duration
	ConnectTimeout   time.Duration
	StatementTimeout time.Duration
}

// DSN builds a libpq-style connection URL.
//
// Every component is URL-escaped: the local database is called "Krow-force",
// which is both mixed-case and hyphenated, and a password may contain anything
// at all. Escaping is not optional here.
func (d DBConfig) DSN() string {
	u := &url.URL{
		Scheme: "postgres",
		User:   url.UserPassword(d.User, d.Password),
		Host:   fmt.Sprintf("%s:%d", d.Host, d.Port),
		Path:   "/" + d.Name,
	}
	q := u.Query()
	q.Set("sslmode", d.SSLMode)
	// Pin the schema on every connection so no query can accidentally resolve
	// against a different one, and so nothing reaches for a system schema.
	q.Set("search_path", d.Schema)
	q.Set("connect_timeout", strconv.Itoa(int(d.ConnectTimeout.Seconds())))
	q.Set("statement_timeout", strconv.Itoa(int(d.StatementTimeout.Milliseconds())))
	u.RawQuery = q.Encode()
	return u.String()
}

// Redacted returns the DSN with the password replaced, for logs.
func (d DBConfig) Redacted() string {
	u, err := url.Parse(d.DSN())
	if err != nil {
		return "postgres://<unparseable>"
	}
	if _, hasPassword := u.User.Password(); hasPassword {
		u.User = url.UserPassword(u.User.Username(), "xxxxx")
	}
	return u.String()
}

// Load reads the environment, applies defaults and validates the result.
func Load() (*Config, error) {
	loadDotEnv(".env")

	var missing []string
	required := func(key string) string {
		v := strings.TrimSpace(os.Getenv(key))
		if v == "" {
			missing = append(missing, key)
		}
		return v
	}

	// Parsed before the literal below because it can fail, and a malformed
	// entry has to stop startup rather than be dropped: an operator who
	// mistypes the proxy network gets the shared-bucket behaviour back, and
	// silently is the one way they will not find out.
	trustedProxies, trustedProxiesErr := parseTrustedProxies(os.Getenv("HTTP_TRUSTED_PROXIES"))

	cfg := &Config{
		AppEnv: withDefault("APP_ENV", "development"),
		Log:    LogConfig{Level: withDefault("LOG_LEVEL", "info")},
		HTTP: HTTPConfig{
			Host:            withDefault("HTTP_HOST", "127.0.0.1"),
			Port:            intDefault("HTTP_PORT", 8080),
			ReadTimeout:     durationDefault("HTTP_READ_TIMEOUT", 15*time.Second),
			WriteTimeout:    durationDefault("HTTP_WRITE_TIMEOUT", DeepestAgentDeadline+30*time.Second),
			IdleTimeout:     durationDefault("HTTP_IDLE_TIMEOUT", 60*time.Second),
			ShutdownTimeout: durationDefault("HTTP_SHUTDOWN_TIMEOUT", 10*time.Second),
			CORSOrigins:     corsOrigins(withDefault("APP_ENV", "development")),
			// Empty when unset, which is NOT the same as "lax": unset means "let
			// the server derive it from the CORS posture", and an explicit value
			// overrides that derivation. See Server.sessionSameSite.
			CookieSameSite: strings.ToLower(strings.TrimSpace(os.Getenv("HTTP_COOKIE_SAMESITE"))),
			TrustedProxies: trustedProxies,
		},
		Seed: SeedConfig{
			FixturePath: withDefault("SEED_FIXTURE_PATH", "./seed/fixtures/seed.json"),
		},
		Agents: AgentsConfig{
			CuratedPath: withDefault("CURATED_AGENTS_PATH", "./agents"),
		},
		OAuth: OAuthConfig{
			// Trailing slashes trimmed here rather than at every use: the
			// canonical form of a resource URI has none, and a token minted
			// against ".../mcp/" would fail to validate against ".../mcp".
			Issuer:    strings.TrimRight(strings.TrimSpace(os.Getenv("OAUTH_ISSUER")), "/"),
			Resource:  strings.TrimRight(strings.TrimSpace(os.Getenv("MCP_RESOURCE")), "/"),
			LoginPath: withDefault("OAUTH_LOGIN_PATH", "/login"),
		},
		Knowledge: KnowledgeConfig{
			EmbedProvider: strings.ToLower(strings.TrimSpace(os.Getenv("EMBED_PROVIDER"))),
			EmbedAPIKey:   strings.TrimSpace(os.Getenv("VOYAGE_API_KEY")),
			EmbedBaseURL:  strings.TrimSpace(os.Getenv("EMBED_BASE_URL")),
			// No default model or width here: they differ per provider, and one
			// shared default would silently hand Ollama's dimensions to Voyage.
			// Resolved where the provider is chosen — see runtime.NewEmbedder.
			EmbedModel:         strings.TrimSpace(os.Getenv("EMBED_MODEL")),
			EmbedDims:          intDefault("EMBED_DIMENSIONS", 0),
			UseLexicalEmbedder: boolDefault("EMBED_USE_LEXICAL", false),
		},
		Model: ModelConfig{
			Provider: strings.ToLower(strings.TrimSpace(os.Getenv("MODEL_PROVIDER"))),
			// One spelling. ANTHROPIC_API_KEY used to be accepted as a
			// fallback and is now deliberately NOT read: with the Anthropic
			// path gone it would name a vendor this service cannot call, and
			// silently authenticating to Groq with a variable called
			// ANTHROPIC_API_KEY is the kind of lie an operator has to keep
			// re-reading. A stale one is caught at startup, not ignored.
			APIKey:   strings.TrimSpace(os.Getenv("MODEL_API_KEY")),
			BaseURL:  withDefault("MODEL_BASE_URL", defaultBaseURL),
			Fast:     withDefault("MODEL_FAST", defaultFastModel),
			Balanced: withDefault("MODEL_BALANCED", defaultBalancedModel),
			Deep:     withDefault("MODEL_DEEP", defaultDeepModel),
			// 16k keeps a non-streaming response inside the SDK's HTTP
			// timeout. The loop raises it and switches to streaming when it
			// needs a long answer; this is the ceiling for a single
			// unstreamed call, not the run's budget.
			MaxOutputTokens: intDefault("MODEL_MAX_OUTPUT_TOKENS", 16000),
			ReasoningEffort: boolDefault("MODEL_REASONING_EFFORT", false),
		},
		DB: DBConfig{
			Host:             required("DATABASE_HOST"),
			Port:             intDefault("DATABASE_PORT", 5432),
			Name:             required("DATABASE_NAME"),
			User:             required("DATABASE_USER"),
			Password:         os.Getenv("DATABASE_PASSWORD"), // may legitimately be empty (trust/peer auth)
			Schema:           withDefault("DATABASE_SCHEMA", "public"),
			SSLMode:          withDefault("DATABASE_SSLMODE", "disable"),
			MaxOpenConns:     int32(intDefault("DATABASE_MAX_OPEN_CONNS", 25)),
			MinIdleConns:     int32(intDefault("DATABASE_MIN_IDLE_CONNS", 2)),
			ConnMaxLifetime:  durationDefault("DATABASE_CONN_MAX_LIFETIME", 30*time.Minute),
			ConnectTimeout:   durationDefault("DATABASE_CONNECT_TIMEOUT", 5*time.Second),
			StatementTimeout: durationDefault("DATABASE_STATEMENT_TIMEOUT", 10*time.Second),
		},
	}

	if trustedProxiesErr != nil {
		return nil, trustedProxiesErr
	}
	if len(missing) > 0 {
		return nil, fmt.Errorf("missing required environment variables: %s "+
			"(copy .env.example to .env and fill them in)", strings.Join(missing, ", "))
	}
	if err := cfg.validate(); err != nil {
		return nil, err
	}
	return cfg, nil
}

// DeepestAgentDeadline is the longest a single agent run may take — the
// `deep` tier's deadline in runtime.LimitsForTier.
//
// Duplicated rather than imported because internal/runtime already imports
// this package, and a cycle to share one number is a bad trade. A test in
// internal/runtime asserts the two agree, so this drifting is a build failure
// rather than a discovery.
const DeepestAgentDeadline = 120 * time.Second

// validateWriteTimeout refuses a server that would cut off a run the runtime
// considers legal.
//
// HTTP_WRITE_TIMEOUT was 30s in production while every shipped agent runs at
// the `balanced` tier, whose deadline is 60s. The server therefore aborted the
// response on any run over half its allowed time, and the caller saw 502 Bad
// Gateway from the proxy in front — a gateway error for something no gateway
// did, which is why it read as an infrastructure fault for so long.
//
// Delegation made it routine rather than causing it: a parent that asks two
// subagents spends longer than one that answers alone. The misconfiguration
// predates it.
//
// Streaming hides it, and that is the trap. The chat panel uses SSE and
// survives, so the product looks healthy while every non-streaming caller — a
// webhook, a script, an integration — gets 502 on a slow question.
// validateModel refuses a model configuration that cannot work.
//
// Its own method for the same reason validateWriteTimeout is: these are the
// mistakes that produce a *runtime* symptom far from their cause — a deployment
// that believes it switched providers and is still being billed by the old one,
// or a production install with no credential that fails one run at a time
// instead of once at startup.
func (c *Config) validateModel() error {
	// "anthropic" is named separately from every other wrong value because it
	// is the one that used to be correct. A deployment still carrying it is not
	// a typo, it is a stack that has not been told the path was removed — and
	// the silent alternative is a service that believes it is on Claude while
	// every run goes to Groq and is billed there.
	switch c.Model.Provider {
	case "", "openai":
	case "anthropic":
		return fmt.Errorf("MODEL_PROVIDER=anthropic is no longer supported: the Anthropic " +
			"path was removed and this service speaks only the openai chat-completions " +
			"shape. Unset MODEL_PROVIDER (or set it to openai) and point MODEL_BASE_URL " +
			"at your provider")
	default:
		return fmt.Errorf("MODEL_PROVIDER must be openai (or empty, which means openai), got %q", c.Model.Provider)
	}
	// A credential under the old name is refused rather than ignored. Ignoring
	// it produces the worst version of this failure: a deployment that set a
	// key, sees no error, and fails every run on a missing credential it is
	// looking straight at.
	if os.Getenv("ANTHROPIC_API_KEY") != "" && c.Model.APIKey == "" {
		return fmt.Errorf("ANTHROPIC_API_KEY is set but is no longer read, and MODEL_API_KEY is " +
			"empty: the Anthropic path was removed. Rename the variable to MODEL_API_KEY " +
			"— and if that value is an Anthropic key, replace it, because nothing here can " +
			"call Anthropic any more")
	}
	// A local model needs no credential, and demanding one would make the
	// zero-cost development path impossible to configure. Everything else does:
	// a production deployment without a key fails every run at the gateway,
	// which is a misconfiguration wearing a runtime error's clothes.
	if c.AppEnv == "production" && c.Model.APIKey == "" && !isLoopback(c.Model.BaseURL) {
		return fmt.Errorf("MODEL_API_KEY is required when APP_ENV=production; " +
			"without it every agent run fails at the model gateway")
	}
	// A model id left over from the Anthropic path. THIS IS THE CHECK THAT
	// REPLACED the old "base URL set against the wrong provider" one, and it
	// guards the same failure from the other side.
	//
	// It is not hypothetical. A `claude-*` id sent to an OpenAI-compatible
	// endpoint is accepted by this process, rejected by the provider, and
	// surfaces as a 400 on EVERY run — which is exactly the incident that made
	// the gateway start carrying upstream error text in the first place. One
	// loud failure at startup is worth more than one per run.
	for _, m := range []struct{ key, id string }{
		{"MODEL_FAST", c.Model.Fast},
		{"MODEL_BALANCED", c.Model.Balanced},
		{"MODEL_DEEP", c.Model.Deep},
	} {
		if strings.HasPrefix(strings.ToLower(m.id), "claude") {
			return fmt.Errorf("%s is %q, but the Anthropic path was removed: no configured "+
				"provider serves a claude model, so every run on this tier would fail at "+
				"the gateway. Set it to a model id your MODEL_BASE_URL (%s) serves",
				m.key, m.id, c.Model.BaseURL)
		}
	}
	if c.Model.BaseURL != "" {
		u, err := url.Parse(c.Model.BaseURL)
		if err != nil || (u.Scheme != "http" && u.Scheme != "https") || u.Host == "" {
			return fmt.Errorf("MODEL_BASE_URL must be an http or https URL, got %q", c.Model.BaseURL)
		}
	}
	return nil
}

func (c *Config) validateWriteTimeout() error {
	if c.HTTP.WriteTimeout <= 0 {
		return nil // no deadline set; the server will not cut anything off
	}
	if c.HTTP.WriteTimeout < DeepestAgentDeadline {
		return fmt.Errorf(
			"HTTP_WRITE_TIMEOUT is %s but an agent run may take %s (the deep tier's "+
				"deadline); the server would abort the response while the run is still "+
				"legal, and the caller would see 502 from the proxy. Set it above %s",
			c.HTTP.WriteTimeout, DeepestAgentDeadline, DeepestAgentDeadline)
	}
	return nil
}

func (c *Config) validate() error {
	if err := c.validateWriteTimeout(); err != nil {
		return err
	}
	switch c.AppEnv {
	case "development", "staging", "production":
	default:
		return fmt.Errorf("APP_ENV must be development, staging or production, got %q", c.AppEnv)
	}
	if c.HTTP.Port < 1 || c.HTTP.Port > 65535 {
		return fmt.Errorf("HTTP_PORT out of range: %d", c.HTTP.Port)
	}
	if c.DB.Port < 1 || c.DB.Port > 65535 {
		return fmt.Errorf("DATABASE_PORT out of range: %d", c.DB.Port)
	}
	// The application owns exactly one schema and it is never a system schema.
	switch c.DB.Schema {
	case "pg_catalog", "pg_toast", "information_schema":
		return fmt.Errorf("DATABASE_SCHEMA must not be a PostgreSQL system schema, got %q", c.DB.Schema)
	}
	if strings.HasPrefix(c.DB.Schema, "pg_") {
		return fmt.Errorf("DATABASE_SCHEMA must not start with \"pg_\", got %q", c.DB.Schema)
	}
	if c.DB.MinIdleConns > c.DB.MaxOpenConns {
		return fmt.Errorf("DATABASE_MIN_IDLE_CONNS (%d) exceeds DATABASE_MAX_OPEN_CONNS (%d)",
			c.DB.MinIdleConns, c.DB.MaxOpenConns)
	}
	if c.AppEnv == "production" && c.DB.SSLMode == "disable" {
		return fmt.Errorf("DATABASE_SSLMODE=disable is not allowed when APP_ENV=production")
	}
	// A production deployment with no model credentials would accept agent runs
	// and fail every one of them at the gateway. That is a boot-time
	// misconfiguration wearing a runtime error's clothes, so it is caught here.
	// Development is left alone deliberately: working on migrations or the
	// definitions API must not require a key.
	if err := c.validateModel(); err != nil {
		return err
	}
	if c.Model.MaxOutputTokens < 1 {
		return fmt.Errorf("MODEL_MAX_OUTPUT_TOKENS must be at least 1, got %d", c.Model.MaxOutputTokens)
	}
	// The lexical embedder is a development stand-in that hashes words into a
	// vector. It is not semantic, so a production corpus indexed with it would
	// retrieve on word overlap alone — which looks like working retrieval and is
	// not. Refused here rather than trusted to an operator's reading of a
	// comment, because the failure is invisible from the outside: results come
	// back, they are just the wrong ones.
	switch c.Knowledge.EmbedProvider {
	case "", "voyage", "ollama", "lexical":
	default:
		return fmt.Errorf("EMBED_PROVIDER must be voyage, ollama or lexical, got %q",
			c.Knowledge.EmbedProvider)
	}
	if c.AppEnv == "production" &&
		(c.Knowledge.UseLexicalEmbedder || c.Knowledge.EmbedProvider == "lexical") {
		return fmt.Errorf("EMBED_USE_LEXICAL is a development stand-in and is not allowed when " +
			"APP_ENV=production; it is not a semantic embedder and a corpus indexed with it " +
			"retrieves on word overlap alone")
	}
	// Zero means "the provider's own default", resolved where the provider is
	// chosen. Only a negative value is a mistake.
	if c.Knowledge.EmbedDims < 0 {
		return fmt.Errorf("EMBED_DIMENSIONS cannot be negative, got %d", c.Knowledge.EmbedDims)
	}
	if err := c.validateOAuth(); err != nil {
		return err
	}
	for name, model := range map[string]string{
		"MODEL_FAST": c.Model.Fast, "MODEL_BALANCED": c.Model.Balanced, "MODEL_DEEP": c.Model.Deep,
	} {
		if strings.TrimSpace(model) == "" {
			return fmt.Errorf("%s must name a model", name)
		}
	}
	switch c.HTTP.CookieSameSite {
	// Unset. The server derives the mode from whether a CORS allowlist is
	// configured; there is nothing to validate.
	case "":
	case "lax", "strict":
	case "none":
		// SameSite=None without Secure is ignored — and in current browsers,
		// rejected outright — so the cookie would simply never be stored. The
		// Secure flag is set for every APP_ENV except development, so this is
		// the one combination that produces a silently sessionless deployment.
		if c.AppEnv == "development" {
			return fmt.Errorf("HTTP_COOKIE_SAMESITE=none requires the Secure cookie flag, " +
				"which is not set when APP_ENV=development; SameSite=None over plain HTTP " +
				"is rejected by browsers")
		}
	default:
		return fmt.Errorf("HTTP_COOKIE_SAMESITE must be lax, none or strict, got %q",
			c.HTTP.CookieSameSite)
	}
	for _, origin := range c.HTTP.CORSOrigins {
		// "*" is rejected rather than quietly honoured. The middleware echoes a
		// single matched origin, so a wildcard could only ever be a
		// misunderstanding of what this setting does.
		// "*" is not a stricter-than-necessary policy choice — it cannot work
		// here at all. Authentication is a cookie, so the API must answer
		// Access-Control-Allow-Credentials: true, and every browser REFUSES
		// the pairing of that header with Allow-Origin: "*". A deployment
		// configured this way would send correct-looking headers and have
		// every authenticated call blocked client-side.
		if origin == "*" {
			return fmt.Errorf(`HTTP_CORS_ORIGINS must list explicit origins; "*" cannot be used ` +
				`because this API authenticates with a cookie, and browsers reject ` +
				`Access-Control-Allow-Origin: "*" together with credentials. ` +
				`List each frontend origin, or serve the frontend from the API's own origin ` +
				`(then leave this unset and CORS is not involved at all)`)
		}
		if !strings.HasPrefix(origin, "http://") && !strings.HasPrefix(origin, "https://") {
			return fmt.Errorf("HTTP_CORS_ORIGINS entry %q must be a full origin including the scheme", origin)
		}
	}
	return nil
}

// devCORSOrigins are the origins the Vite dev server can occupy. Vite binds
// localhost by default and 127.0.0.1 when asked, and a browser treats those two
// as different origins, so both are listed. 4173 is `vite preview`.
// 5174 is where Vite lands when 5173 is already taken, which happens whenever a
// second dev server is started; an origin missing from this list is refused at
// the preflight with a bare 403 and no CORS headers, which reads as a server
// fault rather than a misconfigured port.
var devCORSOrigins = []string{
	"http://localhost:5173", "http://127.0.0.1:5173",
	"http://localhost:5174", "http://127.0.0.1:5174",
	"http://localhost:4173", "http://127.0.0.1:4173",
}

// corsOrigins reads HTTP_CORS_ORIGINS, a comma-separated allowlist.
//
// The development default is the Vite dev server, because that is the whole
// point of the setting in Phase 2D. Outside development the default is empty:
// a staging or production deployment that genuinely serves its frontend from
// another origin has to say so explicitly, rather than inheriting a list of
// localhost origins nobody reviewed.
func corsOrigins(appEnv string) []string {
	raw, set := os.LookupEnv("HTTP_CORS_ORIGINS")
	if !set {
		if appEnv == "development" {
			return devCORSOrigins
		}
		return nil
	}
	var out []string
	for _, part := range strings.Split(raw, ",") {
		// A trailing slash makes the string unequal to the Origin header the
		// browser actually sends, which fails in a way that looks like a
		// server bug rather than a typo.
		if o := strings.TrimRight(strings.TrimSpace(part), "/"); o != "" {
			out = append(out, o)
		}
	}
	return out
}

// parseTrustedProxies reads HTTP_TRUSTED_PROXIES, a comma-separated list of
// CIDR blocks or bare addresses.
//
// Unset or empty yields nil, which means no proxy is trusted and forwarded
// client addresses are ignored entirely. That is the safe default and the
// behaviour this API had before the setting existed.
//
// A bare address is accepted and widened to a single-host prefix, because
// "10.0.0.7" is what an operator reaches for when there is exactly one ingress
// and requiring them to write "10.0.0.7/32" only invites a mistake.
//
// Malformed entries are an error rather than a skip. Skipping one would leave
// the deployment quietly trusting a shorter list than the operator wrote, and
// the consequence — a proxy that is not believed, so every user shares one
// rate-limit bucket again — is precisely the fault this setting exists to fix.
func parseTrustedProxies(raw string) ([]netip.Prefix, error) {
	var out []netip.Prefix
	for _, part := range strings.Split(raw, ",") {
		entry := strings.TrimSpace(part)
		if entry == "" {
			continue
		}
		if prefix, err := netip.ParsePrefix(entry); err == nil {
			// Masked so that a block written with host bits set — 10.0.0.7/8,
			// which is easy to write and easy to misread — still contains what
			// its author meant. Unmasked, Prefix.Contains always reports false.
			out = append(out, prefix.Masked())
			continue
		}
		addr, err := netip.ParseAddr(entry)
		if err != nil {
			return nil, fmt.Errorf("HTTP_TRUSTED_PROXIES entry %q is not an IP address "+
				"or CIDR block (for example 10.0.0.0/8, 172.17.0.1 or fd00::/8)", entry)
		}
		// Unmap first: ::ffff:10.0.0.1 and 10.0.0.1 are the same host, and a
		// /128 around the mapped form would not match the peer address Go
		// reports for an IPv4 connection.
		addr = addr.Unmap()
		out = append(out, netip.PrefixFrom(addr, addr.BitLen()))
	}
	return out, nil
}

func withDefault(key, fallback string) string {
	if v := strings.TrimSpace(os.Getenv(key)); v != "" {
		return v
	}
	return fallback
}

// firstSet returns the first of several environment variables that has a value.
//
// For settings that have more than one legitimate spelling — a generic name and
// a provider-specific one — where the order expresses which wins rather than
// leaving it to whichever happens to be read last.
func firstSet(keys ...string) string {
	for _, k := range keys {
		if v := strings.TrimSpace(os.Getenv(k)); v != "" {
			return v
		}
	}
	return ""
}

// isLoopback reports whether a base URL points at this machine.
//
// A model served from localhost needs no credential, and requiring one would
// make the zero-cost local path impossible to configure. Host-only, so a
// remote service that merely mentions "localhost" in a path does not qualify.
func isLoopback(raw string) bool {
	if strings.TrimSpace(raw) == "" {
		return false
	}
	u, err := url.Parse(raw)
	if err != nil {
		return false
	}
	host := u.Hostname()
	return host == "localhost" || host == "127.0.0.1" || host == "::1"
}

// providerName renders the provider for an error message, naming the default
// rather than showing an empty string an operator then has to interpret.
func providerName(p string) string {
	if p == "" {
		return "openai (the default)"
	}
	return p
}

func intDefault(key string, fallback int) int {
	v := strings.TrimSpace(os.Getenv(key))
	if v == "" {
		return fallback
	}
	n, err := strconv.Atoi(v)
	if err != nil {
		return fallback
	}
	return n
}

// boolDefault reads a boolean flag.
//
// An unparseable value falls back rather than erroring, matching intDefault.
// The one asymmetry worth knowing: only the explicit true spellings turn a flag
// on, so a typo'd "yes" leaves a feature off rather than on — the safe
// direction for every flag this file currently carries.
func boolDefault(key string, fallback bool) bool {
	switch strings.ToLower(strings.TrimSpace(os.Getenv(key))) {
	case "":
		return fallback
	case "1", "true", "yes", "on":
		return true
	case "0", "false", "no", "off":
		return false
	default:
		return fallback
	}
}

func durationDefault(key string, fallback time.Duration) time.Duration {
	v := strings.TrimSpace(os.Getenv(key))
	if v == "" {
		return fallback
	}
	d, err := time.ParseDuration(v)
	if err != nil {
		return fallback
	}
	return d
}

// loadDotEnv reads KEY=VALUE lines, walking up from the working directory so
// `go run ./cmd/api` finds the repository-root .env. Existing environment
// variables always win. Absence of the file is not an error.
func loadDotEnv(name string) {
	dir, err := os.Getwd()
	if err != nil {
		return
	}
	for i := 0; i < 5; i++ {
		path := dir + string(os.PathSeparator) + name
		if data, err := os.ReadFile(path); err == nil {
			applyDotEnv(string(data))
			return
		}
		parent := parentDir(dir)
		if parent == dir {
			return
		}
		dir = parent
	}
}

func parentDir(dir string) string {
	i := strings.LastIndex(dir, string(os.PathSeparator))
	if i <= 0 {
		return dir
	}
	return dir[:i]
}

func applyDotEnv(content string) {
	for _, line := range strings.Split(content, "\n") {
		line = strings.TrimSpace(line)
		if line == "" || strings.HasPrefix(line, "#") {
			continue
		}
		key, value, ok := strings.Cut(line, "=")
		if !ok {
			continue
		}
		key = strings.TrimSpace(strings.TrimPrefix(key, "export "))
		value = strings.TrimSpace(value)
		if len(value) >= 2 {
			if (value[0] == '"' && value[len(value)-1] == '"') ||
				(value[0] == '\'' && value[len(value)-1] == '\'') {
				value = value[1 : len(value)-1]
			}
		}
		if _, present := os.LookupEnv(key); !present {
			_ = os.Setenv(key, value)
		}
	}
}

// validateOAuth checks the MCP surface's OAuth identity.
//
// Both values empty is the ordinary case and means the surface is off. Setting
// exactly one is always a mistake — a deployment that named an issuer but no
// resource would serve discovery documents pointing at a resource that does not
// exist — so it is refused at boot rather than at the first client connection.
func (c *Config) validateOAuth() error {
	issuer, resource := c.OAuth.Issuer, c.OAuth.Resource
	if issuer == "" && resource == "" {
		return nil
	}
	if issuer == "" || resource == "" {
		return fmt.Errorf("OAUTH_ISSUER and MCP_RESOURCE must be set together; " +
			"one without the other serves discovery documents that point nowhere")
	}

	for name, raw := range map[string]string{"OAUTH_ISSUER": issuer, "MCP_RESOURCE": resource} {
		parsed, err := url.Parse(raw)
		if err != nil || parsed.Host == "" {
			return fmt.Errorf("%s must be an absolute URL, got %q", name, raw)
		}
		// HTTPS everywhere except a loopback development host. OAuth 2.1
		// requires every authorization server endpoint to be served over
		// HTTPS; a token or code sent over plain http is a token on the wire.
		if parsed.Scheme != "https" && !isLoopback(raw) {
			return fmt.Errorf("%s must use https (http is permitted only on loopback), got %q", name, raw)
		}
		if parsed.Fragment != "" {
			return fmt.Errorf("%s must not contain a fragment, got %q", name, raw)
		}
	}

	// A same-origin path, never an absolute URL: the authorization endpoint
	// redirects here, and an operator-supplied absolute URL would be an open
	// redirect one config mistake away.
	if !strings.HasPrefix(c.OAuth.LoginPath, "/") || strings.HasPrefix(c.OAuth.LoginPath, "//") {
		return fmt.Errorf("OAUTH_LOGIN_PATH must be a same-origin path beginning with a single '/', got %q",
			c.OAuth.LoginPath)
	}
	return nil
}