// Package config parses Tapir's runtime configuration from environment
// variables into a typed struct. No secrets are baked into code: the gateway
// key and OAuth client secret are read from the environment (later resolved via
// op/ESO), and the OAuth refresh token is never held here — it lives behind the
// SecretStore port, addressed by the opaque TokenRef.
//
// Defaults target the homelab snapshot in docs/homelab-integration.md; every
// value is overridable so the same binary runs standalone or in-cluster.
package config

import (
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
	"time"
)

// Config is Tapir's fully-resolved runtime configuration.
type Config struct {
	// UserID is the Tapir user the run operates as. Stage 0 has exactly one.
	// It must be a UUID: it keys the UUID user_id/video_id columns (data-model).
	UserID string

	// GatewayURL is the OpenAI-compatible LiteLLM base URL (".../v1").
	GatewayURL string
	// GatewayKey authorizes the gateway. Read from env, never committed.
	GatewayKey string
	// SummarizerModel is the primary summarizer alias in host/name form, tried
	// first on every video, e.g. "koala/phi4-mini".
	SummarizerModel string
	// FallbackModel is the LOCAL fallback alias tried when the primary fails or
	// returns unparseable output (ADR-022). Kept local so content stays on the
	// homelab stack. Default is an IGUANA model (not koala) so the fallback runs
	// on a different host than the koala primary — koala carries other loads, and
	// a different host also means a different egress IP for the (rare) fallback.
	// Empty disables it.
	FallbackModel string
	// CloudFallbackModel is the worst-case EXTERNAL fallback alias, tried only
	// after every local endpoint has failed (ADR-022). For client deployments set
	// this empty so content never leaves the local stack. Default a berget alias.
	CloudFallbackModel string
	// SummaryMaxTokens caps the completion budget per summary call. Small-context
	// models (koala/phi4-mini, 8k) overflow when prompt + max_tokens exceeds the
	// window; a summary needs only a few hundred tokens, so the default is small.
	SummaryMaxTokens int
	// MaxTranscriptChars bounds the transcript text sent to the model so a long
	// transcript does not overflow a small-context primary. 0 disables truncation.
	MaxTranscriptChars int

	// MinVideoSeconds drops videos shorter than this from discovery (Shorts and
	// other sub-minute clips that are noise and waste the scarce caption-fetch
	// budget, ADR-014/ADR-023). Enforced via a cheap Data API videos.list lookup at
	// discovery, never the rate-limited caption path. 0 disables the filter.
	MinVideoSeconds int

	// ChannelCaptionlessThreshold is how many consecutive no-caption results a
	// channel may yield before its videos are suppressed from caption fetching
	// (ADR-024). 0 disables the per-channel caption memory entirely.
	ChannelCaptionlessThreshold int
	// ChannelCaptionlessWindow is how long a suppressed channel stays suppressed
	// before one video is re-probed (auto-recovery for a channel that adds captions).
	ChannelCaptionlessWindow time.Duration
	// SummarizerTimeout bounds a single completion call. Thinking models are
	// slow, so the default is generous.
	SummarizerTimeout time.Duration

	// DBDSN is the Postgres DSN for the store sink.
	DBDSN string

	// YouTube OAuth app credentials (the registered client), read from env.
	YTClientID     string
	YTClientSecret string
	// YTTokenRef is the opaque SecretStore reference under which the YouTube
	// refresh token is persisted/resolved. Not the token itself.
	YTTokenRef string
	// YTConnectRedirectURL is the public callback URL the web connect flow
	// registers with Google, e.g. "https://tapir.d-ma.be/oauth/youtube/callback".
	// Must be in the OAuth client's authorized redirects. Distinct from the CLI
	// auth command's localhost listener and from the Dex OIDC redirect.
	YTConnectRedirectURL string

	// SecretsFile is the path to the local file-backed SecretStore (0600). A
	// Stage-0 stand-in for op/ESO, swappable behind the SecretStore port.
	SecretsFile string

	// OAuthRedirectAddr is the host:port the `auth` command's local listener
	// binds for the OAuth redirect, e.g. "localhost:8080".
	OAuthRedirectAddr string

	// PollInterval, when > 0, makes `run` loop on that cadence; 0 means run once.
	PollInterval time.Duration

	// FetchBackoff is how long the run loop waits before re-fetching a transcript
	// that previously returned HTTP 429 (rate_limited). Inside the window the video
	// is skipped without hitting the caption endpoint, saving requests; after it
	// expires the video is retried. Zero means "always retry" (no backoff).
	FetchBackoff time.Duration

	// FetchRate is the minimum interval between outbound caption fetches across the
	// whole process — the shared per-egress-IP rate gate (ADR-014 item 2). It is
	// the gate that makes auto-summarize-on-a-schedule safe: scheduler runners and
	// the web click-path serialise through it. Zero = unlimited (dev/tests).
	FetchRate time.Duration

	// AutoSummarizeWindow bounds auto-summarization to recent videos: in automatic
	// mode the scheduler only summarizes videos published within this window of now.
	// Older videos are still discovered and listed, but wait for an explicit manual
	// "Summarize" — so a large back-catalogue does not self-inflict 429s against the
	// caption rate gate. Zero disables the bound (summarize every unseen video, the
	// pre-recency behaviour). Default ~7 days.
	AutoSummarizeWindow time.Duration

	// OnboardSummarizeCount caps how many of a freshly-connected user's newest
	// videos are summarized immediately on connect (the onboarding "it works"
	// burst). HARD-capped at maxOnboardSummarizeCount so onboarding can never
	// bulk-fetch; 0 disables the burst. Every fetch still flows through the shared
	// caption rate gate (ADR-014) — the cap bounds count, never the pacing. Default 3.
	OnboardSummarizeCount int

	// OnboardSummarizerModel is the summarizer alias the connect-time burst leads
	// its chain with (ADR-028) — a stronger model is affordable on the ≤3 summaries
	// that form a new user's first impression. It heads a burst-specific chain;
	// the standard chain (ADR-022) follows as resilience. Empty (or equal to
	// SummarizerModel) collapses the burst back onto the shared processor — the
	// reversibility lever. Default iguana/gemma4-26b (the brain-validated model).
	OnboardSummarizerModel string

	// OnboardMaxVideoSeconds upper-bounds the duration of a video the onboarding
	// burst will pick (ADR-028), so the burst does not spend a scarce caption fetch
	// on a multi-hour livestream VOD that passed the live filter once it ended. Only
	// a KNOWN duration outside [MinVideoSeconds, this] is dropped; a NULL/unknown
	// duration is kept (degrade-open). 0 disables the upper bound. Default 14400 (4h).
	OnboardMaxVideoSeconds int

	// DiscoveryInterval, when > 0, makes `serve` run in-process scheduled discovery
	// for ALL users on that cadence (ADR-018). Zero/unset = disabled, so dev and
	// tests never auto-fetch. Single-replica assumption — see cmdServe.
	DiscoveryInterval time.Duration

	// HTTPAddr is the listen address for `tapir serve` (the Stage-0 web UI).
	HTTPAddr string

	// MetricsAddr is the listen address for the Prometheus /metrics endpoint
	// (ADR-030). A SEPARATE port from HTTPAddr so /metrics is never exposed on the
	// public app — only scraped in-cluster. Empty disables the metrics server.
	MetricsAddr string

	// PublicURL is the externally-reachable base URL of the deployed service,
	// e.g. "https://tapir.d-ma.be". Used to build absolute links handed to humans
	// (the `tapir invite` URL). No trailing slash is assumed — callers trim it.
	PublicURL string

	// Dex OIDC (web login, ADR-011/012). When OIDCIssuer is empty, `serve` falls
	// back to the allow-all StubAuth (local dev). When set, serve uses Dex: any
	// Dex-authenticated subject may sign in, then registers a tapir user (ADR-012).
	OIDCIssuer      string
	DexClientID     string
	DexClientSecret string
	OIDCRedirectURL string
	SessionSecret   string
}

// DexConfigured reports whether Dex OIDC login is wired (issuer present). When
// false, `serve` uses StubAuth (dev only).
func (c Config) DexConfigured() bool { return strings.TrimSpace(c.OIDCIssuer) != "" }

// Defaults (see docs/homelab-integration.md). All overridable via env.
const (
	defaultGatewayURL             = "http://koala:30401/v1"
	defaultSummarizerModel        = "koala/phi4-mini"
	defaultFallbackModel          = "iguana/gemma4-26b"
	defaultCloudFallbackModel     = "berget/mistral-small"
	defaultSummaryMaxTokens       = 1500
	defaultMaxTranscriptChars     = 18000
	defaultMinVideoSeconds        = 60
	defaultCaptionlessThreshold   = 5
	defaultCaptionlessWindow      = 14 * 24 * time.Hour
	defaultSummarizerTimeout      = 5 * time.Minute
	defaultYTTokenRef             = "youtube/refresh_token"
	defaultYTConnectRedirectURL   = "https://tapir.d-ma.be/oauth/youtube/callback"
	defaultOAuthRedirectAddr      = "localhost:8080"
	defaultHTTPAddr               = ":8080"
	defaultMetricsAddr            = ":9090"
	defaultFetchBackoff           = time.Hour
	defaultFetchRate              = 2 * time.Second
	defaultPublicURL              = "https://tapir.d-ma.be"
	defaultAutoSummarizeWindow    = 7 * 24 * time.Hour
	defaultOnboardSummarizeCount  = 3
	maxOnboardSummarizeCount      = 5
	defaultOnboardSummarizerModel = "iguana/gemma4-26b"
	defaultOnboardMaxVideoSeconds = 14400 // 4h
)

// Load reads the environment into a Config, applying defaults. It does not
// validate that required fields are present — call ValidateForAuth or
// ValidateForRun for the command being run, so each command demands only what
// it needs.
func Load() (Config, error) {
	c := Config{
		UserID:                 os.Getenv("TAPIR_USER_ID"),
		GatewayURL:             envOr("TAPIR_GATEWAY_URL", defaultGatewayURL),
		GatewayKey:             os.Getenv("TAPIR_GATEWAY_KEY"),
		SummarizerModel:        envOr("TAPIR_SUMMARIZER_MODEL", defaultSummarizerModel),
		OnboardSummarizerModel: lookupOr("TAPIR_ONBOARD_SUMMARIZER_MODEL", defaultOnboardSummarizerModel),
		FallbackModel:          lookupOr("TAPIR_FALLBACK_MODEL", defaultFallbackModel),
		CloudFallbackModel:     lookupOr("TAPIR_CLOUD_FALLBACK_MODEL", defaultCloudFallbackModel),
		DBDSN:                  os.Getenv("TAPIR_DB_DSN"),
		YTClientID:             os.Getenv("TAPIR_YT_CLIENT_ID"),
		YTClientSecret:         os.Getenv("TAPIR_YT_CLIENT_SECRET"),
		YTTokenRef:             envOr("TAPIR_YT_TOKEN_REF", defaultYTTokenRef),
		YTConnectRedirectURL:   envOr("TAPIR_YT_CONNECT_REDIRECT_URL", defaultYTConnectRedirectURL),
		SecretsFile:            envOr("TAPIR_SECRETS_FILE", defaultSecretsFile()),
		OAuthRedirectAddr:      envOr("TAPIR_OAUTH_REDIRECT_ADDR", defaultOAuthRedirectAddr),
		HTTPAddr:               envOr("TAPIR_HTTP_ADDR", defaultHTTPAddr),
		MetricsAddr:            lookupOr("TAPIR_METRICS_ADDR", defaultMetricsAddr),
		PublicURL:              envOr("TAPIR_PUBLIC_URL", defaultPublicURL),
		OIDCIssuer:             os.Getenv("TAPIR_OIDC_ISSUER"),
		DexClientID:            os.Getenv("TAPIR_DEX_CLIENT_ID"),
		DexClientSecret:        os.Getenv("TAPIR_DEX_CLIENT_SECRET"),
		OIDCRedirectURL:        os.Getenv("TAPIR_OIDC_REDIRECT_URL"),
		SessionSecret:          os.Getenv("TAPIR_SESSION_SECRET"),
	}

	timeout, err := durationOr("TAPIR_SUMMARIZER_TIMEOUT", defaultSummarizerTimeout)
	if err != nil {
		return Config{}, err
	}
	c.SummarizerTimeout = timeout

	interval, err := durationOr("TAPIR_POLL_INTERVAL", 0)
	if err != nil {
		return Config{}, err
	}
	c.PollInterval = interval

	backoff, err := durationOr("TAPIR_FETCH_BACKOFF", defaultFetchBackoff)
	if err != nil {
		return Config{}, err
	}
	c.FetchBackoff = backoff

	fetchRate, err := durationOr("TAPIR_FETCH_RATE", defaultFetchRate)
	if err != nil {
		return Config{}, err
	}
	c.FetchRate = fetchRate

	discovery, err := durationOr("TAPIR_DISCOVERY_INTERVAL", 0)
	if err != nil {
		return Config{}, err
	}
	c.DiscoveryInterval = discovery

	autoWindow, err := durationOr("TAPIR_AUTO_SUMMARIZE_WINDOW", defaultAutoSummarizeWindow)
	if err != nil {
		return Config{}, err
	}
	c.AutoSummarizeWindow = autoWindow

	summaryTokens, err := intOr("TAPIR_SUMMARY_MAX_TOKENS", defaultSummaryMaxTokens)
	if err != nil {
		return Config{}, err
	}
	c.SummaryMaxTokens = summaryTokens

	maxChars, err := intOr("TAPIR_MAX_TRANSCRIPT_CHARS", defaultMaxTranscriptChars)
	if err != nil {
		return Config{}, err
	}
	if maxChars < 0 {
		maxChars = 0
	}
	c.MaxTranscriptChars = maxChars

	minVideo, err := intOr("TAPIR_MIN_VIDEO_SECONDS", defaultMinVideoSeconds)
	if err != nil {
		return Config{}, err
	}
	if minVideo < 0 {
		minVideo = 0
	}
	c.MinVideoSeconds = minVideo

	captionThreshold, err := intOr("TAPIR_CHANNEL_CAPTIONLESS_THRESHOLD", defaultCaptionlessThreshold)
	if err != nil {
		return Config{}, err
	}
	if captionThreshold < 0 {
		captionThreshold = 0
	}
	c.ChannelCaptionlessThreshold = captionThreshold

	captionWindow, err := durationOr("TAPIR_CHANNEL_CAPTIONLESS_WINDOW", defaultCaptionlessWindow)
	if err != nil {
		return Config{}, err
	}
	c.ChannelCaptionlessWindow = captionWindow

	onboard, err := intOr("TAPIR_ONBOARD_SUMMARIZE_COUNT", defaultOnboardSummarizeCount)
	if err != nil {
		return Config{}, err
	}
	if onboard < 0 {
		onboard = 0
	}
	if onboard > maxOnboardSummarizeCount {
		onboard = maxOnboardSummarizeCount
	}
	c.OnboardSummarizeCount = onboard

	onboardMax, err := intOr("TAPIR_ONBOARD_MAX_VIDEO_SECONDS", defaultOnboardMaxVideoSeconds)
	if err != nil {
		return Config{}, err
	}
	if onboardMax < 0 {
		onboardMax = 0
	}
	c.OnboardMaxVideoSeconds = onboardMax

	return c, nil
}

// ValidateForAuth checks the fields the `auth` command needs: the YouTube OAuth
// app credentials, a place to persist the token, and the redirect listener.
func (c Config) ValidateForAuth() error {
	return c.require(map[string]string{
		"TAPIR_YT_CLIENT_ID":     c.YTClientID,
		"TAPIR_YT_CLIENT_SECRET": c.YTClientSecret,
		"TAPIR_YT_TOKEN_REF":     c.YTTokenRef,
		"TAPIR_SECRETS_FILE":     c.SecretsFile,
	})
}

// ValidateForRun checks the fields the `run` command needs end to end.
func (c Config) ValidateForRun() error {
	return c.require(map[string]string{
		"TAPIR_USER_ID":          c.UserID,
		"TAPIR_GATEWAY_URL":      c.GatewayURL,
		"TAPIR_SUMMARIZER_MODEL": c.SummarizerModel,
		"TAPIR_DB_DSN":           c.DBDSN,
		"TAPIR_YT_CLIENT_ID":     c.YTClientID,
		"TAPIR_YT_CLIENT_SECRET": c.YTClientSecret,
		"TAPIR_YT_TOKEN_REF":     c.YTTokenRef,
		"TAPIR_SECRETS_FILE":     c.SecretsFile,
	})
}

// ValidateForServe checks the fields the `serve` command needs: a user to act
// as, the store DSN, and a listen address. Auth (Dex) config is validated by the
// auth layer the Conductor wires in, not here.
func (c Config) ValidateForServe() error {
	return c.require(map[string]string{
		"TAPIR_USER_ID":   c.UserID,
		"TAPIR_DB_DSN":    c.DBDSN,
		"TAPIR_HTTP_ADDR": c.HTTPAddr,
	})
}

func (c Config) require(fields map[string]string) error {
	var missing []string
	for name, val := range fields {
		if strings.TrimSpace(val) == "" {
			missing = append(missing, name)
		}
	}
	if len(missing) > 0 {
		return fmt.Errorf("missing required config: %s", strings.Join(sortedMissing(missing), ", "))
	}
	return nil
}

func sortedMissing(xs []string) []string {
	sort.Strings(xs)
	return xs
}

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

// lookupOr returns the env value when the key is PRESENT (even if empty), else
// fallback. Unlike envOr it lets an explicit empty value override the default —
// needed to DISABLE an optional fallback model (e.g. set the cloud fallback empty
// for a client deployment so content never leaves the local stack).
func lookupOr(key, fallback string) string {
	if v, ok := os.LookupEnv(key); ok {
		return v
	}
	return fallback
}

func intOr(key string, fallback int) (int, error) {
	v := os.Getenv(key)
	if v == "" {
		return fallback, nil
	}
	n, err := strconv.Atoi(v)
	if err != nil {
		return 0, fmt.Errorf("config: %s=%q: %w", key, v, err)
	}
	return n, nil
}

func durationOr(key string, fallback time.Duration) (time.Duration, error) {
	v := os.Getenv(key)
	if v == "" {
		return fallback, nil
	}
	d, err := time.ParseDuration(v)
	if err != nil {
		return 0, fmt.Errorf("config: %s=%q: %w", key, v, err)
	}
	return d, nil
}

// defaultSecretsFile resolves to <user-config-dir>/tapir/secrets.json, falling
// back to a cwd-relative path when the config dir is unavailable.
func defaultSecretsFile() string {
	dir, err := os.UserConfigDir()
	if err != nil {
		return "tapir-secrets.json"
	}
	return filepath.Join(dir, "tapir", "secrets.json")
}
