// Package runtimeconfig loads and persists the runtime-editable provider
// configuration: the independent LLM vendor groups in models.json (design/04
// §3.1). The .env LLM block is the final fallback; a present-and-valid
// models.json takes precedence and is hot-reloaded at runtime without a restart.
//
// models.json is gitignored (local runtime config) and holds API keys, so this
// package never logs a key and never exposes one un-masked in a Config().
package runtimeconfig

import (
	"crypto/rand"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"time"

	"git.yeij.top/AskaEth/Cyrene_v2/internal/config"
)

// Provider names recognized in models.json. They mirror the model adapter
// factory's protocol names so a group maps directly to a wire protocol.
const (
	ProviderOpenAI    = "openai"
	ProviderAnthropic = "anthropic"

	// modelsFileName is the models.json basename stored under the data dir.
	modelsFileName = "models.json"
)

// Group is one independent multi-supplier LLM configuration. Each vendor's
// base/key/model/fallback is a self-contained unit, so multiple vendors coexist
// and Provider selects the active wire protocol.
type Group struct {
	ID         string `json:"id"`
	Provider   string `json:"provider"`
	BaseURL    string `json:"baseUrl"`
	APIKey     string `json:"apiKey"`
	Model      string `json:"model"`
	Fallback   string `json:"fallback,omitempty"`
	Multimodal bool   `json:"multimodal,omitempty"`
}

// ErrInvalidGroup is returned when a group fails schema validation.
var ErrInvalidGroup = errors.New("runtimeconfig: invalid model group")

// DefaultPath returns the models.json path under dataDir.
func DefaultPath(dataDir string) string {
	return filepath.Join(dataDir, modelsFileName)
}

// Validate checks the group's required fields. It fails loudly so a bad group
// never silently produces a half-configured adapter.
func (g Group) Validate() error {
	if strings.TrimSpace(g.ID) == "" {
		return fmt.Errorf("id is required")
	}
	if g.Provider != ProviderOpenAI && g.Provider != ProviderAnthropic {
		return fmt.Errorf("provider %q must be openai or anthropic", g.Provider)
	}
	if strings.TrimSpace(g.BaseURL) == "" {
		return fmt.Errorf("baseUrl is required")
	}
	if strings.TrimSpace(g.Model) == "" {
		return fmt.Errorf("model is required")
	}
	return nil
}

// ToLLMConfig maps a group to the flat LLMConfig consumed by the adapter
// factory. The group's provider selects which config block is populated.
func (g Group) ToLLMConfig() config.LLMConfig {
	if g.Provider == ProviderAnthropic {
		return config.LLMConfig{
			Provider:          ProviderAnthropic,
			AnthropicBaseURL:  g.BaseURL,
			AnthropicAPIKey:   g.APIKey,
			AnthropicModel:    g.Model,
			AnthropicFallback: g.Fallback,
		}
	}
	return config.LLMConfig{
		Provider: ProviderOpenAI,
		BaseURL:  g.BaseURL,
		APIKey:   g.APIKey,
		Model:    g.Model,
		Fallback: g.Fallback,
	}
}

// MaskedKey returns a redacted form of the API key for display/logging. It never
// reveals more than the trailing 4 characters, so a key never lands verbatim in
// a log line or a wire response.
func (g Group) MaskedKey() string {
	k := strings.TrimSpace(g.APIKey)
	if k == "" {
		return ""
	}
	if len(k) <= 4 {
		return "****"
	}
	return "****" + k[len(k)-4:]
}

// LoadModels reads path and returns the effective LLM groups. When the file is
// absent it synthesizes a single group from env (the .env fallback). A
// present-but-invalid file falls back to env and returns a non-nil warning so
// the caller can log it; the returned groups are always non-empty.
func LoadModels(path string, env config.LLMConfig) ([]Group, error) {
	files, readErr := loadFile(path)
	if readErr == nil {
		return files, nil
	}
	// A missing file is the normal case (gitignored runtime config); only a
	// present-but-invalid file warrants a warning to the caller.
	var warn error
	if !os.IsNotExist(readErr) {
		warn = fmt.Errorf("runtimeconfig: %s: %w", path, readErr)
	}
	return GroupFromEnv(env), warn
}

// loadFile decodes and validates the models.json array. A nil/blank file, a
// JSON decode error or an empty array all return an error so the caller falls
// back to env.
func loadFile(path string) ([]Group, error) {
	raw, err := os.ReadFile(path)
	if err != nil {
		return nil, err
	}
	if len(strings.TrimSpace(string(raw))) == 0 {
		return nil, fmt.Errorf("%w: empty file", ErrInvalidGroup)
	}
	var groups []Group
	dec := json.NewDecoder(strings.NewReader(string(raw)))
	if err := dec.Decode(&groups); err != nil {
		return nil, fmt.Errorf("%w: decode: %v", ErrInvalidGroup, err)
	}
	if len(groups) == 0 {
		return nil, fmt.Errorf("%w: no groups", ErrInvalidGroup)
	}
	for i, g := range groups {
		if err := g.Validate(); err != nil {
			return nil, fmt.Errorf("%w: group %d: %v", ErrInvalidGroup, i, err)
		}
	}
	return groups, nil
}

// GroupFromEnv synthesizes a single group from the active env LLM block: the
// anthropic block when LLM_PROVIDER=anthropic, otherwise the flat OpenAI-compatible
// block. It is the .env fallback used when models.json is absent or invalid.
func GroupFromEnv(env config.LLMConfig) []Group {
	if env.Provider == ProviderAnthropic {
		return []Group{{
			ID:         ProviderAnthropic,
			Provider:   ProviderAnthropic,
			BaseURL:    env.AnthropicBaseURL,
			APIKey:     env.AnthropicAPIKey,
			Model:      env.AnthropicModel,
			Fallback:   env.AnthropicFallback,
			Multimodal: env.VisionModel != "",
		}}
	}
	return []Group{{
		ID:         ProviderOpenAI,
		Provider:   ProviderOpenAI,
		BaseURL:    env.BaseURL,
		APIKey:     env.APIKey,
		Model:      env.Model,
		Fallback:   env.Fallback,
		Multimodal: env.VisionModel != "",
	}}
}

// Upsert returns a copy of groups with g inserted or replaced in place by ID,
// preserving order. A blank ID is assigned a generated id so a panel save
// without an explicit id still produces a stable, addressable group.
func Upsert(groups []Group, g Group) []Group {
	if strings.TrimSpace(g.ID) == "" {
		g.ID = NewID()
	}
	out := make([]Group, 0, len(groups)+1)
	replaced := false
	for _, cur := range groups {
		if cur.ID == g.ID {
			out = append(out, g)
			replaced = true
			continue
		}
		out = append(out, cur)
	}
	if !replaced {
		out = append(out, g)
	}
	return out
}

// Activate returns groups with g promoted to the front (index 0 = the group a
// new request uses by default). An existing group with the same id is replaced
// and re-prepended, so a panel save both updates the group and makes it the live
// provider. A blank ID is assigned a generated id.
func Activate(groups []Group, g Group) []Group {
	if strings.TrimSpace(g.ID) == "" {
		g.ID = NewID()
	}
	out := make([]Group, 0, len(groups)+1)
	out = append(out, g)
	for _, cur := range groups {
		if cur.ID == g.ID {
			continue
		}
		out = append(out, cur)
	}
	return out
}

// SaveModels writes groups as a pretty-printed JSON array to path with mode
// 0600 (the file holds API keys). It writes to a temp file then renames so a
// concurrent reader never sees a partial file. Every group is validated first.
func SaveModels(path string, groups []Group) error {
	dir := filepath.Dir(path)
	if dir != "" && dir != "." {
		if err := os.MkdirAll(dir, 0o755); err != nil {
			return fmt.Errorf("runtimeconfig: mkdir: %w", err)
		}
	}
	for _, g := range groups {
		if err := g.Validate(); err != nil {
			return fmt.Errorf("runtimeconfig: save: %w", err)
		}
	}
	raw, err := json.MarshalIndent(groups, "", "  ")
	if err != nil {
		return fmt.Errorf("runtimeconfig: marshal: %w", err)
	}
	tmp := path + ".tmp"
	if err := os.WriteFile(tmp, raw, 0o600); err != nil {
		return fmt.Errorf("runtimeconfig: write %s: %w", tmp, err)
	}
	if err := os.Rename(tmp, path); err != nil {
		return fmt.Errorf("runtimeconfig: rename: %w", err)
	}
	return nil
}

// NewID returns a 16-byte hex id, used for a group saved without an explicit id.
func NewID() string {
	b := make([]byte, 16)
	if _, err := rand.Read(b); err != nil {
		return fmt.Sprintf("id-%d", newTimeUnixNano())
	}
	return hex.EncodeToString(b)
}

// newTimeUnixNano returns the current unix-nano as an integer, as a fallback id
// source when the crypto RNG fails.
func newTimeUnixNano() int64 {
	return time.Now().UnixNano()
}