// Package llamaswap implements majordomo's provider contract for llama-swap
// (https://github.com/mostlygeek/llama-swap), an on-demand model-swapping
// proxy that fronts llama.cpp (and stable-diffusion.cpp) servers, loading and
// hot-swapping the requested model per request.
//
// Chat is OpenAI Chat Completions, byte-for-byte: this package does NOT carry
// its own chat wire client. Provider.Model delegates to provider/openai
// pointed at {baseURL}/v1 (ADR-0007: reuse, don't duplicate). What this
// package adds beyond a bare OpenAI-compat endpoint is the "tailored" surface:
//
//   - llama-swap management endpoints exposed as concrete methods — ListModels
//     (GET /v1/models), Running (GET /running), Unload (POST /api/models/unload),
//     ListVoices (GET /v1/audio/voices), Health (GET /health) — which have no
//     place on the canonical llm.Provider interface;
//   - image generation + editing via the imagegen interfaces (see image.go);
//   - speech synthesis + transcription via the audio interfaces (see audio.go); and
//   - swap-aware defaults: the HTTP client carries NO timeout, because the
//     first request to an unloaded model blocks while llama-swap spawns the
//     upstream (its healthCheckTimeout is at least 15s). Bound a call with a
//     context deadline, never a client timeout.
//
// DSN form (registered as the "llama-swap" scheme): llama-swap://token@host:port
// builds an http:// base URL (llama-swap is local-first; a TLS-fronted instance
// can use the openai:// scheme for chat instead).
package llamaswap

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"mime"
	"mime/multipart"
	"net/http"
	"strings"

	"gitea.stevedudenhoeffer.com/steve/majordomo/llm"
	"gitea.stevedudenhoeffer.com/steve/majordomo/provider/openai"
)

// DefaultName is the registry name used when WithName is not given.
const DefaultName = "llama-swap"

// maxResponseBytes caps the JSON body read on the success path. Generous
// enough for a multi-image b64 payload, bounded so a hostile/buggy upstream
// can't make a decode allocate without limit.
const maxResponseBytes = 64 << 20

// maxVideoResponseBytes caps the /v1/videos/sync body — the response IS an
// encoded clip, which legitimately dwarfs any JSON/audio payload (a long
// high-bitrate generation can pass 64MB). Still bounded so a buggy upstream
// can't allocate without limit.
const maxVideoResponseBytes = 512 << 20

// Provider is a llama-swap client. It satisfies llm.Provider (chat, delegated
// to provider/openai) and imagegen.Provider (image generation), and exposes
// llama-swap's management endpoints as concrete methods.
type Provider struct {
	name    string
	baseURL string // no trailing slash, no /v1 suffix; e.g. "http://host:port"
	token   string // bearer credential; empty = no auth (local)
	client  *http.Client
}

// Option configures the provider.
type Option func(*Provider)

// WithName overrides the registry name (default "llama-swap").
func WithName(name string) Option { return func(p *Provider) { p.name = name } }

// WithBaseURL sets the llama-swap base URL (scheme://host[:port]); the /v1 and
// management paths are appended internally. A trailing slash is trimmed.
func WithBaseURL(u string) Option {
	return func(p *Provider) { p.baseURL = strings.TrimRight(u, "/") }
}

// WithToken sets the bearer token (llama-swap API key). Empty means no
// Authorization header.
func WithToken(token string) Option { return func(p *Provider) { p.token = token } }

// WithHTTPClient overrides the HTTP client. Prefer context deadlines over a
// client timeout: a cold model swap can legitimately take many seconds.
func WithHTTPClient(c *http.Client) Option {
	return func(p *Provider) {
		if c != nil {
			p.client = c
		}
	}
}

// New creates a llama-swap provider. Construction never fails; a missing base
// URL surfaces at request time. The default client has no timeout (swap cold
// starts); bound calls with a context deadline.
func New(opts ...Option) *Provider {
	p := &Provider{name: DefaultName, client: &http.Client{}}
	for _, opt := range opts {
		opt(p)
	}
	return p
}

// Name implements llm.Provider and imagegen.Provider.
func (p *Provider) Name() string { return p.name }

// BaseURL reports the configured base URL (diagnostics).
func (p *Provider) BaseURL() string { return p.baseURL }

// Model implements llm.Provider via llama-swap's OpenAI-compatible chat
// endpoint, delegating to provider/openai. The id is passed through verbatim
// and selects which upstream llama-swap loads.
func (p *Provider) Model(id string, opts ...llm.ModelOption) (llm.Model, error) {
	if err := p.requireBaseURL(); err != nil {
		return nil, err
	}
	return p.chatProvider().Model(id, opts...)
}

// chatProvider builds the OpenAI-compatible client for llama-swap's chat API.
// Why a placeholder key when token is empty: the openai client treats a blank
// key as a synthetic 401, but a local llama-swap may require no auth at all —
// a bearer it ignores is harmless. Why legacy max_tokens: llama.cpp's OpenAI
// shim honors "max_tokens", not "max_completion_tokens".
func (p *Provider) chatProvider() *openai.Provider {
	key := p.token
	if key == "" {
		key = "no-key"
	}
	return openai.New(
		openai.WithName(p.name),
		openai.WithBaseURL(p.baseURL+"/v1"),
		openai.WithAPIKey(key),
		openai.WithLegacyMaxTokens(),
		openai.WithHTTPClient(p.client),
	)
}

// --- management endpoints ---

// ModelInfo is one entry from llama-swap's GET /v1/models (the OpenAI model
// list shape). Fields llama-swap adds beyond these are ignored.
type ModelInfo struct {
	ID      string `json:"id"`
	Object  string `json:"object"`
	OwnedBy string `json:"owned_by"`
}

// ListModels returns the models llama-swap is configured to serve (GET
// /v1/models). Unlisted models are excluded by llama-swap itself.
func (p *Provider) ListModels(ctx context.Context) ([]ModelInfo, error) {
	var out struct {
		Data []ModelInfo `json:"data"`
	}
	if err := p.doJSON(ctx, http.MethodGet, "/v1/models", "", nil, &out); err != nil {
		return nil, err
	}
	return out.Data, nil
}

// Running returns llama-swap's currently-loaded models as the raw GET /running
// payload. Why raw: llama-swap's /running shape is not a stable, OpenAI-style
// contract, so this exposes the endpoint without pinning a schema this package
// would have to guess.
func (p *Provider) Running(ctx context.Context) (json.RawMessage, error) {
	var out json.RawMessage
	if err := p.doJSON(ctx, http.MethodGet, "/running", "", nil, &out); err != nil {
		return nil, err
	}
	return out, nil
}

// Unload unloads a running model to free its resources (POST
// /api/models/unload/:model). An empty model unloads all running models (POST
// /api/models/unload).
func (p *Provider) Unload(ctx context.Context, model string) error {
	path := "/api/models/unload"
	if model != "" {
		// Why reject rather than percent-escape: llama-swap model ids legitimately
		// contain ":" (e.g. "qwen3:14b"), which is path-legal and must reach the
		// server verbatim; only path-structure characters are dangerous (they'd
		// redirect the request to another endpoint), and those never appear in a
		// real model id.
		if strings.ContainsAny(model, "/?#") {
			return fmt.Errorf("llama-swap: invalid model id %q for unload (contains a path separator)", model)
		}
		path += "/" + model
	}
	return p.doJSON(ctx, http.MethodPost, path, "", nil, nil)
}

// --- shared HTTP helpers for management + image + audio endpoints ---

// requireBaseURL is the shared guard for every entry point: construction
// never fails (see New), so a missing base URL surfaces here, at use time.
func (p *Provider) requireBaseURL() error {
	if p.baseURL == "" {
		return fmt.Errorf("llama-swap provider %q: no base URL configured (set one via WithBaseURL or an LLM_* env DSN)", p.name)
	}
	return nil
}

// newRequest builds an authenticated request relative to baseURL.
// contentType is applied only when a body is present.
func (p *Provider) newRequest(ctx context.Context, method, path, contentType string, body io.Reader) (*http.Request, error) {
	req, err := http.NewRequestWithContext(ctx, method, p.baseURL+path, body)
	if err != nil {
		return nil, fmt.Errorf("llama-swap: build request: %w", err)
	}
	if body != nil && contentType != "" {
		req.Header.Set("Content-Type", contentType)
	}
	if p.token != "" {
		req.Header.Set("Authorization", "Bearer "+p.token)
	}
	return req, nil
}

// doJSON performs a request to a llama-swap endpoint relative to baseURL,
// optionally encoding body and decoding into out (either may be nil). model
// labels the failing target in any *llm.APIError ("" for endpoints that aren't
// model-specific). Transport failures are wrapped raw so llm.Classify still
// sees the underlying net error; non-2xx responses become *llm.APIError.
func (p *Provider) doJSON(ctx context.Context, method, path, model string, body, out any) error {
	if err := p.requireBaseURL(); err != nil {
		return err
	}
	var rdr io.Reader
	if body != nil {
		b, err := json.Marshal(body)
		if err != nil {
			return fmt.Errorf("llama-swap: encode request: %w", err)
		}
		rdr = bytes.NewReader(b)
	}
	req, err := p.newRequest(ctx, method, path, "application/json", rdr)
	if err != nil {
		return err
	}
	resp, err := p.client.Do(req)
	if err != nil {
		return fmt.Errorf("llama-swap: do request: %w", err)
	}
	defer resp.Body.Close()
	if resp.StatusCode/100 != 2 {
		return p.apiError(resp, model)
	}
	if out != nil {
		if err := json.NewDecoder(io.LimitReader(resp.Body, maxResponseBytes)).Decode(out); err != nil {
			return fmt.Errorf("llama-swap: decode response: %w", err)
		}
	} else {
		// Drain (bounded) so the connection can be reused.
		_, _ = io.Copy(io.Discard, io.LimitReader(resp.Body, maxResponseBytes))
	}
	return nil
}

// apiError converts a non-2xx response into *llm.APIError, tolerating the
// OpenAI {"error":{"message",...}} envelope, the Ollama-style {"error":"..."}
// string form, and a raw body.
func (p *Provider) apiError(resp *http.Response, model string) error {
	e := &llm.APIError{Provider: p.name, Model: model, Status: resp.StatusCode}
	body, _ := io.ReadAll(io.LimitReader(resp.Body, 1<<20))

	var env struct {
		Error json.RawMessage `json:"error"`
	}
	if json.Unmarshal(body, &env) == nil && len(env.Error) > 0 {
		var obj struct {
			Message string `json:"message"`
			Type    string `json:"type"`
			Code    string `json:"code"`
		}
		if json.Unmarshal(env.Error, &obj) == nil && (obj.Message != "" || obj.Code != "" || obj.Type != "") {
			e.Message = obj.Message
			e.Code = obj.Code
			if e.Code == "" {
				e.Code = obj.Type
			}
			return e
		}
		var msg string
		if json.Unmarshal(env.Error, &msg) == nil && msg != "" {
			e.Message = msg
			return e
		}
	}
	e.Message = strings.TrimSpace(string(body))
	return e
}

// formField is one multipart form entry for the media endpoints. Required
// fields always go on the wire (an empty model id should fail loudly
// upstream, not silently vanish); optional ones only when set.
type formField struct {
	key, value string
	required   bool
}

// writeFormFields appends fields to a multipart writer, skipping unset
// optional entries. wrap labels errors ("build transcription form", ...).
func writeFormFields(w *multipart.Writer, wrap string, fields []formField) error {
	for _, f := range fields {
		if !f.required && f.value == "" {
			continue
		}
		if err := w.WriteField(f.key, f.value); err != nil {
			return fmt.Errorf("llama-swap: %s: %w", wrap, err)
		}
	}
	return nil
}

// mimeFromContentType returns the parsed media type when it matches prefix
// ("audio/", "video/"), else "".
func mimeFromContentType(contentType, prefix string) string {
	if mt, _, err := mime.ParseMediaType(contentType); err == nil && strings.HasPrefix(mt, prefix) {
		return mt
	}
	return ""
}