package llamaswap

import (
	"bytes"
	"fmt"
	"mime/multipart"
	"strings"
)

// upstreamPath builds a path through llama-swap's generic /upstream/<model>/
// passthrough, which pins the model (triggering the normal load/swap queue)
// and forwards the remaining path to the upstream verbatim. This is how the
// provider reaches upstreams whose native APIs carry no routable `model`
// field (rembg, mediautils, WhisperX, ACE-Step, ...) without needing a
// llama-swap route per endpoint (ADR-0020).
//
// Why reject rather than escape: same rationale as Unload — model ids
// legitimately contain ":" but never path-structure characters, and escaping
// would mask a config error instead of surfacing it.
func upstreamPath(model, rest string) (string, error) {
	if strings.TrimSpace(model) == "" {
		return "", fmt.Errorf("llama-swap: upstream call requires a model id")
	}
	if strings.ContainsAny(model, "/?#") {
		return "", fmt.Errorf("llama-swap: invalid model id %q for upstream call (contains a path separator)", model)
	}
	if !strings.HasPrefix(rest, "/") {
		rest = "/" + rest
	}
	return "/upstream/" + model + rest, nil
}

// filePart is the single file entry of a media multipart form.
type filePart struct {
	field    string // form field name ("file", "audio_file", ...)
	filename string // already sanitized
	data     []byte
}

// buildMultipart assembles a one-file multipart body: the file part first,
// then the given fields (optional fields skipped when empty, matching
// writeFormFields). wrap labels errors. Returns the body and its content
// type.
func buildMultipart(wrap string, file filePart, fields []formField) (*bytes.Buffer, string, error) {
	var buf bytes.Buffer
	w := multipart.NewWriter(&buf)
	fw, err := w.CreateFormFile(file.field, file.filename)
	if err != nil {
		return nil, "", fmt.Errorf("llama-swap: %s: %w", wrap, err)
	}
	if _, err := fw.Write(file.data); err != nil {
		return nil, "", fmt.Errorf("llama-swap: %s: %w", wrap, err)
	}
	if err := writeFormFields(w, wrap, fields); err != nil {
		return nil, "", err
	}
	if err := w.Close(); err != nil {
		return nil, "", fmt.Errorf("llama-swap: %s: %w", wrap, err)
	}
	return &buf, w.FormDataContentType(), nil
}