package mpvembed

/*
#cgo pkg-config: mpv
#include <mpv/render.h>
#include <stdlib.h>

static inline const char* mpv_errstr_render(int err) { return mpv_error_string(err); }
*/
import "C"
import (
	"fmt"
	"unsafe"
)

// RenderParam is a small helper to build mpv_render_param arrays.
type RenderParam struct {
	Type int
	Data unsafe.Pointer
}

// RenderContext wraps mpv_render_context for render API (OpenGL/Vulkan, etc.).
type RenderContext struct {
	ctx *C.mpv_render_context
}

// NewRenderContext creates a render context for the given client with the provided params.
// The params slice is terminated with MPV_RENDER_PARAM_INVALID automatically.
func NewRenderContext(c *Client, params []RenderParam) (*RenderContext, error) {
	if c == nil || c.handle == nil {
		return nil, fmt.Errorf("mpv client is nil")
	}
	cparams := make([]C.mpv_render_param, len(params)+1)
	for i, p := range params {
		cparams[i]._type = uint32(p.Type)
		cparams[i].data = p.Data
	}
	cparams[len(params)]._type = uint32(C.MPV_RENDER_PARAM_INVALID)

	var rctx *C.mpv_render_context
	if res := C.mpv_render_context_create(&rctx, c.handle, &cparams[0]); res < 0 {
		return nil, fmt.Errorf("mpv_render_context_create failed: %s", C.GoString(C.mpv_errstr_render(res)))
	}
	return &RenderContext{ctx: rctx}, nil
}

// Destroy frees the render context.
func (r *RenderContext) Destroy() {
	if r != nil && r.ctx != nil {
		C.mpv_render_context_free(r.ctx)
		r.ctx = nil
	}
}

// SetUpdateCallback registers a callback that mpv will invoke when a new frame should be drawn.
// The callback must be thread-safe.
func (r *RenderContext) SetUpdateCallback(cb unsafe.Pointer, userdata unsafe.Pointer) error {
	if r == nil || r.ctx == nil {
		return fmt.Errorf("render context is nil")
	}
	C.mpv_render_context_set_update_callback(r.ctx, (C.mpv_render_update_fn)(cb), userdata)
	return nil
}

// Render issues a render call with the provided params (e.g., target FBO, dimensions).
// The params slice is terminated automatically.
func (r *RenderContext) Render(params []RenderParam) error {
	if r == nil || r.ctx == nil {
		return fmt.Errorf("render context is nil")
	}
	cparams := make([]C.mpv_render_param, len(params)+1)
	for i, p := range params {
		cparams[i]._type = uint32(p.Type)
		cparams[i].data = p.Data
	}
	cparams[len(params)]._type = uint32(C.MPV_RENDER_PARAM_INVALID)

	if res := C.mpv_render_context_render(r.ctx, &cparams[0]); res < 0 {
		return fmt.Errorf("mpv_render_context_render failed: %s", C.GoString(C.mpv_errstr_render(res)))
	}
	return nil
}