// Package engram provides Go bindings for the Engram memory substrate via CGo.
//
// Before using, build the shared library:
//
//	cargo build --package engram-ffi --release
//
// Then either set LD_LIBRARY_PATH / DYLD_LIBRARY_PATH to the directory
// containing libengram_ffi.so/.dylib, or copy the library to a standard path.
//
// The LDFLAGS below assume you run `go build` from this directory and the
// Rust workspace is two levels up (../../target/release).
package engram

/*
#cgo LDFLAGS: -L../../target/release -lengram_ffi
#include "engram.h"
#include <stdlib.h>
*/
import "C"
import (
	"encoding/json"
	"errors"
	"fmt"
	"unsafe"
)

// ── Types ─────────────────────────────────────────────────────────────────────

// DB is a handle to an open Engram database.
type DB struct {
	ptr *C.EngramHandle
}

// Node mirrors the Rust Node struct.
type Node struct {
	ID              string    `json:"id"`
	Content         string    `json:"content"`
	NodeType        string    `json:"node_type"`
	Tier            string    `json:"tier"`
	Salience        float32   `json:"salience"`
	Importance      float32   `json:"importance"`
	ActivationCount uint64    `json:"activation_count"`
	Embedding       []float32 `json:"embedding"`
}

// NodeInput is used when creating a new node.
type NodeInput struct {
	Content   string    `json:"content"`
	NodeType  string    `json:"node_type,omitempty"`
	Tier      string    `json:"tier,omitempty"`
	Importance float32  `json:"importance,omitempty"`
	Embedding []float32 `json:"embedding"`
}

// ActivatedNode is a node returned from spreading activation.
type ActivatedNode struct {
	Node               Node    `json:"node"`
	ActivationStrength float32 `json:"activation_strength"`
	Hops               uint8   `json:"hops"`
}

// ActivateRequest is the JSON payload sent to engram_activate.
type activateRequest struct {
	Seeds          []string  `json:"seeds"`
	QueryEmbedding []float32 `json:"query_embedding"`
	MaxDepth       uint8     `json:"max_depth"`
	Limit          int       `json:"limit"`
}

// ── Lifecycle ─────────────────────────────────────────────────────────────────

// Open opens or creates an Engram database at the given path.
func Open(path string) (*DB, error) {
	cpath := C.CString(path)
	defer C.free(unsafe.Pointer(cpath))

	ptr := C.engram_open(cpath)
	if ptr == nil {
		return nil, fmt.Errorf("engram_open failed for path %q", path)
	}
	return &DB{ptr: ptr}, nil
}

// Close closes the database and frees the native handle.
func (db *DB) Close() {
	if db.ptr != nil {
		C.engram_close(db.ptr)
		db.ptr = nil
	}
}

// ── Statistics ────────────────────────────────────────────────────────────────

// NodeCount returns the total number of nodes.
func (db *DB) NodeCount() (uint64, error) {
	n := C.engram_node_count(db.ptr)
	if n < 0 {
		return 0, errors.New("engram_node_count returned error")
	}
	return uint64(n), nil
}

// EdgeCount returns the total number of edges.
func (db *DB) EdgeCount() (uint64, error) {
	n := C.engram_edge_count(db.ptr)
	if n < 0 {
		return 0, errors.New("engram_edge_count returned error")
	}
	return uint64(n), nil
}

// ── Node operations ───────────────────────────────────────────────────────────

// PutNode stores a node and returns its UUID.
func (db *DB) PutNode(node *NodeInput) (string, error) {
	jsonBytes, err := json.Marshal(node)
	if err != nil {
		return "", fmt.Errorf("marshal node: %w", err)
	}

	cjson := C.CString(string(jsonBytes))
	defer C.free(unsafe.Pointer(cjson))

	result := C.engram_put_node(db.ptr, cjson)
	if result == nil {
		return "", errors.New("engram_put_node returned null")
	}
	defer C.engram_free_string(result)

	return C.GoString(result), nil
}

// GetNode retrieves a node by UUID. Returns nil if not found.
func (db *DB) GetNode(id string) (*Node, error) {
	cid := C.CString(id)
	defer C.free(unsafe.Pointer(cid))

	result := C.engram_get_node(db.ptr, cid)
	if result == nil {
		return nil, nil
	}
	defer C.engram_free_string(result)

	var node Node
	if err := json.Unmarshal([]byte(C.GoString(result)), &node); err != nil {
		return nil, fmt.Errorf("unmarshal node: %w", err)
	}
	return &node, nil
}

// ── Spreading activation ──────────────────────────────────────────────────────

// Activate runs spreading activation from seed node UUIDs.
func (db *DB) Activate(
	seeds []string,
	queryEmbedding []float32,
	maxDepth uint8,
	limit int,
) ([]*ActivatedNode, error) {
	req := activateRequest{
		Seeds:          seeds,
		QueryEmbedding: queryEmbedding,
		MaxDepth:       maxDepth,
		Limit:          limit,
	}
	jsonBytes, err := json.Marshal(req)
	if err != nil {
		return nil, fmt.Errorf("marshal activate request: %w", err)
	}

	cjson := C.CString(string(jsonBytes))
	defer C.free(unsafe.Pointer(cjson))

	result := C.engram_activate(db.ptr, cjson)
	if result == nil {
		return nil, errors.New("engram_activate returned null")
	}
	defer C.engram_free_string(result)

	var nodes []*ActivatedNode
	if err := json.Unmarshal([]byte(C.GoString(result)), &nodes); err != nil {
		return nil, fmt.Errorf("unmarshal activate result: %w", err)
	}
	return nodes, nil
}

// ── Salience management ───────────────────────────────────────────────────────

// Decay applies multiplicative salience decay to all nodes.
// factor should be in (0.0, 1.0). Returns the number of nodes updated.
func (db *DB) Decay(factor float32) (uint64, error) {
	n := C.engram_decay(db.ptr, C.float(factor))
	if n < 0 {
		return 0, errors.New("engram_decay returned error")
	}
	return uint64(n), nil
}