package weightmap

import (
	"fmt"
	"strings"
	"sync"
)

// WeightMapper maps HuggingFace weight names to internal structure.
// Returns:
// - layerIdx: layer index for layer-scoped weights
// - fieldName: internal field name
// - ok: whether mapping matched
type WeightMapper interface {
	MapName(name string) (layerIdx int, fieldName string, ok bool)
}

// MapperFunc is a helper to turn a function into a WeightMapper.
type MapperFunc func(name string) (int, string, bool)

func (f MapperFunc) MapName(name string) (int, string, bool) { return f(name) }

var (
	mu       sync.RWMutex
	mappers  = map[string]WeightMapper{}
	fallback WeightMapper
)

// Register registers a mapper for an architecture key.
// The key should be stable (e.g. "qwen3").
func Register(key string, mapper WeightMapper) {
	key = strings.ToLower(key)
	mu.Lock()
	defer mu.Unlock()
	mappers[key] = mapper
	if fallback == nil {
		fallback = mapper
	}
}

// Get returns a mapper by key. If missing, returns the first registered mapper (if any).
func Get(key string) (WeightMapper, bool) {
	key = strings.ToLower(key)
	mu.RLock()
	defer mu.RUnlock()
	m, ok := mappers[key]
	if ok {
		return m, true
	}
	return fallback, false
}

// GetForArchitecture resolves a mapper for a raw architecture string.
// It first tries exact match, then substring match over registered keys.
func GetForArchitecture(arch string) WeightMapper {
	archLower := strings.ToLower(arch)
	if m, ok := Get(archLower); ok {
		return m
	}

	mu.RLock()
	defer mu.RUnlock()
	for k, m := range mappers {
		if strings.Contains(archLower, k) {
			return m
		}
	}
	return fallback
}

// ParseLayerName extracts layer index and field name from HF weight name.
func ParseLayerName(name, prefix string, fields map[string]string) (int, string, bool) {
	if !strings.HasPrefix(name, prefix) {
		return -1, "", false
	}

	rest := name[len(prefix):]
	var layerIdx int
	var suffix string

	if _, err := fmt.Sscanf(rest, "%d.%s", &layerIdx, &suffix); err != nil {
		return -1, "", false
	}

	if field, ok := fields[suffix]; ok {
		return layerIdx, field, true
	}

	return layerIdx, suffix, true
}