package behavior

import (
	"fmt"
	"math/rand"
	"os"
	"path/filepath"
	"strings"
	"sync"

	"gopkg.in/yaml.v3"
)

func BuildPathIndex(dir string) map[string]string {
	index := make(map[string]string)
	filepath.WalkDir(dir, func(path string, d os.DirEntry, err error) error {
		if err != nil || d.IsDir() || !strings.HasSuffix(d.Name(), ".yaml") {
			return nil
		}
		id := strings.TrimSuffix(d.Name(), ".yaml")
		index[id] = path
		return nil
	})
	return index
}

func BuildRoomIndex(dir string) map[int]string {
	index := make(map[int]string)
	filepath.WalkDir(dir, func(path string, d os.DirEntry, err error) error {
		if err != nil || d.IsDir() || !strings.HasSuffix(d.Name(), ".yaml") {
			return nil
		}
		id := strings.TrimSuffix(d.Name(), ".yaml")
		var n int
		if _, scanErr := fmt.Sscanf(id, "%d", &n); scanErr == nil {
			index[n] = path
		}
		return nil
	})
	return index
}

func WalkYAMLDir(dir string, fn func(path, id string, data []byte) error) error {
	return filepath.WalkDir(dir, func(path string, d os.DirEntry, err error) error {
		if err != nil || d.IsDir() || !strings.HasSuffix(d.Name(), ".yaml") {
			return nil
		}
		data, readErr := os.ReadFile(path)
		if readErr != nil {
			return nil
		}
		id := strings.TrimSuffix(d.Name(), ".yaml")
		return fn(path, id, data)
	})
}

type Duplicate struct {
	ID    string
	Paths []string
}

func CheckDuplicateIDs(dir string) []Duplicate {
	seen := make(map[string][]string)
	filepath.WalkDir(dir, func(path string, d os.DirEntry, err error) error {
		if err != nil || d.IsDir() || !strings.HasSuffix(d.Name(), ".yaml") {
			return nil
		}
		id := strings.TrimSuffix(d.Name(), ".yaml")
		seen[id] = append(seen[id], path)
		return nil
	})
	var dups []Duplicate
	for id, paths := range seen {
		if len(paths) > 1 {
			dups = append(dups, Duplicate{ID: id, Paths: paths})
		}
	}
	return dups
}

func SuccessChance(cfg SuccessFormula, level int, requiredLevel int) float64 {
	chance := cfg.Base + float64(level-requiredLevel)*cfg.PerLevel
	if chance > cfg.Cap {
		chance = cfg.Cap
	}
	if chance < 0 {
		chance = 0
	}
	return chance
}

var (
	dropIndex   map[string]string
	dropIndexMu sync.Mutex
)

func loadDropIndex(dataDir string) map[string]string {
	dropIndexMu.Lock()
	defer dropIndexMu.Unlock()
	if dropIndex == nil {
		dropIndex = BuildPathIndex(filepath.Join(dataDir, "drops"))
	}
	return dropIndex
}

func ClearDropIndex() {
	dropIndexMu.Lock()
	defer dropIndexMu.Unlock()
	dropIndex = nil
}

func LoadDropTable(dataDir, id string) (*DropTableDef, error) {
	index := loadDropIndex(dataDir)
	path, ok := index[id]
	if !ok {
		path = filepath.Join(dataDir, "drops", id+".yaml")
	}
	data, err := os.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("read drop table %s: %w", id, err)
	}
	var dt DropTableDef
	if err := yaml.Unmarshal(data, &dt); err != nil {
		return nil, fmt.Errorf("parse drop table %s: %w", id, err)
	}
	return &dt, nil
}

// pickWeighted returns a single entry chosen by weight, without resolving any
// table reference on it. Returns nil if the list is empty or has no weight.
func pickWeighted(drops []DropEntry) *DropEntry {
	if len(drops) == 0 {
		return nil
	}
	total := 0
	for _, d := range drops {
		total += d.Weight
	}
	if total <= 0 {
		return nil
	}
	roll := rand.Intn(total)
	cumulative := 0
	for i := range drops {
		cumulative += drops[i].Weight
		if roll < cumulative {
			return &drops[i]
		}
	}
	return &drops[0]
}

func ResolveDrop(dataDir string, drops []DropEntry) *DropEntry {
	picked := pickWeighted(drops)
	if picked == nil {
		return nil
	}
	if picked.Table != "" {
		sub, err := LoadDropTable(dataDir, picked.Table)
		if err != nil {
			return nil
		}
		resolved := ResolveDrop(dataDir, sub.Drops)
		if resolved == nil {
			return nil
		}
		qty := picked.Quantity
		if qty <= 0 {
			qty = resolved.Quantity
		}
		if qty <= 0 {
			qty = 1
		}
		return &DropEntry{
			ItemID:         resolved.ItemID,
			Quantity:       qty,
			Depletes:       picked.Depletes,
			SuccessMessage: picked.SuccessMessage,
		}
	}
	return picked
}

// ResolveDropList performs one weighted pick from drops. A plain item entry
// yields a single result. When the picked entry references a sub-table, its
// Quantity is treated as the number of INDEPENDENT rolls against that sub-table
// (default 1) — each roll may produce a different item — and all results are
// returned. Tables are just weighted lists of items; this is skill-independent.
func ResolveDropList(dataDir string, drops []DropEntry) []DropEntry {
	picked := pickWeighted(drops)
	if picked == nil {
		return nil
	}
	if picked.Table == "" {
		return []DropEntry{*picked}
	}
	sub, err := LoadDropTable(dataDir, picked.Table)
	if err != nil {
		return nil
	}
	rolls := picked.Quantity
	if rolls <= 0 {
		rolls = 1
	}
	var out []DropEntry
	for i := 0; i < rolls; i++ {
		if resolved := ResolveDrop(dataDir, sub.Drops); resolved != nil && resolved.ItemID != "" {
			out = append(out, *resolved)
		}
	}
	return out
}