// Copyright (c) 2026 Charles KWON OhJun (charleskwonohjun@gmail.com)
// All rights reserved.

// Workarea cache for FiveSql2 DML — opt-in persistent workarea slots
// keyed by alias. Eliminates per-query dbUseArea + dbCloseArea syscall
// overhead for repeated INSERT / UPDATE / DELETE against the same table.
//
// Semantics:
//   * Disabled by default. Callers opt in via SqlWACacheEnable(). Tests
//     and short one-shot scripts can stay on the safe per-query open/
//     close behavior; long-running bench loops or servers pay the open
//     cost once.
//   * Entries map uppercase alias → workarea number. The PRG side is
//     responsible for the actual dbUseArea / dbSelectArea — this layer
//     only stores the handle.
//   * Invalidation is explicit. CREATE TABLE / DROP TABLE in
//     TSqlDDL.prg call SqlWACacheInvalidate before any filesystem
//     operation that would otherwise collide with a still-open handle.
//   * SqlWACacheCloseAll drops every entry; callers then decide how
//     to actually close the workareas (dbCloseAll, per-alias close, …).

package hbrtl

import (
	"strings"
	"sync"

	"five/hbrt"
)

var (
	waCacheMu      sync.Mutex
	waCacheEntries = map[string]int{}
	waCacheEnabled bool
)

// SqlWACacheEnable() → NIL
// Turns on the workarea cache for this process. Existing opens are not
// retroactively registered — the cache populates on next SqlWAOpenCached.
func SqlWACacheEnable(t *hbrt.Thread) {
	t.Frame(0, 0)
	defer t.EndProc()
	waCacheMu.Lock()
	waCacheEnabled = true
	waCacheMu.Unlock()
	t.RetNil()
}

// SqlWACacheDisable() → NIL
// Turns the cache off and drops all entries. Workareas themselves
// are left in whatever state the caller last put them in — callers
// typically follow with dbCloseAll() or per-table close.
func SqlWACacheDisable(t *hbrt.Thread) {
	t.Frame(0, 0)
	defer t.EndProc()
	waCacheMu.Lock()
	waCacheEnabled = false
	waCacheEntries = map[string]int{}
	waCacheMu.Unlock()
	t.RetNil()
}

// SqlWACacheIsEnabled() → lBool
func SqlWACacheIsEnabled(t *hbrt.Thread) {
	t.Frame(0, 0)
	defer t.EndProc()
	waCacheMu.Lock()
	on := waCacheEnabled
	waCacheMu.Unlock()
	t.RetBool(on)
}

// SqlWACacheGet(cAlias) → nWA | 0
// Lookup a cached workarea number by alias. Returns 0 if disabled or
// no entry. PRG side still verifies Used() / Select() before relying
// on the number — another process or manual close may have invalidated
// the handle between cache hits.
func SqlWACacheGet(t *hbrt.Thread) {
	t.Frame(1, 0)
	defer t.EndProc()
	waCacheMu.Lock()
	on := waCacheEnabled
	nWA := 0
	if on {
		nWA = waCacheEntries[strings.ToUpper(t.Local(1).AsString())]
	}
	waCacheMu.Unlock()
	t.RetInt(int64(nWA))
}

// SqlWACachePut(cAlias, nWA) → NIL
// Register (or overwrite) a cache entry. No-op when cache is disabled
// so callers can unconditionally call Put after a successful open.
func SqlWACachePut(t *hbrt.Thread) {
	t.Frame(2, 0)
	defer t.EndProc()
	alias := strings.ToUpper(t.Local(1).AsString())
	nWA := int(t.Local(2).AsNumInt())
	waCacheMu.Lock()
	if waCacheEnabled && nWA > 0 {
		waCacheEntries[alias] = nWA
	}
	waCacheMu.Unlock()
	t.RetNil()
}

// SqlWACacheInvalidate(cAlias) → NIL
// Drop a single cache entry. Called before CREATE TABLE / DROP TABLE /
// FErase so the PRG side can then close and recreate the file without
// conflicting with a stale cached open.
func SqlWACacheInvalidate(t *hbrt.Thread) {
	t.Frame(1, 0)
	defer t.EndProc()
	alias := strings.ToUpper(t.Local(1).AsString())
	waCacheMu.Lock()
	delete(waCacheEntries, alias)
	waCacheMu.Unlock()
	t.RetNil()
}

// SqlWACacheCloseAll() → aKeys
// Empties the cache and returns the list of aliases that were in it.
// Callers can iterate and close each corresponding workarea.
func SqlWACacheCloseAll(t *hbrt.Thread) {
	t.Frame(0, 0)
	defer t.EndProc()

	waCacheMu.Lock()
	keys := make([]string, 0, len(waCacheEntries))
	for k := range waCacheEntries {
		keys = append(keys, k)
	}
	waCacheEntries = map[string]int{}
	waCacheMu.Unlock()

	out := make([]hbrt.Value, len(keys))
	for i, k := range keys {
		out[i] = hbrt.MakeString(k)
	}
	t.PushValue(hbrt.MakeArrayFrom(out))
	t.RetValue()
}