package app

import (
	"database/sql"
	"encoding/json"
	"errors"
	"net/http"
	"strings"
)

type RuntimeSettings struct {
	FileBudget         int64 `json:"file_budget"`
	DataBudget         int64 `json:"data_budget"`
	MinFreeBytes       int64 `json:"min_free_bytes"`
	AuditRetentionDays int   `json:"audit_retention_days"`
	AuditMaxRecords    int   `json:"audit_max_records"`
	AuditMaxBytes      int64 `json:"audit_max_bytes"`
}

func (c Config) InitialRuntimeSettings() RuntimeSettings {
	return RuntimeSettings{c.FileBudget, c.DataBudget, c.MinFreeBytes, c.AuditRetentionDays, c.AuditMaxRecords, c.AuditMaxBytes}
}
func (s RuntimeSettings) Validate() error {
	if s.FileBudget < 1 || s.FileBudget > 1<<50 || s.DataBudget > 1<<51 || s.DataBudget-s.FileBudget < 64<<20 || s.MinFreeBytes < 0 || s.MinFreeBytes > 1<<50 {
		return errors.New("文件预算须为正数，数据预算须另留至少64MiB维护空间")
	}
	if s.AuditRetentionDays < 1 || s.AuditRetentionDays > 3650 || s.AuditMaxRecords < 1 || s.AuditMaxRecords > 1000000 || s.AuditMaxBytes < 1024 || s.AuditMaxBytes > 1<<30 || s.AuditMaxBytes > s.DataBudget-s.FileBudget {
		return errors.New("审计需保留1–3650天，条数1–100万，内容预算1KiB–1GiB且不超过维护空间")
	}
	return nil
}
func readRuntime(q interface{ QueryRow(string, ...any) *sql.Row }) (RuntimeSettings, error) {
	var text string
	s := RuntimeSettings{}
	e := q.QueryRow("SELECT json FROM runtime_settings WHERE id=1").Scan(&text)
	if e == nil {
		e = json.Unmarshal([]byte(text), &s)
	}
	if e == nil {
		e = s.Validate()
	}
	return s, e
}
func (a *App) runtimeSettings() (RuntimeSettings, error) { return readRuntime(a.db) }
func (a *App) adminRuntime(w http.ResponseWriter, r *http.Request) {
	if !a.requireAdmin(w, r) {
		return
	}
	if r.Method == "GET" {
		s, e := a.runtimeSettings()
		if e != nil {
			a.serverError(w, e)
			return
		}
		respond(w, 200, s)
		return
	}
	var settings RuntimeSettings
	if !decode(w, r, &settings) {
		return
	}
	if e := settings.Validate(); e != nil {
		fail(w, 400, e.Error())
		return
	}
	a.mu.Lock()
	defer a.mu.Unlock()
	b, e := json.Marshal(settings)
	if e != nil {
		a.serverError(w, e)
		return
	}
	tx, e := a.db.Begin()
	if e != nil {
		a.serverError(w, e)
		return
	}
	defer tx.Rollback()
	_, e = tx.Exec("UPDATE runtime_settings SET json=? WHERE id=1", string(b))
	if e == nil {
		e = a.trimAuditTx(tx)
	}
	if e == nil {
		e = tx.Commit()
	}
	if e != nil {
		a.serverError(w, e)
		return
	}
	a.audit("runtime.update", "", a.remoteIP(r))
	respond(w, 200, settings)
}

// The content budget includes UTF-8 fields and a conservative per-record allowance.
// SQLite reuses freed pages; this budget is not the physical database-file size.
const auditRecordBytes = "length(CAST(action AS BLOB))+length(CAST(target AS BLOB))+length(CAST(source AS BLOB))+96"

func (a *App) initializeAuditUsage() error {
	expression := func(prefix string) string {
		s := auditRecordBytes
		for _, name := range []string{"action", "target", "source"} {
			s = strings.ReplaceAll(s, name, prefix+"."+name)
		}
		return s
	}
	_, e := a.db.Exec("CREATE TABLE IF NOT EXISTS audit_usage(id INTEGER PRIMARY KEY CHECK(id=1),records INTEGER NOT NULL,content_bytes INTEGER NOT NULL); INSERT OR IGNORE INTO audit_usage SELECT 1,count(*),COALESCE(sum(" + auditRecordBytes + "),0) FROM audit; CREATE TRIGGER IF NOT EXISTS audit_insert_usage AFTER INSERT ON audit BEGIN UPDATE audit_usage SET records=records+1,content_bytes=content_bytes+(" + expression("NEW") + ") WHERE id=1; END; CREATE TRIGGER IF NOT EXISTS audit_delete_usage AFTER DELETE ON audit BEGIN UPDATE audit_usage SET records=records-1,content_bytes=content_bytes-(" + expression("OLD") + ") WHERE id=1; END;")
	return e
}

func (a *App) trimAuditTx(tx *sql.Tx) error {
	s, e := readRuntime(tx)
	if e != nil {
		return e
	}
	if _, e = tx.Exec("DELETE FROM audit WHERE created<?", a.now().Unix()-int64(s.AuditRetentionDays)*86400); e != nil {
		return e
	}
	var count, bytes int64
	if e = tx.QueryRow("SELECT records,content_bytes FROM audit_usage WHERE id=1").Scan(&count, &bytes); e != nil {
		return e
	}
	if count > int64(s.AuditMaxRecords) {
		if _, e = tx.Exec("DELETE FROM audit WHERE id IN(SELECT id FROM audit ORDER BY id DESC LIMIT -1 OFFSET ?)", s.AuditMaxRecords); e != nil {
			return e
		}
	}
	if bytes <= s.AuditMaxBytes {
		return nil
	}
	_, e = tx.Exec("WITH sizes AS (SELECT id,sum("+auditRecordBytes+") OVER(ORDER BY id DESC ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS bytes FROM audit) DELETE FROM audit WHERE id IN(SELECT id FROM sizes WHERE bytes>?)", s.AuditMaxBytes)
	return e
}
func (a *App) trimAudit() error {
	tx, e := a.db.Begin()
	if e != nil {
		return e
	}
	defer tx.Rollback()
	if e = a.trimAuditTx(tx); e != nil {
		return e
	}
	return tx.Commit()
}