// Package metrics implements the three Prometheus counters the reconciler
// exposes, without pulling the prometheus/client_golang module. The /metrics
// handler prints the standard text exposition format.
package metrics

import (
	"fmt"
	"io"
	"net/http"
	"sync/atomic"
)

// Registry holds the reconciler's counters. Use New() to construct and share
// one instance across the scheduler and the HTTP handler.
type Registry struct {
	dirtyRows                atomic.Int64
	reconciliationAttempts   atomic.Int64
	reconciliationFailures   atomic.Int64
	reconciliationNoopHits   atomic.Int64
}

func New() *Registry { return &Registry{} }

// SetDirtyRows sets the current pending-row count. Called at the top of each
// tick, before any attempts land.
func (r *Registry) SetDirtyRows(n int64) { r.dirtyRows.Store(n) }

func (r *Registry) IncAttempts()            { r.reconciliationAttempts.Add(1) }
func (r *Registry) IncFailures()            { r.reconciliationFailures.Add(1) }
func (r *Registry) IncIdempotentNoopHits()  { r.reconciliationNoopHits.Add(1) }

// Snapshot returns a point-in-time copy; useful for tests.
type Snapshot struct {
	DirtyRows              int64
	ReconciliationAttempts int64
	ReconciliationFailures int64
	IdempotentNoopHits     int64
}

func (r *Registry) Snapshot() Snapshot {
	return Snapshot{
		DirtyRows:              r.dirtyRows.Load(),
		ReconciliationAttempts: r.reconciliationAttempts.Load(),
		ReconciliationFailures: r.reconciliationFailures.Load(),
		IdempotentNoopHits:     r.reconciliationNoopHits.Load(),
	}
}

// Handler returns an http.HandlerFunc that writes the Prometheus text format.
func (r *Registry) Handler() http.HandlerFunc {
	return func(w http.ResponseWriter, _ *http.Request) {
		w.Header().Set("Content-Type", "text/plain; version=0.0.4; charset=utf-8")
		r.write(w)
	}
}

func (r *Registry) write(w io.Writer) {
	s := r.Snapshot()
	fmt.Fprintln(w, "# HELP attest_reconciler_dirty_rows_total Current count of per_diem_rates rows missing an attestation reference (gauge-style, overwritten each tick).")
	fmt.Fprintln(w, "# TYPE attest_reconciler_dirty_rows_total gauge")
	fmt.Fprintf(w, "attest_reconciler_dirty_rows_total %d\n", s.DirtyRows)

	fmt.Fprintln(w, "# HELP attest_reconciler_reconciliation_attempts_total Total pending rows the reconciler attempted to re-sign.")
	fmt.Fprintln(w, "# TYPE attest_reconciler_reconciliation_attempts_total counter")
	fmt.Fprintf(w, "attest_reconciler_reconciliation_attempts_total %d\n", s.ReconciliationAttempts)

	fmt.Fprintln(w, "# HELP attest_reconciler_reconciliation_failures_total Total pending-row attempts that returned an error from the signer or transparency log.")
	fmt.Fprintln(w, "# TYPE attest_reconciler_reconciliation_failures_total counter")
	fmt.Fprintf(w, "attest_reconciler_reconciliation_failures_total %d\n", s.ReconciliationFailures)

	fmt.Fprintln(w, "# HELP attest_reconciler_idempotent_noop_total Rows the reconciler re-signed where the TLog already had the entry (safe no-op; proves the idempotency contract works).")
	fmt.Fprintln(w, "# TYPE attest_reconciler_idempotent_noop_total counter")
	fmt.Fprintf(w, "attest_reconciler_idempotent_noop_total %d\n", s.IdempotentNoopHits)
}