// Package reconciliation provides read-only integrity checks for the GL.
package reconciliation

import (
	"context"
	"fmt"

	"gl/domain/ledger"
)

type Repository interface {
	List(context.Context, ledger.JournalFilter) ([]ledger.Journal, error)
}

type Report struct {
	Scanned int
	Valid   int
	Invalid []Issue
}

type Issue struct {
	JournalID string
	Error     string
}

// Run scans all posted journals without mutating the ledger.
func Run(ctx context.Context, repository Repository, pageSize int) (Report, error) {
	if repository == nil {
		return Report{}, fmt.Errorf("reconciliation repository is required")
	}
	if pageSize <= 0 || pageSize > 200 {
		pageSize = 100
	}
	report := Report{Invalid: make([]Issue, 0)}
	seen := make(map[string]string)
	for offset := 0; ; offset += pageSize {
		journals, err := repository.List(ctx, ledger.JournalFilter{Limit: pageSize, Offset: offset})
		if err != nil {
			return Report{}, fmt.Errorf("list journals at offset %d: %w", offset, err)
		}
		for _, journal := range journals {
			report.Scanned++
			if err := journal.Validate(); err != nil {
				report.Invalid = append(report.Invalid, Issue{JournalID: journal.ID, Error: err.Error()})
				continue
			}
			key := evidenceKey(journal.SourceService, journal.SourceTransactionID, journal.EventVersion)
			if previous, exists := seen[key]; exists {
				report.Invalid = append(report.Invalid, Issue{JournalID: journal.ID, Error: fmt.Sprintf("duplicate source transaction/version; first journal %s", previous)})
				continue
			}
			seen[key] = journal.ID
			report.Valid++
		}
		if len(journals) < pageSize {
			break
		}
	}
	return report, nil
}