package vultr

import (
	"context"
	"fmt"
	"strings"
	"sync"

	"golang.org/x/oauth2"

	"github.com/libdns/libdns"
	"github.com/vultr/govultr/v3"
)

// vultrDuplicateErr is matched against Vultr API response text.
// May need updating if Vultr changes their error message wording.
const vultrDuplicateErr = "Duplicate records"

type Client struct {
	vultr *govultr.Client
	// mutex serializes write operations (add/remove/update).
	// getDNSEntries does NOT acquire this lock because it is called
	// from within write methods that already hold it.
	mutex sync.Mutex
}

func (p *Provider) getClient() error {
	if p.client.vultr == nil {
		oauth_cfg := &oauth2.Config{}
		oauth_token_source := oauth_cfg.TokenSource(context.TODO(), &oauth2.Token{AccessToken: p.APIToken})

		p.client.vultr = govultr.NewClient(oauth2.NewClient(context.TODO(), oauth_token_source))
	}

	return nil
}

func (p *Provider) getDNSEntries(ctx context.Context, domain string) ([]libdns.Record, error) {
	p.getClient()

	listOptions := &govultr.ListOptions{}

	var records []libdns.Record
	for {
		dns_entries, meta, _, err := p.client.vultr.DomainRecord.List(ctx, domain, listOptions)
		if err != nil {
			return records, err
		}

		for _, entry := range dns_entries {
			record := fromAPIRecord(entry, domain)
			records = append(records, record)
		}

		if meta.Links.Next == "" {
			break
		}

		listOptions.Cursor = meta.Links.Next
	}

	return records, nil
}

func (p *Provider) addDNSRecord(ctx context.Context, domain string, r libdns.Record) (libdns.Record, error) {
	p.client.mutex.Lock()
	defer p.client.mutex.Unlock()

	p.getClient()

	domainRecordReq := toDomainRecordReq(r)

	rec, _, err := p.client.vultr.DomainRecord.Create(ctx, domain, &domainRecordReq)
	if err != nil {
		if !strings.Contains(err.Error(), vultrDuplicateErr) {
			return r, err
		}

		// Duplicate record exists — find it and update with the new data.
		// This handles stale ACME challenge TXT records left from previous runs.
		records, lookupErr := p.getDNSEntries(ctx, domain)
		if lookupErr != nil {
			return r, fmt.Errorf("duplicate record and could not look up existing: %w", lookupErr)
		}

		rr := r.RR()
		var existingID string
		for _, existing := range records {
			exRR := existing.RR()
			if exRR.Name == rr.Name && exRR.Type == rr.Type {
				if vr, ok := existing.(VultrRecord); ok {
					existingID = vr.ID
					break
				}
			}
		}

		if existingID == "" {
			return r, fmt.Errorf("duplicate record reported but not found in zone: %w", err)
		}

		updateErr := p.client.vultr.DomainRecord.Update(ctx, domain, existingID, &domainRecordReq)
		if updateErr != nil {
			return r, fmt.Errorf("failed to update duplicate record %s: %w", existingID, updateErr)
		}

		return fromLibdnsRecord(r, existingID), nil
	}

	record := fromLibdnsRecord(r, rec.ID)

	return record, nil
}

func (p *Provider) removeDNSRecord(ctx context.Context, domain string, record libdns.Record) (libdns.Record, error) {
	p.client.mutex.Lock()
	defer p.client.mutex.Unlock()

	p.getClient()

	recordId, err := getRecordId(record)
	if err != nil {
		// try to get the ID from API if we don't have it
		records, lookupErr := p.getDNSEntries(ctx, domain)
		if lookupErr != nil {
			return record, fmt.Errorf("could not get record ID from API: %w", lookupErr)
		}

		rr := record.RR()
		for _, rec := range records {
			recRR := rec.RR()
			// Match by name, type, AND data to avoid deleting the wrong record
			// when multiple records share the same name (e.g. _acme-challenge TXT).
			if recRR.Name == rr.Name && recRR.Type == rr.Type && recRR.Data == rr.Data {
				if vr, ok := rec.(VultrRecord); ok {
					recordId = vr.ID
					break
				}
			}
		}

		// Fall back to name+type match if exact data match wasn't found
		if recordId == "" {
			for _, rec := range records {
				recRR := rec.RR()
				if recRR.Name == rr.Name && recRR.Type == rr.Type {
					if vr, ok := rec.(VultrRecord); ok {
						recordId = vr.ID
						break
					}
				}
			}
		}

		if recordId == "" {
			return record, fmt.Errorf("no matching record found for %s %s in zone %s", rr.Type, rr.Name, domain)
		}
	}

	err = p.client.vultr.DomainRecord.Delete(ctx, domain, recordId)
	if err != nil {
		return record, err
	}

	return record, nil
}

func (p *Provider) updateDNSRecord(ctx context.Context, domain string, record libdns.Record) (libdns.Record, error) {
	p.client.mutex.Lock()
	defer p.client.mutex.Unlock()

	p.getClient()

	recordId, err := getRecordId(record)
	if err != nil {
		// try to get the ID from API if we don't have it
		records, lookupErr := p.getDNSEntries(ctx, domain)
		if lookupErr != nil {
			return record, fmt.Errorf("could not get record ID from API: %w", lookupErr)
		}

		rr := record.RR()
		for _, rec := range records {
			recRR := rec.RR()
			// Match by name+type+data first for precision
			if recRR.Name == rr.Name && recRR.Type == rr.Type && recRR.Data == rr.Data {
				if vr, ok := rec.(VultrRecord); ok {
					recordId = vr.ID
					break
				}
			}
		}

		// Fall back to name+type if exact data match not found
		if recordId == "" {
			for _, rec := range records {
				recRR := rec.RR()
				if recRR.Name == rr.Name && recRR.Type == rr.Type {
					if vr, ok := rec.(VultrRecord); ok {
						recordId = vr.ID
						break
					}
				}
			}
		}

		if recordId == "" {
			return record, fmt.Errorf("no matching record found for %s %s in zone %s", rr.Type, rr.Name, domain)
		}
	}

	domainRecordReq := toDomainRecordReq(record)

	err = p.client.vultr.DomainRecord.Update(ctx, domain, recordId, &domainRecordReq)
	if err != nil {
		return record, err
	}

	return record, nil
}

func (p *Provider) getDNSZones(ctx context.Context) ([]libdns.Zone, error) {
	p.client.mutex.Lock()
	defer p.client.mutex.Unlock()

	p.getClient()

	listOptions := &govultr.ListOptions{}

	var zones []libdns.Zone
	for {
		dns_zones, meta, _, err := p.client.vultr.Domain.List(ctx, listOptions)
		if err != nil {
			return zones, err
		}

		for _, entry := range dns_zones {
			zone := libdns.Zone{
				Name: entry.Domain,
			}
			zones = append(zones, zone)
		}

		if meta.Links.Next == "" {
			break
		}

		listOptions.Cursor = meta.Links.Next
	}

	return zones, nil
}