package services

import (
	"fmt"
)

// Repairing the pointers a shop's products keep back into the global catalogue.
//
// Every product imported from the catalogue stores the id of the row it came
// from. That id is not stable: the catalogue is rebuilt by scrape and renumbered
// each time, so pepsico's live ids run 3, 6, 9 … 27, 30 and a product imported
// when it was id 26 now points at nothing. Measured 2026-08-31: eleven of the
// nineteen links on the platform were dangling.
//
// Three things break, all of them quietly:
//
//  1. The catalogue browser's "already imported" ticks land on ids that no
//     longer exist, so the rows a shop really holds show as not imported —
//     and importing them again makes a duplicate.
//  2. Re-importing fails outright: the import reads the catalogue row by id
//     first, and answers "catalogue product not found".
//  3. The next scrape creates duplicates, because the dedupe keys on the id
//     that just changed.
//
// `image_id` fixes all three going forward. This pass fixes what is already
// stored, and it can only do one of two things to a product — neither of which
// invents anything:
//
//   - The id still resolves: adopt that row's `image_id`. The link now survives
//     the next scrape.
//   - It does not: clear the id. NOT a repair by name — the re-scrape that
//     renumbered these also changed their pack sizes (Cheetos Chips 100g became
//     250g, Kurkure Menthol 10g became 50g), so the product the link named no
//     longer exists in any form and matching by name would attach a shop's
//     product to a DIFFERENT one. Clearing is the honest outcome: the pointer
//     already pointed at nothing, and the product goes on selling from its own
//     row exactly as before.

// RelinkOutcome is what happened to one product.
type RelinkOutcome struct {
	Productid   int    `json:"productid"`
	Productname string `json:"productname"`
	Brand       string `json:"brand"`
	Catalogueid int    `json:"catalogueid"`
	// "linked" — the id resolved and the stable key was adopted.
	// "cleared" — the id resolved to nothing and was removed.
	// "already" — the product already carried the right stable key.
	Action  string `json:"action"`
	Imageid string `json:"imageid,omitempty"`
	Reason  string `json:"reason,omitempty"`
}

// RelinkReport is the whole pass over one tenant.
type RelinkReport struct {
	Tenantid int             `json:"tenantid"`
	Checked  int             `json:"checked"`
	Linked   int             `json:"linked"`
	Cleared  int             `json:"cleared"`
	Already  int             `json:"already"`
	DryRun   bool            `json:"dryrun"`
	Outcomes []RelinkOutcome `json:"outcomes"`
}

// RelinkCatalogue checks every catalogue-linked product of one tenant.
//
// `dryRun` is the default at the caller, deliberately: this rewrites a column
// that decides what a browse screen claims a shop already has, and it should be
// possible to read the whole plan before any of it happens.
func (s *productService) RelinkCatalogue(tenantid int, dryRun bool) (*RelinkReport, error) {
	products, err := s.repo.ListCatalogueLinkedProducts(tenantid)
	if err != nil {
		return nil, err
	}

	report := &RelinkReport{Tenantid: tenantid, DryRun: dryRun, Outcomes: []RelinkOutcome{}}

	for _, product := range products {
		report.Checked++
		outcome := RelinkOutcome{
			Productid:   product.Productid,
			Productname: product.Productname,
			Brand:       product.Productbrand,
			Catalogueid: product.Catalogueid,
		}

		row, err := s.catalogueService.GetProductByID(product.Productbrand, int64(product.Catalogueid))
		// A lookup that ERRORS is not the same as one that finds nothing, and
		// the difference decides whether a link is cleared. A catalogue that is
		// down would otherwise read as "every row is gone" and wipe every link
		// on the platform in one pass.
		if err != nil {
			return nil, fmt.Errorf("catalogue lookup failed for %s/%d: %w",
				product.Productbrand, product.Catalogueid, err)
		}

		if row == nil {
			outcome.Action = "cleared"
			outcome.Reason = "no catalogue row with this id — the scrape that renumbered it also removed this pack size"
			if !dryRun {
				if err := s.repo.SetCatalogueLink(product.Productid, "", 0); err != nil {
					return nil, err
				}
			}
			report.Cleared++
			report.Outcomes = append(report.Outcomes, outcome)
			continue
		}

		outcome.Imageid = row.ImageID
		if product.Imageid == row.ImageID && row.ImageID != "" {
			outcome.Action = "already"
			report.Already++
			report.Outcomes = append(report.Outcomes, outcome)
			continue
		}

		// The id resolves, but to a DIFFERENT product than the one stored.
		// Cleared rather than adopted: a renumber can hand an id to an unrelated
		// product, and silently repointing a shop's row at it would attach the
		// wrong catalogue entry — worse than no link at all.
		if !sameProduct(row.ProductName, product.Productname) {
			outcome.Action = "cleared"
			outcome.Reason = fmt.Sprintf("id %d now names %q, not %q",
				product.Catalogueid, row.ProductName, product.Productname)
			outcome.Imageid = ""
			if !dryRun {
				if err := s.repo.SetCatalogueLink(product.Productid, "", 0); err != nil {
					return nil, err
				}
			}
			report.Cleared++
			report.Outcomes = append(report.Outcomes, outcome)
			continue
		}

		outcome.Action = "linked"
		if !dryRun {
			if err := s.repo.SetCatalogueLink(product.Productid, row.ImageID, int(row.ID)); err != nil {
				return nil, err
			}
		}
		report.Linked++
		report.Outcomes = append(report.Outcomes, outcome)
	}

	return report, nil
}

// sameProduct is deliberately strict: a name differing by one character is a
// different image_id and therefore a different product in the catalogue's own
// terms, so anything looser here would adopt the wrong row.
func sameProduct(a, b string) bool {
	return normaliseName(a) == normaliseName(b)
}

func normaliseName(value string) string {
	out := make([]rune, 0, len(value))
	for _, r := range value {
		switch {
		case r >= 'a' && r <= 'z', r >= '0' && r <= '9':
			out = append(out, r)
		case r >= 'A' && r <= 'Z':
			out = append(out, r+('a'-'A'))
		}
	}
	return string(out)
}