// SPDX-FileCopyrightText: 2026 Coffey Labs
// SPDX-License-Identifier: GPL-3.0-or-later

package backup

import (
	"fmt"
	"sort"
	"strings"
)

// Disposition is what an operator actually has to do about a group of
// settings migrate_v016.py didn't carry over.
//
// The raw count is misleading on its own, and alarmingly so. A real
// production instance reported 12,182 unmigrated settings, which reads as
// an impossible amount of manual work. Categorised, 8,547 of them
// repopulate themselves, 3,337 ship with v0.16, ~198 had already been
// carried by another mechanism, and roughly 290 genuinely needed a human.
// The difference between those two framings is the difference between a
// migration nobody attempts and an afternoon's review.
type Disposition string

const (
	// DispositionRegenerates: runtime state, not configuration. Nothing to
	// do; it rebuilds itself in normal operation.
	DispositionRegenerates Disposition = "regenerates"
	// DispositionShipped: v0.16 provides its own copy, and restoring
	// v0.15's would duplicate it or replace newer definitions with older
	// ones.
	DispositionShipped Disposition = "shipped with v0.16"
	// DispositionCarried: the substance came across by another route even
	// though these particular keys are listed as unmigrated.
	DispositionCarried Disposition = "already carried"
	// DispositionReview: genuinely site-specific. This is the real work.
	DispositionReview Disposition = "needs review"
)

// dispositionRule maps a setting prefix to what to do about it.
//
// Every entry here was checked against a v0.16.14 instance migrated from a
// real v0.15.5 - by snapshotting the migrated store and counting what was
// already in it - not inferred from documentation. Rules are matched
// longest-prefix-first, because "server.blocked-ip" is runtime state while
// "server.auto-ban" right next to it is configuration.
type dispositionRule struct {
	prefix      string
	disposition Disposition
	note        string
}

var dispositionRules = []dispositionRule{
	{"server.blocked-ip", DispositionRegenerates,
		"auto-ban repopulates these from live traffic; a migrated instance simply starts with an empty list"},

	{"lookup.url-redirectors", DispositionShipped,
		"v0.16 ships this list itself (observed as MemoryLookupKey/SpamUrlRedirector entries in a migrated store)"},
	{"lookup.trusted-domains", DispositionShipped,
		"v0.16 ships this list itself (MemoryLookupKey/SpamTrustedDomain)"},
	{"lookup.surbl-hashbl", DispositionShipped,
		"v0.16 ships this list itself (MemoryLookupKey)"},
	{"spam-filter.rule", DispositionShipped,
		"v0.16 ships its own rules - 66 SpamRule objects were present in a migrated store, the same stock set under v0.16's naming (stwt_x -> STWT_X). Restoring v0.15's would duplicate them and revert a year of updates"},
	{"spam-filter.dnsbl", DispositionShipped,
		"v0.16 ships its own DNSBL servers (18 SpamDnsblServer objects present after migration)"},
	{"spam-filter.list", DispositionShipped,
		"stock lists (file extensions and similar) that v0.16 provides itself"},

	{"signature.", DispositionCarried,
		"DKIM: carried across as DkimSignature objects, private keys included - verified on a migrated instance"},
	{"server.listener", DispositionCarried,
		"regenerated by this tool's own apply plan (see the supplement)"},
}

// Classification is one group of unmigrated settings with its disposition.
type Classification struct {
	Prefix      string
	Keys        int
	Disposition Disposition
	Note        string
}

// ClassifiedReport is an UnmigratedReport with each group's disposition
// resolved, and totals per disposition.
type ClassifiedReport struct {
	TotalKeys int
	Groups    []Classification
	Counts    map[Disposition]int
}

// Classify resolves what to do about each group in the report.
func (r *UnmigratedReport) Classify() *ClassifiedReport {
	out := &ClassifiedReport{Counts: map[Disposition]int{}}
	if r == nil {
		return out
	}
	out.TotalKeys = r.TotalKeys
	for _, p := range r.Prefixes {
		disposition, note := classifyPrefix(p.Prefix)
		out.Groups = append(out.Groups, Classification{
			Prefix: p.Prefix, Keys: p.Keys, Disposition: disposition, Note: note,
		})
		out.Counts[disposition] += p.Keys
	}
	sort.Slice(out.Groups, func(i, j int) bool { return out.Groups[i].Keys > out.Groups[j].Keys })
	return out
}

func classifyPrefix(prefix string) (Disposition, string) {
	best := -1
	var disposition Disposition = DispositionReview
	var note string
	for _, rule := range dispositionRules {
		if !strings.HasPrefix(prefix, rule.prefix) {
			continue
		}
		if len(rule.prefix) > best {
			best, disposition, note = len(rule.prefix), rule.disposition, rule.note
		}
	}
	return disposition, note
}

// NeedsReview returns just the groups a human has to deal with, largest
// first - the actual worklist, as opposed to the raw count.
func (c *ClassifiedReport) NeedsReview() []Classification {
	var out []Classification
	for _, g := range c.Groups {
		if g.Disposition == DispositionReview {
			out = append(out, g)
		}
	}
	return out
}

// Summary renders the categorised report, leading with what needs a human
// rather than with the total.
func (c *ClassifiedReport) Summary(worklistPath string) string {
	if c == nil || c.TotalKeys == 0 {
		return "no unmigrated settings were reported"
	}
	var b strings.Builder
	fmt.Fprintf(&b, "%d setting(s) were not carried over by migrate_v016.py. What they actually are:\n", c.TotalKeys)

	for _, d := range []Disposition{DispositionRegenerates, DispositionShipped, DispositionCarried, DispositionReview} {
		n := c.Counts[d]
		if n == 0 {
			continue
		}
		label := string(d)
		if d == DispositionReview {
			label = "NEED YOUR REVIEW"
		}
		fmt.Fprintf(&b, "\n      %6d  %-18s", n, label)
		groups := []string{}
		for _, g := range c.Groups {
			if g.Disposition == d && g.Keys > 0 {
				groups = append(groups, fmt.Sprintf("%s (%d)", g.Prefix, g.Keys))
			}
		}
		shown := groups
		if len(shown) > 6 {
			shown = shown[:6]
		}
		fmt.Fprintf(&b, "  %s", strings.Join(shown, ", "))
		if len(groups) > len(shown) {
			fmt.Fprintf(&b, ", +%d more", len(groups)-len(shown))
		}
	}

	review := c.Counts[DispositionReview]
	fmt.Fprintf(&b, "\n\n      Only the %d needing review are work. The rest either rebuild themselves,\n", review)
	fmt.Fprintf(&b, "      ship with v0.16 (restoring v0.15's copies would revert them), or came\n")
	fmt.Fprintf(&b, "      across by another route. Full key list: %s", worklistPath)
	return b.String()
}