package preflight

import (
	"context"
	"fmt"
	"net/http"
	"sort"
	"strings"
	"time"

	"github.com/LINUXexpert-org/stalwart-migrator/internal/checkpoint"
	"github.com/LINUXexpert-org/stalwart-migrator/internal/stalwartapi"
)

// Options configures a Checker. Every field has a conservative default
// applied by New except the ones that must name a real path on this host.
type Options struct {
	BinaryPath      string // installed stalwart binary, e.g. /usr/local/bin/stalwart
	ConfigPath      string // its config file (TOML pre-0.16, JSON 0.16+)
	DataDir         string // data directory to size/space-check
	ContainerName   string // docker container name, if applicable
	AdminURL        string // base URL for the JMAP reachability check; empty skips it
	AdminUser       string
	AdminPassword   string
	TargetVersion   string // e.g. "0.16.14" or "latest"
	MinFreeMultiple float64
	HTTPClient      *http.Client
}

// Checker runs the preflight checks described in ARCHITECTURE.md §4.1.
type Checker struct {
	opts Options
}

func New(opts Options) *Checker {
	if opts.MinFreeMultiple <= 0 {
		opts.MinFreeMultiple = 2.0
	}
	return &Checker{opts: opts}
}

// Run executes every preflight check, checkpointing each one so a killed
// and re-invoked run skips checks that already completed - see
// checkpoint.Store.RunStep. It never aborts early on a single Fail: the
// point of preflight is to surface every blocking issue in one pass rather
// than fail-stop-fix-retry one at a time. Callers decide what to do with a
// Report whose Blocking() is true. It only returns a non-nil error for a
// genuine execution fault (e.g. the checkpoint store itself can't be
// written to) - a check finding a real problem is reported via
// Status: StatusFail in the Report, not a Go error.
func (c *Checker) Run(ctx context.Context, store *checkpoint.Store, rs *checkpoint.RunState) (Report, error) {
	var report Report

	// runCheck wraps fn as a checkpointed step and appends its result to
	// report, whether fn actually ran or was skipped because a prior
	// attempt already completed it - either way report ends up with the
	// same entries, and the returned checkpoint.StepOutcome.Extra carries
	// whatever machine-readable value a later check in this same Run needs.
	runCheck := func(name string, fn func() (CheckResult, string)) (checkpoint.StepOutcome, error) {
		outcome, err := store.RunStep(rs, checkpoint.PhasePreflight, name, func() (checkpoint.StepOutcome, error) {
			res, extra := fn()
			return checkpoint.StepOutcome{Verdict: string(res.Status), Detail: res.Detail, Extra: extra}, nil
		})
		if err != nil {
			return checkpoint.StepOutcome{}, err
		}
		report.Results = append(report.Results, CheckResult{Name: name, Status: Status(outcome.Verdict), Detail: outcome.Detail})
		return outcome, nil
	}

	versionOutcome, err := runCheck("version", func() (CheckResult, string) {
		cur, err := DetectVersion(ctx, c.opts.BinaryPath)
		if err != nil {
			return CheckResult{Status: StatusFail, Detail: err.Error()}, ""
		}
		curV, _ := parseSemver(cur)
		if curV.Compare(minSupportedSource) < 0 {
			return CheckResult{
				Status: StatusFail,
				Detail: fmt.Sprintf("current version %s is older than the minimum supported %s - upgrade to 0.15.x first", cur, minSupportedSource),
			}, cur
		}
		return CheckResult{Status: StatusOK, Detail: fmt.Sprintf("current version %s", cur)}, cur
	})
	if err != nil {
		return report, err
	}

	targetOutcome, err := runCheck("target-release", func() (CheckResult, string) {
		rel, err := ResolveRelease(ctx, c.opts.HTTPClient, c.opts.TargetVersion)
		if err != nil {
			return CheckResult{Status: StatusFail, Detail: err.Error()}, ""
		}
		tag := strings.TrimPrefix(rel.TagName, "v")
		detail := fmt.Sprintf("resolved target to %s (%d release assets)", rel.TagName, len(rel.Assets))
		if asset := ChecksumAsset(rel); asset != nil {
			detail += fmt.Sprintf(", checksum manifest available: %s", asset.Name)
		} else {
			detail += "; no published checksum manifest found - integrity relies on the one-time HTTPS download only"
		}
		return CheckResult{Status: StatusOK, Detail: detail}, tag
	})
	if err != nil {
		return report, err
	}

	if _, err := runCheck("upgrade-direction", func() (CheckResult, string) {
		curV, errCur := parseSemver(versionOutcome.Extra)
		tgtV, errTgt := parseSemver(targetOutcome.Extra)
		if errCur != nil || errTgt != nil {
			return CheckResult{Status: StatusWarn, Detail: "could not compare current and target versions (one or both unresolved above)"}, ""
		}
		if curV.Compare(tgtV) >= 0 {
			return CheckResult{
				Status: StatusFail,
				Detail: fmt.Sprintf("current version %s is already at or beyond target %s - nothing to migrate", curV, tgtV),
			}, ""
		}
		if curV.Major == 0 && curV.Minor < 16 && (tgtV.Major > 0 || tgtV.Minor >= 16) {
			return CheckResult{
				Status: StatusOK,
				Detail: fmt.Sprintf("%s -> %s crosses the 0.15/0.16 major boundary: full recovery-mode migration plan required (ARCHITECTURE.md §4.4)", curV, tgtV),
			}, ""
		}
		return CheckResult{
			Status: StatusOK,
			Detail: fmt.Sprintf("%s -> %s is a same-boundary patch upgrade: fast-path plan applies (ARCHITECTURE.md §4.6)", curV, tgtV),
		}, ""
	}); err != nil {
		return report, err
	}

	deploymentOutcome, err := runCheck("deployment-kind", func() (CheckResult, string) {
		kind := DetectDeploymentKind(ctx, c.opts.ContainerName)
		status := StatusOK
		if kind == DeploymentUnknown {
			status = StatusWarn
		}
		return CheckResult{Status: status, Detail: fmt.Sprintf("detected deployment kind: %s", kind)}, string(kind)
	})
	if err != nil {
		return report, err
	}

	storeOutcome, err := runCheck("store-backend", func() (CheckResult, string) {
		matches, err := DetectStoreBackends(c.opts.ConfigPath)
		if err != nil {
			return CheckResult{Status: StatusFail, Detail: err.Error()}, ""
		}
		if len(matches) == 0 {
			return CheckResult{Status: StatusWarn, Detail: "no known store backend type found in config - confirm manually before proceeding"}, ""
		}
		names := make([]string, len(matches))
		backends := make([]string, len(matches))
		for i, m := range matches {
			names[i] = fmt.Sprintf("%s (%s)", m.Backend, m.Path)
			backends[i] = m.Backend
		}
		return CheckResult{Status: StatusOK, Detail: "found: " + strings.Join(names, ", ")}, strings.Join(backends, ",")
	})
	if err != nil {
		return report, err
	}

	if _, err := runCheck("cluster-config", func() (CheckResult, string) {
		clustered, err := LooksClustered(c.opts.ConfigPath)
		if err != nil {
			return CheckResult{Status: StatusFail, Detail: err.Error()}, ""
		}
		if clustered {
			return CheckResult{
				Status: StatusWarn,
				Detail: "config mentions clustering - confirm every peer node is stopped before this run proceeds; the tool does not verify this for you",
			}, ""
		}
		return CheckResult{Status: StatusOK, Detail: "no cluster configuration detected"}, ""
	}); err != nil {
		return report, err
	}

	if _, err := runCheck("disk-space", func() (CheckResult, string) {
		size, err := DirSize(c.opts.DataDir)
		if err != nil {
			return CheckResult{Status: StatusFail, Detail: err.Error()}, ""
		}
		free, err := FreeBytes(c.opts.DataDir)
		if err != nil {
			return CheckResult{Status: StatusFail, Detail: err.Error()}, ""
		}
		required := uint64(float64(size) * c.opts.MinFreeMultiple)
		detail := fmt.Sprintf("data dir %s is %s, %s free, need >= %s (%.1fx, for the fs-snapshot backup)",
			c.opts.DataDir, humanBytes(uint64(size)), humanBytes(free), humanBytes(required), c.opts.MinFreeMultiple)
		if free < required {
			return CheckResult{Status: StatusFail, Detail: detail}, ""
		}
		return CheckResult{Status: StatusOK, Detail: detail}, ""
	}); err != nil {
		return report, err
	}

	if c.opts.AdminURL != "" {
		if _, err := runCheck("admin-reachable", func() (CheckResult, string) {
			client := &stalwartapi.Client{
				BaseURL:    c.opts.AdminURL,
				Username:   c.opts.AdminUser,
				Password:   c.opts.AdminPassword,
				HTTPClient: c.opts.HTTPClient,
			}
			if err := client.Ping(ctx); err != nil {
				return CheckResult{Status: StatusFail, Detail: err.Error()}, ""
			}
			return CheckResult{Status: StatusOK, Detail: fmt.Sprintf("JMAP session reachable at %s with the given credentials", c.opts.AdminURL)}, ""
		}); err != nil {
			return report, err
		}

		if _, err := runCheck("account-snapshot", func() (CheckResult, string) {
			client := &stalwartapi.Client{
				BaseURL:    c.opts.AdminURL,
				Username:   c.opts.AdminUser,
				Password:   c.opts.AdminPassword,
				HTTPClient: c.opts.HTTPClient,
			}
			snap, err := client.AccountSnapshot(ctx)
			if err != nil {
				return CheckResult{
					Status: StatusWarn,
					Detail: fmt.Sprintf("could not capture the account/domain snapshot: %v - the post-migration directory-integrity check won't have anything to compare against", err),
				}, ""
			}
			mailboxCounts := make(map[string][]checkpoint.MailboxCount, len(snap.MailboxCounts))
			for account, counts := range snap.MailboxCounts {
				converted := make([]checkpoint.MailboxCount, len(counts))
				for i, mc := range counts {
					converted[i] = checkpoint.MailboxCount{Mailbox: mc.Mailbox, Messages: mc.Messages}
				}
				mailboxCounts[account] = converted
			}
			rs.PreflightSnapshot = &checkpoint.PreflightSnapshot{
				TakenAt:       time.Now().UTC(),
				AccountCount:  snap.AccountCount,
				Domains:       snap.Domains,
				MailboxCounts: mailboxCounts,
			}
			detail := fmt.Sprintf("captured snapshot: %d account(s) across %d domain(s), mailbox counts for %d account(s)",
				snap.AccountCount, len(snap.Domains), len(mailboxCounts))
			status := StatusOK
			if len(snap.MailboxErrors) > 0 {
				status = StatusWarn
				accounts := make([]string, 0, len(snap.MailboxErrors))
				for account := range snap.MailboxErrors {
					accounts = append(accounts, account)
				}
				sort.Strings(accounts)
				for i, account := range accounts {
					if i >= 3 {
						detail += fmt.Sprintf(" (and %d more)", len(accounts)-3)
						break
					}
					detail += fmt.Sprintf("; mailbox count failed for %s: %s", account, snap.MailboxErrors[account])
				}
			}
			return CheckResult{Status: status, Detail: detail}, ""
		}); err != nil {
			return report, err
		}
	} else {
		report.Results = append(report.Results, CheckResult{
			Name:   "admin-reachable",
			Status: StatusWarn,
			Detail: "no --admin-url configured - skipped; the account/mailbox snapshot validate needs later can't be captured without it",
		})
	}

	rs.Topology = checkpoint.Topology{
		DeploymentKind: deploymentOutcome.Extra,
		StoreBackend:   storeOutcome.Extra,
	}
	if versionOutcome.Extra != "" {
		rs.SourceVersion = versionOutcome.Extra
	}
	if targetOutcome.Extra != "" {
		rs.TargetVersion = targetOutcome.Extra
	}
	if err := store.Save(rs); err != nil {
		return report, fmt.Errorf("preflight: persist topology: %w", err)
	}

	return report, nil
}