package zddc

import (
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"strings"
)

// ResolveCanonicalPath substitutes on-disk casing for any canonical
// ancestor segment of target, without creating anything. Returns target
// unchanged when no case variant exists or when target is at fsRoot or
// outside it.
//
// Use this before authorization to make ACL lookups operate against the
// real on-disk path without side effects. EnsureCanonicalAncestors
// performs the same substitution AND creates missing ancestors —
// authorization should run between the two.
func ResolveCanonicalPath(fsRoot, target string) (string, error) {
	rel, err := filepath.Rel(fsRoot, target)
	if err != nil {
		return target, err
	}
	rel = filepath.ToSlash(rel)
	if rel == "." || strings.HasPrefix(rel, "../") || rel == ".." {
		return target, nil
	}
	parts := strings.Split(rel, "/")
	resolvedSegs := make([]string, len(parts))
	copy(resolvedSegs, parts)

	join := func(n int) string {
		segs := append([]string{fsRoot}, resolvedSegs[:n]...)
		return filepath.Join(segs...)
	}
	resolveAt := func(n int, logical string) error {
		parent := join(n)
		if _, err := os.Stat(filepath.Join(parent, resolvedSegs[n])); err == nil {
			return nil
		}
		actual, err := ResolveCanonical(parent, logical)
		if err != nil {
			return err
		}
		if actual != "" {
			resolvedSegs[n] = actual
		}
		return nil
	}

	if len(parts) >= 2 {
		seg := strings.ToLower(parts[1])
		if IsProjectPeer(seg) {
			if err := resolveAt(1, seg); err != nil {
				return target, err
			}
		}
	}
	if len(parts) >= 4 && strings.EqualFold(resolvedSegs[1], "archive") {
		seg := strings.ToLower(parts[3])
		if IsPerPartySlot(seg) {
			if err := resolveAt(3, seg); err != nil {
				return target, err
			}
		}
	}
	return filepath.Join(append([]string{fsRoot}, resolvedSegs...)...), nil
}

// EnsureCanonicalAncestors walks from fsRoot down to filepath.Dir(target),
// creating any missing canonical-folder ancestor with MkdirAll(perm).
// For freshly-created auto-own ancestors (the workspace party folders),
// it also writes a creator-owned .zddc using principalEmail (skipped if
// principalEmail is empty) — auto-own + fence are resolved per-dir via
// the .zddc cascade (AutoOwnAt / AutoOwnFencedAt).
//
// Returns the resolved version of target with on-disk casing substituted
// for any canonical ancestor whose disk variant differs from the requested
// casing — so a pre-existing Archive/ is reused rather than shadowed by a
// new archive/ sibling. The basename of target is never altered.
//
// Canonical positions, relative to fsRoot:
//
//   - <project>/<peer>   for any top-level peer (IsProjectPeer: archive,
//     incoming, working, staging, reviewing, mdl, rsk, ssr) — all are
//     physical directories.
//
//   - <project>/archive/<party>/<slot> where <slot> ∈ {received, issued}
//     (IsPerPartySlot) — the WORM record folders.
//
// fsRoot and target must be absolute filesystem paths under the same
// volume; target may not yet exist on disk.
func EnsureCanonicalAncestors(fsRoot, target, principalEmail string, perm fs.FileMode) (string, error) {
	rel, err := filepath.Rel(fsRoot, target)
	if err != nil {
		return target, fmt.Errorf("rel: %w", err)
	}
	rel = filepath.ToSlash(rel)
	if rel == "." || strings.HasPrefix(rel, "../") || rel == ".." {
		return target, fmt.Errorf("target %q escapes fsRoot %q", target, fsRoot)
	}

	parts := strings.Split(rel, "/")
	if len(parts) < 2 {
		// target is at fsRoot/<single-segment>; no canonical ancestors apply.
		return target, nil
	}

	resolvedSegs := make([]string, len(parts))
	copy(resolvedSegs, parts)

	// Track which ancestor directories we end up creating so we can seed
	// auto-own .zddc files on the right ones afterwards.
	type created struct {
		absPath string
		autoOwn bool
		fenced  bool
		roles   []string
	}
	var freshlyCreated []created

	// joinUnder builds an absolute path from fsRoot + the first n resolved
	// segments.
	joinUnder := func(n int) string {
		segs := append([]string{fsRoot}, resolvedSegs[:n]...)
		return filepath.Join(segs...)
	}

	// resolveAt(n) tries to use the on-disk casing for resolvedSegs[n] inside
	// joinUnder(n), substituting if a case-variant directory exists.
	resolveAt := func(n int, logical string) error {
		parent := joinUnder(n)
		// Only substitute if the requested segment doesn't already match
		// on disk (cheap optimisation to avoid a ReadDir on the hot path).
		if _, err := os.Stat(filepath.Join(parent, resolvedSegs[n])); err == nil {
			return nil
		}
		actual, err := ResolveCanonical(parent, logical)
		if err != nil {
			return err
		}
		if actual != "" {
			resolvedSegs[n] = actual
		}
		return nil
	}

	// Walk depth 1 (project) → deeper levels, resolving + tracking as we go.
	// Depth 0 is the project segment; not a canonical name.
	if len(parts) >= 2 {
		// Depth 1 candidate: any top-level peer (all physical now).
		seg := strings.ToLower(parts[1])
		if IsProjectPeer(seg) {
			if err := resolveAt(1, seg); err != nil {
				return target, err
			}
		}
	}

	// Depth 3 candidate (archive/<party>/<slot>): the WORM record slots
	// received/issued. Only meaningful when depth 1 is "archive".
	if len(parts) >= 4 && strings.EqualFold(resolvedSegs[1], "archive") {
		seg := strings.ToLower(parts[3])
		if IsPerPartySlot(seg) {
			if err := resolveAt(3, seg); err != nil {
				return target, err
			}
		}
	}

	// Now create any missing ancestors. We MkdirAll up to (but not
	// including) the basename. The handler's actual write call still does
	// its own parent-dir creation; this is the proactive seeding pass.
	parentDir := filepath.Dir(filepath.Join(append([]string{fsRoot}, resolvedSegs...)...))
	rootRel, _ := filepath.Rel(fsRoot, parentDir)
	rootRel = filepath.ToSlash(rootRel)
	if rootRel == "." || strings.HasPrefix(rootRel, "../") {
		return filepath.Join(append([]string{fsRoot}, resolvedSegs...)...), nil
	}

	// Walk segment-by-segment. For each ancestor that doesn't exist yet,
	// create it and record whether the position is auto-own.
	pathSoFar := fsRoot
	parentSegs := strings.Split(rootRel, "/")
	for i, name := range parentSegs {
		pathSoFar = filepath.Join(pathSoFar, name)
		if info, err := os.Stat(pathSoFar); err == nil {
			if !info.IsDir() {
				return target, fmt.Errorf("ancestor %q exists but is not a directory", pathSoFar)
			}
			continue
		} else if !os.IsNotExist(err) {
			return target, err
		}

		if err := os.MkdirAll(pathSoFar, perm); err != nil {
			return target, err
		}

		// Determine if this newly-created ancestor is an auto-own
		// position and whether it should be fenced (inherit: false).
		// Resolved via the .zddc cascade — the embedded defaults
		// (internal/zddc/defaults/) declare auto_own at the working/
		// staging/ incoming/ reviewing/ <party> homes but do NOT fence
		// them (they are shared team folders); an on-disk .zddc can opt
		// a directory into fencing per-directory with auto_own_fenced.
		_ = parentSegs // depth-tracking no longer needed
		_ = i
		autoOwn := AutoOwnAt(fsRoot, pathSoFar)
		fenced := autoOwn && AutoOwnFencedAt(fsRoot, pathSoFar)
		var roles []string
		if autoOwn {
			roles = AutoOwnRolesAt(fsRoot, pathSoFar)
		}
		freshlyCreated = append(freshlyCreated, created{
			absPath: pathSoFar,
			autoOwn: autoOwn,
			fenced:  fenced,
			roles:   roles,
		})
	}

	// Seed auto-own .zddc on the canonical positions that were freshly
	// created. Skip if no principal email is available (anonymous or
	// system writes). The fenced variant (inherit:false, private to the
	// creator) is an opt-in the default tree does not use — see
	// AutoOwnFencedAt. Role grants (from the cascade's auto_own_roles
	// list) are written alongside the creator email so role-level peer
	// authority survives without needing a subtree-admin grant.
	if principalEmail != "" {
		for _, c := range freshlyCreated {
			if !c.autoOwn {
				continue
			}
			var werr error
			if c.fenced {
				werr = WriteAutoOwnZddcFenced(c.absPath, principalEmail, c.roles)
			} else {
				werr = WriteAutoOwnZddc(c.absPath, principalEmail, c.roles)
			}
			if werr != nil {
				return target, fmt.Errorf("auto-own .zddc at %q: %w", c.absPath, werr)
			}
		}
	}

	return filepath.Join(append([]string{fsRoot}, resolvedSegs...)...), nil
}

// (autoOwnDepthMatch / isAutoOwnDepthMatch removed in Phase 3c —
// auto-own + fence determination now flows through the .zddc cascade
// via AutoOwnAt / AutoOwnFencedAt.)