// Package continuity implements the validated, artifact-backed rotation contract.
package continuity

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"orchestra/internal/domain"
	"os"
	"os/exec"
	"path/filepath"
	"regexp"
	"strings"
	"time"
)

// RenderTaskFile produces the immutable §6.2 TASK.md content for a task.
// Deterministic in every field that comes from the task itself, so the same
// task always hashes to the same content.
func RenderTaskFile(t domain.Task) []byte {
	var b strings.Builder
	fmt.Fprintf(&b, "# Task %s\n\n", t.ID)
	if t.Title != "" {
		fmt.Fprintf(&b, "%s\n\n", t.Title)
	}
	fmt.Fprintf(&b, "- Project: %s\n", t.Project)
	fmt.Fprintf(&b, "- Source: %s/%s\n", t.Source, t.ExternalID)
	fmt.Fprintf(&b, "- Priority: %d\n", t.InherentPriority)
	if len(t.Capability) > 0 {
		fmt.Fprintf(&b, "- Capability: %s\n", strings.Join(t.Capability, ", "))
	}
	if t.Due != nil {
		fmt.Fprintf(&b, "- Due: %s\n", t.Due.UTC().Format(time.RFC3339))
	}
	if t.Parent != "" {
		fmt.Fprintf(&b, "- Parent: %s\n", t.Parent)
	}
	if strings.TrimSpace(t.Description) != "" {
		fmt.Fprintf(&b, "\n## Instructions\n\n%s\n", t.Description)
	}
	if len(t.Acceptance) > 0 {
		b.WriteString("\n## Acceptance criteria\n")
		for _, criterion := range t.Acceptance {
			fmt.Fprintf(&b, "\n- %s", criterion)
		}
		b.WriteByte('\n')
	}
	if t.QualityGate != "" {
		fmt.Fprintf(&b, "\n## Quality gate\n\n%s\n", t.QualityGate)
	}
	b.WriteString("\n## Completion\n\nRun the configured quality gate. When the task is ready for the worker to verify and deliver, create `.orchestra/done`. Do not write a prose completion report.\n\nThis file is immutable for the lifetime of the task (§6.2) — its hash is\ncarried in every handoff and re-verified on every pickup. Do not edit it.\n")
	return []byte(b.String())
}

// TaskFileHash returns the sha256 of the TASK.md at the root of a worktree.
func TaskFileHash(root string) (string, error) {
	b, err := os.ReadFile(filepath.Join(root, "TASK.md"))
	if err != nil {
		return "", err
	}
	sum := sha256.Sum256(b)
	return hex.EncodeToString(sum[:]), nil
}

// ConventionsFiles are the §6.3 shared docs ("Shared *.md ... all agents
// contribute") whose staleness the orchestra is responsible for tracking —
// never the agent, which only sees its own cached copy.
var ConventionsFiles = []string{"AGENTS.md", "CLAUDE.md", "VOCAB.md"}

// ConventionsHash hashes the concatenation of whichever ConventionsFiles
// exist at root, in that fixed order, so the result changes iff any of their
// contents change (a file appearing/disappearing also changes it, since a
// length-prefixed marker precedes each file's bytes). A repo with none of
// these files hashes to a stable, comparable empty-set value rather than
// erroring — §6.3 is optional infrastructure, not every project uses it.
func ConventionsHash(root string) (string, error) {
	h := sha256.New()
	for _, name := range ConventionsFiles {
		b, err := os.ReadFile(filepath.Join(root, name))
		if err != nil {
			fmt.Fprintf(h, "%s:0\n", name)
			continue
		}
		fmt.Fprintf(h, "%s:%d\n", name, len(b))
		h.Write(b)
	}
	return hex.EncodeToString(h.Sum(nil)), nil
}

type Dirty struct {
	Path    string `json:"path"`
	SHA256  string `json:"sha256"`
	Deleted bool   `json:"deleted,omitempty"`
}
type Completed struct {
	What     string `json:"what"`
	Evidence string `json:"evidence"`
}
type DeadEnd struct {
	Tried     string `json:"tried"`
	WhyFailed string `json:"why_failed"`
}
type Anchor struct {
	GitSHA string  `json:"git_sha"`
	Branch string  `json:"branch"`
	Dirty  []Dirty `json:"dirty,omitempty"`
}
type Meta struct {
	ID            string `json:"id"`
	Parent        string `json:"parent,omitempty"`
	Reason        string `json:"reason"`
	RotationIndex int    `json:"rotation_index"`
}
type Handoff struct {
	Meta          Meta      `json:"meta"`
	Anchor        Anchor    `json:"anchor"`
	Remaining     []string  `json:"remaining"`
	Action        string    `json:"action"`
	Command       string    `json:"command"`
	DeadEnds      []DeadEnd `json:"dead_ends"`
	OpenQuestions []string  `json:"open_questions"`
	Learned       []string  `json:"learned"`
}
type Result struct {
	Command  string `json:"command"`
	ExitCode int    `json:"exit_code"`
	AtSHA    string `json:"at_sha"`
}

// reconcile_failure is Orchestra's own trigger: human input could not be
// reconciled at repeated verified turn boundaries, so the session is handed to
// a successor rather than left running on intent that cannot be refreshed.
// phase_changed is a rotation Orchestra itself triggers when a phase request
// is accepted. The adapter has produced it since phase rotations landed
// (handoffReason), but this list was never extended, so every phase rotation
// built a handoff the validator then refused as "invalid handoff meta" (F36).
// The two halves of one contract have to name the same vocabulary.
var reasons = map[string]bool{"threshold": true, "milestone": true, "thrash": true, "manual": true, "reconcile_failure": true, "phase_changed": true}

const maxAuthoredLine = 200

// Action is not one authored line. parseHandoffAnswer joins the agent's NEXT
// and WHY answers with " — ", and the prompt asks for a sentence each without
// naming any budget. Two ordinary sentences cleared 200 characters and every
// rotation on workpc failed at "prose smuggled into list" (F31). Budget the
// joined field for the two lines it is actually made of.
const maxAuthoredAction = 2*maxAuthoredLine + len(" — ")

var circularAction = regexp.MustCompile(`(?i)handoff|report\.md|^continue the task`)
var circularCommand = regexp.MustCompile(`(?i)\.orchestra-handoff|handoff-report|report\.md`)

// IsCircularCommand reports whether Validate would reject this as a command
// that points at a handoff. Producers need the same answer before they build a
// handoff, so the rule lives in one place rather than being restated as a
// second regexp that can drift.
func IsCircularCommand(s string) bool { return circularCommand.MatchString(s) }

func (h Handoff) Validate() error {
	if strings.TrimSpace(h.Meta.ID) == "" || !reasons[h.Meta.Reason] || h.Meta.RotationIndex < 0 {
		return errors.New("invalid handoff meta")
	}
	if len(h.Anchor.GitSHA) != 40 || h.Anchor.Branch == "" || strings.TrimSpace(h.Action) == "" {
		return errors.New("invalid handoff required fields")
	}
	if circularAction.MatchString(h.Action) {
		return errors.New("invalid handoff action: must name concrete next work, not a handoff")
	}
	if err := validateAuthored(h.Action, maxAuthoredAction); err != nil {
		return err
	}
	if circularCommand.MatchString(h.Command) {
		return errors.New("invalid handoff command: must not point to a handoff or report")
	}
	for _, item := range append(append([]string{}, h.Remaining...), append(h.OpenQuestions, h.Learned...)...) {
		if err := validateAuthoredLine(item); err != nil {
			return err
		}
	}
	for _, d := range h.Anchor.Dirty {
		if filepath.IsAbs(d.Path) || d.Path == "" || (!d.Deleted && len(d.SHA256) != 64) {
			return errors.New("invalid dirty anchor")
		}
	}
	for _, d := range h.DeadEnds {
		if strings.TrimSpace(d.Tried) == "" || strings.TrimSpace(d.WhyFailed) == "" {
			return errors.New("invalid dead end")
		}
		if err := validateAuthoredLine(d.Tried); err != nil {
			return err
		}
		if err := validateAuthoredLine(d.WhyFailed); err != nil {
			return err
		}
	}
	return nil
}

func validateAuthoredLine(s string) error {
	return validateAuthored(s, maxAuthoredLine)
}

// The two rejections used to share one message, which named the cause the
// agent had not hit. An answer over budget was reported as smuggled prose, so
// the agent could not tell what to shorten and retried the same text.
func validateAuthored(s string, limit int) error {
	if strings.TrimSpace(s) == "" {
		return errors.New("invalid handoff authored field: empty item")
	}
	if strings.Contains(s, "\n#") {
		return errors.New("invalid handoff authored field: prose smuggled into list")
	}
	if len(s) > limit {
		return fmt.Errorf("invalid handoff authored field: %d characters, limit %d", len(s), limit)
	}
	return nil
}
func Encode(h Handoff) ([]byte, error) {
	if err := h.Validate(); err != nil {
		return nil, err
	}
	return json.Marshal(h)
}
func Decode(b []byte) (Handoff, error) {
	var h Handoff
	d := json.NewDecoder(strings.NewReader(string(b)))
	d.DisallowUnknownFields()
	if err := d.Decode(&h); err != nil {
		return h, err
	}
	return h, h.Validate()
}

func ValidatePickup(root string, h Handoff, taskFileSHA string) error {
	if err := h.Validate(); err != nil {
		return err
	}
	out, err := exec.Command("git", "-C", root, "rev-parse", "HEAD").Output()
	if err != nil || strings.TrimSpace(string(out)) != h.Anchor.GitSHA {
		return errors.New("handoff anchor HEAD mismatch")
	}
	for _, d := range h.Anchor.Dirty {
		if d.Deleted {
			if _, e := os.Stat(filepath.Join(root, d.Path)); !errors.Is(e, os.ErrNotExist) {
				return fmt.Errorf("handoff deleted file restored: %s", d.Path)
			}
			continue
		}
		b, e := os.ReadFile(filepath.Join(root, d.Path))
		if e != nil {
			return e
		}
		sum := sha256.Sum256(b)
		if hex.EncodeToString(sum[:]) != d.SHA256 {
			return fmt.Errorf("handoff dirty file changed: %s", d.Path)
		}
	}
	if taskFileSHA != "" {
		b, e := os.ReadFile(filepath.Join(root, "TASK.md"))
		if e != nil {
			return e
		}
		sum := sha256.Sum256(b)
		if hex.EncodeToString(sum[:]) != taskFileSHA {
			return errors.New("TASK.md changed")
		}
	}
	return nil
}

// VerifyTaskFile ensures the worktree contains the original, immutable task.
func VerifyTaskFile(root, taskFileSHA string) error {
	if taskFileSHA == "" {
		return errors.New("TASK.md hash required")
	}
	b, err := os.ReadFile(filepath.Join(root, "TASK.md"))
	if err != nil {
		return err
	}
	sum := sha256.Sum256(b)
	if hex.EncodeToString(sum[:]) != taskFileSHA {
		return errors.New("TASK.md changed")
	}
	return nil
}

type CAS interface {
	PutArtifact([]byte) (string, error)
	Artifact(string) ([]byte, error)
}

func Save(h Handoff, cas CAS) (string, error) {
	b, e := Encode(h)
	if e != nil {
		return "", e
	}
	return cas.PutArtifact(b)
}
func Load(ref string, cas CAS) (Handoff, error) {
	b, e := cas.Artifact(ref)
	if e != nil {
		return Handoff{}, e
	}
	return Decode(b)
}

// ScratchCommit records every piece of repository work except Orchestra's
// ephemeral protocol markers.  In particular, git add -A is intentional: it
// includes already-staged changes, deletions, renames, and untracked files.
// TASK.md is checked before touching the index; it is an immutable input, not
// deliverable work.  The report/done markers remain local so a successor never
// mistakes an old protocol signal for a new one.
func ScratchCommit(root, branch, message string) error {
	if branch == "" || strings.ContainsAny(branch, " \t\n") {
		return errors.New("invalid scratch branch")
	}
	if strings.TrimSpace(message) == "" {
		return errors.New("scratch commit message required")
	}
	status, err := exec.Command("git", "-C", root, "status", "--porcelain", "--", "TASK.md").Output()
	if err != nil {
		return err
	}
	if len(status) != 0 {
		return errors.New("TASK.md is immutable")
	}
	// Reuse the branch across rotations of the same task rather than failing
	// on "branch already exists" — a task can rotate more than once.
	if err := exec.Command("git", "-C", root, "switch", branch).Run(); err != nil {
		if err := exec.Command("git", "-C", root, "switch", "-c", branch).Run(); err != nil {
			return err
		}
	}
	// A harness may have staged a protocol marker itself. Remove it from the
	// index before staging the real checkpoint; this does not alter its working
	// tree contents and makes the exclusion apply to staged state too.
	for _, marker := range []string{".orchestra", ".orchestra-handoff.json", ".orchestra-handoff-report.md"} {
		if err := exec.Command("git", "-C", root, "reset", "-q", "HEAD", "--", marker).Run(); err != nil {
			return err
		}
	}
	if err := exec.Command("git", "-C", root, "add", "-A", "--", ".", ":(exclude)TASK.md", ":(exclude).orchestra", ":(exclude).orchestra-handoff.json", ":(exclude).orchestra-handoff-report.md").Run(); err != nil {
		return err
	}
	// Only staged non-protocol work is committed. Remaining marker files are
	// expected and must not suppress a clean committed-anchor checkpoint.
	if exec.Command("git", "-C", root, "diff", "--cached", "--quiet").Run() == nil {
		return nil // nothing to snapshot; branch already reflects the worktree
	}
	return exec.Command("git", "-C", root, "commit", "-m", message).Run()
}

func ScratchPush(root, branch, remote string) error {
	if branch == "" || remote == "" {
		return errors.New("scratch branch and remote required")
	}
	return exec.Command("git", "-C", root, "push", remote, branch).Run()
}

func ScratchPull(root, branch, remote string) error {
	if branch == "" || remote == "" {
		return errors.New("scratch branch and remote required")
	}
	if err := exec.Command("git", "-C", root, "fetch", remote, branch).Run(); err != nil {
		return err
	}
	return exec.Command("git", "-C", root, "merge", "--ff-only", "FETCH_HEAD").Run()
}

// ScratchSync pushes/pulls a scratch branch. Pull uses fast-forward-only to
// avoid silently merging independent WIP histories.
func ScratchSync(root, branch, remote string, push bool) error {
	if branch == "" || strings.ContainsAny(branch, " \t\n") || remote == "" {
		return errors.New("invalid scratch sync")
	}
	args := []string{"-C", root, "push", remote, branch}
	if !push {
		args = []string{"-C", root, "fetch", remote, branch}
	}
	if err := exec.Command("git", args...).Run(); err != nil {
		return err
	}
	if !push {
		return exec.Command("git", "-C", root, "merge", "--ff-only", "FETCH_HEAD").Run()
	}
	return nil
}