// Package candidate captures and validates a committed local release candidate.
package candidate

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"os/exec"
	"strings"

	"gitea.maximumdirect.net/eric/ReleaseKit/internal/git"
	"gitea.maximumdirect.net/eric/ReleaseKit/internal/gotool"
	"gitea.maximumdirect.net/eric/ReleaseKit/internal/process"
	"gitea.maximumdirect.net/eric/ReleaseKit/internal/releaseidentity"
	"gitea.maximumdirect.net/eric/ReleaseKit/internal/validation"
	"gitea.maximumdirect.net/eric/ReleaseKit/internal/versioncontract"
)

var ErrInvalidVersion = errors.New("invalid stable version")

type Candidate struct {
	RepositoryDir string
	ModuleDir     string
	ModulePath    string
	Tag           string
	Commit        string
	Version       string
	Note          string
}

type Request struct {
	RepositoryDir    string
	ModuleDir        string
	Product          string
	Version          string
	Validation       validation.Settings
	AdditionalChecks func(context.Context, Candidate) error
	AfterValidate    func(context.Context, Candidate, *gotool.Owner) error
	Output           io.Writer
	ToolOwner        *gotool.Owner
}

func Check(ctx context.Context, request Request) (Candidate, error) {
	captured, err := Capture(ctx, request)
	if err != nil {
		return captured, err
	}
	request.ToolOwner = gotool.NewOwner(captured.ModuleDir)
	if err := Validate(ctx, request, captured); err != nil {
		return captured, err
	}
	if request.AfterValidate != nil {
		callbackErr := request.AfterValidate(ctx, captured, request.ToolOwner)
		if callbackErr != nil {
			return captured, fmt.Errorf("after candidate validation: %w", callbackErr)
		}
	}
	if err := Recheck(ctx, captured, ""); err != nil {
		return captured, err
	}
	return captured, nil
}

// Capture validates request identity and records one clean local candidate,
// including the note bytes from the captured commit. It does not run checks.
func Capture(ctx context.Context, request Request) (Candidate, error) {
	captured := Candidate{Version: request.Version}
	if !validStableVersion(request.Version) {
		return captured, fmt.Errorf("%w: %q", ErrInvalidVersion, request.Version)
	}
	if strings.TrimSpace(request.Product) == "" {
		return captured, errors.New("product is required")
	}

	repositoryDir, err := git.RepositoryRoot(ctx, request.RepositoryDir)
	if err != nil {
		return captured, fmt.Errorf("resolve repository directory: %w", err)
	}
	captured.RepositoryDir = repositoryDir
	state, err := inspectLocalState(ctx, repositoryDir)
	if err != nil {
		return captured, err
	}
	captured.Commit = state.commit
	if state.branch != "main" {
		return captured, fmt.Errorf("release candidate must be on main; current branch is %q", state.branch)
	}
	if state.status != "" {
		return captured, fmt.Errorf("release candidate worktree and index must be clean:\n%s", state.status)
	}

	identity, err := releaseidentity.FromCommitted(ctx, repositoryDir, request.ModuleDir, request.Version, state.commit)
	captured.ModuleDir = identity.ModuleDir
	captured.ModulePath = identity.ModulePath
	captured.Tag = identity.Tag
	if err != nil {
		return captured, fmt.Errorf("resolve selected module release identity: %w", err)
	}
	note, err := git.ReadCommitFile(ctx, identity.RepositoryDir, state.commit, identity.NotePath)
	if err != nil {
		return captured, fmt.Errorf("read committed release note %q: %w", identity.NotePath, err)
	}
	if err := validateNote(note, request.Product, request.Version); err != nil {
		return captured, fmt.Errorf("release note %q: %w", identity.NotePath, err)
	}
	if exists, err := hasLocalTag(ctx, repositoryDir, identity.Tag); err != nil {
		return captured, fmt.Errorf("inspect local tag %q: %w", identity.Tag, err)
	} else if exists {
		return captured, fmt.Errorf("local tag %q already exists", identity.Tag)
	}

	captured.Note = string(note)
	return captured, nil
}

// Validate runs the selected offline Go suite, followed by AdditionalChecks
// when supplied, for the captured candidate.
func Validate(ctx context.Context, request Request, captured Candidate) error {
	owner := request.ToolOwner
	if owner == nil {
		owner = gotool.NewOwner(captured.ModuleDir)
	}
	if err := validation.Run(ctx, validation.Request{
		RepositoryDir: captured.RepositoryDir,
		ModuleDir:     captured.ModuleDir,
		Commit:        captured.Commit,
		Output:        request.Output,
		Settings:      request.Validation,
		ToolOwner:     owner,
	}); err != nil {
		return fmt.Errorf("validate candidate %s: %w", captured.Commit, err)
	}
	if request.AdditionalChecks != nil {
		callbackErr := request.AdditionalChecks(ctx, captured)
		if callbackErr != nil {
			return fmt.Errorf("validate candidate %s: %w", captured.Commit, callbackErr)
		}
	}
	return nil
}

// Recheck verifies that the captured local source is unchanged. When
// expectedTagObject is empty, the selected local version tag must still be
// absent; otherwise the existing annotated tag must still have that object ID.
func Recheck(ctx context.Context, captured Candidate, expectedTagObject string) error {
	current, err := inspectLocalState(ctx, captured.RepositoryDir)
	if err != nil {
		return fmt.Errorf("recheck local candidate state: %w", err)
	}
	if current.branch != "main" {
		return fmt.Errorf("release candidate branch changed to %q", current.branch)
	}
	if current.commit != captured.Commit {
		return fmt.Errorf("HEAD changed from %s to %s", captured.Commit, current.commit)
	}
	if current.status != "" {
		return fmt.Errorf("worktree or index changed:\n%s", current.status)
	}
	if expectedTagObject == "" {
		if exists, err := hasLocalTag(ctx, captured.RepositoryDir, captured.Tag); err != nil {
			return fmt.Errorf("recheck local tag %q: %w", captured.Tag, err)
		} else if exists {
			return fmt.Errorf("local tag %q appeared during validation", captured.Tag)
		}
		return nil
	}
	object, err := gitOutput(ctx, captured.RepositoryDir, "rev-parse", "--verify", "refs/tags/"+captured.Tag)
	if err != nil {
		return fmt.Errorf("read local tag %q: %w", captured.Tag, err)
	}
	tagType, err := gitOutput(ctx, captured.RepositoryDir, "cat-file", "-t", "refs/tags/"+captured.Tag)
	if err != nil {
		return fmt.Errorf("inspect local tag %q: %w", captured.Tag, err)
	}
	if strings.TrimSpace(string(object)) != expectedTagObject || strings.TrimSpace(string(tagType)) != "tag" {
		return fmt.Errorf("local tag %q no longer identifies annotated tag object %s", captured.Tag, expectedTagObject)
	}
	return nil
}

type localState struct {
	branch string
	commit string
	status string
}

func inspectLocalState(ctx context.Context, repositoryDir string) (localState, error) {
	branchOutput, err := gitOutput(ctx, repositoryDir, "branch", "--show-current")
	if err != nil {
		return localState{}, fmt.Errorf("inspect current branch: %w", err)
	}
	commitOutput, err := gitOutput(ctx, repositoryDir, "rev-parse", "--verify", "HEAD^{commit}")
	if err != nil {
		return localState{}, fmt.Errorf("capture HEAD commit: %w", err)
	}
	statusOutput, err := gitOutput(ctx, repositoryDir, "status", "--porcelain=v1", "--untracked-files=all")
	if err != nil {
		return localState{}, fmt.Errorf("inspect worktree and index: %w", err)
	}
	return localState{
		branch: strings.TrimSpace(string(branchOutput)),
		commit: strings.TrimSpace(string(commitOutput)),
		status: strings.TrimSpace(string(statusOutput)),
	}, nil
}

func gitOutput(ctx context.Context, repositoryDir string, args ...string) ([]byte, error) {
	var stdout, stderr bytes.Buffer
	commandArgs := append([]string{"git"}, args...)
	err := process.Run(ctx, process.Invocation{
		Args:   commandArgs,
		Dir:    repositoryDir,
		Stdout: &stdout,
		Stderr: &stderr,
	})
	if err != nil {
		message := strings.TrimSpace(stderr.String())
		if message != "" {
			return nil, fmt.Errorf("git %s: %s: %w", strings.Join(args, " "), message, err)
		}
		return nil, fmt.Errorf("git %s: %w", strings.Join(args, " "), err)
	}
	return stdout.Bytes(), nil
}

func hasLocalTag(ctx context.Context, repositoryDir, tag string) (bool, error) {
	var stderr bytes.Buffer
	err := process.Run(ctx, process.Invocation{
		Args:   []string{"git", "show-ref", "--verify", "--quiet", "refs/tags/" + tag},
		Dir:    repositoryDir,
		Stderr: &stderr,
	})
	if err == nil {
		return true, nil
	}
	var exitErr *exec.ExitError
	if errors.As(err, &exitErr) && exitErr.ExitCode() == 1 {
		return false, nil
	}
	message := strings.TrimSpace(stderr.String())
	if message != "" {
		return false, fmt.Errorf("%s: %w", message, err)
	}
	return false, err
}

func validStableVersion(version string) bool {
	return versioncontract.ValidStableVersion(version)
}

func validateNote(note []byte, product, version string) error {
	line := string(note)
	if firstLine, _, ok := strings.Cut(line, "\n"); ok {
		line = firstLine
	}
	line = strings.TrimSuffix(line, "\r")
	if !strings.HasPrefix(line, "# ") {
		return errors.New("first line must be a level-one Markdown heading")
	}
	elements := strings.Fields(strings.TrimPrefix(line, "# "))
	productElements := strings.Fields(product)
	if !containsSequence(elements, productElements) || !containsSequence(elements, []string{version}) {
		return fmt.Errorf("first heading must contain product %q and exact version %q as title elements", product, version)
	}
	return nil
}

// ValidateReleaseNote checks the title contract for a committed release note.
func ValidateReleaseNote(note []byte, product, version string) error {
	return validateNote(note, product, version)
}

func containsSequence(elements, sequence []string) bool {
	if len(sequence) == 0 || len(sequence) > len(elements) {
		return false
	}
	for start := 0; start+len(sequence) <= len(elements); start++ {
		match := true
		for i, element := range sequence {
			if elements[start+i] != element {
				match = false
				break
			}
		}
		if match {
			return true
		}
	}
	return false
}